feat(build): Better support for custom codecs (#999)

BREAKING CHANGE: `CODEC_PATH` moved from const to fn

examples/Cargo.toml

@@ -186,6 +186,14 @@ path = "src/streaming/client.rs"
 name = "streaming-server"
 path = "src/streaming/server.rs"
 
+[[bin]]
+name = "json-codec-client"
+path = "src/json-codec/client.rs"
+
+[[bin]]
+name = "json-codec-server"
+path = "src/json-codec/server.rs"
+
 [dependencies]
 async-stream = "0.3"
 futures = { version = "0.3", default-features = false, features = ["alloc"] }

examples/build.rs

@@ -1,5 +1,4 @@
-use std::env;
-use std::path::PathBuf;
+use std::{env, path::PathBuf};
 
 fn main() {
     tonic_build::configure()
@@ -30,4 +29,30 @@ fn main() {
             &["proto/googleapis"],
         )
         .unwrap();
+
+    build_json_codec_service();
+}
+
+// Manually define the json.helloworld.Greeter service which used a custom JsonCodec to use json
+// serialization instead of protobuf for sending messages on the wire.
+// This will result in generated client and server code which relies on its request, response and
+// codec types being defined in a module `crate::common`.
+//
+// See the client/server examples defined in `src/json-codec` for more information.
+fn build_json_codec_service() {
+    let greeter_service = tonic_build::manual::Service::builder()
+        .name("Greeter")
+        .package("json.helloworld")
+        .method(
+            tonic_build::manual::Method::builder()
+                .name("say_hello")
+                .route_name("SayHello")
+                .input_type("crate::common::HelloRequest")
+                .output_type("crate::common::HelloResponse")
+                .codec_path("crate::common::JsonCodec")
+                .build(),
+        )
+        .build();
+
+    tonic_build::manual::Builder::new().compile(&[greeter_service]);
 }

examples/src/json-codec/client.rs

@@ -0,0 +1,28 @@
+//! A HelloWorld example that uses JSON instead of protobuf as the message serialization format.
+//!
+//! Generated code is the output of codegen as defined in the `build_json_codec_service` function
+//! in the `examples/build.rs` file. As defined there, the generated code assumes that a module
+//! `crate::common` exists which defines `HelloRequest`, `HelloResponse`, and `JsonCodec`.
+
+pub mod common;
+use common::HelloRequest;
+
+pub mod hello_world {
+    include!(concat!(env!("OUT_DIR"), "/json.helloworld.Greeter.rs"));
+}
+use hello_world::greeter_client::GreeterClient;
+
+#[tokio::main]
+async fn main() -> Result<(), Box<dyn std::error::Error>> {
+    let mut client = GreeterClient::connect("http://[::1]:50051").await?;
+
+    let request = tonic::Request::new(HelloRequest {
+        name: "Tonic".into(),
+    });
+
+    let response = client.say_hello(request).await?;
+
+    println!("RESPONSE={:?}", response);
+
+    Ok(())
+}

examples/src/json-codec/common.rs

@@ -0,0 +1,80 @@
+//! This module defines common request/response types as well as the JsonCodec that is used by the
+//! json.helloworld.Greeter service which is defined manually (instead of via proto files) by the
+//! `build_json_codec_service` function in the `examples/build.rs` file.
+
+use bytes::{Buf, BufMut};
+use serde::{Deserialize, Serialize};
+use std::marker::PhantomData;
+use tonic::{
+    codec::{Codec, DecodeBuf, Decoder, EncodeBuf, Encoder},
+    Status,
+};
+
+#[derive(Debug, Deserialize, Serialize)]
+pub struct HelloRequest {
+    pub name: String,
+}
+
+#[derive(Debug, Deserialize, Serialize)]
+pub struct HelloResponse {
+    pub message: String,
+}
+
+#[derive(Debug)]
+pub struct JsonEncoder<T>(PhantomData<T>);
+
+impl<T: serde::Serialize> Encoder for JsonEncoder<T> {
+    type Item = T;
+    type Error = Status;
+
+    fn encode(&mut self, item: Self::Item, buf: &mut EncodeBuf<'_>) -> Result<(), Self::Error> {
+        serde_json::to_writer(buf.writer(), &item).map_err(|e| Status::internal(e.to_string()))
+    }
+}
+
+#[derive(Debug)]
+pub struct JsonDecoder<U>(PhantomData<U>);
+
+impl<U: serde::de::DeserializeOwned> Decoder for JsonDecoder<U> {
+    type Item = U;
+    type Error = Status;
+
+    fn decode(&mut self, buf: &mut DecodeBuf<'_>) -> Result<Option<Self::Item>, Self::Error> {
+        if !buf.has_remaining() {
+            return Ok(None);
+        }
+
+        let item: Self::Item =
+            serde_json::from_reader(buf.reader()).map_err(|e| Status::internal(e.to_string()))?;
+        Ok(Some(item))
+    }
+}
+
+/// A [`Codec`] that implements `application/grpc+json` via the serde library.
+#[derive(Debug, Clone)]
+pub struct JsonCodec<T, U>(PhantomData<(T, U)>);
+
+impl<T, U> Default for JsonCodec<T, U> {
+    fn default() -> Self {
+        Self(PhantomData)
+    }
+}
+
+impl<T, U> Codec for JsonCodec<T, U>
+where
+    T: serde::Serialize + Send + 'static,
+    U: serde::de::DeserializeOwned + Send + 'static,
+{
+    type Encode = T;
+    type Decode = U;
+    type Encoder = JsonEncoder<T>;
+    type Decoder = JsonDecoder<U>;
+
+    fn encoder(&mut self) -> Self::Encoder {
+        JsonEncoder(PhantomData)
+    }
+
+    fn decoder(&mut self) -> Self::Decoder {
+        JsonDecoder(PhantomData)
+    }
+}

examples/src/json-codec/server.rs

@@ -0,0 +1,48 @@
+//! A HelloWorld example that uses JSON instead of protobuf as the message serialization format.
+//!
+//! Generated code is the output of codegen as defined in the `build_json_codec_service` function
+//! in the `examples/build.rs` file. As defined there, the generated code assumes that a module
+//! `crate::common` exists which defines `HelloRequest`, `HelloResponse`, and `JsonCodec`.
+
+use tonic::{transport::Server, Request, Response, Status};
+
+pub mod common;
+use common::{HelloRequest, HelloResponse};
+
+pub mod hello_world {
+    include!(concat!(env!("OUT_DIR"), "/json.helloworld.Greeter.rs"));
+}
+use hello_world::greeter_server::{Greeter, GreeterServer};
+
+#[derive(Default)]
+pub struct MyGreeter {}
+
+#[tonic::async_trait]
+impl Greeter for MyGreeter {
+    async fn say_hello(
+        &self,
+        request: Request<HelloRequest>,
+    ) -> Result<Response<HelloResponse>, Status> {
+        println!("Got a request from {:?}", request.remote_addr());
+
+        let reply = HelloResponse {
+            message: format!("Hello {}!", request.into_inner().name),
+        };
+        Ok(Response::new(reply))
+    }
+}
+
+#[tokio::main]
+async fn main() -> Result<(), Box<dyn std::error::Error>> {
+    let addr = "[::1]:50051".parse().unwrap();
+    let greeter = MyGreeter::default();
+
+    println!("GreeterServer listening on {}", addr);
+
+    Server::builder()
+        .add_service(GreeterServer::new(greeter))
+        .serve(addr)
+        .await?;
+
+    Ok(())
+}