Prepare release of 0.28.0

This was stabilized in Rust 1.58.0: https://blog.rust-lang.org/2022/01/13/Rust-1.58.0.html

.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 = "0.5.1"
+tarpc = "0.28"
 ```
 
+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 = "0.28", 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

@@ -1,3 +1,409 @@
+## 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.
+
 ## 0.5 (2016-04-24)
 
 ### Breaking Changes

example-service/Cargo.toml

@@ -0,0 +1,40 @@
+[package]
+name = "tarpc-example-service"
+version = "0.10.0"
+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 = "0.16", features = ["rt-tokio"] }
+opentelemetry-jaeger = { version = "0.15", features = ["rt-tokio"] }
+rand = "0.8"
+tarpc = { version = "0.28", path = "../tarpc", features = ["full"] }
+tokio = { version = "1", features = ["macros", "net", "rt-multi-thread"] }
+tracing = { version = "0.1" }
+tracing-opentelemetry = "0.15"
+tracing-subscriber = "0.2"
+
+[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/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 = "0.5.1"
-authors = ["Adam Wright <adam.austin.wright@gmail.com>", "Tim Kuehn <timothy.j.kuehn@gmail.com>"]
+version = "0.28.0"
+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 = "0.6.9", 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/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 +1,47 @@
+use tarpc::serde_transport as transport;
+use tarpc::server::{BaseChannel, Channel};
+use tarpc::{context::Context, tokio_serde::formats::Bincode};
+use tokio::net::{UnixListener, UnixStream};
+use tokio_util::codec::length_delimited::LengthDelimitedCodec;
+
+#[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 +1,360 @@
+// 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},
+};
+use tokio::net::ToSocketAddrs;
+use tokio_serde::formats::Json;
+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 {
+    subscriber: subscriber::SubscriberClient,
+    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 {
+                    subscriber: subscriber.clone(),
+                    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 +1,113 @@
+// 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 std::env;
+use tarpc::{
+    client, context,
+    server::{incoming::Incoming, BaseChannel},
+};
+use 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<()> {
+    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(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/client.rs

@@ -0,0 +1,916 @@
+// 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::{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,
+            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::warn!(
+                "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.
+#[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)
+            .map_err(ChannelError::Timer)?
+        {
+            // 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)?;
+        let deadline = ctx.deadline;
+        tracing::info!(
+            tarpc.deadline = %humantime::format_rfc3339(deadline),
+            "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>>,
+}
+
+/// Sends request cancellation signals.
+#[derive(Debug, Clone)]
+struct RequestCancellation(mpsc::UnboundedSender<u64>);
+
+/// A stream of IDs of requests that have been canceled.
+#[derive(Debug)]
+struct CanceledRequests(mpsc::UnboundedReceiver<u64>);
+
+/// Returns a channel to send request cancellation messages.
+fn cancellations() -> (RequestCancellation, CanceledRequests) {
+    // Unbounded because messages are sent in the drop fn. This is fine, because it's still
+    // bounded by the number of in-flight requests.
+    let (tx, rx) = mpsc::unbounded_channel();
+    (RequestCancellation(tx), CanceledRequests(rx))
+}
+
+impl RequestCancellation {
+    /// Cancels the request with ID `request_id`.
+    fn cancel(&self, request_id: u64) {
+        let _ = self.0.send(request_id);
+    }
+}
+
+impl CanceledRequests {
+    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)
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::{
+        cancellations, CanceledRequests, Channel, DispatchRequest, RequestCancellation,
+        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.0.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.0.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;
+
+        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();
+    }
+
+    #[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());
+    }
+
+    #[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 (cancel_tx, canceled_requests) = mpsc::unbounded_channel();
+        let (client_channel, server_channel) = transport::channel::unbounded();
+
+        let dispatch = RequestDispatch::<String, String, _> {
+            transport: client_channel.fuse(),
+            pending_requests: pending_requests,
+            canceled_requests: CanceledRequests(canceled_requests),
+            in_flight_requests: InFlightRequests::default(),
+            config: Config::default(),
+        };
+
+        let cancellation = RequestCancellation(cancel_tx);
+        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,
+        };
+        channel.to_dispatch.send(request).await.unwrap();
+
+        ResponseGuard {
+            response,
+            cancellation: &channel.cancellation,
+            request_id,
+        }
+    }
+
+    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 +1,137 @@
+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<Result<u64, tokio::time::error::Error>>> {
+        self.deadlines.poll_expired(cx).map_ok(|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));
+            }
+            request_id
+        })
+    }
+}

tarpc/src/context.rs

@@ -0,0 +1,102 @@
+// 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"))]
+    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,
+}
+
+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 +1,421 @@
-// 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 = "0.28"
 //! ```
-//! #[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 = "0.28", 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;
+
+#[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 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 +1,395 @@
+// 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.
+    #[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 +1,223 @@
+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<Result<u64, tokio::time::error::Error>>> {
+        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_ok(|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");
+            }
+            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(Ok(_)))
+        );
+        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 +1,127 @@
+// 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::{
+    context,
+    server::{Channel, Config, TrackedRequest},
+    Request, Response,
+};
+use futures::{task::*, Sink, Stream};
+use pin_project::pin_project;
+use std::{collections::VecDeque, io, 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,
+}
+
+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();
+        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(),
+        }));
+    }
+}
+
+impl FakeChannel<(), ()> {
+    pub fn default<Req, Resp>() -> FakeChannel<io::Result<TrackedRequest<Req>>, Response<Resp>> {
+        FakeChannel {
+            stream: Default::default(),
+            sink: Default::default(),
+            config: Default::default(),
+            in_flight_requests: Default::default(),
+        }
+    }
+}
+
+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 +1,111 @@
+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).
+#[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).
+#[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 +1,5 @@
+#[test]
+fn ui() {
+    let t = trybuild::TestCases::new();
+    t.compile_fail("tests/compile_fail/*.rs");
+}

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/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();
-                }
-            }
-        });
-    }
-}