Prepare release of 0.30.0

This trait fn returns a private type, which means it's useless for
anyone using the Channel.

Instead, add an inert (now-public) ResponseGuard to TrackedRequest that,
when taken out of the ManuallyDrop, ensures a Channel's request state is
cleaned up. It's preferable to make ResponseGuard public instead of
RequestCancellations because it's a smaller API surface (no public
methods, just a Drop fn) and harder to misuse, because it is already
associated with the correct request ID to cancel.

.github/workflows/main.yml

@@ -0,0 +1,112 @@
+on:
+  push:
+    branches:
+    - master
+  pull_request:
+    branches:
+    - master
+
+name: Continuous integration
+
+jobs:
+  check:
+    name: Check
+    runs-on: ubuntu-latest
+    steps:
+      - name: Cancel previous
+        uses: styfle/cancel-workflow-action@0.7.0
+        with:
+          access_token: ${{ github.token }}
+      - uses: actions/checkout@v1
+      - uses: actions-rs/toolchain@v1
+        with:
+          profile: minimal
+          toolchain: stable
+          target: mipsel-unknown-linux-gnu
+          override: true
+      - uses: actions-rs/cargo@v1
+        with:
+          command: check
+          args: --all-features
+      - uses: actions-rs/cargo@v1
+        with:
+          command: check
+          args: --all-features --target mipsel-unknown-linux-gnu
+
+  test:
+    name: Test Suite
+    runs-on: ubuntu-latest
+    steps:
+      - name: Cancel previous
+        uses: styfle/cancel-workflow-action@0.7.0
+        with:
+          access_token: ${{ github.token }}
+      - uses: actions/checkout@v1
+      - uses: actions-rs/toolchain@v1
+        with:
+          profile: minimal
+          toolchain: stable
+          override: true
+      - uses: actions-rs/cargo@v1
+        with:
+          command: test
+      - uses: actions-rs/cargo@v1
+        with:
+          command: test
+          args: --manifest-path tarpc/Cargo.toml --features serde1
+      - uses: actions-rs/cargo@v1
+        with:
+          command: test
+          args: --manifest-path tarpc/Cargo.toml --features tokio1
+      - uses: actions-rs/cargo@v1
+        with:
+          command: test
+          args: --manifest-path tarpc/Cargo.toml --features serde-transport
+      - uses: actions-rs/cargo@v1
+        with:
+          command: test
+          args: --manifest-path tarpc/Cargo.toml --features tcp
+      - uses: actions-rs/cargo@v1
+        with:
+          command: test
+          args: --all-features
+
+  fmt:
+    name: Rustfmt
+    runs-on: ubuntu-latest
+    steps:
+      - name: Cancel previous
+        uses: styfle/cancel-workflow-action@0.7.0
+        with:
+          access_token: ${{ github.token }}
+      - uses: actions/checkout@v1
+      - uses: actions-rs/toolchain@v1
+        with:
+          profile: minimal
+          toolchain: stable
+          override: true
+      - run: rustup component add rustfmt
+      - uses: actions-rs/cargo@v1
+        with:
+          command: fmt
+          args: --all -- --check
+
+  clippy:
+    name: Clippy
+    runs-on: ubuntu-latest
+    steps:
+      - name: Cancel previous
+        uses: styfle/cancel-workflow-action@0.7.0
+        with:
+          access_token: ${{ github.token }}
+      - uses: actions/checkout@v1
+      - uses: actions-rs/toolchain@v1
+        with:
+          profile: minimal
+          toolchain: stable
+          override: true
+      - run: rustup component add clippy
+      - uses: actions-rs/cargo@v1
+        with:
+          command: clippy
+          args: --all-features -- -D warnings

.gitignore

@@ -1,3 +1,7 @@
 target
 Cargo.lock
+.cargo
 *.swp
+*.bk
+tarpc.iml
+.idea

.travis.yml

@@ -1,32 +0,0 @@
-language: rust
-sudo: false
-
-rust:
-    - stable
-    - beta
-    - nightly
-
-addons:
-  apt:
-    packages:
-    - libcurl4-openssl-dev
-    - libelf-dev
-    - libdw-dev
-
-before_script:
-- |
-    pip install 'travis-cargo<0.2' --user &&
-    export PATH=$HOME/.local/bin:$PATH
-
-script:
-- |
-    (cd tarpc && travis-cargo build) &&
-    (cd tarpc && travis-cargo test)
-
-after_success:
-- (cd tarpc && travis-cargo coveralls --no-sudo)
-
-env:
-  global:
-    # override the default `--features unstable` used for the nightly branch
-    - TRAVIS_CARGO_NIGHTLY_FEATURE=""

Cargo.toml

@@ -0,0 +1,11 @@
+[workspace]
+resolver = "2"
+
+members = [
+    "example-service",
+    "tarpc",
+    "plugins",
+]
+
+[profile.dev]
+split-debuginfo = "unpacked"

README.md

@@ -1,92 +1,171 @@
-## tarpc: Tim & Adam's RPC lib
-[![Travis-CI Status](https://travis-ci.org/google/tarpc.png?branch=master)](https://travis-ci.org/google/tarpc)
-[![Coverage Status](https://coveralls.io/repos/github/google/tarpc/badge.svg?branch=master)](https://coveralls.io/github/google/tarpc?branch=master)
-[![Software License](https://img.shields.io/badge/license-MIT-brightgreen.svg)](LICENSE.txt)
-[![Latest Version](https://img.shields.io/crates/v/tarpc.svg)](https://crates.io/crates/tarpc)
+[![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 service can be done in
-just a few lines of code, and most of the boilerplate of writing a server is taken care of for you.
+tarpc is an RPC framework for rust with a focus on ease of use. Defining a
+service can be done in just a few lines of code, and most of the boilerplate of
+writing a server is taken care of for you.
 
-[Documentation](https://google.github.io/tarpc)
+[Documentation](https://docs.rs/crate/tarpc/)
 
 ## 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 and asks them to compute the function instead. The original
-function then returns the value produced by that other server.
+"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
+and asks them to evaluate the function instead. The original function then
+returns the value produced by the other process.
 
-[More information](https://www.cs.cf.ac.uk/Dave/C/node33.html)
+RPC frameworks are a fundamental building block of most microservices-oriented
+architectures. Two well-known ones are [gRPC](http://www.grpc.io) and
+[Cap'n Proto](https://capnproto.org/).
+
+tarpc differentiates itself from other RPC frameworks by defining the schema in code,
+rather than in a separate language such as .proto. This means there's no separate compilation
+process, and no context switching between different languages.
+
+Some other features of tarpc:
+- 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.
+  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.
+- Configurable deadlines and deadline propagation: request deadlines default to 10s if
+  unspecified. The server will automatically cease work when the deadline has passed. Any
+  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
 Add to your `Cargo.toml` dependencies:
 
 ```toml
-tarpc = "0.6"
+tarpc = "0.29"
 ```
 
+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
+
+This example uses [tokio](https://tokio.rs), so add the following dependencies to
+your `Cargo.toml`:
+
+```toml
+anyhow = "1.0"
+futures = "0.3"
+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
+client and server. In real code, you will likely communicate over the network.
+For a more real-world example, see [example-service](example-service).
+
+First, let's set up the dependencies and service definition.
+
 ```rust
-#[macro_use]
-extern crate tarpc;
 
-mod hello_service {
-    service! {
-        rpc hello(name: String) -> String;
-    }
-}
-use hello_service::Service as HelloService;
+use futures::{
+    future::{self, Ready},
+    prelude::*,
+};
+use tarpc::{
+    client, context,
+    server::{self, incoming::Incoming, Channel},
+};
 
-struct HelloServer;
-impl HelloService for HelloServer {
-    fn hello(&self, name: String) -> String {
-        format!("Hello, {}!", name)
-    }
-}
-
-fn main() {
-    let addr = "localhost:10000";
-    let server_handle = HelloServer.spawn(addr).unwrap();
-    let client = hello_service::Client::new(addr).unwrap();
-    assert_eq!("Hello, Mom!", client.hello("Mom".into()).unwrap());
-    drop(client);
-    server_handle.shutdown();
+// 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]
+trait World {
+    /// Returns a greeting for name.
+    async fn hello(name: String) -> String;
 }
 ```
 
-The `service!` macro expands to a collection of items that collectively form an rpc service. In the
-above example, the macro is called within the `hello_service` module. This module will contain a
-`Client` (and `AsyncClient`) type, and a `Service` trait. The trait provides default `fn`s for
-starting the service: `spawn` and `spawn_with_config`, which start the service listening over an
-arbitrary transport. A `Client` (or `AsyncClient`) can connect to such a service. These generated
-types make it easy and ergonomic to write servers without dealing with sockets or serialization
-directly. See the tarpc_examples package for more sophisticated examples.
+This service definition generates a trait called `World`. Next we need to
+implement it for our Server struct.
+
+```rust
+// This is the type that implements the generated World trait. It is the business logic
+// and is used to start the server.
+#[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}!"))
+    }
+}
+```
+
+Lastly let's write our `main` that will start the server. While this example uses an
+[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() -> anyhow::Result<()> {
+    let (client_transport, server_transport) = tarpc::transport::channel::unbounded();
+
+    let server = server::BaseChannel::with_defaults(server_transport);
+    tokio::spawn(server.execute(HelloServer.serve()));
+
+    // 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}");
+
+    Ok(())
+}
+```
+
+## Service Documentation
 
-## Documentation
 Use `cargo doc` as you normally would to see the documentation created for all
 items expanded by a `service!` invocation.
 
-## Additional Features
-- Connect over any transport that `impl`s the `Transport` trait.
-- Concurrent requests from a single client.
-- Any type that `impl`s `serde`'s `Serialize` and `Deserialize` can be used in the rpc signatures.
-- Attributes can be specified on rpc methods. These will be included on both the `Service` trait
-  methods as well as on the `Client`'s stub methods.
-- Just like regular fns, the return type can be left off when it's `-> ()`.
-- Arg-less rpc's are also allowed.
+<!-- cargo-sync-readme end -->
 
-## Planned Improvements (actively being worked on)
-- Automatically reconnect on the client side when the connection cuts out.
-- Support asynchronous server implementations (currently thread per connection).
-- Support generic serialization protocols.
-
-## Contributing
-
-To contribute to tarpc, please see [CONTRIBUTING](CONTRIBUTING.md).
-
-## License
-
-tarpc is distributed under the terms of the MIT license.
-
-See [LICENSE](LICENSE) for details.
+License: MIT

RELEASES.md

@@ -1,4 +1,432 @@
-## 0.6 (20216-08-07)
+## 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
+
+1. tarpc has updated its tokio dependency to the latest 0.2 version.
+2. The tarpc crates have been unified into just `tarpc`, with new Cargo features to enable
+   functionality.
+   - The bincode-transport and json-transport crates are deprecated and superseded by
+     the `serde_transport` module, which unifies much of the logic present in both crates.
+
+## 0.13.0 (2018-10-16)
+
+### 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
+replaced with a homegrown rpc framework. Additionally, the crate has been
+modularized, so that the tarpc crate itself contains only the macro code.
+
+### New Crates
+
+- crate rpc contains the core client/server request-response framework, as well as a transport trait.
+- crate bincode-transport implements a transport that works almost exactly as tarpc works today (not to say it's wire-compatible).
+- crate trace has some foundational types for tracing. This isn't really fleshed out yet, but it's useful for in-process log tracing, at least.
+
+All crates are now at the top level. e.g. tarpc-plugins is now tarpc/plugins rather than tarpc/src/plugins. tarpc itself is now a *very* small code surface, as most functionality has been moved into the other more granular crates.
+
+### New Features
+- deadlines: all requests specify a deadline, and a server will stop processing a response when past its deadline.
+- client cancellation propagation: when a client drops a request, the client sends a message to the server informing it to cancel its response. This means cancellations can propagate across multiple server hops.
+- trace context stuff as mentioned above
+- more server configuration for total connection limits, per-connection request limits, etc.
+
+### Removals
+- no more shutdown handle.  I left it out for now because of time and not being sure what the right solution is.
+- all async now, no blocking stub or server interface. This helps with maintainability, and async/await makes async code much more usable. The service trait is thusly renamed Service, and the client is renamed Client.
+- no built-in transport. Tarpc is now transport agnostic (see bincode-transport for transitioning existing uses).
+- going along with the previous bullet, no preferred transport means no TLS support at this time. We could make a tls transport or make bincode-transport compatible with TLS.
+- a lot of examples were removed because I couldn't keep up with maintaining all of them. Hopefully the ones I kept are still illustrative.
+- no more plugins!
+
+## 0.10.0 (2018-04-08)
+
+### Breaking Changes
+Fixed rustc breakage in tarpc-plugins. These changes require a recent version of rustc.
+
+## 0.10.0 (2018-03-26)
+
+### Breaking Changes
+Updates bincode to version 1.0.
+
+## 0.9.0 (2017-09-17)
+
+### Breaking Changes
+Updates tarpc to use tarpc-plugins 0.2.
+
+## 0.8.0 (2017-05-05)
+
+### Breaking Changes
+This release updates tarpc to use serde 1.0.
+As such, users must also update to use serde 1.0.
+The serde 1.0 [release notes](https://github.com/serde-rs/serde/releases/tag/v1.0.0)
+detail migration paths.
+
+## 0.7.3 (2017-04-26)
+
+This release removes the `Sync` bound on RPC args for both sync and future
+clients. No breaking changes.
+
+## 0.7.2 (2017-04-22)
+
+### Breaking Changes
+This release updates tarpc-plugins to work with rustc master. Thus, older
+versions of rustc are no longer supported. We chose a minor version bump
+because it is still source-compatible with existing code using tarpc.
+
+## 0.7.1 (2017-03-31)
+
+This release was purely doc fixes. No breaking changes.
+
+## 0.7 (2017-03-31)
+
+### Breaking Changes
+This release is a complete overhaul to build tarpc on top of the tokio stack.
+It's safe to assume that everything broke with this release.
+
+Two traits are now generated by the macro, `FutureService` and `SyncService`.
+`SyncService` is the successor to the original `Service` trait. It uses a configurable
+thread pool to serve requests. `FutureService`, as the name implies, uses futures
+to serve requests and is single-threaded by default.
+
+The easiest way to upgrade from a 0.6 service impl is to `impl SyncService for MyService`.
+For more complete information, see the readme and the examples directory.
+
+## 0.6 (2016-08-07)
 
 ### Breaking Changes
 * Updated serde to 0.8. Requires dependents to update as well.

example-service/Cargo.toml

@@ -0,0 +1,40 @@
+[package]
+name = "tarpc-example-service"
+version = "0.12.0"
+rust-version = "1.56"
+authors = ["Tim Kuehn <tikue@google.com>"]
+edition = "2021"
+license = "MIT"
+documentation = "https://docs.rs/tarpc-example-service"
+homepage = "https://github.com/google/tarpc"
+repository = "https://github.com/google/tarpc"
+keywords = ["rpc", "network", "server", "microservices", "example"]
+categories = ["asynchronous", "network-programming"]
+readme = "../README.md"
+description = "An example server built on tarpc."
+
+[dependencies]
+anyhow = "1.0"
+clap = { version = "3.0.0-rc.9", features = ["derive"] }
+log = "0.4"
+futures = "0.3"
+opentelemetry = { version = "0.17", features = ["rt-tokio"] }
+opentelemetry-jaeger = { version = "0.16", features = ["rt-tokio"] }
+rand = "0.8"
+tarpc = { version = "0.30", path = "../tarpc", features = ["full"] }
+tokio = { version = "1", features = ["macros", "net", "rt-multi-thread"] }
+tracing = { version = "0.1" }
+tracing-opentelemetry = "0.17"
+tracing-subscriber = {version = "0.3", features = ["env-filter"]}
+
+[lib]
+name = "service"
+path = "src/lib.rs"
+
+[[bin]]
+name = "server"
+path = "src/server.rs"
+
+[[bin]]
+name = "client"
+path = "src/client.rs"

example-service/src/client.rs

@@ -0,0 +1,52 @@
+// 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 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() -> anyhow::Result<()> {
+    let flags = Flags::parse();
+    init_tracing("Tarpc Example Client")?;
+
+    let transport = tarpc::serde_transport::tcp::connect(flags.server_addr, Json::default);
+
+    // WorldClient is generated by the service attribute. It has a constructor `new` that takes a
+    // config and any Transport as input.
+    let client = WorldClient::new(client::Config::default(), transport.await?).spawn();
+
+    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;
+
+    tracing::info!("{:?}", hello);
+
+    // Let the background span processor finish.
+    sleep(Duration::from_micros(1)).await;
+    opentelemetry::global::shutdown_tracer_provider();
+
+    Ok(())
+}

example-service/src/lib.rs

@@ -0,0 +1,34 @@
+// 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 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]
+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_pipeline()
+        .with_service_name(service_name)
+        .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_span_events(FmtSpan::NEW | FmtSpan::CLOSE))
+        .with(tracing_opentelemetry::layer().with_tracer(tracer))
+        .try_init()?;
+
+    Ok(())
+}

example-service/src/server.rs

@@ -0,0 +1,76 @@
+// 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 clap::Parser;
+use futures::{future, prelude::*};
+use rand::{
+    distributions::{Distribution, Uniform},
+    thread_rng,
+};
+use service::{init_tracing, World};
+use std::{
+    net::{IpAddr, Ipv6Addr, SocketAddr},
+    time::Duration,
+};
+use tarpc::{
+    context,
+    server::{self, incoming::Incoming, Channel},
+    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.
+#[derive(Clone)]
+struct HelloServer(SocketAddr);
+
+#[tarpc::server]
+impl World for HelloServer {
+    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)
+    }
+}
+
+#[tokio::main]
+async fn main() -> anyhow::Result<()> {
+    let flags = Flags::parse();
+    init_tracing("Tarpc Example Server")?;
+
+    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.
+    let mut listener = tarpc::serde_transport::tcp::listen(&server_addr, Json::default).await?;
+    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.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.transport().peer_addr().unwrap());
+            channel.execute(server.serve())
+        })
+        // Max 10 channels.
+        .buffer_unordered(10)
+        .for_each(|_| async {})
+        .await;
+
+    Ok(())
+}

hooks/pre-commit

@@ -89,13 +89,14 @@ fi
 # not only contain discrete files.
 printf "${PREFIX} Checking formatting ... "
 FMTRESULT=0
+diff=""
 for file in $(git diff --name-only --cached);
 do
 	if [ ${file: -3} == ".rs" ]; then
-        diff=$(rustfmt --skip-children --write-mode=diff $file)
-        if grep --quiet "^Diff at line" <<< "$diff"; then
-			FMTRESULT=1
-		fi
+        diff="$diff$(rustfmt --edition 2018 --check $file)"
+        if [ $? != 0 ]; then
+            FMTRESULT=1
+        fi
 	fi
 done
 
@@ -104,7 +105,7 @@ if [ "${TARPC_SKIP_RUSTFMT}" == 1 ]; then
 elif [ ${FMTRESULT} != 0 ]; then
 	FAILED=1
 	printf "${FAILURE}\n"
-    echo "$diff" | sed '/Using rustfmt.*$/d'
+    echo "$diff"
 else
 	printf "${SUCCESS}\n"
 fi

hooks/pre-push

@@ -20,11 +20,6 @@
 #   copy. Set to 0 by default, since the intent is to test the code that's being pushed, not changes
 #   still in the working copy.
 #
-# - TARPC_USE_CURRENT_TOOLCHAIN, default = 0
-#
-#   Setting this variable to 1 will just run cargo build and cargo test, rather than running
-#   stable/beta/nightly.
-#
 # Note that these options are most useful for testing the hooks themselves. Use git push --no-verify
 # to skip the pre-push hook altogether.
 
@@ -42,86 +37,67 @@ SUCCESS="${GREEN}ok${NC}"
 printf "${PREFIX} Clean working copy ... "
 git diff --exit-code &>/dev/null
 if [ "$?" == 0 ]; then
-	printf "${SUCCESS}\n"
+    printf "${SUCCESS}\n"
 else
-	if [ "${TARPC_ALLOW_DIRTY}" == "1" ]
-	then
-		printf "${SKIPPED}\n"
-	else
-		printf "${FAILURE}\n"
-		exit 1
-	fi
+    if [ "${TARPC_ALLOW_DIRTY}" == "1" ]
+    then
+        printf "${SKIPPED}\n"
+    else
+        printf "${FAILURE}\n"
+        exit 1
+    fi
 fi
 
 PREPUSH_RESULT=0
 
-# args:
-# 1 - cargo command to run (build/test)
-# 2 - directory name of crate to build
-# 3 - rust toolchain (nightly/stable/beta)
-run_cargo() {
-	if [ "$1" == "build" ]; then
-		VERB=Building
-	else
-		VERB=Testing
-	fi
-	if [ "$3" != "" ]; then
-		printf "${PREFIX} $VERB $2 on $3 ... "
-		rustup run $3 cargo $1 --manifest-path $2/Cargo.toml &>/dev/null
-	else
-		printf "${PREFIX} $VERB $2 ... "
-		cargo $1 --manifest-path $2/Cargo.toml &>/dev/null
-	fi
-	if [ "$?" != "0" ]; then
-		printf "${FAILURE}\n"
+try_run() {
+    TEXT=$1
+    shift
+    printf "${PREFIX} ${TEXT}"
+    OUTPUT=$($@ 2>&1)
+    if [ "$?" != "0" ]; then
+        printf "${FAILURE}, output shown below\n"
+        printf "\n\n"
+        printf "$OUTPUT"
+        printf "\n\n"
 		PREPUSH_RESULT=1
-	else
-		printf "${SUCCESS}\n"
-	fi
+        return 1
+    else
+        printf "${SUCCESS}\n"
+    fi
 }
 
 TOOLCHAIN_RESULT=0
 check_toolchain() {
-	printf "${PREFIX} Checking for $1 toolchain ... "
-	if [[ $(rustup toolchain list) =~ $1 ]]; then
-		printf "${SUCCESS}\n"
-	else
-		TOOLCHAIN_RESULT=1
-		PREPUSH_RESULT=1
-		printf "${FAILURE}\n"
-	fi
+    printf "${PREFIX} Checking for $1 toolchain ... "
+    if [[ $(rustup toolchain list) =~ $1 ]]; then
+        printf "${SUCCESS}\n"
+    else
+        TOOLCHAIN_RESULT=1
+        PREPUSH_RESULT=1
+        printf "${FAILURE}\n"
+    fi
 }
 
-printf "${PREFIX} Checking for rustup ... "
+printf "${PREFIX} Checking for rustup or current toolchain directive... "
 command -v rustup &>/dev/null
-if [ "$?" == 0 ] && [ "${TARPC_USE_CURRENT_TOOLCHAIN}" == "" ]; then
-	printf "${SUCCESS}\n"
+if [ "$?" == 0 ]; then
+    printf "${SUCCESS}\n"
 
-	check_toolchain stable
-	check_toolchain beta
-	check_toolchain nightly
-	if [ ${TOOLCHAIN_RESULT} == 1 ]; then
-		exit 1
-	fi
+    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
 
-	run_cargo build tarpc stable
-	run_cargo build tarpc_examples stable
+    check_toolchain nightly
+    if [ ${TOOLCHAIN_RESULT} != 1 ]; then
+        try_run "Running clippy ... " cargo +nightly clippy --color=always -Z unstable-options -- --deny warnings
+    fi
 
-	run_cargo build tarpc beta
-	run_cargo build tarpc_examples beta
 
-	run_cargo build tarpc nightly
-	run_cargo build tarpc_examples nightly
-
-	# We still rely on some nightly stuff for tests
-	run_cargo test tarpc nightly
-	run_cargo test tarpc_examples nightly
-else
-	printf "${YELLOW}NOT FOUND${NC}\n"
-	printf "${WARNING} Falling back to current toolchain: $(rustc -V)\n"
-
-	run_cargo test tarpc
-	run_cargo test tarpc_examples
 fi
 
 exit $PREPUSH_RESULT

plugins/Cargo.toml

@@ -0,0 +1,34 @@
+[package]
+name = "tarpc-plugins"
+version = "0.12.0"
+rust-version = "1.56"
+authors = ["Adam Wright <adam.austin.wright@gmail.com>", "Tim Kuehn <timothy.j.kuehn@gmail.com>"]
+edition = "2021"
+license = "MIT"
+documentation = "https://docs.rs/tarpc-plugins"
+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"
+description = "Proc macros for tarpc."
+
+[features]
+serde1 = []
+
+[badges]
+travis-ci = { repository = "google/tarpc" }
+
+[dependencies]
+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", 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/rustfmt.toml

@@ -0,0 +1 @@
+edition = "2018"

plugins/src/lib.rs

@@ -0,0 +1,825 @@
+// 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.
+
+#![recursion_limit = "512"]
+
+extern crate proc_macro;
+extern crate proc_macro2;
+extern crate quote;
+extern crate syn;
+
+use proc_macro::TokenStream;
+use proc_macro2::{Span, TokenStream as TokenStream2};
+use quote::{format_ident, quote, ToTokens};
+use syn::{
+    braced,
+    ext::IdentExt,
+    parenthesized,
+    parse::{Parse, ParseStream},
+    parse_macro_input, parse_quote, parse_str,
+    spanned::Spanned,
+    token::Comma,
+    Attribute, FnArg, Ident, ImplItem, ImplItemMethod, ImplItemType, ItemImpl, 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,
+    ident: Ident,
+    rpcs: Vec<RpcMethod>,
+}
+
+struct RpcMethod {
+    attrs: Vec<Attribute>,
+    ident: Ident,
+    args: Vec<PatType>,
+    output: ReturnType,
+}
+
+impl Parse for Service {
+    fn parse(input: ParseStream) -> syn::Result<Self> {
+        let attrs = input.call(Attribute::parse_outer)?;
+        let vis = input.parse()?;
+        input.parse::<Token![trait]>()?;
+        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" {
+                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" {
+                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,
+            ident,
+            rpcs,
+        })
+    }
+}
+
+impl Parse for RpcMethod {
+    fn parse(input: ParseStream) -> syn::Result<Self> {
+        let attrs = input.call(Attribute::parse_outer)?;
+        input.parse::<Token![async]>()?;
+        input.parse::<Token![fn]>()?;
+        let ident = input.parse()?;
+        let content;
+        parenthesized!(content in input);
+        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![;]>()?;
+
+        Ok(Self {
+            attrs,
+            ident,
+            args,
+            output,
+        })
+    }
+}
+
+// If `derive_serde` meta item is not present, defaults to cfg!(feature = "serde1").
+// `derive_serde` can only be true when serde1 is enabled.
+struct DeriveSerde(bool);
+
+impl Parse for DeriveSerde {
+    fn parse(input: ParseStream) -> syn::Result<Self> {
+        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`"
+                    )
+                ),
+            }
+            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
+/// - client stub struct
+/// - new_stub client factory fn
+/// - Request and Response enums
+/// - ResponseFut Future
+#[proc_macro_attribute]
+pub fn service(attr: TokenStream, input: TokenStream) -> TokenStream {
+    let derive_serde = parse_macro_input!(attr as DeriveSerde);
+    let unit_type: &Type = &parse_quote!(());
+    let Service {
+        ref attrs,
+        ref vis,
+        ref ident,
+        ref rpcs,
+    } = parse_macro_input!(input as Service);
+
+    let camel_case_fn_names: &Vec<_> = &rpcs
+        .iter()
+        .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.unraw());
+    let derive_serialize = if derive_serde.0 {
+        Some(
+            quote! {#[derive(tarpc::serde::Serialize, tarpc::serde::Deserialize)]
+            #[serde(crate = "tarpc::serde")]},
+        )
+    } else {
+        None
+    };
+
+    let methods = rpcs.iter().map(|rpc| &rpc.ident).collect::<Vec<_>>();
+    let request_names = methods
+        .iter()
+        .map(|m| format!("{ident}.{m}"))
+        .collect::<Vec<_>>();
+
+    ServiceGenerator {
+        response_fut_name,
+        service_ident: 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_idents: &methods,
+        request_names: &*request_names,
+        attrs,
+        rpcs,
+        return_types: &rpcs
+            .iter()
+            .map(|rpc| match rpc.output {
+                ReturnType::Type(_, ref ty) => ty,
+                ReturnType::Default => unit_type,
+            })
+            .collect::<Vec<_>>(),
+        arg_pats: &args
+            .iter()
+            .map(|args| args.iter().map(|arg| &*arg.pat).collect())
+            .collect::<Vec<_>>(),
+        camel_case_idents: &rpcs
+            .iter()
+            .zip(camel_case_fn_names.iter())
+            .map(|(rpc, name)| Ident::new(name, rpc.ident.span()))
+            .collect::<Vec<_>>(),
+        future_types: &camel_case_fn_names
+            .iter()
+            .map(|name| parse_str(&format!("{name}Fut")).unwrap())
+            .collect::<Vec<_>>(),
+        derive_serialize: derive_serialize.as_ref(),
+    }
+    .into_token_stream()
+    .into()
+}
+
+/// generate an identifier consisting of the method name to CamelCase with
+/// Fut appended to it.
+fn associated_type_for_rpc(method: &ImplItemMethod) -> String {
+    snake_to_camel(&method.sig.ident.unraw().to_string()) + "Fut"
+}
+
+/// Transforms an async function into a sync one, returning a type declaration
+/// for the return type (a future).
+fn transform_method(method: &mut ImplItemMethod) -> ImplItemType {
+    method.sig.asyncness = None;
+
+    // get either the return type or ().
+    let ret = match &method.sig.output {
+        ReturnType::Default => quote!(()),
+        ReturnType::Type(_, ret) => quote!(#ret),
+    };
+
+    let fut_name = associated_type_for_rpc(method);
+    let fut_name_ident = Ident::new(&fut_name, method.sig.ident.span());
+
+    // generate the updated return signature.
+    method.sig.output = parse_quote! {
+        -> ::core::pin::Pin<Box<
+                dyn ::core::future::Future<Output = #ret> + ::core::marker::Send
+            >>
+    };
+
+    // transform the body of the method into Box::pin(async move { body }).
+    let block = method.block.clone();
+    method.block = parse_quote! [{
+        Box::pin(async move
+            #block
+        )
+    }];
+
+    // generate and return type declaration for return type.
+    let t: ImplItemType = parse_quote! {
+        type #fut_name_ident = ::core::pin::Pin<Box<dyn ::core::future::Future<Output = #ret> + ::core::marker::Send>>;
+    };
+
+    t
+}
+
+#[proc_macro_attribute]
+pub fn server(_attr: TokenStream, input: TokenStream) -> TokenStream {
+    let mut item = syn::parse_macro_input!(input as ItemImpl);
+    let span = item.span();
+
+    // the generated type declarations
+    let mut types: Vec<ImplItemType> = Vec::new();
+    let mut expected_non_async_types: Vec<(&ImplItemMethod, String)> = Vec::new();
+    let mut found_non_async_types: Vec<&ImplItemType> = Vec::new();
+
+    for inner in &mut item.items {
+        match inner {
+            ImplItem::Method(method) => {
+                if method.sig.asyncness.is_some() {
+                    // if this function is declared async, transform it into a regular function
+                    let typedecl = transform_method(method);
+                    types.push(typedecl);
+                } else {
+                    // If it's not async, keep track of all required associated types for better
+                    // error reporting.
+                    expected_non_async_types.push((method, associated_type_for_rpc(method)));
+                }
+            }
+            ImplItem::Type(typedecl) => found_non_async_types.push(typedecl),
+            _ => {}
+        }
+    }
+
+    if let Err(e) =
+        verify_types_were_provided(span, &expected_non_async_types, &found_non_async_types)
+    {
+        return TokenStream::from(e.to_compile_error());
+    }
+
+    // add the type declarations into the impl block
+    for t in types.into_iter() {
+        item.items.push(syn::ImplItem::Type(t));
+    }
+
+    TokenStream::from(quote!(#item))
+}
+
+fn verify_types_were_provided(
+    span: Span,
+    expected: &[(&ImplItemMethod, String)],
+    provided: &[&ImplItemType],
+) -> syn::Result<()> {
+    let mut result = Ok(());
+    for (method, expected) in expected {
+        if !provided.iter().any(|typedecl| typedecl.ident == expected) {
+            let mut e = syn::Error::new(
+                span,
+                format!("not all trait items implemented, missing: `{expected}`"),
+            );
+            let fn_span = method.sig.fn_token.span();
+            e.extend(syn::Error::new(
+                fn_span.join(method.sig.ident.span()).unwrap_or(fn_span),
+                format!(
+                    "hint: `#[tarpc::server]` only rewrites async fns, and `fn {}` is not async",
+                    method.sig.ident
+                ),
+            ));
+            match result {
+                Ok(_) => result = Err(e),
+                Err(ref mut error) => error.extend(Some(e)),
+            }
+        }
+    }
+    result
+}
+
+// Things needed to generate the service items: trait, serve impl, request/response enums, and
+// the client stub.
+struct ServiceGenerator<'a> {
+    service_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,
+    vis: &'a Visibility,
+    attrs: &'a [Attribute],
+    rpcs: &'a [RpcMethod],
+    camel_case_idents: &'a [Ident],
+    future_types: &'a [Type],
+    method_idents: &'a [&'a Ident],
+    request_names: &'a [String],
+    method_attrs: &'a [&'a [Attribute]],
+    args: &'a [&'a [PatType]],
+    return_types: &'a [&'a Type],
+    arg_pats: &'a [Vec<&'a Pat>],
+    derive_serialize: Option<&'a TokenStream2>,
+}
+
+impl<'a> ServiceGenerator<'a> {
+    fn trait_service(&self) -> TokenStream2 {
+        let &Self {
+            attrs,
+            rpcs,
+            vis,
+            future_types,
+            return_types,
+            service_ident,
+            server_ident,
+            ..
+        } = self;
+
+        let types_and_fns = rpcs
+            .iter()
+            .zip(future_types.iter())
+            .zip(return_types.iter())
+            .map(
+                |(
+                    (
+                        RpcMethod {
+                            attrs, ident, args, ..
+                        },
+                        future_type,
+                    ),
+                    output,
+                )| {
+                    let ty_doc = format!("The response future returned by [`{service_ident}::{ident}`].");
+                    quote! {
+                        #[doc = #ty_doc]
+                        type #future_type: std::future::Future<Output = #output>;
+
+                        #( #attrs )*
+                        fn #ident(self, context: tarpc::context::Context, #( #args ),*) -> Self::#future_type;
+                    }
+                },
+            );
+
+        quote! {
+            #( #attrs )*
+            #vis trait #service_ident: Sized {
+                #( #types_and_fns )*
+
+                /// Returns a serving function to use with
+                /// [InFlightRequest::execute](tarpc::server::InFlightRequest::execute).
+                fn serve(self) -> #server_ident<Self> {
+                    #server_ident { service: 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,
+            response_fut_ident,
+            camel_case_idents,
+            arg_pats,
+            method_idents,
+            request_names,
+            ..
+        } = self;
+
+        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 method(&self, req: &#request_ident) -> Option<&'static str> {
+                    Some(match req {
+                        #(
+                            #request_ident::#camel_case_idents{..} => {
+                                #request_names
+                            }
+                        )*
+                    })
+                }
+
+                fn serve(self, ctx: tarpc::context::Context, req: #request_ident) -> Self::Fut {
+                    match req {
+                        #(
+                            #request_ident::#camel_case_idents{ #( #arg_pats ),* } => {
+                                #response_fut_ident::#camel_case_idents(
+                                    #service_ident::#method_idents(
+                                        self.service, ctx, #( #arg_pats ),*
+                                    )
+                                )
+                            }
+                        )*
+                    }
+                }
+            }
+        }
+    }
+
+    fn enum_request(&self) -> TokenStream2 {
+        let &Self {
+            derive_serialize,
+            vis,
+            request_ident,
+            camel_case_idents,
+            args,
+            ..
+        } = self;
+
+        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 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 enum_response_future(&self) -> TokenStream2 {
+        let &Self {
+            vis,
+            service_ident,
+            response_fut_ident,
+            camel_case_idents,
+            future_types,
+            ..
+        } = self;
+
+        quote! {
+            /// A future resolving to a server response.
+            #[allow(missing_docs)]
+            #vis enum #response_fut_ident<S: #service_ident> {
+                #( #camel_case_idents(<S as #service_ident>::#future_types) ),*
+            }
+        }
+    }
+
+    fn impl_debug_for_response_future(&self) -> TokenStream2 {
+        let &Self {
+            service_ident,
+            response_fut_ident,
+            response_fut_name,
+            ..
+        } = self;
+
+        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()
+                }
+            }
+        }
+    }
+
+    fn impl_future_for_response_future(&self) -> TokenStream2 {
+        let &Self {
+            service_ident,
+            response_fut_ident,
+            response_ident,
+            camel_case_idents,
+            ..
+        } = self;
+
+        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>
+                {
+                    unsafe {
+                        match std::pin::Pin::get_unchecked_mut(self) {
+                            #(
+                                #response_fut_ident::#camel_case_idents(resp) =>
+                                    std::pin::Pin::new_unchecked(resp)
+                                        .poll(cx)
+                                        .map(#response_ident::#camel_case_idents),
+                            )*
+                        }
+                    }
+                }
+            }
+        }
+    }
+
+    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](std::future::Future).
+            #vis struct #client_ident(tarpc::client::Channel<#request_ident, #response_ident>);
+        }
+    }
+
+    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,
+                    }
+                }
+
+            }
+        }
+    }
+
+    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 #client_ident {
+                #(
+                    #[allow(unused)]
+                    #( #method_attrs )*
+                    #vis fn #method_idents(&self, ctx: tarpc::context::Context, #( #args ),*)
+                        -> impl std::future::Future<Output = 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) => std::result::Result::Ok(msg),
+                                _ => 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.enum_response_future(),
+            self.impl_debug_for_response_future(),
+            self.impl_future_for_response_future(),
+            self.struct_client(),
+            self.impl_client_new(),
+            self.impl_client_rpc_methods(),
+        ])
+    }
+}
+
+fn snake_to_camel(ident_str: &str) -> String {
+    let mut camel_ty = String::with_capacity(ident_str.len());
+
+    let mut last_char_was_underscore = true;
+    for c in ident_str.chars() {
+        match c {
+            '_' => last_char_was_underscore = true,
+            c if last_char_was_underscore => {
+                camel_ty.extend(c.to_uppercase());
+                last_char_was_underscore = false;
+            }
+            c => camel_ty.extend(c.to_lowercase()),
+        }
+    }
+
+    camel_ty.shrink_to_fit();
+    camel_ty
+}
+
+#[test]
+fn snake_to_camel_basic() {
+    assert_eq!(snake_to_camel("abc_def"), "AbcDef");
+}
+
+#[test]
+fn snake_to_camel_underscore_suffix() {
+    assert_eq!(snake_to_camel("abc_def_"), "AbcDef");
+}
+
+#[test]
+fn snake_to_camel_underscore_prefix() {
+    assert_eq!(snake_to_camel("_abc_def"), "AbcDef");
+}
+
+#[test]
+fn snake_to_camel_underscore_consecutive() {
+    assert_eq!(snake_to_camel("abc__def"), "AbcDef");
+}
+
+#[test]
+fn snake_to_camel_capital_in_middle() {
+    assert_eq!(snake_to_camel("aBc_dEf"), "AbcDef");
+}

plugins/tests/server.rs

@@ -0,0 +1,144 @@
+use assert_type_eq::assert_type_eq;
+use futures::Future;
+use std::pin::Pin;
+use tarpc::context;
+
+// 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();
+}
+
+#[test]
+fn type_generation_works() {
+    #[tarpc::server]
+    impl Foo for () {
+        async fn two_part(self, _: context::Context, s: String, i: i32) -> (String, i32) {
+            (s, i)
+        }
+
+        async fn bar(self, _: context::Context, s: String) -> String {
+            s
+        }
+
+        async fn baz(self, _: context::Context) {}
+    }
+
+    // the assert_type_eq macro can only be used once per block.
+    {
+        assert_type_eq!(
+            <() as Foo>::TwoPartFut,
+            Pin<Box<dyn Future<Output = (String, i32)> + Send>>
+        );
+    }
+    {
+        assert_type_eq!(
+            <() as Foo>::BarFut,
+            Pin<Box<dyn Future<Output = String> + Send>>
+        );
+    }
+    {
+        assert_type_eq!(
+            <() as Foo>::BazFut,
+            Pin<Box<dyn Future<Output = ()> + Send>>
+        );
+    }
+}
+
+#[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();
+    }
+
+    #[tarpc::server]
+    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) {}
+    }
+}
+
+#[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);
+    }
+
+    #[tarpc::server]
+    impl Syntax for () {
+        #[deny(warnings)]
+        #[allow(non_snake_case)]
+        async fn TestCamelCaseDoesntConflict(self, _: context::Context) {}
+
+        async fn hello(self, _: context::Context) -> String {
+            String::new()
+        }
+
+        async fn attr(self, _: context::Context, _s: String) -> String {
+            String::new()
+        }
+
+        async fn no_args_no_return(self, _: context::Context) {}
+
+        async fn no_args(self, _: context::Context) -> () {}
+
+        async fn one_arg(self, _: context::Context, _one: String) -> i32 {
+            0
+        }
+
+        async fn two_args_no_return(self, _: context::Context, _one: String, _two: u64) {}
+
+        async fn two_args(self, _: context::Context, _one: String, _two: u64) -> String {
+            String::new()
+        }
+
+        async fn no_args_ret_error(self, _: context::Context) -> i32 {
+            0
+        }
+
+        async fn one_arg_ret_error(self, _: context::Context, _one: String) -> String {
+            String::new()
+        }
+
+        async fn no_arg_implicit_return_error(self, _: context::Context) {}
+
+        async fn one_arg_implicit_return_error(self, _: context::Context, _one: String) {}
+    }
+}

plugins/tests/service.rs

@@ -0,0 +1,85 @@
+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);
+        async fn bar(s: String) -> String;
+        async fn baz();
+    }
+
+    impl Foo for () {
+        type TwoPartFut = Ready<(String, i32)>;
+        fn two_part(self, _: context::Context, s: String, i: i32) -> Self::TwoPartFut {
+            ready((s, i))
+        }
+
+        type BarFut = Ready<String>;
+        fn bar(self, _: context::Context, s: String) -> Self::BarFut {
+            ready(s)
+        }
+
+        type BazFut = Ready<()>;
+        fn baz(self, _: context::Context) -> Self::BazFut {
+            ready(())
+        }
+    }
+}
+
+#[allow(non_camel_case_types)]
+#[test]
+fn raw_idents() {
+    use futures::future::{ready, Ready};
+
+    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 () {
+        type AwaitFut = Ready<(r#yield, i32)>;
+        fn r#await(self, _: context::Context, r#struct: r#yield, r#enum: i32) -> Self::AwaitFut {
+            ready((r#struct, r#enum))
+        }
+
+        type FnFut = Ready<r#yield>;
+        fn r#fn(self, _: context::Context, r#impl: r#yield) -> Self::FnFut {
+            ready(r#impl)
+        }
+
+        type AsyncFut = Ready<()>;
+        fn r#async(self, _: context::Context) -> Self::AsyncFut {
+            ready(())
+        }
+    }
+}
+
+#[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);
+    }
+}

tarpc/Cargo.toml

@@ -1,23 +1,110 @@
 [package]
 name = "tarpc"
-version = "0.6.0"
-authors = ["Adam Wright <adam.austin.wright@gmail.com>", "Tim Kuehn <timothy.j.kuehn@gmail.com>"]
+version = "0.30.0"
+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://google.github.io/tarpc"
+documentation = "https://docs.rs/tarpc"
 homepage = "https://github.com/google/tarpc"
 repository = "https://github.com/google/tarpc"
-keywords = ["rpc", "protocol", "remote", "procedure", "serialize"]
+keywords = ["rpc", "network", "server", "api", "microservices"]
+categories = ["asynchronous", "network-programming"]
 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 = ["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"]
+
+full = [
+    "serde1",
+    "tokio1",
+    "serde-transport",
+    "serde-transport-json",
+    "serde-transport-bincode",
+    "tcp",
+]
+
+[badges]
+travis-ci = { repository = "google/tarpc" }
+
 [dependencies]
-bincode = "0.6"
-log = "0.3"
-scoped-pool = "1.0"
-serde = "0.8"
-unix_socket = "0.5"
+anyhow = "1.0"
+fnv = "1.0"
+futures = "0.3"
+humantime = "2.0"
+pin-project = "1.0"
+rand = "0.8"
+serde = { optional = true, version = "1.0", features = ["derive"] }
+static_assertions = "1.1.0"
+tarpc-plugins = { path = "../plugins", version = "0.12" }
+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 = "0.17.2", default-features = false }
+opentelemetry = { version = "0.17.0", default-features = false }
+
 
 [dev-dependencies]
-lazy_static = "0.2"
-env_logger = "0.3"
-tempdir = "0.3"
+assert_matches = "1.4"
+bincode = "1.3"
+bytes = { version = "1", features = ["serde"] }
+flate2 = "1.0"
+futures-test = "0.3"
+opentelemetry = { version = "0.17.0", default-features = false, features = [
+    "rt-tokio",
+] }
+opentelemetry-jaeger = { version = "0.16.0", features = ["rt-tokio"] }
+pin-utils = "0.1.0-alpha"
+serde_bytes = "0.11"
+tracing-subscriber = { version = "0.3", features = ["env-filter"] }
+tokio = { version = "1", features = ["full", "test-util"] }
+tokio-serde = { version = "0.8", features = ["json", "bincode"] }
+trybuild = "1.0"
+
+[package.metadata.docs.rs]
+all-features = true
+rustdoc-args = ["--cfg", "docsrs"]
+
+[[example]]
+name = "compression"
+required-features = ["serde-transport", "tcp"]
+
+[[example]]
+name = "tracing"
+required-features = ["full"]
+
+[[example]]
+name = "readme"
+required-features = ["full"]
+
+[[example]]
+name = "pubsub"
+required-features = ["full"]
+
+[[example]]
+name = "custom_transport"
+required-features = ["serde1", "tokio1", "serde-transport"]
+
+[[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/README.md

@@ -0,0 +1 @@
+../README.md

tarpc/clippy.toml

@@ -0,0 +1 @@
+doc-valid-idents = ["gRPC"]

tarpc/examples/compression.rs

@@ -0,0 +1,128 @@
+use flate2::{read::DeflateDecoder, write::DeflateEncoder, Compression};
+use futures::{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;
+
+#[tarpc::server]
+impl World for HelloServer {
+    async fn hello(self, _: context::Context, name: String) -> String {
+        format!("Hey, {name}!")
+    }
+}
+
+#[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())
+            .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 +1,48 @@
+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;
+
+#[tarpc::server]
+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();
+    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());
+            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

@@ -0,0 +1,358 @@
+// 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.
+
+/// - 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::{
+    channel::oneshot,
+    future::{self, AbortHandle},
+    prelude::*,
+};
+use publisher::Publisher as _;
+use std::{
+    collections::HashMap,
+    env,
+    error::Error,
+    io,
+    net::SocketAddr,
+    sync::{Arc, Mutex, RwLock},
+};
+use subscriber::Subscriber as _;
+use tarpc::{
+    client, context,
+    serde_transport::tcp,
+    server::{self, Channel},
+    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 topics() -> Vec<String>;
+        async fn receive(topic: String, message: String);
+    }
+}
+
+pub mod publisher {
+    #[tarpc::service]
+    pub trait Publisher {
+        async fn publish(topic: String, message: String);
+    }
+}
+
+#[derive(Clone, Debug)]
+struct Subscriber {
+    local_addr: SocketAddr,
+    topics: Vec<String>,
+}
+
+#[tarpc::server]
+impl subscriber::Subscriber for Subscriber {
+    async fn topics(self, _: context::Context) -> Vec<String> {
+        self.topics.clone()
+    }
+
+    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 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()));
+        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<SocketAddr, Subscription>>>,
+    subscriptions: Arc<RwLock<HashMap<String, HashMap<SocketAddr, subscriber::SubscriberClient>>>>,
+}
+
+struct PublisherAddrs {
+    publisher: SocketAddr,
+    subscriptions: SocketAddr,
+}
+
+impl Publisher {
+    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())
+                .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);
+                    }
+                }
+            }
+        });
+    }
+}
+
+#[tarpc::server]
+impl publisher::Publisher for Publisher {
+    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);
+            }
+        }
+    }
+}
+
+/// 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_pipeline()
+        .with_service_name(service_name)
+        .with_max_packet_size(2usize.pow(13))
+        .install_batch(opentelemetry::runtime::Tokio)?;
+
+    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

@@ -0,0 +1,55 @@
+// 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 futures::future::{self, Ready};
+use tarpc::{
+    client, context,
+    server::{self, Channel},
+};
+
+/// 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]
+pub trait World {
+    async fn hello(name: String) -> String;
+}
+
+/// This is the type that implements the generated World trait. It is the business logic
+/// and is used to start the server.
+#[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}!"))
+    }
+}
+
+#[tokio::main]
+async fn main() -> anyhow::Result<()> {
+    let (client_transport, server_transport) = tarpc::transport::channel::unbounded();
+
+    let server = server::BaseChannel::with_defaults(server_transport);
+    tokio::spawn(server.execute(HelloServer.serve()));
+
+    // 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}");
+
+    Ok(())
+}

tarpc/examples/tracing.rs

@@ -0,0 +1,112 @@
+// 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, prelude::*};
+use tarpc::{
+    client, context,
+    server::{incoming::Incoming, BaseChannel},
+    tokio_serde::formats::Json,
+};
+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;
+
+#[tarpc::server]
+impl AddService for AddServer {
+    async fn add(self, _: context::Context, x: i32, y: i32) -> i32 {
+        x + y
+    }
+}
+
+#[derive(Clone)]
+struct DoubleServer {
+    add_client: add::AddClient,
+}
+
+#[tarpc::server]
+impl DoubleService for DoubleServer {
+    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_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(())
+}
+
+#[tokio::main]
+async fn main() -> anyhow::Result<()> {
+    init_tracing("tarpc_tracing_example")?;
+
+    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 = add_listener
+        .map(BaseChannel::with_defaults)
+        .take(1)
+        .execute(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 = double_listener
+        .map(BaseChannel::with_defaults)
+        .take(1)
+        .execute(DoubleServer { add_client }.serve());
+    tokio::spawn(double_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/rustfmt.toml

@@ -1,2 +1 @@
-ideal_width = 100
-reorder_imports = true
+edition = "2018"

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.rs

@@ -0,0 +1,875 @@
+// 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.
+
+mod in_flight_requests;
+
+use crate::{
+    cancellations::{cancellations, CanceledRequests, RequestCancellation},
+    context, trace, ClientMessage, Request, Response, ServerError, Transport,
+};
+use futures::{prelude::*, ready, stream::Fuse, task::*};
+use in_flight_requests::{DeadlineExceededError, InFlightRequests};
+use pin_project::pin_project;
+use std::{
+    convert::TryFrom,
+    error::Error,
+    fmt, mem,
+    pin::Pin,
+    sync::{
+        atomic::{AtomicUsize, Ordering},
+        Arc,
+    },
+};
+use tokio::sync::{mpsc, oneshot};
+use tracing::Span;
+
+/// Settings that control the behavior of the client.
+#[derive(Clone, Debug)]
+#[non_exhaustive]
+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,
+}
+
+impl Default for Config {
+    fn default() -> Self {
+        Config {
+            max_in_flight_requests: 1_000,
+            pending_request_buffer: 100,
+        }
+    }
+}
+
+/// A channel and dispatch pair. The dispatch drives the sending and receiving of requests
+/// and must be polled continuously or spawned.
+pub struct NewClient<C, D> {
+    /// The new client.
+    pub client: C,
+    /// The client's dispatch.
+    pub dispatch: D,
+}
+
+impl<C, D, E> NewClient<C, D>
+where
+    D: Future<Output = Result<(), E>> + Send + 'static,
+    E: std::error::Error + Send + Sync + 'static,
+{
+    /// Helper method to spawn the dispatch on the default executor.
+    #[cfg(feature = "tokio1")]
+    #[cfg_attr(docsrs, doc(cfg(feature = "tokio1")))]
+    pub fn spawn(self) -> C {
+        let dispatch = self.dispatch.unwrap_or_else(move |e| {
+            let e = anyhow::Error::new(e);
+            tracing::warn!("Connection broken: {:?}", e);
+        });
+        tokio::spawn(dispatch);
+        self.client
+    }
+}
+
+impl<C, D> fmt::Debug for NewClient<C, D> {
+    fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
+        write!(fmt, "NewClient")
+    }
+}
+
+const _CHECK_USIZE: () = assert!(
+    std::mem::size_of::<usize>() <= std::mem::size_of::<u64>(),
+    "usize is too big to fit in u64"
+);
+
+/// 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<AtomicUsize>,
+}
+
+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(),
+        }
+    }
+}
+
+impl<Req, Resp> Channel<Req, Resp> {
+    /// Sends a request to the dispatch task to forward to the server, returning a [`Future`] that
+    /// resolves to the response.
+    #[tracing::instrument(
+        name = "RPC",
+        skip(self, ctx, request_name, request),
+        fields(
+            rpc.trace_id = tracing::field::Empty,
+            rpc.deadline = %humantime::format_rfc3339(ctx.deadline),
+            otel.kind = "client",
+            otel.name = request_name)
+        )]
+    pub async fn call(
+        &self,
+        mut ctx: context::Context,
+        request_name: &str,
+        request: Req,
+    ) -> Result<Resp, RpcError> {
+        let span = Span::current();
+        ctx.trace_context = trace::Context::try_from(&span).unwrap_or_else(|_| {
+            tracing::trace!(
+                "OpenTelemetry subscriber not installed; making unsampled child context."
+            );
+            ctx.trace_context.new_child()
+        });
+        span.record("rpc.trace_id", &tracing::field::display(ctx.trace_id()));
+        let (response_completion, mut response) = oneshot::channel();
+        let request_id =
+            u64::try_from(self.next_request_id.fetch_add(1, Ordering::Relaxed)).unwrap();
+
+        // ResponseGuard impls Drop to cancel in-flight requests. It should be created before
+        // sending out the request; otherwise, the response future could be dropped after the
+        // request is sent out but before ResponseGuard is created, rendering the cancellation
+        // logic inactive.
+        let response_guard = ResponseGuard {
+            response: &mut response,
+            request_id,
+            cancellation: &self.cancellation,
+        };
+        self.to_dispatch
+            .send(DispatchRequest {
+                ctx,
+                span,
+                request_id,
+                request,
+                response_completion,
+            })
+            .await
+            .map_err(|mpsc::error::SendError(_)| RpcError::Disconnected)?;
+        response_guard.response().await
+    }
+}
+
+/// A server response that is completed by request dispatch when the corresponding response
+/// arrives off the wire.
+struct ResponseGuard<'a, Resp> {
+    response: &'a mut oneshot::Receiver<Result<Response<Resp>, DeadlineExceededError>>,
+    cancellation: &'a RequestCancellation,
+    request_id: u64,
+}
+
+/// An error that can occur in the processing of an RPC. This is not request-specific errors but
+/// rather cross-cutting errors that can always occur.
+#[derive(thiserror::Error, Clone, Debug, PartialEq, Eq, Hash)]
+#[cfg_attr(feature = "serde1", derive(serde::Serialize, serde::Deserialize))]
+pub enum RpcError {
+    /// The client disconnected from the server.
+    #[error("the client disconnected from the server")]
+    Disconnected,
+    /// The request exceeded its deadline.
+    #[error("the request exceeded its deadline")]
+    DeadlineExceeded,
+    /// The server aborted request processing.
+    #[error("the server aborted request processing")]
+    Server(#[from] ServerError),
+}
+
+impl From<DeadlineExceededError> for RpcError {
+    fn from(_: DeadlineExceededError) -> Self {
+        RpcError::DeadlineExceeded
+    }
+}
+
+impl<Resp> ResponseGuard<'_, Resp> {
+    async fn response(mut self) -> Result<Resp, RpcError> {
+        let response = (&mut self.response).await;
+        // Cancel drop logic once a response has been received.
+        mem::forget(self);
+        match response {
+            Ok(resp) => Ok(resp?.message?),
+            Err(oneshot::error::RecvError { .. }) => {
+                // 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(RpcError::Disconnected)
+            }
+        }
+    }
+}
+
+// Cancels the request when dropped, if not already complete.
+impl<Resp> Drop for ResponseGuard<'_, Resp> {
+    fn drop(&mut self) {
+        // 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.close();
+        self.cancellation.cancel(self.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;
+
+    NewClient {
+        client: Channel {
+            to_dispatch,
+            cancellation,
+            next_request_id: Arc::new(AtomicUsize::new(0)),
+        },
+        dispatch: RequestDispatch {
+            config,
+            canceled_requests,
+            transport: transport.fuse(),
+            in_flight_requests: InFlightRequests::default(),
+            pending_requests,
+        },
+    }
+}
+
+/// Handles the lifecycle of requests, writing requests to the wire, managing cancellations,
+/// and dispatching responses to the appropriate channel.
+#[must_use]
+#[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.
+    pending_requests: mpsc::Receiver<DispatchRequest<Req, Resp>>,
+    /// Requests that were dropped.
+    canceled_requests: CanceledRequests,
+    /// Requests already written to the wire that haven't yet received responses.
+    in_flight_requests: InFlightRequests<Resp>,
+    /// Configures limits to prevent unlimited resource usage.
+    config: Config,
+}
+
+/// Critical errors that result in a Channel disconnecting.
+#[derive(thiserror::Error, Debug)]
+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] 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),
+    /// Could not poll expired requests.
+    #[error("could not poll expired requests")]
+    Timer(#[source] tokio::time::error::Error),
+}
+
+impl<Req, Resp, C> RequestDispatch<Req, Resp, C>
+where
+    C: Transport<ClientMessage<Req>, Response<Resp>>,
+{
+    fn in_flight_requests<'a>(self: &'a mut Pin<&mut Self>) -> &'a mut InFlightRequests<Resp> {
+        self.as_mut().project().in_flight_requests
+    }
+
+    fn transport_pin_mut<'a>(self: &'a mut Pin<&mut Self>) -> Pin<&'a mut Fuse<C>> {
+        self.as_mut().project().transport
+    }
+
+    fn poll_ready<'a>(
+        self: &'a mut Pin<&mut Self>,
+        cx: &mut Context<'_>,
+    ) -> Poll<Result<(), ChannelError<C::Error>>> {
+        self.transport_pin_mut()
+            .poll_ready(cx)
+            .map_err(ChannelError::Ready)
+    }
+
+    fn start_send(
+        self: &mut Pin<&mut Self>,
+        message: ClientMessage<Req>,
+    ) -> Result<(), ChannelError<C::Error>> {
+        self.transport_pin_mut()
+            .start_send(message)
+            .map_err(ChannelError::Write)
+    }
+
+    fn poll_flush<'a>(
+        self: &'a mut Pin<&mut Self>,
+        cx: &mut Context<'_>,
+    ) -> Poll<Result<(), ChannelError<C::Error>>> {
+        self.transport_pin_mut()
+            .poll_flush(cx)
+            .map_err(ChannelError::Flush)
+    }
+
+    fn poll_close<'a>(
+        self: &'a mut Pin<&mut Self>,
+        cx: &mut Context<'_>,
+    ) -> Poll<Result<(), ChannelError<C::Error>>> {
+        self.transport_pin_mut()
+            .poll_close(cx)
+            .map_err(ChannelError::Close)
+    }
+
+    fn canceled_requests_mut<'a>(self: &'a mut Pin<&mut Self>) -> &'a mut CanceledRequests {
+        self.as_mut().project().canceled_requests
+    }
+
+    fn pending_requests_mut<'a>(
+        self: &'a mut Pin<&mut Self>,
+    ) -> &'a mut mpsc::Receiver<DispatchRequest<Req, Resp>> {
+        self.as_mut().project().pending_requests
+    }
+
+    fn pump_read(
+        mut self: Pin<&mut Self>,
+        cx: &mut Context<'_>,
+    ) -> Poll<Option<Result<(), ChannelError<C::Error>>>> {
+        self.transport_pin_mut()
+            .poll_next(cx)
+            .map_err(ChannelError::Read)
+            .map_ok(|response| {
+                self.complete(response);
+            })
+    }
+
+    fn pump_write(
+        mut self: Pin<&mut Self>,
+        cx: &mut Context<'_>,
+    ) -> Poll<Option<Result<(), ChannelError<C::Error>>>> {
+        enum ReceiverStatus {
+            Pending,
+            Closed,
+        }
+
+        let pending_requests_status = match self.as_mut().poll_write_request(cx)? {
+            Poll::Ready(Some(())) => return Poll::Ready(Some(Ok(()))),
+            Poll::Ready(None) => ReceiverStatus::Closed,
+            Poll::Pending => ReceiverStatus::Pending,
+        };
+
+        let canceled_requests_status = match self.as_mut().poll_write_cancel(cx)? {
+            Poll::Ready(Some(())) => return Poll::Ready(Some(Ok(()))),
+            Poll::Ready(None) => ReceiverStatus::Closed,
+            Poll::Pending => ReceiverStatus::Pending,
+        };
+
+        // Receiving Poll::Ready(None) when polling expired requests never indicates "Closed",
+        // because there can temporarily be zero in-flight rquests. Therefore, there is no need to
+        // track the status like is done with pending and cancelled requests.
+        if let Poll::Ready(Some(_)) = self.in_flight_requests().poll_expired(cx) {
+            // Expired requests are considered complete; there is no compelling reason to send a
+            // cancellation message to the server, since it will have already exhausted its
+            // allotted processing time.
+            return Poll::Ready(Some(Ok(())));
+        }
+
+        match (pending_requests_status, canceled_requests_status) {
+            (ReceiverStatus::Closed, ReceiverStatus::Closed) => {
+                ready!(self.poll_close(cx)?);
+                Poll::Ready(None)
+            }
+            (ReceiverStatus::Pending, _) | (_, ReceiverStatus::Pending) => {
+                // No more messages to process, so flush any messages buffered in the transport.
+                ready!(self.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.
+    ///
+    /// Note that a request will only be yielded if the transport is *ready* to be written to (i.e.
+    /// start_send would succeed).
+    fn poll_next_request(
+        mut self: Pin<&mut Self>,
+        cx: &mut Context<'_>,
+    ) -> Poll<Option<Result<DispatchRequest<Req, Resp>, ChannelError<C::Error>>>> {
+        if self.in_flight_requests().len() >= self.config.max_in_flight_requests {
+            tracing::info!(
+                "At in-flight request capacity ({}/{}).",
+                self.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;
+        }
+
+        ready!(self.ensure_writeable(cx)?);
+
+        loop {
+            match ready!(self.pending_requests_mut().poll_recv(cx)) {
+                Some(request) => {
+                    if request.response_completion.is_closed() {
+                        let _entered = request.span.enter();
+                        tracing::info!("AbortRequest");
+                        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.
+    ///
+    /// Note that a request to cancel will only be yielded if the transport is *ready* to be
+    /// written to (i.e.  start_send would succeed).
+    fn poll_next_cancellation(
+        mut self: Pin<&mut Self>,
+        cx: &mut Context<'_>,
+    ) -> Poll<Option<Result<(context::Context, Span, u64), ChannelError<C::Error>>>> {
+        ready!(self.ensure_writeable(cx)?);
+
+        loop {
+            match ready!(self.canceled_requests_mut().poll_next_unpin(cx)) {
+                Some(request_id) => {
+                    if let Some((ctx, span)) = self.in_flight_requests().cancel_request(request_id)
+                    {
+                        return Poll::Ready(Some(Ok((ctx, span, request_id))));
+                    }
+                }
+                None => return Poll::Ready(None),
+            }
+        }
+    }
+
+    /// Returns Ready if writing a message to the transport (i.e. via write_request or
+    /// write_cancel) would not fail due to a full buffer. If the transport is not ready to be
+    /// written to, flushes it until it is ready.
+    fn ensure_writeable<'a>(
+        self: &'a mut Pin<&mut Self>,
+        cx: &mut Context<'_>,
+    ) -> Poll<Option<Result<(), ChannelError<C::Error>>>> {
+        while self.poll_ready(cx)?.is_pending() {
+            ready!(self.poll_flush(cx)?);
+        }
+        Poll::Ready(Some(Ok(())))
+    }
+
+    fn poll_write_request<'a>(
+        self: &'a mut Pin<&mut Self>,
+        cx: &mut Context<'_>,
+    ) -> Poll<Option<Result<(), ChannelError<C::Error>>>> {
+        let DispatchRequest {
+            ctx,
+            span,
+            request_id,
+            request,
+            response_completion,
+        } = match ready!(self.as_mut().poll_next_request(cx)?) {
+            Some(dispatch_request) => dispatch_request,
+            None => return Poll::Ready(None),
+        };
+        let entered = span.enter();
+        // poll_next_request only returns Ready if there is room to buffer another request.
+        // Therefore, we can call write_request without fear of erroring due to a full
+        // buffer.
+        let request_id = request_id;
+        let request = ClientMessage::Request(Request {
+            id: request_id,
+            message: request,
+            context: context::Context {
+                deadline: ctx.deadline,
+                trace_context: ctx.trace_context,
+            },
+        });
+        self.start_send(request)?;
+        tracing::info!("SendRequest");
+        drop(entered);
+
+        self.in_flight_requests()
+            .insert_request(request_id, ctx, span, response_completion)
+            .expect("Request IDs should be unique");
+        Poll::Ready(Some(Ok(())))
+    }
+
+    fn poll_write_cancel<'a>(
+        self: &'a mut Pin<&mut Self>,
+        cx: &mut Context<'_>,
+    ) -> Poll<Option<Result<(), ChannelError<C::Error>>>> {
+        let (context, span, request_id) = match ready!(self.as_mut().poll_next_cancellation(cx)?) {
+            Some(triple) => triple,
+            None => return Poll::Ready(None),
+        };
+        let _entered = span.enter();
+
+        let cancel = ClientMessage::Cancel {
+            trace_context: context.trace_context,
+            request_id,
+        };
+        self.start_send(cancel)?;
+        tracing::info!("CancelRequest");
+        Poll::Ready(Some(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 {
+        self.in_flight_requests().complete_request(response)
+    }
+}
+
+impl<Req, Resp, C> Future for RequestDispatch<Req, Resp, C>
+where
+    C: Transport<ClientMessage<Req>, Response<Resp>>,
+{
+    type Output = Result<(), ChannelError<C::Error>>;
+
+    fn poll(
+        mut self: Pin<&mut Self>,
+        cx: &mut Context<'_>,
+    ) -> Poll<Result<(), ChannelError<C::Error>>> {
+        loop {
+            match (self.as_mut().pump_read(cx)?, self.as_mut().pump_write(cx)?) {
+                (Poll::Ready(None), _) => {
+                    tracing::info!("Shutdown: read half closed, so shutting down.");
+                    return Poll::Ready(Ok(()));
+                }
+                (read, Poll::Ready(None)) => {
+                    if self.in_flight_requests.is_empty() {
+                        tracing::info!("Shutdown: write half closed, and no requests in flight.");
+                        return Poll::Ready(Ok(()));
+                    }
+                    tracing::info!(
+                        "Shutdown: write half closed, and {} requests in flight.",
+                        self.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> {
+    pub ctx: context::Context,
+    pub span: Span,
+    pub request_id: u64,
+    pub request: Req,
+    pub response_completion: oneshot::Sender<Result<Response<Resp>, DeadlineExceededError>>,
+}
+
+#[cfg(test)]
+mod tests {
+    use super::{cancellations, Channel, DispatchRequest, RequestDispatch, ResponseGuard};
+    use crate::{
+        client::{
+            in_flight_requests::{DeadlineExceededError, InFlightRequests},
+            Config,
+        },
+        context,
+        transport::{self, channel::UnboundedChannel},
+        ClientMessage, Response,
+    };
+    use assert_matches::assert_matches;
+    use futures::{prelude::*, task::*};
+    use std::{
+        convert::TryFrom,
+        pin::Pin,
+        sync::atomic::{AtomicUsize, Ordering},
+        sync::Arc,
+    };
+    use tokio::sync::{mpsc, oneshot};
+    use tracing::Span;
+
+    #[tokio::test]
+    async fn response_completes_request_future() {
+        let (mut dispatch, mut _channel, mut server_channel) = set_up();
+        let cx = &mut Context::from_waker(&noop_waker_ref());
+        let (tx, mut rx) = oneshot::channel();
+
+        dispatch
+            .in_flight_requests
+            .insert_request(0, context::current(), Span::current(), tx)
+            .unwrap();
+        server_channel
+            .send(Response {
+                request_id: 0,
+                message: Ok("Resp".into()),
+            })
+            .await
+            .unwrap();
+        assert_matches!(dispatch.as_mut().poll(cx), Poll::Pending);
+        assert_matches!(rx.try_recv(), Ok(Ok(Response { request_id: 0, message: Ok(resp) })) if resp == "Resp");
+    }
+
+    #[tokio::test]
+    async fn dispatch_response_cancels_on_drop() {
+        let (cancellation, mut canceled_requests) = cancellations();
+        let (_, mut response) = oneshot::channel();
+        drop(ResponseGuard::<u32> {
+            response: &mut response,
+            cancellation: &cancellation,
+            request_id: 3,
+        });
+        // resp's drop() is run, which should send a cancel message.
+        let cx = &mut Context::from_waker(&noop_waker_ref());
+        assert_eq!(canceled_requests.poll_recv(cx), Poll::Ready(Some(3)));
+    }
+
+    #[tokio::test]
+    async fn dispatch_response_doesnt_cancel_after_complete() {
+        let (cancellation, mut canceled_requests) = cancellations();
+        let (tx, mut response) = oneshot::channel();
+        tx.send(Ok(Response {
+            request_id: 0,
+            message: Ok("well done"),
+        }))
+        .unwrap();
+        // resp's drop() is run, but should not send a cancel message.
+        ResponseGuard {
+            response: &mut response,
+            cancellation: &cancellation,
+            request_id: 3,
+        }
+        .response()
+        .await
+        .unwrap();
+        drop(cancellation);
+        let cx = &mut Context::from_waker(&noop_waker_ref());
+        assert_eq!(canceled_requests.poll_recv(cx), Poll::Ready(None));
+    }
+
+    #[tokio::test]
+    async fn stage_request() {
+        let (mut dispatch, mut channel, _server_channel) = set_up();
+        let cx = &mut Context::from_waker(&noop_waker_ref());
+        let (tx, mut rx) = oneshot::channel();
+
+        let _resp = send_request(&mut channel, "hi", tx, &mut rx).await;
+
+        #[allow(unstable_name_collisions)]
+        let req = dispatch.as_mut().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]
+    async fn stage_request_channel_dropped_doesnt_panic() {
+        let (mut dispatch, mut channel, mut server_channel) = set_up();
+        let cx = &mut Context::from_waker(&noop_waker_ref());
+        let (tx, mut rx) = oneshot::channel();
+
+        let _ = send_request(&mut channel, "hi", tx, &mut rx).await;
+        drop(channel);
+
+        assert!(dispatch.as_mut().poll(cx).is_ready());
+        send_response(
+            &mut server_channel,
+            Response {
+                request_id: 0,
+                message: Ok("hello".into()),
+            },
+        )
+        .await;
+        dispatch.await.unwrap();
+    }
+
+    #[allow(unstable_name_collisions)]
+    #[tokio::test]
+    async fn stage_request_response_future_dropped_is_canceled_before_sending() {
+        let (mut dispatch, mut channel, _server_channel) = set_up();
+        let cx = &mut Context::from_waker(&noop_waker_ref());
+        let (tx, mut rx) = oneshot::channel();
+
+        let _ = send_request(&mut channel, "hi", tx, &mut rx).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.as_mut().poll_next_request(cx).ready().is_none());
+    }
+
+    #[allow(unstable_name_collisions)]
+    #[tokio::test]
+    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 (tx, mut rx) = oneshot::channel();
+
+        let req = send_request(&mut channel, "hi", tx, &mut rx).await;
+
+        assert!(dispatch.as_mut().pump_write(cx).ready().is_some());
+        assert!(!dispatch.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);
+        assert_matches!(
+            dispatch.as_mut().poll_next_cancellation(cx),
+            Poll::Ready(Some(Ok(_)))
+        );
+        assert!(dispatch.in_flight_requests.is_empty());
+    }
+
+    #[tokio::test]
+    async fn stage_request_response_closed_skipped() {
+        let (mut dispatch, mut channel, _server_channel) = set_up();
+        let cx = &mut Context::from_waker(&noop_waker_ref());
+        let (tx, mut rx) = oneshot::channel();
+
+        // 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 resp = send_request(&mut channel, "hi", tx, &mut rx).await;
+        resp.response.close();
+
+        assert!(dispatch.as_mut().poll_next_request(cx).is_pending());
+    }
+
+    fn set_up() -> (
+        Pin<
+            Box<
+                RequestDispatch<
+                    String,
+                    String,
+                    UnboundedChannel<Response<String>, ClientMessage<String>>,
+                >,
+            >,
+        >,
+        Channel<String, String>,
+        UnboundedChannel<ClientMessage<String>, Response<String>>,
+    ) {
+        let _ = tracing_subscriber::fmt().with_test_writer().try_init();
+
+        let (to_dispatch, pending_requests) = mpsc::channel(1);
+        let (cancellation, canceled_requests) = cancellations();
+        let (client_channel, server_channel) = transport::channel::unbounded();
+
+        let dispatch = RequestDispatch::<String, String, _> {
+            transport: client_channel.fuse(),
+            pending_requests: pending_requests,
+            canceled_requests,
+            in_flight_requests: InFlightRequests::default(),
+            config: Config::default(),
+        };
+
+        let channel = Channel {
+            to_dispatch,
+            cancellation,
+            next_request_id: Arc::new(AtomicUsize::new(0)),
+        };
+
+        (Box::pin(dispatch), channel, server_channel)
+    }
+
+    async fn send_request<'a>(
+        channel: &'a mut Channel<String, String>,
+        request: &str,
+        response_completion: oneshot::Sender<Result<Response<String>, DeadlineExceededError>>,
+        response: &'a mut oneshot::Receiver<Result<Response<String>, DeadlineExceededError>>,
+    ) -> ResponseGuard<'a, String> {
+        let request_id =
+            u64::try_from(channel.next_request_id.fetch_add(1, Ordering::Relaxed)).unwrap();
+        let request = DispatchRequest {
+            ctx: context::current(),
+            span: Span::current(),
+            request_id,
+            request: request.to_string(),
+            response_completion,
+        };
+        let response_guard = ResponseGuard {
+            response,
+            cancellation: &channel.cancellation,
+            request_id,
+        };
+        channel.to_dispatch.send(request).await.unwrap();
+        response_guard
+    }
+
+    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/client/in_flight_requests.rs

@@ -0,0 +1,134 @@
+use crate::{
+    context,
+    util::{Compact, TimeUntil},
+    Response,
+};
+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(),
+        }
+    }
+}
+
+/// The request exceeded its deadline.
+#[derive(thiserror::Error, Debug)]
+#[non_exhaustive]
+#[error("the request exceeded its deadline")]
+pub struct DeadlineExceededError;
+
+#[derive(Debug)]
+struct RequestData<Resp> {
+    ctx: context::Context,
+    span: Span,
+    response_completion: oneshot::Sender<Result<Response<Resp>, DeadlineExceededError>>,
+    /// 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<Resp> InFlightRequests<Resp> {
+    /// 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<Result<Response<Resp>, DeadlineExceededError>>,
+    ) -> 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, response: Response<Resp>) -> bool {
+        if let Some(request_data) = self.request_data.remove(&response.request_id) {
+            let _entered = request_data.span.enter();
+            tracing::info!("ReceiveResponse");
+            self.request_data.compact(0.1);
+            self.deadlines.remove(&request_data.deadline_key);
+            let _ = request_data.response_completion.send(Ok(response));
+            return true;
+        }
+
+        tracing::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
+    }
+
+    /// 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) -> 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(Err(DeadlineExceededError));
+            }
+            Some(request_id)
+        })
+    }
+}

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

@@ -1,66 +1,422 @@
-// Copyright 2016 Google Inc. All Rights Reserved.
+// Copyright 2018 Google LLC
 //
-// Licensed under the MIT License, <LICENSE or http://opensource.org/licenses/MIT>.
-// This file may not be copied, modified, or distributed except according to those terms.
-
-//! An RPC library for Rust.
+// 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.
+//! *Disclaimer*: This is not an official Google product.
 //!
-//! Example usage:
+//! tarpc is an RPC framework for rust with a focus on ease of use. Defining a
+//! service can be done in just a few lines of code, and most of the boilerplate of
+//! writing a server is taken care of for you.
 //!
+//! [Documentation](https://docs.rs/crate/tarpc/)
+//!
+//! ## 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
+//! and asks them to evaluate the function instead. The original function then
+//! returns the value produced by the other process.
+//!
+//! RPC frameworks are a fundamental building block of most microservices-oriented
+//! architectures. Two well-known ones are [gRPC](http://www.grpc.io) and
+//! [Cap'n Proto](https://capnproto.org/).
+//!
+//! tarpc differentiates itself from other RPC frameworks by defining the schema in code,
+//! rather than in a separate language such as .proto. This means there's no separate compilation
+//! process, and no context switching between different languages.
+//!
+//! Some other features of tarpc:
+//! - 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.
+//!   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.
+//! - Configurable deadlines and deadline propagation: request deadlines default to 10s if
+//!   unspecified. The server will automatically cease work when the deadline has passed. Any
+//!   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
+//! Add to your `Cargo.toml` dependencies:
+//!
+//! ```toml
+//! tarpc = "0.29"
 //! ```
-//! #[macro_use] extern crate tarpc;
-//! mod my_server {
-//!     service! {
-//!         rpc hello(name: String) -> String;
-//!         rpc add(x: i32, y: i32) -> i32;
-//!     }
-//! }
 //!
-//! use self::my_server::*;
-//! use std::time::Duration;
+//! 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!
 //!
-//! struct Server;
-//! impl my_server::Service for Server {
-//!     fn hello(&self, s: String) -> String {
-//!         format!("Hello, {}!", s)
-//!     }
-//!     fn add(&self, x: i32, y: i32) -> i32 {
-//!         x + y
-//!     }
-//! }
+//! ## Example
 //!
-//! fn main() {
-//!     let serve_handle = Server.spawn("localhost:0").unwrap();
-//!     let client = Client::new(serve_handle.dialer()).unwrap();
-//!     assert_eq!(3, client.add(1, 2).unwrap());
-//!     assert_eq!("Hello, Mom!".to_string(),
-//!                client.hello("Mom".to_string()).unwrap());
-//!     drop(client);
-//!     serve_handle.shutdown();
+//! This example uses [tokio](https://tokio.rs), so add the following dependencies to
+//! your `Cargo.toml`:
+//!
+//! ```toml
+//! anyhow = "1.0"
+//! futures = "0.3"
+//! 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
+//! client and server. In real code, you will likely communicate over the network.
+//! For a more real-world example, see [example-service](example-service).
+//!
+//! First, let's set up the dependencies and service definition.
+//!
+//! ```rust
+//! # extern crate futures;
+//!
+//! use futures::{
+//!     future::{self, Ready},
+//!     prelude::*,
+//! };
+//! use tarpc::{
+//!     client, context,
+//!     server::{self, incoming::Incoming, Channel},
+//! };
+//!
+//! // 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]
+//! trait World {
+//!     /// Returns a greeting for name.
+//!     async fn hello(name: String) -> String;
 //! }
 //! ```
-
+//!
+//! This service definition generates a trait called `World`. Next we need to
+//! implement it for our Server struct.
+//!
+//! ```rust
+//! # extern crate futures;
+//! # use futures::{
+//! #     future::{self, Ready},
+//! #     prelude::*,
+//! # };
+//! # use tarpc::{
+//! #     client, context,
+//! #     server::{self, incoming::Incoming},
+//! # };
+//! # // 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]
+//! # trait World {
+//! #     /// Returns a greeting for name.
+//! #     async fn hello(name: String) -> String;
+//! # }
+//! // This is the type that implements the generated World trait. It is the business logic
+//! // and is used to start the server.
+//! #[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}!"))
+//!     }
+//! }
+//! ```
+//!
+//! Lastly let's write our `main` that will start the server. While this example uses an
+//! [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
+//! # extern crate futures;
+//! # use futures::{
+//! #     future::{self, Ready},
+//! #     prelude::*,
+//! # };
+//! # use tarpc::{
+//! #     client, context,
+//! #     server::{self, Channel},
+//! # };
+//! # // 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]
+//! # trait World {
+//! #     /// Returns a greeting for name.
+//! #     async fn hello(name: String) -> String;
+//! # }
+//! # // This is the type that implements the generated World trait. It is the business logic
+//! # // and is used to start the server.
+//! # #[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}!"))
+//! #     }
+//! # }
+//! # #[cfg(not(feature = "tokio1"))]
+//! # fn main() {}
+//! # #[cfg(feature = "tokio1")]
+//! #[tokio::main]
+//! async fn main() -> anyhow::Result<()> {
+//!     let (client_transport, server_transport) = tarpc::transport::channel::unbounded();
+//!
+//!     let server = server::BaseChannel::with_defaults(server_transport);
+//!     tokio::spawn(server.execute(HelloServer.serve()));
+//!
+//!     // 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}");
+//!
+//!     Ok(())
+//! }
+//! ```
+//!
+//! ## Service Documentation
+//!
+//! 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))]
 
-extern crate serde;
-extern crate bincode;
-#[macro_use]
-extern crate log;
-extern crate scoped_pool;
-extern crate unix_socket;
+#[cfg(feature = "serde1")]
+#[doc(hidden)]
+pub use serde;
 
-macro_rules! pos {
-    () => (concat!(file!(), ":", line!()))
+#[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:
+///
+/// ```
+/// #[tarpc::service]
+/// trait Service {
+/// /// Say hello
+/// async fn hello(name: String) -> String;
+/// }
+/// ```
+///
+/// Attributes can be attached to each rpc. These attributes
+/// will then be attached to the generated service traits'
+/// corresponding `fn`s, as well as to the client stubs' RPCs.
+///
+/// The following items are expanded in the enclosing module:
+///
+/// * `trait Service` -- defines the RPC service.
+///   * `fn serve` -- turns a service impl into a request handler.
+/// * `Client` -- a client stub with a fn for each RPC.
+///   * `fn new_stub` -- creates a new Client stub.
+pub use tarpc_plugins::service;
+
+/// A utility macro that can be used for RPC server implementations.
+///
+/// Syntactic sugar to make using async functions in the server implementation
+/// easier. It does this by rewriting code like this, which would normally not
+/// compile because async functions are disallowed in trait implementations:
+///
+/// ```rust
+/// # use tarpc::context;
+/// # use std::net::SocketAddr;
+/// #[tarpc::service]
+/// trait World {
+///     async fn hello(name: String) -> String;
+/// }
+///
+/// #[derive(Clone)]
+/// struct HelloServer(SocketAddr);
+///
+/// #[tarpc::server]
+/// impl World for HelloServer {
+///     async fn hello(self, _: context::Context, name: String) -> String {
+///         format!("Hello, {name}! You are connected from {:?}.", self.0)
+///     }
+/// }
+/// ```
+///
+/// Into code like this, which matches the service trait definition:
+///
+/// ```rust
+/// # use tarpc::context;
+/// # use std::pin::Pin;
+/// # use futures::Future;
+/// # use std::net::SocketAddr;
+/// #[derive(Clone)]
+/// struct HelloServer(SocketAddr);
+///
+/// #[tarpc::service]
+/// trait World {
+///     async fn hello(name: String) -> String;
+/// }
+///
+/// impl World for HelloServer {
+///     type HelloFut = Pin<Box<dyn Future<Output = String> + Send>>;
+///
+///     fn hello(self, _: context::Context, name: String) -> Pin<Box<dyn Future<Output = String>
+///     + Send>> {
+///         Box::pin(async move {
+///             format!("Hello, {name}! You are connected from {:?}.", self.0)
+///         })
+///     }
+/// }
+/// ```
+///
+/// Note that this won't touch functions unless they have been annotated with
+/// `async`, meaning that this should not break existing code.
+pub use tarpc_plugins::server;
+
+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::{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,
+    },
 }
 
-/// Provides the tarpc client and server, which implements the tarpc protocol.
-/// The protocol is defined by the implementation.
-pub mod protocol;
+/// 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,
+}
 
-/// Provides the macro used for constructing rpc services and client stubs.
-pub mod macros;
+/// 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>,
+}
 
-/// Provides transport traits and implementations.
-pub mod transport;
+/// 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,
+}
 
-pub use protocol::{Config, Error, Result, ServeHandle};
+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/macros.rs

@@ -1,632 +0,0 @@
-// Copyright 2016 Google Inc. All Rights Reserved.
-//
-// Licensed under the MIT License, <LICENSE or http://opensource.org/licenses/MIT>.
-// This file may not be copied, modified, or distributed except according to those terms.
-
-/// Serde re-exports required by macros. Not for general use.
-pub mod serde {
-    pub use serde::{Deserialize, Deserializer, Serialize, Serializer};
-    /// Deserialization re-exports required by macros. Not for general use.
-    pub mod de {
-        pub use serde::de::{EnumVisitor, Error, VariantVisitor, Visitor};
-    }
-}
-
-// Required because if-let can't be used with irrefutable patterns, so it needs
-// to be special cased.
-#[doc(hidden)]
-#[macro_export]
-macro_rules! client_methods {
-    (
-        { $(#[$attr:meta])* }
-        $fn_name:ident( ($($arg:ident,)*) : ($($in_:ty,)*) ) -> $out:ty
-    ) => (
-        #[allow(unused)]
-        $(#[$attr])*
-        pub fn $fn_name(&self, $($arg: $in_),*) -> $crate::Result<$out> {
-            let reply = try!((self.0).rpc(__Request::$fn_name(($($arg,)*))));
-            let __Reply::$fn_name(reply) = reply;
-            ::std::result::Result::Ok(reply)
-        }
-    );
-    ($(
-            { $(#[$attr:meta])* }
-            $fn_name:ident( ($( $arg:ident,)*) : ($($in_:ty, )*) ) -> $out:ty
-    )*) => ( $(
-        #[allow(unused)]
-        $(#[$attr])*
-        pub fn $fn_name(&self, $($arg: $in_),*) -> $crate::Result<$out> {
-            let reply = try!((self.0).rpc(__Request::$fn_name(($($arg,)*))));
-            if let __Reply::$fn_name(reply) = reply {
-                ::std::result::Result::Ok(reply)
-            } else {
-                panic!("Incorrect reply variant returned from rpc; expected `{}`, \
-                       but got {:?}",
-                       stringify!($fn_name),
-                       reply);
-            }
-        }
-    )*);
-}
-
-// Required because if-let can't be used with irrefutable patterns, so it needs
-// to be special cased.
-#[doc(hidden)]
-#[macro_export]
-macro_rules! async_client_methods {
-    (
-        { $(#[$attr:meta])* }
-        $fn_name:ident( ($( $arg:ident, )*) : ($( $in_:ty, )*) ) -> $out:ty
-    ) => (
-        #[allow(unused)]
-        $(#[$attr])*
-        pub fn $fn_name(&self, $($arg: $in_),*) -> Future<$out> {
-            fn mapper(reply: __Reply) -> $out {
-                let __Reply::$fn_name(reply) = reply;
-                reply
-            }
-            let reply = (self.0).rpc_async(__Request::$fn_name(($($arg,)*)));
-            Future {
-                future: reply,
-                mapper: mapper,
-            }
-        }
-    );
-    ($(
-            { $(#[$attr:meta])* }
-            $fn_name:ident( ($( $arg:ident, )*) : ($( $in_:ty, )*) ) -> $out:ty
-    )*) => ( $(
-        #[allow(unused)]
-        $(#[$attr])*
-        pub fn $fn_name(&self, $($arg: $in_),*) -> Future<$out> {
-            fn mapper(reply: __Reply) -> $out {
-                if let __Reply::$fn_name(reply) = reply {
-                    reply
-                } else {
-                    panic!("Incorrect reply variant returned from rpc; expected `{}`, but got \
-                           {:?}",
-                           stringify!($fn_name),
-                           reply);
-                }
-            }
-            let reply = (self.0).rpc_async(__Request::$fn_name(($($arg,)*)));
-            Future {
-                future: reply,
-                mapper: mapper,
-            }
-        }
-    )*);
-}
-
-#[doc(hidden)]
-#[macro_export]
-macro_rules! impl_serialize {
-    ($impler:ident, $(@($name:ident $n:expr))* -- #($_n:expr) ) => (
-        impl $crate::macros::serde::Serialize for $impler {
-            #[inline]
-            fn serialize<S>(&self, serializer: &mut S) -> ::std::result::Result<(), S::Error>
-                where S: $crate::macros::serde::Serializer
-            {
-                match *self {
-                    $(
-                        $impler::$name(ref field) =>
-                            $crate::macros::serde::Serializer::serialize_newtype_variant(
-                                serializer,
-                                stringify!($impler),
-                                $n,
-                                stringify!($name),
-                                field,
-                            )
-                    ),*
-                }
-            }
-        }
-    );
-    // All args are wrapped in a tuple so we can use the newtype variant for each one.
-    ($impler:ident, $(@$finished:tt)* -- #($n:expr) $name:ident($field:ty) $($req:tt)*) => (
-        impl_serialize!($impler, $(@$finished)* @($name $n) -- #($n + 1) $($req)*);
-    );
-    // Entry
-    ($impler:ident, $($started:tt)*) => (impl_serialize!($impler, -- #(0) $($started)*););
-}
-
-#[doc(hidden)]
-#[macro_export]
-macro_rules! impl_deserialize {
-    ($impler:ident, $(@($name:ident $n:expr))* -- #($_n:expr) ) => (
-        impl $crate::macros::serde::Deserialize for $impler {
-            #[inline]
-            fn deserialize<D>(deserializer: &mut D)
-                -> ::std::result::Result<$impler, D::Error>
-                where D: $crate::macros::serde::Deserializer
-            {
-                #[allow(non_camel_case_types, unused)]
-                enum __Field {
-                    $($name),*
-                }
-                impl $crate::macros::serde::Deserialize for __Field {
-                    #[inline]
-                    fn deserialize<D>(deserializer: &mut D)
-                        -> ::std::result::Result<__Field, D::Error>
-                        where D: $crate::macros::serde::Deserializer
-                    {
-                        struct __FieldVisitor;
-                        impl $crate::macros::serde::de::Visitor for __FieldVisitor {
-                            type Value = __Field;
-
-                            #[inline]
-                            fn visit_usize<E>(&mut self, value: usize)
-                                -> ::std::result::Result<__Field, E>
-                                where E: $crate::macros::serde::de::Error,
-                            {
-                                $(
-                                    if value == $n {
-                                        return ::std::result::Result::Ok(__Field::$name);
-                                    }
-                                )*
-                                return ::std::result::Result::Err(
-                                    $crate::macros::serde::de::Error::custom(
-                                        format!("No variants have a value of {}!", value))
-                                );
-                            }
-                        }
-                        deserializer.deserialize_struct_field(__FieldVisitor)
-                    }
-                }
-
-                struct __Visitor;
-                impl $crate::macros::serde::de::EnumVisitor for __Visitor {
-                    type Value = $impler;
-
-                    #[inline]
-                    fn visit<__V>(&mut self, mut visitor: __V)
-                        -> ::std::result::Result<$impler, __V::Error>
-                        where __V: $crate::macros::serde::de::VariantVisitor
-                    {
-                        match try!(visitor.visit_variant()) {
-                            $(
-                                __Field::$name => {
-                                    let val = try!(visitor.visit_newtype());
-                                    Ok($impler::$name(val))
-                                }
-                            ),*
-                        }
-                    }
-                }
-                const VARIANTS: &'static [&'static str] = &[
-                    $(
-                        stringify!($name)
-                    ),*
-                ];
-                deserializer.deserialize_enum(stringify!($impler), VARIANTS, __Visitor)
-            }
-        }
-    );
-    // All args are wrapped in a tuple so we can use the newtype variant for each one.
-    ($impler:ident, $(@$finished:tt)* -- #($n:expr) $name:ident($field:ty) $($req:tt)*) => (
-        impl_deserialize!($impler, $(@$finished)* @($name $n) -- #($n + 1) $($req)*);
-    );
-    // Entry
-    ($impler:ident, $($started:tt)*) => (impl_deserialize!($impler, -- #(0) $($started)*););
-}
-
-/// The main macro that creates RPC services.
-///
-/// Rpc methods are specified, mirroring trait syntax:
-///
-/// ```
-/// # #[macro_use] extern crate tarpc;
-/// # fn main() {}
-/// # service! {
-/// #[doc="Say hello"]
-/// rpc hello(name: String) -> String;
-/// # }
-/// ```
-///
-/// There are two rpc names reserved for the default fns `spawn` and `spawn_with_config`.
-///
-/// Attributes can be attached to each rpc. These attributes
-/// will then be attached to the generated `Service` trait's
-/// corresponding method, as well as to the `Client` stub's rpcs methods.
-///
-/// The following items are expanded in the enclosing module:
-///
-/// * `Service` -- the trait defining the RPC service. It comes with two default methods for
-///                starting the server:
-///                1. `spawn` starts the service in another thread using default configuration.
-///                2. `spawn_with_config` starts the service in another thread using the specified
-///                   `Config`.
-/// * `Client` -- a client that makes synchronous requests to the RPC server
-/// * `AsyncClient` -- a client that makes asynchronous requests to the RPC server
-/// * `Future` -- a handle for asynchronously retrieving the result of an RPC
-///
-/// **Warning**: In addition to the above items, there are a few expanded items that
-/// are considered implementation details. As with the above items, shadowing
-/// these item names in the enclosing module is likely to break things in confusing
-/// ways:
-///
-/// * `__Server` -- an implementation detail
-/// * `__Request` -- an implementation detail
-/// * `__Reply` -- an implementation detail
-#[macro_export]
-macro_rules! service {
-// Entry point
-    (
-        $(
-            $(#[$attr:meta])*
-            rpc $fn_name:ident( $( $arg:ident : $in_:ty ),* ) $(-> $out:ty)*;
-        )*
-    ) => {
-        service! {{
-            $(
-                $(#[$attr])*
-                rpc $fn_name( $( $arg : $in_ ),* ) $(-> $out)*;
-            )*
-        }}
-    };
-// Pattern for when the next rpc has an implicit unit return type
-    (
-        {
-            $(#[$attr:meta])*
-            rpc $fn_name:ident( $( $arg:ident : $in_:ty ),* );
-
-            $( $unexpanded:tt )*
-        }
-        $( $expanded:tt )*
-    ) => {
-        service! {
-            { $( $unexpanded )* }
-
-            $( $expanded )*
-
-            $(#[$attr])*
-            rpc $fn_name( $( $arg : $in_ ),* ) -> ();
-        }
-    };
-// Pattern for when the next rpc has an explicit return type
-    (
-        {
-            $(#[$attr:meta])*
-            rpc $fn_name:ident( $( $arg:ident : $in_:ty ),* ) -> $out:ty;
-
-            $( $unexpanded:tt )*
-        }
-        $( $expanded:tt )*
-    ) => {
-        service! {
-            { $( $unexpanded )* }
-
-            $( $expanded )*
-
-            $(#[$attr])*
-            rpc $fn_name( $( $arg : $in_ ),* ) -> $out;
-        }
-    };
-// Pattern for when all return types have been expanded
-    (
-        { } // none left to expand
-        $(
-            $(#[$attr:meta])*
-            rpc $fn_name:ident ( $( $arg:ident : $in_:ty ),* ) -> $out:ty;
-        )*
-    ) => {
-        #[doc="Defines the RPC service"]
-        pub trait Service: Send + Sync + Sized {
-            $(
-                $(#[$attr])*
-                fn $fn_name(&self, $($arg:$in_),*) -> $out;
-            )*
-
-            #[doc="Spawn a running service."]
-            fn spawn<T>(self,
-                        transport: T)
-                        -> $crate::Result<
-                            $crate::protocol::ServeHandle<
-                            <T::Listener as $crate::transport::Listener>::Dialer>>
-                where T: $crate::transport::Transport,
-                      Self: 'static,
-            {
-                self.spawn_with_config(transport, $crate::Config::default())
-            }
-
-            #[doc="Spawn a running service."]
-            fn spawn_with_config<T>(self,
-                                    transport: T,
-                                    config: $crate::Config)
-                                    -> $crate::Result<
-                                        $crate::protocol::ServeHandle<
-                                        <T::Listener as $crate::transport::Listener>::Dialer>>
-                where T: $crate::transport::Transport,
-                      Self: 'static,
-            {
-                let server = __Server(self);
-                let result = $crate::protocol::Serve::spawn_with_config(server, transport, config);
-                let handle = try!(result);
-                ::std::result::Result::Ok(handle)
-            }
-        }
-
-        impl<P, S> Service for P
-            where P: Send + Sync + Sized + 'static + ::std::ops::Deref<Target=S>,
-                  S: Service
-        {
-            $(
-                $(#[$attr])*
-                fn $fn_name(&self, $($arg:$in_),*) -> $out {
-                    Service::$fn_name(&**self, $($arg),*)
-                }
-            )*
-        }
-
-        #[allow(non_camel_case_types, unused)]
-        #[derive(Debug)]
-        enum __Request {
-            $(
-                $fn_name(( $($in_,)* ))
-            ),*
-        }
-
-        impl_serialize!(__Request, $($fn_name(($($in_),*)))*);
-        impl_deserialize!(__Request, $($fn_name(($($in_),*)))*);
-
-        #[allow(non_camel_case_types, unused)]
-        #[derive(Debug)]
-        enum __Reply {
-            $(
-                $fn_name($out),
-            )*
-        }
-
-        impl_serialize!(__Reply, $($fn_name($out))*);
-        impl_deserialize!(__Reply, $($fn_name($out))*);
-
-        #[allow(unused)]
-        #[doc="An asynchronous RPC call"]
-        pub struct Future<T> {
-            future: $crate::protocol::Future<__Reply>,
-            mapper: fn(__Reply) -> T,
-        }
-
-        impl<T> Future<T> {
-            #[allow(unused)]
-            #[doc="Block until the result of the RPC call is available"]
-            pub fn get(self) -> $crate::Result<T> {
-                self.future.get().map(self.mapper)
-            }
-        }
-
-        #[allow(unused)]
-        #[doc="The client stub that makes RPC calls to the server."]
-        pub struct Client<S = ::std::net::TcpStream>(
-            $crate::protocol::Client<__Request, __Reply, S>
-        ) where S: $crate::transport::Stream;
-
-        impl<S> Client<S>
-            where S: $crate::transport::Stream
-        {
-            #[allow(unused)]
-            #[doc="Create a new client with default configuration that connects to the given \
-                   address."]
-            pub fn new<D>(dialer: D) -> $crate::Result<Self>
-                where D: $crate::transport::Dialer<Stream=S>,
-            {
-                Self::with_config(dialer, $crate::Config::default())
-            }
-
-            #[allow(unused)]
-            #[doc="Create a new client with the specified configuration that connects to the \
-                   given address."]
-            pub fn with_config<D>(dialer: D, config: $crate::Config) -> $crate::Result<Self>
-                where D: $crate::transport::Dialer<Stream=S>,
-            {
-                let inner = try!($crate::protocol::Client::with_config(dialer, config));
-                ::std::result::Result::Ok(Client(inner))
-            }
-
-            client_methods!(
-                $(
-                    { $(#[$attr])* }
-                    $fn_name(($($arg,)*) : ($($in_,)*)) -> $out
-                )*
-            );
-
-            #[allow(unused)]
-            #[doc="Attempt to clone the client object. This might fail if the underlying TcpStream \
-                   clone fails."]
-            pub fn try_clone(&self) -> ::std::io::Result<Self> {
-                ::std::result::Result::Ok(Client(try!(self.0.try_clone())))
-            }
-        }
-
-        #[allow(unused)]
-        #[doc="The client stub that makes asynchronous RPC calls to the server."]
-        pub struct AsyncClient<S = ::std::net::TcpStream>(
-            $crate::protocol::Client<__Request, __Reply, S>
-        ) where S: $crate::transport::Stream;
-
-        impl<S> AsyncClient<S>
-            where S: $crate::transport::Stream {
-            #[allow(unused)]
-            #[doc="Create a new asynchronous client with default configuration that connects to \
-                   the given address."]
-            pub fn new<D>(dialer: D) -> $crate::Result<Self>
-                where D: $crate::transport::Dialer<Stream=S>,
-            {
-                Self::with_config(dialer, $crate::Config::default())
-            }
-
-            #[allow(unused)]
-            #[doc="Create a new asynchronous client that connects to the given address."]
-            pub fn with_config<D>(dialer: D, config: $crate::Config) -> $crate::Result<Self>
-                where D: $crate::transport::Dialer<Stream=S>,
-            {
-                let inner = try!($crate::protocol::Client::with_config(dialer, config));
-                ::std::result::Result::Ok(AsyncClient(inner))
-            }
-
-            async_client_methods!(
-                $(
-                    { $(#[$attr])* }
-                    $fn_name(($($arg,)*): ($($in_,)*)) -> $out
-                )*
-            );
-
-            #[allow(unused)]
-            #[doc="Attempt to clone the client object. This might fail if the underlying TcpStream \
-                   clone fails."]
-            pub fn try_clone(&self) -> ::std::io::Result<Self> {
-                ::std::result::Result::Ok(AsyncClient(try!(self.0.try_clone())))
-            }
-        }
-
-        #[allow(unused)]
-        struct __Server<S>(S)
-            where S: 'static + Service;
-
-        impl<S> $crate::protocol::Serve for __Server<S>
-            where S: 'static + Service
-        {
-            type Request = __Request;
-            type Reply = __Reply;
-            fn serve(&self, request: __Request) -> __Reply {
-                match request {
-                    $(
-                        __Request::$fn_name(( $($arg,)* )) =>
-                            __Reply::$fn_name((self.0).$fn_name($($arg),*)),
-                    )*
-                }
-            }
-        }
-    }
-}
-
-#[allow(dead_code)]
-// because we're just testing that the macro expansion compiles
-#[cfg(test)]
-mod syntax_test {
-    // Tests a service definition with a fn that takes no args
-    mod qux {
-        service! {
-            rpc hello() -> String;
-        }
-    }
-    // Tests a service definition with an attribute.
-    mod bar {
-        service! {
-            #[doc="Hello bob"]
-            rpc baz(s: String) -> String;
-        }
-    }
-
-    // Tests a service with implicit return types.
-    mod no_return {
-        service! {
-            rpc ack();
-            rpc apply(foo: String) -> i32;
-            rpc bi_consume(bar: String, baz: u64);
-            rpc bi_fn(bar: String, baz: u64) -> String;
-        }
-    }
-}
-
-#[cfg(test)]
-mod functional_test {
-    extern crate env_logger;
-    extern crate tempdir;
-    use transport::unix::UnixTransport;
-
-    service! {
-        rpc add(x: i32, y: i32) -> i32;
-        rpc hey(name: String) -> String;
-    }
-
-    struct Server;
-
-    impl Service for Server {
-        fn add(&self, x: i32, y: i32) -> i32 {
-            x + y
-        }
-        fn hey(&self, name: String) -> String {
-            format!("Hey, {}.", name)
-        }
-    }
-
-    #[test]
-    fn simple() {
-        let _ = env_logger::init();
-        let handle = Server.spawn("localhost:0").unwrap();
-        let client = Client::new(handle.dialer()).unwrap();
-        assert_eq!(3, client.add(1, 2).unwrap());
-        assert_eq!("Hey, Tim.", client.hey("Tim".into()).unwrap());
-        drop(client);
-        handle.shutdown();
-    }
-
-    #[test]
-    fn simple_async() {
-        let _ = env_logger::init();
-        let handle = Server.spawn("localhost:0").unwrap();
-        let client = AsyncClient::new(handle.dialer()).unwrap();
-        assert_eq!(3, client.add(1, 2).get().unwrap());
-        assert_eq!("Hey, Adam.", client.hey("Adam".into()).get().unwrap());
-        drop(client);
-        handle.shutdown();
-    }
-
-    #[test]
-    fn try_clone() {
-        let handle = Server.spawn("localhost:0").unwrap();
-        let client1 = Client::new(handle.dialer()).unwrap();
-        let client2 = client1.try_clone().unwrap();
-        assert_eq!(3, client1.add(1, 2).unwrap());
-        assert_eq!(3, client2.add(1, 2).unwrap());
-    }
-
-    #[test]
-    fn async_try_clone() {
-        let handle = Server.spawn("localhost:0").unwrap();
-        let client1 = AsyncClient::new(handle.dialer()).unwrap();
-        let client2 = client1.try_clone().unwrap();
-        assert_eq!(3, client1.add(1, 2).get().unwrap());
-        assert_eq!(3, client2.add(1, 2).get().unwrap());
-    }
-
-    #[test]
-    fn async_try_clone_unix() {
-        let temp_dir = tempdir::TempDir::new("tarpc").unwrap();
-        let temp_file = temp_dir.path()
-            .join("async_try_clone_unix.tmp");
-        let handle = Server.spawn(UnixTransport(temp_file)).unwrap();
-        let client1 = AsyncClient::new(handle.dialer()).unwrap();
-        let client2 = client1.try_clone().unwrap();
-        assert_eq!(3, client1.add(1, 2).get().unwrap());
-        assert_eq!(3, client2.add(1, 2).get().unwrap());
-    }
-
-    // Tests that a server can be wrapped in an Arc; no need to run, just compile
-    #[allow(dead_code)]
-    fn serve_arc_server() {
-        let _ = ::std::sync::Arc::new(Server).spawn("localhost:0");
-    }
-
-    // Tests that a tcp client can be created from &str
-    #[allow(dead_code)]
-    fn test_client_str() {
-        let _ = Client::new("localhost:0");
-    }
-
-    #[test]
-    fn serde() {
-        use bincode;
-        let _ = env_logger::init();
-
-        let request = __Request::add((1, 2));
-        let ser = bincode::serde::serialize(&request, bincode::SizeLimit::Infinite).unwrap();
-        let de = bincode::serde::deserialize(&ser).unwrap();
-        if let __Request::add((1, 2)) = de {
-            // success
-        } else {
-            panic!("Expected __Request::add, got {:?}", de);
-        }
-    }
-}

tarpc/src/protocol/client.rs

@@ -1,269 +0,0 @@
-// Copyright 2016 Google Inc. All Rights Reserved.
-//
-// Licensed under the MIT License, <LICENSE or http://opensource.org/licenses/MIT>.
-// This file may not be copied, modified, or distributed except according to those terms.
-
-use serde;
-use std::fmt;
-use std::io::{self, BufReader, BufWriter};
-use std::collections::HashMap;
-use std::mem;
-use std::sync::{Arc, Mutex};
-use std::sync::mpsc::{Receiver, Sender, channel};
-use std::thread;
-
-use super::{Config, Deserialize, Error, Packet, Result, Serialize};
-use transport::{Dialer, Stream};
-
-/// A client stub that connects to a server to run rpcs.
-pub struct Client<Request, Reply, S>
-    where Request: serde::ser::Serialize,
-          S: Stream
-{
-    // The guard is in an option so it can be joined in the drop fn
-    reader_guard: Arc<Option<thread::JoinHandle<()>>>,
-    outbound: Sender<(Request, Sender<Result<Reply>>)>,
-    requests: Arc<Mutex<RpcFutures<Reply>>>,
-    shutdown: S,
-}
-
-impl<Request, Reply, S> Client<Request, Reply, S>
-    where Request: serde::ser::Serialize + Send + 'static,
-          Reply: serde::de::Deserialize + Send + 'static,
-          S: Stream
-{
-    /// Create a new client that connects to `addr`. The client uses the given timeout
-    /// for both reads and writes.
-    pub fn new<D>(dialer: D) -> io::Result<Self>
-        where D: Dialer<Stream = S>
-    {
-        Self::with_config(dialer, Config::default())
-    }
-
-    /// Create a new client that connects to `addr`. The client uses the given timeout
-    /// for both reads and writes.
-    pub fn with_config<D>(dialer: D, config: Config) -> io::Result<Self>
-        where D: Dialer<Stream = S>
-    {
-        let stream = try!(dialer.dial());
-        try!(stream.set_read_timeout(config.timeout));
-        try!(stream.set_write_timeout(config.timeout));
-        let reader_stream = try!(stream.try_clone());
-        let writer_stream = try!(stream.try_clone());
-        let requests = Arc::new(Mutex::new(RpcFutures::new()));
-        let reader_requests = requests.clone();
-        let writer_requests = requests.clone();
-        let (tx, rx) = channel();
-        let reader_guard = thread::spawn(move || read(reader_requests, reader_stream));
-        thread::spawn(move || write(rx, writer_requests, writer_stream));
-        Ok(Client {
-            reader_guard: Arc::new(Some(reader_guard)),
-            outbound: tx,
-            requests: requests,
-            shutdown: stream,
-        })
-    }
-
-    /// Clones the Client so that it can be shared across threads.
-    pub fn try_clone(&self) -> io::Result<Self> {
-        Ok(Client {
-            reader_guard: self.reader_guard.clone(),
-            outbound: self.outbound.clone(),
-            requests: self.requests.clone(),
-            shutdown: try!(self.shutdown.try_clone()),
-        })
-    }
-
-    fn rpc_internal(&self, request: Request) -> Receiver<Result<Reply>>
-        where Request: serde::ser::Serialize + fmt::Debug + Send + 'static
-    {
-        let (tx, rx) = channel();
-        self.outbound.send((request, tx)).expect(pos!());
-        rx
-    }
-
-    /// Run the specified rpc method on the server this client is connected to
-    pub fn rpc(&self, request: Request) -> Result<Reply>
-        where Request: serde::ser::Serialize + fmt::Debug + Send + 'static
-    {
-        self.rpc_internal(request)
-            .recv()
-            .map_err(|_| self.requests.lock().expect(pos!()).get_error())
-            .and_then(|reply| reply)
-    }
-
-    /// Asynchronously run the specified rpc method on the server this client is connected to
-    pub fn rpc_async(&self, request: Request) -> Future<Reply>
-        where Request: serde::ser::Serialize + fmt::Debug + Send + 'static
-    {
-        Future {
-            rx: self.rpc_internal(request),
-            requests: self.requests.clone(),
-        }
-    }
-}
-
-impl<Request, Reply, S> Drop for Client<Request, Reply, S>
-    where Request: serde::ser::Serialize,
-          S: Stream
-{
-    fn drop(&mut self) {
-        debug!("Dropping Client.");
-        if let Some(reader_guard) = Arc::get_mut(&mut self.reader_guard) {
-            debug!("Attempting to shut down writer and reader threads.");
-            if let Err(e) = self.shutdown.shutdown() {
-                warn!("Client: couldn't shutdown writer and reader threads: {:?}",
-                      e);
-            } else {
-                // We only join if we know the TcpStream was shut down. Otherwise we might never
-                // finish.
-                debug!("Joining writer and reader.");
-                reader_guard.take()
-                    .expect(pos!())
-                    .join()
-                    .expect(pos!());
-                debug!("Successfully joined writer and reader.");
-            }
-        }
-    }
-}
-
-/// An asynchronous RPC call
-pub struct Future<T> {
-    rx: Receiver<Result<T>>,
-    requests: Arc<Mutex<RpcFutures<T>>>,
-}
-
-impl<T> Future<T> {
-    /// Block until the result of the RPC call is available
-    pub fn get(self) -> Result<T> {
-        let requests = self.requests;
-        self.rx
-            .recv()
-            .map_err(|_| requests.lock().expect(pos!()).get_error())
-            .and_then(|reply| reply)
-    }
-}
-
-struct RpcFutures<Reply>(Result<HashMap<u64, Sender<Result<Reply>>>>);
-
-impl<Reply> RpcFutures<Reply> {
-    fn new() -> RpcFutures<Reply> {
-        RpcFutures(Ok(HashMap::new()))
-    }
-
-    fn insert_tx(&mut self, id: u64, tx: Sender<Result<Reply>>) -> Result<()> {
-        match self.0 {
-            Ok(ref mut requests) => {
-                requests.insert(id, tx);
-                Ok(())
-            }
-            Err(ref e) => Err(e.clone()),
-        }
-    }
-
-    fn remove_tx(&mut self, id: u64) -> Result<()> {
-        match self.0 {
-            Ok(ref mut requests) => {
-                requests.remove(&id);
-                Ok(())
-            }
-            Err(ref e) => Err(e.clone()),
-        }
-    }
-
-    fn complete_reply(&mut self, packet: Packet<Reply>) {
-        if let Some(tx) = self.0.as_mut().expect(pos!()).remove(&packet.rpc_id) {
-            if let Err(e) = tx.send(Ok(packet.message)) {
-                info!("Reader: could not complete reply: {:?}", e);
-            }
-        } else {
-            warn!("RpcFutures: expected sender for id {} but got None!",
-                  packet.rpc_id);
-        }
-    }
-
-    fn set_error(&mut self, err: Error) {
-        let _ = mem::replace(&mut self.0, Err(err));
-    }
-
-    fn get_error(&self) -> Error {
-        self.0.as_ref().err().expect(pos!()).clone()
-    }
-}
-
-fn write<Request, Reply, S>(outbound: Receiver<(Request, Sender<Result<Reply>>)>,
-                            requests: Arc<Mutex<RpcFutures<Reply>>>,
-                            stream: S)
-    where Request: serde::Serialize,
-          Reply: serde::Deserialize,
-          S: Stream
-{
-    let mut next_id = 0;
-    let mut stream = BufWriter::new(stream);
-    loop {
-        let (request, tx) = match outbound.recv() {
-            Err(e) => {
-                debug!("Writer: all senders have exited ({:?}). Returning.", e);
-                return;
-            }
-            Ok(request) => request,
-        };
-        if let Err(e) = requests.lock().expect(pos!()).insert_tx(next_id, tx.clone()) {
-            report_error(&tx, e);
-            // Once insert_tx returns Err, it will continue to do so. However, continue here so
-            // that any other clients who sent requests will also recv the Err.
-            continue;
-        }
-        let id = next_id;
-        next_id += 1;
-        let packet = Packet {
-            rpc_id: id,
-            message: request,
-        };
-        debug!("Writer: writing rpc, id={:?}", id);
-        if let Err(e) = stream.serialize(&packet) {
-            report_error(&tx, e.into());
-            // Typically we'd want to notify the client of any Err returned by remove_tx, but in
-            // this case the client already hit an Err, and doesn't need to know about this one, as
-            // well.
-            let _ = requests.lock().expect(pos!()).remove_tx(id);
-            continue;
-        }
-    }
-
-    fn report_error<Reply>(tx: &Sender<Result<Reply>>, e: Error)
-        where Reply: serde::Deserialize
-    {
-        // Clone the err so we can log it if sending fails
-        if let Err(e2) = tx.send(Err(e.clone())) {
-            debug!("Error encountered while trying to send an error. Initial error: {:?}; Send \
-                    error: {:?}",
-                   e,
-                   e2);
-        }
-    }
-
-}
-
-fn read<Reply, S>(requests: Arc<Mutex<RpcFutures<Reply>>>, stream: S)
-    where Reply: serde::Deserialize,
-          S: Stream
-{
-    let mut stream = BufReader::new(stream);
-    loop {
-        match stream.deserialize::<Packet<Reply>>() {
-            Ok(packet) => {
-                debug!("Client: received message, id={}", packet.rpc_id);
-                requests.lock().expect(pos!()).complete_reply(packet);
-            }
-            Err(err) => {
-                warn!("Client: reader thread encountered an unexpected error while parsing; \
-                       returning now. Error: {:?}",
-                      err);
-                requests.lock().expect(pos!()).set_error(err);
-                break;
-            }
-        }
-    }
-}

tarpc/src/protocol/mod.rs

@@ -1,249 +0,0 @@
-// Copyright 2016 Google Inc. All Rights Reserved.
-//
-// Licensed under the MIT License, <LICENSE or http://opensource.org/licenses/MIT>.
-// This file may not be copied, modified, or distributed except according to those terms.
-
-use bincode::{self, SizeLimit};
-use bincode::serde::{deserialize_from, serialize_into};
-use serde;
-use serde::de::value::Error::EndOfStream;
-use std::io::{self, Read, Write};
-use std::convert;
-use std::sync::Arc;
-use std::time::Duration;
-
-mod client;
-mod server;
-mod packet;
-
-pub use self::packet::Packet;
-pub use self::client::{Client, Future};
-pub use self::server::{Serve, ServeHandle};
-
-/// Client errors that can occur during rpc calls
-#[derive(Debug, Clone)]
-pub enum Error {
-    /// An IO-related error
-    Io(Arc<io::Error>),
-    /// The server hung up.
-    ConnectionBroken,
-}
-
-impl convert::From<bincode::serde::SerializeError> for Error {
-    fn from(err: bincode::serde::SerializeError) -> Error {
-        match err {
-            bincode::serde::SerializeError::IoError(err) => Error::Io(Arc::new(err)),
-            err => panic!("Unexpected error during serialization: {:?}", err),
-        }
-    }
-}
-
-impl convert::From<bincode::serde::DeserializeError> for Error {
-    fn from(err: bincode::serde::DeserializeError) -> Error {
-        match err {
-            bincode::serde::DeserializeError::Serde(EndOfStream) => Error::ConnectionBroken,
-            bincode::serde::DeserializeError::IoError(err) => {
-                match err.kind() {
-                    io::ErrorKind::ConnectionReset |
-                    io::ErrorKind::UnexpectedEof => Error::ConnectionBroken,
-                    _ => Error::Io(Arc::new(err)),
-                }
-            }
-            err => panic!("Unexpected error during deserialization: {:?}", err),
-        }
-    }
-}
-
-impl convert::From<io::Error> for Error {
-    fn from(err: io::Error) -> Error {
-        Error::Io(Arc::new(err))
-    }
-}
-
-/// Configuration for client and server.
-#[derive(Debug, Default)]
-pub struct Config {
-    /// Request/Response timeout between packet delivery.
-    pub timeout: Option<Duration>,
-}
-
-/// Return type of rpc calls: either the successful return value, or a client error.
-pub type Result<T> = ::std::result::Result<T, Error>;
-
-trait Deserialize: Read + Sized {
-    fn deserialize<T: serde::Deserialize>(&mut self) -> Result<T> {
-        deserialize_from(self, SizeLimit::Infinite).map_err(Error::from)
-    }
-}
-
-impl<R: Read> Deserialize for R {}
-
-trait Serialize: Write + Sized {
-    fn serialize<T: serde::Serialize>(&mut self, value: &T) -> Result<()> {
-        try!(serialize_into(self, value, SizeLimit::Infinite));
-        try!(self.flush());
-        Ok(())
-    }
-}
-
-impl<W: Write> Serialize for W {}
-
-#[cfg(test)]
-mod test {
-    extern crate env_logger;
-    use super::{Client, Config, Serve};
-    use scoped_pool::Pool;
-    use std::net::TcpStream;
-    use std::sync::{Arc, Barrier, Mutex};
-    use std::thread;
-    use std::time::Duration;
-
-    fn test_timeout() -> Option<Duration> {
-        Some(Duration::from_secs(1))
-    }
-
-    struct Server {
-        counter: Mutex<u64>,
-    }
-
-    impl Serve for Server {
-        type Request = ();
-        type Reply = u64;
-
-        fn serve(&self, _: ()) -> u64 {
-            let mut counter = self.counter.lock().unwrap();
-            let reply = *counter;
-            *counter += 1;
-            reply
-        }
-    }
-
-    impl Server {
-        fn new() -> Server {
-            Server { counter: Mutex::new(0) }
-        }
-
-        fn count(&self) -> u64 {
-            *self.counter.lock().unwrap()
-        }
-    }
-
-    #[test]
-    fn handle() {
-        let _ = env_logger::init();
-        let server = Arc::new(Server::new());
-        let serve_handle = server.spawn("localhost:0").unwrap();
-        let client: Client<(), u64, TcpStream> = Client::new(serve_handle.dialer()).unwrap();
-        drop(client);
-        serve_handle.shutdown();
-    }
-
-    #[test]
-    fn simple() {
-        let _ = env_logger::init();
-        let server = Arc::new(Server::new());
-        let serve_handle = server.clone().spawn("localhost:0").unwrap();
-        // The explicit type is required so that it doesn't deserialize a u32 instead of u64
-        let client: Client<(), u64, _> = Client::new(serve_handle.dialer()).unwrap();
-        assert_eq!(0, client.rpc(()).unwrap());
-        assert_eq!(1, server.count());
-        assert_eq!(1, client.rpc(()).unwrap());
-        assert_eq!(2, server.count());
-        drop(client);
-        serve_handle.shutdown();
-    }
-
-    struct BarrierServer {
-        barrier: Barrier,
-        inner: Server,
-    }
-
-    impl Serve for BarrierServer {
-        type Request = ();
-        type Reply = u64;
-        fn serve(&self, request: ()) -> u64 {
-            self.barrier.wait();
-            self.inner.serve(request)
-        }
-    }
-
-    impl BarrierServer {
-        fn new(n: usize) -> BarrierServer {
-            BarrierServer {
-                barrier: Barrier::new(n),
-                inner: Server::new(),
-            }
-        }
-
-        fn count(&self) -> u64 {
-            self.inner.count()
-        }
-    }
-
-    #[test]
-    fn force_shutdown() {
-        let _ = env_logger::init();
-        let server = Arc::new(Server::new());
-        let serve_handle = server.spawn_with_config("localhost:0",
-                               Config { timeout: Some(Duration::new(0, 10)) })
-            .unwrap();
-        let client: Client<(), u64, _> = Client::new(serve_handle.dialer()).unwrap();
-        let thread = thread::spawn(move || serve_handle.shutdown());
-        info!("force_shutdown:: rpc1: {:?}", client.rpc(()));
-        thread.join().unwrap();
-    }
-
-    #[test]
-    fn client_failed_rpc() {
-        let _ = env_logger::init();
-        let server = Arc::new(Server::new());
-        let serve_handle =
-            server.spawn_with_config("localhost:0", Config { timeout: test_timeout() })
-                .unwrap();
-        let client: Arc<Client<(), u64, _>> = Arc::new(Client::new(serve_handle.dialer()).unwrap());
-        client.rpc(()).unwrap();
-        serve_handle.shutdown();
-        match client.rpc(()) {
-            Err(super::Error::ConnectionBroken) => {} // success
-            otherwise => panic!("Expected Err(ConnectionBroken), got {:?}", otherwise),
-        }
-        let _ = client.rpc(()); // Test whether second failure hangs
-    }
-
-    #[test]
-    fn concurrent() {
-        let _ = env_logger::init();
-        let concurrency = 10;
-        let pool = Pool::new(concurrency);
-        let server = Arc::new(BarrierServer::new(concurrency));
-        let serve_handle = server.clone().spawn("localhost:0").unwrap();
-        let client: Client<(), u64, _> = Client::new(serve_handle.dialer()).unwrap();
-        pool.scoped(|scope| {
-            for _ in 0..concurrency {
-                let client = client.try_clone().unwrap();
-                scope.execute(move || {
-                    client.rpc(()).unwrap();
-                });
-            }
-        });
-        assert_eq!(concurrency as u64, server.count());
-        drop(client);
-        serve_handle.shutdown();
-    }
-
-    #[test]
-    fn async() {
-        let _ = env_logger::init();
-        let server = Arc::new(Server::new());
-        let serve_handle = server.spawn("localhost:0").unwrap();
-        let client: Client<(), u64, _> = Client::new(serve_handle.dialer()).unwrap();
-
-        // Drop future immediately; does the reader channel panic when sending?
-        client.rpc_async(());
-        // If the reader panicked, this won't succeed
-        client.rpc_async(());
-
-        drop(client);
-        serve_handle.shutdown();
-    }
-}

tarpc/src/protocol/packet.rs

@@ -1,78 +0,0 @@
-use serde::{Deserialize, Deserializer, Serialize, Serializer, de};
-use std::marker::PhantomData;
-
-/// Packet shared between client and server.
-#[derive(Debug, Clone, PartialEq, Eq, PartialOrd, Ord, Hash)]
-pub struct Packet<T> {
-    /// Packet id to map response to request.
-    pub rpc_id: u64,
-    /// Packet payload.
-    pub message: T,
-}
-
-const PACKET: &'static str = "Packet";
-const RPC_ID: &'static str = "rpc_id";
-const MESSAGE: &'static str = "message";
-
-impl<T: Serialize> Serialize for Packet<T> {
-    #[inline]
-    fn serialize<S>(&self, serializer: &mut S) -> Result<(), S::Error>
-        where S: Serializer
-    {
-        let mut state = try!(serializer.serialize_struct(PACKET, 2));
-        try!(serializer.serialize_struct_elt(&mut state, RPC_ID, &self.rpc_id));
-        try!(serializer.serialize_struct_elt(&mut state, MESSAGE, &self.message));
-        serializer.serialize_struct_end(state)
-    }
-}
-
-impl<T: Deserialize> Deserialize for Packet<T> {
-    #[inline]
-    fn deserialize<D>(deserializer: &mut D) -> Result<Self, D::Error>
-        where D: Deserializer
-    {
-        const FIELDS: &'static [&'static str] = &[RPC_ID, MESSAGE];
-        deserializer.deserialize_struct(PACKET, FIELDS, Visitor(PhantomData))
-    }
-}
-
-struct Visitor<T>(PhantomData<T>);
-
-impl<T: Deserialize> de::Visitor for Visitor<T> {
-    type Value = Packet<T>;
-
-    #[inline]
-    fn visit_seq<V>(&mut self, mut visitor: V) -> Result<Packet<T>, V::Error>
-        where V: de::SeqVisitor
-    {
-        let packet = Packet {
-            rpc_id: match try!(visitor.visit()) {
-                Some(rpc_id) => rpc_id,
-                None => return Err(de::Error::end_of_stream()),
-            },
-            message: match try!(visitor.visit()) {
-                Some(message) => message,
-                None => return Err(de::Error::end_of_stream()),
-            },
-        };
-        try!(visitor.end());
-        Ok(packet)
-    }
-}
-
-#[cfg(test)]
-extern crate env_logger;
-
-#[test]
-fn serde() {
-    use bincode;
-    let _ = env_logger::init();
-
-    let packet = Packet {
-        rpc_id: 1,
-        message: (),
-    };
-    let ser = bincode::serde::serialize(&packet, bincode::SizeLimit::Infinite).unwrap();
-    let de = bincode::serde::deserialize(&ser);
-    assert_eq!(packet, de.unwrap());
-}

tarpc/src/protocol/server.rs

@@ -1,280 +0,0 @@
-// Copyright 2016 Google Inc. All Rights Reserved.
-//
-// Licensed under the MIT License, <LICENSE or http://opensource.org/licenses/MIT>.
-// This file may not be copied, modified, or distributed except according to those terms.
-
-use serde;
-use scoped_pool::{Pool, Scope};
-use std::fmt;
-use std::io::{self, BufReader, BufWriter};
-use std::sync::mpsc::{Receiver, Sender, TryRecvError, channel};
-use std::sync::atomic::{AtomicBool, Ordering};
-use std::time::Duration;
-use std::thread::{self, JoinHandle};
-use super::{Config, Deserialize, Error, Packet, Result, Serialize};
-use transport::{Dialer, Listener, Stream, Transport};
-use transport::tcp::TcpDialer;
-
-struct ConnectionHandler<'a, S, St>
-    where S: Serve,
-          St: Stream
-{
-    read_stream: BufReader<St>,
-    write_stream: BufWriter<St>,
-    server: S,
-    shutdown: &'a AtomicBool,
-}
-
-impl<'a, S, St> ConnectionHandler<'a, S, St>
-    where S: Serve,
-          St: Stream
-{
-    fn handle_conn<'b>(&'b mut self, scope: &Scope<'b>) -> Result<()> {
-        let ConnectionHandler {
-            ref mut read_stream,
-            ref mut write_stream,
-            ref server,
-            shutdown,
-        } = *self;
-        trace!("ConnectionHandler: serving client...");
-        let (tx, rx) = channel();
-        scope.execute(move || Self::write(rx, write_stream));
-        loop {
-            match read_stream.deserialize() {
-                Ok(Packet { rpc_id, message }) => {
-                    let tx = tx.clone();
-                    scope.execute(move || {
-                        let reply = server.serve(message);
-                        let reply_packet = Packet {
-                            rpc_id: rpc_id,
-                            message: reply,
-                        };
-                        tx.send(reply_packet).expect(pos!());
-                    });
-                    if shutdown.load(Ordering::SeqCst) {
-                        info!("ConnectionHandler: server shutdown, so closing connection.");
-                        break;
-                    }
-                }
-                Err(Error::Io(ref err)) if Self::timed_out(err.kind()) => {
-                    if !shutdown.load(Ordering::SeqCst) {
-                        info!("ConnectionHandler: read timed out ({:?}). Server not shutdown, so \
-                               retrying read.",
-                              err);
-                        continue;
-                    } else {
-                        info!("ConnectionHandler: read timed out ({:?}). Server shutdown, so \
-                               closing connection.",
-                              err);
-                        break;
-                    }
-                }
-                Err(e) => {
-                    warn!("ConnectionHandler: closing client connection due to {:?}",
-                          e);
-                    return Err(e.into());
-                }
-            }
-        }
-        Ok(())
-    }
-
-    fn timed_out(error_kind: io::ErrorKind) -> bool {
-        match error_kind {
-            io::ErrorKind::TimedOut |
-            io::ErrorKind::WouldBlock => true,
-            _ => false,
-        }
-    }
-
-    fn write(rx: Receiver<Packet<<S as Serve>::Reply>>, stream: &mut BufWriter<St>) {
-        loop {
-            match rx.recv() {
-                Err(e) => {
-                    debug!("Write thread: returning due to {:?}", e);
-                    return;
-                }
-                Ok(reply_packet) => {
-                    if let Err(e) = stream.serialize(&reply_packet) {
-                        warn!("Writer: failed to write reply to Client: {:?}", e);
-                    }
-                }
-            }
-        }
-    }
-}
-
-/// Provides methods for blocking until the server completes,
-pub struct ServeHandle<D = TcpDialer>
-    where D: Dialer
-{
-    tx: Sender<()>,
-    join_handle: JoinHandle<()>,
-    dialer: D,
-}
-
-impl<D> ServeHandle<D>
-    where D: Dialer
-{
-    /// Block until the server completes
-    pub fn wait(self) {
-        self.join_handle.join().expect(pos!());
-    }
-
-    /// Returns the dialer to the server.
-    pub fn dialer(&self) -> &D {
-        &self.dialer
-    }
-
-    /// Shutdown the server. Gracefully shuts down the serve thread but currently does not
-    /// gracefully close open connections.
-    pub fn shutdown(self) {
-        info!("ServeHandle: attempting to shut down the server.");
-        self.tx.send(()).expect(pos!());
-        if let Ok(_) = self.dialer.dial() {
-            self.join_handle.join().expect(pos!());
-        } else {
-            warn!("ServeHandle: best effort shutdown of serve thread failed");
-        }
-    }
-}
-
-struct Server<'a, S: 'a, L>
-    where L: Listener
-{
-    server: &'a S,
-    listener: L,
-    read_timeout: Option<Duration>,
-    die_rx: Receiver<()>,
-    shutdown: &'a AtomicBool,
-}
-
-impl<'a, S, L> Server<'a, S, L>
-    where S: Serve + 'static,
-          L: Listener
-{
-    fn serve<'b>(self, scope: &Scope<'b>)
-        where 'a: 'b
-    {
-        for conn in self.listener.incoming() {
-            match self.die_rx.try_recv() {
-                Ok(_) => {
-                    info!("serve: shutdown received.");
-                    return;
-                }
-                Err(TryRecvError::Disconnected) => {
-                    info!("serve: shutdown sender disconnected.");
-                    return;
-                }
-                _ => (),
-            }
-            let conn = match conn {
-                Err(err) => {
-                    error!("serve: failed to accept connection: {:?}", err);
-                    return;
-                }
-                Ok(c) => c,
-            };
-            if let Err(err) = conn.set_read_timeout(self.read_timeout) {
-                info!("serve: could not set read timeout: {:?}", err);
-                continue;
-            }
-            let read_conn = match conn.try_clone() {
-                Err(err) => {
-                    error!("serve: could not clone tcp stream; possibly out of file descriptors? \
-                            Err: {:?}",
-                           err);
-                    continue;
-                }
-                Ok(conn) => conn,
-            };
-            let mut handler = ConnectionHandler {
-                read_stream: BufReader::new(read_conn),
-                write_stream: BufWriter::new(conn),
-                server: self.server,
-                shutdown: self.shutdown,
-            };
-            scope.recurse(move |scope| {
-                scope.zoom(|scope| {
-                    if let Err(err) = handler.handle_conn(scope) {
-                        info!("ConnectionHandler: err in connection handling: {:?}", err);
-                    }
-                });
-            });
-        }
-    }
-}
-
-impl<'a, S, L> Drop for Server<'a, S, L>
-    where L: Listener
-{
-    fn drop(&mut self) {
-        debug!("Shutting down connection handlers.");
-        self.shutdown.store(true, Ordering::SeqCst);
-    }
-}
-
-/// A service provided by a server
-pub trait Serve: Send + Sync + Sized {
-    /// The type of request received by the server
-    type Request: 'static + fmt::Debug + serde::ser::Serialize + serde::de::Deserialize + Send;
-    /// The type of reply sent by the server
-    type Reply: 'static + fmt::Debug + serde::ser::Serialize + serde::de::Deserialize + Send;
-
-    /// Return a reply for a given request
-    fn serve(&self, request: Self::Request) -> Self::Reply;
-
-    /// spawn
-    fn spawn<T>(self, transport: T) -> io::Result<ServeHandle<<T::Listener as Listener>::Dialer>>
-        where T: Transport,
-              Self: 'static
-    {
-        self.spawn_with_config(transport, Config::default())
-    }
-
-    /// spawn
-    fn spawn_with_config<T>(self,
-                            transport: T,
-                            config: Config)
-                            -> io::Result<ServeHandle<<T::Listener as Listener>::Dialer>>
-        where T: Transport,
-              Self: 'static
-    {
-        let listener = try!(transport.bind());
-        let dialer = try!(listener.dialer());
-        info!("spawn_with_config: spinning up server.");
-        let (die_tx, die_rx) = channel();
-        let timeout = config.timeout;
-        let join_handle = thread::spawn(move || {
-            let pool = Pool::new(100); // TODO(tjk): make this configurable, and expire idle threads
-            let shutdown = AtomicBool::new(false);
-            let server = Server {
-                server: &self,
-                listener: listener,
-                read_timeout: timeout,
-                die_rx: die_rx,
-                shutdown: &shutdown,
-            };
-            pool.scoped(|scope| {
-                server.serve(scope);
-            });
-        });
-        Ok(ServeHandle {
-            tx: die_tx,
-            join_handle: join_handle,
-            dialer: dialer,
-        })
-    }
-}
-
-impl<P, S> Serve for P
-    where P: Send + Sync + ::std::ops::Deref<Target = S>,
-          S: Serve
-{
-    type Request = S::Request;
-    type Reply = S::Reply;
-
-    fn serve(&self, request: S::Request) -> S::Reply {
-        S::serve(self, request)
-    }
-}

tarpc/src/serde_transport.rs

@@ -0,0 +1,396 @@
+// 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,
+    };
+
+    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()
+        }
+    }
+
+    /// 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,
+    {
+        let listener = TcpListener::bind(addr).await?;
+        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(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, 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(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(())
+    }
+}

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_eq!(in_flight_requests.cancel_request(0), true);
+        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 +1,49 @@
+use super::{
+    limits::{channels_per_key::MaxChannelsPerKey, requests_per_channel::MaxRequestsPerChannel},
+    Channel,
+};
+use futures::prelude::*;
+use std::{fmt, hash::Hash};
+
+#[cfg(feature = "tokio1")]
+use super::{tokio::TokioServerExecutor, Serve};
+
+/// 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)
+    }
+
+    /// [Executes](Channel::execute) each incoming channel. Each channel will be handled
+    /// concurrently by spawning on tokio's default executor, and each request will be also
+    /// be spawned on tokio's default executor.
+    #[cfg(feature = "tokio1")]
+    #[cfg_attr(docsrs, doc(cfg(feature = "tokio1")))]
+    fn execute<S>(self, serve: S) -> TokioServerExecutor<Self, S>
+    where
+        S: Serve<C::Req, Resp = C::Resp>,
+    {
+        TokioServerExecutor::new(self, serve)
+    }
+}
+
+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

@@ -0,0 +1,480 @@
+// 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::{
+    server::{self, Channel},
+    util::Compact,
+};
+use fnv::FnvHashMap;
+use futures::{prelude::*, ready, stream::Fuse, task::*};
+use pin_project::pin_project;
+use std::sync::{Arc, Weak};
+use std::{
+    collections::hash_map::Entry, convert::TryFrom, fmt, hash::Hash, marker::Unpin, pin::Pin,
+};
+use tokio::sync::mpsc;
+use tracing::{debug, info, trace};
+
+/// 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 MaxChannelsPerKey<S, K, F>
+where
+    K: Eq + Hash,
+{
+    #[pin]
+    listener: Fuse<S>,
+    channels_per_key: u32,
+    dropped_keys: mpsc::UnboundedReceiver<K>,
+    dropped_keys_tx: mpsc::UnboundedSender<K>,
+    key_counts: FnvHashMap<K, Weak<Tracker<K>>>,
+    keymaker: F,
+}
+
+/// A channel that is tracked by [`MaxChannelsPerKey`].
+#[pin_project]
+#[derive(Debug)]
+pub struct TrackedChannel<C, K> {
+    #[pin]
+    inner: C,
+    tracker: Arc<Tracker<K>>,
+}
+
+#[derive(Debug)]
+struct Tracker<K> {
+    key: Option<K>,
+    dropped_keys: mpsc::UnboundedSender<K>,
+}
+
+impl<K> Drop for Tracker<K> {
+    fn drop(&mut self) {
+        // Don't care if the listener is dropped.
+        let _ = self.dropped_keys.send(self.key.take().unwrap());
+    }
+}
+
+impl<C, K> Stream for TrackedChannel<C, K>
+where
+    C: Stream,
+{
+    type Item = <C as Stream>::Item;
+
+    fn poll_next(mut self: Pin<&mut Self>, cx: &mut Context) -> Poll<Option<Self::Item>> {
+        self.inner_pin_mut().poll_next(cx)
+    }
+}
+
+impl<C, I, K> Sink<I> for TrackedChannel<C, K>
+where
+    C: Sink<I>,
+{
+    type Error = C::Error;
+
+    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(mut self: Pin<&mut Self>, item: I) -> Result<(), Self::Error> {
+        self.inner_pin_mut().start_send(item)
+    }
+
+    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(mut self: Pin<&mut Self>, cx: &mut Context) -> Poll<Result<(), Self::Error>> {
+        self.inner_pin_mut().poll_close(cx)
+    }
+}
+
+impl<C, K> AsRef<C> for TrackedChannel<C, K> {
+    fn as_ref(&self) -> &C {
+        &self.inner
+    }
+}
+
+impl<C, K> Channel for TrackedChannel<C, K>
+where
+    C: Channel,
+{
+    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) -> usize {
+        self.inner.in_flight_requests()
+    }
+
+    fn transport(&self) -> &Self::Transport {
+        self.inner.transport()
+    }
+}
+
+impl<C, K> TrackedChannel<C, K> {
+    /// Returns the inner channel.
+    pub fn get_ref(&self) -> &C {
+        &self.inner
+    }
+
+    /// Returns the pinned inner channel.
+    fn inner_pin_mut<'a>(self: &'a mut Pin<&mut Self>) -> Pin<&'a mut C> {
+        self.as_mut().project().inner
+    }
+}
+
+impl<S, K, F> MaxChannelsPerKey<S, K, F>
+where
+    K: Eq + Hash,
+    S: Stream,
+    F: Fn(&S::Item) -> K,
+{
+    /// 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_channel();
+        MaxChannelsPerKey {
+            listener: listener.fuse(),
+            channels_per_key,
+            dropped_keys,
+            dropped_keys_tx,
+            key_counts: FnvHashMap::default(),
+            keymaker,
+        }
+    }
+}
+
+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,
+    ) -> Result<TrackedChannel<S::Item, K>, K> {
+        let key = (self.as_mut().keymaker)(&stream);
+        let tracker = self.as_mut().increment_channels_for_key(key.clone())?;
+
+        trace!(
+            channel_filter_key = %key,
+            open_channels = Arc::strong_count(&tracker),
+            max_open_channels = self.channels_per_key,
+            "Opening channel");
+
+        Ok(TrackedChannel {
+            tracker,
+            inner: stream,
+        })
+    }
+
+    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 tracker = Arc::new(Tracker {
+                    key: Some(key),
+                    dropped_keys: dropped_keys.clone(),
+                });
+
+                vacant.insert(Arc::downgrade(&tracker));
+                Ok(tracker)
+            }
+            Entry::Occupied(mut o) => {
+                let count = o.get().strong_count();
+                if count >= TryFrom::try_from(*self_.channels_per_key).unwrap() {
+                    info!(
+                        channel_filter_key = %key,
+                        open_channels = count,
+                        max_open_channels = *self_.channels_per_key,
+                        "At open channel limit");
+                    Err(key)
+                } else {
+                    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
+                    }))
+                }
+            }
+        }
+    }
+
+    fn poll_listener(
+        mut self: Pin<&mut Self>,
+        cx: &mut Context<'_>,
+    ) -> Poll<Option<Result<TrackedChannel<S::Item, K>, K>>> {
+        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(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<()> {
+        let self_ = self.project();
+        match ready!(self_.dropped_keys.poll_recv(cx)) {
+            Some(key) => {
+                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."),
+        }
+    }
+}
+
+impl<S, K, F> Stream for MaxChannelsPerKey<S, K, F>
+where
+    S: Stream,
+    K: fmt::Display + Eq + Hash + Clone + Unpin,
+    F: Fn(&S::Item) -> K,
+{
+    type Item = TrackedChannel<S::Item, K>;
+
+    fn poll_next(
+        mut self: Pin<&mut Self>,
+        cx: &mut Context<'_>,
+    ) -> Poll<Option<TrackedChannel<S::Item, K>>> {
+        loop {
+            match (
+                self.as_mut().poll_listener(cx),
+                self.as_mut().poll_closed_channels(cx),
+            ) {
+                (Poll::Ready(Some(Ok(channel))), _) => {
+                    return Poll::Ready(Some(channel));
+                }
+                (Poll::Ready(Some(Err(_))), _) => {
+                    continue;
+                }
+                (_, Poll::Ready(())) => continue,
+                (Poll::Pending, Poll::Pending) => return Poll::Pending,
+                (Poll::Ready(None), Poll::Pending) => {
+                    trace!("Shutting down listener.");
+                    return Poll::Ready(None);
+                }
+            }
+        }
+    }
+}
+#[cfg(test)]
+fn ctx() -> Context<'static> {
+    use futures::task::*;
+
+    Context::from_waker(&noop_waker_ref())
+}
+
+#[test]
+fn tracker_drop() {
+    use assert_matches::assert_matches;
+
+    let (tx, mut rx) = mpsc::unbounded_channel();
+    Tracker {
+        key: Some(1),
+        dropped_keys: tx,
+    };
+    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;
+
+    let (chan_tx, chan) = futures::channel::mpsc::unbounded();
+    let (dropped_keys, _) = mpsc::unbounded_channel();
+    let channel = TrackedChannel {
+        inner: chan,
+        tracker: Arc::new(Tracker {
+            key: Some(1),
+            dropped_keys,
+        }),
+    };
+
+    chan_tx.unbounded_send("test").unwrap();
+    pin_mut!(channel);
+    assert_matches!(channel.poll_next(&mut ctx()), Poll::Ready(Some("test")));
+}
+
+#[test]
+fn tracked_channel_sink() {
+    use assert_matches::assert_matches;
+    use pin_utils::pin_mut;
+
+    let (chan, mut chan_rx) = futures::channel::mpsc::unbounded();
+    let (dropped_keys, _) = mpsc::unbounded_channel();
+    let channel = TrackedChannel {
+        inner: chan,
+        tracker: Arc::new(Tracker {
+            key: Some(1),
+            dropped_keys,
+        }),
+    };
+
+    pin_mut!(channel);
+    assert_matches!(channel.as_mut().poll_ready(&mut ctx()), Poll::Ready(Ok(())));
+    assert_matches!(channel.as_mut().start_send("test"), Ok(()));
+    assert_matches!(channel.as_mut().poll_flush(&mut ctx()), Poll::Ready(Ok(())));
+    assert_matches!(chan_rx.try_next(), Ok(Some("test")));
+}
+
+#[test]
+fn channel_filter_increment_channels_for_key() {
+    use assert_matches::assert_matches;
+    use pin_utils::pin_mut;
+
+    struct TestChannel {
+        key: &'static str,
+    }
+    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!(Arc::strong_count(&tracker1), 1);
+    let tracker2 = filter.as_mut().increment_channels_for_key("key").unwrap();
+    assert_eq!(Arc::strong_count(&tracker1), 2);
+    assert_matches!(filter.increment_channels_for_key("key"), Err("key"));
+    drop(tracker2);
+    assert_eq!(Arc::strong_count(&tracker1), 1);
+}
+
+#[test]
+fn channel_filter_handle_new_channel() {
+    use assert_matches::assert_matches;
+    use pin_utils::pin_mut;
+
+    #[derive(Debug)]
+    struct TestChannel {
+        key: &'static str,
+    }
+    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!(Arc::strong_count(&channel1.tracker), 1);
+
+    let channel2 = filter
+        .as_mut()
+        .handle_new_channel(TestChannel { key: "key" })
+        .unwrap();
+    assert_eq!(Arc::strong_count(&channel1.tracker), 2);
+
+    assert_matches!(
+        filter.handle_new_channel(TestChannel { key: "key" }),
+        Err("key")
+    );
+    drop(channel2);
+    assert_eq!(Arc::strong_count(&channel1.tracker), 1);
+}
+
+#[test]
+fn channel_filter_poll_listener() {
+    use assert_matches::assert_matches;
+    use pin_utils::pin_mut;
+
+    #[derive(Debug)]
+    struct TestChannel {
+        key: &'static str,
+    }
+    let (new_channels, listener) = futures::channel::mpsc::unbounded();
+    let filter = MaxChannelsPerKey::new(listener, 2, |chan: &TestChannel| chan.key);
+    pin_mut!(filter);
+
+    new_channels
+        .unbounded_send(TestChannel { key: "key" })
+        .unwrap();
+    let channel1 =
+        assert_matches!(filter.as_mut().poll_listener(&mut ctx()), Poll::Ready(Some(Ok(c))) => c);
+    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!(Arc::strong_count(&channel1.tracker), 2);
+
+    new_channels
+        .unbounded_send(TestChannel { key: "key" })
+        .unwrap();
+    let key =
+        assert_matches!(filter.as_mut().poll_listener(&mut ctx()), Poll::Ready(Some(Err(k))) => k);
+    assert_eq!(key, "key");
+    assert_eq!(Arc::strong_count(&channel1.tracker), 2);
+}
+
+#[test]
+fn channel_filter_poll_closed_channels() {
+    use assert_matches::assert_matches;
+    use pin_utils::pin_mut;
+
+    #[derive(Debug)]
+    struct TestChannel {
+        key: &'static str,
+    }
+    let (new_channels, listener) = futures::channel::mpsc::unbounded();
+    let filter = MaxChannelsPerKey::new(listener, 2, |chan: &TestChannel| chan.key);
+    pin_mut!(filter);
+
+    new_channels
+        .unbounded_send(TestChannel { key: "key" })
+        .unwrap();
+    let channel =
+        assert_matches!(filter.as_mut().poll_listener(&mut ctx()), Poll::Ready(Some(Ok(c))) => c);
+    assert_eq!(filter.key_counts.len(), 1);
+
+    drop(channel);
+    assert_matches!(
+        filter.as_mut().poll_closed_channels(&mut ctx()),
+        Poll::Ready(())
+    );
+    assert!(filter.key_counts.is_empty());
+}
+
+#[test]
+fn channel_filter_stream() {
+    use assert_matches::assert_matches;
+    use pin_utils::pin_mut;
+
+    #[derive(Debug)]
+    struct TestChannel {
+        key: &'static str,
+    }
+    let (new_channels, listener) = futures::channel::mpsc::unbounded();
+    let filter = MaxChannelsPerKey::new(listener, 2, |chan: &TestChannel| chan.key);
+    pin_mut!(filter);
+
+    new_channels
+        .unbounded_send(TestChannel { key: "key" })
+        .unwrap();
+    let channel = assert_matches!(filter.as_mut().poll_next(&mut ctx()), Poll::Ready(Some(c)) => c);
+    assert_eq!(filter.key_counts.len(), 1);
+
+    drop(channel);
+    assert_matches!(filter.as_mut().poll_next(&mut ctx()), Poll::Pending);
+    assert!(filter.key_counts.is_empty());
+}

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/testing.rs

@@ -0,0 +1,138 @@
+// 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, io, mem::ManuallyDrop, pin::Pin, time::SystemTime};
+use tracing::Span;
+
+#[pin_project]
+pub(crate) struct FakeChannel<In, Out> {
+    #[pin]
+    pub stream: VecDeque<In>,
+    #[pin]
+    pub sink: VecDeque<Out>,
+    pub config: Config,
+    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>
+where
+    In: Unpin,
+{
+    type Item = In;
+
+    fn poll_next(self: Pin<&mut Self>, _cx: &mut Context) -> Poll<Option<Self::Item>> {
+        Poll::Ready(self.project().stream.pop_front())
+    }
+}
+
+impl<In, Resp> Sink<Response<Resp>> for FakeChannel<In, Response<Resp>> {
+    type Error = io::Error;
+
+    fn poll_ready(self: Pin<&mut Self>, cx: &mut Context) -> Poll<Result<(), Self::Error>> {
+        self.project().sink.poll_ready(cx).map_err(|e| match e {})
+    }
+
+    fn start_send(mut self: Pin<&mut Self>, response: Response<Resp>) -> Result<(), Self::Error> {
+        self.as_mut()
+            .project()
+            .in_flight_requests
+            .remove_request(response.request_id);
+        self.project()
+            .sink
+            .start_send(response)
+            .map_err(|e| match e {})
+    }
+
+    fn poll_flush(self: Pin<&mut Self>, cx: &mut Context) -> Poll<Result<(), Self::Error>> {
+        self.project().sink.poll_flush(cx).map_err(|e| match e {})
+    }
+
+    fn poll_close(self: Pin<&mut Self>, cx: &mut Context) -> Poll<Result<(), Self::Error>> {
+        self.project().sink.poll_close(cx).map_err(|e| match e {})
+    }
+}
+
+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) -> usize {
+        self.in_flight_requests.len()
+    }
+
+    fn transport(&self) -> &() {
+        &()
+    }
+}
+
+impl<Req, Resp> FakeChannel<io::Result<TrackedRequest<Req>>, Response<Resp>> {
+    pub fn push_req(&mut self, id: u64, message: Req) {
+        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: ManuallyDrop::new(ResponseGuard {
+                request_cancellation,
+                request_id: id,
+            }),
+        }));
+    }
+}
+
+impl FakeChannel<(), ()> {
+    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,
+        }
+    }
+}
+
+pub trait PollExt {
+    fn is_done(&self) -> bool;
+}
+
+impl<T> PollExt for Poll<Option<T>> {
+    fn is_done(&self) -> bool {
+        matches!(self, Poll::Ready(None))
+    }
+}
+
+pub fn cx() -> Context<'static> {
+    Context::from_waker(&noop_waker_ref())
+}

tarpc/src/server/tokio.rs

@@ -0,0 +1,113 @@
+use super::{Channel, Requests, Serve};
+use futures::{prelude::*, ready, task::*};
+use pin_project::pin_project;
+use std::pin::Pin;
+
+/// A future that drives the server by [spawning](tokio::spawn) a [`TokioChannelExecutor`](TokioChannelExecutor)
+/// for each new channel. Returned by
+/// [`Incoming::execute`](crate::server::incoming::Incoming::execute).
+#[must_use]
+#[pin_project]
+#[derive(Debug)]
+pub struct TokioServerExecutor<T, S> {
+    #[pin]
+    inner: T,
+    serve: S,
+}
+
+impl<T, S> TokioServerExecutor<T, S> {
+    pub(crate) fn new(inner: T, serve: S) -> Self {
+        Self { inner, serve }
+    }
+}
+
+/// A future that drives the server by [spawning](tokio::spawn) each [response
+/// handler](super::InFlightRequest::execute) on tokio's default executor. Returned by
+/// [`Channel::execute`](crate::server::Channel::execute).
+#[must_use]
+#[pin_project]
+#[derive(Debug)]
+pub struct TokioChannelExecutor<T, S> {
+    #[pin]
+    inner: T,
+    serve: S,
+}
+
+impl<T, S> TokioServerExecutor<T, S> {
+    fn inner_pin_mut<'a>(self: &'a mut Pin<&mut Self>) -> Pin<&'a mut T> {
+        self.as_mut().project().inner
+    }
+}
+
+impl<T, S> TokioChannelExecutor<T, S> {
+    fn inner_pin_mut<'a>(self: &'a mut Pin<&mut Self>) -> Pin<&'a mut T> {
+        self.as_mut().project().inner
+    }
+}
+
+// Send + 'static execution helper methods.
+
+impl<C> Requests<C>
+where
+    C: Channel,
+    C::Req: Send + 'static,
+    C::Resp: Send + 'static,
+{
+    /// Executes all requests using the given service function. Requests are handled concurrently
+    /// by [spawning](::tokio::spawn) each handler on tokio's default executor.
+    pub fn execute<S>(self, serve: S) -> TokioChannelExecutor<Self, S>
+    where
+        S: Serve<C::Req, Resp = C::Resp> + Send + 'static,
+    {
+        TokioChannelExecutor { inner: self, serve }
+    }
+}
+
+impl<St, C, Se> Future for TokioServerExecutor<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,
+{
+    type Output = ();
+
+    fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<()> {
+        while let Some(channel) = ready!(self.inner_pin_mut().poll_next(cx)) {
+            tokio::spawn(channel.execute(self.serve.clone()));
+        }
+        tracing::info!("Server shutting down.");
+        Poll::Ready(())
+    }
+}
+
+impl<C, S> Future for TokioChannelExecutor<Requests<C>, S>
+where
+    C: Channel + 'static,
+    C::Req: Send + 'static,
+    C::Resp: Send + 'static,
+    S: Serve<C::Req, Resp = C::Resp> + Send + 'static + Clone,
+    S::Fut: Send,
+{
+    type Output = ();
+
+    fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
+        while let Some(response_handler) = ready!(self.inner_pin_mut().poll_next(cx)) {
+            match response_handler {
+                Ok(resp) => {
+                    let server = self.serve.clone();
+                    tokio::spawn(async move {
+                        resp.execute(server).await;
+                    });
+                }
+                Err(e) => {
+                    tracing::warn!("Requests stream errored out: {}", e);
+                    break;
+                }
+            }
+        }
+        Poll::Ready(())
+    }
+}

tarpc/src/trace.rs

@@ -0,0 +1,261 @@
+// 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)]
+
+//! Provides building blocks for tracing distributed programs.
+//!
+//! A trace is logically a tree of causally-related events called spans. Traces are tracked via a
+//! [context](Context) that identifies the current trace, span, and parent of the current span.  In
+//! distributed systems, a context can be sent from client to server to connect events occurring on
+//! either side.
+//!
+//! 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},
+    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 = "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.
+    pub trace_id: TraceId,
+    /// An identifier of the current span. In typical RPC usage, a span is created by a client
+    /// 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,
+    /// 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(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(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 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,
+        }
+    }
+}
+
+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(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.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)?;
+        Ok(())
+    }
+}
+
+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 +1,202 @@
+// 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 sending over the channel.
+    #[error("an error occurred sending over the channel")]
+    Send(#[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))
+    }
+}
+
+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::Send(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))
+    }
+}
+
+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::Send(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(test)]
+#[cfg(feature = "tokio1")]
+mod tests {
+    use crate::{
+        client, context,
+        server::{incoming::Incoming, BaseChannel},
+        transport::{
+            self,
+            channel::{Channel, UnboundedChannel},
+        },
+    };
+    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(|_ctx, request: String| {
+                    future::ready(request.parse::<u64>().map_err(|_| {
+                        io::Error::new(
+                            io::ErrorKind::InvalidInput,
+                            format!("{request:?} is not an int"),
+                        )
+                    }))
+                }),
+        );
+
+        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(ref e) if e.kind() == io::ErrorKind::InvalidInput);
+
+        Ok(())
+    }
+}

tarpc/src/transport/mod.rs

@@ -1,91 +0,0 @@
-use std::io::{self, Read, Write};
-use std::time::Duration;
-
-/// A factory for creating a listener on a given address.
-/// For TCP, an address might be an IPv4 address; for Unix sockets, it
-/// is just a file name.
-pub trait Transport {
-    /// The type of listener that binds to the given address.
-    type Listener: Listener;
-    /// Return a listener on the given address, and a dialer to that address.
-    fn bind(&self) -> io::Result<Self::Listener>;
-}
-
-/// Accepts incoming connections from dialers.
-pub trait Listener: Send + 'static {
-    /// The type of address being listened on.
-    type Dialer: Dialer;
-    /// The type of stream this listener accepts.
-    type Stream: Stream;
-    /// Accept an incoming stream.
-    fn accept(&self) -> io::Result<Self::Stream>;
-    /// Returns the local address being listened on.
-    fn dialer(&self) -> io::Result<Self::Dialer>;
-    /// Iterate over incoming connections.
-    fn incoming(&self) -> Incoming<Self> {
-        Incoming { listener: self }
-    }
-}
-
-/// A cloneable Reader/Writer.
-pub trait Stream: Read + Write + Send + Sized + 'static {
-    /// Creates a new independently owned handle to the Stream.
-    ///
-    /// The returned Stream should reference the same stream that this
-    /// object references. Both handles should read and write the same
-    /// stream of data, and options set on one stream should be propagated
-    /// to the other stream.
-    fn try_clone(&self) -> io::Result<Self>;
-    /// Sets a read timeout.
-    ///
-    /// If the value specified is `None`, then read calls will block indefinitely.
-    /// It is an error to pass the zero `Duration` to this method.
-    fn set_read_timeout(&self, dur: Option<Duration>) -> io::Result<()>;
-    /// Sets a write timeout.
-    ///
-    /// If the value specified is `None`, then write calls will block indefinitely.
-    /// It is an error to pass the zero `Duration` to this method.
-    fn set_write_timeout(&self, dur: Option<Duration>) -> io::Result<()>;
-    /// Shuts down both ends of the stream.
-    ///
-    /// Implementations should cause all pending and future I/O on the specified
-    /// portions to return immediately with an appropriate value.
-    fn shutdown(&self) -> io::Result<()>;
-}
-
-/// A `Stream` factory.
-pub trait Dialer {
-    /// The type of `Stream` this can create.
-    type Stream: Stream;
-    /// Open a stream.
-    fn dial(&self) -> io::Result<Self::Stream>;
-}
-
-impl<P, D: ?Sized> Dialer for P
-    where P: ::std::ops::Deref<Target = D>,
-          D: Dialer + 'static
-{
-    type Stream = D::Stream;
-
-    fn dial(&self) -> io::Result<Self::Stream> {
-        (**self).dial()
-    }
-}
-
-/// Iterates over incoming connections.
-pub struct Incoming<'a, L: Listener + ?Sized + 'a> {
-    listener: &'a L,
-}
-
-impl<'a, L: Listener> Iterator for Incoming<'a, L> {
-    type Item = io::Result<L::Stream>;
-
-    fn next(&mut self) -> Option<Self::Item> {
-        Some(self.listener.accept())
-    }
-}
-
-/// Provides a TCP transport.
-pub mod tcp;
-/// Provides a unix socket transport.
-pub mod unix;

tarpc/src/transport/tcp.rs

@@ -1,77 +0,0 @@
-use std::io;
-use std::net::{SocketAddr, TcpListener, TcpStream, ToSocketAddrs};
-use std::time::Duration;
-
-/// A transport for TCP.
-#[derive(Debug)]
-pub struct TcpTransport<A: ToSocketAddrs>(pub A);
-
-impl<A: ToSocketAddrs> super::Transport for TcpTransport<A> {
-    type Listener = TcpListener;
-
-    fn bind(&self) -> io::Result<TcpListener> {
-        TcpListener::bind(&self.0)
-    }
-}
-
-impl<A: ToSocketAddrs> super::Transport for A {
-    type Listener = TcpListener;
-
-    fn bind(&self) -> io::Result<TcpListener> {
-        TcpListener::bind(self)
-    }
-}
-
-impl super::Listener for TcpListener {
-    type Dialer = TcpDialer<SocketAddr>;
-
-    type Stream = TcpStream;
-
-    fn accept(&self) -> io::Result<TcpStream> {
-        self.accept().map(|(stream, _)| stream)
-    }
-
-    fn dialer(&self) -> io::Result<TcpDialer<SocketAddr>> {
-        self.local_addr().map(|addr| TcpDialer(addr))
-    }
-}
-
-impl super::Stream for TcpStream {
-    fn try_clone(&self) -> io::Result<Self> {
-        self.try_clone()
-    }
-
-    fn set_read_timeout(&self, dur: Option<Duration>) -> io::Result<()> {
-        self.set_read_timeout(dur)
-    }
-
-    fn set_write_timeout(&self, dur: Option<Duration>) -> io::Result<()> {
-        self.set_write_timeout(dur)
-    }
-
-    fn shutdown(&self) -> io::Result<()> {
-        self.shutdown(::std::net::Shutdown::Both)
-    }
-}
-
-/// Connects to a socket address.
-#[derive(Debug)]
-pub struct TcpDialer<A = SocketAddr>(pub A) where A: ToSocketAddrs;
-
-impl<A> super::Dialer for TcpDialer<A>
-    where A: ToSocketAddrs
-{
-    type Stream = TcpStream;
-
-    fn dial(&self) -> io::Result<TcpStream> {
-        TcpStream::connect(&self.0)
-    }
-}
-
-impl super::Dialer for str {
-    type Stream = TcpStream;
-
-    fn dial(&self) -> io::Result<TcpStream> {
-        TcpStream::connect(self)
-    }
-}

tarpc/src/transport/unix.rs

@@ -1,72 +0,0 @@
-use std::io;
-use std::path::{Path, PathBuf};
-use std::time::Duration;
-use unix_socket::{UnixListener, UnixStream};
-
-/// A transport for unix sockets.
-#[derive(Debug)]
-pub struct UnixTransport<P>(pub P) where P: AsRef<Path>;
-
-impl<P> super::Transport for UnixTransport<P>
-    where P: AsRef<Path>
-{
-    type Listener = UnixListener;
-
-    fn bind(&self) -> io::Result<UnixListener> {
-        UnixListener::bind(&self.0)
-    }
-}
-
-/// Connects to a unix socket address.
-#[derive(Debug)]
-pub struct UnixDialer<P>(pub P) where P: AsRef<Path>;
-
-impl<P> super::Dialer for UnixDialer<P>
-    where P: AsRef<Path>
-{
-    type Stream = UnixStream;
-
-    fn dial(&self) -> io::Result<UnixStream> {
-        UnixStream::connect(&self.0)
-    }
-}
-
-impl super::Listener for UnixListener {
-    type Stream = UnixStream;
-
-    type Dialer = UnixDialer<PathBuf>;
-
-    fn accept(&self) -> io::Result<UnixStream> {
-        self.accept().map(|(stream, _)| stream)
-    }
-
-    fn dialer(&self) -> io::Result<UnixDialer<PathBuf>> {
-        self.local_addr().and_then(|addr| {
-            match addr.as_pathname() {
-                Some(path) => Ok(UnixDialer(path.to_owned())),
-                None => {
-                    Err(io::Error::new(io::ErrorKind::AddrNotAvailable,
-                                       "Couldn't get a path to bound unix socket"))
-                }
-            }
-        })
-    }
-}
-
-impl super::Stream for UnixStream {
-    fn try_clone(&self) -> io::Result<Self> {
-        self.try_clone()
-    }
-
-    fn set_read_timeout(&self, timeout: Option<Duration>) -> io::Result<()> {
-        self.set_read_timeout(timeout)
-    }
-
-    fn set_write_timeout(&self, timeout: Option<Duration>) -> io::Result<()> {
-        self.set_write_timeout(timeout)
-    }
-
-    fn shutdown(&self) -> io::Result<()> {
-        self.shutdown(::std::net::Shutdown::Both)
-    }
-}

tarpc/src/util.rs

@@ -0,0 +1,71 @@
+// 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 std::{
+    collections::HashMap,
+    hash::{BuildHasher, Hash},
+    time::{Duration, SystemTime},
+};
+
+#[cfg(feature = "serde1")]
+#[cfg_attr(docsrs, doc(cfg(feature = "serde1")))]
+pub mod serde;
+
+/// Extension trait for [SystemTimes](SystemTime) in the future, i.e. deadlines.
+pub trait TimeUntil {
+    /// How much time from now until this time is reached.
+    fn time_until(&self) -> Duration;
+}
+
+impl TimeUntil for SystemTime {
+    fn time_until(&self) -> Duration {
+        self.duration_since(SystemTime::now()).unwrap_or_default()
+    }
+}
+
+/// Collection compaction; configurable `shrink_to_fit`.
+pub trait Compact {
+    /// Compacts space if the ratio of length : capacity is less than `usage_ratio_threshold`.
+    fn compact(&mut self, usage_ratio_threshold: f64);
+}
+
+impl<K, V, H> Compact for HashMap<K, V, H>
+where
+    K: Eq + Hash,
+    H: BuildHasher,
+{
+    fn compact(&mut self, usage_ratio_threshold: f64) {
+        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

@@ -0,0 +1,73 @@
+// 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 serde::{Deserialize, Deserializer, Serialize, Serializer};
+use std::io;
+
+/// Serializes [`io::ErrorKind`] as a `u32`.
+#[allow(clippy::trivially_copy_pass_by_ref)] // Exact fn signature required by serde derive
+pub fn serialize_io_error_kind_as_u32<S>(
+    kind: &io::ErrorKind,
+    serializer: S,
+) -> Result<S::Ok, S::Error>
+where
+    S: Serializer,
+{
+    use std::io::ErrorKind::*;
+    match *kind {
+        NotFound => 0,
+        PermissionDenied => 1,
+        ConnectionRefused => 2,
+        ConnectionReset => 3,
+        ConnectionAborted => 4,
+        NotConnected => 5,
+        AddrInUse => 6,
+        AddrNotAvailable => 7,
+        BrokenPipe => 8,
+        AlreadyExists => 9,
+        WouldBlock => 10,
+        InvalidInput => 11,
+        InvalidData => 12,
+        TimedOut => 13,
+        WriteZero => 14,
+        Interrupted => 15,
+        Other => 16,
+        UnexpectedEof => 17,
+        _ => 16,
+    }
+    .serialize(serializer)
+}
+
+/// Deserializes [`io::ErrorKind`] from a `u32`.
+pub fn deserialize_io_error_kind_from_u32<'de, D>(
+    deserializer: D,
+) -> Result<io::ErrorKind, D::Error>
+where
+    D: Deserializer<'de>,
+{
+    use std::io::ErrorKind::*;
+    Ok(match u32::deserialize(deserializer)? {
+        0 => NotFound,
+        1 => PermissionDenied,
+        2 => ConnectionRefused,
+        3 => ConnectionReset,
+        4 => ConnectionAborted,
+        5 => NotConnected,
+        6 => AddrInUse,
+        7 => AddrNotAvailable,
+        8 => BrokenPipe,
+        9 => AlreadyExists,
+        10 => WouldBlock,
+        11 => InvalidInput,
+        12 => InvalidData,
+        13 => TimedOut,
+        14 => WriteZero,
+        15 => Interrupted,
+        16 => Other,
+        17 => UnexpectedEof,
+        _ => Other,
+    })
+}

tarpc/tests/compile_fail.rs

@@ -0,0 +1,9 @@
+#[test]
+fn ui() {
+    let t = trybuild::TestCases::new();
+    t.compile_fail("tests/compile_fail/*.rs");
+    #[cfg(feature = "tokio1")]
+    t.compile_fail("tests/compile_fail/tokio/*.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 +1,11 @@
+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)]
+   |            ^^^^^^^^^^^^^^^

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 +1,11 @@
+error: unused `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)]
+  |            ^^^^^^^^^^^^^^^

tarpc/tests/compile_fail/tarpc_server_missing_async.rs

@@ -0,0 +1,15 @@
+#[tarpc::service(derive_serde = false)]
+trait World {
+    async fn hello(name: String) -> String;
+}
+
+struct HelloServer;
+
+#[tarpc::server]
+impl World for HelloServer {
+    fn hello(name: String) -> String {
+        format!("Hello, {name}!", name)
+    }
+}
+
+fn main() {}

tarpc/tests/compile_fail/tarpc_server_missing_async.stderr

@@ -0,0 +1,11 @@
+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 {
+   |     ^^

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/compile_fail/tokio/must_use_channel_executor.rs

@@ -0,0 +1,29 @@
+use tarpc::{
+    context,
+    server::{self, Channel},
+};
+
+#[tarpc::service]
+trait World {
+    async fn hello(name: String) -> String;
+}
+
+#[derive(Clone)]
+struct HelloServer;
+
+#[tarpc::server]
+impl World for HelloServer {
+    async fn hello(self, _: context::Context, name: String) -> String {
+        format!("Hello, {name}!")
+    }
+}
+
+fn main() {
+    let (_, server_transport) = tarpc::transport::channel::unbounded();
+    let server = server::BaseChannel::with_defaults(server_transport);
+
+    #[deny(unused_must_use)]
+    {
+        server.execute(HelloServer.serve());
+    }
+}

tarpc/tests/compile_fail/tokio/must_use_channel_executor.stderr

@@ -0,0 +1,11 @@
+error: unused `TokioChannelExecutor` that must be used
+  --> tests/compile_fail/tokio/must_use_channel_executor.rs:27:9
+   |
+27 |         server.execute(HelloServer.serve());
+   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+note: the lint level is defined here
+  --> tests/compile_fail/tokio/must_use_channel_executor.rs:25:12
+   |
+25 |     #[deny(unused_must_use)]
+   |            ^^^^^^^^^^^^^^^

tarpc/tests/compile_fail/tokio/must_use_server_executor.rs

@@ -0,0 +1,30 @@
+use futures::stream::once;
+use tarpc::{
+    context,
+    server::{self, incoming::Incoming},
+};
+
+#[tarpc::service]
+trait World {
+    async fn hello(name: String) -> String;
+}
+
+#[derive(Clone)]
+struct HelloServer;
+
+#[tarpc::server]
+impl World for HelloServer {
+    async fn hello(self, _: context::Context, name: String) -> String {
+        format!("Hello, {name}!")
+    }
+}
+
+fn main() {
+    let (_, server_transport) = tarpc::transport::channel::unbounded();
+    let server = once(async move { server::BaseChannel::with_defaults(server_transport) });
+
+    #[deny(unused_must_use)]
+    {
+        server.execute(HelloServer.serve());
+    }
+}

tarpc/tests/compile_fail/tokio/must_use_server_executor.stderr

@@ -0,0 +1,11 @@
+error: unused `TokioServerExecutor` that must be used
+  --> tests/compile_fail/tokio/must_use_server_executor.rs:28:9
+   |
+28 |         server.execute(HelloServer.serve());
+   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+note: the lint level is defined here
+  --> tests/compile_fail/tokio/must_use_server_executor.rs:26:12
+   |
+26 |     #[deny(unused_must_use)]
+   |            ^^^^^^^^^^^^^^^

tarpc/tests/dataservice.rs

@@ -0,0 +1,55 @@
+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)]
+pub enum TestData {
+    Black,
+    White,
+}
+
+#[tarpc::service]
+pub trait ColorProtocol {
+    async fn get_opposite_color(color: TestData) -> TestData;
+}
+
+#[derive(Clone)]
+struct ColorServer;
+
+#[tarpc::server]
+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,
+        }
+    }
+}
+
+#[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()),
+    );
+
+    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/service_functional.rs

@@ -0,0 +1,244 @@
+use assert_matches::assert_matches;
+use futures::{
+    future::{join_all, ready, Ready},
+    prelude::*,
+};
+use std::time::{Duration, SystemTime};
+use tarpc::{
+    client::{self},
+    context,
+    server::{self, incoming::Incoming, BaseChannel, Channel},
+    transport::channel,
+};
+use tokio::join;
+
+#[tarpc_plugins::service]
+trait Service {
+    async fn add(x: i32, y: i32) -> i32;
+    async fn hey(name: String) -> String;
+}
+
+#[derive(Clone)]
+struct Server;
+
+impl Service for Server {
+    type AddFut = Ready<i32>;
+
+    fn add(self, _: context::Context, x: i32, y: i32) -> Self::AddFut {
+        ready(x + y)
+    }
+
+    type HeyFut = Ready<String>;
+
+    fn hey(self, _: context::Context, name: String) -> Self::HeyFut {
+        ready(format!("Hey, {name}."))
+    }
+}
+
+#[tokio::test]
+async fn sequential() -> anyhow::Result<()> {
+    let _ = tracing_subscriber::fmt::try_init();
+
+    let (tx, rx) = channel::unbounded();
+
+    tokio::spawn(
+        BaseChannel::new(server::Config::default(), rx)
+            .requests()
+            .execute(Server.serve()),
+    );
+
+    let client = ServiceClient::new(client::Config::default(), tx).spawn();
+
+    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.");
+
+    Ok(())
+}
+
+#[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;
+
+    #[tarpc::server]
+    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();
+
+    // 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 ctx = context::current();
+        ctx.deadline = SystemTime::now() + Duration::from_secs(60 * 60);
+        let _ = client.r#loop(ctx).await;
+    });
+
+    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(all(feature = "serde-transport", feature = "tcp"))]
+#[tokio::test]
+async fn serde() -> anyhow::Result<()> {
+    use tarpc::serde_transport;
+    use tokio_serde::formats::Json;
+
+    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(
+        transport
+            .take(1)
+            .filter_map(|r| async { r.ok() })
+            .map(BaseChannel::with_defaults)
+            .execute(Server.serve()),
+    );
+
+    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!(
+        client.hey(context::current(), "Tim".to_string()).await,
+        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(
+        stream::once(ready(rx))
+            .map(BaseChannel::with_defaults)
+            .execute(Server.serve()),
+    );
+
+    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());
+
+    assert_matches!(req1.await, Ok(3));
+    assert_matches!(req2.await, Ok(7));
+    assert_matches!(req3.await, Ok(ref s) if s == "Hey, Tim.");
+
+    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()),
+    );
+
+    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(())
+}
+
+#[tokio::test]
+async fn concurrent_join_all() -> 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()),
+    );
+
+    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 {
+        type CountFut = futures::future::Ready<u32>;
+
+        fn count(self, _: context::Context) -> Self::CountFut {
+            self.0 += 1;
+            futures::future::ready(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(())
+}

tarpc_examples/Cargo.toml

@@ -1,9 +0,0 @@
-[package]
-name = "tarpc_examples"
-version = "0.1.0"
-authors = ["Adam Wright <adam.austin.wright@gmail.com>", "Tim Kuehn <timothy.j.kuehn@gmail.com>"]
-
-[dev-dependencies]
-tarpc = { path = "../tarpc" }
-lazy_static = "0.2"
-env_logger = "0.3"

tarpc_examples/src/lib.rs

@@ -1,74 +0,0 @@
-// Copyright 2016 Google Inc. All Rights Reserved.
-//
-// Licensed under the MIT License, <LICENSE or http://opensource.org/licenses/MIT>.
-// This file may not be copied, modified, or distributed except according to those terms.
-
-#![cfg_attr(test, feature(test))]
-
-#[cfg(test)]
-#[macro_use]
-extern crate lazy_static;
-
-#[cfg(test)]
-#[macro_use]
-extern crate tarpc;
-
-#[cfg(test)]
-#[allow(dead_code)] // generated Client isn't used in this benchmark
-mod benchmark {
-    extern crate env_logger;
-    extern crate test;
-
-    use tarpc::ServeHandle;
-    use self::test::Bencher;
-    use std::sync::{Arc, Mutex};
-
-    service! {
-        rpc hello(s: String) -> String;
-    }
-
-    struct HelloServer;
-    impl Service for HelloServer {
-        fn hello(&self, s: String) -> String {
-            format!("Hello, {}!", s)
-        }
-    }
-
-    // Prevents resource exhaustion when benching
-    lazy_static! {
-        static ref HANDLE: Arc<Mutex<ServeHandle>> = {
-            let handle = HelloServer.spawn("localhost:0").unwrap();
-            Arc::new(Mutex::new(handle))
-        };
-        static ref CLIENT: Arc<Mutex<AsyncClient>> = {
-            let lock = HANDLE.lock().unwrap();
-            let dialer = lock.dialer();
-            let client = AsyncClient::new(dialer).unwrap();
-            Arc::new(Mutex::new(client))
-        };
-    }
-
-    #[bench]
-    fn hello(bencher: &mut Bencher) {
-        let _ = env_logger::init();
-        let client = CLIENT.lock().unwrap();
-        let concurrency = 100;
-        let mut futures = Vec::with_capacity(concurrency);
-        let mut count = 0;
-        bencher.iter(|| {
-            futures.push(client.hello("Bob".into()));
-            count += 1;
-            if count % concurrency == 0 {
-                // We can't block on each rpc call, otherwise we'd be
-                // benchmarking latency instead of throughput. It's also
-                // not ideal to call more than one rpc per iteration, because
-                // it makes the output of the bencher harder to parse (you have
-                // to mentally divide the number by `concurrency` to get
-                // the ns / iter for one rpc
-                for f in futures.drain(..) {
-                    f.get().unwrap();
-                }
-            }
-        });
-    }
-}