fix test needing serde1 feature

see https://doc.rust-lang.org/reference/procedural-macros.html#procedural-macro-hygiene

.github/workflows/main.yml

@@ -1,4 +1,10 @@
-on: [push, pull_request]
+on:
+  push:
+    branches:
+    - master
+  pull_request:
+    branches:
+    - master
 
 name: Continuous integration
 
@@ -7,60 +13,55 @@ jobs:
     name: Check
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v1
-      - uses: actions-rs/toolchain@v1
+      - name: Cancel previous
+        uses: styfle/cancel-workflow-action@0.10.0
         with:
-          profile: minimal
-          toolchain: stable
-          override: true
-      - uses: actions-rs/cargo@v1
-        with:
-          command: check
-          args: --all-features
+          access_token: ${{ github.token }}
+      - uses: actions/checkout@v3
+      - uses: dtolnay/rust-toolchain@stable
+      - run: cargo check --all-features
 
   test:
     name: Test Suite
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v1
-      - uses: actions-rs/toolchain@v1
+      - name: Cancel previous
+        uses: styfle/cancel-workflow-action@0.10.0
         with:
-          profile: minimal
-          toolchain: stable
-          override: true
-      - uses: actions-rs/cargo@v1
-        with:
-          command: test
-          args: --all-features
+          access_token: ${{ github.token }}
+      - uses: actions/checkout@v3
+      - uses: dtolnay/rust-toolchain@stable
+      - run: cargo test
+      - run: cargo test --manifest-path tarpc/Cargo.toml --features serde1
+      - run: cargo test --manifest-path tarpc/Cargo.toml --features tokio1
+      - run: cargo test --manifest-path tarpc/Cargo.toml --features serde-transport
+      - run: cargo test --manifest-path tarpc/Cargo.toml --features tcp
+      - run: cargo test --all-features
 
   fmt:
     name: Rustfmt
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v1
-      - uses: actions-rs/toolchain@v1
+      - name: Cancel previous
+        uses: styfle/cancel-workflow-action@0.10.0
         with:
-          profile: minimal
-          toolchain: stable
-          override: true
-      - run: rustup component add rustfmt
-      - uses: actions-rs/cargo@v1
+          access_token: ${{ github.token }}
+      - uses: actions/checkout@v3
+      - uses: dtolnay/rust-toolchain@stable
         with:
-          command: fmt
-          args: --all -- --check
+          components: rustfmt
+      - run: cargo fmt --all -- --check
 
   clippy:
     name: Clippy
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v1
-      - uses: actions-rs/toolchain@v1
+      - name: Cancel previous
+        uses: styfle/cancel-workflow-action@0.10.0
         with:
-          profile: minimal
-          toolchain: stable
-          override: true
-      - run: rustup component add clippy
-      - uses: actions-rs/cargo@v1
+          access_token: ${{ github.token }}
+      - uses: actions/checkout@v3
+      - uses: dtolnay/rust-toolchain@stable
         with:
-          command: clippy
-          args: --all-features -- -D warnings
+          components: clippy
+      - run: cargo clippy --all-features -- -D warnings

Cargo.toml

@@ -1,7 +1,11 @@
 [workspace]
+resolver = "2"
 
 members = [
     "example-service",
     "tarpc",
     "plugins",
 ]
+
+[profile.dev]
+split-debuginfo = "unpacked"

README.md

@@ -1,9 +1,21 @@
-[![Build Status](https://github.com/google/tarpc/workflows/Continuous%20integration/badge.svg)](https://github.com/google/tarpc/actions?query=workflow%3A%22Continuous+integration%22)
-[![Latest Version](https://img.shields.io/crates/v/tarpc.svg)](https://crates.io/crates/tarpc)
-[![Chat on Discord](https://img.shields.io/discord/647529123996237854)](https://discordapp.com/channels/647529123996237854)
+[![Crates.io][crates-badge]][crates-url]
+[![MIT licensed][mit-badge]][mit-url]
+[![Build status][gh-actions-badge]][gh-actions-url]
+[![Discord chat][discord-badge]][discord-url]
+
+[crates-badge]: https://img.shields.io/crates/v/tarpc.svg
+[crates-url]: https://crates.io/crates/tarpc
+[mit-badge]: https://img.shields.io/badge/license-MIT-blue.svg
+[mit-url]: LICENSE
+[gh-actions-badge]: https://github.com/google/tarpc/workflows/Continuous%20integration/badge.svg
+[gh-actions-url]: https://github.com/google/tarpc/actions?query=workflow%3A%22Continuous+integration%22
+[discord-badge]: https://img.shields.io/discord/647529123996237854.svg?logo=discord&style=flat-square
+[discord-url]: https://discord.gg/gXwpdSt
 
 # tarpc
 
+<!-- cargo-sync-readme start -->
+
 *Disclaimer*: This is not an official Google product.
 
 tarpc is an RPC framework for rust with a focus on ease of use. Defining a
@@ -12,7 +24,7 @@ writing a server is taken care of for you.
 
 [Documentation](https://docs.rs/crate/tarpc/)
 
-### What is an RPC framework?
+## What is an RPC framework?
 "RPC" stands for "Remote Procedure Call," a function call where the work of
 producing the return value is being done somewhere else. When an rpc function is
 invoked, behind the scenes the function contacts some other process somewhere
@@ -28,9 +40,9 @@ rather than in a separate language such as .proto. This means there's no separat
 process, and no context switching between different languages.
 
 Some other features of tarpc:
-- Pluggable transport: any type impling `Stream<Item = Request> + Sink<Response>` can be
+- Pluggable transport: any type implementing `Stream<Item = Request> + Sink<Response>` can be
   used as a transport to connect the client and server.
-- `Send` optional: if the transport doesn't require it, neither does tarpc!
+- `Send + 'static` optional: if the transport doesn't require it, neither does tarpc!
 - Cascading cancellation: dropping a request will send a cancellation message to the server.
   The server will cease any unfinished work on the request, subsequently cancelling any of its
   own requests, repeating for the entire chain of transitive dependencies.
@@ -39,29 +51,39 @@ Some other features of tarpc:
   requests sent by the server that use the request context will propagate the request deadline.
   For example, if a server is handling a request with a 10s deadline, does 2s of work, then
   sends a request to another server, that server will see an 8s deadline.
+- Distributed tracing: tarpc is instrumented with
+  [tracing](https://github.com/tokio-rs/tracing) primitives extended with
+  [OpenTelemetry](https://opentelemetry.io/) traces. Using a compatible tracing subscriber like
+  [Jaeger](https://github.com/open-telemetry/opentelemetry-rust/tree/main/opentelemetry-jaeger),
+  each RPC can be traced through the client, server, and other dependencies downstream of the
+  server. Even for applications not connected to a distributed tracing collector, the
+  instrumentation can also be ingested by regular loggers like
+  [env_logger](https://github.com/env-logger-rs/env_logger/).
 - Serde serialization: enabling the `serde1` Cargo feature will make service requests and
   responses `Serialize + Deserialize`. It's entirely optional, though: in-memory transports can
   be used, as well, so the price of serialization doesn't have to be paid when it's not needed.
 
-### Usage
+## Usage
 Add to your `Cargo.toml` dependencies:
 
 ```toml
-tarpc = { version = "0.18.0", features = ["full"] }
+tarpc = "0.34"
 ```
 
 The `tarpc::service` attribute expands to a collection of items that form an rpc service.
 These generated types make it easy and ergonomic to write servers with less boilerplate.
 Simply implement the generated service trait, and you're off to the races!
 
-### Example
+## Example
 
-For this example, in addition to tarpc, also add two other dependencies to
+This example uses [tokio](https://tokio.rs), so add the following dependencies to
 your `Cargo.toml`:
 
 ```toml
+anyhow = "1.0"
 futures = "0.3"
-tokio = "0.2"
+tarpc = { version = "0.31", features = ["tokio1"] }
+tokio = { version = "1.0", features = ["rt-multi-thread", "macros"] }
 ```
 
 In the following example, we use an in-process channel for communication between
@@ -71,15 +93,11 @@ For a more real-world example, see [example-service](example-service).
 First, let's set up the dependencies and service definition.
 
 ```rust
-use futures::{
-    future::{self, Ready},
-    prelude::*,
-};
+use futures::future::{self, Ready};
 use tarpc::{
     client, context,
-    server::{self, Handler},
+    server::{self, Channel},
 };
-use std::io;
 
 // This is the service definition. It looks a lot like a trait definition.
 // It defines one RPC, hello, which takes one arg, name, and returns a String.
@@ -100,54 +118,45 @@ implement it for our Server struct.
 struct HelloServer;
 
 impl World for HelloServer {
-    // Each defined rpc generates two items in the trait, a fn that serves the RPC, and
-    // an associated type representing the future output by the fn.
-
-    type HelloFut = Ready<String>;
-
-    fn hello(self, _: context::Context, name: String) -> Self::HelloFut {
-        future::ready(format!("Hello, {}!", name))
+    async fn hello(self, _: context::Context, name: String) -> String {
+        format!("Hello, {name}!")
     }
 }
 ```
 
 Lastly let's write our `main` that will start the server. While this example uses an
-[in-process
-channel](https://docs.rs/tarpc/0.18.0/tarpc/transport/channel/struct.UnboundedChannel.html),
-tarpc also ships bincode and JSON
-tokio-net based TCP transports that are generic over all serializable types.
+[in-process channel](transport::channel), tarpc also ships a generic [`serde_transport`]
+behind the `serde-transport` feature, with additional [TCP](serde_transport::tcp) functionality
+available behind the `tcp` feature.
 
 ```rust
 #[tokio::main]
-async fn main() -> io::Result<()> {
+async fn main() -> anyhow::Result<()> {
     let (client_transport, server_transport) = tarpc::transport::channel::unbounded();
 
-    let server = server::new(server::Config::default())
-        // incoming() takes a stream of transports such as would be returned by
-        // TcpListener::incoming (but a stream instead of an iterator).
-        .incoming(stream::once(future::ready(server_transport)))
-        .respond_with(HelloServer.serve());
+    let server = server::BaseChannel::with_defaults(server_transport);
+    tokio::spawn(server.execute(HelloServer.serve()));
 
-    tokio::spawn(server);
-
-    // WorldClient is generated by the macro. It has a constructor `new` that takes a config and
-    // any Transport as input
-    let mut client = WorldClient::new(client::Config::default(), client_transport).spawn()?;
+    // WorldClient is generated by the #[tarpc::service] attribute. It has a constructor `new`
+    // that takes a config and any Transport as input.
+    let client = WorldClient::new(client::Config::default(), client_transport).spawn();
 
     // The client has an RPC method for each RPC defined in the annotated trait. It takes the same
     // args as defined, with the addition of a Context, which is always the first arg. The Context
     // specifies a deadline and trace information which can be helpful in debugging requests.
     let hello = client.hello(context::current(), "Stim".to_string()).await?;
 
-    println!("{}", hello);
+    println!("{hello}");
 
     Ok(())
 }
 ```
 
-### Service Documentation
+## Service Documentation
 
 Use `cargo doc` as you normally would to see the documentation created for all
 items expanded by a `service!` invocation.
 
+<!-- cargo-sync-readme end -->
+
 License: MIT

RELEASES.md

@@ -1,3 +1,388 @@
+## 0.34.0 (2023-12-29)
+
+### Breaking Changes
+
+- `#[tarpc::server]` is no more! Service traits now use async fns.
+- `Channel::execute` no longer spawns request handlers. Async-fn-in-traits makes it impossible to
+  add a Send bound to the future returned by `Serve::serve`. Instead, `Channel::execute` returns a
+  stream of futures, where each future is a request handler. To achieve the former behavior:
+  ```rust
+  channel.execute(server.serve())
+         .for_each(|rpc| { tokio::spawn(rpc); })
+  ```
+
+### New Features
+
+- Request hooks are added to the serve trait, so that it's easy to hook in cross-cutting
+  functionality like throttling, authorization, etc.
+- The Client trait is back! This makes it possible to hook in generic client functionality like load
+  balancing, retries, etc.
+
+## 0.33.0 (2023-04-01)
+
+### Breaking Changes
+
+Opentelemetry dependency version increased to 0.18.
+
+## 0.32.0 (2023-03-24)
+
+### Breaking Changes
+
+- As part of a fix to return more channel errors in RPC results, a few error types have changed:
+
+  0. `client::RpcError::Disconnected` was split into the following errors:
+    - Shutdown: the client was shutdown, either intentionally or due to an error. If due to an
+      error, pending RPCs should see the more specific errors below.
+    - Send: an RPC message failed to send over the transport. Only the RPC that failed to be sent
+      will see this error.
+    - Receive: a fatal error occurred while receiving from the transport. All in-flight RPCs will
+      receive this error.
+  0. `client::ChannelError` and `server::ChannelError` are unified in `tarpc::ChannelError`.
+     Previously, server transport errors would not indicate during which activity the transport
+     error occurred. Now, just like the client already was, it will be specific: reading, readying,
+     sending, flushing, or closing.
+
+## 0.31.0 (2022-11-03)
+
+### New Features
+
+This release adds Unix Domain Sockets to the `serde_transport` module.
+To use it, enable the "unix" feature. See the docs for more information.
+
+## 0.30.0 (2022-08-12)
+
+### Breaking Changes
+
+- Some types that impl Future are now annotated with `#[must_use]`. Code that previously created
+  these types but did not use them will now receive a warning. Code that disallows warnings will
+  receive a compilation error.
+
+### Fixes
+
+- Servers will more reliably clean up request state for requests with long deadlines when response
+processing is aborted without sending a response.
+
+### Other Changes
+
+- `TrackedRequest` now contains a response guard that can be used to ensure state cleanup for
+  aborted requests. (This was already handled automatically by `InFlightRequests`).
+- When the feature serde-transport is enabled, the crate tokio_serde is now re-exported.
+
+## 0.29.0 (2022-05-26)
+
+### Breaking Changes
+
+`Context.deadline` is now serialized as a Duration. This prevents clock skew from affecting deadline
+behavior. For more details see https://github.com/google/tarpc/pull/367 and its [related
+issue](https://github.com/google/tarpc/issues/366).
+
+## 0.28.0 (2022-04-06)
+
+### Breaking Changes
+
+- The minimum supported Rust version has increased to 1.58.0.
+- The version of opentelemetry depended on by tarpc has increased to 0.17.0.
+
+## 0.27.2 (2021-10-08)
+
+### Fixes
+
+Clients will now close their transport before dropping it. An attempt at a clean shutdown can help
+the server drop its connections more quickly.
+
+## 0.27.1 (2021-09-22)
+
+### Breaking Changes
+
+#### RPC error type is changing
+
+RPC return types are changing from `Result<Response, io::Error>` to `Result<Response,
+tarpc::client::RpcError>`.
+
+Becaue tarpc is a library, not an application, it should strive to
+use structured errors in its API so that users have maximal flexibility
+in how they handle errors. io::Error makes that hard, because it is a
+kitchen-sink error type.
+
+RPCs in particular only have 3 classes of errors:
+
+- The connection breaks.
+- The request expires.
+- The server decides not to process the request.
+
+RPC responses can also contain application-specific errors, but from the
+perspective of the RPC library, those are opaque to the framework, classified
+as successful responsees.
+
+### Open Telemetry
+
+The Opentelemetry dependency is updated to version 0.16.x.
+
+## 0.27.0 (2021-09-22)
+
+This version was yanked due to tarpc-plugins version mismatches.
+
+
+## 0.26.0 (2021-04-14)
+
+### New Features
+
+#### Tracing
+
+tarpc is now instrumented with tracing primitives extended with
+OpenTelemetry traces. Using a compatible tracing-opentelemetry
+subscriber like Jaeger, each RPC can be traced through the client,
+server, amd other dependencies downstream of the server. Even for
+applications not connected to a distributed tracing collector, the
+instrumentation can also be ingested by regular loggers like env_logger.
+
+### Breaking Changes
+
+#### Logging
+
+Logged events are now structured using tracing. For applications using a
+logger and not a tracing subscriber, these logs may look different or
+contain information in a less consumable manner. The easiest solution is
+to add a tracing subscriber that logs to stdout, such as
+tracing_subscriber::fmt.
+
+####  Context
+
+- Context no longer has parent_span, which was actually never needed,
+  because the context sent in an RPC is inherently the parent context.
+  For purposes of distributed tracing, the client side of the RPC has all
+  necessary information to link the span to its parent; the server side
+  need do nothing more than export the (trace ID, span ID) tuple.
+- Context has a new field, SamplingDecision, which has two variants,
+  Sampled and Unsampled. This field can be used by downstream systems to
+  determine whether a trace needs to be exported. If the parent span is
+  sampled, the expectation is that all child spans be exported, as well;
+  to do otherwise could result in lossy traces being exported. Note that
+  if an Openetelemetry tracing subscriber is not installed, the fallback
+  context will still be used, but the Context's sampling decision will
+  always be inherited by the parent Context's sampling decision.
+- Context::scope has been removed. Context propagation is now done via
+  tracing's task-local spans. Spans can be propagated across tasks via
+  Span::in_scope. When a service receives a request, it attaches an
+  Opentelemetry context to the local Span created before request handling,
+  and this context contains the request deadline. This span-local deadline
+  is retrieved by Context::current, but it cannot be modified so that
+  future Context::current calls contain a different deadline. However, the
+  deadline in the context passed into an RPC call will override it, so
+  users can retrieve the current context and then modify the deadline
+  field, as has been historically possible.
+- Context propgation precedence changes: when an RPC is initiated, the
+  current Span's Opentelemetry context takes precedence over the trace
+  context passed into the RPC method. If there is no current Span, then
+  the trace context argument is used as it has been historically. Note
+  that Opentelemetry context propagation requires an Opentelemetry
+  tracing subscriber to be installed.
+
+#### Server
+
+- The server::Channel trait now has an additional required associated
+  type and method which returns the underlying transport. This makes it
+  more ergonomic for users to retrieve transport-specific information,
+  like IP Address. BaseChannel implements Channel::transport by returning
+  the underlying transport, and channel decorators like Throttler just
+  delegate to the Channel::transport method of the wrapped channel.
+
+#### Client
+
+- NewClient::spawn no longer returns a result, as spawn can't fail.
+
+### References
+
+1. https://github.com/tokio-rs/tracing
+2. https://opentelemetry.io
+3. https://github.com/open-telemetry/opentelemetry-rust/tree/main/opentelemetry-jaeger
+4. https://github.com/env-logger-rs/env_logger
+
+## 0.25.0 (2021-03-10)
+
+### Breaking Changes
+
+#### Major server module refactoring
+
+1. Renames
+
+Some of the items in this module were renamed to be less generic:
+
+- Handler => Incoming
+- ClientHandler => Requests
+- ResponseHandler => InFlightRequest
+- Channel::{respond_with => requests}
+
+In the case of Handler: handler of *what*? Now it's a bit clearer that this is a stream of Channels
+(aka *incoming* connections).
+
+Similarly, ClientHandler was a stream of requests over a single connection. Hopefully Requests
+better reflects that.
+
+ResponseHandler was renamed InFlightRequest because it no longer contains the serving function.
+Instead, it is just the request, plus the response channel and an abort hook. As a result of this,
+Channel::respond_with underwent a big change: it used to take the serving function and return a
+ClientHandler; now it has been renamed Channel::requests and does not take any args.
+
+2. Execute methods
+
+All methods thats actually result in responses being generated have been consolidated into methods
+named `execute`:
+
+- InFlightRequest::execute returns a future that completes when a response has been generated and
+  sent to the server Channel.
+- Requests::execute automatically spawns response handlers for all requests over a single channel.
+- Channel::execute is a convenience for `channel.requests().execute()`.
+- Incoming::execute automatically spawns response handlers for all requests over all channels.
+
+3. Removal of Server.
+
+server::Server was removed, as it provided no value over the Incoming/Channel abstractions.
+Additionally, server::new was removed, since it just returned a Server.
+
+#### Client RPC methods now take &self
+
+This required the breaking change of removing the Client trait. The intent of the Client trait was
+to facilitate the decorator pattern by allowing users to create their own Clients that added
+behavior on top of the base client. Unfortunately, this trait had become a maintenance burden,
+consistently causing issues with lifetimes and the lack of generic associated types. Specifically,
+it meant that Client impls could not use async fns, which is no longer tenable today, with channel
+libraries moving to async fns.
+
+#### Servers no longer send deadline-exceed responses.
+
+The deadline-exceeded response was largely redundant, because the client
+shouldn't normally be waiting for such a response, anyway -- the normal
+client will automatically remove the in-flight request when it reaches
+the deadline.
+
+This also allows for internalizing the expiration+cleanup logic entirely
+within BaseChannel, without having it leak into the Channel trait and
+requiring action taken by the Requests struct.
+
+#### Clients no longer send cancel messages when the request deadline is exceeded.
+
+The server already knows when the request deadline was exceeded, so the client didn't need to inform
+it.
+
+### Fixes
+
+- When a channel is dropped, all in-flight requests for that channel are now aborted.
+
+## 0.24.1 (2020-12-28)
+
+### Breaking Changes
+
+Upgrades tokio to 1.0.
+
+## 0.24.0 (2020-12-28)
+
+This release was yanked.
+
+## 0.23.0 (2020-10-19)
+
+### Breaking Changes
+
+Upgrades tokio to 0.3.
+
+## 0.22.0 (2020-08-02)
+
+This release adds some flexibility and consistency to `serde_transport`, with one new feature and
+one small breaking change.
+
+### New Features
+
+`serde_transport::tcp` now exposes framing configuration on `connect()` and `listen()`. This is
+useful if, for instance, you want to send requests or responses that are larger than the maximum
+payload allowed by default:
+
+```rust
+let mut transport = tarpc::serde_transport::tcp::connect(server_addr, Json::default);
+transport.config_mut().max_frame_length(4294967296);
+let mut client = MyClient::new(client::Config::default(), transport.await?).spawn()?;
+```
+
+### Breaking Changes
+
+The codec argument to `serde_transport::tcp::connect` changed from a Codec to impl Fn() -> Codec,
+to be consistent with `serde_transport::tcp::listen`. While only one Codec is needed, more than one
+person has been tripped up by the inconsistency between `connect` and `listen`. Unfortunately, the
+compiler errors are not much help in this case, so it was decided to simply do the more intuitive
+thing so that the compiler doesn't need to step in in the first place.
+
+
+## 0.21.1 (2020-08-02)
+
+### New Features
+
+#### #[tarpc::server] diagnostics
+
+When a service impl uses #[tarpc::server], only `async fn`s are re-written. This can lead to
+confusing compiler errors about missing associated types:
+
+```
+error: not all trait items implemented, missing: `HelloFut`
+ --> $DIR/tarpc_server_missing_async.rs:9:1
+  |
+9 | impl World for HelloServer {
+  | ^^^^
+```
+
+The proc macro now provides better diagnostics for this case:
+
+```
+error: not all trait items implemented, missing: `HelloFut`
+ --> $DIR/tarpc_server_missing_async.rs:9:1
+  |
+9 | impl World for HelloServer {
+  | ^^^^
+
+error: hint: `#[tarpc::server]` only rewrites async fns, and `fn hello` is not async
+  --> $DIR/tarpc_server_missing_async.rs:10:5
+   |
+10 |     fn hello(name: String) ->  String {
+   |     ^^
+```
+
+### Bug Fixes
+
+#### Fixed client hanging when server shuts down
+
+Previously, clients would ignore when the read half of the transport was closed, continuing to
+write requests. This didn't make much sense, because without the ability to receive responses,
+clients have no way to know if requests were actually processed by the server. It basically just
+led to clients that would hang for a few seconds before shutting down. This has now been
+corrected: clients will immediately shut down when the read-half of the transport is closed.
+
+#### More docs.rs documentation
+
+Previously, docs.rs only documented items enabled by default, notably leaving out documentation
+for tokio and serde features. This has now been corrected: docs.rs should have documentation
+for all optional features.
+
+## 0.21.0 (2020-06-26)
+
+### New Features
+
+A new proc macro, `#[tarpc::server]` was added! This enables service impls to elide the boilerplate
+of specifying associated types for each RPC. With the ubiquity of async-await, most code won't have
+nameable futures and will just be boxing the return type anyway. This macro does that for you.
+
+### Breaking Changes
+
+- Enums had `_non_exhaustive` fields replaced with the #[non_exhaustive] attribute.
+
+### Bug Fixes
+
+- https://github.com/google/tarpc/issues/304
+
+  A race condition in code that limits number of connections per client caused occasional panics.
+
+- https://github.com/google/tarpc/pull/295
+
+  Made request timeouts account for time spent in the outbound buffer. Previously, a large outbound
+  queue would lead to requests not timing out correctly.
+
 ## 0.20.0 (2019-12-11)
 
 ### Breaking Changes
@@ -10,7 +395,7 @@
 
 ## 0.13.0 (2018-10-16)
 
-### Breaking Changes 
+### Breaking Changes
 
 Version 0.13 marks a significant departure from previous versions of tarpc. The
 API has changed significantly. The tokio-proto crate has been torn out and

example-service/Cargo.toml

@@ -1,8 +1,9 @@
 [package]
 name = "tarpc-example-service"
-version = "0.6.0"
+version = "0.15.0"
+rust-version = "1.56"
 authors = ["Tim Kuehn <tikue@google.com>"]
-edition = "2018"
+edition = "2021"
 license = "MIT"
 documentation = "https://docs.rs/tarpc-example-service"
 homepage = "https://github.com/google/tarpc"
@@ -13,13 +14,19 @@ readme = "../README.md"
 description = "An example server built on tarpc."
 
 [dependencies]
-clap = "2.0"
+anyhow = "1.0"
+clap = { version = "3.0.0-rc.9", features = ["derive"] }
+log = "0.4"
 futures = "0.3"
-serde = { version = "1.0" }
-tarpc = { version = "0.20", path = "../tarpc", features = ["full"] }
-tokio = { version = "0.2", features = ["full"] }
-tokio-serde = { version = "0.6", features = ["json"] }
-env_logger = "0.6"
+opentelemetry = { version = "0.21.0" }
+opentelemetry-jaeger = { version = "0.20.0", features = ["rt-tokio"] }
+rand = "0.8"
+tarpc = { version = "0.34", path = "../tarpc", features = ["full"] }
+tokio = { version = "1", features = ["macros", "net", "rt-multi-thread"] }
+tracing = { version = "0.1" }
+tracing-opentelemetry = "0.22.0"
+tracing-subscriber = { version = "0.3.18", features = ["env-filter"] }
+opentelemetry_sdk = "0.21.1"
 
 [lib]
 name = "service"

example-service/README.md

@@ -0,0 +1,15 @@
+# Example
+
+Example service to demonstrate how to set up `tarpc` with [Jaeger](https://www.jaegertracing.io). To see traces Jaeger, run the following with `RUST_LOG=trace`.
+
+## Server
+
+```bash
+cargo run --bin server -- --port 50051
+```
+
+## Client
+
+```bash
+cargo run --bin client -- --server-addr "[::1]:50051" --name "Bob"
+```

example-service/src/client.rs

@@ -4,55 +4,53 @@
 // license that can be found in the LICENSE file or at
 // https://opensource.org/licenses/MIT.
 
-use clap::{App, Arg};
-use std::{io, net::SocketAddr};
-use tarpc::{client, context};
-use tokio_serde::formats::Json;
+use clap::Parser;
+use service::{init_tracing, WorldClient};
+use std::{net::SocketAddr, time::Duration};
+use tarpc::{client, context, tokio_serde::formats::Json};
+use tokio::time::sleep;
+use tracing::Instrument;
+
+#[derive(Parser)]
+struct Flags {
+    /// Sets the server address to connect to.
+    #[clap(long)]
+    server_addr: SocketAddr,
+    /// Sets the name to say hello to.
+    #[clap(long)]
+    name: String,
+}
 
 #[tokio::main]
-async fn main() -> io::Result<()> {
-    let flags = App::new("Hello Client")
-        .version("0.1")
-        .author("Tim <tikue@google.com>")
-        .about("Say hello!")
-        .arg(
-            Arg::with_name("server_addr")
-                .long("server_addr")
-                .value_name("ADDRESS")
-                .help("Sets the server address to connect to.")
-                .required(true)
-                .takes_value(true),
-        )
-        .arg(
-            Arg::with_name("name")
-                .short("n")
-                .long("name")
-                .value_name("STRING")
-                .help("Sets the name to say hello to.")
-                .required(true)
-                .takes_value(true),
-        )
-        .get_matches();
+async fn main() -> anyhow::Result<()> {
+    let flags = Flags::parse();
+    init_tracing("Tarpc Example Client")?;
 
-    let server_addr = flags.value_of("server_addr").unwrap();
-    let server_addr = server_addr
-        .parse::<SocketAddr>()
-        .unwrap_or_else(|e| panic!(r#"--server_addr value "{}" invalid: {}"#, server_addr, e));
-
-    let name = flags.value_of("name").unwrap().into();
-
-    let transport = tarpc::serde_transport::tcp::connect(server_addr, Json::default()).await?;
+    let mut transport = tarpc::serde_transport::tcp::connect(flags.server_addr, Json::default);
+    transport.config_mut().max_frame_length(usize::MAX);
 
     // WorldClient is generated by the service attribute. It has a constructor `new` that takes a
     // config and any Transport as input.
-    let mut client = service::WorldClient::new(client::Config::default(), transport).spawn()?;
+    let client = WorldClient::new(client::Config::default(), transport.await?).spawn();
 
-    // The client has an RPC method for each RPC defined in the annotated trait. It takes the same
-    // args as defined, with the addition of a Context, which is always the first arg. The Context
-    // specifies a deadline and trace information which can be helpful in debugging requests.
-    let hello = client.hello(context::current(), name).await?;
+    let hello = async move {
+        // Send the request twice, just to be safe! ;)
+        tokio::select! {
+            hello1 = client.hello(context::current(), format!("{}1", flags.name)) => { hello1 }
+            hello2 = client.hello(context::current(), format!("{}2", flags.name)) => { hello2 }
+        }
+    }
+    .instrument(tracing::info_span!("Two Hellos"))
+    .await;
 
-    println!("{}", hello);
+    match hello {
+        Ok(hello) => tracing::info!("{hello:?}"),
+        Err(e) => tracing::warn!("{:?}", anyhow::Error::from(e)),
+    }
+
+    // Let the background span processor finish.
+    sleep(Duration::from_micros(1)).await;
+    opentelemetry::global::shutdown_tracer_provider();
 
     Ok(())
 }

example-service/src/lib.rs

@@ -4,6 +4,9 @@
 // license that can be found in the LICENSE file or at
 // https://opensource.org/licenses/MIT.
 
+use std::env;
+use tracing_subscriber::{fmt::format::FmtSpan, prelude::*};
+
 /// This is the service definition. It looks a lot like a trait definition.
 /// It defines one RPC, hello, which takes one arg, name, and returns a String.
 #[tarpc::service]
@@ -11,3 +14,21 @@ pub trait World {
     /// Returns a greeting for name.
     async fn hello(name: String) -> String;
 }
+
+/// Initializes an OpenTelemetry tracing subscriber with a Jaeger backend.
+pub fn init_tracing(service_name: &str) -> anyhow::Result<()> {
+    env::set_var("OTEL_BSP_MAX_EXPORT_BATCH_SIZE", "12");
+
+    let tracer = opentelemetry_jaeger::new_agent_pipeline()
+        .with_service_name(service_name)
+        .with_max_packet_size(2usize.pow(13))
+        .install_batch(opentelemetry_sdk::runtime::Tokio)?;
+
+    tracing_subscriber::registry()
+        .with(tracing_subscriber::EnvFilter::from_default_env())
+        .with(tracing_subscriber::fmt::layer().with_span_events(FmtSpan::NEW | FmtSpan::CLOSE))
+        .with(tracing_opentelemetry::layer().with_tracer(tracer))
+        .try_init()?;
+
+    Ok(())
+}

example-service/src/server.rs

@@ -4,21 +4,30 @@
 // license that can be found in the LICENSE file or at
 // https://opensource.org/licenses/MIT.
 
-use clap::{App, Arg};
-use futures::{
-    future::{self, Ready},
-    prelude::*,
+use clap::Parser;
+use futures::{future, prelude::*};
+use rand::{
+    distributions::{Distribution, Uniform},
+    thread_rng,
 };
-use service::World;
+use service::{init_tracing, World};
 use std::{
-    io,
-    net::{IpAddr, SocketAddr},
+    net::{IpAddr, Ipv6Addr, SocketAddr},
+    time::Duration,
 };
 use tarpc::{
     context,
-    server::{self, Channel, Handler},
+    server::{self, incoming::Incoming, Channel},
+    tokio_serde::formats::Json,
 };
-use tokio_serde::formats::Json;
+use tokio::time;
+
+#[derive(Parser)]
+struct Flags {
+    /// Sets the port number to listen on.
+    #[clap(long)]
+    port: u16,
+}
 
 // This is the type that implements the generated World trait. It is the business logic
 // and is used to start the server.
@@ -26,59 +35,41 @@ use tokio_serde::formats::Json;
 struct HelloServer(SocketAddr);
 
 impl World for HelloServer {
-    // Each defined rpc generates two items in the trait, a fn that serves the RPC, and
-    // an associated type representing the future output by the fn.
-
-    type HelloFut = Ready<String>;
-
-    fn hello(self, _: context::Context, name: String) -> Self::HelloFut {
-        future::ready(format!(
-            "Hello, {}! You are connected from {:?}.",
-            name, self.0
-        ))
+    async fn hello(self, _: context::Context, name: String) -> String {
+        let sleep_time =
+            Duration::from_millis(Uniform::new_inclusive(1, 10).sample(&mut thread_rng()));
+        time::sleep(sleep_time).await;
+        format!("Hello, {name}! You are connected from {}", self.0)
     }
 }
 
+async fn spawn(fut: impl Future<Output = ()> + Send + 'static) {
+    tokio::spawn(fut);
+}
+
 #[tokio::main]
-async fn main() -> io::Result<()> {
-    env_logger::init();
+async fn main() -> anyhow::Result<()> {
+    let flags = Flags::parse();
+    init_tracing("Tarpc Example Server")?;
 
-    let flags = App::new("Hello Server")
-        .version("0.1")
-        .author("Tim <tikue@google.com>")
-        .about("Say hello!")
-        .arg(
-            Arg::with_name("port")
-                .short("p")
-                .long("port")
-                .value_name("NUMBER")
-                .help("Sets the port number to listen on")
-                .required(true)
-                .takes_value(true),
-        )
-        .get_matches();
-
-    let port = flags.value_of("port").unwrap();
-    let port = port
-        .parse()
-        .unwrap_or_else(|e| panic!(r#"--port value "{}" invalid: {}"#, port, e));
-
-    let server_addr = (IpAddr::from([0, 0, 0, 0]), port);
+    let server_addr = (IpAddr::V6(Ipv6Addr::LOCALHOST), flags.port);
 
     // JSON transport is provided by the json_transport tarpc module. It makes it easy
     // to start up a serde-powered json serialization strategy over TCP.
-    tarpc::serde_transport::tcp::listen(&server_addr, Json::default)
-        .await?
+    let mut listener = tarpc::serde_transport::tcp::listen(&server_addr, Json::default).await?;
+    tracing::info!("Listening on port {}", listener.local_addr().port());
+    listener.config_mut().max_frame_length(usize::MAX);
+    listener
         // Ignore accept errors.
         .filter_map(|r| future::ready(r.ok()))
         .map(server::BaseChannel::with_defaults)
         // Limit channels to 1 per IP.
-        .max_channels_per_key(1, |t| t.as_ref().peer_addr().unwrap().ip())
+        .max_channels_per_key(1, |t| t.transport().peer_addr().unwrap().ip())
         // serve is generated by the service attribute. It takes as input any type implementing
         // the generated World trait.
         .map(|channel| {
-            let server = HelloServer(channel.as_ref().as_ref().peer_addr().unwrap());
-            channel.respond_with(server.serve()).execute()
+            let server = HelloServer(channel.transport().peer_addr().unwrap());
+            channel.execute(server.serve()).for_each(spawn)
         })
         // Max 10 channels.
         .buffer_unordered(10)

hooks/pre-commit

@@ -67,7 +67,7 @@ else
 fi
 
 printf "${PREFIX} Checking for rustfmt ... "
-command -v cargo fmt &>/dev/null
+command -v rustfmt &>/dev/null
 if [ $? == 0 ]; then
 	printf "${SUCCESS}\n"
 else
@@ -93,19 +93,19 @@ diff=""
 for file in $(git diff --name-only --cached);
 do
 	if [ ${file: -3} == ".rs" ]; then
-        diff="$diff$(cargo fmt -- --skip-children --write-mode=diff $file)"
+        diff="$diff$(rustfmt --edition 2018 --check $file)"
+        if [ $? != 0 ]; then
+            FMTRESULT=1
+        fi
 	fi
 done
-if grep --quiet "^[-+]" <<< "$diff"; then
-    FMTRESULT=1
-fi
 
 if [ "${TARPC_SKIP_RUSTFMT}" == 1 ]; then
 	printf "${SKIPPED}\n"$?
 elif [ ${FMTRESULT} != 0 ]; then
 	FAILED=1
 	printf "${FAILURE}\n"
-    echo "$diff" | sed 's/Using rustfmt config file.*$/d/'
+    echo "$diff"
 else
 	printf "${SUCCESS}\n"
 fi

hooks/pre-push

@@ -84,18 +84,19 @@ command -v rustup &>/dev/null
 if [ "$?" == 0 ]; then
     printf "${SUCCESS}\n"
 
+    try_run "Building ... " cargo +stable build --color=always
+    try_run "Testing ... " cargo +stable test --color=always
+    try_run "Testing with all features enabled ... " cargo +stable test --all-features --color=always
+    for EXAMPLE in $(cargo +stable run --example 2>&1 | grep '    ' | awk '{print $1}')
+    do
+        try_run "Running example \"$EXAMPLE\" ... " cargo +stable run --example $EXAMPLE
+    done
+
     check_toolchain nightly
-    if [ ${TOOLCHAIN_RESULT} == 1 ]; then
-        exit 1
+    if [ ${TOOLCHAIN_RESULT} != 1 ]; then
+        try_run "Running clippy ... " cargo +nightly clippy --color=always -Z unstable-options -- --deny warnings
     fi
 
-    try_run "Building ... " cargo build --color=always
-    try_run "Testing ... " cargo test --color=always
-    try_run "Testing with all features enabled ... " cargo test --all-features --color=always
-    for EXAMPLE in $(cargo run --example 2>&1 | grep '    ' | awk '{print $1}')
-    do
-        try_run "Running example \"$EXAMPLE\" ... " cargo run --example $EXAMPLE
-    done
 
 fi
 

plugins/Cargo.toml

@@ -1,8 +1,9 @@
 [package]
 name = "tarpc-plugins"
-version = "0.7.0"
+version = "0.13.0"
+rust-version = "1.56"
 authors = ["Adam Wright <adam.austin.wright@gmail.com>", "Tim Kuehn <timothy.j.kuehn@gmail.com>"]
-edition = "2018"
+edition = "2021"
 license = "MIT"
 documentation = "https://docs.rs/tarpc-plugins"
 homepage = "https://github.com/google/tarpc"
@@ -19,14 +20,15 @@ serde1 = []
 travis-ci = { repository = "google/tarpc" }
 
 [dependencies]
-syn = { version = "1.0.11", features = ["full"] }
-quote = "1.0.2"
-proc-macro2 = "1.0.6"
+proc-macro2 = "1.0"
+quote = "1.0"
+syn = { version = "1.0", features = ["full"] }
 
 [lib]
 proc-macro = true
 
 [dev-dependencies]
+assert-type-eq = "0.1.0"
 futures = "0.3"
 serde = { version = "1.0", features = ["derive"] }
-tarpc = { path = "../tarpc" }
+tarpc = { path = "../tarpc", features = ["serde1"] }

plugins/LICENSE

@@ -0,0 +1,9 @@
+The MIT License (MIT)
+
+Copyright 2016 Google Inc. All Rights Reserved.
+
+Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.

plugins/src/lib.rs

@@ -12,17 +12,32 @@ extern crate quote;
 extern crate syn;
 
 use proc_macro::TokenStream;
-use quote::{format_ident, quote};
+use proc_macro2::TokenStream as TokenStream2;
+use quote::{format_ident, quote, ToTokens};
 use syn::{
-    braced, parenthesized,
+    braced,
+    ext::IdentExt,
+    parenthesized,
     parse::{Parse, ParseStream},
     parse_macro_input, parse_quote,
-    punctuated::Punctuated,
+    spanned::Spanned,
     token::Comma,
     Attribute, FnArg, Ident, Lit, LitBool, MetaNameValue, Pat, PatType, ReturnType, Token, Type,
     Visibility,
 };
 
+/// Accumulates multiple errors into a result.
+/// Only use this for recoverable errors, i.e. non-parse errors. Fatal errors should early exit to
+/// avoid further complications.
+macro_rules! extend_errors {
+    ($errors: ident, $e: expr) => {
+        match $errors {
+            Ok(_) => $errors = Err($e),
+            Err(ref mut errors) => errors.extend($e),
+        }
+    };
+}
+
 struct Service {
     attrs: Vec<Attribute>,
     vis: Visibility,
@@ -42,27 +57,39 @@ impl Parse for Service {
         let attrs = input.call(Attribute::parse_outer)?;
         let vis = input.parse()?;
         input.parse::<Token![trait]>()?;
-        let ident = input.parse()?;
+        let ident: Ident = input.parse()?;
         let content;
         braced!(content in input);
         let mut rpcs = Vec::<RpcMethod>::new();
         while !content.is_empty() {
             rpcs.push(content.parse()?);
         }
+        let mut ident_errors = Ok(());
         for rpc in &rpcs {
             if rpc.ident == "new" {
-                return Err(input.error(format!(
-                    "method name conflicts with generated fn `{}Client::new`",
-                    ident
-                )));
+                extend_errors!(
+                    ident_errors,
+                    syn::Error::new(
+                        rpc.ident.span(),
+                        format!(
+                            "method name conflicts with generated fn `{}Client::new`",
+                            ident.unraw()
+                        )
+                    )
+                );
             }
             if rpc.ident == "serve" {
-                return Err(input.error(format!(
-                    "method name conflicts with generated fn `{}::serve`",
-                    ident
-                )));
+                extend_errors!(
+                    ident_errors,
+                    syn::Error::new(
+                        rpc.ident.span(),
+                        format!("method name conflicts with generated fn `{ident}::serve`")
+                    )
+                );
             }
         }
+        ident_errors?;
+
         Ok(Self {
             attrs,
             vis,
@@ -80,17 +107,28 @@ impl Parse for RpcMethod {
         let ident = input.parse()?;
         let content;
         parenthesized!(content in input);
-        let args: Punctuated<FnArg, Comma> = content.parse_terminated(FnArg::parse)?;
-        let args = args
-            .into_iter()
-            .map(|arg| match arg {
-                FnArg::Typed(captured) => match *captured.pat {
-                    Pat::Ident(_) => Ok(captured),
-                    _ => Err(input.error("patterns aren't allowed in RPC args")),
-                },
-                FnArg::Receiver(_) => Err(input.error("method args cannot start with self")),
-            })
-            .collect::<Result<_, _>>()?;
+        let mut args = Vec::new();
+        let mut errors = Ok(());
+        for arg in content.parse_terminated::<FnArg, Comma>(FnArg::parse)? {
+            match arg {
+                FnArg::Typed(captured) if matches!(&*captured.pat, Pat::Ident(_)) => {
+                    args.push(captured);
+                }
+                FnArg::Typed(captured) => {
+                    extend_errors!(
+                        errors,
+                        syn::Error::new(captured.pat.span(), "patterns aren't allowed in RPC args")
+                    );
+                }
+                FnArg::Receiver(_) => {
+                    extend_errors!(
+                        errors,
+                        syn::Error::new(arg.span(), "method args cannot start with self")
+                    );
+                }
+            }
+        }
+        errors?;
         let output = input.parse()?;
         input.parse::<Token![;]>()?;
 
@@ -109,35 +147,93 @@ struct DeriveSerde(bool);
 
 impl Parse for DeriveSerde {
     fn parse(input: ParseStream) -> syn::Result<Self> {
-        if input.is_empty() {
-            return Ok(Self(cfg!(feature = "serde1")));
-        }
-        match input.parse::<MetaNameValue>()? {
-            MetaNameValue {
-                ref path, ref lit, ..
-            } if path.segments.len() == 1
-                && path.segments.first().unwrap().ident == "derive_serde" =>
-            {
-                match lit {
-                    Lit::Bool(LitBool { value: true, .. }) if cfg!(feature = "serde1") => {
-                        Ok(Self(true))
-                    }
-                    Lit::Bool(LitBool { value: true, .. }) => {
-                        Err(input
-                            .error("To enable serde, first enable the `serde1` feature of tarpc"))
-                    }
-                    Lit::Bool(LitBool { value: false, .. }) => Ok(Self(false)),
-                    _ => Err(input.error("`derive_serde` expects a value of type `bool`")),
+        let mut result = Ok(None);
+        let mut derive_serde = Vec::new();
+        let meta_items = input.parse_terminated::<MetaNameValue, Comma>(MetaNameValue::parse)?;
+        for meta in meta_items {
+            if meta.path.segments.len() != 1 {
+                extend_errors!(
+                    result,
+                    syn::Error::new(
+                        meta.span(),
+                        "tarpc::service does not support this meta item"
+                    )
+                );
+                continue;
+            }
+            let segment = meta.path.segments.first().unwrap();
+            if segment.ident != "derive_serde" {
+                extend_errors!(
+                    result,
+                    syn::Error::new(
+                        meta.span(),
+                        "tarpc::service does not support this meta item"
+                    )
+                );
+                continue;
+            }
+            match meta.lit {
+                Lit::Bool(LitBool { value: true, .. }) if cfg!(feature = "serde1") => {
+                    result = result.and(Ok(Some(true)))
                 }
+                Lit::Bool(LitBool { value: true, .. }) => {
+                    extend_errors!(
+                        result,
+                        syn::Error::new(
+                            meta.span(),
+                            "To enable serde, first enable the `serde1` feature of tarpc"
+                        )
+                    );
+                }
+                Lit::Bool(LitBool { value: false, .. }) => result = result.and(Ok(Some(false))),
+                _ => extend_errors!(
+                    result,
+                    syn::Error::new(
+                        meta.lit.span(),
+                        "`derive_serde` expects a value of type `bool`"
+                    )
+                ),
             }
-            _ => {
-                Err(input
-                    .error("tarpc::service only supports one meta item, `derive_serde = {bool}`"))
+            derive_serde.push(meta);
+        }
+        if derive_serde.len() > 1 {
+            for (i, derive_serde) in derive_serde.iter().enumerate() {
+                extend_errors!(
+                    result,
+                    syn::Error::new(
+                        derive_serde.span(),
+                        format!(
+                            "`derive_serde` appears more than once (occurrence #{})",
+                            i + 1
+                        )
+                    )
+                );
             }
         }
+        let derive_serde = result?.unwrap_or(cfg!(feature = "serde1"));
+        Ok(Self(derive_serde))
     }
 }
 
+/// A helper attribute to avoid a direct dependency on Serde.
+///
+/// Adds the following annotations to the annotated item:
+///
+/// ```rust
+/// #[derive(::tarpc::serde::Serialize, ::tarpc::serde::Deserialize)]
+/// #[serde(crate = "tarpc::serde")]
+/// # struct Foo;
+/// ```
+#[proc_macro_attribute]
+pub fn derive_serde(_attr: TokenStream, item: TokenStream) -> TokenStream {
+    let mut gen: proc_macro2::TokenStream = quote! {
+        #[derive(::tarpc::serde::Serialize, ::tarpc::serde::Deserialize)]
+        #[serde(crate = "::tarpc::serde")]
+    };
+    gen.extend(proc_macro2::TokenStream::from(item));
+    proc_macro::TokenStream::from(gen)
+}
+
 /// Generates:
 /// - service trait
 /// - serve fn
@@ -156,28 +252,40 @@ pub fn service(attr: TokenStream, input: TokenStream) -> TokenStream {
         ref rpcs,
     } = parse_macro_input!(input as Service);
 
-    let camel_case_fn_names: &[String] = &rpcs
+    let camel_case_fn_names: &Vec<_> = &rpcs
         .iter()
-        .map(|rpc| snake_to_camel(&rpc.ident.to_string()))
-        .collect::<Vec<_>>();
+        .map(|rpc| snake_to_camel(&rpc.ident.unraw().to_string()))
+        .collect();
     let args: &[&[PatType]] = &rpcs.iter().map(|rpc| &*rpc.args).collect::<Vec<_>>();
-    let response_fut_name = &format!("{}ResponseFut", ident);
-    let derive_serialize = quote!(#[derive(serde::Serialize, serde::Deserialize)]);
+    let derive_serialize = if derive_serde.0 {
+        Some(
+            quote! {#[derive(::tarpc::serde::Serialize, ::tarpc::serde::Deserialize)]
+            #[serde(crate = "::tarpc::serde")]},
+        )
+    } else {
+        None
+    };
 
-    let gen_args = &GenArgs {
-        attrs,
-        vis,
-        rpcs,
-        args,
-        response_fut_name,
+    let methods = rpcs.iter().map(|rpc| &rpc.ident).collect::<Vec<_>>();
+    let request_names = methods
+        .iter()
+        .map(|m| format!("{ident}.{m}"))
+        .collect::<Vec<_>>();
+
+    ServiceGenerator {
         service_ident: ident,
+        client_stub_ident: &format_ident!("{}Stub", ident),
         server_ident: &format_ident!("Serve{}", ident),
-        response_fut_ident: &Ident::new(&response_fut_name, ident.span()),
         client_ident: &format_ident!("{}Client", ident),
         request_ident: &format_ident!("{}Request", ident),
         response_ident: &format_ident!("{}Response", ident),
+        vis,
+        args,
         method_attrs: &rpcs.iter().map(|rpc| &*rpc.attrs).collect::<Vec<_>>(),
-        method_names: &rpcs.iter().map(|rpc| &rpc.ident).collect::<Vec<_>>(),
+        method_idents: &methods,
+        request_names: &request_names,
+        attrs,
+        rpcs,
         return_types: &rpcs
             .iter()
             .map(|rpc| match rpc.output {
@@ -185,7 +293,7 @@ pub fn service(attr: TokenStream, input: TokenStream) -> TokenStream {
                 ReturnType::Default => unit_type,
             })
             .collect::<Vec<_>>(),
-        arg_vars: &args
+        arg_pats: &args
             .iter()
             .map(|args| args.iter().map(|arg| &*arg.pat).collect())
             .collect::<Vec<_>>(),
@@ -194,375 +302,318 @@ pub fn service(attr: TokenStream, input: TokenStream) -> TokenStream {
             .zip(camel_case_fn_names.iter())
             .map(|(rpc, name)| Ident::new(name, rpc.ident.span()))
             .collect::<Vec<_>>(),
-        future_idents: &camel_case_fn_names
-            .iter()
-            .map(|name| format_ident!("{}Fut", name))
-            .collect::<Vec<_>>(),
-        derive_serialize: if derive_serde.0 {
-            Some(&derive_serialize)
-        } else {
-            None
-        },
-    };
-
-    let tokens = vec![
-        trait_service(gen_args),
-        struct_server(gen_args),
-        impl_serve_for_server(gen_args),
-        enum_request(gen_args),
-        enum_response(gen_args),
-        enum_response_future(gen_args),
-        impl_debug_for_response_future(gen_args),
-        impl_future_for_response_future(gen_args),
-        struct_client(gen_args),
-        impl_from_for_client(gen_args),
-        impl_client_new(gen_args),
-        impl_client_rpc_methods(gen_args),
-    ];
-
-    tokens
-        .into_iter()
-        .collect::<proc_macro2::TokenStream>()
-        .into()
+        derive_serialize: derive_serialize.as_ref(),
+    }
+    .into_token_stream()
+    .into()
 }
 
 // Things needed to generate the service items: trait, serve impl, request/response enums, and
 // the client stub.
-struct GenArgs<'a> {
-    attrs: &'a [Attribute],
-    rpcs: &'a [RpcMethod],
+struct ServiceGenerator<'a> {
     service_ident: &'a Ident,
+    client_stub_ident: &'a Ident,
     server_ident: &'a Ident,
-    response_fut_ident: &'a Ident,
-    response_fut_name: &'a str,
     client_ident: &'a Ident,
     request_ident: &'a Ident,
     response_ident: &'a Ident,
-    method_attrs: &'a [&'a [Attribute]],
     vis: &'a Visibility,
-    method_names: &'a [&'a Ident],
+    attrs: &'a [Attribute],
+    rpcs: &'a [RpcMethod],
+    camel_case_idents: &'a [Ident],
+    method_idents: &'a [&'a Ident],
+    request_names: &'a [String],
+    method_attrs: &'a [&'a [Attribute]],
     args: &'a [&'a [PatType]],
     return_types: &'a [&'a Type],
-    arg_vars: &'a [Vec<&'a Pat>],
-    camel_case_idents: &'a [Ident],
-    future_idents: &'a [Ident],
-    derive_serialize: Option<&'a proc_macro2::TokenStream>,
+    arg_pats: &'a [Vec<&'a Pat>],
+    derive_serialize: Option<&'a TokenStream2>,
 }
 
-fn trait_service(
-    &GenArgs {
-        attrs,
-        rpcs,
-        vis,
-        future_idents,
-        return_types,
-        service_ident,
-        server_ident,
-        ..
-    }: &GenArgs,
-) -> proc_macro2::TokenStream {
-    let types_and_fns = rpcs
-        .iter()
-        .zip(future_idents.iter())
-        .zip(return_types.iter())
-        .map(
-            |(
-                (
+impl<'a> ServiceGenerator<'a> {
+    fn trait_service(&self) -> TokenStream2 {
+        let &Self {
+            attrs,
+            rpcs,
+            vis,
+            return_types,
+            service_ident,
+            client_stub_ident,
+            request_ident,
+            response_ident,
+            server_ident,
+            ..
+        } = self;
+
+        let rpc_fns = rpcs
+            .iter()
+            .zip(return_types.iter())
+            .map(
+                |(
                     RpcMethod {
                         attrs, ident, args, ..
                     },
-                    future_type,
-                ),
-                output,
-            )| {
-                let ty_doc = format!("The response future returned by {}.", ident);
-                quote! {
-                    #[doc = #ty_doc]
-                    type #future_type: std::future::Future<Output = #output>;
+                    output,
+                )| {
+                    quote! {
+                        #( #attrs )*
+                        async fn #ident(self, context: ::tarpc::context::Context, #( #args ),*) -> #output;
+                    }
+                },
+            );
 
-                    #( #attrs )*
-                    fn #ident(self, context: tarpc::context::Context, #( #args ),*) -> Self::#future_type;
-                }
-            },
-        );
+        let stub_doc = format!("The stub trait for service [`{service_ident}`].");
+        quote! {
+            #( #attrs )*
+            #vis trait #service_ident: ::core::marker::Sized {
+                #( #rpc_fns )*
 
-    quote! {
-        #( #attrs )*
-        #vis trait #service_ident: Clone {
-            #( #types_and_fns )*
-
-            /// Returns a serving function to use with tarpc::server::Server.
-            fn serve(self) -> #server_ident<Self> {
-                #server_ident { service: self }
-            }
-        }
-    }
-}
-
-fn struct_server(
-    &GenArgs {
-        vis, server_ident, ..
-    }: &GenArgs,
-) -> proc_macro2::TokenStream {
-    quote! {
-        #[derive(Clone)]
-        #vis struct #server_ident<S> {
-            service: S,
-        }
-    }
-}
-
-fn impl_serve_for_server(
-    &GenArgs {
-        request_ident,
-        server_ident,
-        service_ident,
-        response_ident,
-        response_fut_ident,
-        camel_case_idents,
-        arg_vars,
-        method_names,
-        ..
-    }: &GenArgs,
-) -> proc_macro2::TokenStream {
-    quote! {
-        impl<S> tarpc::server::Serve<#request_ident> for #server_ident<S>
-            where S: #service_ident
-        {
-            type Resp = #response_ident;
-            type Fut = #response_fut_ident<S>;
-
-            fn serve(self, ctx: tarpc::context::Context, req: #request_ident) -> Self::Fut {
-                match req {
-                    #(
-                        #request_ident::#camel_case_idents{ #( #arg_vars ),* } => {
-                            #response_fut_ident::#camel_case_idents(
-                                #service_ident::#method_names(
-                                    self.service, ctx, #( #arg_vars ),*))
-                        }
-                    )*
+                /// Returns a serving function to use with
+                /// [InFlightRequest::execute](::tarpc::server::InFlightRequest::execute).
+                fn serve(self) -> #server_ident<Self> {
+                    #server_ident { service: self }
                 }
             }
-        }
-    }
-}
 
-fn enum_request(
-    &GenArgs {
-        derive_serialize,
-        vis,
-        request_ident,
-        camel_case_idents,
-        args,
-        ..
-    }: &GenArgs,
-) -> proc_macro2::TokenStream {
-    quote! {
-        /// The request sent over the wire from the client to the server.
-        #[derive(Debug)]
-        #derive_serialize
-        #vis enum #request_ident {
-            #( #camel_case_idents{ #( #args ),* } ),*
-        }
-    }
-}
-
-fn enum_response(
-    &GenArgs {
-        derive_serialize,
-        vis,
-        response_ident,
-        camel_case_idents,
-        return_types,
-        ..
-    }: &GenArgs,
-) -> proc_macro2::TokenStream {
-    quote! {
-        /// The response sent over the wire from the server to the client.
-        #[derive(Debug)]
-        #derive_serialize
-        #vis enum #response_ident {
-            #( #camel_case_idents(#return_types) ),*
-        }
-    }
-}
-
-fn enum_response_future(
-    &GenArgs {
-        vis,
-        service_ident,
-        response_fut_ident,
-        camel_case_idents,
-        future_idents,
-        ..
-    }: &GenArgs,
-) -> proc_macro2::TokenStream {
-    quote! {
-        /// A future resolving to a server response.
-        #vis enum #response_fut_ident<S: #service_ident> {
-            #( #camel_case_idents(<S as #service_ident>::#future_idents) ),*
-        }
-    }
-}
-
-fn impl_debug_for_response_future(
-    &GenArgs {
-        service_ident,
-        response_fut_ident,
-        response_fut_name,
-        ..
-    }: &GenArgs,
-) -> proc_macro2::TokenStream {
-    quote! {
-        impl<S: #service_ident> std::fmt::Debug for #response_fut_ident<S> {
-            fn fmt(&self, fmt: &mut std::fmt::Formatter) -> std::fmt::Result {
-                fmt.debug_struct(#response_fut_name).finish()
+            #[doc = #stub_doc]
+            #vis trait #client_stub_ident: ::tarpc::client::stub::Stub<Req = #request_ident, Resp = #response_ident> {
             }
-        }
-    }
-}
 
-fn impl_future_for_response_future(
-    &GenArgs {
-        service_ident,
-        response_fut_ident,
-        response_ident,
-        camel_case_idents,
-        ..
-    }: &GenArgs,
-) -> proc_macro2::TokenStream {
-    quote! {
-        impl<S: #service_ident> std::future::Future for #response_fut_ident<S> {
-            type Output = #response_ident;
-
-            fn poll(self: std::pin::Pin<&mut Self>, cx: &mut std::task::Context<'_>)
-                -> std::task::Poll<#response_ident>
+            impl<S> #client_stub_ident for S
+                where S: ::tarpc::client::stub::Stub<Req = #request_ident, Resp = #response_ident>
             {
-                unsafe {
-                    match std::pin::Pin::get_unchecked_mut(self) {
+            }
+        }
+    }
+
+    fn struct_server(&self) -> TokenStream2 {
+        let &Self {
+            vis, server_ident, ..
+        } = self;
+
+        quote! {
+            /// A serving function to use with [::tarpc::server::InFlightRequest::execute].
+            #[derive(Clone)]
+            #vis struct #server_ident<S> {
+                service: S,
+            }
+        }
+    }
+
+    fn impl_serve_for_server(&self) -> TokenStream2 {
+        let &Self {
+            request_ident,
+            server_ident,
+            service_ident,
+            response_ident,
+            camel_case_idents,
+            arg_pats,
+            method_idents,
+            request_names,
+            ..
+        } = self;
+
+        quote! {
+            impl<S> ::tarpc::server::Serve for #server_ident<S>
+                where S: #service_ident
+            {
+                type Req = #request_ident;
+                type Resp = #response_ident;
+
+                fn method(&self, req: &#request_ident) -> ::core::option::Option<&'static str> {
+                    ::core::option::Option::Some(match req {
                         #(
-                            #response_fut_ident::#camel_case_idents(resp) =>
-                                std::pin::Pin::new_unchecked(resp)
-                                    .poll(cx)
-                                    .map(#response_ident::#camel_case_idents),
+                            #request_ident::#camel_case_idents{..} => {
+                                #request_names
+                            }
+                        )*
+                    })
+                }
+
+                async fn serve(self, ctx: ::tarpc::context::Context, req: #request_ident)
+                    -> ::core::result::Result<#response_ident, ::tarpc::ServerError> {
+                    match req {
+                        #(
+                            #request_ident::#camel_case_idents{ #( #arg_pats ),* } => {
+                                ::core::result::Result::Ok(#response_ident::#camel_case_idents(
+                                    #service_ident::#method_idents(
+                                        self.service, ctx, #( #arg_pats ),*
+                                    ).await
+                                ))
+                            }
                         )*
                     }
                 }
             }
         }
     }
-}
 
-fn struct_client(
-    &GenArgs {
-        vis,
-        client_ident,
-        request_ident,
-        response_ident,
-        ..
-    }: &GenArgs,
-) -> proc_macro2::TokenStream {
-    quote! {
-        #[allow(unused)]
-        #[derive(Clone, Debug)]
-        /// The client stub that makes RPC calls to the server. Exposes a Future interface.
-        #vis struct #client_ident<C = tarpc::client::Channel<#request_ident, #response_ident>>(C);
-    }
-}
+    fn enum_request(&self) -> TokenStream2 {
+        let &Self {
+            derive_serialize,
+            vis,
+            request_ident,
+            camel_case_idents,
+            args,
+            ..
+        } = self;
 
-fn impl_from_for_client(
-    &GenArgs {
-        client_ident,
-        request_ident,
-        response_ident,
-        ..
-    }: &GenArgs,
-) -> proc_macro2::TokenStream {
-    quote! {
-        impl<C> From<C> for #client_ident<C>
-            where for <'a> C: tarpc::Client<'a, #request_ident, Response = #response_ident>
-        {
-            fn from(client: C) -> Self {
-                #client_ident(client)
+        quote! {
+            /// The request sent over the wire from the client to the server.
+            #[allow(missing_docs)]
+            #[derive(Debug)]
+            #derive_serialize
+            #vis enum #request_ident {
+                #( #camel_case_idents{ #( #args ),* } ),*
             }
         }
     }
-}
 
-fn impl_client_new(
-    &GenArgs {
-        client_ident,
-        vis,
-        request_ident,
-        response_ident,
-        ..
-    }: &GenArgs,
-) -> proc_macro2::TokenStream {
-    quote! {
-        impl #client_ident {
-            /// Returns a new client stub that sends requests over the given transport.
-            #vis fn new<T>(config: tarpc::client::Config, transport: T)
-                -> tarpc::client::NewClient<
-                    Self,
-                    tarpc::client::channel::RequestDispatch<#request_ident, #response_ident, T>>
-            where
-                T: tarpc::Transport<tarpc::ClientMessage<#request_ident>, tarpc::Response<#response_ident>>
-            {
-                let new_client = tarpc::client::new(config, transport);
-                tarpc::client::NewClient {
-                    client: #client_ident(new_client.client),
-                    dispatch: new_client.dispatch,
-                }
+    fn enum_response(&self) -> TokenStream2 {
+        let &Self {
+            derive_serialize,
+            vis,
+            response_ident,
+            camel_case_idents,
+            return_types,
+            ..
+        } = self;
+
+        quote! {
+            /// The response sent over the wire from the server to the client.
+            #[allow(missing_docs)]
+            #[derive(Debug)]
+            #derive_serialize
+            #vis enum #response_ident {
+                #( #camel_case_idents(#return_types) ),*
             }
-
         }
     }
-}
 
-fn impl_client_rpc_methods(
-    &GenArgs {
-        client_ident,
-        request_ident,
-        response_ident,
-        method_attrs,
-        vis,
-        method_names,
-        args,
-        return_types,
-        arg_vars,
-        camel_case_idents,
-        ..
-    }: &GenArgs,
-) -> proc_macro2::TokenStream {
-    quote! {
-        impl<C> #client_ident<C>
-            where for<'a> C: tarpc::Client<'a, #request_ident, Response = #response_ident>
-        {
-            #(
-                #[allow(unused)]
-                #( #method_attrs )*
-                #vis fn #method_names(&mut self, ctx: tarpc::context::Context, #( #args ),*)
-                    -> impl std::future::Future<Output = std::io::Result<#return_types>> + '_ {
-                    let request = #request_ident::#camel_case_idents { #( #arg_vars ),* };
-                    let resp = tarpc::Client::call(&mut self.0, ctx, request);
-                    async move {
-                        match resp.await? {
-                            #response_ident::#camel_case_idents(msg) => std::result::Result::Ok(msg),
-                            _ => unreachable!(),
-                        }
+    fn struct_client(&self) -> TokenStream2 {
+        let &Self {
+            vis,
+            client_ident,
+            request_ident,
+            response_ident,
+            ..
+        } = self;
+
+        quote! {
+            #[allow(unused)]
+            #[derive(Clone, Debug)]
+            /// The client stub that makes RPC calls to the server. All request methods return
+            /// [Futures](::core::future::Future).
+            #vis struct #client_ident<
+                Stub = ::tarpc::client::Channel<#request_ident, #response_ident>
+            >(Stub);
+        }
+    }
+
+    fn impl_client_new(&self) -> TokenStream2 {
+        let &Self {
+            client_ident,
+            vis,
+            request_ident,
+            response_ident,
+            ..
+        } = self;
+
+        quote! {
+            impl #client_ident {
+                /// Returns a new client stub that sends requests over the given transport.
+                #vis fn new<T>(config: ::tarpc::client::Config, transport: T)
+                    -> ::tarpc::client::NewClient<
+                        Self,
+                        ::tarpc::client::RequestDispatch<#request_ident, #response_ident, T>
+                    >
+                where
+                    T: ::tarpc::Transport<::tarpc::ClientMessage<#request_ident>, ::tarpc::Response<#response_ident>>
+                {
+                    let new_client = ::tarpc::client::new(config, transport);
+                    ::tarpc::client::NewClient {
+                        client: #client_ident(new_client.client),
+                        dispatch: new_client.dispatch,
                     }
                 }
-            )*
+            }
+
+            impl<Stub> ::core::convert::From<Stub> for #client_ident<Stub>
+                where Stub: ::tarpc::client::stub::Stub<
+                    Req = #request_ident,
+                    Resp = #response_ident>
+            {
+                /// Returns a new client stub that sends requests over the given transport.
+                fn from(stub: Stub) -> Self {
+                    #client_ident(stub)
+                }
+
+            }
         }
     }
+
+    fn impl_client_rpc_methods(&self) -> TokenStream2 {
+        let &Self {
+            client_ident,
+            request_ident,
+            response_ident,
+            method_attrs,
+            vis,
+            method_idents,
+            request_names,
+            args,
+            return_types,
+            arg_pats,
+            camel_case_idents,
+            ..
+        } = self;
+
+        quote! {
+            impl<Stub> #client_ident<Stub>
+                where Stub: ::tarpc::client::stub::Stub<
+                    Req = #request_ident,
+                    Resp = #response_ident>
+            {
+                #(
+                    #[allow(unused)]
+                    #( #method_attrs )*
+                    #vis fn #method_idents(&self, ctx: ::tarpc::context::Context, #( #args ),*)
+                        -> impl ::core::future::Future<Output = ::core::result::Result<#return_types, ::tarpc::client::RpcError>> + '_ {
+                        let request = #request_ident::#camel_case_idents { #( #arg_pats ),* };
+                        let resp = self.0.call(ctx, #request_names, request);
+                        async move {
+                            match resp.await? {
+                                #response_ident::#camel_case_idents(msg) => ::core::result::Result::Ok(msg),
+                                _ => ::core::unreachable!(),
+                            }
+                        }
+                    }
+                )*
+            }
+        }
+    }
+}
+
+impl<'a> ToTokens for ServiceGenerator<'a> {
+    fn to_tokens(&self, output: &mut TokenStream2) {
+        output.extend(vec![
+            self.trait_service(),
+            self.struct_server(),
+            self.impl_serve_for_server(),
+            self.enum_request(),
+            self.enum_response(),
+            self.struct_client(),
+            self.impl_client_new(),
+            self.impl_client_rpc_methods(),
+        ])
+    }
 }
 
 fn snake_to_camel(ident_str: &str) -> String {
-    let chars = ident_str.chars();
     let mut camel_ty = String::with_capacity(ident_str.len());
 
     let mut last_char_was_underscore = true;
-    for c in chars {
+    for c in ident_str.chars() {
         match c {
             '_' => last_char_was_underscore = true,
             c if last_char_was_underscore => {

plugins/tests/server.rs

@@ -0,0 +1,44 @@
+// these need to be out here rather than inside the function so that the
+// assert_type_eq macro can pick them up.
+#[tarpc::service]
+trait Foo {
+    async fn two_part(s: String, i: i32) -> (String, i32);
+    async fn bar(s: String) -> String;
+    async fn baz();
+}
+
+#[allow(non_camel_case_types)]
+#[test]
+fn raw_idents_work() {
+    type r#yield = String;
+
+    #[tarpc::service]
+    trait r#trait {
+        async fn r#await(r#struct: r#yield, r#enum: i32) -> (r#yield, i32);
+        async fn r#fn(r#impl: r#yield) -> r#yield;
+        async fn r#async();
+    }
+}
+
+#[test]
+fn syntax() {
+    #[tarpc::service]
+    trait Syntax {
+        #[deny(warnings)]
+        #[allow(non_snake_case)]
+        async fn TestCamelCaseDoesntConflict();
+        async fn hello() -> String;
+        #[doc = "attr"]
+        async fn attr(s: String) -> String;
+        async fn no_args_no_return();
+        async fn no_args() -> ();
+        async fn one_arg(one: String) -> i32;
+        async fn two_args_no_return(one: String, two: u64);
+        async fn two_args(one: String, two: u64) -> String;
+        async fn no_args_ret_error() -> i32;
+        async fn one_arg_ret_error(one: String) -> String;
+        async fn no_arg_implicit_return_error();
+        #[doc = "attr"]
+        async fn one_arg_implicit_return_error(one: String);
+    }
+}

plugins/tests/service.rs

@@ -2,8 +2,6 @@ use tarpc::context;
 
 #[test]
 fn att_service_trait() {
-    use futures::future::{ready, Ready};
-
     #[tarpc::service]
     trait Foo {
         async fn two_part(s: String, i: i32) -> (String, i32);
@@ -12,19 +10,48 @@ fn att_service_trait() {
     }
 
     impl Foo for () {
-        type TwoPartFut = Ready<(String, i32)>;
-        fn two_part(self, _: context::Context, s: String, i: i32) -> Self::TwoPartFut {
-            ready((s, i))
+        async fn two_part(self, _: context::Context, s: String, i: i32) -> (String, i32) {
+            (s, i)
         }
 
-        type BarFut = Ready<String>;
-        fn bar(self, _: context::Context, s: String) -> Self::BarFut {
-            ready(s)
+        async fn bar(self, _: context::Context, s: String) -> String {
+            s
         }
 
-        type BazFut = Ready<()>;
-        fn baz(self, _: context::Context) -> Self::BazFut {
-            ready(())
+        async fn baz(self, _: context::Context) {
+            ()
+        }
+    }
+}
+
+#[allow(non_camel_case_types)]
+#[test]
+fn raw_idents() {
+    type r#yield = String;
+
+    #[tarpc::service]
+    trait r#trait {
+        async fn r#await(r#struct: r#yield, r#enum: i32) -> (r#yield, i32);
+        async fn r#fn(r#impl: r#yield) -> r#yield;
+        async fn r#async();
+    }
+
+    impl r#trait for () {
+        async fn r#await(
+            self,
+            _: context::Context,
+            r#struct: r#yield,
+            r#enum: i32,
+        ) -> (r#yield, i32) {
+            (r#struct, r#enum)
+        }
+
+        async fn r#fn(self, _: context::Context, r#impl: r#yield) -> r#yield {
+            r#impl
+        }
+
+        async fn r#async(self, _: context::Context) {
+            ()
         }
     }
 }

tarpc/Cargo.toml

@@ -1,57 +1,97 @@
 [package]
 name = "tarpc"
-version = "0.20.0"
-authors = ["Adam Wright <adam.austin.wright@gmail.com>", "Tim Kuehn <timothy.j.kuehn@gmail.com>"]
-edition = "2018"
+version = "0.34.0"
+rust-version = "1.58.0"
+authors = [
+    "Adam Wright <adam.austin.wright@gmail.com>",
+    "Tim Kuehn <timothy.j.kuehn@gmail.com>",
+]
+edition = "2021"
 license = "MIT"
 documentation = "https://docs.rs/tarpc"
 homepage = "https://github.com/google/tarpc"
 repository = "https://github.com/google/tarpc"
 keywords = ["rpc", "network", "server", "api", "microservices"]
 categories = ["asynchronous", "network-programming"]
-readme = "../README.md"
+readme = "README.md"
 description = "An RPC framework for Rust with a focus on ease of use."
 
 [features]
 default = []
 
-serde1 = ["tarpc-plugins/serde1", "serde", "serde/derive"]
-tokio1 = []
-serde-transport = ["tokio-serde", "tokio-util/codec"]
-tcp = ["tokio/net", "tokio/stream"]
+serde1 = ["tarpc-plugins/serde1", "serde", "serde/derive", "serde/rc"]
+tokio1 = ["tokio/rt"]
+serde-transport = ["serde1", "tokio1", "tokio-serde", "tokio-util/codec"]
+serde-transport-json = ["tokio-serde/json"]
+serde-transport-bincode = ["tokio-serde/bincode"]
+tcp = ["tokio/net"]
+unix = ["tokio/net"]
 
-full = ["serde1", "tokio1", "serde-transport", "tcp"]
+full = [
+    "serde1",
+    "tokio1",
+    "serde-transport",
+    "serde-transport-json",
+    "serde-transport-bincode",
+    "tcp",
+    "unix",
+]
 
 [badges]
 travis-ci = { repository = "google/tarpc" }
 
 [dependencies]
+anyhow = "1.0"
 fnv = "1.0"
 futures = "0.3"
-humantime = "1.0"
-log = "0.4"
-pin-project = "0.4"
-raii-counter = "0.2"
-rand = "0.7"
-tokio = { version = "0.2", features = ["time"] }
+humantime = "2.0"
+pin-project = "1.0"
+rand = "0.8"
 serde = { optional = true, version = "1.0", features = ["derive"] }
-tokio-util = { optional = true, version = "0.2" }
-tarpc-plugins = { path = "../plugins", version = "0.7" }
-tokio-serde = { optional = true, version = "0.6" }
+static_assertions = "1.1.0"
+tarpc-plugins = { path = "../plugins", version = "0.13" }
+thiserror = "1.0"
+tokio = { version = "1", features = ["time"] }
+tokio-util = { version = "0.7.3", features = ["time"] }
+tokio-serde = { optional = true, version = "0.8" }
+tracing = { version = "0.1", default-features = false, features = [
+    "attributes",
+    "log",
+] }
+tracing-opentelemetry = { version = "0.18.0", default-features = false }
+opentelemetry = { version = "0.18.0", default-features = false }
+
 
 [dev-dependencies]
-assert_matches = "1.0"
-bytes = { version = "0.5", features = ["serde"] }
-env_logger = "0.6"
-futures = "0.3"
-humantime = "1.0"
-log = "0.4"
+assert_matches = "1.4"
+bincode = "1.3"
+bytes = { version = "1", features = ["serde"] }
+flate2 = "1.0"
+futures-test = "0.3"
+opentelemetry = { version = "0.18.0", default-features = false, features = [
+    "rt-tokio",
+] }
+opentelemetry-jaeger = { version = "0.17.0", features = ["rt-tokio"] }
 pin-utils = "0.1.0-alpha"
-tokio = { version = "0.2", features = ["full"] }
-tokio-serde = { version = "0.6", features = ["json"] }
+serde_bytes = "0.11"
+tracing-subscriber = { version = "0.3", features = ["env-filter"] }
+tokio = { version = "1", features = ["full", "test-util", "tracing"] }
+console-subscriber = "0.1"
+tokio-serde = { version = "0.8", features = ["json", "bincode"] }
+trybuild = "1.0"
+tokio-rustls = "0.23"
+rustls-pemfile = "1.0"
+
+[package.metadata.docs.rs]
+all-features = true
+rustdoc-args = ["--cfg", "docsrs"]
 
 [[example]]
-name = "server_calling_server"
+name = "compression"
+required-features = ["serde-transport", "tcp"]
+
+[[example]]
+name = "tracing"
 required-features = ["full"]
 
 [[example]]
@@ -62,3 +102,18 @@ required-features = ["full"]
 name = "pubsub"
 required-features = ["full"]
 
+[[example]]
+name = "custom_transport"
+required-features = ["serde1", "tokio1", "serde-transport"]
+
+[[example]]
+name = "tls_over_tcp"
+required-features = ["full"]
+
+[[test]]
+name = "service_functional"
+required-features = ["serde-transport"]
+
+[[test]]
+name = "dataservice"
+required-features = ["serde-transport", "tcp"]

tarpc/LICENSE

@@ -0,0 +1,9 @@
+The MIT License (MIT)
+
+Copyright 2016 Google Inc. All Rights Reserved.
+
+Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.

tarpc/examples/certs/eddsa/client.cert

@@ -0,0 +1,11 @@
+-----BEGIN CERTIFICATE-----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+-----END CERTIFICATE-----

tarpc/examples/certs/eddsa/client.chain

@@ -0,0 +1,19 @@
+-----BEGIN CERTIFICATE-----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=
+-----END CERTIFICATE-----
+-----BEGIN CERTIFICATE-----
+MIIBTDCB/6ADAgECAhRZLuF0TWjDs/31OO8VeKHkNIJQaDAFBgMrZXAwHDEaMBgG
+A1UEAwwRcG9ueXRvd24gRWREU0EgQ0EwHhcNMjMwMzE3MTAxMTA0WhcNMzMwMzE0
+MTAxMTA0WjAcMRowGAYDVQQDDBFwb255dG93biBFZERTQSBDQTAqMAUGAytlcAMh
+ABRPZ4TiuBE8CqAFByZvqpMo/unjnnryfG2AkkWGXpa3o1MwUTAdBgNVHQ4EFgQU
+phSgt0p5juantCAxkquRW1JZgEowHwYDVR0jBBgwFoAUphSgt0p5juantCAxkquR
+W1JZgEowDwYDVR0TAQH/BAUwAwEB/zAFBgMrZXADQQB29o8erJA0/a8/xOHilOCC
+t/s5wPHHnS5NSKx/m2N2nRn3zPxEnETlrAmGulJoeKOx8OblwmPi9rBT2K+QY2UB
+-----END CERTIFICATE-----

tarpc/examples/certs/eddsa/client.key

@@ -0,0 +1,3 @@
+-----BEGIN PRIVATE KEY-----
+MC4CAQAwBQYDK2VwBCIEIIJX9ThTHpVS1SNZb6HP4myg4fRInIVGunTRdgnc+weH
+-----END PRIVATE KEY-----

tarpc/examples/certs/eddsa/end.cert

@@ -0,0 +1,12 @@
+-----BEGIN CERTIFICATE-----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+-----END CERTIFICATE-----

tarpc/examples/certs/eddsa/end.chain

@@ -0,0 +1,19 @@
+-----BEGIN CERTIFICATE-----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=
+-----END CERTIFICATE-----
+-----BEGIN CERTIFICATE-----
+MIIBTDCB/6ADAgECAhRZLuF0TWjDs/31OO8VeKHkNIJQaDAFBgMrZXAwHDEaMBgG
+A1UEAwwRcG9ueXRvd24gRWREU0EgQ0EwHhcNMjMwMzE3MTAxMTA0WhcNMzMwMzE0
+MTAxMTA0WjAcMRowGAYDVQQDDBFwb255dG93biBFZERTQSBDQTAqMAUGAytlcAMh
+ABRPZ4TiuBE8CqAFByZvqpMo/unjnnryfG2AkkWGXpa3o1MwUTAdBgNVHQ4EFgQU
+phSgt0p5juantCAxkquRW1JZgEowHwYDVR0jBBgwFoAUphSgt0p5juantCAxkquR
+W1JZgEowDwYDVR0TAQH/BAUwAwEB/zAFBgMrZXADQQB29o8erJA0/a8/xOHilOCC
+t/s5wPHHnS5NSKx/m2N2nRn3zPxEnETlrAmGulJoeKOx8OblwmPi9rBT2K+QY2UB
+-----END CERTIFICATE-----

tarpc/examples/certs/eddsa/end.key

@@ -0,0 +1,3 @@
+-----BEGIN PRIVATE KEY-----
+MC4CAQAwBQYDK2VwBCIEIMU6xGVe8JTpZ3bN/wajHfw6pEHt0Rd7wPBxds9eEFy2
+-----END PRIVATE KEY-----

tarpc/examples/compression.rs

@@ -0,0 +1,138 @@
+// Copyright 2022 Google LLC
+//
+// Use of this source code is governed by an MIT-style
+// license that can be found in the LICENSE file or at
+// https://opensource.org/licenses/MIT.
+
+use flate2::{read::DeflateDecoder, write::DeflateEncoder, Compression};
+use futures::{prelude::*, Sink, SinkExt, Stream, StreamExt, TryStreamExt};
+use serde::{Deserialize, Serialize};
+use serde_bytes::ByteBuf;
+use std::{io, io::Read, io::Write};
+use tarpc::{
+    client, context,
+    serde_transport::tcp,
+    server::{BaseChannel, Channel},
+    tokio_serde::formats::Bincode,
+};
+
+/// Type of compression that should be enabled on the request. The transport is free to ignore this.
+#[derive(Debug, PartialEq, Eq, Clone, Copy, Deserialize, Serialize)]
+pub enum CompressionAlgorithm {
+    Deflate,
+}
+
+#[derive(Debug, Deserialize, Serialize)]
+pub enum CompressedMessage<T> {
+    Uncompressed(T),
+    Compressed {
+        algorithm: CompressionAlgorithm,
+        payload: ByteBuf,
+    },
+}
+
+#[derive(Deserialize, Serialize)]
+enum CompressionType {
+    Uncompressed,
+    Compressed,
+}
+
+async fn compress<T>(message: T) -> io::Result<CompressedMessage<T>>
+where
+    T: Serialize,
+{
+    let message = serialize(message)?;
+    let mut encoder = DeflateEncoder::new(Vec::new(), Compression::default());
+    encoder.write_all(&message).unwrap();
+    let compressed = encoder.finish()?;
+    Ok(CompressedMessage::Compressed {
+        algorithm: CompressionAlgorithm::Deflate,
+        payload: ByteBuf::from(compressed),
+    })
+}
+
+async fn decompress<T>(message: CompressedMessage<T>) -> io::Result<T>
+where
+    for<'a> T: Deserialize<'a>,
+{
+    match message {
+        CompressedMessage::Compressed { algorithm, payload } => {
+            if algorithm != CompressionAlgorithm::Deflate {
+                return Err(io::Error::new(
+                    io::ErrorKind::InvalidData,
+                    format!("Compression algorithm {algorithm:?} not supported"),
+                ));
+            }
+            let mut deflater = DeflateDecoder::new(payload.as_slice());
+            let mut payload = ByteBuf::new();
+            deflater.read_to_end(&mut payload)?;
+            let message = deserialize(payload)?;
+            Ok(message)
+        }
+        CompressedMessage::Uncompressed(message) => Ok(message),
+    }
+}
+
+fn serialize<T: Serialize>(t: T) -> io::Result<ByteBuf> {
+    bincode::serialize(&t)
+        .map(ByteBuf::from)
+        .map_err(|e| io::Error::new(io::ErrorKind::Other, e))
+}
+
+fn deserialize<D>(message: ByteBuf) -> io::Result<D>
+where
+    for<'a> D: Deserialize<'a>,
+{
+    bincode::deserialize(message.as_ref()).map_err(|e| io::Error::new(io::ErrorKind::Other, e))
+}
+
+fn add_compression<In, Out>(
+    transport: impl Stream<Item = io::Result<CompressedMessage<In>>>
+        + Sink<CompressedMessage<Out>, Error = io::Error>,
+) -> impl Stream<Item = io::Result<In>> + Sink<Out, Error = io::Error>
+where
+    Out: Serialize,
+    for<'a> In: Deserialize<'a>,
+{
+    transport.with(compress).and_then(decompress)
+}
+
+#[tarpc::service]
+pub trait World {
+    async fn hello(name: String) -> String;
+}
+
+#[derive(Clone, Debug)]
+struct HelloServer;
+
+impl World for HelloServer {
+    async fn hello(self, _: context::Context, name: String) -> String {
+        format!("Hey, {name}!")
+    }
+}
+
+async fn spawn(fut: impl Future<Output = ()> + Send + 'static) {
+    tokio::spawn(fut);
+}
+
+#[tokio::main]
+async fn main() -> anyhow::Result<()> {
+    let mut incoming = tcp::listen("localhost:0", Bincode::default).await?;
+    let addr = incoming.local_addr();
+    tokio::spawn(async move {
+        let transport = incoming.next().await.unwrap().unwrap();
+        BaseChannel::with_defaults(add_compression(transport))
+            .execute(HelloServer.serve())
+            .for_each(spawn)
+            .await;
+    });
+
+    let transport = tcp::connect(addr, Bincode::default).await?;
+    let client = WorldClient::new(client::Config::default(), add_compression(transport)).spawn();
+
+    println!(
+        "{}",
+        client.hello(context::current(), "friend".into()).await?
+    );
+    Ok(())
+}

tarpc/examples/custom_transport.rs

@@ -0,0 +1,59 @@
+// Copyright 2022 Google LLC
+//
+// Use of this source code is governed by an MIT-style
+// license that can be found in the LICENSE file or at
+// https://opensource.org/licenses/MIT.
+
+use futures::prelude::*;
+use tarpc::context::Context;
+use tarpc::serde_transport as transport;
+use tarpc::server::{BaseChannel, Channel};
+use tarpc::tokio_serde::formats::Bincode;
+use tarpc::tokio_util::codec::length_delimited::LengthDelimitedCodec;
+use tokio::net::{UnixListener, UnixStream};
+
+#[tarpc::service]
+pub trait PingService {
+    async fn ping();
+}
+
+#[derive(Clone)]
+struct Service;
+
+impl PingService for Service {
+    async fn ping(self, _: Context) {}
+}
+
+#[tokio::main]
+async fn main() -> anyhow::Result<()> {
+    let bind_addr = "/tmp/tarpc_on_unix_example.sock";
+
+    let _ = std::fs::remove_file(bind_addr);
+
+    let listener = UnixListener::bind(bind_addr).unwrap();
+    let codec_builder = LengthDelimitedCodec::builder();
+    async fn spawn(fut: impl Future<Output = ()> + Send + 'static) {
+        tokio::spawn(fut);
+    }
+    tokio::spawn(async move {
+        loop {
+            let (conn, _addr) = listener.accept().await.unwrap();
+            let framed = codec_builder.new_framed(conn);
+            let transport = transport::new(framed, Bincode::default());
+
+            let fut = BaseChannel::with_defaults(transport)
+                .execute(Service.serve())
+                .for_each(spawn);
+            tokio::spawn(fut);
+        }
+    });
+
+    let conn = UnixStream::connect(bind_addr).await?;
+    let transport = transport::new(codec_builder.new_framed(conn), Bincode::default());
+    PingServiceClient::new(Default::default(), transport)
+        .spawn()
+        .ping(tarpc::context::current())
+        .await?;
+
+    Ok(())
+}

tarpc/examples/pubsub.rs

@@ -4,192 +4,359 @@
 // license that can be found in the LICENSE file or at
 // https://opensource.org/licenses/MIT.
 
+/// - The PubSub server sets up TCP listeners on 2 ports, the "subscriber" port and the "publisher"
+///   port. Because both publishers and subscribers initiate their connections to the PubSub
+///   server, the server requires no prior knowledge of either publishers or subscribers.
+///
+/// - Subscribers connect to the server on the server's "subscriber" port. Once a connection is
+///   established, the server acts as the client of the Subscriber service, initially requesting
+///   the topics the subscriber is interested in, and subsequently sending topical messages to the
+///   subscriber.
+///
+/// - Publishers connect to the server on the "publisher" port and, once connected, they send
+///   topical messages via Publisher service to the server. The server then broadcasts each
+///   messages to all clients subscribed to the topic of that message.
+///
+///       Subscriber                        Publisher                       PubSub Server
+/// T1        |                                 |                                 |
+/// T2        |-----Connect------------------------------------------------------>|
+/// T3        |                                 |                                 |
+/// T2        |<-------------------------------------------------------Topics-----|
+/// T2        |-----(OK) Topics-------------------------------------------------->|
+/// T3        |                                 |                                 |
+/// T4        |                                 |-----Connect-------------------->|
+/// T5        |                                 |                                 |
+/// T6        |                                 |-----Publish-------------------->|
+/// T7        |                                 |                                 |
+/// T8        |<------------------------------------------------------Receive-----|
+/// T9        |-----(OK) Receive------------------------------------------------->|
+/// T10       |                                 |                                 |
+/// T11       |                                 |<--------------(OK) Publish------|
+use anyhow::anyhow;
 use futures::{
-    future::{self, Ready},
+    channel::oneshot,
+    future::{self, AbortHandle},
     prelude::*,
-    Future,
 };
 use publisher::Publisher as _;
 use std::{
     collections::HashMap,
+    env,
+    error::Error,
     io,
     net::SocketAddr,
-    pin::Pin,
-    sync::{Arc, Mutex},
-    time::Duration,
+    sync::{Arc, Mutex, RwLock},
 };
 use subscriber::Subscriber as _;
 use tarpc::{
     client, context,
-    server::{self, Handler},
+    serde_transport::tcp,
+    server::{self, Channel},
+    tokio_serde::formats::Json,
 };
-use tokio_serde::formats::Json;
+use tokio::net::ToSocketAddrs;
+use tracing::info;
+use tracing_subscriber::prelude::*;
 
 pub mod subscriber {
     #[tarpc::service]
     pub trait Subscriber {
-        async fn receive(message: String);
+        async fn topics() -> Vec<String>;
+        async fn receive(topic: String, message: String);
     }
 }
 
 pub mod publisher {
-    use std::net::SocketAddr;
-
     #[tarpc::service]
     pub trait Publisher {
-        async fn broadcast(message: String);
-        async fn subscribe(id: u32, address: SocketAddr) -> Result<(), String>;
-        async fn unsubscribe(id: u32);
+        async fn publish(topic: String, message: String);
     }
 }
 
 #[derive(Clone, Debug)]
 struct Subscriber {
-    id: u32,
+    local_addr: SocketAddr,
+    topics: Vec<String>,
 }
 
 impl subscriber::Subscriber for Subscriber {
-    type ReceiveFut = Ready<()>;
+    async fn topics(self, _: context::Context) -> Vec<String> {
+        self.topics.clone()
+    }
 
-    fn receive(self, _: context::Context, message: String) -> Self::ReceiveFut {
-        eprintln!("{} received message: {}", self.id, message);
-        future::ready(())
+    async fn receive(self, _: context::Context, topic: String, message: String) {
+        info!(local_addr = %self.local_addr, %topic, %message, "ReceivedMessage")
+    }
+}
+
+struct SubscriberHandle(AbortHandle);
+
+impl Drop for SubscriberHandle {
+    fn drop(&mut self) {
+        self.0.abort();
     }
 }
 
 impl Subscriber {
-    async fn listen(id: u32, config: server::Config) -> io::Result<SocketAddr> {
-        let incoming = tarpc::serde_transport::tcp::listen("localhost:0", Json::default)
-            .await?
-            .filter_map(|r| future::ready(r.ok()));
-        let addr = incoming.get_ref().local_addr();
-        tokio::spawn(
-            server::new(config)
-                .incoming(incoming)
-                .take(1)
-                .respond_with(Subscriber { id }.serve()),
-        );
-        Ok(addr)
+    async fn connect(
+        publisher_addr: impl ToSocketAddrs,
+        topics: Vec<String>,
+    ) -> anyhow::Result<SubscriberHandle> {
+        let publisher = tcp::connect(publisher_addr, Json::default).await?;
+        let local_addr = publisher.local_addr()?;
+        let mut handler = server::BaseChannel::with_defaults(publisher).requests();
+        let subscriber = Subscriber { local_addr, topics };
+        // The first request is for the topics being subscribed to.
+        match handler.next().await {
+            Some(init_topics) => init_topics?.execute(subscriber.clone().serve()).await,
+            None => {
+                return Err(anyhow!(
+                    "[{}] Server never initialized the subscriber.",
+                    local_addr
+                ))
+            }
+        };
+        let (handler, abort_handle) =
+            future::abortable(handler.execute(subscriber.serve()).for_each(spawn));
+        tokio::spawn(async move {
+            match handler.await {
+                Ok(()) | Err(future::Aborted) => info!(?local_addr, "subscriber shutdown."),
+            }
+        });
+        Ok(SubscriberHandle(abort_handle))
     }
 }
 
+#[derive(Debug)]
+struct Subscription {
+    topics: Vec<String>,
+}
+
 #[derive(Clone, Debug)]
 struct Publisher {
-    clients: Arc<Mutex<HashMap<u32, subscriber::SubscriberClient>>>,
+    clients: Arc<Mutex<HashMap<SocketAddr, Subscription>>>,
+    subscriptions: Arc<RwLock<HashMap<String, HashMap<SocketAddr, subscriber::SubscriberClient>>>>,
+}
+
+struct PublisherAddrs {
+    publisher: SocketAddr,
+    subscriptions: SocketAddr,
+}
+
+async fn spawn(fut: impl Future<Output = ()> + Send + 'static) {
+    tokio::spawn(fut);
 }
 
 impl Publisher {
-    fn new() -> Publisher {
-        Publisher {
-            clients: Arc::new(Mutex::new(HashMap::new())),
+    async fn start(self) -> io::Result<PublisherAddrs> {
+        let mut connecting_publishers = tcp::listen("localhost:0", Json::default).await?;
+
+        let publisher_addrs = PublisherAddrs {
+            publisher: connecting_publishers.local_addr(),
+            subscriptions: self.clone().start_subscription_manager().await?,
+        };
+
+        info!(publisher_addr = %publisher_addrs.publisher, "listening for publishers.",);
+        tokio::spawn(async move {
+            // Because this is just an example, we know there will only be one publisher. In more
+            // realistic code, this would be a loop to continually accept new publisher
+            // connections.
+            let publisher = connecting_publishers.next().await.unwrap().unwrap();
+            info!(publisher.peer_addr = ?publisher.peer_addr(), "publisher connected.");
+
+            server::BaseChannel::with_defaults(publisher)
+                .execute(self.serve())
+                .for_each(spawn)
+                .await
+        });
+
+        Ok(publisher_addrs)
+    }
+
+    async fn start_subscription_manager(mut self) -> io::Result<SocketAddr> {
+        let mut connecting_subscribers = tcp::listen("localhost:0", Json::default)
+            .await?
+            .filter_map(|r| future::ready(r.ok()));
+        let new_subscriber_addr = connecting_subscribers.get_ref().local_addr();
+        info!(?new_subscriber_addr, "listening for subscribers.");
+
+        tokio::spawn(async move {
+            while let Some(conn) = connecting_subscribers.next().await {
+                let subscriber_addr = conn.peer_addr().unwrap();
+
+                let tarpc::client::NewClient {
+                    client: subscriber,
+                    dispatch,
+                } = subscriber::SubscriberClient::new(client::Config::default(), conn);
+                let (ready_tx, ready) = oneshot::channel();
+                self.clone()
+                    .start_subscriber_gc(subscriber_addr, dispatch, ready);
+
+                // Populate the topics
+                self.initialize_subscription(subscriber_addr, subscriber)
+                    .await;
+
+                // Signal that initialization is done.
+                ready_tx.send(()).unwrap();
+            }
+        });
+
+        Ok(new_subscriber_addr)
+    }
+
+    async fn initialize_subscription(
+        &mut self,
+        subscriber_addr: SocketAddr,
+        subscriber: subscriber::SubscriberClient,
+    ) {
+        // Populate the topics
+        if let Ok(topics) = subscriber.topics(context::current()).await {
+            self.clients.lock().unwrap().insert(
+                subscriber_addr,
+                Subscription {
+                    topics: topics.clone(),
+                },
+            );
+
+            info!(%subscriber_addr, ?topics, "subscribed to new topics");
+            let mut subscriptions = self.subscriptions.write().unwrap();
+            for topic in topics {
+                subscriptions
+                    .entry(topic)
+                    .or_insert_with(HashMap::new)
+                    .insert(subscriber_addr, subscriber.clone());
+            }
         }
     }
+
+    fn start_subscriber_gc<E: Error>(
+        self,
+        subscriber_addr: SocketAddr,
+        client_dispatch: impl Future<Output = Result<(), E>> + Send + 'static,
+        subscriber_ready: oneshot::Receiver<()>,
+    ) {
+        tokio::spawn(async move {
+            if let Err(e) = client_dispatch.await {
+                info!(
+                    %subscriber_addr,
+                    error = %e,
+                    "subscriber connection broken");
+            }
+            // Don't clean up the subscriber until initialization is done.
+            let _ = subscriber_ready.await;
+            if let Some(subscription) = self.clients.lock().unwrap().remove(&subscriber_addr) {
+                info!(
+                    "[{} unsubscribing from topics: {:?}",
+                    subscriber_addr, subscription.topics
+                );
+                let mut subscriptions = self.subscriptions.write().unwrap();
+                for topic in subscription.topics {
+                    let subscribers = subscriptions.get_mut(&topic).unwrap();
+                    subscribers.remove(&subscriber_addr);
+                    if subscribers.is_empty() {
+                        subscriptions.remove(&topic);
+                    }
+                }
+            }
+        });
+    }
 }
 
 impl publisher::Publisher for Publisher {
-    type BroadcastFut = Pin<Box<dyn Future<Output = ()> + Send>>;
-
-    fn broadcast(self, _: context::Context, message: String) -> Self::BroadcastFut {
-        async fn broadcast(
-            clients: Arc<Mutex<HashMap<u32, subscriber::SubscriberClient>>>,
-            message: String,
-        ) {
-            let mut clients = clients.lock().unwrap().clone();
-            for client in clients.values_mut() {
-                // Ignore failing subscribers. In a real pubsub,
-                // you'd want to continually retry until subscribers
-                // ack.
-                let _ = client.receive(context::current(), message.clone()).await;
+    async fn publish(self, _: context::Context, topic: String, message: String) {
+        info!("received message to publish.");
+        let mut subscribers = match self.subscriptions.read().unwrap().get(&topic) {
+            None => return,
+            Some(subscriptions) => subscriptions.clone(),
+        };
+        let mut publications = Vec::new();
+        for client in subscribers.values_mut() {
+            publications.push(client.receive(context::current(), topic.clone(), message.clone()));
+        }
+        // Ignore failing subscribers. In a real pubsub, you'd want to continually retry until
+        // subscribers ack. Of course, a lot would be different in a real pubsub :)
+        for response in future::join_all(publications).await {
+            if let Err(e) = response {
+                info!("failed to broadcast to subscriber: {}", e);
             }
         }
-
-        broadcast(self.clients.clone(), message).boxed()
-    }
-
-    type SubscribeFut = Pin<Box<dyn Future<Output = Result<(), String>> + Send>>;
-
-    fn subscribe(self, _: context::Context, id: u32, addr: SocketAddr) -> Self::SubscribeFut {
-        async fn subscribe(
-            clients: Arc<Mutex<HashMap<u32, subscriber::SubscriberClient>>>,
-            id: u32,
-            addr: SocketAddr,
-        ) -> io::Result<()> {
-            let conn = tarpc::serde_transport::tcp::connect(addr, Json::default()).await?;
-            let subscriber =
-                subscriber::SubscriberClient::new(client::Config::default(), conn).spawn()?;
-            eprintln!("Subscribing {}.", id);
-            clients.lock().unwrap().insert(id, subscriber);
-            Ok(())
-        }
-
-        subscribe(Arc::clone(&self.clients), id, addr)
-            .map_err(|e| e.to_string())
-            .boxed()
-    }
-
-    type UnsubscribeFut = Pin<Box<dyn Future<Output = ()> + Send>>;
-
-    fn unsubscribe(self, _: context::Context, id: u32) -> Self::UnsubscribeFut {
-        eprintln!("Unsubscribing {}", id);
-        let mut clients = self.clients.lock().unwrap();
-        if clients.remove(&id).is_none() {
-            eprintln!(
-                "Client {} not found. Existings clients: {:?}",
-                id, &*clients
-            );
-        }
-        future::ready(()).boxed()
     }
 }
 
-#[tokio::main]
-async fn main() -> io::Result<()> {
-    env_logger::init();
+/// Initializes an OpenTelemetry tracing subscriber with a Jaeger backend.
+fn init_tracing(service_name: &str) -> anyhow::Result<()> {
+    env::set_var("OTEL_BSP_MAX_EXPORT_BATCH_SIZE", "12");
+    let tracer = opentelemetry_jaeger::new_agent_pipeline()
+        .with_service_name(service_name)
+        .with_max_packet_size(2usize.pow(13))
+        .install_batch(opentelemetry::runtime::Tokio)?;
 
-    let transport = tarpc::serde_transport::tcp::listen("localhost:0", Json::default)
-        .await?
-        .filter_map(|r| future::ready(r.ok()));
-    let publisher_addr = transport.get_ref().local_addr();
-    tokio::spawn(
-        transport
-            .take(1)
-            .map(server::BaseChannel::with_defaults)
-            .respond_with(Publisher::new().serve()),
-    );
-
-    let subscriber1 = Subscriber::listen(0, server::Config::default()).await?;
-    let subscriber2 = Subscriber::listen(1, server::Config::default()).await?;
-
-    let publisher_conn = tarpc::serde_transport::tcp::connect(publisher_addr, Json::default());
-    let publisher_conn = publisher_conn.await?;
-    let mut publisher =
-        publisher::PublisherClient::new(client::Config::default(), publisher_conn).spawn()?;
-
-    if let Err(e) = publisher
-        .subscribe(context::current(), 0, subscriber1)
-        .await?
-    {
-        eprintln!("Couldn't subscribe subscriber 0: {}", e);
-    }
-    if let Err(e) = publisher
-        .subscribe(context::current(), 1, subscriber2)
-        .await?
-    {
-        eprintln!("Couldn't subscribe subscriber 1: {}", e);
-    }
-
-    println!("Broadcasting...");
-    publisher
-        .broadcast(context::current(), "hello to all".to_string())
-        .await?;
-    publisher.unsubscribe(context::current(), 1).await?;
-    publisher
-        .broadcast(context::current(), "hi again".to_string())
-        .await?;
-    drop(publisher);
-
-    tokio::time::delay_for(Duration::from_millis(100)).await;
-    println!("Done.");
+    tracing_subscriber::registry()
+        .with(tracing_subscriber::filter::EnvFilter::from_default_env())
+        .with(tracing_subscriber::fmt::layer())
+        .with(tracing_opentelemetry::layer().with_tracer(tracer))
+        .try_init()?;
+
+    Ok(())
+}
+
+#[tokio::main]
+async fn main() -> anyhow::Result<()> {
+    init_tracing("Pub/Sub")?;
+
+    let addrs = Publisher {
+        clients: Arc::new(Mutex::new(HashMap::new())),
+        subscriptions: Arc::new(RwLock::new(HashMap::new())),
+    }
+    .start()
+    .await?;
+
+    let _subscriber0 = Subscriber::connect(
+        addrs.subscriptions,
+        vec!["calculus".into(), "cool shorts".into()],
+    )
+    .await?;
+
+    let _subscriber1 = Subscriber::connect(
+        addrs.subscriptions,
+        vec!["cool shorts".into(), "history".into()],
+    )
+    .await?;
+
+    let publisher = publisher::PublisherClient::new(
+        client::Config::default(),
+        tcp::connect(addrs.publisher, Json::default).await?,
+    )
+    .spawn();
+
+    publisher
+        .publish(context::current(), "calculus".into(), "sqrt(2)".into())
+        .await?;
+
+    publisher
+        .publish(
+            context::current(),
+            "cool shorts".into(),
+            "hello to all".into(),
+        )
+        .await?;
+
+    publisher
+        .publish(context::current(), "history".into(), "napoleon".to_string())
+        .await?;
+
+    drop(_subscriber0);
+
+    publisher
+        .publish(
+            context::current(),
+            "cool shorts".into(),
+            "hello to who?".into(),
+        )
+        .await?;
+
+    opentelemetry::global::shutdown_tracer_provider();
+    info!("done.");
 
     Ok(())
 }

tarpc/examples/readme.rs

@@ -4,16 +4,11 @@
 // license that can be found in the LICENSE file or at
 // https://opensource.org/licenses/MIT.
 
-use futures::{
-    future::{self, Ready},
-    prelude::*,
-};
-use std::io;
+use futures::prelude::*;
 use tarpc::{
     client, context,
-    server::{BaseChannel, Channel},
+    server::{self, Channel},
 };
-use tokio_serde::formats::Json;
 
 /// This is the service definition. It looks a lot like a trait definition.
 /// It defines one RPC, hello, which takes one arg, name, and returns a String.
@@ -28,52 +23,32 @@ pub trait World {
 struct HelloServer;
 
 impl World for HelloServer {
-    // Each defined rpc generates two items in the trait, a fn that serves the RPC, and
-    // an associated type representing the future output by the fn.
-
-    type HelloFut = Ready<String>;
-
-    fn hello(self, _: context::Context, name: String) -> Self::HelloFut {
-        future::ready(format!("Hello, {}!", name))
+    async fn hello(self, _: context::Context, name: String) -> String {
+        format!("Hello, {name}!")
     }
 }
 
+async fn spawn(fut: impl Future<Output = ()> + Send + 'static) {
+    tokio::spawn(fut);
+}
+
 #[tokio::main]
-async fn main() -> io::Result<()> {
-    // tarpc_json_transport is provided by the associated crate json_transport. It makes it
-    // easy to start up a serde-powered JSON serialization strategy over TCP.
-    let mut transport = tarpc::serde_transport::tcp::listen("localhost:0", Json::default).await?;
-    let addr = transport.local_addr();
+async fn main() -> anyhow::Result<()> {
+    let (client_transport, server_transport) = tarpc::transport::channel::unbounded();
 
-    let server = async move {
-        // For this example, we're just going to wait for one connection.
-        let client = transport.next().await.unwrap().unwrap();
+    let server = server::BaseChannel::with_defaults(server_transport);
+    tokio::spawn(server.execute(HelloServer.serve()).for_each(spawn));
 
-        // `Channel` is a trait representing a server-side connection. It is a trait to allow
-        // for some channels to be instrumented: for example, to track the number of open connections.
-        // BaseChannel is the most basic channel, simply wrapping a transport with no added
-        // functionality.
-        BaseChannel::with_defaults(client)
-            // serve_world is generated by the tarpc::service attribute. It takes as input any type
-            // implementing the generated World trait.
-            .respond_with(HelloServer.serve())
-            .execute()
-            .await;
-    };
-    tokio::spawn(server);
-
-    let transport = tarpc::serde_transport::tcp::connect(addr, Json::default()).await?;
-
-    // WorldClient is generated by the tarpc::service attribute. It has a constructor `new` that
-    // takes a config and any Transport as input.
-    let mut client = WorldClient::new(client::Config::default(), transport).spawn()?;
+    // WorldClient is generated by the #[tarpc::service] attribute. It has a constructor `new`
+    // that takes a config and any Transport as input.
+    let client = WorldClient::new(client::Config::default(), client_transport).spawn();
 
     // The client has an RPC method for each RPC defined in the annotated trait. It takes the same
     // args as defined, with the addition of a Context, which is always the first arg. The Context
     // specifies a deadline and trace information which can be helpful in debugging requests.
     let hello = client.hello(context::current(), "Stim".to_string()).await?;
 
-    eprintln!("{}", hello);
+    println!("{hello}");
 
     Ok(())
 }

tarpc/examples/server_calling_server.rs

@@ -1,101 +0,0 @@
-// Copyright 2018 Google LLC
-//
-// Use of this source code is governed by an MIT-style
-// license that can be found in the LICENSE file or at
-// https://opensource.org/licenses/MIT.
-
-use crate::{add::Add as AddService, double::Double as DoubleService};
-use futures::{
-    future::{self, Ready},
-    prelude::*,
-};
-use std::{io, pin::Pin};
-use tarpc::{
-    client, context,
-    server::{Handler, Server},
-};
-use tokio_serde::formats::Json;
-
-pub mod add {
-    #[tarpc::service]
-    pub trait Add {
-        /// Add two ints together.
-        async fn add(x: i32, y: i32) -> i32;
-    }
-}
-
-pub mod double {
-    #[tarpc::service]
-    pub trait Double {
-        /// 2 * x
-        async fn double(x: i32) -> Result<i32, String>;
-    }
-}
-
-#[derive(Clone)]
-struct AddServer;
-
-impl AddService for AddServer {
-    type AddFut = Ready<i32>;
-
-    fn add(self, _: context::Context, x: i32, y: i32) -> Self::AddFut {
-        future::ready(x + y)
-    }
-}
-
-#[derive(Clone)]
-struct DoubleServer {
-    add_client: add::AddClient,
-}
-
-impl DoubleService for DoubleServer {
-    type DoubleFut = Pin<Box<dyn Future<Output = Result<i32, String>> + Send>>;
-
-    fn double(self, _: context::Context, x: i32) -> Self::DoubleFut {
-        async fn double(mut client: add::AddClient, x: i32) -> Result<i32, String> {
-            client
-                .add(context::current(), x, x)
-                .await
-                .map_err(|e| e.to_string())
-        }
-
-        double(self.add_client.clone(), x).boxed()
-    }
-}
-
-#[tokio::main]
-async fn main() -> io::Result<()> {
-    env_logger::init();
-
-    let add_listener = tarpc::serde_transport::tcp::listen("localhost:0", Json::default)
-        .await?
-        .filter_map(|r| future::ready(r.ok()));
-    let addr = add_listener.get_ref().local_addr();
-    let add_server = Server::default()
-        .incoming(add_listener)
-        .take(1)
-        .respond_with(AddServer.serve());
-    tokio::spawn(add_server);
-
-    let to_add_server = tarpc::serde_transport::tcp::connect(addr, Json::default()).await?;
-    let add_client = add::AddClient::new(client::Config::default(), to_add_server).spawn()?;
-
-    let double_listener = tarpc::serde_transport::tcp::listen("localhost:0", Json::default)
-        .await?
-        .filter_map(|r| future::ready(r.ok()));
-    let addr = double_listener.get_ref().local_addr();
-    let double_server = tarpc::Server::default()
-        .incoming(double_listener)
-        .take(1)
-        .respond_with(DoubleServer { add_client }.serve());
-    tokio::spawn(double_server);
-
-    let to_double_server = tarpc::serde_transport::tcp::connect(addr, Json::default()).await?;
-    let mut double_client =
-        double::DoubleClient::new(client::Config::default(), to_double_server).spawn()?;
-
-    for i in 1..=5 {
-        eprintln!("{:?}", double_client.double(context::current(), i).await?);
-    }
-    Ok(())
-}

tarpc/examples/tls_over_tcp.rs

@@ -0,0 +1,150 @@
+// Copyright 2023 Google LLC
+//
+// Use of this source code is governed by an MIT-style
+// license that can be found in the LICENSE file or at
+// https://opensource.org/licenses/MIT.
+
+use futures::prelude::*;
+use rustls_pemfile::certs;
+use std::io::{BufReader, Cursor};
+use std::net::{IpAddr, Ipv4Addr};
+use tokio_rustls::rustls::server::AllowAnyAuthenticatedClient;
+
+use std::sync::Arc;
+use tokio::net::TcpListener;
+use tokio::net::TcpStream;
+use tokio_rustls::rustls::{self, RootCertStore};
+use tokio_rustls::{TlsAcceptor, TlsConnector};
+
+use tarpc::context::Context;
+use tarpc::serde_transport as transport;
+use tarpc::server::{BaseChannel, Channel};
+use tarpc::tokio_serde::formats::Bincode;
+use tarpc::tokio_util::codec::length_delimited::LengthDelimitedCodec;
+
+#[tarpc::service]
+pub trait PingService {
+    async fn ping() -> String;
+}
+
+#[derive(Clone)]
+struct Service;
+
+impl PingService for Service {
+    async fn ping(self, _: Context) -> String {
+        "🔒".to_owned()
+    }
+}
+
+// certs were generated with openssl 3 https://github.com/rustls/rustls/tree/main/test-ca
+// used on client-side for server tls
+const END_CHAIN: &str = include_str!("certs/eddsa/end.chain");
+// used on client-side for client-auth
+const CLIENT_PRIVATEKEY_CLIENT_AUTH: &str = include_str!("certs/eddsa/client.key");
+const CLIENT_CERT_CLIENT_AUTH: &str = include_str!("certs/eddsa/client.cert");
+
+// used on server-side for server tls
+const END_CERT: &str = include_str!("certs/eddsa/end.cert");
+const END_PRIVATEKEY: &str = include_str!("certs/eddsa/end.key");
+// used on server-side for client-auth
+const CLIENT_CHAIN_CLIENT_AUTH: &str = include_str!("certs/eddsa/client.chain");
+
+pub fn load_certs(data: &str) -> Vec<rustls::Certificate> {
+    certs(&mut BufReader::new(Cursor::new(data)))
+        .unwrap()
+        .into_iter()
+        .map(rustls::Certificate)
+        .collect()
+}
+
+pub fn load_private_key(key: &str) -> rustls::PrivateKey {
+    let mut reader = BufReader::new(Cursor::new(key));
+    loop {
+        match rustls_pemfile::read_one(&mut reader).expect("cannot parse private key .pem file") {
+            Some(rustls_pemfile::Item::RSAKey(key)) => return rustls::PrivateKey(key),
+            Some(rustls_pemfile::Item::PKCS8Key(key)) => return rustls::PrivateKey(key),
+            Some(rustls_pemfile::Item::ECKey(key)) => return rustls::PrivateKey(key),
+            None => break,
+            _ => {}
+        }
+    }
+    panic!("no keys found in {:?} (encrypted keys not supported)", key);
+}
+
+async fn spawn(fut: impl Future<Output = ()> + Send + 'static) {
+    tokio::spawn(fut);
+}
+
+#[tokio::main]
+async fn main() -> anyhow::Result<()> {
+    // -------------------- start here to setup tls tcp tokio stream --------------------------
+    // ref certs and loading from: https://github.com/tokio-rs/tls/blob/master/tokio-rustls/tests/test.rs
+    // ref basic tls server setup from: https://github.com/tokio-rs/tls/blob/master/tokio-rustls/examples/server/src/main.rs
+    let cert = load_certs(END_CERT);
+    let key = load_private_key(END_PRIVATEKEY);
+    let server_addr = (IpAddr::V4(Ipv4Addr::LOCALHOST), 5000);
+
+    // ------------- server side client_auth cert loading start
+    let mut client_auth_roots = RootCertStore::empty();
+    for root in load_certs(CLIENT_CHAIN_CLIENT_AUTH) {
+        client_auth_roots.add(&root).unwrap();
+    }
+    let client_auth = AllowAnyAuthenticatedClient::new(client_auth_roots);
+    // ------------- server side client_auth cert loading end
+
+    let config = rustls::ServerConfig::builder()
+        .with_safe_defaults()
+        .with_client_cert_verifier(client_auth) // use .with_no_client_auth() instead if you don't want client-auth
+        .with_single_cert(cert, key)
+        .unwrap();
+    let acceptor = TlsAcceptor::from(Arc::new(config));
+    let listener = TcpListener::bind(&server_addr).await.unwrap();
+    let codec_builder = LengthDelimitedCodec::builder();
+
+    // ref ./custom_transport.rs server side
+    tokio::spawn(async move {
+        loop {
+            let (stream, _peer_addr) = listener.accept().await.unwrap();
+            let tls_stream = acceptor.accept(stream).await.unwrap();
+            let framed = codec_builder.new_framed(tls_stream);
+
+            let transport = transport::new(framed, Bincode::default());
+
+            let fut = BaseChannel::with_defaults(transport)
+                .execute(Service.serve())
+                .for_each(spawn);
+            tokio::spawn(fut);
+        }
+    });
+
+    // ---------------------- client connection ---------------------
+    // tls client connection from https://github.com/tokio-rs/tls/blob/master/tokio-rustls/examples/client/src/main.rs
+    let mut root_store = rustls::RootCertStore::empty();
+    for root in load_certs(END_CHAIN) {
+        root_store.add(&root).unwrap();
+    }
+
+    let client_auth_private_key = load_private_key(CLIENT_PRIVATEKEY_CLIENT_AUTH);
+    let client_auth_certs = load_certs(CLIENT_CERT_CLIENT_AUTH);
+
+    let config = rustls::ClientConfig::builder()
+        .with_safe_defaults()
+        .with_root_certificates(root_store)
+        .with_single_cert(client_auth_certs, client_auth_private_key)?; // use .with_no_client_auth() instead if you don't want client-auth
+
+    let domain = rustls::ServerName::try_from("localhost")?;
+    let connector = TlsConnector::from(Arc::new(config));
+
+    let stream = TcpStream::connect(server_addr).await?;
+    let stream = connector.connect(domain, stream).await?;
+
+    let transport = transport::new(codec_builder.new_framed(stream), Bincode::default());
+    let answer = PingServiceClient::new(Default::default(), transport)
+        .spawn()
+        .ping(tarpc::context::current())
+        .await?;
+
+    println!("ping answer: {answer}");
+
+    Ok(())
+}

tarpc/examples/tracing.rs

@@ -0,0 +1,190 @@
+// Copyright 2018 Google LLC
+//
+// Use of this source code is governed by an MIT-style
+// license that can be found in the LICENSE file or at
+// https://opensource.org/licenses/MIT.
+
+use crate::{
+    add::{Add as AddService, AddStub},
+    double::Double as DoubleService,
+};
+use futures::{future, prelude::*};
+use std::{
+    io,
+    sync::{
+        atomic::{AtomicBool, Ordering},
+        Arc,
+    },
+};
+use tarpc::{
+    client::{
+        self,
+        stub::{load_balance, retry},
+        RpcError,
+    },
+    context, serde_transport,
+    server::{
+        incoming::{spawn_incoming, Incoming},
+        request_hook::{self, BeforeRequestList},
+        BaseChannel,
+    },
+    tokio_serde::formats::Json,
+    ClientMessage, Response, ServerError, Transport,
+};
+use tokio::net::TcpStream;
+use tracing_subscriber::prelude::*;
+
+pub mod add {
+    #[tarpc::service]
+    pub trait Add {
+        /// Add two ints together.
+        async fn add(x: i32, y: i32) -> i32;
+    }
+}
+
+pub mod double {
+    #[tarpc::service]
+    pub trait Double {
+        /// 2 * x
+        async fn double(x: i32) -> Result<i32, String>;
+    }
+}
+
+#[derive(Clone)]
+struct AddServer;
+
+impl AddService for AddServer {
+    async fn add(self, _: context::Context, x: i32, y: i32) -> i32 {
+        x + y
+    }
+}
+
+#[derive(Clone)]
+struct DoubleServer<Stub> {
+    add_client: add::AddClient<Stub>,
+}
+
+impl<Stub> DoubleService for DoubleServer<Stub>
+where
+    Stub: AddStub + Clone + Send + Sync + 'static,
+{
+    async fn double(self, _: context::Context, x: i32) -> Result<i32, String> {
+        self.add_client
+            .add(context::current(), x, x)
+            .await
+            .map_err(|e| e.to_string())
+    }
+}
+
+fn init_tracing(service_name: &str) -> anyhow::Result<()> {
+    let tracer = opentelemetry_jaeger::new_agent_pipeline()
+        .with_service_name(service_name)
+        .with_auto_split_batch(true)
+        .with_max_packet_size(2usize.pow(13))
+        .install_batch(opentelemetry::runtime::Tokio)?;
+
+    tracing_subscriber::registry()
+        .with(tracing_subscriber::EnvFilter::from_default_env())
+        .with(tracing_subscriber::fmt::layer())
+        .with(tracing_opentelemetry::layer().with_tracer(tracer))
+        .try_init()?;
+
+    Ok(())
+}
+
+async fn listen_on_random_port<Item, SinkItem>() -> anyhow::Result<(
+    impl Stream<Item = serde_transport::Transport<TcpStream, Item, SinkItem, Json<Item, SinkItem>>>,
+    std::net::SocketAddr,
+)>
+where
+    Item: for<'de> serde::Deserialize<'de>,
+    SinkItem: serde::Serialize,
+{
+    let listener = tarpc::serde_transport::tcp::listen("localhost:0", Json::default)
+        .await?
+        .filter_map(|r| future::ready(r.ok()))
+        .take(1);
+    let addr = listener.get_ref().get_ref().local_addr();
+    Ok((listener, addr))
+}
+
+fn make_stub<Req, Resp, const N: usize>(
+    backends: [impl Transport<ClientMessage<Arc<Req>>, Response<Resp>> + Send + Sync + 'static; N],
+) -> retry::Retry<
+    impl Fn(&Result<Resp, RpcError>, u32) -> bool + Clone,
+    load_balance::RoundRobin<client::Channel<Arc<Req>, Resp>>,
+>
+where
+    Req: Send + Sync + 'static,
+    Resp: Send + Sync + 'static,
+{
+    let stub = load_balance::RoundRobin::new(
+        backends
+            .into_iter()
+            .map(|transport| tarpc::client::new(client::Config::default(), transport).spawn())
+            .collect(),
+    );
+    let stub = retry::Retry::new(stub, |resp, attempts| {
+        if let Err(e) = resp {
+            tracing::warn!("Got an error: {e:?}");
+            attempts < 3
+        } else {
+            false
+        }
+    });
+    stub
+}
+
+#[tokio::main]
+async fn main() -> anyhow::Result<()> {
+    init_tracing("tarpc_tracing_example")?;
+
+    let (add_listener1, addr1) = listen_on_random_port().await?;
+    let (add_listener2, addr2) = listen_on_random_port().await?;
+    let something_bad_happened = Arc::new(AtomicBool::new(false));
+    let server = request_hook::before()
+        .then_fn(move |_: &mut _, _: &_| {
+            let something_bad_happened = something_bad_happened.clone();
+            async move {
+                if something_bad_happened.fetch_xor(true, Ordering::Relaxed) {
+                    Err(ServerError::new(
+                        io::ErrorKind::NotFound,
+                        "Gamma Ray!".into(),
+                    ))
+                } else {
+                    Ok(())
+                }
+            }
+        })
+        .serving(AddServer.serve());
+    let add_server = add_listener1
+        .chain(add_listener2)
+        .map(BaseChannel::with_defaults);
+    tokio::spawn(spawn_incoming(add_server.execute(server)));
+
+    let add_client = add::AddClient::from(make_stub([
+        tarpc::serde_transport::tcp::connect(addr1, Json::default).await?,
+        tarpc::serde_transport::tcp::connect(addr2, Json::default).await?,
+    ]));
+
+    let double_listener = tarpc::serde_transport::tcp::listen("localhost:0", Json::default)
+        .await?
+        .filter_map(|r| future::ready(r.ok()));
+    let addr = double_listener.get_ref().local_addr();
+    let double_server = double_listener.map(BaseChannel::with_defaults).take(1);
+    let server = DoubleServer { add_client }.serve();
+    tokio::spawn(spawn_incoming(double_server.execute(server)));
+
+    let to_double_server = tarpc::serde_transport::tcp::connect(addr, Json::default).await?;
+    let double_client =
+        double::DoubleClient::new(client::Config::default(), to_double_server).spawn();
+
+    let ctx = context::current();
+    for _ in 1..=5 {
+        tracing::info!("{:?}", double_client.double(ctx, 1).await?);
+    }
+
+    opentelemetry::global::shutdown_tracer_provider();
+
+    Ok(())
+}

tarpc/src/cancellations.rs

@@ -0,0 +1,49 @@
+use futures::{prelude::*, task::*};
+use std::pin::Pin;
+use tokio::sync::mpsc;
+
+/// Sends request cancellation signals.
+#[derive(Debug, Clone)]
+pub struct RequestCancellation(mpsc::UnboundedSender<u64>);
+
+/// A stream of IDs of requests that have been canceled.
+#[derive(Debug)]
+pub struct CanceledRequests(mpsc::UnboundedReceiver<u64>);
+
+/// Returns a channel to send request cancellation messages.
+pub fn cancellations() -> (RequestCancellation, CanceledRequests) {
+    // Unbounded because messages are sent in the drop fn. This is fine, because it's still
+    // bounded by the number of in-flight requests.
+    let (tx, rx) = mpsc::unbounded_channel();
+    (RequestCancellation(tx), CanceledRequests(rx))
+}
+
+impl RequestCancellation {
+    /// Cancels the request with ID `request_id`.
+    ///
+    /// No validation is done of `request_id`. There is no way to know if the request id provided
+    /// corresponds to a request actually tracked by the backing channel. `RequestCancellation` is
+    /// a one-way communication channel.
+    ///
+    /// Once request data is cleaned up, a response will never be received by the client. This is
+    /// useful primarily when request processing ends prematurely for requests with long deadlines
+    /// which would otherwise continue to be tracked by the backing channel—a kind of leak.
+    pub fn cancel(&self, request_id: u64) {
+        let _ = self.0.send(request_id);
+    }
+}
+
+impl CanceledRequests {
+    /// Polls for a cancelled request.
+    pub fn poll_recv(&mut self, cx: &mut Context<'_>) -> Poll<Option<u64>> {
+        self.0.poll_recv(cx)
+    }
+}
+
+impl Stream for CanceledRequests {
+    type Item = u64;
+
+    fn poll_next(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Option<u64>> {
+        self.poll_recv(cx)
+    }
+}

tarpc/src/client/in_flight_requests.rs

@@ -0,0 +1,137 @@
+use crate::{
+    context,
+    util::{Compact, TimeUntil},
+};
+use fnv::FnvHashMap;
+use std::{
+    collections::hash_map,
+    task::{Context, Poll},
+};
+use tokio::sync::oneshot;
+use tokio_util::time::delay_queue::{self, DelayQueue};
+use tracing::Span;
+
+/// Requests already written to the wire that haven't yet received responses.
+#[derive(Debug)]
+pub struct InFlightRequests<Resp> {
+    request_data: FnvHashMap<u64, RequestData<Resp>>,
+    deadlines: DelayQueue<u64>,
+}
+
+impl<Resp> Default for InFlightRequests<Resp> {
+    fn default() -> Self {
+        Self {
+            request_data: Default::default(),
+            deadlines: Default::default(),
+        }
+    }
+}
+
+#[derive(Debug)]
+struct RequestData<Res> {
+    ctx: context::Context,
+    span: Span,
+    response_completion: oneshot::Sender<Res>,
+    /// The key to remove the timer for the request's deadline.
+    deadline_key: delay_queue::Key,
+}
+
+/// An error returned when an attempt is made to insert a request with an ID that is already in
+/// use.
+#[derive(Debug)]
+pub struct AlreadyExistsError;
+
+impl<Res> InFlightRequests<Res> {
+    /// Returns the number of in-flight requests.
+    pub fn len(&self) -> usize {
+        self.request_data.len()
+    }
+
+    /// Returns true iff there are no requests in flight.
+    pub fn is_empty(&self) -> bool {
+        self.request_data.is_empty()
+    }
+
+    /// Starts a request, unless a request with the same ID is already in flight.
+    pub fn insert_request(
+        &mut self,
+        request_id: u64,
+        ctx: context::Context,
+        span: Span,
+        response_completion: oneshot::Sender<Res>,
+    ) -> Result<(), AlreadyExistsError> {
+        match self.request_data.entry(request_id) {
+            hash_map::Entry::Vacant(vacant) => {
+                let timeout = ctx.deadline.time_until();
+                let deadline_key = self.deadlines.insert(request_id, timeout);
+                vacant.insert(RequestData {
+                    ctx,
+                    span,
+                    response_completion,
+                    deadline_key,
+                });
+                Ok(())
+            }
+            hash_map::Entry::Occupied(_) => Err(AlreadyExistsError),
+        }
+    }
+
+    /// Removes a request without aborting. Returns true iff the request was found.
+    pub fn complete_request(&mut self, request_id: u64, result: Res) -> Option<Span> {
+        if let Some(request_data) = self.request_data.remove(&request_id) {
+            self.request_data.compact(0.1);
+            self.deadlines.remove(&request_data.deadline_key);
+            let _ = request_data.response_completion.send(result);
+            return Some(request_data.span);
+        }
+
+        tracing::debug!("No in-flight request found for request_id = {request_id}.");
+
+        // If the response completion was absent, then the request was already canceled.
+        None
+    }
+
+    /// Completes all requests using the provided function.
+    /// Returns Spans for all completes requests.
+    pub fn complete_all_requests<'a>(
+        &'a mut self,
+        mut result: impl FnMut() -> Res + 'a,
+    ) -> impl Iterator<Item = Span> + 'a {
+        self.deadlines.clear();
+        self.request_data.drain().map(move |(_, request_data)| {
+            let _ = request_data.response_completion.send(result());
+            request_data.span
+        })
+    }
+
+    /// Cancels a request without completing (typically used when a request handle was dropped
+    /// before the request completed).
+    pub fn cancel_request(&mut self, request_id: u64) -> Option<(context::Context, Span)> {
+        if let Some(request_data) = self.request_data.remove(&request_id) {
+            self.request_data.compact(0.1);
+            self.deadlines.remove(&request_data.deadline_key);
+            Some((request_data.ctx, request_data.span))
+        } else {
+            None
+        }
+    }
+
+    /// Yields a request that has expired, completing it with a TimedOut error.
+    /// The caller should send cancellation messages for any yielded request ID.
+    pub fn poll_expired(
+        &mut self,
+        cx: &mut Context,
+        expired_error: impl Fn() -> Res,
+    ) -> Poll<Option<u64>> {
+        self.deadlines.poll_expired(cx).map(|expired| {
+            let request_id = expired?.into_inner();
+            if let Some(request_data) = self.request_data.remove(&request_id) {
+                let _entered = request_data.span.enter();
+                tracing::error!("DeadlineExceeded");
+                self.request_data.compact(0.1);
+                let _ = request_data.response_completion.send(expired_error());
+            }
+            Some(request_id)
+        })
+    }
+}

tarpc/src/client/stub.rs

@@ -0,0 +1,45 @@
+//! Provides a Stub trait, implemented by types that can call remote services.
+
+use crate::{
+    client::{Channel, RpcError},
+    context,
+};
+
+pub mod load_balance;
+pub mod retry;
+
+#[cfg(test)]
+mod mock;
+
+/// A connection to a remote service.
+/// Calls the service with requests of type `Req` and receives responses of type `Resp`.
+#[allow(async_fn_in_trait)]
+pub trait Stub {
+    /// The service request type.
+    type Req;
+
+    /// The service response type.
+    type Resp;
+
+    /// Calls a remote service.
+    async fn call(
+        &self,
+        ctx: context::Context,
+        request_name: &'static str,
+        request: Self::Req,
+    ) -> Result<Self::Resp, RpcError>;
+}
+
+impl<Req, Resp> Stub for Channel<Req, Resp> {
+    type Req = Req;
+    type Resp = Resp;
+
+    async fn call(
+        &self,
+        ctx: context::Context,
+        request_name: &'static str,
+        request: Req,
+    ) -> Result<Self::Resp, RpcError> {
+        Self::call(self, ctx, request_name, request).await
+    }
+}

tarpc/src/client/stub/load_balance.rs

@@ -0,0 +1,279 @@
+//! Provides load-balancing [Stubs](crate::client::stub::Stub).
+
+pub use consistent_hash::ConsistentHash;
+pub use round_robin::RoundRobin;
+
+/// Provides a stub that load-balances with a simple round-robin strategy.
+mod round_robin {
+    use crate::{
+        client::{stub, RpcError},
+        context,
+    };
+    use cycle::AtomicCycle;
+
+    impl<Stub> stub::Stub for RoundRobin<Stub>
+    where
+        Stub: stub::Stub,
+    {
+        type Req = Stub::Req;
+        type Resp = Stub::Resp;
+
+        async fn call(
+            &self,
+            ctx: context::Context,
+            request_name: &'static str,
+            request: Self::Req,
+        ) -> Result<Stub::Resp, RpcError> {
+            let next = self.stubs.next();
+            next.call(ctx, request_name, request).await
+        }
+    }
+
+    /// A Stub that load-balances across backing stubs by round robin.
+    #[derive(Clone, Debug)]
+    pub struct RoundRobin<Stub> {
+        stubs: AtomicCycle<Stub>,
+    }
+
+    impl<Stub> RoundRobin<Stub>
+    where
+        Stub: stub::Stub,
+    {
+        /// Returns a new RoundRobin stub.
+        pub fn new(stubs: Vec<Stub>) -> Self {
+            Self {
+                stubs: AtomicCycle::new(stubs),
+            }
+        }
+    }
+
+    mod cycle {
+        use std::sync::{
+            atomic::{AtomicUsize, Ordering},
+            Arc,
+        };
+
+        /// Cycles endlessly and atomically over a collection of elements of type T.
+        #[derive(Clone, Debug)]
+        pub struct AtomicCycle<T>(Arc<State<T>>);
+
+        #[derive(Debug)]
+        struct State<T> {
+            elements: Vec<T>,
+            next: AtomicUsize,
+        }
+
+        impl<T> AtomicCycle<T> {
+            pub fn new(elements: Vec<T>) -> Self {
+                Self(Arc::new(State {
+                    elements,
+                    next: Default::default(),
+                }))
+            }
+
+            pub fn next(&self) -> &T {
+                self.0.next()
+            }
+        }
+
+        impl<T> State<T> {
+            pub fn next(&self) -> &T {
+                let next = self.next.fetch_add(1, Ordering::Relaxed);
+                &self.elements[next % self.elements.len()]
+            }
+        }
+
+        #[test]
+        fn test_cycle() {
+            let cycle = AtomicCycle::new(vec![1, 2, 3]);
+            assert_eq!(cycle.next(), &1);
+            assert_eq!(cycle.next(), &2);
+            assert_eq!(cycle.next(), &3);
+            assert_eq!(cycle.next(), &1);
+        }
+    }
+}
+
+/// Provides a stub that load-balances with a consistent hashing strategy.
+///
+/// Each request is hashed, then mapped to a stub based on the hash. Equivalent requests will use
+/// the same stub.
+mod consistent_hash {
+    use crate::{
+        client::{stub, RpcError},
+        context,
+    };
+    use std::{
+        collections::hash_map::RandomState,
+        hash::{BuildHasher, Hash, Hasher},
+        num::TryFromIntError,
+    };
+
+    impl<Stub, S> stub::Stub for ConsistentHash<Stub, S>
+    where
+        Stub: stub::Stub,
+        Stub::Req: Hash,
+        S: BuildHasher,
+    {
+        type Req = Stub::Req;
+        type Resp = Stub::Resp;
+
+        async fn call(
+            &self,
+            ctx: context::Context,
+            request_name: &'static str,
+            request: Self::Req,
+        ) -> Result<Stub::Resp, RpcError> {
+            let index = usize::try_from(self.hash_request(&request) % self.stubs_len).expect(
+                "invariant broken: stubs_len is not larger than a usize, \
+                         so the hash modulo stubs_len should always fit in a usize",
+            );
+            let next = &self.stubs[index];
+            next.call(ctx, request_name, request).await
+        }
+    }
+
+    /// A Stub that load-balances across backing stubs by round robin.
+    #[derive(Clone, Debug)]
+    pub struct ConsistentHash<Stub, S = RandomState> {
+        stubs: Vec<Stub>,
+        stubs_len: u64,
+        hasher: S,
+    }
+
+    impl<Stub> ConsistentHash<Stub, RandomState>
+    where
+        Stub: stub::Stub,
+        Stub::Req: Hash,
+    {
+        /// Returns a new RoundRobin stub.
+        /// Returns an err if the length of `stubs` overflows a u64.
+        pub fn new(stubs: Vec<Stub>) -> Result<Self, TryFromIntError> {
+            Ok(Self {
+                stubs_len: stubs.len().try_into()?,
+                stubs,
+                hasher: RandomState::new(),
+            })
+        }
+    }
+
+    impl<Stub, S> ConsistentHash<Stub, S>
+    where
+        Stub: stub::Stub,
+        Stub::Req: Hash,
+        S: BuildHasher,
+    {
+        /// Returns a new RoundRobin stub.
+        /// Returns an err if the length of `stubs` overflows a u64.
+        pub fn with_hasher(stubs: Vec<Stub>, hasher: S) -> Result<Self, TryFromIntError> {
+            Ok(Self {
+                stubs_len: stubs.len().try_into()?,
+                stubs,
+                hasher,
+            })
+        }
+
+        fn hash_request(&self, req: &Stub::Req) -> u64 {
+            let mut hasher = self.hasher.build_hasher();
+            req.hash(&mut hasher);
+            hasher.finish()
+        }
+    }
+
+    #[cfg(test)]
+    mod tests {
+        use super::ConsistentHash;
+        use crate::{
+            client::stub::{mock::Mock, Stub},
+            context,
+        };
+        use std::{
+            collections::HashMap,
+            hash::{BuildHasher, Hash, Hasher},
+            rc::Rc,
+        };
+
+        #[tokio::test]
+        async fn test() -> anyhow::Result<()> {
+            let stub = ConsistentHash::<_, FakeHasherBuilder>::with_hasher(
+                vec![
+                    // For easier reading of the assertions made in this test, each Mock's response
+                    // value is equal to a hash value that should map to its index: 3 % 3 = 0, 1 %
+                    // 3 = 1, etc.
+                    Mock::new([('a', 3), ('b', 3), ('c', 3)]),
+                    Mock::new([('a', 1), ('b', 1), ('c', 1)]),
+                    Mock::new([('a', 2), ('b', 2), ('c', 2)]),
+                ],
+                FakeHasherBuilder::new([('a', 1), ('b', 2), ('c', 3)]),
+            )?;
+
+            for _ in 0..2 {
+                let resp = stub.call(context::current(), "", 'a').await?;
+                assert_eq!(resp, 1);
+
+                let resp = stub.call(context::current(), "", 'b').await?;
+                assert_eq!(resp, 2);
+
+                let resp = stub.call(context::current(), "", 'c').await?;
+                assert_eq!(resp, 3);
+            }
+
+            Ok(())
+        }
+
+        struct HashRecorder(Vec<u8>);
+        impl Hasher for HashRecorder {
+            fn write(&mut self, bytes: &[u8]) {
+                self.0 = Vec::from(bytes);
+            }
+            fn finish(&self) -> u64 {
+                0
+            }
+        }
+
+        struct FakeHasherBuilder {
+            recorded_hashes: Rc<HashMap<Vec<u8>, u64>>,
+        }
+
+        struct FakeHasher {
+            recorded_hashes: Rc<HashMap<Vec<u8>, u64>>,
+            output: u64,
+        }
+
+        impl BuildHasher for FakeHasherBuilder {
+            type Hasher = FakeHasher;
+
+            fn build_hasher(&self) -> Self::Hasher {
+                FakeHasher {
+                    recorded_hashes: self.recorded_hashes.clone(),
+                    output: 0,
+                }
+            }
+        }
+
+        impl FakeHasherBuilder {
+            fn new<T: Hash, const N: usize>(fake_hashes: [(T, u64); N]) -> Self {
+                let mut recorded_hashes = HashMap::new();
+                for (to_hash, fake_hash) in fake_hashes {
+                    let mut recorder = HashRecorder(vec![]);
+                    to_hash.hash(&mut recorder);
+                    recorded_hashes.insert(recorder.0, fake_hash);
+                }
+                Self {
+                    recorded_hashes: Rc::new(recorded_hashes),
+                }
+            }
+        }
+
+        impl Hasher for FakeHasher {
+            fn write(&mut self, bytes: &[u8]) {
+                if let Some(hash) = self.recorded_hashes.get(bytes) {
+                    self.output = *hash;
+                }
+            }
+            fn finish(&self) -> u64 {
+                self.output
+            }
+        }
+    }
+}

tarpc/src/client/stub/mock.rs

@@ -0,0 +1,49 @@
+use crate::{
+    client::{stub::Stub, RpcError},
+    context, ServerError,
+};
+use std::{collections::HashMap, hash::Hash, io};
+
+/// A mock stub that returns user-specified responses.
+pub struct Mock<Req, Resp> {
+    responses: HashMap<Req, Resp>,
+}
+
+impl<Req, Resp> Mock<Req, Resp>
+where
+    Req: Eq + Hash,
+{
+    /// Returns a new mock, mocking the specified (request, response) pairs.
+    pub fn new<const N: usize>(responses: [(Req, Resp); N]) -> Self {
+        Self {
+            responses: HashMap::from(responses),
+        }
+    }
+}
+
+impl<Req, Resp> Stub for Mock<Req, Resp>
+where
+    Req: Eq + Hash,
+    Resp: Clone,
+{
+    type Req = Req;
+    type Resp = Resp;
+
+    async fn call(
+        &self,
+        _: context::Context,
+        _: &'static str,
+        request: Self::Req,
+    ) -> Result<Resp, RpcError> {
+        self.responses
+            .get(&request)
+            .cloned()
+            .map(Ok)
+            .unwrap_or_else(|| {
+                Err(RpcError::Server(ServerError {
+                    kind: io::ErrorKind::NotFound,
+                    detail: "mock (request, response) entry not found".into(),
+                }))
+            })
+    }
+}

tarpc/src/client/stub/retry.rs

@@ -0,0 +1,56 @@
+//! Provides a stub that retries requests based on response contents..
+
+use crate::{
+    client::{stub, RpcError},
+    context,
+};
+use std::sync::Arc;
+
+impl<Stub, Req, F> stub::Stub for Retry<F, Stub>
+where
+    Stub: stub::Stub<Req = Arc<Req>>,
+    F: Fn(&Result<Stub::Resp, RpcError>, u32) -> bool,
+{
+    type Req = Req;
+    type Resp = Stub::Resp;
+
+    async fn call(
+        &self,
+        ctx: context::Context,
+        request_name: &'static str,
+        request: Self::Req,
+    ) -> Result<Stub::Resp, RpcError> {
+        let request = Arc::new(request);
+        for i in 1.. {
+            let result = self
+                .stub
+                .call(ctx, request_name, Arc::clone(&request))
+                .await;
+            if (self.should_retry)(&result, i) {
+                tracing::trace!("Retrying on attempt {i}");
+                continue;
+            }
+            return result;
+        }
+        unreachable!("Wow, that was a lot of attempts!");
+    }
+}
+
+/// A Stub that retries requests based on response contents.
+/// Note: to use this stub with Serde serialization, the "rc" feature of Serde needs to be enabled.
+#[derive(Clone, Debug)]
+pub struct Retry<F, Stub> {
+    should_retry: F,
+    stub: Stub,
+}
+
+impl<Stub, Req, F> Retry<F, Stub>
+where
+    Stub: stub::Stub<Req = Arc<Req>>,
+    F: Fn(&Result<Stub::Resp, RpcError>, u32) -> bool,
+{
+    /// Creates a new Retry stub that delegates calls to the underlying `stub`.
+    pub fn new(stub: Stub, should_retry: F) -> Self {
+        Self { stub, should_retry }
+    }
+}

tarpc/src/context.rs

@@ -0,0 +1,152 @@
+// Copyright 2018 Google LLC
+//
+// Use of this source code is governed by an MIT-style
+// license that can be found in the LICENSE file or at
+// https://opensource.org/licenses/MIT.
+
+//! Provides a request context that carries a deadline and trace context. This context is sent from
+//! client to server and is used by the server to enforce response deadlines.
+
+use crate::trace::{self, TraceId};
+use opentelemetry::trace::TraceContextExt;
+use static_assertions::assert_impl_all;
+use std::{
+    convert::TryFrom,
+    time::{Duration, SystemTime},
+};
+use tracing_opentelemetry::OpenTelemetrySpanExt;
+
+/// A request context that carries request-scoped information like deadlines and trace information.
+/// It is sent from client to server and is used by the server to enforce response deadlines.
+///
+/// The context should not be stored directly in a server implementation, because the context will
+/// be different for each request in scope.
+#[derive(Clone, Copy, Debug)]
+#[non_exhaustive]
+#[cfg_attr(feature = "serde1", derive(serde::Serialize, serde::Deserialize))]
+pub struct Context {
+    /// When the client expects the request to be complete by. The server should cancel the request
+    /// if it is not complete by this time.
+    #[cfg_attr(feature = "serde1", serde(default = "ten_seconds_from_now"))]
+    // Serialized as a Duration to prevent clock skew issues.
+    #[cfg_attr(feature = "serde1", serde(with = "absolute_to_relative_time"))]
+    pub deadline: SystemTime,
+    /// Uniquely identifies requests originating from the same source.
+    /// When a service handles a request by making requests itself, those requests should
+    /// include the same `trace_id` as that included on the original request. This way,
+    /// users can trace related actions across a distributed system.
+    pub trace_context: trace::Context,
+}
+
+#[cfg(feature = "serde1")]
+mod absolute_to_relative_time {
+    pub use serde::{Deserialize, Deserializer, Serialize, Serializer};
+    pub use std::time::{Duration, SystemTime};
+
+    pub fn serialize<S>(deadline: &SystemTime, serializer: S) -> Result<S::Ok, S::Error>
+    where
+        S: Serializer,
+    {
+        let deadline = deadline
+            .duration_since(SystemTime::now())
+            .unwrap_or(Duration::ZERO);
+        deadline.serialize(serializer)
+    }
+
+    pub fn deserialize<'de, D>(deserializer: D) -> Result<SystemTime, D::Error>
+    where
+        D: Deserializer<'de>,
+    {
+        let deadline = Duration::deserialize(deserializer)?;
+        Ok(SystemTime::now() + deadline)
+    }
+
+    #[cfg(test)]
+    #[derive(serde::Serialize, serde::Deserialize)]
+    struct AbsoluteToRelative(#[serde(with = "self")] SystemTime);
+
+    #[test]
+    fn test_serialize() {
+        let now = SystemTime::now();
+        let deadline = now + Duration::from_secs(10);
+        let serialized_deadline = bincode::serialize(&AbsoluteToRelative(deadline)).unwrap();
+        let deserialized_deadline: Duration = bincode::deserialize(&serialized_deadline).unwrap();
+        // TODO: how to avoid flakiness?
+        assert!(deserialized_deadline > Duration::from_secs(9));
+    }
+
+    #[test]
+    fn test_deserialize() {
+        let deadline = Duration::from_secs(10);
+        let serialized_deadline = bincode::serialize(&deadline).unwrap();
+        let AbsoluteToRelative(deserialized_deadline) =
+            bincode::deserialize(&serialized_deadline).unwrap();
+        // TODO: how to avoid flakiness?
+        assert!(deserialized_deadline > SystemTime::now() + Duration::from_secs(9));
+    }
+}
+
+assert_impl_all!(Context: Send, Sync);
+
+fn ten_seconds_from_now() -> SystemTime {
+    SystemTime::now() + Duration::from_secs(10)
+}
+
+/// Returns the context for the current request, or a default Context if no request is active.
+pub fn current() -> Context {
+    Context::current()
+}
+
+#[derive(Clone)]
+struct Deadline(SystemTime);
+
+impl Default for Deadline {
+    fn default() -> Self {
+        Self(ten_seconds_from_now())
+    }
+}
+
+impl Context {
+    /// Returns the context for the current request, or a default Context if no request is active.
+    pub fn current() -> Self {
+        let span = tracing::Span::current();
+        Self {
+            trace_context: trace::Context::try_from(&span)
+                .unwrap_or_else(|_| trace::Context::default()),
+            deadline: span
+                .context()
+                .get::<Deadline>()
+                .cloned()
+                .unwrap_or_default()
+                .0,
+        }
+    }
+
+    /// Returns the ID of the request-scoped trace.
+    pub fn trace_id(&self) -> &TraceId {
+        &self.trace_context.trace_id
+    }
+}
+
+/// An extension trait for [`tracing::Span`] for propagating tarpc Contexts.
+pub(crate) trait SpanExt {
+    /// Sets the given context on this span. Newly-created spans will be children of the given
+    /// context's trace context.
+    fn set_context(&self, context: &Context);
+}
+
+impl SpanExt for tracing::Span {
+    fn set_context(&self, context: &Context) {
+        self.set_parent(
+            opentelemetry::Context::new()
+                .with_remote_span_context(opentelemetry::trace::SpanContext::new(
+                    opentelemetry::trace::TraceId::from(context.trace_context.trace_id),
+                    opentelemetry::trace::SpanId::from(context.trace_context.span_id),
+                    opentelemetry::trace::TraceFlags::from(context.trace_context.sampling_decision),
+                    true,
+                    opentelemetry::trace::TraceState::default(),
+                ))
+                .with_value(Deadline(context.deadline)),
+        );
+    }
+}

tarpc/src/lib.rs

@@ -3,10 +3,6 @@
 // Use of this source code is governed by an MIT-style
 // license that can be found in the LICENSE file or at
 // https://opensource.org/licenses/MIT.
-
-//! [![Latest Version](https://img.shields.io/crates/v/tarpc.svg)](https://crates.io/crates/tarpc)
-//! [![Join the chat at https://gitter.im/tarpc/Lobby](https://badges.gitter.im/tarpc/Lobby.svg)](https://gitter.im/tarpc/Lobby?utm_source=badge&utm_medium=badge&utm_campaign=pr-badge&utm_content=badge)
-//!
 //! *Disclaimer*: This is not an official Google product.
 //!
 //! tarpc is an RPC framework for rust with a focus on ease of use. Defining a
@@ -31,7 +27,7 @@
 //! process, and no context switching between different languages.
 //!
 //! Some other features of tarpc:
-//! - Pluggable transport: any type impling `Stream<Item = Request> + Sink<Response>` can be
+//! - Pluggable transport: any type implementing `Stream<Item = Request> + Sink<Response>` can be
 //!   used as a transport to connect the client and server.
 //! - `Send + 'static` optional: if the transport doesn't require it, neither does tarpc!
 //! - Cascading cancellation: dropping a request will send a cancellation message to the server.
@@ -42,6 +38,14 @@
 //!   requests sent by the server that use the request context will propagate the request deadline.
 //!   For example, if a server is handling a request with a 10s deadline, does 2s of work, then
 //!   sends a request to another server, that server will see an 8s deadline.
+//! - Distributed tracing: tarpc is instrumented with
+//!   [tracing](https://github.com/tokio-rs/tracing) primitives extended with
+//!   [OpenTelemetry](https://opentelemetry.io/) traces. Using a compatible tracing subscriber like
+//!   [Jaeger](https://github.com/open-telemetry/opentelemetry-rust/tree/main/opentelemetry-jaeger),
+//!   each RPC can be traced through the client, server, and other dependencies downstream of the
+//!   server. Even for applications not connected to a distributed tracing collector, the
+//!   instrumentation can also be ingested by regular loggers like
+//!   [env_logger](https://github.com/env-logger-rs/env_logger/).
 //! - Serde serialization: enabling the `serde1` Cargo feature will make service requests and
 //!   responses `Serialize + Deserialize`. It's entirely optional, though: in-memory transports can
 //!   be used, as well, so the price of serialization doesn't have to be paid when it's not needed.
@@ -50,7 +54,7 @@
 //! Add to your `Cargo.toml` dependencies:
 //!
 //! ```toml
-//! tarpc = "0.20.0"
+//! tarpc = "0.29"
 //! ```
 //!
 //! The `tarpc::service` attribute expands to a collection of items that form an rpc service.
@@ -59,12 +63,14 @@
 //!
 //! ## Example
 //!
-//! For this example, in addition to tarpc, also add two other dependencies to
+//! This example uses [tokio](https://tokio.rs), so add the following dependencies to
 //! your `Cargo.toml`:
 //!
 //! ```toml
+//! anyhow = "1.0"
 //! futures = "0.3"
-//! tokio = "0.2"
+//! tarpc = { version = "0.29", features = ["tokio1"] }
+//! tokio = { version = "1.0", features = ["macros"] }
 //! ```
 //!
 //! In the following example, we use an in-process channel for communication between
@@ -82,9 +88,8 @@
 //! };
 //! use tarpc::{
 //!     client, context,
-//!     server::{self, Handler},
+//!     server::{self, incoming::Incoming, Channel},
 //! };
-//! use std::io;
 //!
 //! // This is the service definition. It looks a lot like a trait definition.
 //! // It defines one RPC, hello, which takes one arg, name, and returns a String.
@@ -106,9 +111,8 @@
 //! # };
 //! # use tarpc::{
 //! #     client, context,
-//! #     server::{self, Handler},
+//! #     server::{self, incoming::Incoming},
 //! # };
-//! # use std::io;
 //! # // This is the service definition. It looks a lot like a trait definition.
 //! # // It defines one RPC, hello, which takes one arg, name, and returns a String.
 //! # #[tarpc::service]
@@ -122,19 +126,15 @@
 //! struct HelloServer;
 //!
 //! impl World for HelloServer {
-//!     // Each defined rpc generates two items in the trait, a fn that serves the RPC, and
-//!     // an associated type representing the future output by the fn.
-//!
-//!     type HelloFut = Ready<String>;
-//!
-//!     fn hello(self, _: context::Context, name: String) -> Self::HelloFut {
-//!         future::ready(format!("Hello, {}!", name))
+//!     // Each defined rpc generates an async fn that serves the RPC
+//!     async fn hello(self, _: context::Context, name: String) -> String {
+//!         format!("Hello, {name}!")
 //!     }
 //! }
 //! ```
 //!
 //! Lastly let's write our `main` that will start the server. While this example uses an
-//! [in-process channel](rpc::transport::channel), tarpc also ships a generic [`serde_transport`]
+//! [in-process channel](transport::channel), tarpc also ships a generic [`serde_transport`]
 //! behind the `serde-transport` feature, with additional [TCP](serde_transport::tcp) functionality
 //! available behind the `tcp` feature.
 //!
@@ -146,9 +146,8 @@
 //! # };
 //! # use tarpc::{
 //! #     client, context,
-//! #     server::{self, Handler},
+//! #     server::{self, Channel},
 //! # };
-//! # use std::io;
 //! # // This is the service definition. It looks a lot like a trait definition.
 //! # // It defines one RPC, hello, which takes one arg, name, and returns a String.
 //! # #[tarpc::service]
@@ -161,35 +160,36 @@
 //! # #[derive(Clone)]
 //! # struct HelloServer;
 //! # impl World for HelloServer {
-//! #     // Each defined rpc generates two items in the trait, a fn that serves the RPC, and
-//! #     // an associated type representing the future output by the fn.
-//! #     type HelloFut = Ready<String>;
-//! #     fn hello(self, _: context::Context, name: String) -> Self::HelloFut {
-//! #         future::ready(format!("Hello, {}!", name))
+//!     // Each defined rpc generates an async fn that serves the RPC
+//! #     async fn hello(self, _: context::Context, name: String) -> String {
+//! #         format!("Hello, {name}!")
 //! #     }
 //! # }
+//! # #[cfg(not(feature = "tokio1"))]
+//! # fn main() {}
+//! # #[cfg(feature = "tokio1")]
 //! #[tokio::main]
-//! async fn main() -> io::Result<()> {
+//! async fn main() -> anyhow::Result<()> {
 //!     let (client_transport, server_transport) = tarpc::transport::channel::unbounded();
 //!
-//!     let server = server::new(server::Config::default())
-//!         // incoming() takes a stream of transports such as would be returned by
-//!         // TcpListener::incoming (but a stream instead of an iterator).
-//!         .incoming(stream::once(future::ready(server_transport)))
-//!         .respond_with(HelloServer.serve());
+//!     let server = server::BaseChannel::with_defaults(server_transport);
+//!     tokio::spawn(
+//!         server.execute(HelloServer.serve())
+//!             // Handle all requests concurrently.
+//!             .for_each(|response| async move {
+//!                 tokio::spawn(response);
+//!             }));
 //!
-//!     tokio::spawn(server);
-//!
-//!     // WorldClient is generated by the macro. It has a constructor `new` that takes a config and
-//!     // any Transport as input
-//!     let mut client = WorldClient::new(client::Config::default(), client_transport).spawn()?;
+//!     // WorldClient is generated by the #[tarpc::service] attribute. It has a constructor `new`
+//!     // that takes a config and any Transport as input.
+//!     let mut client = WorldClient::new(client::Config::default(), client_transport).spawn();
 //!
 //!     // The client has an RPC method for each RPC defined in the annotated trait. It takes the same
 //!     // args as defined, with the addition of a Context, which is always the first arg. The Context
 //!     // specifies a deadline and trace information which can be helpful in debugging requests.
 //!     let hello = client.hello(context::current(), "Stim".to_string()).await?;
 //!
-//!     println!("{}", hello);
+//!     println!("{hello}");
 //!
 //!     Ok(())
 //! }
@@ -199,23 +199,32 @@
 //!
 //! Use `cargo doc` as you normally would to see the documentation created for all
 //! items expanded by a `service!` invocation.
+
 #![deny(missing_docs)]
 #![allow(clippy::type_complexity)]
+#![cfg_attr(docsrs, feature(doc_cfg))]
 
-pub mod rpc;
-pub use rpc::*;
+#[cfg(feature = "serde1")]
+#[doc(hidden)]
+pub use serde;
 
 #[cfg(feature = "serde-transport")]
+pub use {tokio_serde, tokio_util};
+
+#[cfg(feature = "serde-transport")]
+#[cfg_attr(docsrs, doc(cfg(feature = "serde-transport")))]
 pub mod serde_transport;
 
 pub mod trace;
 
+#[cfg(feature = "serde1")]
+pub use tarpc_plugins::derive_serde;
+
 /// The main macro that creates RPC services.
 ///
 /// Rpc methods are specified, mirroring trait syntax:
 ///
 /// ```
-/// # fn main() {}
 /// #[tarpc::service]
 /// trait Service {
 /// /// Say hello
@@ -234,3 +243,155 @@ pub mod trace;
 /// * `Client` -- a client stub with a fn for each RPC.
 ///   * `fn new_stub` -- creates a new Client stub.
 pub use tarpc_plugins::service;
+
+pub(crate) mod cancellations;
+pub mod client;
+pub mod context;
+pub mod server;
+pub mod transport;
+pub(crate) mod util;
+
+pub use crate::transport::sealed::Transport;
+
+use anyhow::Context as _;
+use futures::task::*;
+use std::sync::Arc;
+use std::{error::Error, fmt::Display, io, time::SystemTime};
+
+/// A message from a client to a server.
+#[derive(Debug)]
+#[cfg_attr(feature = "serde1", derive(serde::Serialize, serde::Deserialize))]
+#[non_exhaustive]
+pub enum ClientMessage<T> {
+    /// A request initiated by a user. The server responds to a request by invoking a
+    /// service-provided request handler.  The handler completes with a [`response`](Response), which
+    /// the server sends back to the client.
+    Request(Request<T>),
+    /// A command to cancel an in-flight request, automatically sent by the client when a response
+    /// future is dropped.
+    ///
+    /// When received, the server will immediately cancel the main task (top-level future) of the
+    /// request handler for the associated request. Any tasks spawned by the request handler will
+    /// not be canceled, because the framework layer does not
+    /// know about them.
+    Cancel {
+        /// The trace context associates the message with a specific chain of causally-related actions,
+        /// possibly orchestrated across many distributed systems.
+        #[cfg_attr(feature = "serde1", serde(default))]
+        trace_context: trace::Context,
+        /// The ID of the request to cancel.
+        request_id: u64,
+    },
+}
+
+/// A request from a client to a server.
+#[derive(Clone, Copy, Debug)]
+#[non_exhaustive]
+#[cfg_attr(feature = "serde1", derive(serde::Serialize, serde::Deserialize))]
+pub struct Request<T> {
+    /// Trace context, deadline, and other cross-cutting concerns.
+    pub context: context::Context,
+    /// Uniquely identifies the request across all requests sent over a single channel.
+    pub id: u64,
+    /// The request body.
+    pub message: T,
+}
+
+/// A response from a server to a client.
+#[derive(Clone, Debug, PartialEq, Eq, Hash)]
+#[non_exhaustive]
+#[cfg_attr(feature = "serde1", derive(serde::Serialize, serde::Deserialize))]
+pub struct Response<T> {
+    /// The ID of the request being responded to.
+    pub request_id: u64,
+    /// The response body, or an error if the request failed.
+    pub message: Result<T, ServerError>,
+}
+
+/// An error indicating the server aborted the request early, e.g., due to request throttling.
+#[derive(thiserror::Error, Clone, Debug, PartialEq, Eq, Hash)]
+#[error("{kind:?}: {detail}")]
+#[non_exhaustive]
+#[cfg_attr(feature = "serde1", derive(serde::Serialize, serde::Deserialize))]
+pub struct ServerError {
+    #[cfg_attr(
+        feature = "serde1",
+        serde(serialize_with = "util::serde::serialize_io_error_kind_as_u32")
+    )]
+    #[cfg_attr(
+        feature = "serde1",
+        serde(deserialize_with = "util::serde::deserialize_io_error_kind_from_u32")
+    )]
+    /// The type of error that occurred to fail the request.
+    pub kind: io::ErrorKind,
+    /// A message describing more detail about the error that occurred.
+    pub detail: String,
+}
+
+/// Critical errors that result in a Channel disconnecting.
+#[derive(thiserror::Error, Debug, PartialEq, Eq)]
+pub enum ChannelError<E>
+where
+    E: Error + Send + Sync + 'static,
+{
+    /// Could not read from the transport.
+    #[error("could not read from the transport")]
+    Read(#[source] Arc<E>),
+    /// Could not ready the transport for writes.
+    #[error("could not ready the transport for writes")]
+    Ready(#[source] E),
+    /// Could not write to the transport.
+    #[error("could not write to the transport")]
+    Write(#[source] E),
+    /// Could not flush the transport.
+    #[error("could not flush the transport")]
+    Flush(#[source] E),
+    /// Could not close the write end of the transport.
+    #[error("could not close the write end of the transport")]
+    Close(#[source] E),
+}
+
+impl ServerError {
+    /// Returns a new server error with `kind` and `detail`.
+    pub fn new(kind: io::ErrorKind, detail: String) -> ServerError {
+        Self { kind, detail }
+    }
+}
+
+impl<T> Request<T> {
+    /// Returns the deadline for this request.
+    pub fn deadline(&self) -> &SystemTime {
+        &self.context.deadline
+    }
+}
+
+pub(crate) trait PollContext<T> {
+    fn context<C>(self, context: C) -> Poll<Option<anyhow::Result<T>>>
+    where
+        C: Display + Send + Sync + 'static;
+
+    fn with_context<C, F>(self, f: F) -> Poll<Option<anyhow::Result<T>>>
+    where
+        C: Display + Send + Sync + 'static,
+        F: FnOnce() -> C;
+}
+
+impl<T, E> PollContext<T> for Poll<Option<Result<T, E>>>
+where
+    E: Error + Send + Sync + 'static,
+{
+    fn context<C>(self, context: C) -> Poll<Option<anyhow::Result<T>>>
+    where
+        C: Display + Send + Sync + 'static,
+    {
+        self.map(|o| o.map(|r| r.context(context)))
+    }
+
+    fn with_context<C, F>(self, f: F) -> Poll<Option<anyhow::Result<T>>>
+    where
+        C: Display + Send + Sync + 'static,
+        F: FnOnce() -> C,
+    {
+        self.map(|o| o.map(|r| r.with_context(f)))
+    }
+}

tarpc/src/rpc/client/channel.rs

@@ -1,906 +0,0 @@
-// Copyright 2018 Google LLC
-//
-// Use of this source code is governed by an MIT-style
-// license that can be found in the LICENSE file or at
-// https://opensource.org/licenses/MIT.
-
-use crate::{
-    context,
-    trace::SpanId,
-    util::{Compact, TimeUntil},
-    ClientMessage, PollIo, Request, Response, Transport,
-};
-use fnv::FnvHashMap;
-use futures::{
-    channel::{mpsc, oneshot},
-    prelude::*,
-    ready,
-    stream::Fuse,
-    task::*,
-};
-use log::{debug, info, trace};
-use pin_project::{pin_project, pinned_drop};
-use std::{
-    io,
-    pin::Pin,
-    sync::{
-        atomic::{AtomicU64, Ordering},
-        Arc,
-    },
-};
-
-use super::{Config, NewClient};
-
-/// Handles communication from the client to request dispatch.
-#[derive(Debug)]
-pub struct Channel<Req, Resp> {
-    to_dispatch: mpsc::Sender<DispatchRequest<Req, Resp>>,
-    /// Channel to send a cancel message to the dispatcher.
-    cancellation: RequestCancellation,
-    /// The ID to use for the next request to stage.
-    next_request_id: Arc<AtomicU64>,
-}
-
-impl<Req, Resp> Clone for Channel<Req, Resp> {
-    fn clone(&self) -> Self {
-        Self {
-            to_dispatch: self.to_dispatch.clone(),
-            cancellation: self.cancellation.clone(),
-            next_request_id: self.next_request_id.clone(),
-        }
-    }
-}
-
-/// A future returned by [`Channel::send`] that resolves to a server response.
-#[pin_project]
-#[derive(Debug)]
-#[must_use = "futures do nothing unless polled"]
-struct Send<'a, Req, Resp> {
-    #[pin]
-    fut: MapOkDispatchResponse<SendMapErrConnectionReset<'a, Req, Resp>, Resp>,
-}
-
-type SendMapErrConnectionReset<'a, Req, Resp> = MapErrConnectionReset<
-    futures::sink::Send<'a, mpsc::Sender<DispatchRequest<Req, Resp>>, DispatchRequest<Req, Resp>>,
->;
-
-impl<'a, Req, Resp> Future for Send<'a, Req, Resp> {
-    type Output = io::Result<DispatchResponse<Resp>>;
-
-    fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
-        self.as_mut().project().fut.poll(cx)
-    }
-}
-
-/// A future returned by [`Channel::call`] that resolves to a server response.
-#[pin_project]
-#[derive(Debug)]
-#[must_use = "futures do nothing unless polled"]
-pub struct Call<'a, Req, Resp> {
-    #[pin]
-    fut: AndThenIdent<Send<'a, Req, Resp>, DispatchResponse<Resp>>,
-}
-
-impl<'a, Req, Resp> Future for Call<'a, Req, Resp> {
-    type Output = io::Result<Resp>;
-
-    fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
-        self.as_mut().project().fut.poll(cx)
-    }
-}
-
-impl<Req, Resp> Channel<Req, Resp> {
-    /// Sends a request to the dispatch task to forward to the server, returning a [`Future`] that
-    /// resolves when the request is sent (not when the response is received).
-    fn send(&mut self, mut ctx: context::Context, request: Req) -> Send<Req, Resp> {
-        // Convert the context to the call context.
-        ctx.trace_context.parent_id = Some(ctx.trace_context.span_id);
-        ctx.trace_context.span_id = SpanId::random(&mut rand::thread_rng());
-
-        let timeout = ctx.deadline.time_until();
-        trace!(
-            "[{}] Queuing request with timeout {:?}.",
-            ctx.trace_id(),
-            timeout,
-        );
-
-        let (response_completion, response) = oneshot::channel();
-        let cancellation = self.cancellation.clone();
-        let request_id = self.next_request_id.fetch_add(1, Ordering::Relaxed);
-        Send {
-            fut: MapOkDispatchResponse::new(
-                MapErrConnectionReset::new(self.to_dispatch.send(DispatchRequest {
-                    ctx,
-                    request_id,
-                    request,
-                    response_completion,
-                })),
-                DispatchResponse {
-                    response: tokio::time::timeout(timeout, response),
-                    complete: false,
-                    request_id,
-                    cancellation,
-                    ctx,
-                },
-            ),
-        }
-    }
-
-    /// Sends a request to the dispatch task to forward to the server, returning a [`Future`] that
-    /// resolves to the response.
-    pub fn call(&mut self, context: context::Context, request: Req) -> Call<Req, Resp> {
-        Call {
-            fut: AndThenIdent::new(self.send(context, request)),
-        }
-    }
-}
-
-/// A server response that is completed by request dispatch when the corresponding response
-/// arrives off the wire.
-#[pin_project(PinnedDrop)]
-#[derive(Debug)]
-struct DispatchResponse<Resp> {
-    response: tokio::time::Timeout<oneshot::Receiver<Response<Resp>>>,
-    ctx: context::Context,
-    complete: bool,
-    cancellation: RequestCancellation,
-    request_id: u64,
-}
-
-impl<Resp> Future for DispatchResponse<Resp> {
-    type Output = io::Result<Resp>;
-
-    fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<io::Result<Resp>> {
-        let resp = ready!(self.response.poll_unpin(cx));
-
-        Poll::Ready(match resp {
-            Ok(resp) => {
-                self.complete = true;
-                match resp {
-                    Ok(resp) => Ok(resp.message?),
-                    Err(oneshot::Canceled) => {
-                        // The oneshot is Canceled when the dispatch task ends. In that case,
-                        // there's nothing listening on the other side, so there's no point in
-                        // propagating cancellation.
-                        Err(io::Error::from(io::ErrorKind::ConnectionReset))
-                    }
-                }
-            }
-            Err(tokio::time::Elapsed { .. }) => Err(io::Error::new(
-                io::ErrorKind::TimedOut,
-                "Client dropped expired request.".to_string(),
-            )),
-        })
-    }
-}
-
-// Cancels the request when dropped, if not already complete.
-#[pinned_drop]
-impl<Resp> PinnedDrop for DispatchResponse<Resp> {
-    fn drop(mut self: Pin<&mut Self>) {
-        if !self.complete {
-            // The receiver needs to be closed to handle the edge case that the request has not
-            // yet been received by the dispatch task. It is possible for the cancel message to
-            // arrive before the request itself, in which case the request could get stuck in the
-            // dispatch map forever if the server never responds (e.g. if the server dies while
-            // responding). Even if the server does respond, it will have unnecessarily done work
-            // for a client no longer waiting for a response. To avoid this, the dispatch task
-            // checks if the receiver is closed before inserting the request in the map. By
-            // closing the receiver before sending the cancel message, it is guaranteed that if the
-            // dispatch task misses an early-arriving cancellation message, then it will see the
-            // receiver as closed.
-            self.response.get_mut().close();
-            let request_id = self.request_id;
-            self.cancellation.cancel(request_id);
-        }
-    }
-}
-
-/// Returns a channel and dispatcher that manages the lifecycle of requests initiated by the
-/// channel.
-pub fn new<Req, Resp, C>(
-    config: Config,
-    transport: C,
-) -> NewClient<Channel<Req, Resp>, RequestDispatch<Req, Resp, C>>
-where
-    C: Transport<ClientMessage<Req>, Response<Resp>>,
-{
-    let (to_dispatch, pending_requests) = mpsc::channel(config.pending_request_buffer);
-    let (cancellation, canceled_requests) = cancellations();
-    let canceled_requests = canceled_requests.fuse();
-
-    NewClient {
-        client: Channel {
-            to_dispatch,
-            cancellation,
-            next_request_id: Arc::new(AtomicU64::new(0)),
-        },
-        dispatch: RequestDispatch {
-            config,
-            canceled_requests,
-            transport: transport.fuse(),
-            in_flight_requests: FnvHashMap::default(),
-            pending_requests: pending_requests.fuse(),
-        },
-    }
-}
-
-/// Handles the lifecycle of requests, writing requests to the wire, managing cancellations,
-/// and dispatching responses to the appropriate channel.
-#[pin_project]
-#[derive(Debug)]
-pub struct RequestDispatch<Req, Resp, C> {
-    /// Writes requests to the wire and reads responses off the wire.
-    #[pin]
-    transport: Fuse<C>,
-    /// Requests waiting to be written to the wire.
-    #[pin]
-    pending_requests: Fuse<mpsc::Receiver<DispatchRequest<Req, Resp>>>,
-    /// Requests that were dropped.
-    #[pin]
-    canceled_requests: Fuse<CanceledRequests>,
-    /// Requests already written to the wire that haven't yet received responses.
-    in_flight_requests: FnvHashMap<u64, InFlightData<Resp>>,
-    /// Configures limits to prevent unlimited resource usage.
-    config: Config,
-}
-
-impl<Req, Resp, C> RequestDispatch<Req, Resp, C>
-where
-    C: Transport<ClientMessage<Req>, Response<Resp>>,
-{
-    fn pump_read(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> PollIo<()> {
-        Poll::Ready(
-            match ready!(self.as_mut().project().transport.poll_next(cx)?) {
-                Some(response) => {
-                    self.complete(response);
-                    Some(Ok(()))
-                }
-                None => None,
-            },
-        )
-    }
-
-    fn pump_write(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> PollIo<()> {
-        enum ReceiverStatus {
-            NotReady,
-            Closed,
-        }
-
-        let pending_requests_status = match self.as_mut().poll_next_request(cx)? {
-            Poll::Ready(Some(dispatch_request)) => {
-                self.as_mut().write_request(dispatch_request)?;
-                return Poll::Ready(Some(Ok(())));
-            }
-            Poll::Ready(None) => ReceiverStatus::Closed,
-            Poll::Pending => ReceiverStatus::NotReady,
-        };
-
-        let canceled_requests_status = match self.as_mut().poll_next_cancellation(cx)? {
-            Poll::Ready(Some((context, request_id))) => {
-                self.as_mut().write_cancel(context, request_id)?;
-                return Poll::Ready(Some(Ok(())));
-            }
-            Poll::Ready(None) => ReceiverStatus::Closed,
-            Poll::Pending => ReceiverStatus::NotReady,
-        };
-
-        match (pending_requests_status, canceled_requests_status) {
-            (ReceiverStatus::Closed, ReceiverStatus::Closed) => {
-                ready!(self.as_mut().project().transport.poll_flush(cx)?);
-                Poll::Ready(None)
-            }
-            (ReceiverStatus::NotReady, _) | (_, ReceiverStatus::NotReady) => {
-                // No more messages to process, so flush any messages buffered in the transport.
-                ready!(self.as_mut().project().transport.poll_flush(cx)?);
-
-                // Even if we fully-flush, we return Pending, because we have no more requests
-                // or cancellations right now.
-                Poll::Pending
-            }
-        }
-    }
-
-    /// Yields the next pending request, if one is ready to be sent.
-    fn poll_next_request(
-        mut self: Pin<&mut Self>,
-        cx: &mut Context<'_>,
-    ) -> PollIo<DispatchRequest<Req, Resp>> {
-        if self.as_mut().project().in_flight_requests.len() >= self.config.max_in_flight_requests {
-            info!(
-                "At in-flight request capacity ({}/{}).",
-                self.as_mut().project().in_flight_requests.len(),
-                self.config.max_in_flight_requests
-            );
-
-            // No need to schedule a wakeup, because timers and responses are responsible
-            // for clearing out in-flight requests.
-            return Poll::Pending;
-        }
-
-        while let Poll::Pending = self.as_mut().project().transport.poll_ready(cx)? {
-            // We can't yield a request-to-be-sent before the transport is capable of buffering it.
-            ready!(self.as_mut().project().transport.poll_flush(cx)?);
-        }
-
-        loop {
-            match ready!(self.as_mut().project().pending_requests.poll_next_unpin(cx)) {
-                Some(request) => {
-                    if request.response_completion.is_canceled() {
-                        trace!(
-                            "[{}] Request canceled before being sent.",
-                            request.ctx.trace_id()
-                        );
-                        continue;
-                    }
-
-                    return Poll::Ready(Some(Ok(request)));
-                }
-                None => return Poll::Ready(None),
-            }
-        }
-    }
-
-    /// Yields the next pending cancellation, and, if one is ready, cancels the associated request.
-    fn poll_next_cancellation(
-        mut self: Pin<&mut Self>,
-        cx: &mut Context<'_>,
-    ) -> PollIo<(context::Context, u64)> {
-        while let Poll::Pending = self.as_mut().project().transport.poll_ready(cx)? {
-            ready!(self.as_mut().project().transport.poll_flush(cx)?);
-        }
-
-        loop {
-            let cancellation = self
-                .as_mut()
-                .project()
-                .canceled_requests
-                .poll_next_unpin(cx);
-            match ready!(cancellation) {
-                Some(request_id) => {
-                    if let Some(in_flight_data) = self
-                        .as_mut()
-                        .project()
-                        .in_flight_requests
-                        .remove(&request_id)
-                    {
-                        self.as_mut().project().in_flight_requests.compact(0.1);
-                        debug!("[{}] Removed request.", in_flight_data.ctx.trace_id());
-                        return Poll::Ready(Some(Ok((in_flight_data.ctx, request_id))));
-                    }
-                }
-                None => return Poll::Ready(None),
-            }
-        }
-    }
-
-    fn write_request(
-        mut self: Pin<&mut Self>,
-        dispatch_request: DispatchRequest<Req, Resp>,
-    ) -> io::Result<()> {
-        let request_id = dispatch_request.request_id;
-        let request = ClientMessage::Request(Request {
-            id: request_id,
-            message: dispatch_request.request,
-            context: context::Context {
-                deadline: dispatch_request.ctx.deadline,
-                trace_context: dispatch_request.ctx.trace_context,
-                _non_exhaustive: (),
-            },
-            _non_exhaustive: (),
-        });
-        self.as_mut().project().transport.start_send(request)?;
-        self.as_mut().project().in_flight_requests.insert(
-            request_id,
-            InFlightData {
-                ctx: dispatch_request.ctx,
-                response_completion: dispatch_request.response_completion,
-            },
-        );
-        Ok(())
-    }
-
-    fn write_cancel(
-        mut self: Pin<&mut Self>,
-        context: context::Context,
-        request_id: u64,
-    ) -> io::Result<()> {
-        let trace_id = *context.trace_id();
-        let cancel = ClientMessage::Cancel {
-            trace_context: context.trace_context,
-            request_id,
-        };
-        self.as_mut().project().transport.start_send(cancel)?;
-        trace!("[{}] Cancel message sent.", trace_id);
-        Ok(())
-    }
-
-    /// Sends a server response to the client task that initiated the associated request.
-    fn complete(mut self: Pin<&mut Self>, response: Response<Resp>) -> bool {
-        if let Some(in_flight_data) = self
-            .as_mut()
-            .project()
-            .in_flight_requests
-            .remove(&response.request_id)
-        {
-            self.as_mut().project().in_flight_requests.compact(0.1);
-
-            trace!("[{}] Received response.", in_flight_data.ctx.trace_id());
-            let _ = in_flight_data.response_completion.send(response);
-            return true;
-        }
-
-        debug!(
-            "No in-flight request found for request_id = {}.",
-            response.request_id
-        );
-
-        // If the response completion was absent, then the request was already canceled.
-        false
-    }
-}
-
-impl<Req, Resp, C> Future for RequestDispatch<Req, Resp, C>
-where
-    C: Transport<ClientMessage<Req>, Response<Resp>>,
-{
-    type Output = io::Result<()>;
-
-    fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<io::Result<()>> {
-        loop {
-            match (self.as_mut().pump_read(cx)?, self.as_mut().pump_write(cx)?) {
-                (read, Poll::Ready(None)) => {
-                    if self.as_mut().project().in_flight_requests.is_empty() {
-                        info!("Shutdown: write half closed, and no requests in flight.");
-                        return Poll::Ready(Ok(()));
-                    }
-                    info!(
-                        "Shutdown: write half closed, and {} requests in flight.",
-                        self.as_mut().project().in_flight_requests.len()
-                    );
-                    match read {
-                        Poll::Ready(Some(())) => continue,
-                        _ => return Poll::Pending,
-                    }
-                }
-                (Poll::Ready(Some(())), _) | (_, Poll::Ready(Some(()))) => {}
-                _ => return Poll::Pending,
-            }
-        }
-    }
-}
-
-/// A server-bound request sent from a [`Channel`] to request dispatch, which will then manage
-/// the lifecycle of the request.
-#[derive(Debug)]
-struct DispatchRequest<Req, Resp> {
-    ctx: context::Context,
-    request_id: u64,
-    request: Req,
-    response_completion: oneshot::Sender<Response<Resp>>,
-}
-
-#[derive(Debug)]
-struct InFlightData<Resp> {
-    ctx: context::Context,
-    response_completion: oneshot::Sender<Response<Resp>>,
-}
-
-/// Sends request cancellation signals.
-#[derive(Debug, Clone)]
-struct RequestCancellation(mpsc::UnboundedSender<u64>);
-
-/// A stream of IDs of requests that have been canceled.
-#[derive(Debug)]
-struct CanceledRequests(mpsc::UnboundedReceiver<u64>);
-
-/// Returns a channel to send request cancellation messages.
-fn cancellations() -> (RequestCancellation, CanceledRequests) {
-    // Unbounded because messages are sent in the drop fn. This is fine, because it's still
-    // bounded by the number of in-flight requests. Additionally, each request has a clone
-    // of the sender, so the bounded channel would have the same behavior,
-    // since it guarantees a slot.
-    let (tx, rx) = mpsc::unbounded();
-    (RequestCancellation(tx), CanceledRequests(rx))
-}
-
-impl RequestCancellation {
-    /// Cancels the request with ID `request_id`.
-    fn cancel(&mut self, request_id: u64) {
-        let _ = self.0.unbounded_send(request_id);
-    }
-}
-
-impl Stream for CanceledRequests {
-    type Item = u64;
-
-    fn poll_next(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Option<u64>> {
-        self.0.poll_next_unpin(cx)
-    }
-}
-
-#[pin_project]
-#[derive(Debug)]
-#[must_use = "futures do nothing unless polled"]
-struct MapErrConnectionReset<Fut> {
-    #[pin]
-    future: Fut,
-    finished: Option<()>,
-}
-
-impl<Fut> MapErrConnectionReset<Fut> {
-    fn new(future: Fut) -> MapErrConnectionReset<Fut> {
-        MapErrConnectionReset {
-            future,
-            finished: Some(()),
-        }
-    }
-}
-
-impl<Fut> Future for MapErrConnectionReset<Fut>
-where
-    Fut: TryFuture,
-{
-    type Output = io::Result<Fut::Ok>;
-
-    fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
-        match self.as_mut().project().future.try_poll(cx) {
-            Poll::Pending => Poll::Pending,
-            Poll::Ready(result) => {
-                self.project().finished.take().expect(
-                    "MapErrConnectionReset must not be polled after it returned `Poll::Ready`",
-                );
-                Poll::Ready(result.map_err(|_| io::Error::from(io::ErrorKind::ConnectionReset)))
-            }
-        }
-    }
-}
-
-#[pin_project]
-#[derive(Debug)]
-#[must_use = "futures do nothing unless polled"]
-struct MapOkDispatchResponse<Fut, Resp> {
-    #[pin]
-    future: Fut,
-    response: Option<DispatchResponse<Resp>>,
-}
-
-impl<Fut, Resp> MapOkDispatchResponse<Fut, Resp> {
-    fn new(future: Fut, response: DispatchResponse<Resp>) -> MapOkDispatchResponse<Fut, Resp> {
-        MapOkDispatchResponse {
-            future,
-            response: Some(response),
-        }
-    }
-}
-
-impl<Fut, Resp> Future for MapOkDispatchResponse<Fut, Resp>
-where
-    Fut: TryFuture,
-{
-    type Output = Result<DispatchResponse<Resp>, Fut::Error>;
-
-    fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
-        match self.as_mut().project().future.try_poll(cx) {
-            Poll::Pending => Poll::Pending,
-            Poll::Ready(result) => {
-                let response = self
-                    .as_mut()
-                    .project()
-                    .response
-                    .take()
-                    .expect("MapOk must not be polled after it returned `Poll::Ready`");
-                Poll::Ready(result.map(|_| response))
-            }
-        }
-    }
-}
-
-#[pin_project]
-#[derive(Debug)]
-#[must_use = "futures do nothing unless polled"]
-struct AndThenIdent<Fut1, Fut2> {
-    #[pin]
-    try_chain: TryChain<Fut1, Fut2>,
-}
-
-impl<Fut1, Fut2> AndThenIdent<Fut1, Fut2>
-where
-    Fut1: TryFuture<Ok = Fut2>,
-    Fut2: TryFuture,
-{
-    /// Creates a new `Then`.
-    fn new(future: Fut1) -> AndThenIdent<Fut1, Fut2> {
-        AndThenIdent {
-            try_chain: TryChain::new(future),
-        }
-    }
-}
-
-impl<Fut1, Fut2> Future for AndThenIdent<Fut1, Fut2>
-where
-    Fut1: TryFuture<Ok = Fut2>,
-    Fut2: TryFuture<Error = Fut1::Error>,
-{
-    type Output = Result<Fut2::Ok, Fut2::Error>;
-
-    fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
-        self.project().try_chain.poll(cx, |result| match result {
-            Ok(ok) => TryChainAction::Future(ok),
-            Err(err) => TryChainAction::Output(Err(err)),
-        })
-    }
-}
-
-#[must_use = "futures do nothing unless polled"]
-#[derive(Debug)]
-enum TryChain<Fut1, Fut2> {
-    First(Fut1),
-    Second(Fut2),
-    Empty,
-}
-
-enum TryChainAction<Fut2>
-where
-    Fut2: TryFuture,
-{
-    Future(Fut2),
-    Output(Result<Fut2::Ok, Fut2::Error>),
-}
-
-impl<Fut1, Fut2> TryChain<Fut1, Fut2>
-where
-    Fut1: TryFuture<Ok = Fut2>,
-    Fut2: TryFuture,
-{
-    fn new(fut1: Fut1) -> TryChain<Fut1, Fut2> {
-        TryChain::First(fut1)
-    }
-
-    fn poll<F>(
-        self: Pin<&mut Self>,
-        cx: &mut Context<'_>,
-        f: F,
-    ) -> Poll<Result<Fut2::Ok, Fut2::Error>>
-    where
-        F: FnOnce(Result<Fut1::Ok, Fut1::Error>) -> TryChainAction<Fut2>,
-    {
-        let mut f = Some(f);
-
-        // Safe to call `get_unchecked_mut` because we won't move the futures.
-        let this = unsafe { Pin::get_unchecked_mut(self) };
-
-        loop {
-            let output = match this {
-                TryChain::First(fut1) => {
-                    // Poll the first future
-                    match unsafe { Pin::new_unchecked(fut1) }.try_poll(cx) {
-                        Poll::Pending => return Poll::Pending,
-                        Poll::Ready(output) => output,
-                    }
-                }
-                TryChain::Second(fut2) => {
-                    // Poll the second future
-                    return unsafe { Pin::new_unchecked(fut2) }.try_poll(cx);
-                }
-                TryChain::Empty => {
-                    panic!("future must not be polled after it returned `Poll::Ready`");
-                }
-            };
-
-            *this = TryChain::Empty; // Drop fut1
-            let f = f.take().unwrap();
-            match f(output) {
-                TryChainAction::Future(fut2) => *this = TryChain::Second(fut2),
-                TryChainAction::Output(output) => return Poll::Ready(output),
-            }
-        }
-    }
-}
-
-#[cfg(test)]
-mod tests {
-    use super::{
-        cancellations, CanceledRequests, Channel, DispatchResponse, RequestCancellation,
-        RequestDispatch,
-    };
-    use crate::{
-        client::Config,
-        context,
-        transport::{self, channel::UnboundedChannel},
-        ClientMessage, Response,
-    };
-    use fnv::FnvHashMap;
-    use futures::{
-        channel::{mpsc, oneshot},
-        prelude::*,
-        task::*,
-    };
-    use std::time::Duration;
-    use std::{pin::Pin, sync::atomic::AtomicU64, sync::Arc};
-
-    #[tokio::test(threaded_scheduler)]
-    async fn dispatch_response_cancels_on_timeout() {
-        let (_response_completion, response) = oneshot::channel();
-        let (cancellation, mut canceled_requests) = cancellations();
-        let resp = DispatchResponse::<u64> {
-            // Timeout in the past should cause resp to error out when polled.
-            response: tokio::time::timeout(Duration::from_secs(0), response),
-            complete: false,
-            request_id: 3,
-            cancellation,
-            ctx: context::current(),
-        };
-        let _ = futures::poll!(resp);
-        // resp's drop() is run, which should send a cancel message.
-        assert!(canceled_requests.0.try_next().unwrap() == Some(3));
-    }
-
-    #[tokio::test(threaded_scheduler)]
-    async fn stage_request() {
-        let (mut dispatch, mut channel, _server_channel) = set_up();
-        let dispatch = Pin::new(&mut dispatch);
-        let cx = &mut Context::from_waker(&noop_waker_ref());
-
-        let _resp = send_request(&mut channel, "hi").await;
-
-        let req = dispatch.poll_next_request(cx).ready();
-        assert!(req.is_some());
-
-        let req = req.unwrap();
-        assert_eq!(req.request_id, 0);
-        assert_eq!(req.request, "hi".to_string());
-    }
-
-    // Regression test for  https://github.com/google/tarpc/issues/220
-    #[tokio::test(threaded_scheduler)]
-    async fn stage_request_channel_dropped_doesnt_panic() {
-        let (mut dispatch, mut channel, mut server_channel) = set_up();
-        let mut dispatch = Pin::new(&mut dispatch);
-        let cx = &mut Context::from_waker(&noop_waker_ref());
-
-        let _ = send_request(&mut channel, "hi").await;
-        drop(channel);
-
-        assert!(dispatch.as_mut().poll(cx).is_ready());
-        send_response(
-            &mut server_channel,
-            Response {
-                request_id: 0,
-                message: Ok("hello".into()),
-                _non_exhaustive: (),
-            },
-        )
-        .await;
-        dispatch.await.unwrap();
-    }
-
-    #[tokio::test(threaded_scheduler)]
-    async fn stage_request_response_future_dropped_is_canceled_before_sending() {
-        let (mut dispatch, mut channel, _server_channel) = set_up();
-        let dispatch = Pin::new(&mut dispatch);
-        let cx = &mut Context::from_waker(&noop_waker_ref());
-
-        let _ = send_request(&mut channel, "hi").await;
-
-        // Drop the channel so polling returns none if no requests are currently ready.
-        drop(channel);
-        // Test that a request future dropped before it's processed by dispatch will cause the request
-        // to not be added to the in-flight request map.
-        assert!(dispatch.poll_next_request(cx).ready().is_none());
-    }
-
-    #[tokio::test(threaded_scheduler)]
-    async fn stage_request_response_future_dropped_is_canceled_after_sending() {
-        let (mut dispatch, mut channel, _server_channel) = set_up();
-        let cx = &mut Context::from_waker(&noop_waker_ref());
-        let mut dispatch = Pin::new(&mut dispatch);
-
-        let req = send_request(&mut channel, "hi").await;
-
-        assert!(dispatch.as_mut().pump_write(cx).ready().is_some());
-        assert!(!dispatch.as_mut().project().in_flight_requests.is_empty());
-
-        // Test that a request future dropped after it's processed by dispatch will cause the request
-        // to be removed from the in-flight request map.
-        drop(req);
-        if let Poll::Ready(Some(_)) = dispatch.as_mut().poll_next_cancellation(cx).unwrap() {
-            // ok
-        } else {
-            panic!("Expected request to be cancelled")
-        };
-        assert!(dispatch.project().in_flight_requests.is_empty());
-    }
-
-    #[tokio::test(threaded_scheduler)]
-    async fn stage_request_response_closed_skipped() {
-        let (mut dispatch, mut channel, _server_channel) = set_up();
-        let dispatch = Pin::new(&mut dispatch);
-        let cx = &mut Context::from_waker(&noop_waker_ref());
-
-        // Test that a request future that's closed its receiver but not yet canceled its request --
-        // i.e. still in `drop fn` -- will cause the request to not be added to the in-flight request
-        // map.
-        let mut resp = send_request(&mut channel, "hi").await;
-        resp.response.get_mut().close();
-
-        assert!(dispatch.poll_next_request(cx).is_pending());
-    }
-
-    fn set_up() -> (
-        RequestDispatch<String, String, UnboundedChannel<Response<String>, ClientMessage<String>>>,
-        Channel<String, String>,
-        UnboundedChannel<ClientMessage<String>, Response<String>>,
-    ) {
-        let _ = env_logger::try_init();
-
-        let (to_dispatch, pending_requests) = mpsc::channel(1);
-        let (cancel_tx, canceled_requests) = mpsc::unbounded();
-        let (client_channel, server_channel) = transport::channel::unbounded();
-
-        let dispatch = RequestDispatch::<String, String, _> {
-            transport: client_channel.fuse(),
-            pending_requests: pending_requests.fuse(),
-            canceled_requests: CanceledRequests(canceled_requests).fuse(),
-            in_flight_requests: FnvHashMap::default(),
-            config: Config::default(),
-        };
-
-        let cancellation = RequestCancellation(cancel_tx);
-        let channel = Channel {
-            to_dispatch,
-            cancellation,
-            next_request_id: Arc::new(AtomicU64::new(0)),
-        };
-
-        (dispatch, channel, server_channel)
-    }
-
-    async fn send_request(
-        channel: &mut Channel<String, String>,
-        request: &str,
-    ) -> DispatchResponse<String> {
-        channel
-            .send(context::current(), request.to_string())
-            .await
-            .unwrap()
-    }
-
-    async fn send_response(
-        channel: &mut UnboundedChannel<ClientMessage<String>, Response<String>>,
-        response: Response<String>,
-    ) {
-        channel.send(response).await.unwrap();
-    }
-
-    trait PollTest {
-        type T;
-        fn unwrap(self) -> Poll<Self::T>;
-        fn ready(self) -> Self::T;
-    }
-
-    impl<T, E> PollTest for Poll<Option<Result<T, E>>>
-    where
-        E: ::std::fmt::Display,
-    {
-        type T = Option<T>;
-
-        fn unwrap(self) -> Poll<Option<T>> {
-            match self {
-                Poll::Ready(Some(Ok(t))) => Poll::Ready(Some(t)),
-                Poll::Ready(None) => Poll::Ready(None),
-                Poll::Ready(Some(Err(e))) => panic!(e.to_string()),
-                Poll::Pending => Poll::Pending,
-            }
-        }
-
-        fn ready(self) -> Option<T> {
-            match self {
-                Poll::Ready(Some(Ok(t))) => Some(t),
-                Poll::Ready(None) => None,
-                Poll::Ready(Some(Err(e))) => panic!(e.to_string()),
-                Poll::Pending => panic!("Pending"),
-            }
-        }
-    }
-}

tarpc/src/rpc/client/mod.rs

@@ -1,155 +0,0 @@
-// Copyright 2018 Google LLC
-//
-// Use of this source code is governed by an MIT-style
-// license that can be found in the LICENSE file or at
-// https://opensource.org/licenses/MIT.
-
-//! Provides a client that connects to a server and sends multiplexed requests.
-
-use crate::context;
-use futures::prelude::*;
-use std::io;
-
-/// Provides a [`Client`] backed by a transport.
-pub mod channel;
-pub use channel::{new, Channel};
-
-/// Sends multiplexed requests to, and receives responses from, a server.
-pub trait Client<'a, Req> {
-    /// The response type.
-    type Response;
-
-    /// The future response.
-    type Future: Future<Output = io::Result<Self::Response>> + 'a;
-
-    /// Initiates a request, sending it to the dispatch task.
-    ///
-    /// Returns a [`Future`] that resolves to this client and the future response
-    /// once the request is successfully enqueued.
-    ///
-    /// [`Future`]: futures::Future
-    fn call(&'a mut self, ctx: context::Context, request: Req) -> Self::Future;
-
-    /// Returns a Client that applies a post-processing function to the returned response.
-    fn map_response<F, R>(self, f: F) -> MapResponse<Self, F>
-    where
-        F: FnMut(Self::Response) -> R,
-        Self: Sized,
-    {
-        MapResponse { inner: self, f }
-    }
-
-    /// Returns a Client that applies a pre-processing function to the request.
-    fn with_request<F, Req2>(self, f: F) -> WithRequest<Self, F>
-    where
-        F: FnMut(Req2) -> Req,
-        Self: Sized,
-    {
-        WithRequest { inner: self, f }
-    }
-}
-
-/// A Client that applies a function to the returned response.
-#[derive(Clone, Debug)]
-pub struct MapResponse<C, F> {
-    inner: C,
-    f: F,
-}
-
-impl<'a, C, F, Req, Resp, Resp2> Client<'a, Req> for MapResponse<C, F>
-where
-    C: Client<'a, Req, Response = Resp>,
-    F: FnMut(Resp) -> Resp2 + 'a,
-{
-    type Response = Resp2;
-    type Future = futures::future::MapOk<<C as Client<'a, Req>>::Future, &'a mut F>;
-
-    fn call(&'a mut self, ctx: context::Context, request: Req) -> Self::Future {
-        self.inner.call(ctx, request).map_ok(&mut self.f)
-    }
-}
-
-/// A Client that applies a pre-processing function to the request.
-#[derive(Clone, Debug)]
-pub struct WithRequest<C, F> {
-    inner: C,
-    f: F,
-}
-
-impl<'a, C, F, Req, Req2, Resp> Client<'a, Req2> for WithRequest<C, F>
-where
-    C: Client<'a, Req, Response = Resp>,
-    F: FnMut(Req2) -> Req,
-{
-    type Response = Resp;
-    type Future = <C as Client<'a, Req>>::Future;
-
-    fn call(&'a mut self, ctx: context::Context, request: Req2) -> Self::Future {
-        self.inner.call(ctx, (self.f)(request))
-    }
-}
-
-impl<'a, Req, Resp> Client<'a, Req> for Channel<Req, Resp>
-where
-    Req: 'a,
-    Resp: 'a,
-{
-    type Response = Resp;
-    type Future = channel::Call<'a, Req, Resp>;
-
-    fn call(&'a mut self, ctx: context::Context, request: Req) -> channel::Call<'a, Req, Resp> {
-        self.call(ctx, request)
-    }
-}
-
-/// Settings that control the behavior of the client.
-#[derive(Clone, Debug)]
-pub struct Config {
-    /// The number of requests that can be in flight at once.
-    /// `max_in_flight_requests` controls the size of the map used by the client
-    /// for storing pending requests.
-    pub max_in_flight_requests: usize,
-    /// The number of requests that can be buffered client-side before being sent.
-    /// `pending_requests_buffer` controls the size of the channel clients use
-    /// to communicate with the request dispatch task.
-    pub pending_request_buffer: usize,
-    #[doc(hidden)]
-    _non_exhaustive: (),
-}
-
-impl Default for Config {
-    fn default() -> Self {
-        Config {
-            max_in_flight_requests: 1_000,
-            pending_request_buffer: 100,
-            _non_exhaustive: (),
-        }
-    }
-}
-
-/// A channel and dispatch pair. The dispatch drives the sending and receiving of requests
-/// and must be polled continuously or spawned.
-#[derive(Debug)]
-pub struct NewClient<C, D> {
-    /// The new client.
-    pub client: C,
-    /// The client's dispatch.
-    pub dispatch: D,
-}
-
-impl<C, D> NewClient<C, D>
-where
-    D: Future<Output = io::Result<()>> + Send + 'static,
-{
-    /// Helper method to spawn the dispatch on the default executor.
-    #[cfg(feature = "tokio1")]
-    pub fn spawn(self) -> io::Result<C> {
-        use log::error;
-
-        let dispatch = self
-            .dispatch
-            .unwrap_or_else(move |e| error!("Connection broken: {}", e));
-        tokio::spawn(dispatch);
-        Ok(self.client)
-    }
-}

tarpc/src/rpc/context.rs

@@ -1,63 +0,0 @@
-// Copyright 2018 Google LLC
-//
-// Use of this source code is governed by an MIT-style
-// license that can be found in the LICENSE file or at
-// https://opensource.org/licenses/MIT.
-
-//! Provides a request context that carries a deadline and trace context. This context is sent from
-//! client to server and is used by the server to enforce response deadlines.
-
-use crate::trace::{self, TraceId};
-use std::time::{Duration, SystemTime};
-
-/// A request context that carries request-scoped information like deadlines and trace information.
-/// It is sent from client to server and is used by the server to enforce response deadlines.
-///
-/// The context should not be stored directly in a server implementation, because the context will
-/// be different for each request in scope.
-#[derive(Clone, Copy, Debug)]
-#[cfg_attr(feature = "serde1", derive(serde::Serialize, serde::Deserialize))]
-pub struct Context {
-    /// When the client expects the request to be complete by. The server should cancel the request
-    /// if it is not complete by this time.
-    #[cfg_attr(
-        feature = "serde1",
-        serde(serialize_with = "crate::util::serde::serialize_epoch_secs")
-    )]
-    #[cfg_attr(
-        feature = "serde1",
-        serde(deserialize_with = "crate::util::serde::deserialize_epoch_secs")
-    )]
-    #[cfg_attr(feature = "serde1", serde(default = "ten_seconds_from_now"))]
-    pub deadline: SystemTime,
-    /// Uniquely identifies requests originating from the same source.
-    /// When a service handles a request by making requests itself, those requests should
-    /// include the same `trace_id` as that included on the original request. This way,
-    /// users can trace related actions across a distributed system.
-    pub trace_context: trace::Context,
-    #[doc(hidden)]
-    #[cfg_attr(feature = "serde1", serde(skip_serializing, default))]
-    pub(crate) _non_exhaustive: (),
-}
-
-#[cfg(feature = "serde1")]
-fn ten_seconds_from_now() -> SystemTime {
-    SystemTime::now() + Duration::from_secs(10)
-}
-
-/// Returns the context for the current request, or a default Context if no request is active.
-// TODO: populate Context with request-scoped data, with default fallbacks.
-pub fn current() -> Context {
-    Context {
-        deadline: SystemTime::now() + Duration::from_secs(10),
-        trace_context: trace::Context::new_root(),
-        _non_exhaustive: (),
-    }
-}
-
-impl Context {
-    /// Returns the ID of the request-scoped trace.
-    pub fn trace_id(&self) -> &TraceId {
-        &self.trace_context.trace_id
-    }
-}

tarpc/src/rpc/mod.rs

@@ -1,127 +0,0 @@
-// Copyright 2018 Google LLC
-//
-// Use of this source code is governed by an MIT-style
-// license that can be found in the LICENSE file or at
-// https://opensource.org/licenses/MIT.
-
-#![deny(missing_docs, missing_debug_implementations)]
-
-//! An RPC framework providing client and server.
-//!
-//! Features:
-//! * RPC deadlines, both client- and server-side.
-//! * Cascading cancellation (works with multiple hops).
-//! * Configurable limits
-//!    * In-flight requests, both client and server-side.
-//!        * Server-side limit is per-connection.
-//!        * When the server reaches the in-flight request maximum, it returns a throttled error
-//!          to the client.
-//!        * When the client reaches the in-flight request max, messages are buffered up to a
-//!          configurable maximum, beyond which the requests are back-pressured.
-//!    * Server connections.
-//!        * Total and per-IP limits.
-//!        * When an incoming connection is accepted, if already at maximum, the connection is
-//!          dropped.
-//! * Transport agnostic.
-
-pub mod client;
-pub mod context;
-pub mod server;
-pub mod transport;
-pub(crate) mod util;
-
-pub use crate::{client::Client, server::Server, trace, transport::sealed::Transport};
-
-use futures::task::*;
-use std::{io, time::SystemTime};
-
-/// A message from a client to a server.
-#[derive(Debug)]
-#[cfg_attr(feature = "serde1", derive(serde::Serialize, serde::Deserialize))]
-pub enum ClientMessage<T> {
-    /// A request initiated by a user. The server responds to a request by invoking a
-    /// service-provided request handler.  The handler completes with a [`response`](Response), which
-    /// the server sends back to the client.
-    Request(Request<T>),
-    /// A command to cancel an in-flight request, automatically sent by the client when a response
-    /// future is dropped.
-    ///
-    /// When received, the server will immediately cancel the main task (top-level future) of the
-    /// request handler for the associated request. Any tasks spawned by the request handler will
-    /// not be canceled, because the framework layer does not
-    /// know about them.
-    Cancel {
-        /// The trace context associates the message with a specific chain of causally-related actions,
-        /// possibly orchestrated across many distributed systems.
-        #[cfg_attr(feature = "serde", serde(default))]
-        trace_context: trace::Context,
-        /// The ID of the request to cancel.
-        request_id: u64,
-    },
-    #[doc(hidden)]
-    _NonExhaustive,
-}
-
-/// A request from a client to a server.
-#[derive(Clone, Copy, Debug)]
-#[cfg_attr(feature = "serde1", derive(serde::Serialize, serde::Deserialize))]
-pub struct Request<T> {
-    /// Trace context, deadline, and other cross-cutting concerns.
-    pub context: context::Context,
-    /// Uniquely identifies the request across all requests sent over a single channel.
-    pub id: u64,
-    /// The request body.
-    pub message: T,
-    #[doc(hidden)]
-    #[cfg_attr(feature = "serde1", serde(skip_serializing, default))]
-    _non_exhaustive: (),
-}
-
-/// A response from a server to a client.
-#[derive(Clone, Debug, PartialEq, Eq, Hash)]
-#[cfg_attr(feature = "serde1", derive(serde::Serialize, serde::Deserialize))]
-pub struct Response<T> {
-    /// The ID of the request being responded to.
-    pub request_id: u64,
-    /// The response body, or an error if the request failed.
-    pub message: Result<T, ServerError>,
-    #[doc(hidden)]
-    #[cfg_attr(feature = "serde1", serde(skip_serializing, default))]
-    _non_exhaustive: (),
-}
-
-/// An error response from a server to a client.
-#[derive(Clone, Debug, PartialEq, Eq, Hash)]
-#[cfg_attr(feature = "serde1", derive(serde::Serialize, serde::Deserialize))]
-pub struct ServerError {
-    #[cfg_attr(
-        feature = "serde1",
-        serde(serialize_with = "util::serde::serialize_io_error_kind_as_u32")
-    )]
-    #[cfg_attr(
-        feature = "serde1",
-        serde(deserialize_with = "util::serde::deserialize_io_error_kind_from_u32")
-    )]
-    /// The type of error that occurred to fail the request.
-    pub kind: io::ErrorKind,
-    /// A message describing more detail about the error that occurred.
-    pub detail: Option<String>,
-    #[doc(hidden)]
-    #[cfg_attr(feature = "serde1", serde(skip_serializing, default))]
-    _non_exhaustive: (),
-}
-
-impl From<ServerError> for io::Error {
-    fn from(e: ServerError) -> io::Error {
-        io::Error::new(e.kind, e.detail.unwrap_or_default())
-    }
-}
-
-impl<T> Request<T> {
-    /// Returns the deadline for this request.
-    pub fn deadline(&self) -> &SystemTime {
-        &self.context.deadline
-    }
-}
-
-pub(crate) type PollIo<T> = Poll<Option<io::Result<T>>>;

tarpc/src/rpc/server/mod.rs

@@ -1,702 +0,0 @@
-// Copyright 2018 Google LLC
-//
-// Use of this source code is governed by an MIT-style
-// license that can be found in the LICENSE file or at
-// https://opensource.org/licenses/MIT.
-
-//! Provides a server that concurrently handles many connections sending multiplexed requests.
-
-use crate::{
-    context, trace, util::Compact, util::TimeUntil, ClientMessage, PollIo, Request, Response,
-    ServerError, Transport,
-};
-use fnv::FnvHashMap;
-use futures::{
-    channel::mpsc,
-    future::{AbortHandle, AbortRegistration, Abortable},
-    prelude::*,
-    ready,
-    stream::Fuse,
-    task::*,
-};
-use humantime::format_rfc3339;
-use log::{debug, trace};
-use pin_project::pin_project;
-use std::{fmt, hash::Hash, io, marker::PhantomData, pin::Pin, time::SystemTime};
-use tokio::time::Timeout;
-
-mod filter;
-#[cfg(test)]
-mod testing;
-mod throttle;
-
-pub use self::{
-    filter::ChannelFilter,
-    throttle::{Throttler, ThrottlerStream},
-};
-
-/// Manages clients, serving multiplexed requests over each connection.
-#[derive(Debug)]
-pub struct Server<Req, Resp> {
-    config: Config,
-    ghost: PhantomData<(Req, Resp)>,
-}
-
-impl<Req, Resp> Default for Server<Req, Resp> {
-    fn default() -> Self {
-        new(Config::default())
-    }
-}
-
-/// Settings that control the behavior of the server.
-#[derive(Clone, Debug)]
-pub struct Config {
-    /// The number of responses per client that can be buffered server-side before being sent.
-    /// `pending_response_buffer` controls the buffer size of the channel that a server's
-    /// response tasks use to send responses to the client handler task.
-    pub pending_response_buffer: usize,
-}
-
-impl Default for Config {
-    fn default() -> Self {
-        Config {
-            pending_response_buffer: 100,
-        }
-    }
-}
-
-impl Config {
-    /// Returns a channel backed by `transport` and configured with `self`.
-    pub fn channel<Req, Resp, T>(self, transport: T) -> BaseChannel<Req, Resp, T>
-    where
-        T: Transport<Response<Resp>, ClientMessage<Req>>,
-    {
-        BaseChannel::new(self, transport)
-    }
-}
-
-/// Returns a new server with configuration specified `config`.
-pub fn new<Req, Resp>(config: Config) -> Server<Req, Resp> {
-    Server {
-        config,
-        ghost: PhantomData,
-    }
-}
-
-impl<Req, Resp> Server<Req, Resp> {
-    /// Returns the config for this server.
-    pub fn config(&self) -> &Config {
-        &self.config
-    }
-
-    /// Returns a stream of server channels.
-    pub fn incoming<S, T>(self, listener: S) -> impl Stream<Item = BaseChannel<Req, Resp, T>>
-    where
-        S: Stream<Item = T>,
-        T: Transport<Response<Resp>, ClientMessage<Req>>,
-    {
-        listener.map(move |t| BaseChannel::new(self.config.clone(), t))
-    }
-}
-
-/// Basically a Fn(Req) -> impl Future<Output = Resp>;
-pub trait Serve<Req>: Sized + Clone {
-    /// Type of response.
-    type Resp;
-
-    /// Type of response future.
-    type Fut: Future<Output = Self::Resp>;
-
-    /// Responds to a single request.
-    fn serve(self, ctx: context::Context, req: Req) -> Self::Fut;
-}
-
-impl<Req, Resp, Fut, F> Serve<Req> for F
-where
-    F: FnOnce(context::Context, Req) -> Fut + Clone,
-    Fut: Future<Output = Resp>,
-{
-    type Resp = Resp;
-    type Fut = Fut;
-
-    fn serve(self, ctx: context::Context, req: Req) -> Self::Fut {
-        self(ctx, req)
-    }
-}
-
-/// A utility trait enabling a stream to fluently chain a request handler.
-pub trait Handler<C>
-where
-    Self: Sized + Stream<Item = C>,
-    C: Channel,
-{
-    /// Enforces channel per-key limits.
-    fn max_channels_per_key<K, KF>(self, n: u32, keymaker: KF) -> filter::ChannelFilter<Self, K, KF>
-    where
-        K: fmt::Display + Eq + Hash + Clone + Unpin,
-        KF: Fn(&C) -> K,
-    {
-        ChannelFilter::new(self, n, keymaker)
-    }
-
-    /// Caps the number of concurrent requests per channel.
-    fn max_concurrent_requests_per_channel(self, n: usize) -> ThrottlerStream<Self> {
-        ThrottlerStream::new(self, n)
-    }
-
-    /// Responds to all requests with `server`.
-    #[cfg(feature = "tokio1")]
-    fn respond_with<S>(self, server: S) -> Running<Self, S>
-    where
-        S: Serve<C::Req, Resp = C::Resp>,
-    {
-        Running {
-            incoming: self,
-            server,
-        }
-    }
-}
-
-impl<S, C> Handler<C> for S
-where
-    S: Sized + Stream<Item = C>,
-    C: Channel,
-{
-}
-
-/// BaseChannel lifts a Transport to a Channel by tracking in-flight requests.
-#[pin_project]
-#[derive(Debug)]
-pub struct BaseChannel<Req, Resp, T> {
-    config: Config,
-    /// Writes responses to the wire and reads requests off the wire.
-    #[pin]
-    transport: Fuse<T>,
-    /// Number of requests currently being responded to.
-    in_flight_requests: FnvHashMap<u64, AbortHandle>,
-    /// Types the request and response.
-    ghost: PhantomData<(Req, Resp)>,
-}
-
-impl<Req, Resp, T> BaseChannel<Req, Resp, T>
-where
-    T: Transport<Response<Resp>, ClientMessage<Req>>,
-{
-    /// Creates a new channel backed by `transport` and configured with `config`.
-    pub fn new(config: Config, transport: T) -> Self {
-        BaseChannel {
-            config,
-            transport: transport.fuse(),
-            in_flight_requests: FnvHashMap::default(),
-            ghost: PhantomData,
-        }
-    }
-
-    /// Creates a new channel backed by `transport` and configured with the defaults.
-    pub fn with_defaults(transport: T) -> Self {
-        Self::new(Config::default(), transport)
-    }
-
-    /// Returns the inner transport.
-    pub fn get_ref(&self) -> &T {
-        self.transport.get_ref()
-    }
-
-    fn cancel_request(mut self: Pin<&mut Self>, trace_context: &trace::Context, request_id: u64) {
-        // It's possible the request was already completed, so it's fine
-        // if this is None.
-        if let Some(cancel_handle) = self
-            .as_mut()
-            .project()
-            .in_flight_requests
-            .remove(&request_id)
-        {
-            self.as_mut().project().in_flight_requests.compact(0.1);
-
-            cancel_handle.abort();
-            let remaining = self.as_mut().project().in_flight_requests.len();
-            trace!(
-                "[{}] Request canceled. In-flight requests = {}",
-                trace_context.trace_id,
-                remaining,
-            );
-        } else {
-            trace!(
-                "[{}] Received cancellation, but response handler \
-                 is already complete.",
-                trace_context.trace_id,
-            );
-        }
-    }
-}
-
-/// The server end of an open connection with a client, streaming in requests from, and sinking
-/// responses to, the client.
-///
-/// Channels are free to somewhat rely on the assumption that all in-flight requests are eventually
-/// either [cancelled](BaseChannel::cancel_request) or [responded to](Sink::start_send). Safety cannot
-/// rely on this assumption, but it is best for `Channel` users to always account for all outstanding
-/// requests.
-pub trait Channel
-where
-    Self: Transport<Response<<Self as Channel>::Resp>, Request<<Self as Channel>::Req>>,
-{
-    /// Type of request item.
-    type Req;
-
-    /// Type of response sink item.
-    type Resp;
-
-    /// Configuration of the channel.
-    fn config(&self) -> &Config;
-
-    /// Returns the number of in-flight requests over this channel.
-    fn in_flight_requests(self: Pin<&mut Self>) -> usize;
-
-    /// Caps the number of concurrent requests.
-    fn max_concurrent_requests(self, n: usize) -> Throttler<Self>
-    where
-        Self: Sized,
-    {
-        Throttler::new(self, n)
-    }
-
-    /// Tells the Channel that request with ID `request_id` is being handled.
-    /// The request will be tracked until a response with the same ID is sent
-    /// to the Channel.
-    fn start_request(self: Pin<&mut Self>, request_id: u64) -> AbortRegistration;
-
-    /// Respond to requests coming over the channel with `f`. Returns a future that drives the
-    /// responses and resolves when the connection is closed.
-    fn respond_with<S>(self, server: S) -> ClientHandler<Self, S>
-    where
-        S: Serve<Self::Req, Resp = Self::Resp>,
-        Self: Sized,
-    {
-        let (responses_tx, responses) = mpsc::channel(self.config().pending_response_buffer);
-        let responses = responses.fuse();
-
-        ClientHandler {
-            channel: self,
-            server,
-            pending_responses: responses,
-            responses_tx,
-        }
-    }
-}
-
-impl<Req, Resp, T> Stream for BaseChannel<Req, Resp, T>
-where
-    T: Transport<Response<Resp>, ClientMessage<Req>>,
-{
-    type Item = io::Result<Request<Req>>;
-
-    fn poll_next(mut self: Pin<&mut Self>, cx: &mut Context) -> Poll<Option<Self::Item>> {
-        loop {
-            match ready!(self.as_mut().project().transport.poll_next(cx)?) {
-                Some(message) => match message {
-                    ClientMessage::Request(request) => {
-                        return Poll::Ready(Some(Ok(request)));
-                    }
-                    ClientMessage::Cancel {
-                        trace_context,
-                        request_id,
-                    } => {
-                        self.as_mut().cancel_request(&trace_context, request_id);
-                    }
-                    ClientMessage::_NonExhaustive => unreachable!(),
-                },
-                None => return Poll::Ready(None),
-            }
-        }
-    }
-}
-
-impl<Req, Resp, T> Sink<Response<Resp>> for BaseChannel<Req, Resp, T>
-where
-    T: Transport<Response<Resp>, ClientMessage<Req>>,
-{
-    type Error = io::Error;
-
-    fn poll_ready(self: Pin<&mut Self>, cx: &mut Context) -> Poll<Result<(), Self::Error>> {
-        self.project().transport.poll_ready(cx)
-    }
-
-    fn start_send(mut self: Pin<&mut Self>, response: Response<Resp>) -> Result<(), Self::Error> {
-        if self
-            .as_mut()
-            .project()
-            .in_flight_requests
-            .remove(&response.request_id)
-            .is_some()
-        {
-            self.as_mut().project().in_flight_requests.compact(0.1);
-        }
-
-        self.project().transport.start_send(response)
-    }
-
-    fn poll_flush(self: Pin<&mut Self>, cx: &mut Context) -> Poll<Result<(), Self::Error>> {
-        self.project().transport.poll_flush(cx)
-    }
-
-    fn poll_close(self: Pin<&mut Self>, cx: &mut Context) -> Poll<Result<(), Self::Error>> {
-        self.project().transport.poll_close(cx)
-    }
-}
-
-impl<Req, Resp, T> AsRef<T> for BaseChannel<Req, Resp, T> {
-    fn as_ref(&self) -> &T {
-        self.transport.get_ref()
-    }
-}
-
-impl<Req, Resp, T> Channel for BaseChannel<Req, Resp, T>
-where
-    T: Transport<Response<Resp>, ClientMessage<Req>>,
-{
-    type Req = Req;
-    type Resp = Resp;
-
-    fn config(&self) -> &Config {
-        &self.config
-    }
-
-    fn in_flight_requests(mut self: Pin<&mut Self>) -> usize {
-        self.as_mut().project().in_flight_requests.len()
-    }
-
-    fn start_request(self: Pin<&mut Self>, request_id: u64) -> AbortRegistration {
-        let (abort_handle, abort_registration) = AbortHandle::new_pair();
-        assert!(self
-            .project()
-            .in_flight_requests
-            .insert(request_id, abort_handle)
-            .is_none());
-        abort_registration
-    }
-}
-
-/// A running handler serving all requests coming over a channel.
-#[pin_project]
-#[derive(Debug)]
-pub struct ClientHandler<C, S>
-where
-    C: Channel,
-{
-    #[pin]
-    channel: C,
-    /// Responses waiting to be written to the wire.
-    #[pin]
-    pending_responses: Fuse<mpsc::Receiver<(context::Context, Response<C::Resp>)>>,
-    /// Handed out to request handlers to fan in responses.
-    #[pin]
-    responses_tx: mpsc::Sender<(context::Context, Response<C::Resp>)>,
-    /// Server
-    server: S,
-}
-
-impl<C, S> ClientHandler<C, S>
-where
-    C: Channel,
-    S: Serve<C::Req, Resp = C::Resp>,
-{
-    fn pump_read(
-        mut self: Pin<&mut Self>,
-        cx: &mut Context<'_>,
-    ) -> PollIo<RequestHandler<S::Fut, C::Resp>> {
-        match ready!(self.as_mut().project().channel.poll_next(cx)?) {
-            Some(request) => Poll::Ready(Some(Ok(self.handle_request(request)))),
-            None => Poll::Ready(None),
-        }
-    }
-
-    fn pump_write(
-        mut self: Pin<&mut Self>,
-        cx: &mut Context<'_>,
-        read_half_closed: bool,
-    ) -> PollIo<()> {
-        match self.as_mut().poll_next_response(cx)? {
-            Poll::Ready(Some((ctx, response))) => {
-                trace!(
-                    "[{}] Staging response. In-flight requests = {}.",
-                    ctx.trace_id(),
-                    self.as_mut().project().channel.in_flight_requests(),
-                );
-                self.as_mut().project().channel.start_send(response)?;
-                Poll::Ready(Some(Ok(())))
-            }
-            Poll::Ready(None) => {
-                // Shutdown can't be done before we finish pumping out remaining responses.
-                ready!(self.as_mut().project().channel.poll_flush(cx)?);
-                Poll::Ready(None)
-            }
-            Poll::Pending => {
-                // No more requests to process, so flush any requests buffered in the transport.
-                ready!(self.as_mut().project().channel.poll_flush(cx)?);
-
-                // Being here means there are no staged requests and all written responses are
-                // fully flushed. So, if the read half is closed and there are no in-flight
-                // requests, then we can close the write half.
-                if read_half_closed && self.as_mut().project().channel.in_flight_requests() == 0 {
-                    Poll::Ready(None)
-                } else {
-                    Poll::Pending
-                }
-            }
-        }
-    }
-
-    fn poll_next_response(
-        mut self: Pin<&mut Self>,
-        cx: &mut Context<'_>,
-    ) -> PollIo<(context::Context, Response<C::Resp>)> {
-        // Ensure there's room to write a response.
-        while let Poll::Pending = self.as_mut().project().channel.poll_ready(cx)? {
-            ready!(self.as_mut().project().channel.poll_flush(cx)?);
-        }
-
-        match ready!(self.as_mut().project().pending_responses.poll_next(cx)) {
-            Some((ctx, response)) => Poll::Ready(Some(Ok((ctx, response)))),
-            None => {
-                // This branch likely won't happen, since the ClientHandler is holding a Sender.
-                Poll::Ready(None)
-            }
-        }
-    }
-
-    fn handle_request(
-        mut self: Pin<&mut Self>,
-        request: Request<C::Req>,
-    ) -> RequestHandler<S::Fut, C::Resp> {
-        let request_id = request.id;
-        let deadline = request.context.deadline;
-        let timeout = deadline.time_until();
-        trace!(
-            "[{}] Received request with deadline {} (timeout {:?}).",
-            request.context.trace_id(),
-            format_rfc3339(deadline),
-            timeout,
-        );
-        let ctx = request.context;
-        let request = request.message;
-
-        let response = self.as_mut().project().server.clone().serve(ctx, request);
-        let response = Resp {
-            state: RespState::PollResp,
-            request_id,
-            ctx,
-            deadline,
-            f: tokio::time::timeout(timeout, response),
-            response: None,
-            response_tx: self.as_mut().project().responses_tx.clone(),
-        };
-        let abort_registration = self.as_mut().project().channel.start_request(request_id);
-        RequestHandler {
-            resp: Abortable::new(response, abort_registration),
-        }
-    }
-}
-
-/// A future fulfilling a single client request.
-#[pin_project]
-#[derive(Debug)]
-pub struct RequestHandler<F, R> {
-    #[pin]
-    resp: Abortable<Resp<F, R>>,
-}
-
-impl<F, R> Future for RequestHandler<F, R>
-where
-    F: Future<Output = R>,
-{
-    type Output = ();
-
-    fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<()> {
-        let _ = ready!(self.project().resp.poll(cx));
-        Poll::Ready(())
-    }
-}
-
-#[pin_project]
-#[derive(Debug)]
-struct Resp<F, R> {
-    state: RespState,
-    request_id: u64,
-    ctx: context::Context,
-    deadline: SystemTime,
-    #[pin]
-    f: Timeout<F>,
-    response: Option<Response<R>>,
-    #[pin]
-    response_tx: mpsc::Sender<(context::Context, Response<R>)>,
-}
-
-#[derive(Debug)]
-#[allow(clippy::enum_variant_names)]
-enum RespState {
-    PollResp,
-    PollReady,
-    PollFlush,
-}
-
-impl<F, R> Future for Resp<F, R>
-where
-    F: Future<Output = R>,
-{
-    type Output = ();
-
-    fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<()> {
-        loop {
-            match self.as_mut().project().state {
-                RespState::PollResp => {
-                    let result = ready!(self.as_mut().project().f.poll(cx));
-                    *self.as_mut().project().response = Some(Response {
-                        request_id: self.request_id,
-                        message: match result {
-                            Ok(message) => Ok(message),
-                            Err(tokio::time::Elapsed { .. }) => {
-                                debug!(
-                                    "[{}] Response did not complete before deadline of {}s.",
-                                    self.ctx.trace_id(),
-                                    format_rfc3339(self.deadline)
-                                );
-                                // No point in responding, since the client will have dropped the
-                                // request.
-                                Err(ServerError {
-                                    kind: io::ErrorKind::TimedOut,
-                                    detail: Some(format!(
-                                        "Response did not complete before deadline of {}s.",
-                                        format_rfc3339(self.deadline)
-                                    )),
-                                    _non_exhaustive: (),
-                                })
-                            }
-                        },
-                        _non_exhaustive: (),
-                    });
-                    *self.as_mut().project().state = RespState::PollReady;
-                }
-                RespState::PollReady => {
-                    let ready = ready!(self.as_mut().project().response_tx.poll_ready(cx));
-                    if ready.is_err() {
-                        return Poll::Ready(());
-                    }
-                    let resp = (self.ctx, self.as_mut().project().response.take().unwrap());
-                    if self
-                        .as_mut()
-                        .project()
-                        .response_tx
-                        .start_send(resp)
-                        .is_err()
-                    {
-                        return Poll::Ready(());
-                    }
-                    *self.as_mut().project().state = RespState::PollFlush;
-                }
-                RespState::PollFlush => {
-                    let ready = ready!(self.as_mut().project().response_tx.poll_flush(cx));
-                    if ready.is_err() {
-                        return Poll::Ready(());
-                    }
-                    return Poll::Ready(());
-                }
-            }
-        }
-    }
-}
-
-impl<C, S> Stream for ClientHandler<C, S>
-where
-    C: Channel,
-    S: Serve<C::Req, Resp = C::Resp>,
-{
-    type Item = io::Result<RequestHandler<S::Fut, C::Resp>>;
-
-    fn poll_next(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Option<Self::Item>> {
-        loop {
-            let read = self.as_mut().pump_read(cx)?;
-            let read_closed = if let Poll::Ready(None) = read {
-                true
-            } else {
-                false
-            };
-            match (read, self.as_mut().pump_write(cx, read_closed)?) {
-                (Poll::Ready(None), Poll::Ready(None)) => {
-                    return Poll::Ready(None);
-                }
-                (Poll::Ready(Some(request_handler)), _) => {
-                    return Poll::Ready(Some(Ok(request_handler)));
-                }
-                (_, Poll::Ready(Some(()))) => {}
-                _ => {
-                    return Poll::Pending;
-                }
-            }
-        }
-    }
-}
-
-// Send + 'static execution helper methods.
-
-impl<C, S> ClientHandler<C, S>
-where
-    C: Channel + 'static,
-    C::Req: Send + 'static,
-    C::Resp: Send + 'static,
-    S: Serve<C::Req, Resp = C::Resp> + Send + 'static,
-    S::Fut: Send + 'static,
-{
-    /// Runs the client handler until completion by spawning each
-    /// request handler onto the default executor.
-    #[cfg(feature = "tokio1")]
-    pub fn execute(self) -> impl Future<Output = ()> {
-        use log::info;
-
-        self.try_for_each(|request_handler| {
-            async {
-                tokio::spawn(request_handler);
-                Ok(())
-            }
-        })
-        .unwrap_or_else(|e| info!("ClientHandler errored out: {}", e))
-    }
-}
-
-/// A future that drives the server by spawning channels and request handlers on the default
-/// executor.
-#[pin_project]
-#[derive(Debug)]
-#[cfg(feature = "tokio1")]
-pub struct Running<St, Se> {
-    #[pin]
-    incoming: St,
-    server: Se,
-}
-
-#[cfg(feature = "tokio1")]
-impl<St, C, Se> Future for Running<St, Se>
-where
-    St: Sized + Stream<Item = C>,
-    C: Channel + Send + 'static,
-    C::Req: Send + 'static,
-    C::Resp: Send + 'static,
-    Se: Serve<C::Req, Resp = C::Resp> + Send + 'static + Clone,
-    Se::Fut: Send + 'static,
-{
-    type Output = ();
-
-    fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<()> {
-        use log::info;
-
-        while let Some(channel) = ready!(self.as_mut().project().incoming.poll_next(cx)) {
-            tokio::spawn(
-                channel
-                    .respond_with(self.as_mut().project().server.clone())
-                    .execute(),
-            );
-        }
-        info!("Server shutting down.");
-        Poll::Ready(())
-    }
-}

tarpc/src/rpc/server/throttle.rs

@@ -1,326 +0,0 @@
-use super::{Channel, Config};
-use crate::{Response, ServerError};
-use futures::{future::AbortRegistration, prelude::*, ready, task::*};
-use log::debug;
-use pin_project::pin_project;
-use std::{io, pin::Pin};
-
-/// A [`Channel`] that limits the number of concurrent
-/// requests by throttling.
-#[pin_project]
-#[derive(Debug)]
-pub struct Throttler<C> {
-    max_in_flight_requests: usize,
-    #[pin]
-    inner: C,
-}
-
-impl<C> Throttler<C> {
-    /// Returns the inner channel.
-    pub fn get_ref(&self) -> &C {
-        &self.inner
-    }
-}
-
-impl<C> Throttler<C>
-where
-    C: Channel,
-{
-    /// Returns a new `Throttler` that wraps the given channel and limits concurrent requests to
-    /// `max_in_flight_requests`.
-    pub fn new(inner: C, max_in_flight_requests: usize) -> Self {
-        Throttler {
-            inner,
-            max_in_flight_requests,
-        }
-    }
-}
-
-impl<C> Stream for Throttler<C>
-where
-    C: Channel,
-{
-    type Item = <C as Stream>::Item;
-
-    fn poll_next(mut self: Pin<&mut Self>, cx: &mut Context) -> Poll<Option<Self::Item>> {
-        while self.as_mut().in_flight_requests() >= *self.as_mut().project().max_in_flight_requests
-        {
-            ready!(self.as_mut().project().inner.poll_ready(cx)?);
-
-            match ready!(self.as_mut().project().inner.poll_next(cx)?) {
-                Some(request) => {
-                    debug!(
-                        "[{}] Client has reached in-flight request limit ({}/{}).",
-                        request.context.trace_id(),
-                        self.as_mut().in_flight_requests(),
-                        self.as_mut().project().max_in_flight_requests,
-                    );
-
-                    self.as_mut().start_send(Response {
-                        request_id: request.id,
-                        message: Err(ServerError {
-                            kind: io::ErrorKind::WouldBlock,
-                            detail: Some("Server throttled the request.".into()),
-                            _non_exhaustive: (),
-                        }),
-                        _non_exhaustive: (),
-                    })?;
-                }
-                None => return Poll::Ready(None),
-            }
-        }
-        self.project().inner.poll_next(cx)
-    }
-}
-
-impl<C> Sink<Response<<C as Channel>::Resp>> for Throttler<C>
-where
-    C: Channel,
-{
-    type Error = io::Error;
-
-    fn poll_ready(self: Pin<&mut Self>, cx: &mut Context) -> Poll<Result<(), Self::Error>> {
-        self.project().inner.poll_ready(cx)
-    }
-
-    fn start_send(self: Pin<&mut Self>, item: Response<<C as Channel>::Resp>) -> io::Result<()> {
-        self.project().inner.start_send(item)
-    }
-
-    fn poll_flush(self: Pin<&mut Self>, cx: &mut Context) -> Poll<io::Result<()>> {
-        self.project().inner.poll_flush(cx)
-    }
-
-    fn poll_close(self: Pin<&mut Self>, cx: &mut Context) -> Poll<io::Result<()>> {
-        self.project().inner.poll_close(cx)
-    }
-}
-
-impl<C> AsRef<C> for Throttler<C> {
-    fn as_ref(&self) -> &C {
-        &self.inner
-    }
-}
-
-impl<C> Channel for Throttler<C>
-where
-    C: Channel,
-{
-    type Req = <C as Channel>::Req;
-    type Resp = <C as Channel>::Resp;
-
-    fn in_flight_requests(self: Pin<&mut Self>) -> usize {
-        self.project().inner.in_flight_requests()
-    }
-
-    fn config(&self) -> &Config {
-        self.inner.config()
-    }
-
-    fn start_request(self: Pin<&mut Self>, request_id: u64) -> AbortRegistration {
-        self.project().inner.start_request(request_id)
-    }
-}
-
-/// A stream of throttling channels.
-#[pin_project]
-#[derive(Debug)]
-pub struct ThrottlerStream<S> {
-    #[pin]
-    inner: S,
-    max_in_flight_requests: usize,
-}
-
-impl<S> ThrottlerStream<S>
-where
-    S: Stream,
-    <S as Stream>::Item: Channel,
-{
-    pub(crate) fn new(inner: S, max_in_flight_requests: usize) -> Self {
-        Self {
-            inner,
-            max_in_flight_requests,
-        }
-    }
-}
-
-impl<S> Stream for ThrottlerStream<S>
-where
-    S: Stream,
-    <S as Stream>::Item: Channel,
-{
-    type Item = Throttler<<S as Stream>::Item>;
-
-    fn poll_next(mut self: Pin<&mut Self>, cx: &mut Context) -> Poll<Option<Self::Item>> {
-        match ready!(self.as_mut().project().inner.poll_next(cx)) {
-            Some(channel) => Poll::Ready(Some(Throttler::new(
-                channel,
-                *self.project().max_in_flight_requests,
-            ))),
-            None => Poll::Ready(None),
-        }
-    }
-}
-
-#[cfg(test)]
-use super::testing::{self, FakeChannel, PollExt};
-#[cfg(test)]
-use crate::Request;
-#[cfg(test)]
-use pin_utils::pin_mut;
-#[cfg(test)]
-use std::marker::PhantomData;
-
-#[test]
-fn throttler_in_flight_requests() {
-    let throttler = Throttler {
-        max_in_flight_requests: 0,
-        inner: FakeChannel::default::<isize, isize>(),
-    };
-
-    pin_mut!(throttler);
-    for i in 0..5 {
-        throttler.inner.in_flight_requests.insert(i);
-    }
-    assert_eq!(throttler.as_mut().in_flight_requests(), 5);
-}
-
-#[test]
-fn throttler_start_request() {
-    let throttler = Throttler {
-        max_in_flight_requests: 0,
-        inner: FakeChannel::default::<isize, isize>(),
-    };
-
-    pin_mut!(throttler);
-    throttler.as_mut().start_request(1);
-    assert_eq!(throttler.inner.in_flight_requests.len(), 1);
-}
-
-#[test]
-fn throttler_poll_next_done() {
-    let throttler = Throttler {
-        max_in_flight_requests: 0,
-        inner: FakeChannel::default::<isize, isize>(),
-    };
-
-    pin_mut!(throttler);
-    assert!(throttler.as_mut().poll_next(&mut testing::cx()).is_done());
-}
-
-#[test]
-fn throttler_poll_next_some() -> io::Result<()> {
-    let throttler = Throttler {
-        max_in_flight_requests: 1,
-        inner: FakeChannel::default::<isize, isize>(),
-    };
-
-    pin_mut!(throttler);
-    throttler.inner.push_req(0, 1);
-    assert!(throttler.as_mut().poll_ready(&mut testing::cx()).is_ready());
-    assert_eq!(
-        throttler
-            .as_mut()
-            .poll_next(&mut testing::cx())?
-            .map(|r| r.map(|r| (r.id, r.message))),
-        Poll::Ready(Some((0, 1)))
-    );
-    Ok(())
-}
-
-#[test]
-fn throttler_poll_next_throttled() {
-    let throttler = Throttler {
-        max_in_flight_requests: 0,
-        inner: FakeChannel::default::<isize, isize>(),
-    };
-
-    pin_mut!(throttler);
-    throttler.inner.push_req(1, 1);
-    assert!(throttler.as_mut().poll_next(&mut testing::cx()).is_done());
-    assert_eq!(throttler.inner.sink.len(), 1);
-    let resp = throttler.inner.sink.get(0).unwrap();
-    assert_eq!(resp.request_id, 1);
-    assert!(resp.message.is_err());
-}
-
-#[test]
-fn throttler_poll_next_throttled_sink_not_ready() {
-    let throttler = Throttler {
-        max_in_flight_requests: 0,
-        inner: PendingSink::default::<isize, isize>(),
-    };
-    pin_mut!(throttler);
-    assert!(throttler.poll_next(&mut testing::cx()).is_pending());
-
-    struct PendingSink<In, Out> {
-        ghost: PhantomData<fn(Out) -> In>,
-    }
-    impl PendingSink<(), ()> {
-        pub fn default<Req, Resp>() -> PendingSink<io::Result<Request<Req>>, Response<Resp>> {
-            PendingSink { ghost: PhantomData }
-        }
-    }
-    impl<In, Out> Stream for PendingSink<In, Out> {
-        type Item = In;
-        fn poll_next(self: Pin<&mut Self>, _: &mut Context) -> Poll<Option<Self::Item>> {
-            unimplemented!()
-        }
-    }
-    impl<In, Out> Sink<Out> for PendingSink<In, Out> {
-        type Error = io::Error;
-        fn poll_ready(self: Pin<&mut Self>, _: &mut Context) -> Poll<Result<(), Self::Error>> {
-            Poll::Pending
-        }
-        fn start_send(self: Pin<&mut Self>, _: Out) -> Result<(), Self::Error> {
-            Err(io::Error::from(io::ErrorKind::WouldBlock))
-        }
-        fn poll_flush(self: Pin<&mut Self>, _: &mut Context) -> Poll<Result<(), Self::Error>> {
-            Poll::Pending
-        }
-        fn poll_close(self: Pin<&mut Self>, _: &mut Context) -> Poll<Result<(), Self::Error>> {
-            Poll::Pending
-        }
-    }
-    impl<Req, Resp> Channel for PendingSink<io::Result<Request<Req>>, Response<Resp>> {
-        type Req = Req;
-        type Resp = Resp;
-        fn config(&self) -> &Config {
-            unimplemented!()
-        }
-        fn in_flight_requests(self: Pin<&mut Self>) -> usize {
-            0
-        }
-        fn start_request(self: Pin<&mut Self>, _: u64) -> AbortRegistration {
-            unimplemented!()
-        }
-    }
-}
-
-#[test]
-fn throttler_start_send() {
-    let throttler = Throttler {
-        max_in_flight_requests: 0,
-        inner: FakeChannel::default::<isize, isize>(),
-    };
-
-    pin_mut!(throttler);
-    throttler.inner.in_flight_requests.insert(0);
-    throttler
-        .as_mut()
-        .start_send(Response {
-            request_id: 0,
-            message: Ok(1),
-            _non_exhaustive: (),
-        })
-        .unwrap();
-    assert!(throttler.inner.in_flight_requests.is_empty());
-    assert_eq!(
-        throttler.inner.sink.get(0),
-        Some(&Response {
-            request_id: 0,
-            message: Ok(1),
-            _non_exhaustive: ()
-        })
-    );
-}

tarpc/src/rpc/transport/channel.rs

@@ -1,123 +0,0 @@
-// Copyright 2018 Google LLC
-//
-// Use of this source code is governed by an MIT-style
-// license that can be found in the LICENSE file or at
-// https://opensource.org/licenses/MIT.
-
-//! Transports backed by in-memory channels.
-
-use crate::PollIo;
-use futures::{channel::mpsc, task::*, Sink, Stream};
-use pin_project::pin_project;
-use std::io;
-use std::pin::Pin;
-
-/// Returns two unbounded channel peers. Each [`Stream`] yields items sent through the other's
-/// [`Sink`].
-pub fn unbounded<SinkItem, Item>() -> (
-    UnboundedChannel<SinkItem, Item>,
-    UnboundedChannel<Item, SinkItem>,
-) {
-    let (tx1, rx2) = mpsc::unbounded();
-    let (tx2, rx1) = mpsc::unbounded();
-    (
-        UnboundedChannel { tx: tx1, rx: rx1 },
-        UnboundedChannel { tx: tx2, rx: rx2 },
-    )
-}
-
-/// A bi-directional channel backed by an [`UnboundedSender`](mpsc::UnboundedSender)
-/// and [`UnboundedReceiver`](mpsc::UnboundedReceiver).
-#[pin_project]
-#[derive(Debug)]
-pub struct UnboundedChannel<Item, SinkItem> {
-    #[pin]
-    rx: mpsc::UnboundedReceiver<Item>,
-    #[pin]
-    tx: mpsc::UnboundedSender<SinkItem>,
-}
-
-impl<Item, SinkItem> Stream for UnboundedChannel<Item, SinkItem> {
-    type Item = Result<Item, io::Error>;
-
-    fn poll_next(self: Pin<&mut Self>, cx: &mut Context<'_>) -> PollIo<Item> {
-        self.project().rx.poll_next(cx).map(|option| option.map(Ok))
-    }
-}
-
-impl<Item, SinkItem> Sink<SinkItem> for UnboundedChannel<Item, SinkItem> {
-    type Error = io::Error;
-
-    fn poll_ready(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<io::Result<()>> {
-        self.project()
-            .tx
-            .poll_ready(cx)
-            .map_err(|_| io::Error::from(io::ErrorKind::NotConnected))
-    }
-
-    fn start_send(self: Pin<&mut Self>, item: SinkItem) -> io::Result<()> {
-        self.project()
-            .tx
-            .start_send(item)
-            .map_err(|_| io::Error::from(io::ErrorKind::NotConnected))
-    }
-
-    fn poll_flush(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Result<(), Self::Error>> {
-        self.project()
-            .tx
-            .poll_flush(cx)
-            .map_err(|_| io::Error::from(io::ErrorKind::NotConnected))
-    }
-
-    fn poll_close(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<io::Result<()>> {
-        self.project()
-            .tx
-            .poll_close(cx)
-            .map_err(|_| io::Error::from(io::ErrorKind::NotConnected))
-    }
-}
-
-#[cfg(test)]
-mod tests {
-    use crate::{
-        client, context,
-        server::{Handler, Server},
-        transport,
-    };
-    use assert_matches::assert_matches;
-    use futures::{prelude::*, stream};
-    use log::trace;
-    use std::io;
-
-    #[cfg(feature = "tokio1")]
-    #[tokio::test(threaded_scheduler)]
-    async fn integration() -> io::Result<()> {
-        let _ = env_logger::try_init();
-
-        let (client_channel, server_channel) = transport::channel::unbounded();
-        tokio::spawn(
-            Server::default()
-                .incoming(stream::once(future::ready(server_channel)))
-                .respond_with(|_ctx, request: String| {
-                    future::ready(request.parse::<u64>().map_err(|_| {
-                        io::Error::new(
-                            io::ErrorKind::InvalidInput,
-                            format!("{:?} is not an int", request),
-                        )
-                    }))
-                }),
-        );
-
-        let mut client = client::new(client::Config::default(), client_channel).spawn()?;
-
-        let response1 = client.call(context::current(), "123".into()).await?;
-        let response2 = client.call(context::current(), "abc".into()).await?;
-
-        trace!("response1: {:?}, response2: {:?}", response1, response2);
-
-        assert_matches!(response1, Ok(123));
-        assert_matches!(response2, Err(ref e) if e.kind() == io::ErrorKind::InvalidInput);
-
-        Ok(())
-    }
-}

tarpc/src/rpc/transport/mod.rs

@@ -1,30 +0,0 @@
-// Copyright 2018 Google LLC
-//
-// Use of this source code is governed by an MIT-style
-// license that can be found in the LICENSE file or at
-// https://opensource.org/licenses/MIT.
-
-//! Provides a [`Transport`] trait as well as implementations.
-//!
-//! The rpc crate is transport- and protocol-agnostic. Any transport that impls [`Transport`]
-//! can be plugged in, using whatever protocol it wants.
-
-use futures::prelude::*;
-use std::io;
-
-pub mod channel;
-
-pub(crate) mod sealed {
-    use super::*;
-
-    /// A bidirectional stream ([`Sink`] + [`Stream`]) of messages.
-    pub trait Transport<SinkItem, Item>:
-        Stream<Item = io::Result<Item>> + Sink<SinkItem, Error = io::Error>
-    {
-    }
-
-    impl<T, SinkItem, Item> Transport<SinkItem, Item> for T where
-        T: Stream<Item = io::Result<Item>> + Sink<SinkItem, Error = io::Error> + ?Sized
-    {
-    }
-}

tarpc/src/serde_transport.rs

@@ -0,0 +1,735 @@
+// Copyright 2019 Google LLC
+//
+// Use of this source code is governed by an MIT-style
+// license that can be found in the LICENSE file or at
+// https://opensource.org/licenses/MIT.
+
+//! A generic Serde-based `Transport` that can serialize anything supported by `tokio-serde` via any medium that implements `AsyncRead` and `AsyncWrite`.
+
+#![deny(missing_docs)]
+
+use futures::{prelude::*, task::*};
+use pin_project::pin_project;
+use serde::{Deserialize, Serialize};
+use std::{error::Error, io, pin::Pin};
+use tokio::io::{AsyncRead, AsyncWrite};
+use tokio_serde::{Framed as SerdeFramed, *};
+use tokio_util::codec::{length_delimited::LengthDelimitedCodec, Framed};
+
+/// A transport that serializes to, and deserializes from, a byte stream.
+#[pin_project]
+pub struct Transport<S, Item, SinkItem, Codec> {
+    #[pin]
+    inner: SerdeFramed<Framed<S, LengthDelimitedCodec>, Item, SinkItem, Codec>,
+}
+
+impl<S, Item, SinkItem, Codec> Transport<S, Item, SinkItem, Codec> {
+    /// Returns the inner transport over which messages are sent and received.
+    pub fn get_ref(&self) -> &S {
+        self.inner.get_ref().get_ref()
+    }
+}
+
+impl<S, Item, SinkItem, Codec, CodecError> Stream for Transport<S, Item, SinkItem, Codec>
+where
+    S: AsyncWrite + AsyncRead,
+    Item: for<'a> Deserialize<'a>,
+    Codec: Deserializer<Item>,
+    CodecError: Into<Box<dyn std::error::Error + Send + Sync>>,
+    SerdeFramed<Framed<S, LengthDelimitedCodec>, Item, SinkItem, Codec>:
+        Stream<Item = Result<Item, CodecError>>,
+{
+    type Item = io::Result<Item>;
+
+    fn poll_next(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Option<io::Result<Item>>> {
+        self.project()
+            .inner
+            .poll_next(cx)
+            .map_err(|e| io::Error::new(io::ErrorKind::Other, e))
+    }
+}
+
+impl<S, Item, SinkItem, Codec, CodecError> Sink<SinkItem> for Transport<S, Item, SinkItem, Codec>
+where
+    S: AsyncWrite,
+    SinkItem: Serialize,
+    Codec: Serializer<SinkItem>,
+    CodecError: Into<Box<dyn Error + Send + Sync>>,
+    SerdeFramed<Framed<S, LengthDelimitedCodec>, Item, SinkItem, Codec>:
+        Sink<SinkItem, Error = CodecError>,
+{
+    type Error = io::Error;
+
+    fn poll_ready(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<io::Result<()>> {
+        self.project()
+            .inner
+            .poll_ready(cx)
+            .map_err(|e| io::Error::new(io::ErrorKind::Other, e))
+    }
+
+    fn start_send(self: Pin<&mut Self>, item: SinkItem) -> io::Result<()> {
+        self.project()
+            .inner
+            .start_send(item)
+            .map_err(|e| io::Error::new(io::ErrorKind::Other, e))
+    }
+
+    fn poll_flush(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<io::Result<()>> {
+        self.project()
+            .inner
+            .poll_flush(cx)
+            .map_err(|e| io::Error::new(io::ErrorKind::Other, e))
+    }
+
+    fn poll_close(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<io::Result<()>> {
+        self.project()
+            .inner
+            .poll_close(cx)
+            .map_err(|e| io::Error::new(io::ErrorKind::Other, e))
+    }
+}
+
+/// Constructs a new transport from a framed transport and a serialization codec.
+pub fn new<S, Item, SinkItem, Codec>(
+    framed_io: Framed<S, LengthDelimitedCodec>,
+    codec: Codec,
+) -> Transport<S, Item, SinkItem, Codec>
+where
+    S: AsyncWrite + AsyncRead,
+    Item: for<'de> Deserialize<'de>,
+    SinkItem: Serialize,
+    Codec: Serializer<SinkItem> + Deserializer<Item>,
+{
+    Transport {
+        inner: SerdeFramed::new(framed_io, codec),
+    }
+}
+
+impl<S, Item, SinkItem, Codec> From<(S, Codec)> for Transport<S, Item, SinkItem, Codec>
+where
+    S: AsyncWrite + AsyncRead,
+    Item: for<'de> Deserialize<'de>,
+    SinkItem: Serialize,
+    Codec: Serializer<SinkItem> + Deserializer<Item>,
+{
+    fn from((io, codec): (S, Codec)) -> Self {
+        new(Framed::new(io, LengthDelimitedCodec::new()), codec)
+    }
+}
+
+#[cfg(feature = "tcp")]
+#[cfg_attr(docsrs, doc(cfg(feature = "tcp")))]
+/// TCP support for generic transport using Tokio.
+pub mod tcp {
+    use {
+        super::*,
+        futures::ready,
+        std::{marker::PhantomData, net::SocketAddr},
+        tokio::net::{TcpListener, TcpStream, ToSocketAddrs},
+        tokio_util::codec::length_delimited,
+    };
+
+    impl<Item, SinkItem, Codec> Transport<TcpStream, Item, SinkItem, Codec> {
+        /// Returns the peer address of the underlying TcpStream.
+        pub fn peer_addr(&self) -> io::Result<SocketAddr> {
+            self.inner.get_ref().get_ref().peer_addr()
+        }
+        /// Returns the local address of the underlying TcpStream.
+        pub fn local_addr(&self) -> io::Result<SocketAddr> {
+            self.inner.get_ref().get_ref().local_addr()
+        }
+    }
+
+    /// A connection Future that also exposes the length-delimited framing config.
+    #[must_use]
+    #[pin_project]
+    pub struct Connect<T, Item, SinkItem, CodecFn> {
+        #[pin]
+        inner: T,
+        codec_fn: CodecFn,
+        config: length_delimited::Builder,
+        ghost: PhantomData<(fn(SinkItem), fn() -> Item)>,
+    }
+
+    impl<T, Item, SinkItem, Codec, CodecFn> Future for Connect<T, Item, SinkItem, CodecFn>
+    where
+        T: Future<Output = io::Result<TcpStream>>,
+        Item: for<'de> Deserialize<'de>,
+        SinkItem: Serialize,
+        Codec: Serializer<SinkItem> + Deserializer<Item>,
+        CodecFn: Fn() -> Codec,
+    {
+        type Output = io::Result<Transport<TcpStream, Item, SinkItem, Codec>>;
+
+        fn poll(mut self: Pin<&mut Self>, cx: &mut Context) -> Poll<Self::Output> {
+            let io = ready!(self.as_mut().project().inner.poll(cx))?;
+            Poll::Ready(Ok(new(self.config.new_framed(io), (self.codec_fn)())))
+        }
+    }
+
+    impl<T, Item, SinkItem, CodecFn> Connect<T, Item, SinkItem, CodecFn> {
+        /// Returns an immutable reference to the length-delimited codec's config.
+        pub fn config(&self) -> &length_delimited::Builder {
+            &self.config
+        }
+
+        /// Returns a mutable reference to the length-delimited codec's config.
+        pub fn config_mut(&mut self) -> &mut length_delimited::Builder {
+            &mut self.config
+        }
+    }
+
+    /// Connects to `addr`, wrapping the connection in a TCP transport.
+    pub fn connect<A, Item, SinkItem, Codec, CodecFn>(
+        addr: A,
+        codec_fn: CodecFn,
+    ) -> Connect<impl Future<Output = io::Result<TcpStream>>, Item, SinkItem, CodecFn>
+    where
+        A: ToSocketAddrs,
+        Item: for<'de> Deserialize<'de>,
+        SinkItem: Serialize,
+        Codec: Serializer<SinkItem> + Deserializer<Item>,
+        CodecFn: Fn() -> Codec,
+    {
+        Connect {
+            inner: TcpStream::connect(addr),
+            codec_fn,
+            config: LengthDelimitedCodec::builder(),
+            ghost: PhantomData,
+        }
+    }
+
+    /// Listens on `addr`, wrapping accepted connections in TCP transports.
+    pub async fn listen<A, Item, SinkItem, Codec, CodecFn>(
+        addr: A,
+        codec_fn: CodecFn,
+    ) -> io::Result<Incoming<Item, SinkItem, Codec, CodecFn>>
+    where
+        A: ToSocketAddrs,
+        Item: for<'de> Deserialize<'de>,
+        Codec: Serializer<SinkItem> + Deserializer<Item>,
+        CodecFn: Fn() -> Codec,
+    {
+        listen_on(TcpListener::bind(addr).await?, codec_fn).await
+    }
+
+    /// Wrap accepted connections from `listener` in TCP transports.
+    pub async fn listen_on<Item, SinkItem, Codec, CodecFn>(
+        listener: TcpListener,
+        codec_fn: CodecFn,
+    ) -> io::Result<Incoming<Item, SinkItem, Codec, CodecFn>>
+    where
+        Item: for<'de> Deserialize<'de>,
+        Codec: Serializer<SinkItem> + Deserializer<Item>,
+        CodecFn: Fn() -> Codec,
+    {
+        let local_addr = listener.local_addr()?;
+        Ok(Incoming {
+            listener,
+            codec_fn,
+            local_addr,
+            config: LengthDelimitedCodec::builder(),
+            ghost: PhantomData,
+        })
+    }
+
+    /// A [`TcpListener`] that wraps connections in [transports](Transport).
+    #[pin_project]
+    #[derive(Debug)]
+    pub struct Incoming<Item, SinkItem, Codec, CodecFn> {
+        listener: TcpListener,
+        local_addr: SocketAddr,
+        codec_fn: CodecFn,
+        config: length_delimited::Builder,
+        ghost: PhantomData<(fn() -> Item, fn(SinkItem), Codec)>,
+    }
+
+    impl<Item, SinkItem, Codec, CodecFn> Incoming<Item, SinkItem, Codec, CodecFn> {
+        /// Returns the address being listened on.
+        pub fn local_addr(&self) -> SocketAddr {
+            self.local_addr
+        }
+
+        /// Returns an immutable reference to the length-delimited codec's config.
+        pub fn config(&self) -> &length_delimited::Builder {
+            &self.config
+        }
+
+        /// Returns a mutable reference to the length-delimited codec's config.
+        pub fn config_mut(&mut self) -> &mut length_delimited::Builder {
+            &mut self.config
+        }
+    }
+
+    impl<Item, SinkItem, Codec, CodecFn> Stream for Incoming<Item, SinkItem, Codec, CodecFn>
+    where
+        Item: for<'de> Deserialize<'de>,
+        SinkItem: Serialize,
+        Codec: Serializer<SinkItem> + Deserializer<Item>,
+        CodecFn: Fn() -> Codec,
+    {
+        type Item = io::Result<Transport<TcpStream, Item, SinkItem, Codec>>;
+
+        fn poll_next(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Option<Self::Item>> {
+            let conn: TcpStream =
+                ready!(Pin::new(&mut self.as_mut().project().listener).poll_accept(cx)?).0;
+            Poll::Ready(Some(Ok(new(
+                self.config.new_framed(conn),
+                (self.codec_fn)(),
+            ))))
+        }
+    }
+}
+
+#[cfg(all(unix, feature = "unix"))]
+#[cfg_attr(docsrs, doc(cfg(all(unix, feature = "unix"))))]
+/// Unix Domain Socket support for generic transport using Tokio.
+pub mod unix {
+    use {
+        super::*,
+        futures::ready,
+        std::{marker::PhantomData, path::Path},
+        tokio::net::{unix::SocketAddr, UnixListener, UnixStream},
+        tokio_util::codec::length_delimited,
+    };
+
+    impl<Item, SinkItem, Codec> Transport<UnixStream, Item, SinkItem, Codec> {
+        /// Returns the socket address of the remote half of the underlying [`UnixStream`].
+        pub fn peer_addr(&self) -> io::Result<SocketAddr> {
+            self.inner.get_ref().get_ref().peer_addr()
+        }
+        /// Returns the socket address of the local half of the underlying [`UnixStream`].
+        pub fn local_addr(&self) -> io::Result<SocketAddr> {
+            self.inner.get_ref().get_ref().local_addr()
+        }
+    }
+
+    /// A connection Future that also exposes the length-delimited framing config.
+    #[must_use]
+    #[pin_project]
+    pub struct Connect<T, Item, SinkItem, CodecFn> {
+        #[pin]
+        inner: T,
+        codec_fn: CodecFn,
+        config: length_delimited::Builder,
+        ghost: PhantomData<(fn(SinkItem), fn() -> Item)>,
+    }
+
+    impl<T, Item, SinkItem, Codec, CodecFn> Future for Connect<T, Item, SinkItem, CodecFn>
+    where
+        T: Future<Output = io::Result<UnixStream>>,
+        Item: for<'de> Deserialize<'de>,
+        SinkItem: Serialize,
+        Codec: Serializer<SinkItem> + Deserializer<Item>,
+        CodecFn: Fn() -> Codec,
+    {
+        type Output = io::Result<Transport<UnixStream, Item, SinkItem, Codec>>;
+
+        fn poll(mut self: Pin<&mut Self>, cx: &mut Context) -> Poll<Self::Output> {
+            let io = ready!(self.as_mut().project().inner.poll(cx))?;
+            Poll::Ready(Ok(new(self.config.new_framed(io), (self.codec_fn)())))
+        }
+    }
+
+    impl<T, Item, SinkItem, CodecFn> Connect<T, Item, SinkItem, CodecFn> {
+        /// Returns an immutable reference to the length-delimited codec's config.
+        pub fn config(&self) -> &length_delimited::Builder {
+            &self.config
+        }
+
+        /// Returns a mutable reference to the length-delimited codec's config.
+        pub fn config_mut(&mut self) -> &mut length_delimited::Builder {
+            &mut self.config
+        }
+    }
+
+    /// Connects to socket named by `path`, wrapping the connection in a Unix Domain Socket
+    /// transport.
+    pub fn connect<P, Item, SinkItem, Codec, CodecFn>(
+        path: P,
+        codec_fn: CodecFn,
+    ) -> Connect<impl Future<Output = io::Result<UnixStream>>, Item, SinkItem, CodecFn>
+    where
+        P: AsRef<Path>,
+        Item: for<'de> Deserialize<'de>,
+        SinkItem: Serialize,
+        Codec: Serializer<SinkItem> + Deserializer<Item>,
+        CodecFn: Fn() -> Codec,
+    {
+        Connect {
+            inner: UnixStream::connect(path),
+            codec_fn,
+            config: LengthDelimitedCodec::builder(),
+            ghost: PhantomData,
+        }
+    }
+
+    /// Listens on the socket named by `path`, wrapping accepted connections in Unix Domain Socket
+    /// transports.
+    pub async fn listen<P, Item, SinkItem, Codec, CodecFn>(
+        path: P,
+        codec_fn: CodecFn,
+    ) -> io::Result<Incoming<Item, SinkItem, Codec, CodecFn>>
+    where
+        P: AsRef<Path>,
+        Item: for<'de> Deserialize<'de>,
+        Codec: Serializer<SinkItem> + Deserializer<Item>,
+        CodecFn: Fn() -> Codec,
+    {
+        listen_on(UnixListener::bind(path)?, codec_fn).await
+    }
+
+    /// Wrap accepted connections from `listener` in Unix Domain Socket transports.
+    pub async fn listen_on<Item, SinkItem, Codec, CodecFn>(
+        listener: UnixListener,
+        codec_fn: CodecFn,
+    ) -> io::Result<Incoming<Item, SinkItem, Codec, CodecFn>>
+    where
+        Item: for<'de> Deserialize<'de>,
+        Codec: Serializer<SinkItem> + Deserializer<Item>,
+        CodecFn: Fn() -> Codec,
+    {
+        let local_addr = listener.local_addr()?;
+        Ok(Incoming {
+            listener,
+            codec_fn,
+            local_addr,
+            config: LengthDelimitedCodec::builder(),
+            ghost: PhantomData,
+        })
+    }
+
+    /// A [`UnixListener`] that wraps connections in [transports](Transport).
+    #[pin_project]
+    #[derive(Debug)]
+    pub struct Incoming<Item, SinkItem, Codec, CodecFn> {
+        listener: UnixListener,
+        local_addr: SocketAddr,
+        codec_fn: CodecFn,
+        config: length_delimited::Builder,
+        ghost: PhantomData<(fn() -> Item, fn(SinkItem), Codec)>,
+    }
+
+    impl<Item, SinkItem, Codec, CodecFn> Incoming<Item, SinkItem, Codec, CodecFn> {
+        /// Returns the the socket address being listened on.
+        pub fn local_addr(&self) -> &SocketAddr {
+            &self.local_addr
+        }
+
+        /// Returns an immutable reference to the length-delimited codec's config.
+        pub fn config(&self) -> &length_delimited::Builder {
+            &self.config
+        }
+
+        /// Returns a mutable reference to the length-delimited codec's config.
+        pub fn config_mut(&mut self) -> &mut length_delimited::Builder {
+            &mut self.config
+        }
+    }
+
+    impl<Item, SinkItem, Codec, CodecFn> Stream for Incoming<Item, SinkItem, Codec, CodecFn>
+    where
+        Item: for<'de> Deserialize<'de>,
+        SinkItem: Serialize,
+        Codec: Serializer<SinkItem> + Deserializer<Item>,
+        CodecFn: Fn() -> Codec,
+    {
+        type Item = io::Result<Transport<UnixStream, Item, SinkItem, Codec>>;
+
+        fn poll_next(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Option<Self::Item>> {
+            let conn: UnixStream = ready!(self.as_mut().project().listener.poll_accept(cx)?).0;
+            Poll::Ready(Some(Ok(new(
+                self.config.new_framed(conn),
+                (self.codec_fn)(),
+            ))))
+        }
+    }
+
+    /// A temporary `PathBuf` that lives in `std::env::temp_dir` and is removed on drop.
+    pub struct TempPathBuf(std::path::PathBuf);
+
+    impl TempPathBuf {
+        /// A named socket that results in `<tempdir>/<name>`
+        pub fn new<S: AsRef<str>>(name: S) -> Self {
+            let mut sock = std::env::temp_dir();
+            sock.push(name.as_ref());
+            Self(sock)
+        }
+
+        /// Appends a random hex string to the socket name resulting in
+        /// `<tempdir>/<name>_<xxxxx>`
+        pub fn with_random<S: AsRef<str>>(name: S) -> Self {
+            Self::new(format!("{}_{:016x}", name.as_ref(), rand::random::<u64>()))
+        }
+    }
+
+    impl AsRef<std::path::Path> for TempPathBuf {
+        fn as_ref(&self) -> &std::path::Path {
+            self.0.as_path()
+        }
+    }
+
+    impl Drop for TempPathBuf {
+        fn drop(&mut self) {
+            // This will remove the file pointed to by this PathBuf if it exists, however Err's can
+            // be returned such as attempting to remove a non-existing file, or one which we don't
+            // have permission to remove. In these cases the Err is swallowed
+            let _ = std::fs::remove_file(&self.0);
+        }
+    }
+
+    #[cfg(test)]
+    mod tests {
+        use super::*;
+        use tokio_serde::formats::SymmetricalJson;
+
+        #[test]
+        fn temp_path_buf_non_random() {
+            let sock = TempPathBuf::new("test");
+            let mut good = std::env::temp_dir();
+            good.push("test");
+            assert_eq!(sock.as_ref(), good);
+            assert_eq!(sock.as_ref().file_name().unwrap(), "test");
+        }
+
+        #[test]
+        fn temp_path_buf_random() {
+            let sock = TempPathBuf::with_random("test");
+            let good = std::env::temp_dir();
+            assert!(sock.as_ref().starts_with(good));
+            // Since there are 16 random characters we just assert the file_name has the right name
+            // and starts with the correct string 'test_'
+            // file name: test_xxxxxxxxxxxxxxxx
+            // test  = 4
+            // _     = 1
+            // <hex> = 16
+            // total = 21
+            let fname = sock.as_ref().file_name().unwrap().to_string_lossy();
+            assert!(fname.starts_with("test_"));
+            assert_eq!(fname.len(), 21);
+        }
+
+        #[test]
+        fn temp_path_buf_non_existing() {
+            let sock = TempPathBuf::with_random("test");
+            let sock_path = std::path::PathBuf::from(sock.as_ref());
+
+            // No actual file has been created yet
+            assert!(!sock_path.exists());
+            // Should not panic
+            std::mem::drop(sock);
+            assert!(!sock_path.exists());
+        }
+
+        #[test]
+        fn temp_path_buf_existing_file() {
+            let sock = TempPathBuf::with_random("test");
+            let sock_path = std::path::PathBuf::from(sock.as_ref());
+            let _file = std::fs::File::create(&sock).unwrap();
+            assert!(sock_path.exists());
+            std::mem::drop(sock);
+            assert!(!sock_path.exists());
+        }
+
+        #[test]
+        fn temp_path_buf_preexisting_file() {
+            let mut pre_existing = std::env::temp_dir();
+            pre_existing.push("test");
+            let _file = std::fs::File::create(&pre_existing).unwrap();
+            let sock = TempPathBuf::new("test");
+            let sock_path = std::path::PathBuf::from(sock.as_ref());
+            assert!(sock_path.exists());
+            std::mem::drop(sock);
+            assert!(!sock_path.exists());
+        }
+
+        #[tokio::test]
+        async fn temp_path_buf_for_socket() {
+            let sock = TempPathBuf::with_random("test");
+            // Save path for testing after drop
+            let sock_path = std::path::PathBuf::from(sock.as_ref());
+            // create the actual socket
+            let _ = listen(&sock, SymmetricalJson::<String>::default).await;
+            assert!(sock_path.exists());
+            std::mem::drop(sock);
+            assert!(!sock_path.exists());
+        }
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::Transport;
+    use assert_matches::assert_matches;
+    use futures::{task::*, Sink, SinkExt, Stream, StreamExt};
+    use pin_utils::pin_mut;
+    use std::{
+        io::{self, Cursor},
+        pin::Pin,
+    };
+    use tokio::io::{AsyncRead, AsyncWrite, ReadBuf};
+    use tokio_serde::formats::SymmetricalJson;
+
+    fn ctx() -> Context<'static> {
+        Context::from_waker(noop_waker_ref())
+    }
+
+    struct TestIo(Cursor<Vec<u8>>);
+
+    impl AsyncRead for TestIo {
+        fn poll_read(
+            mut self: Pin<&mut Self>,
+            cx: &mut Context<'_>,
+            buf: &mut ReadBuf<'_>,
+        ) -> Poll<io::Result<()>> {
+            AsyncRead::poll_read(Pin::new(&mut self.0), cx, buf)
+        }
+    }
+
+    impl AsyncWrite for TestIo {
+        fn poll_write(
+            mut self: Pin<&mut Self>,
+            cx: &mut Context<'_>,
+            buf: &[u8],
+        ) -> Poll<io::Result<usize>> {
+            AsyncWrite::poll_write(Pin::new(&mut self.0), cx, buf)
+        }
+
+        fn poll_flush(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<io::Result<()>> {
+            AsyncWrite::poll_flush(Pin::new(&mut self.0), cx)
+        }
+
+        fn poll_shutdown(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<io::Result<()>> {
+            AsyncWrite::poll_shutdown(Pin::new(&mut self.0), cx)
+        }
+    }
+
+    #[test]
+    fn close() {
+        let (tx, _rx) = crate::transport::channel::bounded::<(), ()>(0);
+        pin_mut!(tx);
+        assert_matches!(tx.as_mut().poll_close(&mut ctx()), Poll::Ready(Ok(())));
+        assert_matches!(tx.as_mut().start_send(()), Err(_));
+    }
+
+    #[test]
+    fn test_stream() {
+        let data: &[u8] = b"\x00\x00\x00\x18\"Test one, check check.\"";
+        let transport = Transport::from((
+            TestIo(Cursor::new(Vec::from(data))),
+            SymmetricalJson::<String>::default(),
+        ));
+        pin_mut!(transport);
+
+        assert_matches!(
+            transport.as_mut().poll_next(&mut ctx()),
+            Poll::Ready(Some(Ok(ref s))) if s == "Test one, check check.");
+        assert_matches!(transport.as_mut().poll_next(&mut ctx()), Poll::Ready(None));
+    }
+
+    #[test]
+    fn test_sink() {
+        let writer = Cursor::new(vec![]);
+        let mut transport = Box::pin(Transport::from((
+            TestIo(writer),
+            SymmetricalJson::<String>::default(),
+        )));
+
+        assert_matches!(
+            transport.as_mut().poll_ready(&mut ctx()),
+            Poll::Ready(Ok(()))
+        );
+        assert_matches!(
+            transport
+                .as_mut()
+                .start_send("Test one, check check.".into()),
+            Ok(())
+        );
+        assert_matches!(
+            transport.as_mut().poll_flush(&mut ctx()),
+            Poll::Ready(Ok(()))
+        );
+        assert_eq!(
+            transport.get_ref().0.get_ref(),
+            b"\x00\x00\x00\x18\"Test one, check check.\""
+        );
+    }
+
+    #[cfg(feature = "tcp")]
+    #[tokio::test]
+    async fn tcp() -> io::Result<()> {
+        use super::tcp;
+
+        let mut listener = tcp::listen("0.0.0.0:0", SymmetricalJson::<String>::default).await?;
+        let addr = listener.local_addr();
+        tokio::spawn(async move {
+            let mut transport = listener.next().await.unwrap().unwrap();
+            let message = transport.next().await.unwrap().unwrap();
+            transport.send(message).await.unwrap();
+        });
+        let mut transport = tcp::connect(addr, SymmetricalJson::<String>::default).await?;
+        transport.send(String::from("test")).await?;
+        assert_matches!(transport.next().await, Some(Ok(s)) if s == "test");
+        assert_matches!(transport.next().await, None);
+        Ok(())
+    }
+
+    #[cfg(feature = "tcp")]
+    #[tokio::test]
+    async fn tcp_on_existing_transport() -> io::Result<()> {
+        use super::tcp;
+
+        let transport = tokio::net::TcpListener::bind("0.0.0.0:0").await?;
+        let mut listener = tcp::listen_on(transport, SymmetricalJson::<String>::default).await?;
+        let addr = listener.local_addr();
+        tokio::spawn(async move {
+            let mut transport = listener.next().await.unwrap().unwrap();
+            let message = transport.next().await.unwrap().unwrap();
+            transport.send(message).await.unwrap();
+        });
+        let mut transport = tcp::connect(addr, SymmetricalJson::<String>::default).await?;
+        transport.send(String::from("test")).await?;
+        assert_matches!(transport.next().await, Some(Ok(s)) if s == "test");
+        assert_matches!(transport.next().await, None);
+        Ok(())
+    }
+
+    #[cfg(all(unix, feature = "unix"))]
+    #[tokio::test]
+    async fn uds() -> io::Result<()> {
+        use super::unix;
+
+        let sock = unix::TempPathBuf::with_random("uds");
+        let mut listener = unix::listen(&sock, SymmetricalJson::<String>::default).await?;
+        tokio::spawn(async move {
+            let mut transport = listener.next().await.unwrap().unwrap();
+            let message = transport.next().await.unwrap().unwrap();
+            transport.send(message).await.unwrap();
+        });
+        let mut transport = unix::connect(&sock, SymmetricalJson::<String>::default).await?;
+        transport.send(String::from("test")).await?;
+        assert_matches!(transport.next().await, Some(Ok(s)) if s == "test");
+        assert_matches!(transport.next().await, None);
+        Ok(())
+    }
+
+    #[cfg(all(unix, feature = "unix"))]
+    #[tokio::test]
+    async fn uds_on_existing_transport() -> io::Result<()> {
+        use super::unix;
+
+        let sock = unix::TempPathBuf::with_random("uds");
+        let transport = tokio::net::UnixListener::bind(&sock)?;
+        let mut listener = unix::listen_on(transport, SymmetricalJson::<String>::default).await?;
+        tokio::spawn(async move {
+            let mut transport = listener.next().await.unwrap().unwrap();
+            let message = transport.next().await.unwrap().unwrap();
+            transport.send(message).await.unwrap();
+        });
+        let mut transport = unix::connect(&sock, SymmetricalJson::<String>::default).await?;
+        transport.send(String::from("test")).await?;
+        assert_matches!(transport.next().await, Some(Ok(s)) if s == "test");
+        assert_matches!(transport.next().await, None);
+        Ok(())
+    }
+}

tarpc/src/serde_transport/mod.rs

@@ -1,326 +0,0 @@
-// Copyright 2019 Google LLC
-//
-// Use of this source code is governed by an MIT-style
-// license that can be found in the LICENSE file or at
-// https://opensource.org/licenses/MIT.
-
-//! A generic Serde-based `Transport` that can serialize anything supported by `tokio-serde` via any medium that implements `AsyncRead` and `AsyncWrite`.
-
-#![deny(missing_docs)]
-
-use futures::{prelude::*, task::*};
-use pin_project::pin_project;
-use serde::{Deserialize, Serialize};
-use std::{error::Error, io, pin::Pin};
-use tokio::io::{AsyncRead, AsyncWrite};
-use tokio_serde::{Framed as SerdeFramed, *};
-use tokio_util::codec::{length_delimited::LengthDelimitedCodec, Framed};
-
-/// A transport that serializes to, and deserializes from, a [`TcpStream`].
-#[pin_project]
-pub struct Transport<S, Item, SinkItem, Codec> {
-    #[pin]
-    inner: SerdeFramed<Framed<S, LengthDelimitedCodec>, Item, SinkItem, Codec>,
-}
-
-impl<S, Item, SinkItem, Codec, CodecError> Stream for Transport<S, Item, SinkItem, Codec>
-where
-    S: AsyncWrite + AsyncRead,
-    Item: for<'a> Deserialize<'a>,
-    Codec: Deserializer<Item>,
-    CodecError: Into<Box<dyn std::error::Error + Send + Sync>>,
-    SerdeFramed<Framed<S, LengthDelimitedCodec>, Item, SinkItem, Codec>:
-        Stream<Item = Result<Item, CodecError>>,
-{
-    type Item = io::Result<Item>;
-
-    fn poll_next(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Option<io::Result<Item>>> {
-        match self.project().inner.poll_next(cx) {
-            Poll::Pending => Poll::Pending,
-            Poll::Ready(None) => Poll::Ready(None),
-            Poll::Ready(Some(Ok::<_, CodecError>(next))) => Poll::Ready(Some(Ok(next))),
-            Poll::Ready(Some(Err::<_, CodecError>(e))) => {
-                Poll::Ready(Some(Err(io::Error::new(io::ErrorKind::Other, e))))
-            }
-        }
-    }
-}
-
-impl<S, Item, SinkItem, Codec, CodecError> Sink<SinkItem> for Transport<S, Item, SinkItem, Codec>
-where
-    S: AsyncWrite,
-    SinkItem: Serialize,
-    Codec: Serializer<SinkItem>,
-    CodecError: Into<Box<dyn Error + Send + Sync>>,
-    SerdeFramed<Framed<S, LengthDelimitedCodec>, Item, SinkItem, Codec>:
-        Sink<SinkItem, Error = CodecError>,
-{
-    type Error = io::Error;
-
-    fn poll_ready(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<io::Result<()>> {
-        convert(self.project().inner.poll_ready(cx))
-    }
-
-    fn start_send(self: Pin<&mut Self>, item: SinkItem) -> io::Result<()> {
-        self.project()
-            .inner
-            .start_send(item)
-            .map_err(|e| io::Error::new(io::ErrorKind::Other, e))
-    }
-
-    fn poll_flush(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<io::Result<()>> {
-        convert(self.project().inner.poll_flush(cx))
-    }
-
-    fn poll_close(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<io::Result<()>> {
-        convert(self.project().inner.poll_close(cx))
-    }
-}
-
-fn convert<E: Into<Box<dyn Error + Send + Sync>>>(
-    poll: Poll<Result<(), E>>,
-) -> Poll<io::Result<()>> {
-    poll.map(|ready| ready.map_err(|e| io::Error::new(io::ErrorKind::Other, e)))
-}
-
-impl<S, Item, SinkItem, Codec> From<(S, Codec)> for Transport<S, Item, SinkItem, Codec>
-where
-    S: AsyncWrite + AsyncRead,
-    Item: for<'de> Deserialize<'de>,
-    SinkItem: Serialize,
-    Codec: Serializer<SinkItem> + Deserializer<Item>,
-{
-    fn from((inner, codec): (S, Codec)) -> Self {
-        Transport {
-            inner: SerdeFramed::new(Framed::new(inner, LengthDelimitedCodec::new()), codec),
-        }
-    }
-}
-
-#[cfg(feature = "tcp")]
-#[cfg_attr(docsrs, doc(cfg(feature = "tcp")))]
-/// TCP support for generic transport using Tokio.
-pub mod tcp {
-    use {
-        super::*,
-        futures::ready,
-        std::{marker::PhantomData, net::SocketAddr},
-        tokio::net::{TcpListener, TcpStream, ToSocketAddrs},
-    };
-
-    mod private {
-        use super::*;
-
-        pub trait Sealed {}
-
-        impl<Item, SinkItem, Codec> Sealed for Transport<TcpStream, Item, SinkItem, Codec> {}
-    }
-
-    impl<Item, SinkItem, Codec> Transport<TcpStream, Item, SinkItem, Codec> {
-        /// Returns the peer address of the underlying TcpStream.
-        pub fn peer_addr(&self) -> io::Result<SocketAddr> {
-            self.inner.get_ref().get_ref().peer_addr()
-        }
-        /// Returns the local address of the underlying TcpStream.
-        pub fn local_addr(&self) -> io::Result<SocketAddr> {
-            self.inner.get_ref().get_ref().local_addr()
-        }
-    }
-
-    /// Returns a new JSON transport that reads from and writes to `io`.
-    pub fn new<Item, SinkItem, Codec>(
-        io: TcpStream,
-        codec: Codec,
-    ) -> Transport<TcpStream, Item, SinkItem, Codec>
-    where
-        Item: for<'de> Deserialize<'de>,
-        SinkItem: Serialize,
-        Codec: Serializer<SinkItem> + Deserializer<Item>,
-    {
-        Transport::from((io, codec))
-    }
-
-    /// Connects to `addr`, wrapping the connection in a JSON transport.
-    pub async fn connect<A, Item, SinkItem, Codec>(
-        addr: A,
-        codec: Codec,
-    ) -> io::Result<Transport<TcpStream, Item, SinkItem, Codec>>
-    where
-        A: ToSocketAddrs,
-        Item: for<'de> Deserialize<'de>,
-        SinkItem: Serialize,
-        Codec: Serializer<SinkItem> + Deserializer<Item>,
-    {
-        Ok(new(TcpStream::connect(addr).await?, codec))
-    }
-
-    /// Listens on `addr`, wrapping accepted connections in JSON transports.
-    pub async fn listen<A, Item, SinkItem, Codec, CodecFn>(
-        addr: A,
-        codec_fn: CodecFn,
-    ) -> io::Result<Incoming<Item, SinkItem, Codec, CodecFn>>
-    where
-        A: ToSocketAddrs,
-        Item: for<'de> Deserialize<'de>,
-        Codec: Serializer<SinkItem> + Deserializer<Item>,
-        CodecFn: Fn() -> Codec,
-    {
-        let listener = TcpListener::bind(addr).await?;
-        let local_addr = listener.local_addr()?;
-        Ok(Incoming {
-            listener,
-            codec_fn,
-            local_addr,
-            ghost: PhantomData,
-        })
-    }
-
-    /// A [`TcpListener`] that wraps connections in JSON transports.
-    #[pin_project]
-    #[derive(Debug)]
-    pub struct Incoming<Item, SinkItem, Codec, CodecFn> {
-        listener: TcpListener,
-        local_addr: SocketAddr,
-        codec_fn: CodecFn,
-        ghost: PhantomData<(Item, SinkItem, Codec)>,
-    }
-
-    impl<Item, SinkItem, Codec, CodecFn> Incoming<Item, SinkItem, Codec, CodecFn> {
-        /// Returns the address being listened on.
-        pub fn local_addr(&self) -> SocketAddr {
-            self.local_addr
-        }
-    }
-
-    impl<Item, SinkItem, Codec, CodecFn> Stream for Incoming<Item, SinkItem, Codec, CodecFn>
-    where
-        Item: for<'de> Deserialize<'de>,
-        SinkItem: Serialize,
-        Codec: Serializer<SinkItem> + Deserializer<Item>,
-        CodecFn: Fn() -> Codec,
-    {
-        type Item = io::Result<Transport<TcpStream, Item, SinkItem, Codec>>;
-
-        fn poll_next(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Option<Self::Item>> {
-            let next =
-                ready!(Pin::new(&mut self.as_mut().project().listener.incoming()).poll_next(cx)?);
-            Poll::Ready(next.map(|conn| Ok(new(conn, (self.codec_fn)()))))
-        }
-    }
-}
-
-#[cfg(test)]
-mod tests {
-    use super::Transport;
-    use assert_matches::assert_matches;
-    use futures::{task::*, Sink, Stream};
-    use pin_utils::pin_mut;
-    use std::{
-        io::{self, Cursor},
-        pin::Pin,
-    };
-    use tokio::io::{AsyncRead, AsyncWrite};
-    use tokio_serde::formats::SymmetricalJson;
-
-    fn ctx() -> Context<'static> {
-        Context::from_waker(&noop_waker_ref())
-    }
-
-    #[test]
-    fn test_stream() {
-        struct TestIo(Cursor<&'static [u8]>);
-
-        impl AsyncRead for TestIo {
-            fn poll_read(
-                mut self: Pin<&mut Self>,
-                cx: &mut Context<'_>,
-                buf: &mut [u8],
-            ) -> Poll<io::Result<usize>> {
-                AsyncRead::poll_read(Pin::new(self.0.get_mut()), cx, buf)
-            }
-        }
-
-        impl AsyncWrite for TestIo {
-            fn poll_write(
-                self: Pin<&mut Self>,
-                _cx: &mut Context<'_>,
-                _buf: &[u8],
-            ) -> Poll<io::Result<usize>> {
-                unreachable!()
-            }
-
-            fn poll_flush(self: Pin<&mut Self>, _cx: &mut Context<'_>) -> Poll<io::Result<()>> {
-                unreachable!()
-            }
-
-            fn poll_shutdown(self: Pin<&mut Self>, _cx: &mut Context<'_>) -> Poll<io::Result<()>> {
-                unreachable!()
-            }
-        }
-
-        let data = b"\x00\x00\x00\x18\"Test one, check check.\"";
-        let transport = Transport::from((
-            TestIo(Cursor::new(data)),
-            SymmetricalJson::<String>::default(),
-        ));
-        pin_mut!(transport);
-
-        assert_matches!(
-            transport.poll_next(&mut ctx()),
-            Poll::Ready(Some(Ok(ref s))) if s == "Test one, check check.");
-    }
-
-    #[test]
-    fn test_sink() {
-        struct TestIo<'a>(&'a mut Vec<u8>);
-
-        impl<'a> AsyncRead for TestIo<'a> {
-            fn poll_read(
-                self: Pin<&mut Self>,
-                _cx: &mut Context<'_>,
-                _buf: &mut [u8],
-            ) -> Poll<io::Result<usize>> {
-                unreachable!()
-            }
-        }
-
-        impl<'a> AsyncWrite for TestIo<'a> {
-            fn poll_write(
-                mut self: Pin<&mut Self>,
-                cx: &mut Context<'_>,
-                buf: &[u8],
-            ) -> Poll<io::Result<usize>> {
-                AsyncWrite::poll_write(Pin::new(&mut *self.0), cx, buf)
-            }
-
-            fn poll_flush(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<io::Result<()>> {
-                AsyncWrite::poll_flush(Pin::new(&mut *self.0), cx)
-            }
-
-            fn poll_shutdown(
-                mut self: Pin<&mut Self>,
-                cx: &mut Context<'_>,
-            ) -> Poll<io::Result<()>> {
-                AsyncWrite::poll_shutdown(Pin::new(&mut *self.0), cx)
-            }
-        }
-
-        let mut writer = vec![];
-        let transport =
-            Transport::from((TestIo(&mut writer), SymmetricalJson::<String>::default()));
-        pin_mut!(transport);
-
-        assert_matches!(
-            transport.as_mut().poll_ready(&mut ctx()),
-            Poll::Ready(Ok(()))
-        );
-        assert_matches!(
-            transport
-                .as_mut()
-                .start_send("Test one, check check.".into()),
-            Ok(())
-        );
-        assert_matches!(transport.poll_flush(&mut ctx()), Poll::Ready(Ok(())));
-        assert_eq!(writer, b"\x00\x00\x00\x18\"Test one, check check.\"");
-    }
-}

tarpc/src/server/in_flight_requests.rs

@@ -0,0 +1,221 @@
+use crate::util::{Compact, TimeUntil};
+use fnv::FnvHashMap;
+use futures::future::{AbortHandle, AbortRegistration};
+use std::{
+    collections::hash_map,
+    task::{Context, Poll},
+    time::SystemTime,
+};
+use tokio_util::time::delay_queue::{self, DelayQueue};
+use tracing::Span;
+
+/// A data structure that tracks in-flight requests. It aborts requests,
+/// either on demand or when a request deadline expires.
+#[derive(Debug, Default)]
+pub struct InFlightRequests {
+    request_data: FnvHashMap<u64, RequestData>,
+    deadlines: DelayQueue<u64>,
+}
+
+/// Data needed to clean up a single in-flight request.
+#[derive(Debug)]
+struct RequestData {
+    /// Aborts the response handler for the associated request.
+    abort_handle: AbortHandle,
+    /// The key to remove the timer for the request's deadline.
+    deadline_key: delay_queue::Key,
+    /// The client span.
+    span: Span,
+}
+
+/// An error returned when a request attempted to start with the same ID as a request already
+/// in flight.
+#[derive(Debug)]
+pub struct AlreadyExistsError;
+
+impl InFlightRequests {
+    /// Returns the number of in-flight requests.
+    pub fn len(&self) -> usize {
+        self.request_data.len()
+    }
+
+    /// Starts a request, unless a request with the same ID is already in flight.
+    pub fn start_request(
+        &mut self,
+        request_id: u64,
+        deadline: SystemTime,
+        span: Span,
+    ) -> Result<AbortRegistration, AlreadyExistsError> {
+        match self.request_data.entry(request_id) {
+            hash_map::Entry::Vacant(vacant) => {
+                let timeout = deadline.time_until();
+                let (abort_handle, abort_registration) = AbortHandle::new_pair();
+                let deadline_key = self.deadlines.insert(request_id, timeout);
+                vacant.insert(RequestData {
+                    abort_handle,
+                    deadline_key,
+                    span,
+                });
+                Ok(abort_registration)
+            }
+            hash_map::Entry::Occupied(_) => Err(AlreadyExistsError),
+        }
+    }
+
+    /// Cancels an in-flight request. Returns true iff the request was found.
+    pub fn cancel_request(&mut self, request_id: u64) -> bool {
+        if let Some(RequestData {
+            span,
+            abort_handle,
+            deadline_key,
+        }) = self.request_data.remove(&request_id)
+        {
+            let _entered = span.enter();
+            self.request_data.compact(0.1);
+            abort_handle.abort();
+            self.deadlines.remove(&deadline_key);
+            tracing::info!("ReceiveCancel");
+            true
+        } else {
+            false
+        }
+    }
+
+    /// Removes a request without aborting. Returns true iff the request was found.
+    /// This method should be used when a response is being sent.
+    pub fn remove_request(&mut self, request_id: u64) -> Option<Span> {
+        if let Some(request_data) = self.request_data.remove(&request_id) {
+            self.request_data.compact(0.1);
+            self.deadlines.remove(&request_data.deadline_key);
+            Some(request_data.span)
+        } else {
+            None
+        }
+    }
+
+    /// Yields a request that has expired, aborting any ongoing processing of that request.
+    pub fn poll_expired(&mut self, cx: &mut Context) -> Poll<Option<u64>> {
+        if self.deadlines.is_empty() {
+            // TODO(https://github.com/tokio-rs/tokio/issues/4161)
+            // This is a workaround for DelayQueue not always treating this case correctly.
+            return Poll::Ready(None);
+        }
+        self.deadlines.poll_expired(cx).map(|expired| {
+            let expired = expired?;
+            if let Some(RequestData {
+                abort_handle, span, ..
+            }) = self.request_data.remove(expired.get_ref())
+            {
+                let _entered = span.enter();
+                self.request_data.compact(0.1);
+                abort_handle.abort();
+                tracing::error!("DeadlineExceeded");
+            }
+            Some(expired.into_inner())
+        })
+    }
+}
+
+/// When InFlightRequests is dropped, any outstanding requests are aborted.
+impl Drop for InFlightRequests {
+    fn drop(&mut self) {
+        self.request_data
+            .values()
+            .for_each(|request_data| request_data.abort_handle.abort())
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    use assert_matches::assert_matches;
+    use futures::{
+        future::{pending, Abortable},
+        FutureExt,
+    };
+    use futures_test::task::noop_context;
+
+    #[tokio::test]
+    async fn start_request_increases_len() {
+        let mut in_flight_requests = InFlightRequests::default();
+        assert_eq!(in_flight_requests.len(), 0);
+        in_flight_requests
+            .start_request(0, SystemTime::now(), Span::current())
+            .unwrap();
+        assert_eq!(in_flight_requests.len(), 1);
+    }
+
+    #[tokio::test]
+    async fn polling_expired_aborts() {
+        let mut in_flight_requests = InFlightRequests::default();
+        let abort_registration = in_flight_requests
+            .start_request(0, SystemTime::now(), Span::current())
+            .unwrap();
+        let mut abortable_future = Box::new(Abortable::new(pending::<()>(), abort_registration));
+
+        tokio::time::pause();
+        tokio::time::advance(std::time::Duration::from_secs(1000)).await;
+
+        assert_matches!(
+            in_flight_requests.poll_expired(&mut noop_context()),
+            Poll::Ready(Some(_))
+        );
+        assert_matches!(
+            abortable_future.poll_unpin(&mut noop_context()),
+            Poll::Ready(Err(_))
+        );
+        assert_eq!(in_flight_requests.len(), 0);
+    }
+
+    #[tokio::test]
+    async fn cancel_request_aborts() {
+        let mut in_flight_requests = InFlightRequests::default();
+        let abort_registration = in_flight_requests
+            .start_request(0, SystemTime::now(), Span::current())
+            .unwrap();
+        let mut abortable_future = Box::new(Abortable::new(pending::<()>(), abort_registration));
+
+        assert!(in_flight_requests.cancel_request(0));
+        assert_matches!(
+            abortable_future.poll_unpin(&mut noop_context()),
+            Poll::Ready(Err(_))
+        );
+        assert_eq!(in_flight_requests.len(), 0);
+    }
+
+    #[tokio::test]
+    async fn remove_request_doesnt_abort() {
+        let mut in_flight_requests = InFlightRequests::default();
+        assert!(in_flight_requests.deadlines.is_empty());
+
+        let abort_registration = in_flight_requests
+            .start_request(
+                0,
+                SystemTime::now() + std::time::Duration::from_secs(10),
+                Span::current(),
+            )
+            .unwrap();
+        let mut abortable_future = Box::new(Abortable::new(pending::<()>(), abort_registration));
+
+        // Precondition: Pending expiration
+        assert_matches!(
+            in_flight_requests.poll_expired(&mut noop_context()),
+            Poll::Pending
+        );
+        assert!(!in_flight_requests.deadlines.is_empty());
+
+        assert_matches!(in_flight_requests.remove_request(0), Some(_));
+        // Postcondition: No pending expirations
+        assert!(in_flight_requests.deadlines.is_empty());
+        assert_matches!(
+            in_flight_requests.poll_expired(&mut noop_context()),
+            Poll::Ready(None)
+        );
+        assert_matches!(
+            abortable_future.poll_unpin(&mut noop_context()),
+            Poll::Pending
+        );
+        assert_eq!(in_flight_requests.len(), 0);
+    }
+}

tarpc/src/server/incoming.rs

@@ -0,0 +1,92 @@
+use super::{
+    limits::{channels_per_key::MaxChannelsPerKey, requests_per_channel::MaxRequestsPerChannel},
+    Channel, Serve,
+};
+use futures::prelude::*;
+use std::{fmt, hash::Hash};
+
+/// An extension trait for [streams](futures::prelude::Stream) of [`Channels`](Channel).
+pub trait Incoming<C>
+where
+    Self: Sized + Stream<Item = C>,
+    C: Channel,
+{
+    /// Enforces channel per-key limits.
+    fn max_channels_per_key<K, KF>(self, n: u32, keymaker: KF) -> MaxChannelsPerKey<Self, K, KF>
+    where
+        K: fmt::Display + Eq + Hash + Clone + Unpin,
+        KF: Fn(&C) -> K,
+    {
+        MaxChannelsPerKey::new(self, n, keymaker)
+    }
+
+    /// Caps the number of concurrent requests per channel.
+    fn max_concurrent_requests_per_channel(self, n: usize) -> MaxRequestsPerChannel<Self> {
+        MaxRequestsPerChannel::new(self, n)
+    }
+
+    /// Returns a stream of channels in execution. Each channel in execution is a stream of
+    /// futures, where each future is an in-flight request being rsponded to.
+    fn execute<S>(
+        self,
+        serve: S,
+    ) -> impl Stream<Item = impl Stream<Item = impl Future<Output = ()>>>
+    where
+        S: Serve<Req = C::Req, Resp = C::Resp> + Clone,
+    {
+        self.map(move |channel| channel.execute(serve.clone()))
+    }
+}
+
+#[cfg(feature = "tokio1")]
+/// Spawns all channels-in-execution, delegating to the tokio runtime to manage their completion.
+/// Each channel is spawned, and each request from each channel is spawned.
+/// Note that this function is generic over any stream-of-streams-of-futures, but it is intended
+/// for spawning streams of channels.
+///
+/// # Example
+/// ```rust
+/// use tarpc::{
+///     context,
+///     client::{self, NewClient},
+///     server::{self, BaseChannel, Channel, incoming::{Incoming, spawn_incoming}, serve},
+///     transport,
+/// };
+/// use futures::prelude::*;
+///
+/// #[tokio::main]
+/// async fn main() {
+///     let (tx, rx) = transport::channel::unbounded();
+///     let NewClient { client, dispatch } = client::new(client::Config::default(), tx);
+///     tokio::spawn(dispatch);
+///
+///     let incoming = stream::once(async move {
+///         BaseChannel::new(server::Config::default(), rx)
+///     }).execute(serve(|_, i| async move { Ok(i + 1) }));
+///     tokio::spawn(spawn_incoming(incoming));
+///     assert_eq!(client.call(context::current(), "AddOne", 1).await.unwrap(), 2);
+/// }
+/// ```
+pub async fn spawn_incoming(
+    incoming: impl Stream<
+        Item = impl Stream<Item = impl Future<Output = ()> + Send + 'static> + Send + 'static,
+    >,
+) {
+    use futures::pin_mut;
+    pin_mut!(incoming);
+    while let Some(channel) = incoming.next().await {
+        tokio::spawn(async move {
+            pin_mut!(channel);
+            while let Some(request) = channel.next().await {
+                tokio::spawn(request);
+            }
+        });
+    }
+}
+
+impl<S, C> Incoming<C> for S
+where
+    S: Sized + Stream<Item = C>,
+    C: Channel,
+{
+}

tarpc/src/server/limits.rs

@@ -0,0 +1,5 @@
+/// Provides functionality to limit the number of active channels.
+pub mod channels_per_key;
+
+/// Provides a [channel](crate::server::Channel) that limits the number of in-flight requests.
+pub mod requests_per_channel;

tarpc/src/server/limits/channels_per_key.rs

@@ -9,78 +9,65 @@ use crate::{
     util::Compact,
 };
 use fnv::FnvHashMap;
-use futures::{channel::mpsc, future::AbortRegistration, prelude::*, ready, stream::Fuse, task::*};
-use log::{debug, info, trace};
+use futures::{prelude::*, ready, stream::Fuse, task::*};
 use pin_project::pin_project;
-use raii_counter::{Counter, WeakCounter};
 use std::sync::{Arc, Weak};
 use std::{
-    collections::hash_map::Entry, convert::TryInto, fmt, hash::Hash, marker::Unpin, pin::Pin,
+    collections::hash_map::Entry, convert::TryFrom, fmt, hash::Hash, marker::Unpin, pin::Pin,
 };
+use tokio::sync::mpsc;
+use tracing::{debug, info, trace};
 
-/// A single-threaded filter that drops channels based on per-key limits.
+/// An [`Incoming`](crate::server::incoming::Incoming) stream that drops new channels based on
+/// per-key limits.
+///
+/// The decision to drop a Channel is made once at the time the Channel materializes. Once a
+/// Channel is yielded, it will not be prematurely dropped.
 #[pin_project]
 #[derive(Debug)]
-pub struct ChannelFilter<S, K, F>
+pub struct MaxChannelsPerKey<S, K, F>
 where
     K: Eq + Hash,
 {
     #[pin]
     listener: Fuse<S>,
     channels_per_key: u32,
-    #[pin]
     dropped_keys: mpsc::UnboundedReceiver<K>,
-    #[pin]
     dropped_keys_tx: mpsc::UnboundedSender<K>,
-    key_counts: FnvHashMap<K, TrackerPrototype<K>>,
+    key_counts: FnvHashMap<K, Weak<Tracker<K>>>,
     keymaker: F,
 }
 
-/// A channel that is tracked by a ChannelFilter.
+/// A channel that is tracked by [`MaxChannelsPerKey`].
 #[pin_project]
 #[derive(Debug)]
 pub struct TrackedChannel<C, K> {
     #[pin]
     inner: C,
-    tracker: Tracker<K>,
+    tracker: Arc<Tracker<K>>,
 }
 
-#[derive(Clone, Debug)]
+#[derive(Debug)]
 struct Tracker<K> {
-    key: Option<Arc<K>>,
-    counter: Counter,
+    key: Option<K>,
     dropped_keys: mpsc::UnboundedSender<K>,
 }
 
 impl<K> Drop for Tracker<K> {
     fn drop(&mut self) {
-        if self.counter.count() <= 1 {
-            // Don't care if the listener is dropped.
-            match Arc::try_unwrap(self.key.take().unwrap()) {
-                Ok(key) => {
-                    let _ = self.dropped_keys.unbounded_send(key);
-                }
-                _ => unreachable!(),
-            }
-        }
+        // Don't care if the listener is dropped.
+        let _ = self.dropped_keys.send(self.key.take().unwrap());
     }
 }
 
-#[derive(Clone, Debug)]
-struct TrackerPrototype<K> {
-    key: Weak<K>,
-    counter: WeakCounter,
-    dropped_keys: mpsc::UnboundedSender<K>,
-}
-
 impl<C, K> Stream for TrackedChannel<C, K>
 where
     C: Stream,
 {
     type Item = <C as Stream>::Item;
 
-    fn poll_next(self: Pin<&mut Self>, cx: &mut Context) -> Poll<Option<Self::Item>> {
-        self.channel().poll_next(cx)
+    fn poll_next(mut self: Pin<&mut Self>, cx: &mut Context) -> Poll<Option<Self::Item>> {
+        self.inner_pin_mut().poll_next(cx)
     }
 }
 
@@ -90,20 +77,20 @@ where
 {
     type Error = C::Error;
 
-    fn poll_ready(self: Pin<&mut Self>, cx: &mut Context) -> Poll<Result<(), Self::Error>> {
-        self.channel().poll_ready(cx)
+    fn poll_ready(mut self: Pin<&mut Self>, cx: &mut Context) -> Poll<Result<(), Self::Error>> {
+        self.inner_pin_mut().poll_ready(cx)
     }
 
-    fn start_send(self: Pin<&mut Self>, item: I) -> Result<(), Self::Error> {
-        self.channel().start_send(item)
+    fn start_send(mut self: Pin<&mut Self>, item: I) -> Result<(), Self::Error> {
+        self.inner_pin_mut().start_send(item)
     }
 
-    fn poll_flush(self: Pin<&mut Self>, cx: &mut Context) -> Poll<Result<(), Self::Error>> {
-        self.channel().poll_flush(cx)
+    fn poll_flush(mut self: Pin<&mut Self>, cx: &mut Context) -> Poll<Result<(), Self::Error>> {
+        self.inner_pin_mut().poll_flush(cx)
     }
 
-    fn poll_close(self: Pin<&mut Self>, cx: &mut Context) -> Poll<Result<(), Self::Error>> {
-        self.channel().poll_close(cx)
+    fn poll_close(mut self: Pin<&mut Self>, cx: &mut Context) -> Poll<Result<(), Self::Error>> {
+        self.inner_pin_mut().poll_close(cx)
     }
 }
 
@@ -119,17 +106,18 @@ where
 {
     type Req = C::Req;
     type Resp = C::Resp;
+    type Transport = C::Transport;
 
     fn config(&self) -> &server::Config {
         self.inner.config()
     }
 
-    fn in_flight_requests(self: Pin<&mut Self>) -> usize {
-        self.project().inner.in_flight_requests()
+    fn in_flight_requests(&self) -> usize {
+        self.inner.in_flight_requests()
     }
 
-    fn start_request(self: Pin<&mut Self>, request_id: u64) -> AbortRegistration {
-        self.project().inner.start_request(request_id)
+    fn transport(&self) -> &Self::Transport {
+        self.inner.transport()
     }
 }
 
@@ -140,12 +128,12 @@ impl<C, K> TrackedChannel<C, K> {
     }
 
     /// Returns the pinned inner channel.
-    fn channel<'a>(self: Pin<&'a mut Self>) -> Pin<&'a mut C> {
-        self.project().inner
+    fn inner_pin_mut<'a>(self: &'a mut Pin<&mut Self>) -> Pin<&'a mut C> {
+        self.as_mut().project().inner
     }
 }
 
-impl<S, K, F> ChannelFilter<S, K, F>
+impl<S, K, F> MaxChannelsPerKey<S, K, F>
 where
     K: Eq + Hash,
     S: Stream,
@@ -153,8 +141,8 @@ where
 {
     /// Sheds new channels to stay under configured limits.
     pub(crate) fn new(listener: S, channels_per_key: u32, keymaker: F) -> Self {
-        let (dropped_keys_tx, dropped_keys) = mpsc::unbounded();
-        ChannelFilter {
+        let (dropped_keys_tx, dropped_keys) = mpsc::unbounded_channel();
+        MaxChannelsPerKey {
             listener: listener.fuse(),
             channels_per_key,
             dropped_keys,
@@ -165,12 +153,16 @@ where
     }
 }
 
-impl<S, K, F> ChannelFilter<S, K, F>
+impl<S, K, F> MaxChannelsPerKey<S, K, F>
 where
     S: Stream,
     K: fmt::Display + Eq + Hash + Clone + Unpin,
     F: Fn(&S::Item) -> K,
 {
+    fn listener_pin_mut<'a>(self: &'a mut Pin<&mut Self>) -> Pin<&'a mut Fuse<S>> {
+        self.as_mut().project().listener
+    }
+
     fn handle_new_channel(
         mut self: Pin<&mut Self>,
         stream: S::Item,
@@ -179,11 +171,10 @@ where
         let tracker = self.as_mut().increment_channels_for_key(key.clone())?;
 
         trace!(
-            "[{}] Opening channel ({}/{}) channels for key.",
-            key,
-            tracker.counter.count(),
-            self.as_mut().project().channels_per_key
-        );
+            channel_filter_key = %key,
+            open_channels = Arc::strong_count(&tracker),
+            max_open_channels = self.channels_per_key,
+            "Opening channel");
 
         Ok(TrackedChannel {
             tracker,
@@ -191,45 +182,38 @@ where
         })
     }
 
-    fn increment_channels_for_key(mut self: Pin<&mut Self>, key: K) -> Result<Tracker<K>, K> {
-        let channels_per_key = self.channels_per_key;
-        let dropped_keys = self.dropped_keys_tx.clone();
-        let key_counts = &mut self.as_mut().project().key_counts;
-        match key_counts.entry(key.clone()) {
+    fn increment_channels_for_key(self: Pin<&mut Self>, key: K) -> Result<Arc<Tracker<K>>, K> {
+        let self_ = self.project();
+        let dropped_keys = self_.dropped_keys_tx;
+        match self_.key_counts.entry(key.clone()) {
             Entry::Vacant(vacant) => {
-                let key = Arc::new(key);
-                let counter = WeakCounter::new();
-
-                vacant.insert(TrackerPrototype {
-                    key: Arc::downgrade(&key),
-                    counter: counter.clone(),
+                let tracker = Arc::new(Tracker {
+                    key: Some(key),
                     dropped_keys: dropped_keys.clone(),
                 });
-                Ok(Tracker {
-                    key: Some(key),
-                    counter: counter.upgrade(),
-                    dropped_keys,
-                })
+
+                vacant.insert(Arc::downgrade(&tracker));
+                Ok(tracker)
             }
-            Entry::Occupied(o) => {
-                let count = o.get().counter.count();
-                if count >= channels_per_key.try_into().unwrap() {
+            Entry::Occupied(mut o) => {
+                let count = o.get().strong_count();
+                if count >= TryFrom::try_from(*self_.channels_per_key).unwrap() {
                     info!(
-                        "[{}] Opened max channels from key ({}/{}).",
-                        key, count, channels_per_key
-                    );
+                        channel_filter_key = %key,
+                        open_channels = count,
+                        max_open_channels = *self_.channels_per_key,
+                        "At open channel limit");
                     Err(key)
                 } else {
-                    let TrackerPrototype {
-                        key,
-                        counter,
-                        dropped_keys,
-                    } = o.get().clone();
-                    Ok(Tracker {
-                        counter: counter.upgrade(),
-                        key: Some(key.upgrade().unwrap()),
-                        dropped_keys,
-                    })
+                    Ok(o.get().upgrade().unwrap_or_else(|| {
+                        let tracker = Arc::new(Tracker {
+                            key: Some(key),
+                            dropped_keys: dropped_keys.clone(),
+                        });
+
+                        *o.get_mut() = Arc::downgrade(&tracker);
+                        tracker
+                    }))
                 }
             }
         }
@@ -239,18 +223,21 @@ where
         mut self: Pin<&mut Self>,
         cx: &mut Context<'_>,
     ) -> Poll<Option<Result<TrackedChannel<S::Item, K>, K>>> {
-        match ready!(self.as_mut().project().listener.poll_next_unpin(cx)) {
+        match ready!(self.listener_pin_mut().poll_next_unpin(cx)) {
             Some(codec) => Poll::Ready(Some(self.handle_new_channel(codec))),
             None => Poll::Ready(None),
         }
     }
 
-    fn poll_closed_channels(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<()> {
-        match ready!(self.as_mut().project().dropped_keys.poll_next_unpin(cx)) {
+    fn poll_closed_channels(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<()> {
+        let self_ = self.project();
+        match ready!(self_.dropped_keys.poll_recv(cx)) {
             Some(key) => {
-                debug!("All channels dropped for key [{}]", key);
-                self.as_mut().project().key_counts.remove(&key);
-                self.as_mut().project().key_counts.compact(0.1);
+                debug!(
+                    channel_filter_key = %key,
+                    "All channels dropped");
+                self_.key_counts.remove(&key);
+                self_.key_counts.compact(0.1);
                 Poll::Ready(())
             }
             None => unreachable!("Holding a copy of closed_channels and didn't close it."),
@@ -258,7 +245,7 @@ where
     }
 }
 
-impl<S, K, F> Stream for ChannelFilter<S, K, F>
+impl<S, K, F> Stream for MaxChannelsPerKey<S, K, F>
 where
     S: Stream,
     K: fmt::Display + Eq + Hash + Clone + Unpin,
@@ -291,43 +278,38 @@ where
         }
     }
 }
-
 #[cfg(test)]
 fn ctx() -> Context<'static> {
     use futures::task::*;
 
-    Context::from_waker(&noop_waker_ref())
+    Context::from_waker(noop_waker_ref())
 }
 
 #[test]
 fn tracker_drop() {
     use assert_matches::assert_matches;
-    use raii_counter::Counter;
 
-    let (tx, mut rx) = mpsc::unbounded();
+    let (tx, mut rx) = mpsc::unbounded_channel();
     Tracker {
-        key: Some(Arc::new(1)),
-        counter: Counter::new(),
+        key: Some(1),
         dropped_keys: tx,
     };
-    assert_matches!(rx.try_next(), Ok(Some(1)));
+    assert_matches!(rx.poll_recv(&mut ctx()), Poll::Ready(Some(1)));
 }
 
 #[test]
 fn tracked_channel_stream() {
     use assert_matches::assert_matches;
     use pin_utils::pin_mut;
-    use raii_counter::Counter;
 
-    let (chan_tx, chan) = mpsc::unbounded();
-    let (dropped_keys, _) = mpsc::unbounded();
+    let (chan_tx, chan) = futures::channel::mpsc::unbounded();
+    let (dropped_keys, _) = mpsc::unbounded_channel();
     let channel = TrackedChannel {
         inner: chan,
-        tracker: Tracker {
-            key: Some(Arc::new(1)),
-            counter: Counter::new(),
+        tracker: Arc::new(Tracker {
+            key: Some(1),
             dropped_keys,
-        },
+        }),
     };
 
     chan_tx.unbounded_send("test").unwrap();
@@ -339,17 +321,15 @@ fn tracked_channel_stream() {
 fn tracked_channel_sink() {
     use assert_matches::assert_matches;
     use pin_utils::pin_mut;
-    use raii_counter::Counter;
 
-    let (chan, mut chan_rx) = mpsc::unbounded();
-    let (dropped_keys, _) = mpsc::unbounded();
+    let (chan, mut chan_rx) = futures::channel::mpsc::unbounded();
+    let (dropped_keys, _) = mpsc::unbounded_channel();
     let channel = TrackedChannel {
         inner: chan,
-        tracker: Tracker {
-            key: Some(Arc::new(1)),
-            counter: Counter::new(),
+        tracker: Arc::new(Tracker {
+            key: Some(1),
             dropped_keys,
-        },
+        }),
     };
 
     pin_mut!(channel);
@@ -367,16 +347,16 @@ fn channel_filter_increment_channels_for_key() {
     struct TestChannel {
         key: &'static str,
     }
-    let (_, listener) = mpsc::unbounded();
-    let filter = ChannelFilter::new(listener, 2, |chan: &TestChannel| chan.key);
+    let (_, listener) = futures::channel::mpsc::unbounded();
+    let filter = MaxChannelsPerKey::new(listener, 2, |chan: &TestChannel| chan.key);
     pin_mut!(filter);
     let tracker1 = filter.as_mut().increment_channels_for_key("key").unwrap();
-    assert_eq!(tracker1.counter.count(), 1);
+    assert_eq!(Arc::strong_count(&tracker1), 1);
     let tracker2 = filter.as_mut().increment_channels_for_key("key").unwrap();
-    assert_eq!(tracker1.counter.count(), 2);
+    assert_eq!(Arc::strong_count(&tracker1), 2);
     assert_matches!(filter.increment_channels_for_key("key"), Err("key"));
     drop(tracker2);
-    assert_eq!(tracker1.counter.count(), 1);
+    assert_eq!(Arc::strong_count(&tracker1), 1);
 }
 
 #[test]
@@ -388,27 +368,27 @@ fn channel_filter_handle_new_channel() {
     struct TestChannel {
         key: &'static str,
     }
-    let (_, listener) = mpsc::unbounded();
-    let filter = ChannelFilter::new(listener, 2, |chan: &TestChannel| chan.key);
+    let (_, listener) = futures::channel::mpsc::unbounded();
+    let filter = MaxChannelsPerKey::new(listener, 2, |chan: &TestChannel| chan.key);
     pin_mut!(filter);
     let channel1 = filter
         .as_mut()
         .handle_new_channel(TestChannel { key: "key" })
         .unwrap();
-    assert_eq!(channel1.tracker.counter.count(), 1);
+    assert_eq!(Arc::strong_count(&channel1.tracker), 1);
 
     let channel2 = filter
         .as_mut()
         .handle_new_channel(TestChannel { key: "key" })
         .unwrap();
-    assert_eq!(channel1.tracker.counter.count(), 2);
+    assert_eq!(Arc::strong_count(&channel1.tracker), 2);
 
     assert_matches!(
         filter.handle_new_channel(TestChannel { key: "key" }),
         Err("key")
     );
     drop(channel2);
-    assert_eq!(channel1.tracker.counter.count(), 1);
+    assert_eq!(Arc::strong_count(&channel1.tracker), 1);
 }
 
 #[test]
@@ -420,8 +400,8 @@ fn channel_filter_poll_listener() {
     struct TestChannel {
         key: &'static str,
     }
-    let (new_channels, listener) = mpsc::unbounded();
-    let filter = ChannelFilter::new(listener, 2, |chan: &TestChannel| chan.key);
+    let (new_channels, listener) = futures::channel::mpsc::unbounded();
+    let filter = MaxChannelsPerKey::new(listener, 2, |chan: &TestChannel| chan.key);
     pin_mut!(filter);
 
     new_channels
@@ -429,14 +409,14 @@ fn channel_filter_poll_listener() {
         .unwrap();
     let channel1 =
         assert_matches!(filter.as_mut().poll_listener(&mut ctx()), Poll::Ready(Some(Ok(c))) => c);
-    assert_eq!(channel1.tracker.counter.count(), 1);
+    assert_eq!(Arc::strong_count(&channel1.tracker), 1);
 
     new_channels
         .unbounded_send(TestChannel { key: "key" })
         .unwrap();
     let _channel2 =
         assert_matches!(filter.as_mut().poll_listener(&mut ctx()), Poll::Ready(Some(Ok(c))) => c);
-    assert_eq!(channel1.tracker.counter.count(), 2);
+    assert_eq!(Arc::strong_count(&channel1.tracker), 2);
 
     new_channels
         .unbounded_send(TestChannel { key: "key" })
@@ -444,7 +424,7 @@ fn channel_filter_poll_listener() {
     let key =
         assert_matches!(filter.as_mut().poll_listener(&mut ctx()), Poll::Ready(Some(Err(k))) => k);
     assert_eq!(key, "key");
-    assert_eq!(channel1.tracker.counter.count(), 2);
+    assert_eq!(Arc::strong_count(&channel1.tracker), 2);
 }
 
 #[test]
@@ -456,8 +436,8 @@ fn channel_filter_poll_closed_channels() {
     struct TestChannel {
         key: &'static str,
     }
-    let (new_channels, listener) = mpsc::unbounded();
-    let filter = ChannelFilter::new(listener, 2, |chan: &TestChannel| chan.key);
+    let (new_channels, listener) = futures::channel::mpsc::unbounded();
+    let filter = MaxChannelsPerKey::new(listener, 2, |chan: &TestChannel| chan.key);
     pin_mut!(filter);
 
     new_channels
@@ -484,8 +464,8 @@ fn channel_filter_stream() {
     struct TestChannel {
         key: &'static str,
     }
-    let (new_channels, listener) = mpsc::unbounded();
-    let filter = ChannelFilter::new(listener, 2, |chan: &TestChannel| chan.key);
+    let (new_channels, listener) = futures::channel::mpsc::unbounded();
+    let filter = MaxChannelsPerKey::new(listener, 2, |chan: &TestChannel| chan.key);
     pin_mut!(filter);
 
     new_channels

tarpc/src/server/limits/requests_per_channel.rs

@@ -0,0 +1,349 @@
+// Copyright 2020 Google LLC
+//
+// Use of this source code is governed by an MIT-style
+// license that can be found in the LICENSE file or at
+// https://opensource.org/licenses/MIT.
+
+use crate::{
+    server::{Channel, Config},
+    Response, ServerError,
+};
+use futures::{prelude::*, ready, task::*};
+use pin_project::pin_project;
+use std::{io, pin::Pin};
+
+/// A [`Channel`] that limits the number of concurrent requests by throttling.
+///
+/// Note that this is a very basic throttling heuristic. It is easy to set a number that is too low
+/// for the resources available to the server. For production use cases, a more advanced throttler
+/// is likely needed.
+#[pin_project]
+#[derive(Debug)]
+pub struct MaxRequests<C> {
+    max_in_flight_requests: usize,
+    #[pin]
+    inner: C,
+}
+
+impl<C> MaxRequests<C> {
+    /// Returns the inner channel.
+    pub fn get_ref(&self) -> &C {
+        &self.inner
+    }
+}
+
+impl<C> MaxRequests<C>
+where
+    C: Channel,
+{
+    /// Returns a new `MaxRequests` that wraps the given channel and limits concurrent requests to
+    /// `max_in_flight_requests`.
+    pub fn new(inner: C, max_in_flight_requests: usize) -> Self {
+        MaxRequests {
+            max_in_flight_requests,
+            inner,
+        }
+    }
+}
+
+impl<C> Stream for MaxRequests<C>
+where
+    C: Channel,
+{
+    type Item = <C as Stream>::Item;
+
+    fn poll_next(mut self: Pin<&mut Self>, cx: &mut Context) -> Poll<Option<Self::Item>> {
+        while self.as_mut().in_flight_requests() >= *self.as_mut().project().max_in_flight_requests
+        {
+            ready!(self.as_mut().project().inner.poll_ready(cx)?);
+
+            match ready!(self.as_mut().project().inner.poll_next(cx)?) {
+                Some(r) => {
+                    let _entered = r.span.enter();
+                    tracing::info!(
+                        in_flight_requests = self.as_mut().in_flight_requests(),
+                        "ThrottleRequest",
+                    );
+
+                    self.as_mut().start_send(Response {
+                        request_id: r.request.id,
+                        message: Err(ServerError {
+                            kind: io::ErrorKind::WouldBlock,
+                            detail: "server throttled the request.".into(),
+                        }),
+                    })?;
+                }
+                None => return Poll::Ready(None),
+            }
+        }
+        self.project().inner.poll_next(cx)
+    }
+}
+
+impl<C> Sink<Response<<C as Channel>::Resp>> for MaxRequests<C>
+where
+    C: Channel,
+{
+    type Error = C::Error;
+
+    fn poll_ready(self: Pin<&mut Self>, cx: &mut Context) -> Poll<Result<(), Self::Error>> {
+        self.project().inner.poll_ready(cx)
+    }
+
+    fn start_send(
+        self: Pin<&mut Self>,
+        item: Response<<C as Channel>::Resp>,
+    ) -> Result<(), Self::Error> {
+        self.project().inner.start_send(item)
+    }
+
+    fn poll_flush(self: Pin<&mut Self>, cx: &mut Context) -> Poll<Result<(), Self::Error>> {
+        self.project().inner.poll_flush(cx)
+    }
+
+    fn poll_close(self: Pin<&mut Self>, cx: &mut Context) -> Poll<Result<(), Self::Error>> {
+        self.project().inner.poll_close(cx)
+    }
+}
+
+impl<C> AsRef<C> for MaxRequests<C> {
+    fn as_ref(&self) -> &C {
+        &self.inner
+    }
+}
+
+impl<C> Channel for MaxRequests<C>
+where
+    C: Channel,
+{
+    type Req = <C as Channel>::Req;
+    type Resp = <C as Channel>::Resp;
+    type Transport = <C as Channel>::Transport;
+
+    fn in_flight_requests(&self) -> usize {
+        self.inner.in_flight_requests()
+    }
+
+    fn config(&self) -> &Config {
+        self.inner.config()
+    }
+
+    fn transport(&self) -> &Self::Transport {
+        self.inner.transport()
+    }
+}
+
+/// An [`Incoming`](crate::server::incoming::Incoming) stream of channels that enforce limits on
+/// the number of in-flight requests.
+#[pin_project]
+#[derive(Debug)]
+pub struct MaxRequestsPerChannel<S> {
+    #[pin]
+    inner: S,
+    max_in_flight_requests: usize,
+}
+
+impl<S> MaxRequestsPerChannel<S>
+where
+    S: Stream,
+    <S as Stream>::Item: Channel,
+{
+    pub(crate) fn new(inner: S, max_in_flight_requests: usize) -> Self {
+        Self {
+            inner,
+            max_in_flight_requests,
+        }
+    }
+}
+
+impl<S> Stream for MaxRequestsPerChannel<S>
+where
+    S: Stream,
+    <S as Stream>::Item: Channel,
+{
+    type Item = MaxRequests<<S as Stream>::Item>;
+
+    fn poll_next(mut self: Pin<&mut Self>, cx: &mut Context) -> Poll<Option<Self::Item>> {
+        match ready!(self.as_mut().project().inner.poll_next(cx)) {
+            Some(channel) => Poll::Ready(Some(MaxRequests::new(
+                channel,
+                *self.project().max_in_flight_requests,
+            ))),
+            None => Poll::Ready(None),
+        }
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    use crate::server::{
+        testing::{self, FakeChannel, PollExt},
+        TrackedRequest,
+    };
+    use pin_utils::pin_mut;
+    use std::{
+        marker::PhantomData,
+        time::{Duration, SystemTime},
+    };
+    use tracing::Span;
+
+    #[tokio::test]
+    async fn throttler_in_flight_requests() {
+        let throttler = MaxRequests {
+            max_in_flight_requests: 0,
+            inner: FakeChannel::default::<isize, isize>(),
+        };
+
+        pin_mut!(throttler);
+        for i in 0..5 {
+            throttler
+                .inner
+                .in_flight_requests
+                .start_request(
+                    i,
+                    SystemTime::now() + Duration::from_secs(1),
+                    Span::current(),
+                )
+                .unwrap();
+        }
+        assert_eq!(throttler.as_mut().in_flight_requests(), 5);
+    }
+
+    #[test]
+    fn throttler_poll_next_done() {
+        let throttler = MaxRequests {
+            max_in_flight_requests: 0,
+            inner: FakeChannel::default::<isize, isize>(),
+        };
+
+        pin_mut!(throttler);
+        assert!(throttler.as_mut().poll_next(&mut testing::cx()).is_done());
+    }
+
+    #[test]
+    fn throttler_poll_next_some() -> io::Result<()> {
+        let throttler = MaxRequests {
+            max_in_flight_requests: 1,
+            inner: FakeChannel::default::<isize, isize>(),
+        };
+
+        pin_mut!(throttler);
+        throttler.inner.push_req(0, 1);
+        assert!(throttler.as_mut().poll_ready(&mut testing::cx()).is_ready());
+        assert_eq!(
+            throttler
+                .as_mut()
+                .poll_next(&mut testing::cx())?
+                .map(|r| r.map(|r| (r.request.id, r.request.message))),
+            Poll::Ready(Some((0, 1)))
+        );
+        Ok(())
+    }
+
+    #[test]
+    fn throttler_poll_next_throttled() {
+        let throttler = MaxRequests {
+            max_in_flight_requests: 0,
+            inner: FakeChannel::default::<isize, isize>(),
+        };
+
+        pin_mut!(throttler);
+        throttler.inner.push_req(1, 1);
+        assert!(throttler.as_mut().poll_next(&mut testing::cx()).is_done());
+        assert_eq!(throttler.inner.sink.len(), 1);
+        let resp = throttler.inner.sink.get(0).unwrap();
+        assert_eq!(resp.request_id, 1);
+        assert!(resp.message.is_err());
+    }
+
+    #[test]
+    fn throttler_poll_next_throttled_sink_not_ready() {
+        let throttler = MaxRequests {
+            max_in_flight_requests: 0,
+            inner: PendingSink::default::<isize, isize>(),
+        };
+        pin_mut!(throttler);
+        assert!(throttler.poll_next(&mut testing::cx()).is_pending());
+
+        struct PendingSink<In, Out> {
+            ghost: PhantomData<fn(Out) -> In>,
+        }
+        impl PendingSink<(), ()> {
+            pub fn default<Req, Resp>(
+            ) -> PendingSink<io::Result<TrackedRequest<Req>>, Response<Resp>> {
+                PendingSink { ghost: PhantomData }
+            }
+        }
+        impl<In, Out> Stream for PendingSink<In, Out> {
+            type Item = In;
+            fn poll_next(self: Pin<&mut Self>, _: &mut Context) -> Poll<Option<Self::Item>> {
+                unimplemented!()
+            }
+        }
+        impl<In, Out> Sink<Out> for PendingSink<In, Out> {
+            type Error = io::Error;
+            fn poll_ready(self: Pin<&mut Self>, _: &mut Context) -> Poll<Result<(), Self::Error>> {
+                Poll::Pending
+            }
+            fn start_send(self: Pin<&mut Self>, _: Out) -> Result<(), Self::Error> {
+                Err(io::Error::from(io::ErrorKind::WouldBlock))
+            }
+            fn poll_flush(self: Pin<&mut Self>, _: &mut Context) -> Poll<Result<(), Self::Error>> {
+                Poll::Pending
+            }
+            fn poll_close(self: Pin<&mut Self>, _: &mut Context) -> Poll<Result<(), Self::Error>> {
+                Poll::Pending
+            }
+        }
+        impl<Req, Resp> Channel for PendingSink<io::Result<TrackedRequest<Req>>, Response<Resp>> {
+            type Req = Req;
+            type Resp = Resp;
+            type Transport = ();
+            fn config(&self) -> &Config {
+                unimplemented!()
+            }
+            fn in_flight_requests(&self) -> usize {
+                0
+            }
+            fn transport(&self) -> &() {
+                &()
+            }
+        }
+    }
+
+    #[tokio::test]
+    async fn throttler_start_send() {
+        let throttler = MaxRequests {
+            max_in_flight_requests: 0,
+            inner: FakeChannel::default::<isize, isize>(),
+        };
+
+        pin_mut!(throttler);
+        throttler
+            .inner
+            .in_flight_requests
+            .start_request(
+                0,
+                SystemTime::now() + Duration::from_secs(1),
+                Span::current(),
+            )
+            .unwrap();
+        throttler
+            .as_mut()
+            .start_send(Response {
+                request_id: 0,
+                message: Ok(1),
+            })
+            .unwrap();
+        assert_eq!(throttler.inner.in_flight_requests.len(), 0);
+        assert_eq!(
+            throttler.inner.sink.get(0),
+            Some(&Response {
+                request_id: 0,
+                message: Ok(1),
+            })
+        );
+    }
+}

tarpc/src/server/request_hook.rs

@@ -0,0 +1,25 @@
+// Copyright 2022 Google LLC
+//
+// Use of this source code is governed by an MIT-style
+// license that can be found in the LICENSE file or at
+// https://opensource.org/licenses/MIT.
+
+//! Hooks for horizontal functionality that can run either before or after a request is executed.
+
+/// A request hook that runs before a request is executed.
+mod before;
+
+/// A request hook that runs after a request is completed.
+mod after;
+
+/// A request hook that runs both before a request is executed and after it is completed.
+mod before_and_after;
+
+pub use {
+    after::{AfterRequest, ServeThenHook},
+    before::{
+        before, BeforeRequest, BeforeRequestCons, BeforeRequestList, BeforeRequestNil,
+        HookThenServe,
+    },
+    before_and_after::HookThenServeThenHook,
+};

tarpc/src/server/request_hook/after.rs

@@ -0,0 +1,72 @@
+// Copyright 2022 Google LLC
+//
+// Use of this source code is governed by an MIT-style
+// license that can be found in the LICENSE file or at
+// https://opensource.org/licenses/MIT.
+
+//! Provides a hook that runs after request execution.
+
+use crate::{context, server::Serve, ServerError};
+use futures::prelude::*;
+
+/// A hook that runs after request execution.
+#[allow(async_fn_in_trait)]
+pub trait AfterRequest<Resp> {
+    /// The function that is called after request execution.
+    ///
+    /// The hook can modify the request context and the response.
+    async fn after(&mut self, ctx: &mut context::Context, resp: &mut Result<Resp, ServerError>);
+}
+
+impl<F, Fut, Resp> AfterRequest<Resp> for F
+where
+    F: FnMut(&mut context::Context, &mut Result<Resp, ServerError>) -> Fut,
+    Fut: Future<Output = ()>,
+{
+    async fn after(&mut self, ctx: &mut context::Context, resp: &mut Result<Resp, ServerError>) {
+        self(ctx, resp).await
+    }
+}
+
+/// A Service function that runs a hook after request execution.
+pub struct ServeThenHook<Serv, Hook> {
+    serve: Serv,
+    hook: Hook,
+}
+
+impl<Serv, Hook> ServeThenHook<Serv, Hook> {
+    pub(crate) fn new(serve: Serv, hook: Hook) -> Self {
+        Self { serve, hook }
+    }
+}
+
+impl<Serv: Clone, Hook: Clone> Clone for ServeThenHook<Serv, Hook> {
+    fn clone(&self) -> Self {
+        Self {
+            serve: self.serve.clone(),
+            hook: self.hook.clone(),
+        }
+    }
+}
+
+impl<Serv, Hook> Serve for ServeThenHook<Serv, Hook>
+where
+    Serv: Serve,
+    Hook: AfterRequest<Serv::Resp>,
+{
+    type Req = Serv::Req;
+    type Resp = Serv::Resp;
+
+    async fn serve(
+        self,
+        mut ctx: context::Context,
+        req: Serv::Req,
+    ) -> Result<Serv::Resp, ServerError> {
+        let ServeThenHook {
+            serve, mut hook, ..
+        } = self;
+        let mut resp = serve.serve(ctx, req).await;
+        hook.after(&mut ctx, &mut resp).await;
+        resp
+    }
+}

tarpc/src/server/request_hook/before.rs

@@ -0,0 +1,210 @@
+// Copyright 2022 Google LLC
+//
+// Use of this source code is governed by an MIT-style
+// license that can be found in the LICENSE file or at
+// https://opensource.org/licenses/MIT.
+
+//! Provides a hook that runs before request execution.
+
+use crate::{context, server::Serve, ServerError};
+use futures::prelude::*;
+
+/// A hook that runs before request execution.
+#[allow(async_fn_in_trait)]
+pub trait BeforeRequest<Req> {
+    /// The function that is called before request execution.
+    ///
+    /// If this function returns an error, the request will not be executed and the error will be
+    /// returned instead.
+    ///
+    /// This function can also modify the request context. This could be used, for example, to
+    /// enforce a maximum deadline on all requests.
+    async fn before(&mut self, ctx: &mut context::Context, req: &Req) -> Result<(), ServerError>;
+}
+
+/// A list of hooks that run in order before request execution.
+pub trait BeforeRequestList<Req>: BeforeRequest<Req> {
+    /// The hook returned by `BeforeRequestList::then`.
+    type Then<Next>: BeforeRequest<Req>
+    where
+        Next: BeforeRequest<Req>;
+
+    /// Returns a hook that, when run, runs two hooks, first `self` and then `next`.
+    fn then<Next: BeforeRequest<Req>>(self, next: Next) -> Self::Then<Next>;
+
+    /// Same as `then`, but helps the compiler with type inference when Next is a closure.
+    fn then_fn<
+        Next: FnMut(&mut context::Context, &Req) -> Fut,
+        Fut: Future<Output = Result<(), ServerError>>,
+    >(
+        self,
+        next: Next,
+    ) -> Self::Then<Next>
+    where
+        Self: Sized,
+    {
+        self.then(next)
+    }
+
+    /// The service fn returned by `BeforeRequestList::serving`.
+    type Serve<S: Serve<Req = Req>>: Serve<Req = Req>;
+
+    /// Runs the list of request hooks before execution of the given serve fn.
+    /// This is equivalent to `serve.before(before_request_chain)` but may be syntactically nicer.
+    fn serving<S: Serve<Req = Req>>(self, serve: S) -> Self::Serve<S>;
+}
+
+impl<F, Fut, Req> BeforeRequest<Req> for F
+where
+    F: FnMut(&mut context::Context, &Req) -> Fut,
+    Fut: Future<Output = Result<(), ServerError>>,
+{
+    async fn before(&mut self, ctx: &mut context::Context, req: &Req) -> Result<(), ServerError> {
+        self(ctx, req).await
+    }
+}
+
+/// A Service function that runs a hook before request execution.
+#[derive(Clone)]
+pub struct HookThenServe<Serv, Hook> {
+    serve: Serv,
+    hook: Hook,
+}
+
+impl<Serv, Hook> HookThenServe<Serv, Hook> {
+    pub(crate) fn new(serve: Serv, hook: Hook) -> Self {
+        Self { serve, hook }
+    }
+}
+
+impl<Serv, Hook> Serve for HookThenServe<Serv, Hook>
+where
+    Serv: Serve,
+    Hook: BeforeRequest<Serv::Req>,
+{
+    type Req = Serv::Req;
+    type Resp = Serv::Resp;
+
+    async fn serve(
+        self,
+        mut ctx: context::Context,
+        req: Self::Req,
+    ) -> Result<Serv::Resp, ServerError> {
+        let HookThenServe {
+            serve, mut hook, ..
+        } = self;
+        hook.before(&mut ctx, &req).await?;
+        serve.serve(ctx, req).await
+    }
+}
+
+/// Returns a request hook builder that runs a series of hooks before request execution.
+///
+/// Example
+///
+/// ```rust
+/// use futures::{executor::block_on, future};
+/// use tarpc::{context, ServerError, server::{Serve, serve, request_hook::{self,
+///             BeforeRequest, BeforeRequestList}}};
+/// use std::{cell::Cell, io};
+///
+/// let i = Cell::new(0);
+/// let serve = request_hook::before()
+///     .then_fn(|_, _| async {
+///         assert!(i.get() == 0);
+///         i.set(1);
+///         Ok(())
+///     })
+///     .then_fn(|_, _| async {
+///         assert!(i.get() == 1);
+///         i.set(2);
+///         Ok(())
+///     })
+///     .serving(serve(|_ctx, i| async move { Ok(i + 1) }));
+/// let response = serve.clone().serve(context::current(), 1);
+/// assert!(block_on(response).is_ok());
+/// assert!(i.get() == 2);
+/// ```
+pub fn before() -> BeforeRequestNil {
+    BeforeRequestNil
+}
+
+/// A list of hooks that run in order before a request is executed.
+#[derive(Clone, Copy)]
+pub struct BeforeRequestCons<First, Rest>(First, Rest);
+
+/// A noop hook that runs before a request is executed.
+#[derive(Clone, Copy)]
+pub struct BeforeRequestNil;
+
+impl<Req, First: BeforeRequest<Req>, Rest: BeforeRequest<Req>> BeforeRequest<Req>
+    for BeforeRequestCons<First, Rest>
+{
+    async fn before(&mut self, ctx: &mut context::Context, req: &Req) -> Result<(), ServerError> {
+        let BeforeRequestCons(first, rest) = self;
+        first.before(ctx, req).await?;
+        rest.before(ctx, req).await?;
+        Ok(())
+    }
+}
+
+impl<Req> BeforeRequest<Req> for BeforeRequestNil {
+    async fn before(&mut self, _: &mut context::Context, _: &Req) -> Result<(), ServerError> {
+        Ok(())
+    }
+}
+
+impl<Req, First: BeforeRequest<Req>, Rest: BeforeRequestList<Req>> BeforeRequestList<Req>
+    for BeforeRequestCons<First, Rest>
+{
+    type Then<Next> = BeforeRequestCons<First, Rest::Then<Next>> where Next: BeforeRequest<Req>;
+
+    fn then<Next: BeforeRequest<Req>>(self, next: Next) -> Self::Then<Next> {
+        let BeforeRequestCons(first, rest) = self;
+        BeforeRequestCons(first, rest.then(next))
+    }
+
+    type Serve<S: Serve<Req = Req>> = HookThenServe<S, Self>;
+
+    fn serving<S: Serve<Req = Req>>(self, serve: S) -> Self::Serve<S> {
+        HookThenServe::new(serve, self)
+    }
+}
+
+impl<Req> BeforeRequestList<Req> for BeforeRequestNil {
+    type Then<Next> = BeforeRequestCons<Next, BeforeRequestNil> where Next: BeforeRequest<Req>;
+
+    fn then<Next: BeforeRequest<Req>>(self, next: Next) -> Self::Then<Next> {
+        BeforeRequestCons(next, BeforeRequestNil)
+    }
+
+    type Serve<S: Serve<Req = Req>> = S;
+
+    fn serving<S: Serve<Req = Req>>(self, serve: S) -> S {
+        serve
+    }
+}
+
+#[test]
+fn before_request_list() {
+    use crate::server::serve;
+    use futures::executor::block_on;
+    use std::cell::Cell;
+
+    let i = Cell::new(0);
+    let serve = before()
+        .then_fn(|_, _| async {
+            assert!(i.get() == 0);
+            i.set(1);
+            Ok(())
+        })
+        .then_fn(|_, _| async {
+            assert!(i.get() == 1);
+            i.set(2);
+            Ok(())
+        })
+        .serving(serve(|_ctx, i| async move { Ok(i + 1) }));
+    let response = serve.clone().serve(context::current(), 1);
+    assert!(block_on(response).is_ok());
+    assert!(i.get() == 2);
+}

tarpc/src/server/request_hook/before_and_after.rs

@@ -0,0 +1,57 @@
+// Copyright 2022 Google LLC
+//
+// Use of this source code is governed by an MIT-style
+// license that can be found in the LICENSE file or at
+// https://opensource.org/licenses/MIT.
+
+//! Provides a hook that runs both before and after request execution.
+
+use super::{after::AfterRequest, before::BeforeRequest};
+use crate::{context, server::Serve, ServerError};
+use std::marker::PhantomData;
+
+/// A Service function that runs a hook both before and after request execution.
+pub struct HookThenServeThenHook<Req, Resp, Serv, Hook> {
+    serve: Serv,
+    hook: Hook,
+    fns: PhantomData<(fn(Req), fn(Resp))>,
+}
+
+impl<Req, Resp, Serv, Hook> HookThenServeThenHook<Req, Resp, Serv, Hook> {
+    pub(crate) fn new(serve: Serv, hook: Hook) -> Self {
+        Self {
+            serve,
+            hook,
+            fns: PhantomData,
+        }
+    }
+}
+
+impl<Req, Resp, Serv: Clone, Hook: Clone> Clone for HookThenServeThenHook<Req, Resp, Serv, Hook> {
+    fn clone(&self) -> Self {
+        Self {
+            serve: self.serve.clone(),
+            hook: self.hook.clone(),
+            fns: PhantomData,
+        }
+    }
+}
+
+impl<Req, Resp, Serv, Hook> Serve for HookThenServeThenHook<Req, Resp, Serv, Hook>
+where
+    Serv: Serve<Req = Req, Resp = Resp>,
+    Hook: BeforeRequest<Req> + AfterRequest<Resp>,
+{
+    type Req = Req;
+    type Resp = Resp;
+
+    async fn serve(self, mut ctx: context::Context, req: Req) -> Result<Serv::Resp, ServerError> {
+        let HookThenServeThenHook {
+            serve, mut hook, ..
+        } = self;
+        hook.before(&mut ctx, &req).await?;
+        let mut resp = serve.serve(ctx, req).await;
+        hook.after(&mut ctx, &mut resp).await;
+        resp
+    }
+}

tarpc/src/server/testing.rs

@@ -1,16 +1,19 @@
-use crate::server::{Channel, Config};
-use crate::{context, Request, Response};
-use fnv::FnvHashSet;
-use futures::{
-    future::{AbortHandle, AbortRegistration},
-    task::*,
-    Sink, Stream,
+// Copyright 2020 Google LLC
+//
+// Use of this source code is governed by an MIT-style
+// license that can be found in the LICENSE file or at
+// https://opensource.org/licenses/MIT.
+
+use crate::{
+    cancellations::{cancellations, CanceledRequests, RequestCancellation},
+    context,
+    server::{Channel, Config, ResponseGuard, TrackedRequest},
+    Request, Response,
 };
+use futures::{task::*, Sink, Stream};
 use pin_project::pin_project;
-use std::collections::VecDeque;
-use std::io;
-use std::pin::Pin;
-use std::time::SystemTime;
+use std::{collections::VecDeque, io, pin::Pin, time::SystemTime};
+use tracing::Span;
 
 #[pin_project]
 pub(crate) struct FakeChannel<In, Out> {
@@ -19,7 +22,9 @@ pub(crate) struct FakeChannel<In, Out> {
     #[pin]
     pub sink: VecDeque<Out>,
     pub config: Config,
-    pub in_flight_requests: FnvHashSet<u64>,
+    pub in_flight_requests: super::in_flight_requests::InFlightRequests,
+    pub request_cancellation: RequestCancellation,
+    pub canceled_requests: CanceledRequests,
 }
 
 impl<In, Out> Stream for FakeChannel<In, Out>
@@ -44,7 +49,7 @@ impl<In, Resp> Sink<Response<Resp>> for FakeChannel<In, Response<Resp>> {
         self.as_mut()
             .project()
             .in_flight_requests
-            .remove(&response.request_id);
+            .remove_request(response.request_id);
         self.project()
             .sink
             .start_send(response)
@@ -60,49 +65,61 @@ impl<In, Resp> Sink<Response<Resp>> for FakeChannel<In, Response<Resp>> {
     }
 }
 
-impl<Req, Resp> Channel for FakeChannel<io::Result<Request<Req>>, Response<Resp>>
+impl<Req, Resp> Channel for FakeChannel<io::Result<TrackedRequest<Req>>, Response<Resp>>
 where
     Req: Unpin,
 {
     type Req = Req;
     type Resp = Resp;
+    type Transport = ();
 
     fn config(&self) -> &Config {
         &self.config
     }
 
-    fn in_flight_requests(self: Pin<&mut Self>) -> usize {
+    fn in_flight_requests(&self) -> usize {
         self.in_flight_requests.len()
     }
 
-    fn start_request(self: Pin<&mut Self>, id: u64) -> AbortRegistration {
-        self.project().in_flight_requests.insert(id);
-        AbortHandle::new_pair().1
+    fn transport(&self) -> &() {
+        &()
     }
 }
 
-impl<Req, Resp> FakeChannel<io::Result<Request<Req>>, Response<Resp>> {
+impl<Req, Resp> FakeChannel<io::Result<TrackedRequest<Req>>, Response<Resp>> {
     pub fn push_req(&mut self, id: u64, message: Req) {
-        self.stream.push_back(Ok(Request {
-            context: context::Context {
-                deadline: SystemTime::UNIX_EPOCH,
-                trace_context: Default::default(),
-                _non_exhaustive: (),
+        let (_, abort_registration) = futures::future::AbortHandle::new_pair();
+        let (request_cancellation, _) = cancellations();
+        self.stream.push_back(Ok(TrackedRequest {
+            request: Request {
+                context: context::Context {
+                    deadline: SystemTime::UNIX_EPOCH,
+                    trace_context: Default::default(),
+                },
+                id,
+                message,
+            },
+            abort_registration,
+            span: Span::none(),
+            response_guard: ResponseGuard {
+                request_cancellation,
+                request_id: id,
+                cancel: false,
             },
-            id,
-            message,
-            _non_exhaustive: (),
         }));
     }
 }
 
 impl FakeChannel<(), ()> {
-    pub fn default<Req, Resp>() -> FakeChannel<io::Result<Request<Req>>, Response<Resp>> {
+    pub fn default<Req, Resp>() -> FakeChannel<io::Result<TrackedRequest<Req>>, Response<Resp>> {
+        let (request_cancellation, canceled_requests) = cancellations();
         FakeChannel {
             stream: Default::default(),
             sink: Default::default(),
             config: Default::default(),
             in_flight_requests: Default::default(),
+            request_cancellation,
+            canceled_requests,
         }
     }
 }
@@ -113,13 +130,10 @@ pub trait PollExt {
 
 impl<T> PollExt for Poll<Option<T>> {
     fn is_done(&self) -> bool {
-        match self {
-            Poll::Ready(None) => true,
-            _ => false,
-        }
+        matches!(self, Poll::Ready(None))
     }
 }
 
 pub fn cx() -> Context<'static> {
-    Context::from_waker(&noop_waker_ref())
+    Context::from_waker(noop_waker_ref())
 }

tarpc/src/trace.rs

@@ -16,18 +16,21 @@
 //! This crate's design is based on [opencensus
 //! tracing](https://opencensus.io/core-concepts/tracing/).
 
+use opentelemetry::trace::TraceContextExt;
 use rand::Rng;
 use std::{
+    convert::TryFrom,
     fmt::{self, Formatter},
-    mem,
+    num::{NonZeroU128, NonZeroU64},
 };
+use tracing_opentelemetry::OpenTelemetrySpanExt;
 
 /// A context for tracing the execution of processes, distributed or otherwise.
 ///
 /// Consists of a span identifying an event, an optional parent span identifying a causal event
 /// that triggered the current span, and a trace with which all related spans are associated.
 #[derive(Debug, Default, PartialEq, Eq, Hash, Clone, Copy)]
-#[cfg_attr(feature = "serde", derive(serde::Serialize, serde::Deserialize))]
+#[cfg_attr(feature = "serde1", derive(serde::Serialize, serde::Deserialize))]
 pub struct Context {
     /// An identifier of the trace associated with the current context. A trace ID is typically
     /// created at a root span and passed along through all causal events.
@@ -36,33 +39,50 @@ pub struct Context {
     /// before making an RPC, and the span ID is sent to the server. The server is free to create
     /// its own spans, for which it sets the client's span as the parent span.
     pub span_id: SpanId,
-    /// An identifier of the span that originated the current span. For example, if a server sends
-    /// an RPC in response to a client request that included a span, the server would create a span
-    /// for the RPC and set its parent to the span_id in the incoming request's context.
-    ///
-    /// If `parent_id` is `None`, then this is a root context.
-    pub parent_id: Option<SpanId>,
+    /// Indicates whether a sampler has already decided whether or not to sample the trace
+    /// associated with the Context. If `sampling_decision` is None, then a decision has not yet
+    /// been made. Downstream samplers do not need to abide by "no sample" decisions--for example,
+    /// an upstream client may choose to never sample, which may not make sense for the client's
+    /// dependencies. On the other hand, if an upstream process has chosen to sample this trace,
+    /// then the downstream samplers are expected to respect that decision and also sample the
+    /// trace. Otherwise, the full trace would not be able to be reconstructed.
+    pub sampling_decision: SamplingDecision,
 }
 
 /// A 128-bit UUID identifying a trace. All spans caused by the same originating span share the
 /// same trace ID.
-#[derive(Debug, Default, PartialEq, Eq, Hash, Clone, Copy)]
-#[cfg_attr(feature = "serde", derive(serde::Serialize, serde::Deserialize))]
-pub struct TraceId(u128);
+#[derive(Default, PartialEq, Eq, Hash, Clone, Copy)]
+#[cfg_attr(feature = "serde1", derive(serde::Serialize, serde::Deserialize))]
+pub struct TraceId(#[cfg_attr(feature = "serde1", serde(with = "u128_serde"))] u128);
 
 /// A 64-bit identifier of a span within a trace. The identifier is unique within the span's trace.
-#[derive(Debug, Default, PartialEq, Eq, Hash, Clone, Copy)]
-#[cfg_attr(feature = "serde", derive(serde::Serialize, serde::Deserialize))]
+#[derive(Default, PartialEq, Eq, Hash, Clone, Copy)]
+#[cfg_attr(feature = "serde1", derive(serde::Serialize, serde::Deserialize))]
 pub struct SpanId(u64);
 
+/// Indicates whether a sampler has decided whether or not to sample the trace associated with the
+/// Context. Downstream samplers do not need to abide by "no sample" decisions--for example, an
+/// upstream client may choose to never sample, which may not make sense for the client's
+/// dependencies. On the other hand, if an upstream process has chosen to sample this trace, then
+/// the downstream samplers are expected to respect that decision and also sample the trace.
+/// Otherwise, the full trace would not be able to be reconstructed reliably.
+#[derive(Debug, PartialEq, Eq, Hash, Clone, Copy)]
+#[cfg_attr(feature = "serde1", derive(serde::Serialize, serde::Deserialize))]
+#[repr(u8)]
+pub enum SamplingDecision {
+    /// The associated span was sampled by its creating process. Child spans must also be sampled.
+    Sampled,
+    /// The associated span was not sampled by its creating process.
+    Unsampled,
+}
+
 impl Context {
-    /// Constructs a new root context. A root context is one with no parent span.
-    pub fn new_root() -> Self {
-        let rng = &mut rand::thread_rng();
-        Context {
-            trace_id: TraceId::random(rng),
-            span_id: SpanId::random(rng),
-            parent_id: None,
+    /// Constructs a new context with the trace ID and sampling decision inherited from the parent.
+    pub(crate) fn new_child(&self) -> Self {
+        Self {
+            trace_id: self.trace_id,
+            span_id: SpanId::random(&mut rand::thread_rng()),
+            sampling_decision: self.sampling_decision,
         }
     }
 }
@@ -71,17 +91,128 @@ impl TraceId {
     /// Returns a random trace ID that can be assumed to be globally unique if `rng` generates
     /// actually-random numbers.
     pub fn random<R: Rng>(rng: &mut R) -> Self {
-        TraceId(u128::from(rng.next_u64()) << mem::size_of::<u64>() | u128::from(rng.next_u64()))
+        TraceId(rng.gen::<NonZeroU128>().get())
+    }
+
+    /// Returns true iff the trace ID is 0.
+    pub fn is_none(&self) -> bool {
+        self.0 == 0
     }
 }
 
 impl SpanId {
     /// Returns a random span ID that can be assumed to be unique within a single trace.
     pub fn random<R: Rng>(rng: &mut R) -> Self {
-        SpanId(rng.next_u64())
+        SpanId(rng.gen::<NonZeroU64>().get())
+    }
+
+    /// Returns true iff the span ID is 0.
+    pub fn is_none(&self) -> bool {
+        self.0 == 0
     }
 }
 
+impl From<TraceId> for u128 {
+    fn from(trace_id: TraceId) -> Self {
+        trace_id.0
+    }
+}
+
+impl From<u128> for TraceId {
+    fn from(trace_id: u128) -> Self {
+        Self(trace_id)
+    }
+}
+
+impl From<SpanId> for u64 {
+    fn from(span_id: SpanId) -> Self {
+        span_id.0
+    }
+}
+
+impl From<u64> for SpanId {
+    fn from(span_id: u64) -> Self {
+        Self(span_id)
+    }
+}
+
+impl From<opentelemetry::trace::TraceId> for TraceId {
+    fn from(trace_id: opentelemetry::trace::TraceId) -> Self {
+        Self::from(u128::from_be_bytes(trace_id.to_bytes()))
+    }
+}
+
+impl From<TraceId> for opentelemetry::trace::TraceId {
+    fn from(trace_id: TraceId) -> Self {
+        Self::from_bytes(u128::from(trace_id).to_be_bytes())
+    }
+}
+
+impl From<opentelemetry::trace::SpanId> for SpanId {
+    fn from(span_id: opentelemetry::trace::SpanId) -> Self {
+        Self::from(u64::from_be_bytes(span_id.to_bytes()))
+    }
+}
+
+impl From<SpanId> for opentelemetry::trace::SpanId {
+    fn from(span_id: SpanId) -> Self {
+        Self::from_bytes(u64::from(span_id).to_be_bytes())
+    }
+}
+
+impl TryFrom<&tracing::Span> for Context {
+    type Error = NoActiveSpan;
+
+    fn try_from(span: &tracing::Span) -> Result<Self, NoActiveSpan> {
+        let context = span.context();
+        if context.has_active_span() {
+            Ok(Self::from(context.span()))
+        } else {
+            Err(NoActiveSpan)
+        }
+    }
+}
+
+impl From<opentelemetry::trace::SpanRef<'_>> for Context {
+    fn from(span: opentelemetry::trace::SpanRef<'_>) -> Self {
+        let otel_ctx = span.span_context();
+        Self {
+            trace_id: TraceId::from(otel_ctx.trace_id()),
+            span_id: SpanId::from(otel_ctx.span_id()),
+            sampling_decision: SamplingDecision::from(otel_ctx),
+        }
+    }
+}
+
+impl From<SamplingDecision> for opentelemetry::trace::TraceFlags {
+    fn from(decision: SamplingDecision) -> Self {
+        match decision {
+            SamplingDecision::Sampled => opentelemetry::trace::TraceFlags::SAMPLED,
+            SamplingDecision::Unsampled => opentelemetry::trace::TraceFlags::default(),
+        }
+    }
+}
+
+impl From<&opentelemetry::trace::SpanContext> for SamplingDecision {
+    fn from(context: &opentelemetry::trace::SpanContext) -> Self {
+        if context.is_sampled() {
+            SamplingDecision::Sampled
+        } else {
+            SamplingDecision::Unsampled
+        }
+    }
+}
+
+impl Default for SamplingDecision {
+    fn default() -> Self {
+        Self::Unsampled
+    }
+}
+
+/// Returned when a [`Context`] cannot be constructed from a [`Span`](tracing::Span).
+#[derive(Debug)]
+pub struct NoActiveSpan;
+
 impl fmt::Display for TraceId {
     fn fmt(&self, f: &mut Formatter) -> Result<(), fmt::Error> {
         write!(f, "{:02x}", self.0)?;
@@ -89,9 +220,42 @@ impl fmt::Display for TraceId {
     }
 }
 
+impl fmt::Debug for TraceId {
+    fn fmt(&self, f: &mut Formatter) -> Result<(), fmt::Error> {
+        write!(f, "{:02x}", self.0)?;
+        Ok(())
+    }
+}
+
 impl fmt::Display for SpanId {
     fn fmt(&self, f: &mut Formatter) -> Result<(), fmt::Error> {
         write!(f, "{:02x}", self.0)?;
         Ok(())
     }
 }
+
+impl fmt::Debug for SpanId {
+    fn fmt(&self, f: &mut Formatter) -> Result<(), fmt::Error> {
+        write!(f, "{:02x}", self.0)?;
+        Ok(())
+    }
+}
+
+#[cfg(feature = "serde1")]
+mod u128_serde {
+    pub fn serialize<S>(u: &u128, serializer: S) -> Result<S::Ok, S::Error>
+    where
+        S: serde::Serializer,
+    {
+        serde::Serialize::serialize(&u.to_le_bytes(), serializer)
+    }
+
+    pub fn deserialize<'de, D>(deserializer: D) -> Result<u128, D::Error>
+    where
+        D: serde::Deserializer<'de>,
+    {
+        Ok(u128::from_le_bytes(serde::Deserialize::deserialize(
+            deserializer,
+        )?))
+    }
+}

tarpc/src/transport.rs

@@ -0,0 +1,40 @@
+// Copyright 2018 Google LLC
+//
+// Use of this source code is governed by an MIT-style
+// license that can be found in the LICENSE file or at
+// https://opensource.org/licenses/MIT.
+
+//! Provides a [`Transport`](sealed::Transport) trait as well as implementations.
+//!
+//! The rpc crate is transport- and protocol-agnostic. Any transport that impls [`Transport`](sealed::Transport)
+//! can be plugged in, using whatever protocol it wants.
+
+pub mod channel;
+
+pub(crate) mod sealed {
+    use futures::prelude::*;
+    use std::error::Error;
+
+    /// A bidirectional stream ([`Sink`] + [`Stream`]) of messages.
+    pub trait Transport<SinkItem, Item>
+    where
+        Self: Stream<Item = Result<Item, <Self as Sink<SinkItem>>::Error>>,
+        Self: Sink<SinkItem, Error = <Self as Transport<SinkItem, Item>>::TransportError>,
+        <Self as Sink<SinkItem>>::Error: Error,
+    {
+        /// Associated type where clauses are not elaborated; this associated type allows users
+        /// bounding types by Transport to avoid having to explicitly add `T::Error: Error` to their
+        /// bounds.
+        type TransportError: Error + Send + Sync + 'static;
+    }
+
+    impl<T, SinkItem, Item, E> Transport<SinkItem, Item> for T
+    where
+        T: ?Sized,
+        T: Stream<Item = Result<Item, E>>,
+        T: Sink<SinkItem, Error = E>,
+        T::Error: Error + Send + Sync + 'static,
+    {
+        type TransportError = E;
+    }
+}

tarpc/src/transport/channel.rs

@@ -0,0 +1,219 @@
+// Copyright 2018 Google LLC
+//
+// Use of this source code is governed by an MIT-style
+// license that can be found in the LICENSE file or at
+// https://opensource.org/licenses/MIT.
+
+//! Transports backed by in-memory channels.
+
+use futures::{task::*, Sink, Stream};
+use pin_project::pin_project;
+use std::{error::Error, pin::Pin};
+use tokio::sync::mpsc;
+
+/// Errors that occur in the sending or receiving of messages over a channel.
+#[derive(thiserror::Error, Debug)]
+pub enum ChannelError {
+    /// An error occurred readying to send into the channel.
+    #[error("an error occurred readying to send into the channel")]
+    Ready(#[source] Box<dyn Error + Send + Sync + 'static>),
+    /// An error occurred sending into the channel.
+    #[error("an error occurred sending into the channel")]
+    Send(#[source] Box<dyn Error + Send + Sync + 'static>),
+    /// An error occurred receiving from the channel.
+    #[error("an error occurred receiving from the channel")]
+    Receive(#[source] Box<dyn Error + Send + Sync + 'static>),
+}
+
+/// Returns two unbounded channel peers. Each [`Stream`] yields items sent through the other's
+/// [`Sink`].
+pub fn unbounded<SinkItem, Item>() -> (
+    UnboundedChannel<SinkItem, Item>,
+    UnboundedChannel<Item, SinkItem>,
+) {
+    let (tx1, rx2) = mpsc::unbounded_channel();
+    let (tx2, rx1) = mpsc::unbounded_channel();
+    (
+        UnboundedChannel { tx: tx1, rx: rx1 },
+        UnboundedChannel { tx: tx2, rx: rx2 },
+    )
+}
+
+/// A bi-directional channel backed by an [`UnboundedSender`](mpsc::UnboundedSender)
+/// and [`UnboundedReceiver`](mpsc::UnboundedReceiver).
+#[derive(Debug)]
+pub struct UnboundedChannel<Item, SinkItem> {
+    rx: mpsc::UnboundedReceiver<Item>,
+    tx: mpsc::UnboundedSender<SinkItem>,
+}
+
+impl<Item, SinkItem> Stream for UnboundedChannel<Item, SinkItem> {
+    type Item = Result<Item, ChannelError>;
+
+    fn poll_next(
+        mut self: Pin<&mut Self>,
+        cx: &mut Context<'_>,
+    ) -> Poll<Option<Result<Item, ChannelError>>> {
+        self.rx
+            .poll_recv(cx)
+            .map(|option| option.map(Ok))
+            .map_err(ChannelError::Receive)
+    }
+}
+
+const CLOSED_MESSAGE: &str = "the channel is closed and cannot accept new items for sending";
+
+impl<Item, SinkItem> Sink<SinkItem> for UnboundedChannel<Item, SinkItem> {
+    type Error = ChannelError;
+
+    fn poll_ready(self: Pin<&mut Self>, _: &mut Context<'_>) -> Poll<Result<(), Self::Error>> {
+        Poll::Ready(if self.tx.is_closed() {
+            Err(ChannelError::Ready(CLOSED_MESSAGE.into()))
+        } else {
+            Ok(())
+        })
+    }
+
+    fn start_send(self: Pin<&mut Self>, item: SinkItem) -> Result<(), Self::Error> {
+        self.tx
+            .send(item)
+            .map_err(|_| ChannelError::Send(CLOSED_MESSAGE.into()))
+    }
+
+    fn poll_flush(self: Pin<&mut Self>, _: &mut Context<'_>) -> Poll<Result<(), Self::Error>> {
+        // UnboundedSender requires no flushing.
+        Poll::Ready(Ok(()))
+    }
+
+    fn poll_close(self: Pin<&mut Self>, _: &mut Context<'_>) -> Poll<Result<(), Self::Error>> {
+        // UnboundedSender can't initiate closure.
+        Poll::Ready(Ok(()))
+    }
+}
+
+/// Returns two channel peers with buffer equal to `capacity`. Each [`Stream`] yields items sent
+/// through the other's [`Sink`].
+pub fn bounded<SinkItem, Item>(
+    capacity: usize,
+) -> (Channel<SinkItem, Item>, Channel<Item, SinkItem>) {
+    let (tx1, rx2) = futures::channel::mpsc::channel(capacity);
+    let (tx2, rx1) = futures::channel::mpsc::channel(capacity);
+    (Channel { tx: tx1, rx: rx1 }, Channel { tx: tx2, rx: rx2 })
+}
+
+/// A bi-directional channel backed by a [`Sender`](futures::channel::mpsc::Sender)
+/// and [`Receiver`](futures::channel::mpsc::Receiver).
+#[pin_project]
+#[derive(Debug)]
+pub struct Channel<Item, SinkItem> {
+    #[pin]
+    rx: futures::channel::mpsc::Receiver<Item>,
+    #[pin]
+    tx: futures::channel::mpsc::Sender<SinkItem>,
+}
+
+impl<Item, SinkItem> Stream for Channel<Item, SinkItem> {
+    type Item = Result<Item, ChannelError>;
+
+    fn poll_next(
+        self: Pin<&mut Self>,
+        cx: &mut Context<'_>,
+    ) -> Poll<Option<Result<Item, ChannelError>>> {
+        self.project()
+            .rx
+            .poll_next(cx)
+            .map(|option| option.map(Ok))
+            .map_err(ChannelError::Receive)
+    }
+}
+
+impl<Item, SinkItem> Sink<SinkItem> for Channel<Item, SinkItem> {
+    type Error = ChannelError;
+
+    fn poll_ready(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Result<(), Self::Error>> {
+        self.project()
+            .tx
+            .poll_ready(cx)
+            .map_err(|e| ChannelError::Ready(Box::new(e)))
+    }
+
+    fn start_send(self: Pin<&mut Self>, item: SinkItem) -> Result<(), Self::Error> {
+        self.project()
+            .tx
+            .start_send(item)
+            .map_err(|e| ChannelError::Send(Box::new(e)))
+    }
+
+    fn poll_flush(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Result<(), Self::Error>> {
+        self.project()
+            .tx
+            .poll_flush(cx)
+            .map_err(|e| ChannelError::Send(Box::new(e)))
+    }
+
+    fn poll_close(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Result<(), Self::Error>> {
+        self.project()
+            .tx
+            .poll_close(cx)
+            .map_err(|e| ChannelError::Send(Box::new(e)))
+    }
+}
+
+#[cfg(all(test, feature = "tokio1"))]
+mod tests {
+    use crate::{
+        client::{self, RpcError},
+        context,
+        server::{incoming::Incoming, serve, BaseChannel},
+        transport::{
+            self,
+            channel::{Channel, UnboundedChannel},
+        },
+        ServerError,
+    };
+    use assert_matches::assert_matches;
+    use futures::{prelude::*, stream};
+    use std::io;
+    use tracing::trace;
+
+    #[test]
+    fn ensure_is_transport() {
+        fn is_transport<SinkItem, Item, T: crate::Transport<SinkItem, Item>>() {}
+        is_transport::<(), (), UnboundedChannel<(), ()>>();
+        is_transport::<(), (), Channel<(), ()>>();
+    }
+
+    #[tokio::test]
+    async fn integration() -> anyhow::Result<()> {
+        let _ = tracing_subscriber::fmt::try_init();
+
+        let (client_channel, server_channel) = transport::channel::unbounded();
+        tokio::spawn(
+            stream::once(future::ready(server_channel))
+                .map(BaseChannel::with_defaults)
+                .execute(serve(|_ctx, request: String| async move {
+                    request.parse::<u64>().map_err(|_| {
+                        ServerError::new(
+                            io::ErrorKind::InvalidInput,
+                            format!("{request:?} is not an int"),
+                        )
+                    })
+                }))
+                .for_each(|channel| async move {
+                    tokio::spawn(channel.for_each(|response| response));
+                }),
+        );
+
+        let client = client::new(client::Config::default(), client_channel).spawn();
+
+        let response1 = client.call(context::current(), "", "123".into()).await;
+        let response2 = client.call(context::current(), "", "abc".into()).await;
+
+        trace!("response1: {:?}, response2: {:?}", response1, response2);
+
+        assert_matches!(response1, Ok(123));
+        assert_matches!(response2, Err(RpcError::Server(e)) if e.kind == io::ErrorKind::InvalidInput);
+
+        Ok(())
+    }
+}

tarpc/src/util.rs

@@ -10,7 +10,8 @@ use std::{
     time::{Duration, SystemTime},
 };
 
-#[cfg(feature = "serde")]
+#[cfg(feature = "serde1")]
+#[cfg_attr(docsrs, doc(cfg(feature = "serde1")))]
 pub mod serde;
 
 /// Extension trait for [SystemTimes](SystemTime) in the future, i.e. deadlines.
@@ -37,11 +38,34 @@ where
     H: BuildHasher,
 {
     fn compact(&mut self, usage_ratio_threshold: f64) {
-        if self.capacity() > 1000 {
-            let usage_ratio = self.len() as f64 / self.capacity() as f64;
-            if usage_ratio < usage_ratio_threshold {
-                self.shrink_to_fit();
-            }
-        }
+        let usage_ratio_threshold = usage_ratio_threshold.clamp(f64::MIN_POSITIVE, 1.);
+        let cap = f64::max(1000., self.len() as f64 / usage_ratio_threshold);
+        self.shrink_to(cap as usize);
     }
 }
+
+#[test]
+fn test_compact() {
+    let mut map = HashMap::with_capacity(2048);
+    assert_eq!(map.capacity(), 3584);
+
+    // Make usage ratio 25%
+    for i in 0..896 {
+        map.insert(format!("k{i}"), "v");
+    }
+
+    map.compact(-1.0);
+    assert_eq!(map.capacity(), 3584);
+
+    map.compact(0.25);
+    assert_eq!(map.capacity(), 3584);
+
+    map.compact(0.50);
+    assert_eq!(map.capacity(), 1792);
+
+    map.compact(1.0);
+    assert_eq!(map.capacity(), 1792);
+
+    map.compact(2.0);
+    assert_eq!(map.capacity(), 1792);
+}

tarpc/src/util/serde.rs

@@ -5,30 +5,7 @@
 // https://opensource.org/licenses/MIT.
 
 use serde::{Deserialize, Deserializer, Serialize, Serializer};
-use std::{
-    io,
-    time::{Duration, SystemTime},
-};
-
-/// Serializes `system_time` as a `u64` equal to the number of seconds since the epoch.
-pub fn serialize_epoch_secs<S>(system_time: &SystemTime, serializer: S) -> Result<S::Ok, S::Error>
-where
-    S: Serializer,
-{
-    system_time
-        .duration_since(SystemTime::UNIX_EPOCH)
-        .unwrap_or(Duration::from_secs(0))
-        .as_secs() // Only care about second precision
-        .serialize(serializer)
-}
-
-/// Deserializes [`SystemTime`] from a `u64` equal to the number of seconds since the epoch.
-pub fn deserialize_epoch_secs<'de, D>(deserializer: D) -> Result<SystemTime, D::Error>
-where
-    D: Deserializer<'de>,
-{
-    Ok(SystemTime::UNIX_EPOCH + Duration::from_secs(u64::deserialize(deserializer)?))
-}
+use std::io;
 
 /// Serializes [`io::ErrorKind`] as a `u32`.
 #[allow(clippy::trivially_copy_pass_by_ref)] // Exact fn signature required by serde derive

tarpc/tests/compile_fail.rs

@@ -0,0 +1,7 @@
+#[test]
+fn ui() {
+    let t = trybuild::TestCases::new();
+    t.compile_fail("tests/compile_fail/*.rs");
+    #[cfg(all(feature = "serde-transport", feature = "tcp"))]
+    t.compile_fail("tests/compile_fail/serde_transport/*.rs");
+}

tarpc/tests/compile_fail/must_use_request_dispatch.rs

@@ -0,0 +1,15 @@
+use tarpc::client;
+
+#[tarpc::service]
+trait World {
+    async fn hello(name: String) -> String;
+}
+
+fn main() {
+    let (client_transport, _) = tarpc::transport::channel::unbounded();
+
+    #[deny(unused_must_use)]
+    {
+        WorldClient::new(client::Config::default(), client_transport).dispatch;
+    }
+}

tarpc/tests/compile_fail/must_use_request_dispatch.stderr

@@ -0,0 +1,15 @@
+error: unused `RequestDispatch` that must be used
+  --> tests/compile_fail/must_use_request_dispatch.rs:13:9
+   |
+13 |         WorldClient::new(client::Config::default(), client_transport).dispatch;
+   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+note: the lint level is defined here
+  --> tests/compile_fail/must_use_request_dispatch.rs:11:12
+   |
+11 |     #[deny(unused_must_use)]
+   |            ^^^^^^^^^^^^^^^
+help: use `let _ = ...` to ignore the resulting value
+   |
+13 |         let _ = WorldClient::new(client::Config::default(), client_transport).dispatch;
+   |         +++++++

tarpc/tests/compile_fail/serde_transport/must_use_tcp_connect.rs

@@ -0,0 +1,9 @@
+use tarpc::serde_transport;
+use tokio_serde::formats::Json;
+
+fn main() {
+    #[deny(unused_must_use)]
+    {
+        serde_transport::tcp::connect::<_, (), (), _, _>("0.0.0.0:0", Json::default);
+    }
+}

tarpc/tests/compile_fail/serde_transport/must_use_tcp_connect.stderr

@@ -0,0 +1,15 @@
+error: unused `tarpc::serde_transport::tcp::Connect` that must be used
+ --> tests/compile_fail/serde_transport/must_use_tcp_connect.rs:7:9
+  |
+7 |         serde_transport::tcp::connect::<_, (), (), _, _>("0.0.0.0:0", Json::default);
+  |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+  |
+note: the lint level is defined here
+ --> tests/compile_fail/serde_transport/must_use_tcp_connect.rs:5:12
+  |
+5 |     #[deny(unused_must_use)]
+  |            ^^^^^^^^^^^^^^^
+help: use `let _ = ...` to ignore the resulting value
+  |
+7 |         let _ = serde_transport::tcp::connect::<_, (), (), _, _>("0.0.0.0:0", Json::default);
+  |         +++++++

tarpc/tests/compile_fail/tarpc_service_arg_pat.rs

@@ -0,0 +1,6 @@
+#[tarpc::service]
+trait World {
+    async fn pat((a, b): (u8, u32));
+}
+
+fn main() {}

tarpc/tests/compile_fail/tarpc_service_arg_pat.stderr

@@ -0,0 +1,5 @@
+error: patterns aren't allowed in RPC args
+ --> $DIR/tarpc_service_arg_pat.rs:3:18
+  |
+3 |     async fn pat((a, b): (u8, u32));
+  |                  ^^^^^^

tarpc/tests/compile_fail/tarpc_service_fn_new.rs

@@ -0,0 +1,6 @@
+#[tarpc::service]
+trait World {
+    async fn new();
+}
+
+fn main() {}

tarpc/tests/compile_fail/tarpc_service_fn_new.stderr

@@ -0,0 +1,5 @@
+error: method name conflicts with generated fn `WorldClient::new`
+ --> $DIR/tarpc_service_fn_new.rs:3:14
+  |
+3 |     async fn new();
+  |              ^^^

tarpc/tests/compile_fail/tarpc_service_fn_serve.rs

@@ -0,0 +1,6 @@
+#[tarpc::service]
+trait World {
+    async fn serve();
+}
+
+fn main() {}

tarpc/tests/compile_fail/tarpc_service_fn_serve.stderr

@@ -0,0 +1,5 @@
+error: method name conflicts with generated fn `World::serve`
+ --> $DIR/tarpc_service_fn_serve.rs:3:14
+  |
+3 |     async fn serve();
+  |              ^^^^^

tarpc/tests/dataservice.rs

@@ -0,0 +1,61 @@
+use futures::prelude::*;
+use tarpc::serde_transport;
+use tarpc::{
+    client, context,
+    server::{incoming::Incoming, BaseChannel},
+};
+use tokio_serde::formats::Json;
+
+#[tarpc::derive_serde]
+#[derive(Debug, PartialEq, Eq)]
+pub enum TestData {
+    Black,
+    White,
+}
+
+#[tarpc::service]
+pub trait ColorProtocol {
+    async fn get_opposite_color(color: TestData) -> TestData;
+}
+
+#[derive(Clone)]
+struct ColorServer;
+
+impl ColorProtocol for ColorServer {
+    async fn get_opposite_color(self, _: context::Context, color: TestData) -> TestData {
+        match color {
+            TestData::White => TestData::Black,
+            TestData::Black => TestData::White,
+        }
+    }
+}
+
+#[cfg(test)]
+async fn spawn(fut: impl Future<Output = ()> + Send + 'static) {
+    tokio::spawn(fut);
+}
+
+#[tokio::test]
+async fn test_call() -> anyhow::Result<()> {
+    let transport = tarpc::serde_transport::tcp::listen("localhost:56797", Json::default).await?;
+    let addr = transport.local_addr();
+    tokio::spawn(
+        transport
+            .take(1)
+            .filter_map(|r| async { r.ok() })
+            .map(BaseChannel::with_defaults)
+            .execute(ColorServer.serve())
+            .map(|channel| channel.for_each(spawn))
+            .for_each(spawn),
+    );
+
+    let transport = serde_transport::tcp::connect(addr, Json::default).await?;
+    let client = ColorProtocolClient::new(client::Config::default(), transport).spawn();
+
+    let color = client
+        .get_opposite_color(context::current(), TestData::White)
+        .await?;
+    assert_eq!(color, TestData::Black);
+
+    Ok(())
+}

tarpc/tests/proc_macro_hygene.rs

@@ -0,0 +1,17 @@
+#![no_implicit_prelude]
+extern crate tarpc as some_random_other_name;
+
+#[cfg(feature = "serde1")]
+mod serde1_feature {
+    #[::tarpc::derive_serde]
+    #[derive(Debug, PartialEq, Eq)]
+    pub enum TestData {
+        Black,
+        White,
+    }
+}
+
+#[::tarpc::service]
+pub trait ColorProtocol {
+    async fn get_opposite_color(color: u8) -> u8;
+}

tarpc/tests/service_functional.rs

@@ -1,16 +1,16 @@
 use assert_matches::assert_matches;
 use futures::{
-    future::{ready, Ready},
+    future::{join_all, ready},
     prelude::*,
 };
-use std::io;
+use std::time::{Duration, SystemTime};
 use tarpc::{
     client::{self},
-    context, serde_transport,
-    server::{self, BaseChannel, Channel, Handler},
+    context,
+    server::{incoming::Incoming, BaseChannel, Channel},
     transport::channel,
 };
-use tokio_serde::formats::Json;
+use tokio::join;
 
 #[tarpc_plugins::service]
 trait Service {
@@ -22,56 +22,101 @@ trait Service {
 struct Server;
 
 impl Service for Server {
-    type AddFut = Ready<i32>;
-
-    fn add(self, _: context::Context, x: i32, y: i32) -> Self::AddFut {
-        ready(x + y)
+    async fn add(self, _: context::Context, x: i32, y: i32) -> i32 {
+        x + y
     }
 
-    type HeyFut = Ready<String>;
-
-    fn hey(self, _: context::Context, name: String) -> Self::HeyFut {
-        ready(format!("Hey, {}.", name))
+    async fn hey(self, _: context::Context, name: String) -> String {
+        format!("Hey, {name}.")
     }
 }
 
-#[tokio::test(threaded_scheduler)]
-async fn sequential() -> io::Result<()> {
-    let _ = env_logger::try_init();
+#[tokio::test]
+async fn sequential() {
+    let (tx, rx) = tarpc::transport::channel::unbounded();
+    let client = client::new(client::Config::default(), tx).spawn();
+    let channel = BaseChannel::with_defaults(rx);
+    tokio::spawn(
+        channel
+            .execute(tarpc::server::serve(|_, i| async move { Ok(i + 1) }))
+            .for_each(|response| response),
+    );
+    assert_eq!(
+        client.call(context::current(), "AddOne", 1).await.unwrap(),
+        2
+    );
+}
+
+#[tokio::test]
+async fn dropped_channel_aborts_in_flight_requests() -> anyhow::Result<()> {
+    #[tarpc_plugins::service]
+    trait Loop {
+        async fn r#loop();
+    }
+
+    #[derive(Clone)]
+    struct LoopServer;
+
+    #[derive(Debug)]
+    struct AllHandlersComplete;
+
+    impl Loop for LoopServer {
+        async fn r#loop(self, _: context::Context) {
+            loop {
+                futures::pending!();
+            }
+        }
+    }
+
+    let _ = tracing_subscriber::fmt::try_init();
 
     let (tx, rx) = channel::unbounded();
 
-    tokio::spawn(
-        BaseChannel::new(server::Config::default(), rx)
-            .respond_with(Server.serve())
-            .execute(),
-    );
+    // Set up a client that initiates a long-lived request.
+    // The request will complete in error when the server drops the connection.
+    tokio::spawn(async move {
+        let client = LoopClient::new(client::Config::default(), tx).spawn();
 
-    let mut client = ServiceClient::new(client::Config::default(), tx).spawn()?;
+        let mut ctx = context::current();
+        ctx.deadline = SystemTime::now() + Duration::from_secs(60 * 60);
+        let _ = client.r#loop(ctx).await;
+    });
 
-    assert_matches!(client.add(context::current(), 1, 2).await, Ok(3));
-    assert_matches!(
-        client.hey(context::current(), "Tim".into()).await,
-        Ok(ref s) if s == "Hey, Tim.");
+    let mut requests = BaseChannel::with_defaults(rx).requests();
+    // Reading a request should trigger the request being registered with BaseChannel.
+    let first_request = requests.next().await.unwrap()?;
+    // Dropping the channel should trigger cleanup of outstanding requests.
+    drop(requests);
+    // In-flight requests should be aborted by channel cleanup.
+    // The first and only request sent by the client is `loop`, which is an infinite loop
+    // on the server side, so if cleanup was not triggered, this line should hang indefinitely.
+    first_request.execute(LoopServer.serve()).await;
 
     Ok(())
 }
 
-#[cfg(feature = "serde1")]
-#[tokio::test(threaded_scheduler)]
-async fn serde() -> io::Result<()> {
-    let _ = env_logger::try_init();
+#[cfg(all(feature = "serde-transport", feature = "tcp"))]
+#[tokio::test]
+async fn serde_tcp() -> anyhow::Result<()> {
+    use tarpc::serde_transport;
+    use tokio_serde::formats::Json;
 
-    let transport = serde_transport::tcp::listen("localhost:56789", Json::default).await?;
+    let _ = tracing_subscriber::fmt::try_init();
+
+    let transport = tarpc::serde_transport::tcp::listen("localhost:56789", Json::default).await?;
     let addr = transport.local_addr();
     tokio::spawn(
-        tarpc::Server::default()
-            .incoming(transport.take(1).filter_map(|r| async { r.ok() }))
-            .respond_with(Server.serve()),
+        transport
+            .take(1)
+            .filter_map(|r| async { r.ok() })
+            .map(BaseChannel::with_defaults)
+            .execute(Server.serve())
+            .map(|channel| channel.for_each(spawn))
+            .for_each(spawn),
     );
 
-    let transport = serde_transport::tcp::connect(addr, Json::default()).await?;
-    let mut client = ServiceClient::new(client::Config::default(), transport).spawn()?;
+    let transport = serde_transport::tcp::connect(addr, Json::default).await?;
+    let client = ServiceClient::new(client::Config::default(), transport).spawn();
 
     assert_matches!(client.add(context::current(), 1, 2).await, Ok(3));
     assert_matches!(
@@ -82,27 +127,57 @@ async fn serde() -> io::Result<()> {
     Ok(())
 }
 
-#[tokio::test(threaded_scheduler)]
-async fn concurrent() -> io::Result<()> {
-    let _ = env_logger::try_init();
+#[cfg(all(feature = "serde-transport", feature = "unix", unix))]
+#[tokio::test]
+async fn serde_uds() -> anyhow::Result<()> {
+    use tarpc::serde_transport;
+    use tokio_serde::formats::Json;
+
+    let _ = tracing_subscriber::fmt::try_init();
+
+    let sock = tarpc::serde_transport::unix::TempPathBuf::with_random("uds");
+    let transport = tarpc::serde_transport::unix::listen(&sock, Json::default).await?;
+    tokio::spawn(
+        transport
+            .take(1)
+            .filter_map(|r| async { r.ok() })
+            .map(BaseChannel::with_defaults)
+            .execute(Server.serve())
+            .map(|channel| channel.for_each(spawn))
+            .for_each(spawn),
+    );
+
+    let transport = serde_transport::unix::connect(&sock, Json::default).await?;
+    let client = ServiceClient::new(client::Config::default(), transport).spawn();
+
+    // Save results using socket so we can clean the socket even if our test assertions fail
+    let res1 = client.add(context::current(), 1, 2).await;
+    let res2 = client.hey(context::current(), "Tim".to_string()).await;
+
+    assert_matches!(res1, Ok(3));
+    assert_matches!(res2, Ok(ref s) if s == "Hey, Tim.");
+
+    Ok(())
+}
+
+#[tokio::test]
+async fn concurrent() -> anyhow::Result<()> {
+    let _ = tracing_subscriber::fmt::try_init();
 
     let (tx, rx) = channel::unbounded();
     tokio::spawn(
-        tarpc::Server::default()
-            .incoming(stream::once(ready(rx)))
-            .respond_with(Server.serve()),
+        stream::once(ready(rx))
+            .map(BaseChannel::with_defaults)
+            .execute(Server.serve())
+            .map(|channel| channel.for_each(spawn))
+            .for_each(spawn),
     );
 
-    let client = ServiceClient::new(client::Config::default(), tx).spawn()?;
+    let client = ServiceClient::new(client::Config::default(), tx).spawn();
 
-    let mut c = client.clone();
-    let req1 = c.add(context::current(), 1, 2);
-
-    let mut c = client.clone();
-    let req2 = c.add(context::current(), 3, 4);
-
-    let mut c = client.clone();
-    let req3 = c.hey(context::current(), "Tim".to_string());
+    let req1 = client.add(context::current(), 1, 2);
+    let req2 = client.add(context::current(), 3, 4);
+    let req3 = client.hey(context::current(), "Tim".to_string());
 
     assert_matches!(req1.await, Ok(3));
     assert_matches!(req2.await, Ok(7));
@@ -110,3 +185,91 @@ async fn concurrent() -> io::Result<()> {
 
     Ok(())
 }
+
+#[tokio::test]
+async fn concurrent_join() -> anyhow::Result<()> {
+    let _ = tracing_subscriber::fmt::try_init();
+
+    let (tx, rx) = channel::unbounded();
+    tokio::spawn(
+        stream::once(ready(rx))
+            .map(BaseChannel::with_defaults)
+            .execute(Server.serve())
+            .map(|channel| channel.for_each(spawn))
+            .for_each(spawn),
+    );
+
+    let client = ServiceClient::new(client::Config::default(), tx).spawn();
+
+    let req1 = client.add(context::current(), 1, 2);
+    let req2 = client.add(context::current(), 3, 4);
+    let req3 = client.hey(context::current(), "Tim".to_string());
+
+    let (resp1, resp2, resp3) = join!(req1, req2, req3);
+    assert_matches!(resp1, Ok(3));
+    assert_matches!(resp2, Ok(7));
+    assert_matches!(resp3, Ok(ref s) if s == "Hey, Tim.");
+
+    Ok(())
+}
+
+#[cfg(test)]
+async fn spawn(fut: impl Future<Output = ()> + Send + 'static) {
+    tokio::spawn(fut);
+}
+
+#[tokio::test]
+async fn concurrent_join_all() -> anyhow::Result<()> {
+    let _ = tracing_subscriber::fmt::try_init();
+
+    let (tx, rx) = channel::unbounded();
+    tokio::spawn(
+        BaseChannel::with_defaults(rx)
+            .execute(Server.serve())
+            .for_each(spawn),
+    );
+
+    let client = ServiceClient::new(client::Config::default(), tx).spawn();
+
+    let req1 = client.add(context::current(), 1, 2);
+    let req2 = client.add(context::current(), 3, 4);
+
+    let responses = join_all(vec![req1, req2]).await;
+    assert_matches!(responses[0], Ok(3));
+    assert_matches!(responses[1], Ok(7));
+
+    Ok(())
+}
+
+#[tokio::test]
+async fn counter() -> anyhow::Result<()> {
+    #[tarpc::service]
+    trait Counter {
+        async fn count() -> u32;
+    }
+
+    struct CountService(u32);
+
+    impl Counter for &mut CountService {
+        async fn count(self, _: context::Context) -> u32 {
+            self.0 += 1;
+            self.0
+        }
+    }
+
+    let (tx, rx) = channel::unbounded();
+    tokio::spawn(async {
+        let mut requests = BaseChannel::with_defaults(rx).requests();
+        let mut counter = CountService(0);
+
+        while let Some(Ok(request)) = requests.next().await {
+            request.execute(counter.serve()).await;
+        }
+    });
+
+    let client = CounterClient::new(client::Config::default(), tx).spawn();
+    assert_matches!(client.count(context::current()).await, Ok(1));
+    assert_matches!(client.count(context::current()).await, Ok(2));
+
+    Ok(())
+}