Prepare for v0.34.0 release

- Stub
- BeforeRequest
- AfterRequest

Also removed the last remaining usage of an unstable feature,
iter_intersperse.

.github/workflows/main.yml

@@ -14,99 +14,54 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - name: Cancel previous
-        uses: styfle/cancel-workflow-action@0.7.0
+        uses: styfle/cancel-workflow-action@0.10.0
         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
+      - uses: actions/checkout@v3
+      - uses: dtolnay/rust-toolchain@stable
+      - run: cargo check --all-features
 
   test:
     name: Test Suite
     runs-on: ubuntu-latest
     steps:
       - name: Cancel previous
-        uses: styfle/cancel-workflow-action@0.7.0
+        uses: styfle/cancel-workflow-action@0.10.0
         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
+      - uses: actions/checkout@v3
+      - uses: dtolnay/rust-toolchain@stable
+      - run: cargo test
+      - run: cargo test --manifest-path tarpc/Cargo.toml --features serde1
+      - run: cargo test --manifest-path tarpc/Cargo.toml --features tokio1
+      - run: cargo test --manifest-path tarpc/Cargo.toml --features serde-transport
+      - run: cargo test --manifest-path tarpc/Cargo.toml --features tcp
+      - run: cargo test --all-features
 
   fmt:
     name: Rustfmt
     runs-on: ubuntu-latest
     steps:
       - name: Cancel previous
-        uses: styfle/cancel-workflow-action@0.7.0
+        uses: styfle/cancel-workflow-action@0.10.0
         with:
           access_token: ${{ github.token }}
-      - uses: actions/checkout@v1
-      - uses: actions-rs/toolchain@v1
+      - uses: actions/checkout@v3
+      - uses: dtolnay/rust-toolchain@stable
         with:
-          profile: minimal
-          toolchain: stable
-          override: true
-      - run: rustup component add rustfmt
-      - uses: actions-rs/cargo@v1
-        with:
-          command: fmt
-          args: --all -- --check
+          components: rustfmt
+      - run: cargo fmt --all -- --check
 
   clippy:
     name: Clippy
     runs-on: ubuntu-latest
     steps:
       - name: Cancel previous
-        uses: styfle/cancel-workflow-action@0.7.0
+        uses: styfle/cancel-workflow-action@0.10.0
         with:
           access_token: ${{ github.token }}
-      - uses: actions/checkout@v1
-      - uses: actions-rs/toolchain@v1
+      - uses: actions/checkout@v3
+      - uses: dtolnay/rust-toolchain@stable
         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
+          components: clippy
+      - run: cargo clippy --all-features -- -D warnings

Cargo.toml

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

README.md

@@ -40,7 +40,7 @@ rather than in a separate language such as .proto. This means there's no separat
 process, and no context switching between different languages.
 
 Some other features of tarpc:
-- Pluggable transport: any type impling `Stream<Item = Request> + Sink<Response>` can be
+- Pluggable transport: any type implementing `Stream<Item = Request> + Sink<Response>` can be
   used as a transport to connect the client and server.
 - `Send + '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.
@@ -51,6 +51,14 @@ Some other features of tarpc:
   requests sent by the server that use the request context will propagate the request deadline.
   For example, if a server is handling a request with a 10s deadline, does 2s of work, then
   sends a request to another server, that server will see an 8s deadline.
+- Distributed tracing: tarpc is instrumented with
+  [tracing](https://github.com/tokio-rs/tracing) primitives extended with
+  [OpenTelemetry](https://opentelemetry.io/) traces. Using a compatible tracing subscriber like
+  [Jaeger](https://github.com/open-telemetry/opentelemetry-rust/tree/main/opentelemetry-jaeger),
+  each RPC can be traced through the client, server, and other dependencies downstream of the
+  server. Even for applications not connected to a distributed tracing collector, the
+  instrumentation can also be ingested by regular loggers like
+  [env_logger](https://github.com/env-logger-rs/env_logger/).
 - Serde serialization: enabling the `serde1` Cargo feature will make service requests and
   responses `Serialize + Deserialize`. It's entirely optional, though: in-memory transports can
   be used, as well, so the price of serialization doesn't have to be paid when it's not needed.
@@ -59,7 +67,7 @@ Some other features of tarpc:
 Add to your `Cargo.toml` dependencies:
 
 ```toml
-tarpc = "0.25"
+tarpc = "0.34"
 ```
 
 The `tarpc::service` attribute expands to a collection of items that form an rpc service.
@@ -72,9 +80,10 @@ This example uses [tokio](https://tokio.rs), so add the following dependencies t
 your `Cargo.toml`:
 
 ```toml
-futures = "1.0"
-tarpc = { version = "0.25", features = ["tokio1"] }
-tokio = { version = "1.0", features = ["macros"] }
+anyhow = "1.0"
+futures = "0.3"
+tarpc = { version = "0.31", features = ["tokio1"] }
+tokio = { version = "1.0", features = ["rt-multi-thread", "macros"] }
 ```
 
 In the following example, we use an in-process channel for communication between
@@ -84,16 +93,11 @@ For a more real-world example, see [example-service](example-service).
 First, let's set up the dependencies and service definition.
 
 ```rust
-
-use futures::{
-    future::{self, Ready},
-    prelude::*,
-};
+use futures::future::{self, Ready};
 use tarpc::{
     client, context,
-    server::{self, Incoming},
+    server::{self, Channel},
 };
-use std::io;
 
 // This is the service definition. It looks a lot like a trait definition.
 // It defines one RPC, hello, which takes one arg, name, and returns a String.
@@ -120,7 +124,7 @@ impl World for HelloServer {
     type HelloFut = Ready<String>;
 
     fn hello(self, _: context::Context, name: String) -> Self::HelloFut {
-        future::ready(format!("Hello, {}!", name))
+        future::ready(format!("Hello, {name}!"))
     }
 }
 ```
@@ -132,7 +136,7 @@ available behind the `tcp` feature.
 
 ```rust
 #[tokio::main]
-async fn main() -> io::Result<()> {
+async fn main() -> anyhow::Result<()> {
     let (client_transport, server_transport) = tarpc::transport::channel::unbounded();
 
     let server = server::BaseChannel::with_defaults(server_transport);
@@ -140,14 +144,14 @@ async fn main() -> io::Result<()> {
 
     // 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()?;
+    let client = WorldClient::new(client::Config::default(), client_transport).spawn();
 
     // The client has an RPC method for each RPC defined in the annotated trait. It takes the same
     // args as defined, with the addition of a Context, which is always the first arg. The Context
     // specifies a deadline and trace information which can be helpful in debugging requests.
     let hello = client.hello(context::current(), "Stim".to_string()).await?;
 
-    println!("{}", hello);
+    println!("{hello}");
 
     Ok(())
 }

RELEASES.md

@@ -1,3 +1,203 @@
+## 0.34.0 (2023-12-29)
+
+### Breaking Changes
+
+- `#[tarpc::server]` is no more! Service traits now use async fns.
+- `Channel::execute` no longer spawns request handlers. Async-fn-in-traits makes it impossible to
+  add a Send bound to the future returned by `Serve::serve`. Instead, `Channel::execute` returns a
+  stream of futures, where each future is a request handler. To achieve the former behavior:
+  ```rust
+  channel.execute(server.serve())
+         .for_each(|rpc| { tokio::spawn(rpc); })
+  ```
+
+### New Features
+
+- Request hooks are added to the serve trait, so that it's easy to hook in cross-cutting
+  functionality look throttling, authorization, etc.
+- The Client trait is back! This makes it possible to hook in generic client functionality like load
+  balancing, retries, etc.
+
+## 0.33.0 (2023-04-01)
+
+### Breaking Changes
+
+Opentelemetry dependency version increased to 0.18.
+
+## 0.32.0 (2023-03-24)
+
+### Breaking Changes
+
+- As part of a fix to return more channel errors in RPC results, a few error types have changed:
+
+  0. `client::RpcError::Disconnected` was split into the following errors:
+    - Shutdown: the client was shutdown, either intentionally or due to an error. If due to an
+      error, pending RPCs should see the more specific errors below.
+    - Send: an RPC message failed to send over the transport. Only the RPC that failed to be sent
+      will see this error.
+    - Receive: a fatal error occurred while receiving from the transport. All in-flight RPCs will
+      receive this error.
+  0. `client::ChannelError` and `server::ChannelError` are unified in `tarpc::ChannelError`.
+     Previously, server transport errors would not indicate during which activity the transport
+     error occurred. Now, just like the client already was, it will be specific: reading, readying,
+     sending, flushing, or closing.
+
+## 0.31.0 (2022-11-03)
+
+### New Features
+
+This release adds Unix Domain Sockets to the `serde_transport` module.
+To use it, enable the "unix" feature. See the docs for more information.
+
+## 0.30.0 (2022-08-12)
+
+### Breaking Changes
+
+- Some types that impl Future are now annotated with `#[must_use]`. Code that previously created
+  these types but did not use them will now receive a warning. Code that disallows warnings will
+  receive a compilation error.
+
+### Fixes
+
+- Servers will more reliably clean up request state for requests with long deadlines when response
+processing is aborted without sending a response.
+
+### Other Changes
+
+- `TrackedRequest` now contains a response guard that can be used to ensure state cleanup for
+  aborted requests. (This was already handled automatically by `InFlightRequests`).
+- When the feature serde-transport is enabled, the crate tokio_serde is now re-exported.
+
+## 0.29.0 (2022-05-26)
+
+### Breaking Changes
+
+`Context.deadline` is now serialized as a Duration. This prevents clock skew from affecting deadline
+behavior. For more details see https://github.com/google/tarpc/pull/367 and its [related
+issue](https://github.com/google/tarpc/issues/366).
+
+## 0.28.0 (2022-04-06)
+
+### Breaking Changes
+
+- The minimum supported Rust version has increased to 1.58.0.
+- The version of opentelemetry depended on by tarpc has increased to 0.17.0.
+
+## 0.27.2 (2021-10-08)
+
+### Fixes
+
+Clients will now close their transport before dropping it. An attempt at a clean shutdown can help
+the server drop its connections more quickly.
+
+## 0.27.1 (2021-09-22)
+
+### Breaking Changes
+
+#### RPC error type is changing
+
+RPC return types are changing from `Result<Response, io::Error>` to `Result<Response,
+tarpc::client::RpcError>`.
+
+Becaue tarpc is a library, not an application, it should strive to
+use structured errors in its API so that users have maximal flexibility
+in how they handle errors. io::Error makes that hard, because it is a
+kitchen-sink error type.
+
+RPCs in particular only have 3 classes of errors:
+
+- The connection breaks.
+- The request expires.
+- The server decides not to process the request.
+
+RPC responses can also contain application-specific errors, but from the
+perspective of the RPC library, those are opaque to the framework, classified
+as successful responsees.
+
+### Open Telemetry
+
+The Opentelemetry dependency is updated to version 0.16.x.
+
+## 0.27.0 (2021-09-22)
+
+This version was yanked due to tarpc-plugins version mismatches.
+
+
+## 0.26.0 (2021-04-14)
+
+### New Features
+
+#### Tracing
+
+tarpc is now instrumented with tracing primitives extended with
+OpenTelemetry traces. Using a compatible tracing-opentelemetry
+subscriber like Jaeger, each RPC can be traced through the client,
+server, amd other dependencies downstream of the server. Even for
+applications not connected to a distributed tracing collector, the
+instrumentation can also be ingested by regular loggers like env_logger.
+
+### Breaking Changes
+
+#### Logging
+
+Logged events are now structured using tracing. For applications using a
+logger and not a tracing subscriber, these logs may look different or
+contain information in a less consumable manner. The easiest solution is
+to add a tracing subscriber that logs to stdout, such as
+tracing_subscriber::fmt.
+
+####  Context
+
+- Context no longer has parent_span, which was actually never needed,
+  because the context sent in an RPC is inherently the parent context.
+  For purposes of distributed tracing, the client side of the RPC has all
+  necessary information to link the span to its parent; the server side
+  need do nothing more than export the (trace ID, span ID) tuple.
+- Context has a new field, SamplingDecision, which has two variants,
+  Sampled and Unsampled. This field can be used by downstream systems to
+  determine whether a trace needs to be exported. If the parent span is
+  sampled, the expectation is that all child spans be exported, as well;
+  to do otherwise could result in lossy traces being exported. Note that
+  if an Openetelemetry tracing subscriber is not installed, the fallback
+  context will still be used, but the Context's sampling decision will
+  always be inherited by the parent Context's sampling decision.
+- Context::scope has been removed. Context propagation is now done via
+  tracing's task-local spans. Spans can be propagated across tasks via
+  Span::in_scope. When a service receives a request, it attaches an
+  Opentelemetry context to the local Span created before request handling,
+  and this context contains the request deadline. This span-local deadline
+  is retrieved by Context::current, but it cannot be modified so that
+  future Context::current calls contain a different deadline. However, the
+  deadline in the context passed into an RPC call will override it, so
+  users can retrieve the current context and then modify the deadline
+  field, as has been historically possible.
+- Context propgation precedence changes: when an RPC is initiated, the
+  current Span's Opentelemetry context takes precedence over the trace
+  context passed into the RPC method. If there is no current Span, then
+  the trace context argument is used as it has been historically. Note
+  that Opentelemetry context propagation requires an Opentelemetry
+  tracing subscriber to be installed.
+
+#### Server
+
+- The server::Channel trait now has an additional required associated
+  type and method which returns the underlying transport. This makes it
+  more ergonomic for users to retrieve transport-specific information,
+  like IP Address. BaseChannel implements Channel::transport by returning
+  the underlying transport, and channel decorators like Throttler just
+  delegate to the Channel::transport method of the wrapped channel.
+
+#### Client
+
+- NewClient::spawn no longer returns a result, as spawn can't fail.
+
+### References
+
+1. https://github.com/tokio-rs/tracing
+2. https://opentelemetry.io
+3. https://github.com/open-telemetry/opentelemetry-rust/tree/main/opentelemetry-jaeger
+4. https://github.com/env-logger-rs/env_logger
+
 ## 0.25.0 (2021-03-10)
 
 ### Breaking Changes
@@ -170,7 +370,7 @@ nameable futures and will just be boxing the return type anyway. This macro does
 
 ### Breaking Changes
 
-- Enums had _non_exhaustive fields replaced with the #[non_exhaustive] attribute.
+- Enums had `_non_exhaustive` fields replaced with the #[non_exhaustive] attribute.
 
 ### Bug Fixes
 

example-service/Cargo.toml

@@ -1,8 +1,9 @@
 [package]
 name = "tarpc-example-service"
-version = "0.9.0"
+version = "0.15.0"
+rust-version = "1.56"
 authors = ["Tim Kuehn <tikue@google.com>"]
-edition = "2018"
+edition = "2021"
 license = "MIT"
 documentation = "https://docs.rs/tarpc-example-service"
 homepage = "https://github.com/google/tarpc"
@@ -13,12 +14,19 @@ readme = "../README.md"
 description = "An example server built on tarpc."
 
 [dependencies]
-clap = "2.33"
-env_logger = "0.8"
+anyhow = "1.0"
+clap = { version = "3.0.0-rc.9", features = ["derive"] }
+log = "0.4"
 futures = "0.3"
-serde = { version = "1.0" }
-tarpc = { version = "0.25", path = "../tarpc", features = ["full"] }
-tokio = { version = "1", features = ["full"] }
+opentelemetry = { version = "0.21.0" }
+opentelemetry-jaeger = { version = "0.20.0", features = ["rt-tokio"] }
+rand = "0.8"
+tarpc = { version = "0.34", path = "../tarpc", features = ["full"] }
+tokio = { version = "1", features = ["macros", "net", "rt-multi-thread"] }
+tracing = { version = "0.1" }
+tracing-opentelemetry = "0.22.0"
+tracing-subscriber = { version = "0.3.18", features = ["env-filter"] }
+opentelemetry_sdk = "0.21.1"
 
 [lib]
 name = "service"

example-service/README.md

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

example-service/src/client.rs

@@ -4,57 +4,53 @@
 // license that can be found in the LICENSE file or at
 // https://opensource.org/licenses/MIT.
 
-use clap::{App, Arg};
-use std::{io, net::SocketAddr};
+use clap::Parser;
+use service::{init_tracing, WorldClient};
+use std::{net::SocketAddr, time::Duration};
 use tarpc::{client, context, tokio_serde::formats::Json};
+use tokio::time::sleep;
+use tracing::Instrument;
+
+#[derive(Parser)]
+struct Flags {
+    /// Sets the server address to connect to.
+    #[clap(long)]
+    server_addr: SocketAddr,
+    /// Sets the name to say hello to.
+    #[clap(long)]
+    name: String,
+}
 
 #[tokio::main]
-async fn main() -> io::Result<()> {
-    env_logger::init();
+async fn main() -> anyhow::Result<()> {
+    let flags = Flags::parse();
+    init_tracing("Tarpc Example Client")?;
 
-    let flags = App::new("Hello Client")
-        .version("0.1")
-        .author("Tim <tikue@google.com>")
-        .about("Say hello!")
-        .arg(
-            Arg::with_name("server_addr")
-                .long("server_addr")
-                .value_name("ADDRESS")
-                .help("Sets the server address to connect to.")
-                .required(true)
-                .takes_value(true),
-        )
-        .arg(
-            Arg::with_name("name")
-                .short("n")
-                .long("name")
-                .value_name("STRING")
-                .help("Sets the name to say hello to.")
-                .required(true)
-                .takes_value(true),
-        )
-        .get_matches();
-
-    let server_addr = flags.value_of("server_addr").unwrap();
-    let server_addr = server_addr
-        .parse::<SocketAddr>()
-        .unwrap_or_else(|e| panic!(r#"--server_addr value "{}" invalid: {}"#, server_addr, e));
-
-    let name = flags.value_of("name").unwrap().into();
-
-    let mut transport = tarpc::serde_transport::tcp::connect(server_addr, Json::default);
+    let mut transport = tarpc::serde_transport::tcp::connect(flags.server_addr, Json::default);
     transport.config_mut().max_frame_length(usize::MAX);
 
     // WorldClient is generated by the service attribute. It has a constructor `new` that takes a
     // config and any Transport as input.
-    let client = service::WorldClient::new(client::Config::default(), transport.await?).spawn()?;
+    let client = WorldClient::new(client::Config::default(), transport.await?).spawn();
 
-    // The client has an RPC method for each RPC defined in the annotated trait. It takes the same
-    // args as defined, with the addition of a Context, which is always the first arg. The Context
-    // specifies a deadline and trace information which can be helpful in debugging requests.
-    let hello = client.hello(context::current(), name).await?;
+    let hello = async move {
+        // Send the request twice, just to be safe! ;)
+        tokio::select! {
+            hello1 = client.hello(context::current(), format!("{}1", flags.name)) => { hello1 }
+            hello2 = client.hello(context::current(), format!("{}2", flags.name)) => { hello2 }
+        }
+    }
+    .instrument(tracing::info_span!("Two Hellos"))
+    .await;
 
-    println!("{}", hello);
+    match hello {
+        Ok(hello) => tracing::info!("{hello:?}"),
+        Err(e) => tracing::warn!("{:?}", anyhow::Error::from(e)),
+    }
+
+    // Let the background span processor finish.
+    sleep(Duration::from_micros(1)).await;
+    opentelemetry::global::shutdown_tracer_provider();
 
     Ok(())
 }

example-service/src/lib.rs

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

example-service/src/server.rs

@@ -4,72 +4,72 @@
 // license that can be found in the LICENSE file or at
 // https://opensource.org/licenses/MIT.
 
-use clap::{App, Arg};
+use clap::Parser;
 use futures::{future, prelude::*};
-use service::World;
+use rand::{
+    distributions::{Distribution, Uniform},
+    thread_rng,
+};
+use service::{init_tracing, World};
 use std::{
-    io,
-    net::{IpAddr, SocketAddr},
+    net::{IpAddr, Ipv6Addr, SocketAddr},
+    time::Duration,
 };
 use tarpc::{
     context,
-    server::{self, Channel, Incoming},
+    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 {
-        format!("Hello, {}! You are connected from {:?}.", name, self.0)
+        let sleep_time =
+            Duration::from_millis(Uniform::new_inclusive(1, 10).sample(&mut thread_rng()));
+        time::sleep(sleep_time).await;
+        format!("Hello, {name}! You are connected from {}", self.0)
     }
 }
 
+async fn spawn(fut: impl Future<Output = ()> + Send + 'static) {
+    tokio::spawn(fut);
+}
+
 #[tokio::main]
-async fn main() -> io::Result<()> {
-    env_logger::init();
+async fn main() -> anyhow::Result<()> {
+    let flags = Flags::parse();
+    init_tracing("Tarpc Example Server")?;
 
-    let flags = App::new("Hello Server")
-        .version("0.1")
-        .author("Tim <tikue@google.com>")
-        .about("Say hello!")
-        .arg(
-            Arg::with_name("port")
-                .short("p")
-                .long("port")
-                .value_name("NUMBER")
-                .help("Sets the port number to listen on")
-                .required(true)
-                .takes_value(true),
-        )
-        .get_matches();
-
-    let port = flags.value_of("port").unwrap();
-    let port = port
-        .parse()
-        .unwrap_or_else(|e| panic!(r#"--port value "{}" invalid: {}"#, port, e));
-
-    let server_addr = (IpAddr::from([0, 0, 0, 0]), port);
+    let server_addr = (IpAddr::V6(Ipv6Addr::LOCALHOST), flags.port);
 
     // JSON transport is provided by the json_transport tarpc module. It makes it easy
     // to start up a serde-powered json serialization strategy over TCP.
     let mut listener = tarpc::serde_transport::tcp::listen(&server_addr, Json::default).await?;
+    tracing::info!("Listening on port {}", listener.local_addr().port());
     listener.config_mut().max_frame_length(usize::MAX);
     listener
         // Ignore accept errors.
         .filter_map(|r| future::ready(r.ok()))
         .map(server::BaseChannel::with_defaults)
         // Limit channels to 1 per IP.
-        .max_channels_per_key(1, |t| t.as_ref().peer_addr().unwrap().ip())
+        .max_channels_per_key(1, |t| t.transport().peer_addr().unwrap().ip())
         // serve is generated by the service attribute. It takes as input any type implementing
         // the generated World trait.
         .map(|channel| {
-            let server = HelloServer(channel.as_ref().as_ref().peer_addr().unwrap());
-            channel.requests().execute(server.serve())
+            let server = HelloServer(channel.transport().peer_addr().unwrap());
+            channel.execute(server.serve()).for_each(spawn)
         })
         // Max 10 channels.
         .buffer_unordered(10)

hooks/pre-commit

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

plugins/Cargo.toml

@@ -1,8 +1,9 @@
 [package]
 name = "tarpc-plugins"
-version = "0.10.0"
+version = "0.13.0"
+rust-version = "1.56"
 authors = ["Adam Wright <adam.austin.wright@gmail.com>", "Tim Kuehn <timothy.j.kuehn@gmail.com>"]
-edition = "2018"
+edition = "2021"
 license = "MIT"
 documentation = "https://docs.rs/tarpc-plugins"
 homepage = "https://github.com/google/tarpc"
@@ -30,4 +31,4 @@ proc-macro = true
 assert-type-eq = "0.1.0"
 futures = "0.3"
 serde = { version = "1.0", features = ["derive"] }
-tarpc = { path = "../tarpc" }
+tarpc = { path = "../tarpc", features = ["serde1"] }

plugins/LICENSE

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

plugins/src/lib.rs

@@ -12,18 +12,18 @@ extern crate quote;
 extern crate syn;
 
 use proc_macro::TokenStream;
-use proc_macro2::{Span, TokenStream as TokenStream2};
+use proc_macro2::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,
+    parse_macro_input, parse_quote,
     spanned::Spanned,
     token::Comma,
-    Attribute, FnArg, Ident, ImplItem, ImplItemMethod, ImplItemType, ItemImpl, Lit, LitBool,
-    MetaNameValue, Pat, PatType, ReturnType, Token, Type, Visibility,
+    Attribute, FnArg, Ident, Lit, LitBool, MetaNameValue, Pat, PatType, ReturnType, Token, Type,
+    Visibility,
 };
 
 /// Accumulates multiple errors into a result.
@@ -83,7 +83,7 @@ impl Parse for Service {
                     ident_errors,
                     syn::Error::new(
                         rpc.ident.span(),
-                        format!("method name conflicts with generated fn `{}::serve`", ident)
+                        format!("method name conflicts with generated fn `{ident}::serve`")
                     )
                 );
             }
@@ -257,7 +257,6 @@ pub fn service(attr: TokenStream, input: TokenStream) -> TokenStream {
         .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)]
@@ -267,18 +266,24 @@ pub fn service(attr: TokenStream, input: TokenStream) -> TokenStream {
         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,
+        client_stub_ident: &format_ident!("{}Stub", ident),
         server_ident: &format_ident!("Serve{}", ident),
-        response_fut_ident: &Ident::new(&response_fut_name, ident.span()),
         client_ident: &format_ident!("{}Client", ident),
         request_ident: &format_ident!("{}Request", ident),
         response_ident: &format_ident!("{}Response", ident),
         vis,
         args,
         method_attrs: &rpcs.iter().map(|rpc| &*rpc.attrs).collect::<Vec<_>>(),
-        method_idents: &rpcs.iter().map(|rpc| &rpc.ident).collect::<Vec<_>>(),
+        method_idents: &methods,
+        request_names: &request_names,
         attrs,
         rpcs,
         return_types: &rpcs
@@ -297,141 +302,18 @@ pub fn service(attr: TokenStream, input: TokenStream) -> TokenStream {
             .zip(camel_case_fn_names.iter())
             .map(|(rpc, name)| Ident::new(name, rpc.ident.span()))
             .collect::<Vec<_>>(),
-        future_types: &camel_case_fn_names
-            .iter()
-            .map(|name| parse_str(&format!("{}Fut", name)).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()
-            .find(|typedecl| typedecl.ident == expected)
-            .is_none()
-        {
-            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,
+    client_stub_ident: &'a Ident,
     server_ident: &'a Ident,
-    response_fut_ident: &'a Ident,
-    response_fut_name: &'a str,
     client_ident: &'a Ident,
     request_ident: &'a Ident,
     response_ident: &'a Ident,
@@ -439,8 +321,8 @@ struct ServiceGenerator<'a> {
     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],
@@ -454,42 +336,37 @@ impl<'a> ServiceGenerator<'a> {
             attrs,
             rpcs,
             vis,
-            future_types,
             return_types,
             service_ident,
+            client_stub_ident,
+            request_ident,
+            response_ident,
             server_ident,
             ..
         } = self;
 
-        let types_and_fns = rpcs
+        let rpc_fns = rpcs
             .iter()
-            .zip(future_types.iter())
             .zip(return_types.iter())
             .map(
                 |(
-                    (
-                        RpcMethod {
-                            attrs, ident, args, ..
-                        },
-                        future_type,
-                    ),
+                    RpcMethod {
+                        attrs, ident, args, ..
+                    },
                     output,
                 )| {
-                    let ty_doc = format!("The response future returned by {}.", 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;
+                        async fn #ident(self, context: tarpc::context::Context, #( #args ),*) -> #output;
                     }
                 },
             );
 
+        let stub_doc = format!("The stub trait for service [`{service_ident}`].");
         quote! {
             #( #attrs )*
             #vis trait #service_ident: Sized {
-                #( #types_and_fns )*
+                #( #rpc_fns )*
 
                 /// Returns a serving function to use with
                 /// [InFlightRequest::execute](tarpc::server::InFlightRequest::execute).
@@ -497,6 +374,15 @@ impl<'a> ServiceGenerator<'a> {
                     #server_ident { service: self }
                 }
             }
+
+            #[doc = #stub_doc]
+            #vis trait #client_stub_ident: tarpc::client::stub::Stub<Req = #request_ident, Resp = #response_ident> {
+            }
+
+            impl<S> #client_stub_ident for S
+                where S: tarpc::client::stub::Stub<Req = #request_ident, Resp = #response_ident>
+            {
+            }
         }
     }
 
@@ -520,29 +406,40 @@ impl<'a> ServiceGenerator<'a> {
             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>
+            impl<S> tarpc::server::Serve for #server_ident<S>
                 where S: #service_ident
             {
+                type Req = #request_ident;
                 type Resp = #response_ident;
-                type Fut = #response_fut_ident<S>;
 
-                fn serve(self, ctx: tarpc::context::Context, req: #request_ident) -> Self::Fut {
+                fn method(&self, req: &#request_ident) -> Option<&'static str> {
+                    Some(match req {
+                        #(
+                            #request_ident::#camel_case_idents{..} => {
+                                #request_names
+                            }
+                        )*
+                    })
+                }
+
+                async fn serve(self, ctx: tarpc::context::Context, req: #request_ident)
+                    -> Result<#response_ident, tarpc::ServerError> {
                     match req {
                         #(
                             #request_ident::#camel_case_idents{ #( #arg_pats ),* } => {
-                                #response_fut_ident::#camel_case_idents(
+                                Ok(#response_ident::#camel_case_idents(
                                     #service_ident::#method_idents(
                                         self.service, ctx, #( #arg_pats ),*
-                                    )
-                                )
+                                    ).await
+                                ))
                             }
                         )*
                     }
@@ -563,6 +460,7 @@ impl<'a> ServiceGenerator<'a> {
 
         quote! {
             /// The request sent over the wire from the client to the server.
+            #[allow(missing_docs)]
             #[derive(Debug)]
             #derive_serialize
             #vis enum #request_ident {
@@ -583,6 +481,7 @@ impl<'a> ServiceGenerator<'a> {
 
         quote! {
             /// The response sent over the wire from the server to the client.
+            #[allow(missing_docs)]
             #[derive(Debug)]
             #derive_serialize
             #vis enum #response_ident {
@@ -591,72 +490,6 @@ impl<'a> ServiceGenerator<'a> {
         }
     }
 
-    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.
-            #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,
@@ -671,7 +504,9 @@ impl<'a> ServiceGenerator<'a> {
             #[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>);
+            #vis struct #client_ident<
+                Stub = tarpc::client::Channel<#request_ident, #response_ident>
+            >(Stub);
         }
     }
 
@@ -701,6 +536,17 @@ impl<'a> ServiceGenerator<'a> {
                         dispatch: new_client.dispatch,
                     }
                 }
+            }
+
+            impl<Stub> From<Stub> for #client_ident<Stub>
+                where Stub: tarpc::client::stub::Stub<
+                    Req = #request_ident,
+                    Resp = #response_ident>
+            {
+                /// Returns a new client stub that sends requests over the given transport.
+                fn from(stub: Stub) -> Self {
+                    #client_ident(stub)
+                }
 
             }
         }
@@ -714,6 +560,7 @@ impl<'a> ServiceGenerator<'a> {
             method_attrs,
             vis,
             method_idents,
+            request_names,
             args,
             return_types,
             arg_pats,
@@ -722,14 +569,18 @@ impl<'a> ServiceGenerator<'a> {
         } = self;
 
         quote! {
-            impl #client_ident {
+            impl<Stub> #client_ident<Stub>
+                where Stub: tarpc::client::stub::Stub<
+                    Req = #request_ident,
+                    Resp = #response_ident>
+            {
                 #(
                     #[allow(unused)]
                     #( #method_attrs )*
                     #vis fn #method_idents(&self, ctx: tarpc::context::Context, #( #args ),*)
-                        -> impl std::future::Future<Output = std::io::Result<#return_types>> + '_ {
+                        -> 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);
+                        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),
@@ -751,9 +602,6 @@ impl<'a> ToTokens for ServiceGenerator<'a> {
             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(),

plugins/tests/server.rs

@@ -1,8 +1,3 @@
-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]
@@ -12,42 +7,6 @@ trait Foo {
     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() {
@@ -59,24 +18,6 @@ fn raw_idents_work() {
         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]
@@ -100,45 +41,4 @@ fn syntax() {
         #[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

@@ -2,8 +2,6 @@ use tarpc::context;
 
 #[test]
 fn att_service_trait() {
-    use futures::future::{ready, Ready};
-
     #[tarpc::service]
     trait Foo {
         async fn two_part(s: String, i: i32) -> (String, i32);
@@ -12,19 +10,16 @@ fn att_service_trait() {
     }
 
     impl Foo for () {
-        type TwoPartFut = Ready<(String, i32)>;
-        fn two_part(self, _: context::Context, s: String, i: i32) -> Self::TwoPartFut {
-            ready((s, i))
+        async fn two_part(self, _: context::Context, s: String, i: i32) -> (String, i32) {
+            (s, i)
         }
 
-        type BarFut = Ready<String>;
-        fn bar(self, _: context::Context, s: String) -> Self::BarFut {
-            ready(s)
+        async fn bar(self, _: context::Context, s: String) -> String {
+            s
         }
 
-        type BazFut = Ready<()>;
-        fn baz(self, _: context::Context) -> Self::BazFut {
-            ready(())
+        async fn baz(self, _: context::Context) {
+            ()
         }
     }
 }
@@ -32,8 +27,6 @@ fn att_service_trait() {
 #[allow(non_camel_case_types)]
 #[test]
 fn raw_idents() {
-    use futures::future::{ready, Ready};
-
     type r#yield = String;
 
     #[tarpc::service]
@@ -44,19 +37,21 @@ fn raw_idents() {
     }
 
     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))
+        async fn r#await(
+            self,
+            _: context::Context,
+            r#struct: r#yield,
+            r#enum: i32,
+        ) -> (r#yield, i32) {
+            (r#struct, r#enum)
         }
 
-        type FnFut = Ready<r#yield>;
-        fn r#fn(self, _: context::Context, r#impl: r#yield) -> Self::FnFut {
-            ready(r#impl)
+        async fn r#fn(self, _: context::Context, r#impl: r#yield) -> r#yield {
+            r#impl
         }
 
-        type AsyncFut = Ready<()>;
-        fn r#async(self, _: context::Context) -> Self::AsyncFut {
-            ready(())
+        async fn r#async(self, _: context::Context) {
+            ()
         }
     }
 }

tarpc/Cargo.toml

@@ -1,26 +1,41 @@
 [package]
 name = "tarpc"
-version = "0.25.1"
-authors = ["Adam Wright <adam.austin.wright@gmail.com>", "Tim Kuehn <timothy.j.kuehn@gmail.com>"]
-edition = "2018"
+version = "0.34.0"
+rust-version = "1.58.0"
+authors = [
+    "Adam Wright <adam.austin.wright@gmail.com>",
+    "Tim Kuehn <timothy.j.kuehn@gmail.com>",
+]
+edition = "2021"
 license = "MIT"
 documentation = "https://docs.rs/tarpc"
 homepage = "https://github.com/google/tarpc"
 repository = "https://github.com/google/tarpc"
 keywords = ["rpc", "network", "server", "api", "microservices"]
 categories = ["asynchronous", "network-programming"]
-readme = "../README.md"
+readme = "README.md"
 description = "An RPC framework for Rust with a focus on ease of use."
 
 [features]
 default = []
 
-serde1 = ["tarpc-plugins/serde1", "serde", "serde/derive"]
-tokio1 = ["tokio/rt-multi-thread"]
-serde-transport = ["serde1", "tokio1", "tokio-serde/json", "tokio-util/codec"]
+serde1 = ["tarpc-plugins/serde1", "serde", "serde/derive", "serde/rc"]
+tokio1 = ["tokio/rt"]
+serde-transport = ["serde1", "tokio1", "tokio-serde", "tokio-util/codec"]
+serde-transport-json = ["tokio-serde/json"]
+serde-transport-bincode = ["tokio-serde/bincode"]
 tcp = ["tokio/net"]
+unix = ["tokio/net"]
 
-full = ["serde1", "tokio1", "serde-transport", "tcp"]
+full = [
+    "serde1",
+    "tokio1",
+    "serde-transport",
+    "serde-transport-json",
+    "serde-transport-bincode",
+    "tcp",
+    "unix",
+]
 
 [badges]
 travis-ci = { repository = "google/tarpc" }
@@ -30,29 +45,42 @@ anyhow = "1.0"
 fnv = "1.0"
 futures = "0.3"
 humantime = "2.0"
-log = "0.4"
 pin-project = "1.0"
-rand = "0.7"
+rand = "0.8"
 serde = { optional = true, version = "1.0", features = ["derive"] }
 static_assertions = "1.1.0"
-tarpc-plugins = { path = "../plugins", version = "0.10" }
+tarpc-plugins = { path = "../plugins", version = "0.13" }
+thiserror = "1.0"
 tokio = { version = "1", features = ["time"] }
-tokio-util = { version = "0.6.3", features = ["time"] }
+tokio-util = { version = "0.7.3", features = ["time"] }
 tokio-serde = { optional = true, version = "0.8" }
+tracing = { version = "0.1", default-features = false, features = [
+    "attributes",
+    "log",
+] }
+tracing-opentelemetry = { version = "0.18.0", default-features = false }
+opentelemetry = { version = "0.18.0", default-features = false }
+
 
 [dev-dependencies]
 assert_matches = "1.4"
 bincode = "1.3"
 bytes = { version = "1", features = ["serde"] }
-env_logger = "0.8"
 flate2 = "1.0"
 futures-test = "0.3"
-log = "0.4"
+opentelemetry = { version = "0.18.0", default-features = false, features = [
+    "rt-tokio",
+] }
+opentelemetry-jaeger = { version = "0.17.0", features = ["rt-tokio"] }
 pin-utils = "0.1.0-alpha"
 serde_bytes = "0.11"
-tokio = { version = "1", features = ["full", "test-util"] }
+tracing-subscriber = { version = "0.3", features = ["env-filter"] }
+tokio = { version = "1", features = ["full", "test-util", "tracing"] }
+console-subscriber = "0.1"
 tokio-serde = { version = "0.8", features = ["json", "bincode"] }
 trybuild = "1.0"
+tokio-rustls = "0.23"
+rustls-pemfile = "1.0"
 
 [package.metadata.docs.rs]
 all-features = true
@@ -63,7 +91,7 @@ name = "compression"
 required-features = ["serde-transport", "tcp"]
 
 [[example]]
-name = "server_calling_server"
+name = "tracing"
 required-features = ["full"]
 
 [[example]]
@@ -78,6 +106,10 @@ required-features = ["full"]
 name = "custom_transport"
 required-features = ["serde1", "tokio1", "serde-transport"]
 
+[[example]]
+name = "tls_over_tcp"
+required-features = ["full"]
+
 [[test]]
 name = "service_functional"
 required-features = ["serde-transport"]

tarpc/LICENSE

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

tarpc/examples/certs/eddsa/client.cert

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

tarpc/examples/certs/eddsa/client.chain

@@ -0,0 +1,19 @@
+-----BEGIN CERTIFICATE-----
+MIIBeDCCASqgAwIBAgIBezAFBgMrZXAwHDEaMBgGA1UEAwwRcG9ueXRvd24gRWRE
+U0EgQ0EwHhcNMjMwMzE3MTAxMTA0WhcNMzMwMzE0MTAxMTA0WjAuMSwwKgYDVQQD
+DCNwb255dG93biBFZERTQSBsZXZlbCAyIGludGVybWVkaWF0ZTAqMAUGAytlcAMh
+AEFsAexz4x2R4k4+PnTbvRVn0r3F/qw/zVnNBxfGcoEpo38wfTAdBgNVHQ4EFgQU
+ciXt8cpY/r+XwUR8jZgQgzegfEowIAYDVR0lAQH/BBYwFAYIKwYBBQUHAwEGCCsG
+AQUFBwMCMAwGA1UdEwQFMAMBAf8wCwYDVR0PBAQDAgH+MB8GA1UdIwQYMBaAFKYU
+oLdKeY7mp7QgMZKrkVtSWYBKMAUGAytlcANBAHVpNpCV8nu4fkH3Smikx5A9qtHc
+zgLIyp+wrF1a4YSa6sfTvuQmJd5aF23OXgq5grCOPXtdpHO50Mx5Qy74zQg=
+-----END CERTIFICATE-----
+-----BEGIN CERTIFICATE-----
+MIIBTDCB/6ADAgECAhRZLuF0TWjDs/31OO8VeKHkNIJQaDAFBgMrZXAwHDEaMBgG
+A1UEAwwRcG9ueXRvd24gRWREU0EgQ0EwHhcNMjMwMzE3MTAxMTA0WhcNMzMwMzE0
+MTAxMTA0WjAcMRowGAYDVQQDDBFwb255dG93biBFZERTQSBDQTAqMAUGAytlcAMh
+ABRPZ4TiuBE8CqAFByZvqpMo/unjnnryfG2AkkWGXpa3o1MwUTAdBgNVHQ4EFgQU
+phSgt0p5juantCAxkquRW1JZgEowHwYDVR0jBBgwFoAUphSgt0p5juantCAxkquR
+W1JZgEowDwYDVR0TAQH/BAUwAwEB/zAFBgMrZXADQQB29o8erJA0/a8/xOHilOCC
+t/s5wPHHnS5NSKx/m2N2nRn3zPxEnETlrAmGulJoeKOx8OblwmPi9rBT2K+QY2UB
+-----END CERTIFICATE-----

tarpc/examples/certs/eddsa/client.key

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

tarpc/examples/certs/eddsa/end.cert

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

tarpc/examples/certs/eddsa/end.chain

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

tarpc/examples/certs/eddsa/end.key

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

tarpc/examples/compression.rs

@@ -1,5 +1,11 @@
+// Copyright 2022 Google LLC
+//
+// Use of this source code is governed by an MIT-style
+// license that can be found in the LICENSE file or at
+// https://opensource.org/licenses/MIT.
+
 use flate2::{read::DeflateDecoder, write::DeflateEncoder, Compression};
-use futures::{Sink, SinkExt, Stream, StreamExt, TryStreamExt};
+use futures::{prelude::*, Sink, SinkExt, Stream, StreamExt, TryStreamExt};
 use serde::{Deserialize, Serialize};
 use serde_bytes::ByteBuf;
 use std::{io, io::Read, io::Write};
@@ -7,8 +13,8 @@ use tarpc::{
     client, context,
     serde_transport::tcp,
     server::{BaseChannel, Channel},
+    tokio_serde::formats::Bincode,
 };
-use 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)]
@@ -54,7 +60,7 @@ where
             if algorithm != CompressionAlgorithm::Deflate {
                 return Err(io::Error::new(
                     io::ErrorKind::InvalidData,
-                    format!("Compression algorithm {:?} not supported", algorithm),
+                    format!("Compression algorithm {algorithm:?} not supported"),
                 ));
             }
             let mut deflater = DeflateDecoder::new(payload.as_slice());
@@ -99,13 +105,16 @@ pub trait World {
 #[derive(Clone, Debug)]
 struct HelloServer;
 
-#[tarpc::server]
 impl World for HelloServer {
     async fn hello(self, _: context::Context, name: String) -> String {
-        format!("Hey, {}!", name)
+        format!("Hey, {name}!")
     }
 }
 
+async fn spawn(fut: impl Future<Output = ()> + Send + 'static) {
+    tokio::spawn(fut);
+}
+
 #[tokio::main]
 async fn main() -> anyhow::Result<()> {
     let mut incoming = tcp::listen("localhost:0", Bincode::default).await?;
@@ -114,11 +123,12 @@ async fn main() -> anyhow::Result<()> {
         let transport = incoming.next().await.unwrap().unwrap();
         BaseChannel::with_defaults(add_compression(transport))
             .execute(HelloServer.serve())
+            .for_each(spawn)
             .await;
     });
 
     let transport = tcp::connect(addr, Bincode::default).await?;
-    let client = WorldClient::new(client::Config::default(), add_compression(transport)).spawn()?;
+    let client = WorldClient::new(client::Config::default(), add_compression(transport)).spawn();
 
     println!(
         "{}",

tarpc/examples/custom_transport.rs

@@ -1,10 +1,16 @@
-use futures::future;
+// Copyright 2022 Google LLC
+//
+// Use of this source code is governed by an MIT-style
+// license that can be found in the LICENSE file or at
+// https://opensource.org/licenses/MIT.
+
+use futures::prelude::*;
 use tarpc::context::Context;
 use tarpc::serde_transport as transport;
 use tarpc::server::{BaseChannel, Channel};
+use tarpc::tokio_serde::formats::Bincode;
+use tarpc::tokio_util::codec::length_delimited::LengthDelimitedCodec;
 use tokio::net::{UnixListener, UnixStream};
-use tokio_serde::formats::Bincode;
-use tokio_util::codec::length_delimited::LengthDelimitedCodec;
 
 #[tarpc::service]
 pub trait PingService {
@@ -15,28 +21,29 @@ pub trait PingService {
 struct Service;
 
 impl PingService for Service {
-    type PingFut = future::Ready<()>;
-
-    fn ping(self, _: Context) -> Self::PingFut {
-        future::ready(())
-    }
+    async fn ping(self, _: Context) {}
 }
 
 #[tokio::main]
-async fn main() -> std::io::Result<()> {
+async fn main() -> anyhow::Result<()> {
     let bind_addr = "/tmp/tarpc_on_unix_example.sock";
 
     let _ = std::fs::remove_file(bind_addr);
 
     let listener = UnixListener::bind(bind_addr).unwrap();
     let codec_builder = LengthDelimitedCodec::builder();
+    async fn spawn(fut: impl Future<Output = ()> + Send + 'static) {
+        tokio::spawn(fut);
+    }
     tokio::spawn(async move {
         loop {
             let (conn, _addr) = listener.accept().await.unwrap();
             let framed = codec_builder.new_framed(conn);
             let transport = transport::new(framed, Bincode::default());
 
-            let fut = BaseChannel::with_defaults(transport).execute(Service.serve());
+            let fut = BaseChannel::with_defaults(transport)
+                .execute(Service.serve())
+                .for_each(spawn);
             tokio::spawn(fut);
         }
     });
@@ -44,7 +51,9 @@ async fn main() -> std::io::Result<()> {
     let conn = UnixStream::connect(bind_addr).await?;
     let transport = transport::new(codec_builder.new_framed(conn), Bincode::default());
     PingServiceClient::new(Default::default(), transport)
-        .spawn()?
+        .spawn()
         .ping(tarpc::context::current())
-        .await
+        .await?;
+
+    Ok(())
 }

tarpc/examples/pubsub.rs

@@ -38,10 +38,11 @@ use futures::{
     future::{self, AbortHandle},
     prelude::*,
 };
-use log::info;
 use publisher::Publisher as _;
 use std::{
     collections::HashMap,
+    env,
+    error::Error,
     io,
     net::SocketAddr,
     sync::{Arc, Mutex, RwLock},
@@ -51,9 +52,11 @@ use tarpc::{
     client, context,
     serde_transport::tcp,
     server::{self, Channel},
+    tokio_serde::formats::Json,
 };
 use tokio::net::ToSocketAddrs;
-use tokio_serde::formats::Json;
+use tracing::info;
+use tracing_subscriber::prelude::*;
 
 pub mod subscriber {
     #[tarpc::service]
@@ -76,17 +79,13 @@ struct Subscriber {
     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!(
-            "[{}] received message on topic '{}': {}",
-            self.local_addr, topic, message
-        );
+        info!(local_addr = %self.local_addr, %topic, %message, "ReceivedMessage")
     }
 }
 
@@ -117,10 +116,11 @@ impl Subscriber {
                 ))
             }
         };
-        let (handler, abort_handle) = future::abortable(handler.execute(subscriber.serve()));
+        let (handler, abort_handle) =
+            future::abortable(handler.execute(subscriber.serve()).for_each(spawn));
         tokio::spawn(async move {
             match handler.await {
-                Ok(()) | Err(future::Aborted) => info!("[{}] subscriber shutdown.", local_addr),
+                Ok(()) | Err(future::Aborted) => info!(?local_addr, "subscriber shutdown."),
             }
         });
         Ok(SubscriberHandle(abort_handle))
@@ -129,7 +129,6 @@ impl Subscriber {
 
 #[derive(Debug)]
 struct Subscription {
-    subscriber: subscriber::SubscriberClient,
     topics: Vec<String>,
 }
 
@@ -144,6 +143,10 @@ struct PublisherAddrs {
     subscriptions: SocketAddr,
 }
 
+async fn spawn(fut: impl Future<Output = ()> + Send + 'static) {
+    tokio::spawn(fut);
+}
+
 impl Publisher {
     async fn start(self) -> io::Result<PublisherAddrs> {
         let mut connecting_publishers = tcp::listen("localhost:0", Json::default).await?;
@@ -153,16 +156,17 @@ impl Publisher {
             subscriptions: self.clone().start_subscription_manager().await?,
         };
 
-        info!("[{}] listening for publishers.", publisher_addrs.publisher);
+        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 connected.", publisher.peer_addr().unwrap());
+            info!(publisher.peer_addr = ?publisher.peer_addr(), "publisher connected.");
 
             server::BaseChannel::with_defaults(publisher)
                 .execute(self.serve())
+                .for_each(spawn)
                 .await
         });
 
@@ -174,7 +178,7 @@ impl Publisher {
             .await?
             .filter_map(|r| future::ready(r.ok()));
         let new_subscriber_addr = connecting_subscribers.get_ref().local_addr();
-        info!("[{}] listening for subscribers.", new_subscriber_addr);
+        info!(?new_subscriber_addr, "listening for subscribers.");
 
         tokio::spawn(async move {
             while let Some(conn) = connecting_subscribers.next().await {
@@ -210,12 +214,11 @@ impl Publisher {
             self.clients.lock().unwrap().insert(
                 subscriber_addr,
                 Subscription {
-                    subscriber: subscriber.clone(),
                     topics: topics.clone(),
                 },
             );
 
-            info!("[{}] subscribed to topics: {:?}", subscriber_addr, topics);
+            info!(%subscriber_addr, ?topics, "subscribed to new topics");
             let mut subscriptions = self.subscriptions.write().unwrap();
             for topic in topics {
                 subscriptions
@@ -226,18 +229,18 @@ impl Publisher {
         }
     }
 
-    fn start_subscriber_gc(
+    fn start_subscriber_gc<E: Error>(
         self,
         subscriber_addr: SocketAddr,
-        client_dispatch: impl Future<Output = anyhow::Result<()>> + Send + 'static,
+        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 connection broken: {:?}",
-                    subscriber_addr, e
-                )
+                    %subscriber_addr,
+                    error = %e,
+                    "subscriber connection broken");
             }
             // Don't clean up the subscriber until initialization is done.
             let _ = subscriber_ready.await;
@@ -259,7 +262,6 @@ impl Publisher {
     }
 }
 
-#[tarpc::server]
 impl publisher::Publisher for Publisher {
     async fn publish(self, _: context::Context, topic: String, message: String) {
         info!("received message to publish.");
@@ -281,13 +283,29 @@ impl publisher::Publisher for Publisher {
     }
 }
 
+/// Initializes an OpenTelemetry tracing subscriber with a Jaeger backend.
+fn init_tracing(service_name: &str) -> anyhow::Result<()> {
+    env::set_var("OTEL_BSP_MAX_EXPORT_BATCH_SIZE", "12");
+    let tracer = opentelemetry_jaeger::new_agent_pipeline()
+        .with_service_name(service_name)
+        .with_max_packet_size(2usize.pow(13))
+        .install_batch(opentelemetry::runtime::Tokio)?;
+
+    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<()> {
-    env_logger::init();
+    init_tracing("Pub/Sub")?;
 
-    let clients = Arc::new(Mutex::new(HashMap::new()));
     let addrs = Publisher {
-        clients,
+        clients: Arc::new(Mutex::new(HashMap::new())),
         subscriptions: Arc::new(RwLock::new(HashMap::new())),
     }
     .start()
@@ -309,7 +327,7 @@ async fn main() -> anyhow::Result<()> {
         client::Config::default(),
         tcp::connect(addrs.publisher, Json::default).await?,
     )
-    .spawn()?;
+    .spawn();
 
     publisher
         .publish(context::current(), "calculus".into(), "sqrt(2)".into())
@@ -337,6 +355,7 @@ async fn main() -> anyhow::Result<()> {
         )
         .await?;
 
+    opentelemetry::global::shutdown_tracer_provider();
     info!("done.");
 
     Ok(())

tarpc/examples/readme.rs

@@ -4,8 +4,7 @@
 // license that can be found in the LICENSE file or at
 // https://opensource.org/licenses/MIT.
 
-use futures::future::{self, Ready};
-use std::io;
+use futures::prelude::*;
 use tarpc::{
     client, context,
     server::{self, Channel},
@@ -24,33 +23,32 @@ pub trait World {
 struct HelloServer;
 
 impl World for HelloServer {
-    // Each defined rpc generates two items in the trait, a fn that serves the RPC, and
-    // an associated type representing the future output by the fn.
-
-    type HelloFut = Ready<String>;
-
-    fn hello(self, _: context::Context, name: String) -> Self::HelloFut {
-        future::ready(format!("Hello, {}!", name))
+    async fn hello(self, _: context::Context, name: String) -> String {
+        format!("Hello, {name}!")
     }
 }
 
+async fn spawn(fut: impl Future<Output = ()> + Send + 'static) {
+    tokio::spawn(fut);
+}
+
 #[tokio::main]
-async fn main() -> io::Result<()> {
+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()));
+    tokio::spawn(server.execute(HelloServer.serve()).for_each(spawn));
 
     // WorldClient is generated by the #[tarpc::service] attribute. It has a constructor `new`
     // that takes a config and any Transport as input.
-    let client = WorldClient::new(client::Config::default(), client_transport).spawn()?;
+    let client = WorldClient::new(client::Config::default(), client_transport).spawn();
 
     // The client has an RPC method for each RPC defined in the annotated trait. It takes the same
     // args as defined, with the addition of a Context, which is always the first arg. The Context
     // specifies a deadline and trace information which can be helpful in debugging requests.
     let hello = client.hello(context::current(), "Stim".to_string()).await?;
 
-    println!("{}", hello);
+    println!("{hello}");
 
     Ok(())
 }

tarpc/examples/server_calling_server.rs

@@ -1,92 +0,0 @@
-// Copyright 2018 Google LLC
-//
-// Use of this source code is governed by an MIT-style
-// license that can be found in the LICENSE file or at
-// https://opensource.org/licenses/MIT.
-
-use crate::{add::Add as AddService, double::Double as DoubleService};
-use futures::{future, prelude::*};
-use std::io;
-use tarpc::{
-    client, context,
-    server::{BaseChannel, Incoming},
-};
-use tokio_serde::formats::Json;
-
-pub mod add {
-    #[tarpc::service]
-    pub trait Add {
-        /// Add two ints together.
-        async fn add(x: i32, y: i32) -> i32;
-    }
-}
-
-pub mod double {
-    #[tarpc::service]
-    pub trait Double {
-        /// 2 * x
-        async fn double(x: i32) -> Result<i32, String>;
-    }
-}
-
-#[derive(Clone)]
-struct AddServer;
-
-#[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())
-    }
-}
-
-#[tokio::main]
-async fn main() -> io::Result<()> {
-    env_logger::init();
-
-    let add_listener = tarpc::serde_transport::tcp::listen("localhost:0", Json::default)
-        .await?
-        .filter_map(|r| future::ready(r.ok()));
-    let addr = add_listener.get_ref().local_addr();
-    let add_server = 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()?;
-
-    for i in 1..=5 {
-        eprintln!("{:?}", double_client.double(context::current(), i).await?);
-    }
-    Ok(())
-}

tarpc/examples/tls_over_tcp.rs

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

tarpc/examples/tracing.rs

@@ -0,0 +1,187 @@
+// Copyright 2018 Google LLC
+//
+// Use of this source code is governed by an MIT-style
+// license that can be found in the LICENSE file or at
+// https://opensource.org/licenses/MIT.
+
+use crate::{
+    add::{Add as AddService, AddStub},
+    double::Double as DoubleService,
+};
+use futures::{future, prelude::*};
+use std::{
+    io,
+    sync::{
+        atomic::{AtomicBool, Ordering},
+        Arc,
+    },
+};
+use tarpc::{
+    client::{
+        self,
+        stub::{load_balance, retry},
+        RpcError,
+    },
+    context, serde_transport,
+    server::{
+        incoming::{spawn_incoming, Incoming},
+        BaseChannel, Serve,
+    },
+    tokio_serde::formats::Json,
+    ClientMessage, Response, ServerError, Transport,
+};
+use tokio::net::TcpStream;
+use tracing_subscriber::prelude::*;
+
+pub mod add {
+    #[tarpc::service]
+    pub trait Add {
+        /// Add two ints together.
+        async fn add(x: i32, y: i32) -> i32;
+    }
+}
+
+pub mod double {
+    #[tarpc::service]
+    pub trait Double {
+        /// 2 * x
+        async fn double(x: i32) -> Result<i32, String>;
+    }
+}
+
+#[derive(Clone)]
+struct AddServer;
+
+impl AddService for AddServer {
+    async fn add(self, _: context::Context, x: i32, y: i32) -> i32 {
+        x + y
+    }
+}
+
+#[derive(Clone)]
+struct DoubleServer<Stub> {
+    add_client: add::AddClient<Stub>,
+}
+
+impl<Stub> DoubleService for DoubleServer<Stub>
+where
+    Stub: AddStub + Clone + Send + Sync + 'static,
+{
+    async fn double(self, _: context::Context, x: i32) -> Result<i32, String> {
+        self.add_client
+            .add(context::current(), x, x)
+            .await
+            .map_err(|e| e.to_string())
+    }
+}
+
+fn init_tracing(service_name: &str) -> anyhow::Result<()> {
+    let tracer = opentelemetry_jaeger::new_agent_pipeline()
+        .with_service_name(service_name)
+        .with_auto_split_batch(true)
+        .with_max_packet_size(2usize.pow(13))
+        .install_batch(opentelemetry::runtime::Tokio)?;
+
+    tracing_subscriber::registry()
+        .with(tracing_subscriber::EnvFilter::from_default_env())
+        .with(tracing_subscriber::fmt::layer())
+        .with(tracing_opentelemetry::layer().with_tracer(tracer))
+        .try_init()?;
+
+    Ok(())
+}
+
+async fn listen_on_random_port<Item, SinkItem>() -> anyhow::Result<(
+    impl Stream<Item = serde_transport::Transport<TcpStream, Item, SinkItem, Json<Item, SinkItem>>>,
+    std::net::SocketAddr,
+)>
+where
+    Item: for<'de> serde::Deserialize<'de>,
+    SinkItem: serde::Serialize,
+{
+    let listener = tarpc::serde_transport::tcp::listen("localhost:0", Json::default)
+        .await?
+        .filter_map(|r| future::ready(r.ok()))
+        .take(1);
+    let addr = listener.get_ref().get_ref().local_addr();
+    Ok((listener, addr))
+}
+
+fn make_stub<Req, Resp, const N: usize>(
+    backends: [impl Transport<ClientMessage<Arc<Req>>, Response<Resp>> + Send + Sync + 'static; N],
+) -> retry::Retry<
+    impl Fn(&Result<Resp, RpcError>, u32) -> bool + Clone,
+    load_balance::RoundRobin<client::Channel<Arc<Req>, Resp>>,
+>
+where
+    Req: Send + Sync + 'static,
+    Resp: Send + Sync + 'static,
+{
+    let stub = load_balance::RoundRobin::new(
+        backends
+            .into_iter()
+            .map(|transport| tarpc::client::new(client::Config::default(), transport).spawn())
+            .collect(),
+    );
+    let stub = retry::Retry::new(stub, |resp, attempts| {
+        if let Err(e) = resp {
+            tracing::warn!("Got an error: {e:?}");
+            attempts < 3
+        } else {
+            false
+        }
+    });
+    stub
+}
+
+#[tokio::main]
+async fn main() -> anyhow::Result<()> {
+    init_tracing("tarpc_tracing_example")?;
+
+    let (add_listener1, addr1) = listen_on_random_port().await?;
+    let (add_listener2, addr2) = listen_on_random_port().await?;
+    let something_bad_happened = Arc::new(AtomicBool::new(false));
+    let server = AddServer.serve().before(move |_: &mut _, _: &_| {
+        let something_bad_happened = something_bad_happened.clone();
+        async move {
+            if something_bad_happened.fetch_xor(true, Ordering::Relaxed) {
+                Err(ServerError::new(
+                    io::ErrorKind::NotFound,
+                    "Gamma Ray!".into(),
+                ))
+            } else {
+                Ok(())
+            }
+        }
+    });
+    let add_server = add_listener1
+        .chain(add_listener2)
+        .map(BaseChannel::with_defaults);
+    tokio::spawn(spawn_incoming(add_server.execute(server)));
+
+    let add_client = add::AddClient::from(make_stub([
+        tarpc::serde_transport::tcp::connect(addr1, Json::default).await?,
+        tarpc::serde_transport::tcp::connect(addr2, Json::default).await?,
+    ]));
+
+    let double_listener = tarpc::serde_transport::tcp::listen("localhost:0", Json::default)
+        .await?
+        .filter_map(|r| future::ready(r.ok()));
+    let addr = double_listener.get_ref().local_addr();
+    let double_server = double_listener.map(BaseChannel::with_defaults).take(1);
+    let server = DoubleServer { add_client }.serve();
+    tokio::spawn(spawn_incoming(double_server.execute(server)));
+
+    let to_double_server = tarpc::serde_transport::tcp::connect(addr, Json::default).await?;
+    let double_client =
+        double::DoubleClient::new(client::Config::default(), to_double_server).spawn();
+
+    let ctx = context::current();
+    for _ in 1..=5 {
+        tracing::info!("{:?}", double_client.double(ctx, 1).await?);
+    }
+
+    opentelemetry::global::shutdown_tracer_provider();
+
+    Ok(())
+}

tarpc/src/cancellations.rs

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

tarpc/src/client/in_flight_requests.rs

@@ -1,18 +1,15 @@
 use crate::{
     context,
     util::{Compact, TimeUntil},
-    PollIo, Response, ServerError,
 };
 use fnv::FnvHashMap;
-use futures::ready;
-use log::{debug, trace};
 use std::{
     collections::hash_map,
-    io,
     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)]
@@ -31,9 +28,10 @@ impl<Resp> Default for InFlightRequests<Resp> {
 }
 
 #[derive(Debug)]
-struct RequestData<Resp> {
+struct RequestData<Res> {
     ctx: context::Context,
-    response_completion: oneshot::Sender<Response<Resp>>,
+    span: Span,
+    response_completion: oneshot::Sender<Res>,
     /// The key to remove the timer for the request's deadline.
     deadline_key: delay_queue::Key,
 }
@@ -43,7 +41,7 @@ struct RequestData<Resp> {
 #[derive(Debug)]
 pub struct AlreadyExistsError;
 
-impl<Resp> InFlightRequests<Resp> {
+impl<Res> InFlightRequests<Res> {
     /// Returns the number of in-flight requests.
     pub fn len(&self) -> usize {
         self.request_data.len()
@@ -59,20 +57,16 @@ impl<Resp> InFlightRequests<Resp> {
         &mut self,
         request_id: u64,
         ctx: context::Context,
-        response_completion: oneshot::Sender<Response<Resp>>,
+        span: Span,
+        response_completion: oneshot::Sender<Res>,
     ) -> Result<(), AlreadyExistsError> {
         match self.request_data.entry(request_id) {
             hash_map::Entry::Vacant(vacant) => {
                 let timeout = ctx.deadline.time_until();
-                trace!(
-                    "[{}] Queuing request with timeout {:?}.",
-                    ctx.trace_id(),
-                    timeout,
-                );
-
                 let deadline_key = self.deadlines.insert(request_id, timeout);
                 vacant.insert(RequestData {
                     ctx,
+                    span,
                     response_completion,
                     deadline_key,
                 });
@@ -83,33 +77,40 @@ impl<Resp> InFlightRequests<Resp> {
     }
 
     /// 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) {
+    pub fn complete_request(&mut self, request_id: u64, result: Res) -> Option<Span> {
+        if let Some(request_data) = self.request_data.remove(&request_id) {
             self.request_data.compact(0.1);
-
-            trace!("[{}] Received response.", request_data.ctx.trace_id());
             self.deadlines.remove(&request_data.deadline_key);
-            request_data.complete(response);
-            return true;
+            let _ = request_data.response_completion.send(result);
+            return Some(request_data.span);
         }
 
-        debug!(
-            "No in-flight request found for request_id = {}.",
-            response.request_id
-        );
+        tracing::debug!("No in-flight request found for request_id = {request_id}.");
 
         // If the response completion was absent, then the request was already canceled.
-        false
+        None
+    }
+
+    /// Completes all requests using the provided function.
+    /// Returns Spans for all completes requests.
+    pub fn complete_all_requests<'a>(
+        &'a mut self,
+        mut result: impl FnMut() -> Res + 'a,
+    ) -> impl Iterator<Item = Span> + 'a {
+        self.deadlines.clear();
+        self.request_data.drain().map(move |(_, request_data)| {
+            let _ = request_data.response_completion.send(result());
+            request_data.span
+        })
     }
 
     /// Cancels a request without completing (typically used when a request handle was dropped
     /// before the request completed).
-    pub fn cancel_request(&mut self, request_id: u64) -> Option<context::Context> {
+    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);
-            trace!("[{}] Cancelling request.", request_data.ctx.trace_id());
             self.deadlines.remove(&request_data.deadline_key);
-            Some(request_data.ctx)
+            Some((request_data.ctx, request_data.span))
         } else {
             None
         }
@@ -117,46 +118,20 @@ impl<Resp> InFlightRequests<Resp> {
 
     /// 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) -> PollIo<u64> {
-        Poll::Ready(match ready!(self.deadlines.poll_expired(cx)) {
-            Some(Ok(expired)) => {
-                let request_id = expired.into_inner();
-                if let Some(request_data) = self.request_data.remove(&request_id) {
-                    self.request_data.compact(0.1);
-                    request_data.complete(Self::deadline_exceeded_error(request_id));
-                }
-                Some(Ok(request_id))
+    pub fn poll_expired(
+        &mut self,
+        cx: &mut Context,
+        expired_error: impl Fn() -> Res,
+    ) -> Poll<Option<u64>> {
+        self.deadlines.poll_expired(cx).map(|expired| {
+            let request_id = expired?.into_inner();
+            if let Some(request_data) = self.request_data.remove(&request_id) {
+                let _entered = request_data.span.enter();
+                tracing::error!("DeadlineExceeded");
+                self.request_data.compact(0.1);
+                let _ = request_data.response_completion.send(expired_error());
             }
-            Some(Err(e)) => Some(Err(io::Error::new(io::ErrorKind::Other, e))),
-            None => None,
+            Some(request_id)
         })
     }
-
-    fn deadline_exceeded_error(request_id: u64) -> Response<Resp> {
-        Response {
-            request_id,
-            message: Err(ServerError {
-                kind: io::ErrorKind::TimedOut,
-                detail: Some("Client dropped expired request.".to_string()),
-            }),
-        }
-    }
-}
-
-/// When InFlightRequests is dropped, any outstanding requests are completed with a
-/// deadline-exceeded error.
-impl<Resp> Drop for InFlightRequests<Resp> {
-    fn drop(&mut self) {
-        let deadlines = &mut self.deadlines;
-        for (_, request_data) in self.request_data.drain() {
-            let expired = deadlines.remove(&request_data.deadline_key);
-            request_data.complete(Self::deadline_exceeded_error(expired.into_inner()));
-        }
-    }
-}
-
-impl<Resp> RequestData<Resp> {
-    fn complete(self, response: Response<Resp>) {
-        let _ = self.response_completion.send(response);
-    }
 }

tarpc/src/client/stub.rs

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

tarpc/src/client/stub/load_balance.rs

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

tarpc/src/client/stub/mock.rs

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

tarpc/src/client/stub/retry.rs

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

tarpc/src/context.rs

@@ -8,8 +8,13 @@
 //! 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::time::{Duration, SystemTime};
+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.
@@ -22,15 +27,9 @@ use std::time::{Duration, SystemTime};
 pub struct Context {
     /// When the client expects the request to be complete by. The server should cancel the request
     /// if it is not complete by this time.
-    #[cfg_attr(
-        feature = "serde1",
-        serde(serialize_with = "crate::util::serde::serialize_epoch_secs")
-    )]
-    #[cfg_attr(
-        feature = "serde1",
-        serde(deserialize_with = "crate::util::serde::deserialize_epoch_secs")
-    )]
     #[cfg_attr(feature = "serde1", serde(default = "ten_seconds_from_now"))]
+    // Serialized as a Duration to prevent clock skew issues.
+    #[cfg_attr(feature = "serde1", serde(with = "absolute_to_relative_time"))]
     pub deadline: SystemTime,
     /// Uniquely identifies requests originating from the same source.
     /// When a service handles a request by making requests itself, those requests should
@@ -39,25 +38,115 @@ pub struct Context {
     pub trace_context: trace::Context,
 }
 
+#[cfg(feature = "serde1")]
+mod absolute_to_relative_time {
+    pub use serde::{Deserialize, Deserializer, Serialize, Serializer};
+    pub use std::time::{Duration, SystemTime};
+
+    pub fn serialize<S>(deadline: &SystemTime, serializer: S) -> Result<S::Ok, S::Error>
+    where
+        S: Serializer,
+    {
+        let deadline = deadline
+            .duration_since(SystemTime::now())
+            .unwrap_or(Duration::ZERO);
+        deadline.serialize(serializer)
+    }
+
+    pub fn deserialize<'de, D>(deserializer: D) -> Result<SystemTime, D::Error>
+    where
+        D: Deserializer<'de>,
+    {
+        let deadline = Duration::deserialize(deserializer)?;
+        Ok(SystemTime::now() + deadline)
+    }
+
+    #[cfg(test)]
+    #[derive(serde::Serialize, serde::Deserialize)]
+    struct AbsoluteToRelative(#[serde(with = "self")] SystemTime);
+
+    #[test]
+    fn test_serialize() {
+        let now = SystemTime::now();
+        let deadline = now + Duration::from_secs(10);
+        let serialized_deadline = bincode::serialize(&AbsoluteToRelative(deadline)).unwrap();
+        let deserialized_deadline: Duration = bincode::deserialize(&serialized_deadline).unwrap();
+        // TODO: how to avoid flakiness?
+        assert!(deserialized_deadline > Duration::from_secs(9));
+    }
+
+    #[test]
+    fn test_deserialize() {
+        let deadline = Duration::from_secs(10);
+        let serialized_deadline = bincode::serialize(&deadline).unwrap();
+        let AbsoluteToRelative(deserialized_deadline) =
+            bincode::deserialize(&serialized_deadline).unwrap();
+        // TODO: how to avoid flakiness?
+        assert!(deserialized_deadline > SystemTime::now() + Duration::from_secs(9));
+    }
+}
+
 assert_impl_all!(Context: Send, Sync);
 
-#[cfg(feature = "serde1")]
 fn ten_seconds_from_now() -> SystemTime {
     SystemTime::now() + Duration::from_secs(10)
 }
 
 /// Returns the context for the current request, or a default Context if no request is active.
-// TODO: populate Context with request-scoped data, with default fallbacks.
 pub fn current() -> Context {
-    Context {
-        deadline: SystemTime::now() + Duration::from_secs(10),
-        trace_context: trace::Context::new_root(),
+    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

@@ -27,7 +27,7 @@
 //! process, and no context switching between different languages.
 //!
 //! Some other features of tarpc:
-//! - Pluggable transport: any type impling `Stream<Item = Request> + Sink<Response>` can be
+//! - Pluggable transport: any type implementing `Stream<Item = Request> + Sink<Response>` can be
 //!   used as a transport to connect the client and server.
 //! - `Send + 'static` optional: if the transport doesn't require it, neither does tarpc!
 //! - Cascading cancellation: dropping a request will send a cancellation message to the server.
@@ -38,6 +38,14 @@
 //!   requests sent by the server that use the request context will propagate the request deadline.
 //!   For example, if a server is handling a request with a 10s deadline, does 2s of work, then
 //!   sends a request to another server, that server will see an 8s deadline.
+//! - Distributed tracing: tarpc is instrumented with
+//!   [tracing](https://github.com/tokio-rs/tracing) primitives extended with
+//!   [OpenTelemetry](https://opentelemetry.io/) traces. Using a compatible tracing subscriber like
+//!   [Jaeger](https://github.com/open-telemetry/opentelemetry-rust/tree/main/opentelemetry-jaeger),
+//!   each RPC can be traced through the client, server, and other dependencies downstream of the
+//!   server. Even for applications not connected to a distributed tracing collector, the
+//!   instrumentation can also be ingested by regular loggers like
+//!   [env_logger](https://github.com/env-logger-rs/env_logger/).
 //! - Serde serialization: enabling the `serde1` Cargo feature will make service requests and
 //!   responses `Serialize + Deserialize`. It's entirely optional, though: in-memory transports can
 //!   be used, as well, so the price of serialization doesn't have to be paid when it's not needed.
@@ -46,7 +54,7 @@
 //! Add to your `Cargo.toml` dependencies:
 //!
 //! ```toml
-//! tarpc = "0.25"
+//! tarpc = "0.29"
 //! ```
 //!
 //! The `tarpc::service` attribute expands to a collection of items that form an rpc service.
@@ -59,8 +67,9 @@
 //! your `Cargo.toml`:
 //!
 //! ```toml
-//! futures = "1.0"
-//! tarpc = { version = "0.25", features = ["tokio1"] }
+//! anyhow = "1.0"
+//! futures = "0.3"
+//! tarpc = { version = "0.29", features = ["tokio1"] }
 //! tokio = { version = "1.0", features = ["macros"] }
 //! ```
 //!
@@ -79,9 +88,8 @@
 //! };
 //! use tarpc::{
 //!     client, context,
-//!     server::{self, Incoming},
+//!     server::{self, incoming::Incoming, Channel},
 //! };
-//! use std::io;
 //!
 //! // This is the service definition. It looks a lot like a trait definition.
 //! // It defines one RPC, hello, which takes one arg, name, and returns a String.
@@ -103,9 +111,8 @@
 //! # };
 //! # use tarpc::{
 //! #     client, context,
-//! #     server::{self, Incoming},
+//! #     server::{self, incoming::Incoming},
 //! # };
-//! # use std::io;
 //! # // This is the service definition. It looks a lot like a trait definition.
 //! # // It defines one RPC, hello, which takes one arg, name, and returns a String.
 //! # #[tarpc::service]
@@ -119,13 +126,9 @@
 //! struct HelloServer;
 //!
 //! impl World for HelloServer {
-//!     // Each defined rpc generates two items in the trait, a fn that serves the RPC, and
-//!     // an associated type representing the future output by the fn.
-//!
-//!     type HelloFut = Ready<String>;
-//!
-//!     fn hello(self, _: context::Context, name: String) -> Self::HelloFut {
-//!         future::ready(format!("Hello, {}!", name))
+//!     // Each defined rpc generates an async fn that serves the RPC
+//!     async fn hello(self, _: context::Context, name: String) -> String {
+//!         format!("Hello, {name}!")
 //!     }
 //! }
 //! ```
@@ -145,7 +148,6 @@
 //! #     client, context,
 //! #     server::{self, Channel},
 //! # };
-//! # use std::io;
 //! # // This is the service definition. It looks a lot like a trait definition.
 //! # // It defines one RPC, hello, which takes one arg, name, and returns a String.
 //! # #[tarpc::service]
@@ -158,33 +160,36 @@
 //! # #[derive(Clone)]
 //! # struct HelloServer;
 //! # impl World for HelloServer {
-//! #     // Each defined rpc generates two items in the trait, a fn that serves the RPC, and
-//! #     // an associated type representing the future output by the fn.
-//! #     type HelloFut = Ready<String>;
-//! #     fn hello(self, _: context::Context, name: String) -> Self::HelloFut {
-//! #         future::ready(format!("Hello, {}!", name))
+//!     // Each defined rpc generates an async fn that serves the RPC
+//! #     async fn hello(self, _: context::Context, name: String) -> String {
+//! #         format!("Hello, {name}!")
 //! #     }
 //! # }
 //! # #[cfg(not(feature = "tokio1"))]
 //! # fn main() {}
 //! # #[cfg(feature = "tokio1")]
 //! #[tokio::main]
-//! async fn main() -> io::Result<()> {
+//! async fn main() -> anyhow::Result<()> {
 //!     let (client_transport, server_transport) = tarpc::transport::channel::unbounded();
 //!
 //!     let server = server::BaseChannel::with_defaults(server_transport);
-//!     tokio::spawn(server.execute(HelloServer.serve()));
+//!     tokio::spawn(
+//!         server.execute(HelloServer.serve())
+//!             // Handle all requests concurrently.
+//!             .for_each(|response| async move {
+//!                 tokio::spawn(response);
+//!             }));
 //!
 //!     // 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()?;
+//!     let mut client = WorldClient::new(client::Config::default(), client_transport).spawn();
 //!
 //!     // The client has an RPC method for each RPC defined in the annotated trait. It takes the same
 //!     // args as defined, with the addition of a Context, which is always the first arg. The Context
 //!     // specifies a deadline and trace information which can be helpful in debugging requests.
 //!     let hello = client.hello(context::current(), "Stim".to_string()).await?;
 //!
-//!     println!("{}", hello);
+//!     println!("{hello}");
 //!
 //!     Ok(())
 //! }
@@ -194,15 +199,17 @@
 //!
 //! 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))]
 
 #[cfg(feature = "serde1")]
+#[doc(hidden)]
 pub use serde;
 
 #[cfg(feature = "serde-transport")]
-pub use tokio_serde;
+pub use {tokio_serde, tokio_util};
 
 #[cfg(feature = "serde-transport")]
 #[cfg_attr(docsrs, doc(cfg(feature = "serde-transport")))]
@@ -237,62 +244,7 @@ pub use tarpc_plugins::derive_serde;
 ///   * `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, {}! You are connected from {:?}.", name, 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, {}! You are connected from {:?}.", name, self.0)
-///         })
-///     }
-/// }
-/// ```
-///
-/// Note that this won't touch functions unless they have been annotated with
-/// `async`, meaning that this should not break existing code.
-pub use tarpc_plugins::server;
-
+pub(crate) mod cancellations;
 pub mod client;
 pub mod context;
 pub mod server;
@@ -303,7 +255,8 @@ pub use crate::transport::sealed::Transport;
 
 use anyhow::Context as _;
 use futures::task::*;
-use std::{fmt::Display, io, time::SystemTime};
+use std::sync::Arc;
+use std::{error::Error, fmt::Display, io, time::SystemTime};
 
 /// A message from a client to a server.
 #[derive(Debug)]
@@ -355,8 +308,9 @@ pub struct Response<T> {
     pub message: Result<T, ServerError>,
 }
 
-/// An error response from a server to a client.
-#[derive(Clone, Debug, PartialEq, Eq, Hash)]
+/// 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 {
@@ -371,12 +325,36 @@ pub struct ServerError {
     /// The type of error that occurred to fail the request.
     pub kind: io::ErrorKind,
     /// A message describing more detail about the error that occurred.
-    pub detail: Option<String>,
+    pub detail: String,
 }
 
-impl From<ServerError> for io::Error {
-    fn from(e: ServerError) -> io::Error {
-        io::Error::new(e.kind, e.detail.unwrap_or_default())
+/// Critical errors that result in a Channel disconnecting.
+#[derive(thiserror::Error, Debug, PartialEq, Eq)]
+pub enum ChannelError<E>
+where
+    E: Error + Send + Sync + 'static,
+{
+    /// Could not read from the transport.
+    #[error("could not read from the transport")]
+    Read(#[source] Arc<E>),
+    /// Could not ready the transport for writes.
+    #[error("could not ready the transport for writes")]
+    Ready(#[source] E),
+    /// Could not write to the transport.
+    #[error("could not write to the transport")]
+    Write(#[source] E),
+    /// Could not flush the transport.
+    #[error("could not flush the transport")]
+    Flush(#[source] E),
+    /// Could not close the write end of the transport.
+    #[error("could not close the write end of the transport")]
+    Close(#[source] E),
+}
+
+impl ServerError {
+    /// Returns a new server error with `kind` and `detail`.
+    pub fn new(kind: io::ErrorKind, detail: String) -> ServerError {
+        Self { kind, detail }
     }
 }
 
@@ -387,7 +365,6 @@ impl<T> Request<T> {
     }
 }
 
-pub(crate) type PollIo<T> = Poll<Option<io::Result<T>>>;
 pub(crate) trait PollContext<T> {
     fn context<C>(self, context: C) -> Poll<Option<anyhow::Result<T>>>
     where
@@ -399,7 +376,10 @@ pub(crate) trait PollContext<T> {
         F: FnOnce() -> C;
 }
 
-impl<T> PollContext<T> for PollIo<T> {
+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,

tarpc/src/serde_transport.rs

@@ -42,14 +42,10 @@ where
     type Item = io::Result<Item>;
 
     fn poll_next(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Option<io::Result<Item>>> {
-        match self.project().inner.poll_next(cx) {
-            Poll::Pending => Poll::Pending,
-            Poll::Ready(None) => Poll::Ready(None),
-            Poll::Ready(Some(Ok::<_, CodecError>(next))) => Poll::Ready(Some(Ok(next))),
-            Poll::Ready(Some(Err::<_, CodecError>(e))) => {
-                Poll::Ready(Some(Err(io::Error::new(io::ErrorKind::Other, e))))
-            }
-        }
+        self.project()
+            .inner
+            .poll_next(cx)
+            .map_err(|e| io::Error::new(io::ErrorKind::Other, e))
     }
 }
 
@@ -65,7 +61,10 @@ where
     type Error = io::Error;
 
     fn poll_ready(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<io::Result<()>> {
-        convert(self.project().inner.poll_ready(cx))
+        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<()> {
@@ -76,20 +75,20 @@ where
     }
 
     fn poll_flush(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<io::Result<()>> {
-        convert(self.project().inner.poll_flush(cx))
+        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<()>> {
-        convert(self.project().inner.poll_close(cx))
+        self.project()
+            .inner
+            .poll_close(cx)
+            .map_err(|e| io::Error::new(io::ErrorKind::Other, e))
     }
 }
 
-fn convert<E: Into<Box<dyn Error + Send + Sync>>>(
-    poll: Poll<Result<(), E>>,
-) -> Poll<io::Result<()>> {
-    poll.map(|ready| ready.map_err(|e| io::Error::new(io::ErrorKind::Other, e)))
-}
-
 /// Constructs a new transport from a framed transport and a serialization codec.
 pub fn new<S, Item, SinkItem, Codec>(
     framed_io: Framed<S, LengthDelimitedCodec>,
@@ -130,14 +129,6 @@ pub mod tcp {
         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> {
@@ -150,6 +141,7 @@ pub mod tcp {
     }
 
     /// A connection Future that also exposes the length-delimited framing config.
+    #[must_use]
     #[pin_project]
     pub struct Connect<T, Item, SinkItem, CodecFn> {
         #[pin]
@@ -277,6 +269,270 @@ pub mod tcp {
     }
 }
 
+#[cfg(all(unix, feature = "unix"))]
+#[cfg_attr(docsrs, doc(cfg(all(unix, feature = "unix"))))]
+/// Unix Domain Socket support for generic transport using Tokio.
+pub mod unix {
+    use {
+        super::*,
+        futures::ready,
+        std::{marker::PhantomData, path::Path},
+        tokio::net::{unix::SocketAddr, UnixListener, UnixStream},
+        tokio_util::codec::length_delimited,
+    };
+
+    impl<Item, SinkItem, Codec> Transport<UnixStream, Item, SinkItem, Codec> {
+        /// Returns the socket address of the remote half of the underlying [`UnixStream`].
+        pub fn peer_addr(&self) -> io::Result<SocketAddr> {
+            self.inner.get_ref().get_ref().peer_addr()
+        }
+        /// Returns the socket address of the local half of the underlying [`UnixStream`].
+        pub fn local_addr(&self) -> io::Result<SocketAddr> {
+            self.inner.get_ref().get_ref().local_addr()
+        }
+    }
+
+    /// A connection Future that also exposes the length-delimited framing config.
+    #[must_use]
+    #[pin_project]
+    pub struct Connect<T, Item, SinkItem, CodecFn> {
+        #[pin]
+        inner: T,
+        codec_fn: CodecFn,
+        config: length_delimited::Builder,
+        ghost: PhantomData<(fn(SinkItem), fn() -> Item)>,
+    }
+
+    impl<T, Item, SinkItem, Codec, CodecFn> Future for Connect<T, Item, SinkItem, CodecFn>
+    where
+        T: Future<Output = io::Result<UnixStream>>,
+        Item: for<'de> Deserialize<'de>,
+        SinkItem: Serialize,
+        Codec: Serializer<SinkItem> + Deserializer<Item>,
+        CodecFn: Fn() -> Codec,
+    {
+        type Output = io::Result<Transport<UnixStream, Item, SinkItem, Codec>>;
+
+        fn poll(mut self: Pin<&mut Self>, cx: &mut Context) -> Poll<Self::Output> {
+            let io = ready!(self.as_mut().project().inner.poll(cx))?;
+            Poll::Ready(Ok(new(self.config.new_framed(io), (self.codec_fn)())))
+        }
+    }
+
+    impl<T, Item, SinkItem, CodecFn> Connect<T, Item, SinkItem, CodecFn> {
+        /// Returns an immutable reference to the length-delimited codec's config.
+        pub fn config(&self) -> &length_delimited::Builder {
+            &self.config
+        }
+
+        /// Returns a mutable reference to the length-delimited codec's config.
+        pub fn config_mut(&mut self) -> &mut length_delimited::Builder {
+            &mut self.config
+        }
+    }
+
+    /// Connects to socket named by `path`, wrapping the connection in a Unix Domain Socket
+    /// transport.
+    pub fn connect<P, Item, SinkItem, Codec, CodecFn>(
+        path: P,
+        codec_fn: CodecFn,
+    ) -> Connect<impl Future<Output = io::Result<UnixStream>>, Item, SinkItem, CodecFn>
+    where
+        P: AsRef<Path>,
+        Item: for<'de> Deserialize<'de>,
+        SinkItem: Serialize,
+        Codec: Serializer<SinkItem> + Deserializer<Item>,
+        CodecFn: Fn() -> Codec,
+    {
+        Connect {
+            inner: UnixStream::connect(path),
+            codec_fn,
+            config: LengthDelimitedCodec::builder(),
+            ghost: PhantomData,
+        }
+    }
+
+    /// Listens on the socket named by `path`, wrapping accepted connections in Unix Domain Socket
+    /// transports.
+    pub async fn listen<P, Item, SinkItem, Codec, CodecFn>(
+        path: P,
+        codec_fn: CodecFn,
+    ) -> io::Result<Incoming<Item, SinkItem, Codec, CodecFn>>
+    where
+        P: AsRef<Path>,
+        Item: for<'de> Deserialize<'de>,
+        Codec: Serializer<SinkItem> + Deserializer<Item>,
+        CodecFn: Fn() -> Codec,
+    {
+        let listener = UnixListener::bind(path)?;
+        let local_addr = listener.local_addr()?;
+        Ok(Incoming {
+            listener,
+            codec_fn,
+            local_addr,
+            config: LengthDelimitedCodec::builder(),
+            ghost: PhantomData,
+        })
+    }
+
+    /// A [`UnixListener`] that wraps connections in [transports](Transport).
+    #[pin_project]
+    #[derive(Debug)]
+    pub struct Incoming<Item, SinkItem, Codec, CodecFn> {
+        listener: UnixListener,
+        local_addr: SocketAddr,
+        codec_fn: CodecFn,
+        config: length_delimited::Builder,
+        ghost: PhantomData<(fn() -> Item, fn(SinkItem), Codec)>,
+    }
+
+    impl<Item, SinkItem, Codec, CodecFn> Incoming<Item, SinkItem, Codec, CodecFn> {
+        /// Returns the the socket address being listened on.
+        pub fn local_addr(&self) -> &SocketAddr {
+            &self.local_addr
+        }
+
+        /// Returns an immutable reference to the length-delimited codec's config.
+        pub fn config(&self) -> &length_delimited::Builder {
+            &self.config
+        }
+
+        /// Returns a mutable reference to the length-delimited codec's config.
+        pub fn config_mut(&mut self) -> &mut length_delimited::Builder {
+            &mut self.config
+        }
+    }
+
+    impl<Item, SinkItem, Codec, CodecFn> Stream for Incoming<Item, SinkItem, Codec, CodecFn>
+    where
+        Item: for<'de> Deserialize<'de>,
+        SinkItem: Serialize,
+        Codec: Serializer<SinkItem> + Deserializer<Item>,
+        CodecFn: Fn() -> Codec,
+    {
+        type Item = io::Result<Transport<UnixStream, Item, SinkItem, Codec>>;
+
+        fn poll_next(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Option<Self::Item>> {
+            let conn: UnixStream = ready!(self.as_mut().project().listener.poll_accept(cx)?).0;
+            Poll::Ready(Some(Ok(new(
+                self.config.new_framed(conn),
+                (self.codec_fn)(),
+            ))))
+        }
+    }
+
+    /// A temporary `PathBuf` that lives in `std::env::temp_dir` and is removed on drop.
+    pub struct TempPathBuf(std::path::PathBuf);
+
+    impl TempPathBuf {
+        /// A named socket that results in `<tempdir>/<name>`
+        pub fn new<S: AsRef<str>>(name: S) -> Self {
+            let mut sock = std::env::temp_dir();
+            sock.push(name.as_ref());
+            Self(sock)
+        }
+
+        /// Appends a random hex string to the socket name resulting in
+        /// `<tempdir>/<name>_<xxxxx>`
+        pub fn with_random<S: AsRef<str>>(name: S) -> Self {
+            Self::new(format!("{}_{:016x}", name.as_ref(), rand::random::<u64>()))
+        }
+    }
+
+    impl AsRef<std::path::Path> for TempPathBuf {
+        fn as_ref(&self) -> &std::path::Path {
+            self.0.as_path()
+        }
+    }
+
+    impl Drop for TempPathBuf {
+        fn drop(&mut self) {
+            // This will remove the file pointed to by this PathBuf if it exists, however Err's can
+            // be returned such as attempting to remove a non-existing file, or one which we don't
+            // have permission to remove. In these cases the Err is swallowed
+            let _ = std::fs::remove_file(&self.0);
+        }
+    }
+
+    #[cfg(test)]
+    mod tests {
+        use super::*;
+        use tokio_serde::formats::SymmetricalJson;
+
+        #[test]
+        fn temp_path_buf_non_random() {
+            let sock = TempPathBuf::new("test");
+            let mut good = std::env::temp_dir();
+            good.push("test");
+            assert_eq!(sock.as_ref(), good);
+            assert_eq!(sock.as_ref().file_name().unwrap(), "test");
+        }
+
+        #[test]
+        fn temp_path_buf_random() {
+            let sock = TempPathBuf::with_random("test");
+            let good = std::env::temp_dir();
+            assert!(sock.as_ref().starts_with(good));
+            // Since there are 16 random characters we just assert the file_name has the right name
+            // and starts with the correct string 'test_'
+            // file name: test_xxxxxxxxxxxxxxxx
+            // test  = 4
+            // _     = 1
+            // <hex> = 16
+            // total = 21
+            let fname = sock.as_ref().file_name().unwrap().to_string_lossy();
+            assert!(fname.starts_with("test_"));
+            assert_eq!(fname.len(), 21);
+        }
+
+        #[test]
+        fn temp_path_buf_non_existing() {
+            let sock = TempPathBuf::with_random("test");
+            let sock_path = std::path::PathBuf::from(sock.as_ref());
+
+            // No actual file has been created yet
+            assert!(!sock_path.exists());
+            // Should not panic
+            std::mem::drop(sock);
+            assert!(!sock_path.exists());
+        }
+
+        #[test]
+        fn temp_path_buf_existing_file() {
+            let sock = TempPathBuf::with_random("test");
+            let sock_path = std::path::PathBuf::from(sock.as_ref());
+            let _file = std::fs::File::create(&sock).unwrap();
+            assert!(sock_path.exists());
+            std::mem::drop(sock);
+            assert!(!sock_path.exists());
+        }
+
+        #[test]
+        fn temp_path_buf_preexisting_file() {
+            let mut pre_existing = std::env::temp_dir();
+            pre_existing.push("test");
+            let _file = std::fs::File::create(&pre_existing).unwrap();
+            let sock = TempPathBuf::new("test");
+            let sock_path = std::path::PathBuf::from(sock.as_ref());
+            assert!(sock_path.exists());
+            std::mem::drop(sock);
+            assert!(!sock_path.exists());
+        }
+
+        #[tokio::test]
+        async fn temp_path_buf_for_socket() {
+            let sock = TempPathBuf::with_random("test");
+            // Save path for testing after drop
+            let sock_path = std::path::PathBuf::from(sock.as_ref());
+            // create the actual socket
+            let _ = listen(&sock, SymmetricalJson::<String>::default).await;
+            assert!(sock_path.exists());
+            std::mem::drop(sock);
+            assert!(!sock_path.exists());
+        }
+    }
+}
+
 #[cfg(test)]
 mod tests {
     use super::Transport;
@@ -291,7 +547,7 @@ mod tests {
     use tokio_serde::formats::SymmetricalJson;
 
     fn ctx() -> Context<'static> {
-        Context::from_waker(&noop_waker_ref())
+        Context::from_waker(noop_waker_ref())
     }
 
     struct TestIo(Cursor<Vec<u8>>);
@@ -393,4 +649,24 @@ mod tests {
         assert_matches!(transport.next().await, None);
         Ok(())
     }
+
+    #[cfg(all(unix, feature = "unix"))]
+    #[tokio::test]
+    async fn uds() -> io::Result<()> {
+        use super::unix;
+        use super::*;
+
+        let sock = unix::TempPathBuf::with_random("uds");
+        let mut listener = unix::listen(&sock, SymmetricalJson::<String>::default).await?;
+        tokio::spawn(async move {
+            let mut transport = listener.next().await.unwrap().unwrap();
+            let message = transport.next().await.unwrap().unwrap();
+            transport.send(message).await.unwrap();
+        });
+        let mut transport = unix::connect(&sock, SymmetricalJson::<String>::default).await?;
+        transport.send(String::from("test")).await?;
+        assert_matches!(transport.next().await, Some(Ok(s)) if s == "test");
+        assert_matches!(transport.next().await, None);
+        Ok(())
+    }
 }

tarpc/src/server/in_flight_requests.rs

@@ -1,19 +1,13 @@
-use crate::{
-    util::{Compact, TimeUntil},
-    PollIo,
-};
+use crate::util::{Compact, TimeUntil};
 use fnv::FnvHashMap;
-use futures::{
-    future::{AbortHandle, AbortRegistration},
-    ready,
-};
+use futures::future::{AbortHandle, AbortRegistration};
 use std::{
     collections::hash_map,
-    io,
     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.
@@ -23,13 +17,15 @@ pub struct InFlightRequests {
     deadlines: DelayQueue<u64>,
 }
 
-#[derive(Debug)]
 /// 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
@@ -48,6 +44,7 @@ impl InFlightRequests {
         &mut self,
         request_id: u64,
         deadline: SystemTime,
+        span: Span,
     ) -> Result<AbortRegistration, AlreadyExistsError> {
         match self.request_data.entry(request_id) {
             hash_map::Entry::Vacant(vacant) => {
@@ -57,6 +54,7 @@ impl InFlightRequests {
                 vacant.insert(RequestData {
                     abort_handle,
                     deadline_key,
+                    span,
                 });
                 Ok(abort_registration)
             }
@@ -66,12 +64,17 @@ impl InFlightRequests {
 
     /// 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(request_data) = self.request_data.remove(&request_id) {
+        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);
-
-            request_data.abort_handle.abort();
-            self.deadlines.remove(&request_data.deadline_key);
-
+            abort_handle.abort();
+            self.deadlines.remove(&deadline_key);
+            tracing::info!("ReceiveCancel");
             true
         } else {
             false
@@ -80,30 +83,35 @@ impl InFlightRequests {
 
     /// 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) -> bool {
+    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);
-
-            true
+            Some(request_data.span)
         } else {
-            false
+            None
         }
     }
 
     /// Yields a request that has expired, aborting any ongoing processing of that request.
-    pub fn poll_expired(&mut self, cx: &mut Context) -> PollIo<u64> {
-        Poll::Ready(match ready!(self.deadlines.poll_expired(cx)) {
-            Some(Ok(expired)) => {
-                if let Some(request_data) = self.request_data.remove(expired.get_ref()) {
-                    self.request_data.compact(0.1);
-                    request_data.abort_handle.abort();
-                }
-                Some(Ok(expired.into_inner()))
+    pub fn poll_expired(&mut self, cx: &mut Context) -> Poll<Option<u64>> {
+        if self.deadlines.is_empty() {
+            // TODO(https://github.com/tokio-rs/tokio/issues/4161)
+            // This is a workaround for DelayQueue not always treating this case correctly.
+            return Poll::Ready(None);
+        }
+        self.deadlines.poll_expired(cx).map(|expired| {
+            let expired = expired?;
+            if let Some(RequestData {
+                abort_handle, span, ..
+            }) = self.request_data.remove(expired.get_ref())
+            {
+                let _entered = span.enter();
+                self.request_data.compact(0.1);
+                abort_handle.abort();
+                tracing::error!("DeadlineExceeded");
             }
-            Some(Err(e)) => Some(Err(io::Error::new(io::ErrorKind::Other, e))),
-            None => None,
+            Some(expired.into_inner())
         })
     }
 }
@@ -118,75 +126,96 @@ impl Drop for InFlightRequests {
 }
 
 #[cfg(test)]
-use {
-    assert_matches::assert_matches,
-    futures::{
+mod tests {
+    use super::*;
+
+    use assert_matches::assert_matches;
+    use futures::{
         future::{pending, Abortable},
         FutureExt,
-    },
-    futures_test::task::noop_context,
-};
+    };
+    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())
-        .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())
-        .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())
-        .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();
-    let abort_registration = in_flight_requests
-        .start_request(0, SystemTime::now())
-        .unwrap();
-    let mut abortable_future = Box::new(Abortable::new(pending::<()>(), abort_registration));
-
-    assert_eq!(in_flight_requests.remove_request(0), true);
-    assert_matches!(
-        abortable_future.poll_unpin(&mut noop_context()),
-        Poll::Pending
-    );
-    assert_eq!(in_flight_requests.len(), 0);
+    #[tokio::test]
+    async fn start_request_increases_len() {
+        let mut in_flight_requests = InFlightRequests::default();
+        assert_eq!(in_flight_requests.len(), 0);
+        in_flight_requests
+            .start_request(0, SystemTime::now(), Span::current())
+            .unwrap();
+        assert_eq!(in_flight_requests.len(), 1);
+    }
+
+    #[tokio::test]
+    async fn polling_expired_aborts() {
+        let mut in_flight_requests = InFlightRequests::default();
+        let abort_registration = in_flight_requests
+            .start_request(0, SystemTime::now(), Span::current())
+            .unwrap();
+        let mut abortable_future = Box::new(Abortable::new(pending::<()>(), abort_registration));
+
+        tokio::time::pause();
+        tokio::time::advance(std::time::Duration::from_secs(1000)).await;
+
+        assert_matches!(
+            in_flight_requests.poll_expired(&mut noop_context()),
+            Poll::Ready(Some(_))
+        );
+        assert_matches!(
+            abortable_future.poll_unpin(&mut noop_context()),
+            Poll::Ready(Err(_))
+        );
+        assert_eq!(in_flight_requests.len(), 0);
+    }
+
+    #[tokio::test]
+    async fn cancel_request_aborts() {
+        let mut in_flight_requests = InFlightRequests::default();
+        let abort_registration = in_flight_requests
+            .start_request(0, SystemTime::now(), Span::current())
+            .unwrap();
+        let mut abortable_future = Box::new(Abortable::new(pending::<()>(), abort_registration));
+
+        assert!(in_flight_requests.cancel_request(0));
+        assert_matches!(
+            abortable_future.poll_unpin(&mut noop_context()),
+            Poll::Ready(Err(_))
+        );
+        assert_eq!(in_flight_requests.len(), 0);
+    }
+
+    #[tokio::test]
+    async fn remove_request_doesnt_abort() {
+        let mut in_flight_requests = InFlightRequests::default();
+        assert!(in_flight_requests.deadlines.is_empty());
+
+        let abort_registration = in_flight_requests
+            .start_request(
+                0,
+                SystemTime::now() + std::time::Duration::from_secs(10),
+                Span::current(),
+            )
+            .unwrap();
+        let mut abortable_future = Box::new(Abortable::new(pending::<()>(), abort_registration));
+
+        // Precondition: Pending expiration
+        assert_matches!(
+            in_flight_requests.poll_expired(&mut noop_context()),
+            Poll::Pending
+        );
+        assert!(!in_flight_requests.deadlines.is_empty());
+
+        assert_matches!(in_flight_requests.remove_request(0), Some(_));
+        // Postcondition: No pending expirations
+        assert!(in_flight_requests.deadlines.is_empty());
+        assert_matches!(
+            in_flight_requests.poll_expired(&mut noop_context()),
+            Poll::Ready(None)
+        );
+        assert_matches!(
+            abortable_future.poll_unpin(&mut noop_context()),
+            Poll::Pending
+        );
+        assert_eq!(in_flight_requests.len(), 0);
+    }
 }

tarpc/src/server/incoming.rs

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

tarpc/src/server/limits.rs

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

tarpc/src/server/limits/channels_per_key.rs

@@ -9,20 +9,23 @@ use crate::{
     util::Compact,
 };
 use fnv::FnvHashMap;
-use futures::{future::AbortRegistration, prelude::*, ready, stream::Fuse, task::*};
-use log::{debug, info, trace};
+use futures::{prelude::*, ready, stream::Fuse, task::*};
 use pin_project::pin_project;
 use std::sync::{Arc, Weak};
 use std::{
     collections::hash_map::Entry, convert::TryFrom, fmt, hash::Hash, marker::Unpin, pin::Pin,
-    time::SystemTime,
 };
 use tokio::sync::mpsc;
+use tracing::{debug, info, trace};
 
-/// A single-threaded filter that drops channels based on per-key limits.
+/// An [`Incoming`](crate::server::incoming::Incoming) stream that drops new channels based on
+/// per-key limits.
+///
+/// The decision to drop a Channel is made once at the time the Channel materializes. Once a
+/// Channel is yielded, it will not be prematurely dropped.
 #[pin_project]
 #[derive(Debug)]
-pub struct ChannelFilter<S, K, F>
+pub struct MaxChannelsPerKey<S, K, F>
 where
     K: Eq + Hash,
 {
@@ -35,7 +38,7 @@ where
     keymaker: F,
 }
 
-/// A channel that is tracked by a ChannelFilter.
+/// A channel that is tracked by [`MaxChannelsPerKey`].
 #[pin_project]
 #[derive(Debug)]
 pub struct TrackedChannel<C, K> {
@@ -103,6 +106,7 @@ where
 {
     type Req = C::Req;
     type Resp = C::Resp;
+    type Transport = C::Transport;
 
     fn config(&self) -> &server::Config {
         self.inner.config()
@@ -112,12 +116,8 @@ where
         self.inner.in_flight_requests()
     }
 
-    fn start_request(
-        mut self: Pin<&mut Self>,
-        id: u64,
-        deadline: SystemTime,
-    ) -> Result<AbortRegistration, super::in_flight_requests::AlreadyExistsError> {
-        self.inner_pin_mut().start_request(id, deadline)
+    fn transport(&self) -> &Self::Transport {
+        self.inner.transport()
     }
 }
 
@@ -133,7 +133,7 @@ impl<C, K> TrackedChannel<C, K> {
     }
 }
 
-impl<S, K, F> ChannelFilter<S, K, F>
+impl<S, K, F> MaxChannelsPerKey<S, K, F>
 where
     K: Eq + Hash,
     S: Stream,
@@ -142,7 +142,7 @@ where
     /// Sheds new channels to stay under configured limits.
     pub(crate) fn new(listener: S, channels_per_key: u32, keymaker: F) -> Self {
         let (dropped_keys_tx, dropped_keys) = mpsc::unbounded_channel();
-        ChannelFilter {
+        MaxChannelsPerKey {
             listener: listener.fuse(),
             channels_per_key,
             dropped_keys,
@@ -153,7 +153,7 @@ where
     }
 }
 
-impl<S, K, F> ChannelFilter<S, K, F>
+impl<S, K, F> MaxChannelsPerKey<S, K, F>
 where
     S: Stream,
     K: fmt::Display + Eq + Hash + Clone + Unpin,
@@ -171,11 +171,10 @@ where
         let tracker = self.as_mut().increment_channels_for_key(key.clone())?;
 
         trace!(
-            "[{}] Opening channel ({}/{}) channels for key.",
-            key,
-            Arc::strong_count(&tracker),
-            self.channels_per_key
-        );
+            channel_filter_key = %key,
+            open_channels = Arc::strong_count(&tracker),
+            max_open_channels = self.channels_per_key,
+            "Opening channel");
 
         Ok(TrackedChannel {
             tracker,
@@ -200,9 +199,10 @@ where
                 let count = o.get().strong_count();
                 if count >= TryFrom::try_from(*self_.channels_per_key).unwrap() {
                     info!(
-                        "[{}] Opened max channels from key ({}/{}).",
-                        key, count, self_.channels_per_key
-                    );
+                        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(|| {
@@ -233,7 +233,9 @@ where
         let self_ = self.project();
         match ready!(self_.dropped_keys.poll_recv(cx)) {
             Some(key) => {
-                debug!("All channels dropped for key [{}]", key);
+                debug!(
+                    channel_filter_key = %key,
+                    "All channels dropped");
                 self_.key_counts.remove(&key);
                 self_.key_counts.compact(0.1);
                 Poll::Ready(())
@@ -243,7 +245,7 @@ where
     }
 }
 
-impl<S, K, F> Stream for ChannelFilter<S, K, F>
+impl<S, K, F> Stream for MaxChannelsPerKey<S, K, F>
 where
     S: Stream,
     K: fmt::Display + Eq + Hash + Clone + Unpin,
@@ -280,7 +282,7 @@ where
 fn ctx() -> Context<'static> {
     use futures::task::*;
 
-    Context::from_waker(&noop_waker_ref())
+    Context::from_waker(noop_waker_ref())
 }
 
 #[test]
@@ -346,7 +348,7 @@ fn channel_filter_increment_channels_for_key() {
         key: &'static str,
     }
     let (_, listener) = futures::channel::mpsc::unbounded();
-    let filter = ChannelFilter::new(listener, 2, |chan: &TestChannel| chan.key);
+    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);
@@ -367,7 +369,7 @@ fn channel_filter_handle_new_channel() {
         key: &'static str,
     }
     let (_, listener) = futures::channel::mpsc::unbounded();
-    let filter = ChannelFilter::new(listener, 2, |chan: &TestChannel| chan.key);
+    let filter = MaxChannelsPerKey::new(listener, 2, |chan: &TestChannel| chan.key);
     pin_mut!(filter);
     let channel1 = filter
         .as_mut()
@@ -399,7 +401,7 @@ fn channel_filter_poll_listener() {
         key: &'static str,
     }
     let (new_channels, listener) = futures::channel::mpsc::unbounded();
-    let filter = ChannelFilter::new(listener, 2, |chan: &TestChannel| chan.key);
+    let filter = MaxChannelsPerKey::new(listener, 2, |chan: &TestChannel| chan.key);
     pin_mut!(filter);
 
     new_channels
@@ -435,7 +437,7 @@ fn channel_filter_poll_closed_channels() {
         key: &'static str,
     }
     let (new_channels, listener) = futures::channel::mpsc::unbounded();
-    let filter = ChannelFilter::new(listener, 2, |chan: &TestChannel| chan.key);
+    let filter = MaxChannelsPerKey::new(listener, 2, |chan: &TestChannel| chan.key);
     pin_mut!(filter);
 
     new_channels
@@ -463,7 +465,7 @@ fn channel_filter_stream() {
         key: &'static str,
     }
     let (new_channels, listener) = futures::channel::mpsc::unbounded();
-    let filter = ChannelFilter::new(listener, 2, |chan: &TestChannel| chan.key);
+    let filter = MaxChannelsPerKey::new(listener, 2, |chan: &TestChannel| chan.key);
     pin_mut!(filter);
 
     new_channels

tarpc/src/server/limits/requests_per_channel.rs

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

tarpc/src/server/request_hook.rs

@@ -0,0 +1,22 @@
+// Copyright 2022 Google LLC
+//
+// Use of this source code is governed by an MIT-style
+// license that can be found in the LICENSE file or at
+// https://opensource.org/licenses/MIT.
+
+//! Hooks for horizontal functionality that can run either before or after a request is executed.
+
+/// A request hook that runs before a request is executed.
+mod before;
+
+/// A request hook that runs after a request is completed.
+mod after;
+
+/// A request hook that runs both before a request is executed and after it is completed.
+mod before_and_after;
+
+pub use {
+    after::{AfterRequest, AfterRequestHook},
+    before::{BeforeRequest, BeforeRequestHook},
+    before_and_after::BeforeAndAfterRequestHook,
+};

tarpc/src/server/request_hook/after.rs

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

tarpc/src/server/request_hook/before.rs

@@ -0,0 +1,75 @@
+// Copyright 2022 Google LLC
+//
+// Use of this source code is governed by an MIT-style
+// license that can be found in the LICENSE file or at
+// https://opensource.org/licenses/MIT.
+
+//! Provides a hook that runs before request execution.
+
+use crate::{context, server::Serve, ServerError};
+use futures::prelude::*;
+
+/// A hook that runs before request execution.
+#[allow(async_fn_in_trait)]
+pub trait BeforeRequest<Req> {
+    /// The function that is called before request execution.
+    ///
+    /// If this function returns an error, the request will not be executed and the error will be
+    /// returned instead.
+    ///
+    /// This function can also modify the request context. This could be used, for example, to
+    /// enforce a maximum deadline on all requests.
+    async fn before(&mut self, ctx: &mut context::Context, req: &Req) -> Result<(), ServerError>;
+}
+
+impl<F, Fut, Req> BeforeRequest<Req> for F
+where
+    F: FnMut(&mut context::Context, &Req) -> Fut,
+    Fut: Future<Output = Result<(), ServerError>>,
+{
+    async fn before(&mut self, ctx: &mut context::Context, req: &Req) -> Result<(), ServerError> {
+        self(ctx, req).await
+    }
+}
+
+/// A Service function that runs a hook before request execution.
+pub struct BeforeRequestHook<Serv, Hook> {
+    serve: Serv,
+    hook: Hook,
+}
+
+impl<Serv, Hook> BeforeRequestHook<Serv, Hook> {
+    pub(crate) fn new(serve: Serv, hook: Hook) -> Self {
+        Self { serve, hook }
+    }
+}
+
+impl<Serv: Clone, Hook: Clone> Clone for BeforeRequestHook<Serv, Hook> {
+    fn clone(&self) -> Self {
+        Self {
+            serve: self.serve.clone(),
+            hook: self.hook.clone(),
+        }
+    }
+}
+
+impl<Serv, Hook> Serve for BeforeRequestHook<Serv, Hook>
+where
+    Serv: Serve,
+    Hook: BeforeRequest<Serv::Req>,
+{
+    type Req = Serv::Req;
+    type Resp = Serv::Resp;
+
+    async fn serve(
+        self,
+        mut ctx: context::Context,
+        req: Self::Req,
+    ) -> Result<Serv::Resp, ServerError> {
+        let BeforeRequestHook {
+            serve, mut hook, ..
+        } = self;
+        hook.before(&mut ctx, &req).await?;
+        serve.serve(ctx, req).await
+    }
+}

tarpc/src/server/request_hook/before_and_after.rs

@@ -0,0 +1,59 @@
+// Copyright 2022 Google LLC
+//
+// Use of this source code is governed by an MIT-style
+// license that can be found in the LICENSE file or at
+// https://opensource.org/licenses/MIT.
+
+//! Provides a hook that runs both before and after request execution.
+
+use super::{after::AfterRequest, before::BeforeRequest};
+use crate::{context, server::Serve, ServerError};
+use std::marker::PhantomData;
+
+/// A Service function that runs a hook both before and after request execution.
+pub struct BeforeAndAfterRequestHook<Req, Resp, Serv, Hook> {
+    serve: Serv,
+    hook: Hook,
+    fns: PhantomData<(fn(Req), fn(Resp))>,
+}
+
+impl<Req, Resp, Serv, Hook> BeforeAndAfterRequestHook<Req, Resp, Serv, Hook> {
+    pub(crate) fn new(serve: Serv, hook: Hook) -> Self {
+        Self {
+            serve,
+            hook,
+            fns: PhantomData,
+        }
+    }
+}
+
+impl<Req, Resp, Serv: Clone, Hook: Clone> Clone
+    for BeforeAndAfterRequestHook<Req, Resp, Serv, Hook>
+{
+    fn clone(&self) -> Self {
+        Self {
+            serve: self.serve.clone(),
+            hook: self.hook.clone(),
+            fns: PhantomData,
+        }
+    }
+}
+
+impl<Req, Resp, Serv, Hook> Serve for BeforeAndAfterRequestHook<Req, Resp, Serv, Hook>
+where
+    Serv: Serve<Req = Req, Resp = Resp>,
+    Hook: BeforeRequest<Req> + AfterRequest<Resp>,
+{
+    type Req = Req;
+    type Resp = Resp;
+
+    async fn serve(self, mut ctx: context::Context, req: Req) -> Result<Serv::Resp, ServerError> {
+        let BeforeAndAfterRequestHook {
+            serve, mut hook, ..
+        } = self;
+        hook.before(&mut ctx, &req).await?;
+        let mut resp = serve.serve(ctx, req).await;
+        hook.after(&mut ctx, &mut resp).await;
+        resp
+    }
+}

tarpc/src/server/testing.rs

@@ -5,16 +5,15 @@
 // https://opensource.org/licenses/MIT.
 
 use crate::{
+    cancellations::{cancellations, CanceledRequests, RequestCancellation},
     context,
-    server::{Channel, Config},
+    server::{Channel, Config, ResponseGuard, TrackedRequest},
     Request, Response,
 };
-use futures::{future::AbortRegistration, task::*, Sink, Stream};
+use futures::{task::*, Sink, Stream};
 use pin_project::pin_project;
-use std::collections::VecDeque;
-use std::io;
-use std::pin::Pin;
-use std::time::SystemTime;
+use std::{collections::VecDeque, io, pin::Pin, time::SystemTime};
+use tracing::Span;
 
 #[pin_project]
 pub(crate) struct FakeChannel<In, Out> {
@@ -24,6 +23,8 @@ pub(crate) struct FakeChannel<In, Out> {
     pub sink: VecDeque<Out>,
     pub config: Config,
     pub in_flight_requests: super::in_flight_requests::InFlightRequests,
+    pub request_cancellation: RequestCancellation,
+    pub canceled_requests: CanceledRequests,
 }
 
 impl<In, Out> Stream for FakeChannel<In, Out>
@@ -64,12 +65,13 @@ impl<In, Resp> Sink<Response<Resp>> for FakeChannel<In, Response<Resp>> {
     }
 }
 
-impl<Req, Resp> Channel for FakeChannel<io::Result<Request<Req>>, Response<Resp>>
+impl<Req, Resp> Channel for FakeChannel<io::Result<TrackedRequest<Req>>, Response<Resp>>
 where
     Req: Unpin,
 {
     type Req = Req;
     type Resp = Resp;
+    type Transport = ();
 
     fn config(&self) -> &Config {
         &self.config
@@ -79,37 +81,45 @@ where
         self.in_flight_requests.len()
     }
 
-    fn start_request(
-        self: Pin<&mut Self>,
-        id: u64,
-        deadline: SystemTime,
-    ) -> Result<AbortRegistration, super::in_flight_requests::AlreadyExistsError> {
-        self.project()
-            .in_flight_requests
-            .start_request(id, deadline)
+    fn transport(&self) -> &() {
+        &()
     }
 }
 
-impl<Req, Resp> FakeChannel<io::Result<Request<Req>>, Response<Resp>> {
+impl<Req, Resp> FakeChannel<io::Result<TrackedRequest<Req>>, Response<Resp>> {
     pub fn push_req(&mut self, id: u64, message: Req) {
-        self.stream.push_back(Ok(Request {
-            context: context::Context {
-                deadline: SystemTime::UNIX_EPOCH,
-                trace_context: Default::default(),
+        let (_, abort_registration) = futures::future::AbortHandle::new_pair();
+        let (request_cancellation, _) = cancellations();
+        self.stream.push_back(Ok(TrackedRequest {
+            request: Request {
+                context: context::Context {
+                    deadline: SystemTime::UNIX_EPOCH,
+                    trace_context: Default::default(),
+                },
+                id,
+                message,
+            },
+            abort_registration,
+            span: Span::none(),
+            response_guard: ResponseGuard {
+                request_cancellation,
+                request_id: id,
+                cancel: false,
             },
-            id,
-            message,
         }));
     }
 }
 
 impl FakeChannel<(), ()> {
-    pub fn default<Req, Resp>() -> FakeChannel<io::Result<Request<Req>>, Response<Resp>> {
+    pub fn default<Req, Resp>() -> FakeChannel<io::Result<TrackedRequest<Req>>, Response<Resp>> {
+        let (request_cancellation, canceled_requests) = cancellations();
         FakeChannel {
             stream: Default::default(),
             sink: Default::default(),
             config: Default::default(),
             in_flight_requests: Default::default(),
+            request_cancellation,
+            canceled_requests,
         }
     }
 }
@@ -125,5 +135,5 @@ impl<T> PollExt for Poll<Option<T>> {
 }
 
 pub fn cx() -> Context<'static> {
-    Context::from_waker(&noop_waker_ref())
+    Context::from_waker(noop_waker_ref())
 }

tarpc/src/server/throttle.rs

@@ -1,347 +0,0 @@
-// 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 super::{Channel, Config};
-use crate::{Response, ServerError};
-use futures::{future::AbortRegistration, prelude::*, ready, task::*};
-use log::debug;
-use pin_project::pin_project;
-use std::{io, pin::Pin, time::SystemTime};
-
-/// A [`Channel`] that limits the number of concurrent
-/// requests by throttling.
-#[pin_project]
-#[derive(Debug)]
-pub struct Throttler<C> {
-    max_in_flight_requests: usize,
-    #[pin]
-    inner: C,
-}
-
-impl<C> Throttler<C> {
-    /// Returns the inner channel.
-    pub fn get_ref(&self) -> &C {
-        &self.inner
-    }
-}
-
-impl<C> Throttler<C>
-where
-    C: Channel,
-{
-    /// Returns a new `Throttler` that wraps the given channel and limits concurrent requests to
-    /// `max_in_flight_requests`.
-    pub fn new(inner: C, max_in_flight_requests: usize) -> Self {
-        Throttler {
-            max_in_flight_requests,
-            inner,
-        }
-    }
-}
-
-impl<C> Stream for Throttler<C>
-where
-    C: Channel,
-{
-    type Item = <C as Stream>::Item;
-
-    fn poll_next(mut self: Pin<&mut Self>, cx: &mut Context) -> Poll<Option<Self::Item>> {
-        while self.as_mut().in_flight_requests() >= *self.as_mut().project().max_in_flight_requests
-        {
-            ready!(self.as_mut().project().inner.poll_ready(cx)?);
-
-            match ready!(self.as_mut().project().inner.poll_next(cx)?) {
-                Some(request) => {
-                    debug!(
-                        "[{}] Client has reached in-flight request limit ({}/{}).",
-                        request.context.trace_id(),
-                        self.as_mut().in_flight_requests(),
-                        self.as_mut().project().max_in_flight_requests,
-                    );
-
-                    self.as_mut().start_send(Response {
-                        request_id: request.id,
-                        message: Err(ServerError {
-                            kind: io::ErrorKind::WouldBlock,
-                            detail: Some("Server throttled the request.".into()),
-                        }),
-                    })?;
-                }
-                None => return Poll::Ready(None),
-            }
-        }
-        self.project().inner.poll_next(cx)
-    }
-}
-
-impl<C> Sink<Response<<C as Channel>::Resp>> for Throttler<C>
-where
-    C: Channel,
-{
-    type Error = io::Error;
-
-    fn poll_ready(self: Pin<&mut Self>, cx: &mut Context) -> Poll<Result<(), Self::Error>> {
-        self.project().inner.poll_ready(cx)
-    }
-
-    fn start_send(self: Pin<&mut Self>, item: Response<<C as Channel>::Resp>) -> io::Result<()> {
-        self.project().inner.start_send(item)
-    }
-
-    fn poll_flush(self: Pin<&mut Self>, cx: &mut Context) -> Poll<io::Result<()>> {
-        self.project().inner.poll_flush(cx)
-    }
-
-    fn poll_close(self: Pin<&mut Self>, cx: &mut Context) -> Poll<io::Result<()>> {
-        self.project().inner.poll_close(cx)
-    }
-}
-
-impl<C> AsRef<C> for Throttler<C> {
-    fn as_ref(&self) -> &C {
-        &self.inner
-    }
-}
-
-impl<C> Channel for Throttler<C>
-where
-    C: Channel,
-{
-    type Req = <C as Channel>::Req;
-    type Resp = <C as Channel>::Resp;
-
-    fn in_flight_requests(&self) -> usize {
-        self.inner.in_flight_requests()
-    }
-
-    fn config(&self) -> &Config {
-        self.inner.config()
-    }
-
-    fn start_request(
-        self: Pin<&mut Self>,
-        id: u64,
-        deadline: SystemTime,
-    ) -> Result<AbortRegistration, super::in_flight_requests::AlreadyExistsError> {
-        self.project().inner.start_request(id, deadline)
-    }
-}
-
-/// A stream of throttling channels.
-#[pin_project]
-#[derive(Debug)]
-pub struct ThrottlerStream<S> {
-    #[pin]
-    inner: S,
-    max_in_flight_requests: usize,
-}
-
-impl<S> ThrottlerStream<S>
-where
-    S: Stream,
-    <S as Stream>::Item: Channel,
-{
-    pub(crate) fn new(inner: S, max_in_flight_requests: usize) -> Self {
-        Self {
-            inner,
-            max_in_flight_requests,
-        }
-    }
-}
-
-impl<S> Stream for ThrottlerStream<S>
-where
-    S: Stream,
-    <S as Stream>::Item: Channel,
-{
-    type Item = Throttler<<S as Stream>::Item>;
-
-    fn poll_next(mut self: Pin<&mut Self>, cx: &mut Context) -> Poll<Option<Self::Item>> {
-        match ready!(self.as_mut().project().inner.poll_next(cx)) {
-            Some(channel) => Poll::Ready(Some(Throttler::new(
-                channel,
-                *self.project().max_in_flight_requests,
-            ))),
-            None => Poll::Ready(None),
-        }
-    }
-}
-
-#[cfg(test)]
-use super::testing::{self, FakeChannel, PollExt};
-#[cfg(test)]
-use crate::Request;
-#[cfg(test)]
-use pin_utils::pin_mut;
-#[cfg(test)]
-use std::{marker::PhantomData, time::Duration};
-
-#[tokio::test]
-async fn throttler_in_flight_requests() {
-    let throttler = Throttler {
-        max_in_flight_requests: 0,
-        inner: FakeChannel::default::<isize, isize>(),
-    };
-
-    pin_mut!(throttler);
-    for i in 0..5 {
-        throttler
-            .inner
-            .in_flight_requests
-            .start_request(i, SystemTime::now() + Duration::from_secs(1))
-            .unwrap();
-    }
-    assert_eq!(throttler.as_mut().in_flight_requests(), 5);
-}
-
-#[tokio::test]
-async fn throttler_start_request() {
-    let throttler = Throttler {
-        max_in_flight_requests: 0,
-        inner: FakeChannel::default::<isize, isize>(),
-    };
-
-    pin_mut!(throttler);
-    throttler
-        .as_mut()
-        .start_request(1, SystemTime::now() + Duration::from_secs(1))
-        .unwrap();
-    assert_eq!(throttler.inner.in_flight_requests.len(), 1);
-}
-
-#[test]
-fn throttler_poll_next_done() {
-    let throttler = Throttler {
-        max_in_flight_requests: 0,
-        inner: FakeChannel::default::<isize, isize>(),
-    };
-
-    pin_mut!(throttler);
-    assert!(throttler.as_mut().poll_next(&mut testing::cx()).is_done());
-}
-
-#[test]
-fn throttler_poll_next_some() -> io::Result<()> {
-    let throttler = Throttler {
-        max_in_flight_requests: 1,
-        inner: FakeChannel::default::<isize, isize>(),
-    };
-
-    pin_mut!(throttler);
-    throttler.inner.push_req(0, 1);
-    assert!(throttler.as_mut().poll_ready(&mut testing::cx()).is_ready());
-    assert_eq!(
-        throttler
-            .as_mut()
-            .poll_next(&mut testing::cx())?
-            .map(|r| r.map(|r| (r.id, r.message))),
-        Poll::Ready(Some((0, 1)))
-    );
-    Ok(())
-}
-
-#[test]
-fn throttler_poll_next_throttled() {
-    let throttler = Throttler {
-        max_in_flight_requests: 0,
-        inner: FakeChannel::default::<isize, isize>(),
-    };
-
-    pin_mut!(throttler);
-    throttler.inner.push_req(1, 1);
-    assert!(throttler.as_mut().poll_next(&mut testing::cx()).is_done());
-    assert_eq!(throttler.inner.sink.len(), 1);
-    let resp = throttler.inner.sink.get(0).unwrap();
-    assert_eq!(resp.request_id, 1);
-    assert!(resp.message.is_err());
-}
-
-#[test]
-fn throttler_poll_next_throttled_sink_not_ready() {
-    let throttler = Throttler {
-        max_in_flight_requests: 0,
-        inner: PendingSink::default::<isize, isize>(),
-    };
-    pin_mut!(throttler);
-    assert!(throttler.poll_next(&mut testing::cx()).is_pending());
-
-    struct PendingSink<In, Out> {
-        ghost: PhantomData<fn(Out) -> In>,
-    }
-    impl PendingSink<(), ()> {
-        pub fn default<Req, Resp>() -> PendingSink<io::Result<Request<Req>>, Response<Resp>> {
-            PendingSink { ghost: PhantomData }
-        }
-    }
-    impl<In, Out> Stream for PendingSink<In, Out> {
-        type Item = In;
-        fn poll_next(self: Pin<&mut Self>, _: &mut Context) -> Poll<Option<Self::Item>> {
-            unimplemented!()
-        }
-    }
-    impl<In, Out> Sink<Out> for PendingSink<In, Out> {
-        type Error = io::Error;
-        fn poll_ready(self: Pin<&mut Self>, _: &mut Context) -> Poll<Result<(), Self::Error>> {
-            Poll::Pending
-        }
-        fn start_send(self: Pin<&mut Self>, _: Out) -> Result<(), Self::Error> {
-            Err(io::Error::from(io::ErrorKind::WouldBlock))
-        }
-        fn poll_flush(self: Pin<&mut Self>, _: &mut Context) -> Poll<Result<(), Self::Error>> {
-            Poll::Pending
-        }
-        fn poll_close(self: Pin<&mut Self>, _: &mut Context) -> Poll<Result<(), Self::Error>> {
-            Poll::Pending
-        }
-    }
-    impl<Req, Resp> Channel for PendingSink<io::Result<Request<Req>>, Response<Resp>> {
-        type Req = Req;
-        type Resp = Resp;
-        fn config(&self) -> &Config {
-            unimplemented!()
-        }
-        fn in_flight_requests(&self) -> usize {
-            0
-        }
-        fn start_request(
-            self: Pin<&mut Self>,
-            _id: u64,
-            _deadline: SystemTime,
-        ) -> Result<AbortRegistration, super::in_flight_requests::AlreadyExistsError> {
-            unimplemented!()
-        }
-    }
-}
-
-#[tokio::test]
-async fn throttler_start_send() {
-    let throttler = Throttler {
-        max_in_flight_requests: 0,
-        inner: FakeChannel::default::<isize, isize>(),
-    };
-
-    pin_mut!(throttler);
-    throttler
-        .inner
-        .in_flight_requests
-        .start_request(0, SystemTime::now() + Duration::from_secs(1))
-        .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/trace.rs

@@ -16,11 +16,14 @@
 //! This crate's design is based on [opencensus
 //! tracing](https://opencensus.io/core-concepts/tracing/).
 
+use opentelemetry::trace::TraceContextExt;
 use rand::Rng;
 use std::{
+    convert::TryFrom,
     fmt::{self, Formatter},
-    mem,
+    num::{NonZeroU128, NonZeroU64},
 };
+use tracing_opentelemetry::OpenTelemetrySpanExt;
 
 /// A context for tracing the execution of processes, distributed or otherwise.
 ///
@@ -36,33 +39,50 @@ pub struct Context {
     /// before making an RPC, and the span ID is sent to the server. The server is free to create
     /// its own spans, for which it sets the client's span as the parent span.
     pub span_id: SpanId,
-    /// An identifier of the span that originated the current span. For example, if a server sends
-    /// an RPC in response to a client request that included a span, the server would create a span
-    /// for the RPC and set its parent to the span_id in the incoming request's context.
-    ///
-    /// If `parent_id` is `None`, then this is a root context.
-    pub parent_id: Option<SpanId>,
+    /// Indicates whether a sampler has already decided whether or not to sample the trace
+    /// associated with the Context. If `sampling_decision` is None, then a decision has not yet
+    /// been made. Downstream samplers do not need to abide by "no sample" decisions--for example,
+    /// an upstream client may choose to never sample, which may not make sense for the client's
+    /// dependencies. On the other hand, if an upstream process has chosen to sample this trace,
+    /// then the downstream samplers are expected to respect that decision and also sample the
+    /// trace. Otherwise, the full trace would not be able to be reconstructed.
+    pub sampling_decision: SamplingDecision,
 }
 
 /// A 128-bit UUID identifying a trace. All spans caused by the same originating span share the
 /// same trace ID.
-#[derive(Debug, Default, PartialEq, Eq, Hash, Clone, Copy)]
+#[derive(Default, PartialEq, Eq, Hash, Clone, Copy)]
 #[cfg_attr(feature = "serde1", derive(serde::Serialize, serde::Deserialize))]
-pub struct TraceId(u128);
+pub struct TraceId(#[cfg_attr(feature = "serde1", serde(with = "u128_serde"))] u128);
 
 /// A 64-bit identifier of a span within a trace. The identifier is unique within the span's trace.
-#[derive(Debug, Default, PartialEq, Eq, Hash, Clone, Copy)]
+#[derive(Default, PartialEq, Eq, Hash, Clone, Copy)]
 #[cfg_attr(feature = "serde1", derive(serde::Serialize, serde::Deserialize))]
 pub struct SpanId(u64);
 
+/// Indicates whether a sampler has decided whether or not to sample the trace associated with the
+/// Context. Downstream samplers do not need to abide by "no sample" decisions--for example, an
+/// upstream client may choose to never sample, which may not make sense for the client's
+/// dependencies. On the other hand, if an upstream process has chosen to sample this trace, then
+/// the downstream samplers are expected to respect that decision and also sample the trace.
+/// Otherwise, the full trace would not be able to be reconstructed reliably.
+#[derive(Debug, PartialEq, Eq, Hash, Clone, Copy)]
+#[cfg_attr(feature = "serde1", derive(serde::Serialize, serde::Deserialize))]
+#[repr(u8)]
+pub enum SamplingDecision {
+    /// The associated span was sampled by its creating process. Child spans must also be sampled.
+    Sampled,
+    /// The associated span was not sampled by its creating process.
+    Unsampled,
+}
+
 impl Context {
-    /// Constructs a new root context. A root context is one with no parent span.
-    pub fn new_root() -> Self {
-        let rng = &mut rand::thread_rng();
-        Context {
-            trace_id: TraceId::random(rng),
-            span_id: SpanId::random(rng),
-            parent_id: None,
+    /// Constructs a new context with the trace ID and sampling decision inherited from the parent.
+    pub(crate) fn new_child(&self) -> Self {
+        Self {
+            trace_id: self.trace_id,
+            span_id: SpanId::random(&mut rand::thread_rng()),
+            sampling_decision: self.sampling_decision,
         }
     }
 }
@@ -71,17 +91,128 @@ impl TraceId {
     /// Returns a random trace ID that can be assumed to be globally unique if `rng` generates
     /// actually-random numbers.
     pub fn random<R: Rng>(rng: &mut R) -> Self {
-        TraceId(u128::from(rng.next_u64()) << mem::size_of::<u64>() | u128::from(rng.next_u64()))
+        TraceId(rng.gen::<NonZeroU128>().get())
+    }
+
+    /// Returns true iff the trace ID is 0.
+    pub fn is_none(&self) -> bool {
+        self.0 == 0
     }
 }
 
 impl SpanId {
     /// Returns a random span ID that can be assumed to be unique within a single trace.
     pub fn random<R: Rng>(rng: &mut R) -> Self {
-        SpanId(rng.next_u64())
+        SpanId(rng.gen::<NonZeroU64>().get())
+    }
+
+    /// Returns true iff the span ID is 0.
+    pub fn is_none(&self) -> bool {
+        self.0 == 0
     }
 }
 
+impl From<TraceId> for u128 {
+    fn from(trace_id: TraceId) -> Self {
+        trace_id.0
+    }
+}
+
+impl From<u128> for TraceId {
+    fn from(trace_id: u128) -> Self {
+        Self(trace_id)
+    }
+}
+
+impl From<SpanId> for u64 {
+    fn from(span_id: SpanId) -> Self {
+        span_id.0
+    }
+}
+
+impl From<u64> for SpanId {
+    fn from(span_id: u64) -> Self {
+        Self(span_id)
+    }
+}
+
+impl From<opentelemetry::trace::TraceId> for TraceId {
+    fn from(trace_id: opentelemetry::trace::TraceId) -> Self {
+        Self::from(u128::from_be_bytes(trace_id.to_bytes()))
+    }
+}
+
+impl From<TraceId> for opentelemetry::trace::TraceId {
+    fn from(trace_id: TraceId) -> Self {
+        Self::from_bytes(u128::from(trace_id).to_be_bytes())
+    }
+}
+
+impl From<opentelemetry::trace::SpanId> for SpanId {
+    fn from(span_id: opentelemetry::trace::SpanId) -> Self {
+        Self::from(u64::from_be_bytes(span_id.to_bytes()))
+    }
+}
+
+impl From<SpanId> for opentelemetry::trace::SpanId {
+    fn from(span_id: SpanId) -> Self {
+        Self::from_bytes(u64::from(span_id).to_be_bytes())
+    }
+}
+
+impl TryFrom<&tracing::Span> for Context {
+    type Error = NoActiveSpan;
+
+    fn try_from(span: &tracing::Span) -> Result<Self, NoActiveSpan> {
+        let context = span.context();
+        if context.has_active_span() {
+            Ok(Self::from(context.span()))
+        } else {
+            Err(NoActiveSpan)
+        }
+    }
+}
+
+impl From<opentelemetry::trace::SpanRef<'_>> for Context {
+    fn from(span: opentelemetry::trace::SpanRef<'_>) -> Self {
+        let otel_ctx = span.span_context();
+        Self {
+            trace_id: TraceId::from(otel_ctx.trace_id()),
+            span_id: SpanId::from(otel_ctx.span_id()),
+            sampling_decision: SamplingDecision::from(otel_ctx),
+        }
+    }
+}
+
+impl From<SamplingDecision> for opentelemetry::trace::TraceFlags {
+    fn from(decision: SamplingDecision) -> Self {
+        match decision {
+            SamplingDecision::Sampled => opentelemetry::trace::TraceFlags::SAMPLED,
+            SamplingDecision::Unsampled => opentelemetry::trace::TraceFlags::default(),
+        }
+    }
+}
+
+impl From<&opentelemetry::trace::SpanContext> for SamplingDecision {
+    fn from(context: &opentelemetry::trace::SpanContext) -> Self {
+        if context.is_sampled() {
+            SamplingDecision::Sampled
+        } else {
+            SamplingDecision::Unsampled
+        }
+    }
+}
+
+impl Default for SamplingDecision {
+    fn default() -> Self {
+        Self::Unsampled
+    }
+}
+
+/// Returned when a [`Context`] cannot be constructed from a [`Span`](tracing::Span).
+#[derive(Debug)]
+pub struct NoActiveSpan;
+
 impl fmt::Display for TraceId {
     fn fmt(&self, f: &mut Formatter) -> Result<(), fmt::Error> {
         write!(f, "{:02x}", self.0)?;
@@ -89,9 +220,42 @@ impl fmt::Display for TraceId {
     }
 }
 
+impl fmt::Debug for TraceId {
+    fn fmt(&self, f: &mut Formatter) -> Result<(), fmt::Error> {
+        write!(f, "{:02x}", self.0)?;
+        Ok(())
+    }
+}
+
 impl fmt::Display for SpanId {
     fn fmt(&self, f: &mut Formatter) -> Result<(), fmt::Error> {
         write!(f, "{:02x}", self.0)?;
         Ok(())
     }
 }
+
+impl fmt::Debug for SpanId {
+    fn fmt(&self, f: &mut Formatter) -> Result<(), fmt::Error> {
+        write!(f, "{:02x}", self.0)?;
+        Ok(())
+    }
+}
+
+#[cfg(feature = "serde1")]
+mod u128_serde {
+    pub fn serialize<S>(u: &u128, serializer: S) -> Result<S::Ok, S::Error>
+    where
+        S: serde::Serializer,
+    {
+        serde::Serialize::serialize(&u.to_le_bytes(), serializer)
+    }
+
+    pub fn deserialize<'de, D>(deserializer: D) -> Result<u128, D::Error>
+    where
+        D: serde::Deserializer<'de>,
+    {
+        Ok(u128::from_le_bytes(serde::Deserialize::deserialize(
+            deserializer,
+        )?))
+    }
+}

tarpc/src/transport.rs

@@ -9,22 +9,32 @@
 //! The rpc crate is transport- and protocol-agnostic. Any transport that impls [`Transport`](sealed::Transport)
 //! can be plugged in, using whatever protocol it wants.
 
-use futures::prelude::*;
-use std::io;
-
 pub mod channel;
 
 pub(crate) mod sealed {
-    use super::*;
+    use futures::prelude::*;
+    use std::error::Error;
 
     /// A bidirectional stream ([`Sink`] + [`Stream`]) of messages.
-    pub trait Transport<SinkItem, Item>:
-        Stream<Item = io::Result<Item>> + Sink<SinkItem, Error = io::Error>
+    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> Transport<SinkItem, Item> for T where
-        T: Stream<Item = io::Result<Item>> + Sink<SinkItem, Error = io::Error> + ?Sized
+    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

@@ -6,13 +6,25 @@
 
 //! Transports backed by in-memory channels.
 
-use crate::PollIo;
 use futures::{task::*, Sink, Stream};
 use pin_project::pin_project;
-use std::io;
-use std::pin::Pin;
+use std::{error::Error, pin::Pin};
 use tokio::sync::mpsc;
 
+/// Errors that occur in the sending or receiving of messages over a channel.
+#[derive(thiserror::Error, Debug)]
+pub enum ChannelError {
+    /// An error occurred readying to send into the channel.
+    #[error("an error occurred readying to send into the channel")]
+    Ready(#[source] Box<dyn Error + Send + Sync + 'static>),
+    /// An error occurred sending into the channel.
+    #[error("an error occurred sending into the channel")]
+    Send(#[source] Box<dyn Error + Send + Sync + 'static>),
+    /// An error occurred receiving from the channel.
+    #[error("an error occurred receiving from the channel")]
+    Receive(#[source] Box<dyn Error + Send + Sync + 'static>),
+}
+
 /// Returns two unbounded channel peers. Each [`Stream`] yields items sent through the other's
 /// [`Sink`].
 pub fn unbounded<SinkItem, Item>() -> (
@@ -36,28 +48,36 @@ pub struct UnboundedChannel<Item, SinkItem> {
 }
 
 impl<Item, SinkItem> Stream for UnboundedChannel<Item, SinkItem> {
-    type Item = Result<Item, io::Error>;
+    type Item = Result<Item, ChannelError>;
 
-    fn poll_next(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> PollIo<Item> {
-        self.rx.poll_recv(cx).map(|option| option.map(Ok))
+    fn poll_next(
+        mut self: Pin<&mut Self>,
+        cx: &mut Context<'_>,
+    ) -> Poll<Option<Result<Item, ChannelError>>> {
+        self.rx
+            .poll_recv(cx)
+            .map(|option| option.map(Ok))
+            .map_err(ChannelError::Receive)
     }
 }
 
-impl<Item, SinkItem> Sink<SinkItem> for UnboundedChannel<Item, SinkItem> {
-    type Error = io::Error;
+const CLOSED_MESSAGE: &str = "the channel is closed and cannot accept new items for sending";
 
-    fn poll_ready(self: Pin<&mut Self>, _: &mut Context<'_>) -> Poll<io::Result<()>> {
+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(io::Error::from(io::ErrorKind::NotConnected))
+            Err(ChannelError::Ready(CLOSED_MESSAGE.into()))
         } else {
             Ok(())
         })
     }
 
-    fn start_send(self: Pin<&mut Self>, item: SinkItem) -> io::Result<()> {
+    fn start_send(self: Pin<&mut Self>, item: SinkItem) -> Result<(), Self::Error> {
         self.tx
             .send(item)
-            .map_err(|_| io::Error::from(io::ErrorKind::NotConnected))
+            .map_err(|_| ChannelError::Send(CLOSED_MESSAGE.into()))
     }
 
     fn poll_flush(self: Pin<&mut Self>, _: &mut Context<'_>) -> Poll<Result<(), Self::Error>> {
@@ -65,7 +85,7 @@ impl<Item, SinkItem> Sink<SinkItem> for UnboundedChannel<Item, SinkItem> {
         Poll::Ready(Ok(()))
     }
 
-    fn poll_close(self: Pin<&mut Self>, _: &mut Context<'_>) -> Poll<io::Result<()>> {
+    fn poll_close(self: Pin<&mut Self>, _: &mut Context<'_>) -> Poll<Result<(), Self::Error>> {
         // UnboundedSender can't initiate closure.
         Poll::Ready(Ok(()))
     }
@@ -93,95 +113,106 @@ pub struct Channel<Item, SinkItem> {
 }
 
 impl<Item, SinkItem> Stream for Channel<Item, SinkItem> {
-    type Item = Result<Item, io::Error>;
+    type Item = Result<Item, ChannelError>;
 
-    fn poll_next(self: Pin<&mut Self>, cx: &mut Context<'_>) -> PollIo<Item> {
-        self.project().rx.poll_next(cx).map(|option| option.map(Ok))
+    fn poll_next(
+        self: Pin<&mut Self>,
+        cx: &mut Context<'_>,
+    ) -> Poll<Option<Result<Item, ChannelError>>> {
+        self.project()
+            .rx
+            .poll_next(cx)
+            .map(|option| option.map(Ok))
+            .map_err(ChannelError::Receive)
     }
 }
 
 impl<Item, SinkItem> Sink<SinkItem> for Channel<Item, SinkItem> {
-    type Error = io::Error;
+    type Error = ChannelError;
 
-    fn poll_ready(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<io::Result<()>> {
+    fn poll_ready(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Result<(), Self::Error>> {
         self.project()
             .tx
             .poll_ready(cx)
-            .map_err(convert_send_err_to_io)
+            .map_err(|e| ChannelError::Ready(Box::new(e)))
     }
 
-    fn start_send(self: Pin<&mut Self>, item: SinkItem) -> io::Result<()> {
+    fn start_send(self: Pin<&mut Self>, item: SinkItem) -> Result<(), Self::Error> {
         self.project()
             .tx
             .start_send(item)
-            .map_err(convert_send_err_to_io)
+            .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(convert_send_err_to_io)
+            .map_err(|e| ChannelError::Send(Box::new(e)))
     }
 
-    fn poll_close(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<io::Result<()>> {
+    fn poll_close(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Result<(), Self::Error>> {
         self.project()
             .tx
             .poll_close(cx)
-            .map_err(convert_send_err_to_io)
+            .map_err(|e| ChannelError::Send(Box::new(e)))
     }
 }
 
-fn convert_send_err_to_io(e: futures::channel::mpsc::SendError) -> io::Error {
-    if e.is_disconnected() {
-        io::Error::from(io::ErrorKind::NotConnected)
-    } else if e.is_full() {
-        io::Error::from(io::ErrorKind::WouldBlock)
-    } else {
-        io::Error::new(io::ErrorKind::Other, e)
-    }
-}
-
-#[cfg(test)]
-#[cfg(feature = "tokio1")]
+#[cfg(all(test, feature = "tokio1"))]
 mod tests {
     use crate::{
-        client, context,
-        server::{BaseChannel, Incoming},
-        transport,
+        client::{self, RpcError},
+        context,
+        server::{incoming::Incoming, serve, BaseChannel},
+        transport::{
+            self,
+            channel::{Channel, UnboundedChannel},
+        },
+        ServerError,
     };
     use assert_matches::assert_matches;
     use futures::{prelude::*, stream};
-    use log::trace;
     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() -> io::Result<()> {
-        let _ = env_logger::try_init();
+    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(
+                .execute(serve(|_ctx, request: String| async move {
+                    request.parse::<u64>().map_err(|_| {
+                        ServerError::new(
                             io::ErrorKind::InvalidInput,
-                            format!("{:?} is not an int", request),
+                            format!("{request:?} is not an int"),
                         )
-                    }))
+                    })
+                }))
+                .for_each(|channel| async move {
+                    tokio::spawn(channel.for_each(|response| response));
                 }),
         );
 
-        let client = client::new(client::Config::default(), client_channel).spawn()?;
+        let 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?;
+        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);
+        assert_matches!(response2, Err(RpcError::Server(e)) if e.kind == io::ErrorKind::InvalidInput);
 
         Ok(())
     }

tarpc/src/util.rs

@@ -38,11 +38,34 @@ where
     H: BuildHasher,
 {
     fn compact(&mut self, usage_ratio_threshold: f64) {
-        if self.capacity() > 1000 {
-            let usage_ratio = self.len() as f64 / self.capacity() as f64;
-            if usage_ratio < usage_ratio_threshold {
-                self.shrink_to_fit();
-            }
-        }
+        let usage_ratio_threshold = usage_ratio_threshold.clamp(f64::MIN_POSITIVE, 1.);
+        let cap = f64::max(1000., self.len() as f64 / usage_ratio_threshold);
+        self.shrink_to(cap as usize);
     }
 }
+
+#[test]
+fn test_compact() {
+    let mut map = HashMap::with_capacity(2048);
+    assert_eq!(map.capacity(), 3584);
+
+    // Make usage ratio 25%
+    for i in 0..896 {
+        map.insert(format!("k{i}"), "v");
+    }
+
+    map.compact(-1.0);
+    assert_eq!(map.capacity(), 3584);
+
+    map.compact(0.25);
+    assert_eq!(map.capacity(), 3584);
+
+    map.compact(0.50);
+    assert_eq!(map.capacity(), 1792);
+
+    map.compact(1.0);
+    assert_eq!(map.capacity(), 1792);
+
+    map.compact(2.0);
+    assert_eq!(map.capacity(), 1792);
+}

tarpc/src/util/serde.rs

@@ -5,31 +5,7 @@
 // https://opensource.org/licenses/MIT.
 
 use serde::{Deserialize, Deserializer, Serialize, Serializer};
-use std::{
-    io,
-    time::{Duration, SystemTime},
-};
-
-/// Serializes `system_time` as a `u64` equal to the number of seconds since the epoch.
-pub fn serialize_epoch_secs<S>(system_time: &SystemTime, serializer: S) -> Result<S::Ok, S::Error>
-where
-    S: Serializer,
-{
-    const ZERO_SECS: Duration = Duration::from_secs(0);
-    system_time
-        .duration_since(SystemTime::UNIX_EPOCH)
-        .unwrap_or(ZERO_SECS)
-        .as_secs() // Only care about second precision
-        .serialize(serializer)
-}
-
-/// Deserializes [`SystemTime`] from a `u64` equal to the number of seconds since the epoch.
-pub fn deserialize_epoch_secs<'de, D>(deserializer: D) -> Result<SystemTime, D::Error>
-where
-    D: Deserializer<'de>,
-{
-    Ok(SystemTime::UNIX_EPOCH + Duration::from_secs(u64::deserialize(deserializer)?))
-}
+use std::io;
 
 /// Serializes [`io::ErrorKind`] as a `u32`.
 #[allow(clippy::trivially_copy_pass_by_ref)] // Exact fn signature required by serde derive

tarpc/tests/compile_fail.rs

@@ -2,4 +2,6 @@
 fn ui() {
     let t = trybuild::TestCases::new();
     t.compile_fail("tests/compile_fail/*.rs");
+    #[cfg(all(feature = "serde-transport", feature = "tcp"))]
+    t.compile_fail("tests/compile_fail/serde_transport/*.rs");
 }

tarpc/tests/compile_fail/must_use_request_dispatch.rs

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

tarpc/tests/compile_fail/must_use_request_dispatch.stderr

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

tarpc/tests/compile_fail/serde_transport/must_use_tcp_connect.rs

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

tarpc/tests/compile_fail/serde_transport/must_use_tcp_connect.stderr

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

tarpc/tests/compile_fail/tarpc_server_missing_async.rs

@@ -1,15 +0,0 @@
-#[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)
-    }
-}
-
-fn main() {}

tarpc/tests/compile_fail/tarpc_server_missing_async.stderr

@@ -1,11 +0,0 @@
-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/dataservice.rs

@@ -1,14 +1,13 @@
 use futures::prelude::*;
-use std::io;
 use tarpc::serde_transport;
 use tarpc::{
     client, context,
-    server::{BaseChannel, Incoming},
+    server::{incoming::Incoming, BaseChannel},
 };
 use tokio_serde::formats::Json;
 
 #[tarpc::derive_serde]
-#[derive(Debug, PartialEq)]
+#[derive(Debug, PartialEq, Eq)]
 pub enum TestData {
     Black,
     White,
@@ -22,7 +21,6 @@ pub trait ColorProtocol {
 #[derive(Clone)]
 struct ColorServer;
 
-#[tarpc::server]
 impl ColorProtocol for ColorServer {
     async fn get_opposite_color(self, _: context::Context, color: TestData) -> TestData {
         match color {
@@ -32,8 +30,13 @@ impl ColorProtocol for ColorServer {
     }
 }
 
+#[cfg(test)]
+async fn spawn(fut: impl Future<Output = ()> + Send + 'static) {
+    tokio::spawn(fut);
+}
+
 #[tokio::test]
-async fn test_call() -> io::Result<()> {
+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(
@@ -41,11 +44,13 @@ async fn test_call() -> io::Result<()> {
             .take(1)
             .filter_map(|r| async { r.ok() })
             .map(BaseChannel::with_defaults)
-            .execute(ColorServer.serve()),
+            .execute(ColorServer.serve())
+            .map(|channel| channel.for_each(spawn))
+            .for_each(spawn),
     );
 
     let transport = serde_transport::tcp::connect(addr, Json::default).await?;
-    let client = ColorProtocolClient::new(client::Config::default(), transport).spawn()?;
+    let client = ColorProtocolClient::new(client::Config::default(), transport).spawn();
 
     let color = client
         .get_opposite_color(context::current(), TestData::White)

tarpc/tests/service_functional.rs

@@ -1,16 +1,13 @@
 use assert_matches::assert_matches;
 use futures::{
-    future::{join_all, ready, Ready},
+    future::{join_all, ready},
     prelude::*,
 };
-use std::{
-    io,
-    time::{Duration, SystemTime},
-};
+use std::time::{Duration, SystemTime};
 use tarpc::{
     client::{self},
     context,
-    server::{self, BaseChannel, Channel, Incoming},
+    server::{incoming::Incoming, BaseChannel, Channel},
     transport::channel,
 };
 use tokio::join;
@@ -25,43 +22,33 @@ trait Service {
 struct Server;
 
 impl Service for Server {
-    type AddFut = Ready<i32>;
-
-    fn add(self, _: context::Context, x: i32, y: i32) -> Self::AddFut {
-        ready(x + y)
+    async fn add(self, _: context::Context, x: i32, y: i32) -> i32 {
+        x + y
     }
 
-    type HeyFut = Ready<String>;
-
-    fn hey(self, _: context::Context, name: String) -> Self::HeyFut {
-        ready(format!("Hey, {}.", name))
+    async fn hey(self, _: context::Context, name: String) -> String {
+        format!("Hey, {name}.")
     }
 }
 
 #[tokio::test]
-async fn sequential() -> io::Result<()> {
-    let _ = env_logger::try_init();
-
-    let (tx, rx) = channel::unbounded();
-
+async fn sequential() {
+    let (tx, rx) = tarpc::transport::channel::unbounded();
+    let client = client::new(client::Config::default(), tx).spawn();
+    let channel = BaseChannel::with_defaults(rx);
     tokio::spawn(
-        BaseChannel::new(server::Config::default(), rx)
-            .requests()
-            .execute(Server.serve()),
+        channel
+            .execute(tarpc::server::serve(|_, i| async move { Ok(i + 1) }))
+            .for_each(|response| response),
+    );
+    assert_eq!(
+        client.call(context::current(), "AddOne", 1).await.unwrap(),
+        2
     );
-
-    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() -> io::Result<()> {
+async fn dropped_channel_aborts_in_flight_requests() -> anyhow::Result<()> {
     #[tarpc_plugins::service]
     trait Loop {
         async fn r#loop();
@@ -73,7 +60,6 @@ async fn dropped_channel_aborts_in_flight_requests() -> io::Result<()> {
     #[derive(Debug)]
     struct AllHandlersComplete;
 
-    #[tarpc::server]
     impl Loop for LoopServer {
         async fn r#loop(self, _: context::Context) {
             loop {
@@ -82,16 +68,14 @@ async fn dropped_channel_aborts_in_flight_requests() -> io::Result<()> {
         }
     }
 
-    let _ = env_logger::try_init();
+    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()
-            .unwrap();
+        let client = LoopClient::new(client::Config::default(), tx).spawn();
 
         let mut ctx = context::current();
         ctx.deadline = SystemTime::now() + Duration::from_secs(60 * 60);
@@ -113,11 +97,11 @@ async fn dropped_channel_aborts_in_flight_requests() -> io::Result<()> {
 
 #[cfg(all(feature = "serde-transport", feature = "tcp"))]
 #[tokio::test]
-async fn serde() -> io::Result<()> {
+async fn serde_tcp() -> anyhow::Result<()> {
     use tarpc::serde_transport;
     use tokio_serde::formats::Json;
 
-    let _ = env_logger::try_init();
+    let _ = tracing_subscriber::fmt::try_init();
 
     let transport = tarpc::serde_transport::tcp::listen("localhost:56789", Json::default).await?;
     let addr = transport.local_addr();
@@ -126,11 +110,13 @@ async fn serde() -> io::Result<()> {
             .take(1)
             .filter_map(|r| async { r.ok() })
             .map(BaseChannel::with_defaults)
-            .execute(Server.serve()),
+            .execute(Server.serve())
+            .map(|channel| channel.for_each(spawn))
+            .for_each(spawn),
     );
 
     let transport = serde_transport::tcp::connect(addr, Json::default).await?;
-    let client = ServiceClient::new(client::Config::default(), transport).spawn()?;
+    let client = ServiceClient::new(client::Config::default(), transport).spawn();
 
     assert_matches!(client.add(context::current(), 1, 2).await, Ok(3));
     assert_matches!(
@@ -141,18 +127,53 @@ async fn serde() -> io::Result<()> {
     Ok(())
 }
 
+#[cfg(all(feature = "serde-transport", feature = "unix", unix))]
 #[tokio::test]
-async fn concurrent() -> io::Result<()> {
-    let _ = env_logger::try_init();
+async fn serde_uds() -> anyhow::Result<()> {
+    use tarpc::serde_transport;
+    use tokio_serde::formats::Json;
+
+    let _ = tracing_subscriber::fmt::try_init();
+
+    let sock = tarpc::serde_transport::unix::TempPathBuf::with_random("uds");
+    let transport = tarpc::serde_transport::unix::listen(&sock, Json::default).await?;
+    tokio::spawn(
+        transport
+            .take(1)
+            .filter_map(|r| async { r.ok() })
+            .map(BaseChannel::with_defaults)
+            .execute(Server.serve())
+            .map(|channel| channel.for_each(spawn))
+            .for_each(spawn),
+    );
+
+    let transport = serde_transport::unix::connect(&sock, Json::default).await?;
+    let client = ServiceClient::new(client::Config::default(), transport).spawn();
+
+    // Save results using socket so we can clean the socket even if our test assertions fail
+    let res1 = client.add(context::current(), 1, 2).await;
+    let res2 = client.hey(context::current(), "Tim".to_string()).await;
+
+    assert_matches!(res1, Ok(3));
+    assert_matches!(res2, Ok(ref s) if s == "Hey, Tim.");
+
+    Ok(())
+}
+
+#[tokio::test]
+async fn concurrent() -> anyhow::Result<()> {
+    let _ = tracing_subscriber::fmt::try_init();
 
     let (tx, rx) = channel::unbounded();
     tokio::spawn(
         stream::once(ready(rx))
             .map(BaseChannel::with_defaults)
-            .execute(Server.serve()),
+            .execute(Server.serve())
+            .map(|channel| channel.for_each(spawn))
+            .for_each(spawn),
     );
 
-    let client = ServiceClient::new(client::Config::default(), tx).spawn()?;
+    let client = ServiceClient::new(client::Config::default(), tx).spawn();
 
     let req1 = client.add(context::current(), 1, 2);
     let req2 = client.add(context::current(), 3, 4);
@@ -166,17 +187,19 @@ async fn concurrent() -> io::Result<()> {
 }
 
 #[tokio::test]
-async fn concurrent_join() -> io::Result<()> {
-    let _ = env_logger::try_init();
+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()),
+            .execute(Server.serve())
+            .map(|channel| channel.for_each(spawn))
+            .for_each(spawn),
     );
 
-    let client = ServiceClient::new(client::Config::default(), tx).spawn()?;
+    let client = ServiceClient::new(client::Config::default(), tx).spawn();
 
     let req1 = client.add(context::current(), 1, 2);
     let req2 = client.add(context::current(), 3, 4);
@@ -190,18 +213,23 @@ async fn concurrent_join() -> io::Result<()> {
     Ok(())
 }
 
+#[cfg(test)]
+async fn spawn(fut: impl Future<Output = ()> + Send + 'static) {
+    tokio::spawn(fut);
+}
+
 #[tokio::test]
-async fn concurrent_join_all() -> io::Result<()> {
-    let _ = env_logger::try_init();
+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()),
+        BaseChannel::with_defaults(rx)
+            .execute(Server.serve())
+            .for_each(spawn),
     );
 
-    let client = ServiceClient::new(client::Config::default(), tx).spawn()?;
+    let client = ServiceClient::new(client::Config::default(), tx).spawn();
 
     let req1 = client.add(context::current(), 1, 2);
     let req2 = client.add(context::current(), 3, 4);
@@ -214,7 +242,7 @@ async fn concurrent_join_all() -> io::Result<()> {
 }
 
 #[tokio::test]
-async fn counter() -> io::Result<()> {
+async fn counter() -> anyhow::Result<()> {
     #[tarpc::service]
     trait Counter {
         async fn count() -> u32;
@@ -223,11 +251,9 @@ async fn counter() -> io::Result<()> {
     struct CountService(u32);
 
     impl Counter for &mut CountService {
-        type CountFut = futures::future::Ready<u32>;
-
-        fn count(self, _: context::Context) -> Self::CountFut {
+        async fn count(self, _: context::Context) -> u32 {
             self.0 += 1;
-            futures::future::ready(self.0)
+            self.0
         }
     }
 
@@ -241,7 +267,7 @@ async fn counter() -> io::Result<()> {
         }
     });
 
-    let client = CounterClient::new(client::Config::default(), tx).spawn()?;
+    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));