Add rest and grpc example (#967)

* Add rest and grpc example

* remove needless dependencies

* Apply suggestions from code review

Co-authored-by: David Pedersen <david.pdrsn@gmail.com>

* Update examples/rest-grpc-multiplex/src/main.rs

Co-authored-by: David Pedersen <david.pdrsn@gmail.com>

* Update examples/rest-grpc-multiplex/src/main.rs

Co-authored-by: David Pedersen <david.pdrsn@gmail.com>

* Update examples/rest-grpc-multiplex/src/multiplex_service.rs

Co-authored-by: David Pedersen <david.pdrsn@gmail.com>

* Update examples/rest-grpc-multiplex/Cargo.toml

Co-authored-by: David Pedersen <david.pdrsn@gmail.com>

* Update examples/rest-grpc-multiplex/src/multiplex_service.rs

Co-authored-by: David Pedersen <david.pdrsn@gmail.com>

* clean noisy code

* fix nitpicks

* missing newline

Co-authored-by: David Pedersen <david.pdrsn@gmail.com>

examples/rest-grpc-multiplex/Cargo.toml

@@ -0,0 +1,19 @@
+[package]
+name = "example-rest-grpc-multiplex"
+version = "0.1.0"
+edition = "2018"
+publish = false
+
+[dependencies]
+axum = { path = "../../axum" }
+futures = "0.3"
+hyper = { version = "0.14",  features = ["full"] }
+prost = "0.10"
+tokio = { version = "1", features = ["full"] }
+tonic = { version = "0.7" }
+tower = { version = "0.4", features = ["full"] }
+tracing = "0.1"
+tracing-subscriber = { version = "0.3", features = ["env-filter"] }
+
+[build-dependencies]
+tonic-build = { version = "0.7", features = ["prost"] }

examples/rest-grpc-multiplex/build.rs

@@ -0,0 +1,3 @@
+fn main() {
+    tonic_build::compile_protos("proto/helloworld.proto").unwrap();
+}

examples/rest-grpc-multiplex/proto/helloworld.proto

@@ -0,0 +1,37 @@
+// Copyright 2015 gRPC authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+syntax = "proto3";
+
+option java_multiple_files = true;
+option java_package = "io.grpc.examples.helloworld";
+option java_outer_classname = "HelloWorldProto";
+
+package helloworld;
+
+// The greeting service definition.
+service Greeter {
+  // Sends a greeting
+  rpc SayHello (HelloRequest) returns (HelloReply) {}
+}
+
+// The request message containing the user's name.
+message HelloRequest {
+  string name = 1;
+}
+
+// The response message containing the greetings
+message HelloReply {
+  string message = 1;
+}

examples/rest-grpc-multiplex/src/main.rs

@@ -0,0 +1,72 @@
+//! Run with
+//!
+//! ```not_rust
+//! cd examples && cargo run -p example-rest-grpc-multiplex
+//! ```
+
+use self::multiplex_service::MultiplexService;
+use axum::{routing::get, Router};
+use proto::{
+    greeter_server::{Greeter, GreeterServer},
+    HelloReply, HelloRequest,
+};
+use std::net::SocketAddr;
+use tonic::{Response as TonicResponse, Status};
+use tracing_subscriber::{layer::SubscriberExt, util::SubscriberInitExt};
+
+mod multiplex_service;
+
+mod proto {
+    tonic::include_proto!("helloworld");
+}
+
+#[derive(Default)]
+struct GrpcServiceImpl {}
+
+#[tonic::async_trait]
+impl Greeter for GrpcServiceImpl {
+    async fn say_hello(
+        &self,
+        request: tonic::Request<HelloRequest>,
+    ) -> Result<TonicResponse<HelloReply>, Status> {
+        tracing::info!("Got a request from {:?}", request.remote_addr());
+
+        let reply = HelloReply {
+            message: format!("Hello {}!", request.into_inner().name),
+        };
+
+        Ok(TonicResponse::new(reply))
+    }
+}
+
+async fn web_root() -> &'static str {
+    "Hello, World!"
+}
+
+#[tokio::main]
+async fn main() {
+    // initialize tracing
+    tracing_subscriber::registry()
+        .with(tracing_subscriber::EnvFilter::new(
+            std::env::var("RUST_LOG")
+                .unwrap_or_else(|_| "example_rest_grpc_multiplex=debug".into()),
+        ))
+        .with(tracing_subscriber::fmt::layer())
+        .init();
+
+    // build the rest service
+    let rest = Router::new().route("/", get(web_root));
+
+    // build the grpc service
+    let grpc = GreeterServer::new(GrpcServiceImpl::default());
+
+    // combine them into one service
+    let service = MultiplexService::new(rest, grpc);
+
+    let addr = SocketAddr::from(([127, 0, 0, 1], 3000));
+    tracing::debug!("listening on {}", addr);
+    axum::Server::bind(&addr)
+        .serve(tower::make::Shared::new(service))
+        .await
+        .unwrap();
+}

examples/rest-grpc-multiplex/src/multiplex_service.rs

@@ -0,0 +1,85 @@
+use axum::{body::BoxBody, response::IntoResponse};
+use futures::{future::BoxFuture, ready};
+use hyper::{Body, Request, Response};
+use std::{
+    convert::Infallible,
+    task::{Context, Poll},
+};
+use tower::Service;
+
+#[derive(Clone)]
+pub struct MultiplexService<A, B> {
+    rest: A,
+    rest_ready: bool,
+    grpc: B,
+    grpc_ready: bool,
+}
+
+impl<A, B> MultiplexService<A, B> {
+    pub fn new(rest: A, grpc: B) -> Self {
+        Self {
+            rest,
+            rest_ready: false,
+            grpc,
+            grpc_ready: false,
+        }
+    }
+}
+
+impl<A, B> Service<Request<Body>> for MultiplexService<A, B>
+where
+    A: Service<Request<Body>, Error = Infallible>,
+    A::Response: IntoResponse,
+    A::Future: Send + 'static,
+    B: Service<Request<Body>, Error = Infallible>,
+    B::Response: IntoResponse,
+    B::Future: Send + 'static,
+{
+    type Response = Response<BoxBody>;
+    type Error = Infallible;
+    type Future = BoxFuture<'static, Result<Self::Response, Self::Error>>;
+
+    fn poll_ready(&mut self, cx: &mut Context<'_>) -> Poll<Result<(), Self::Error>> {
+        loop {
+            match (self.rest_ready, self.grpc_ready) {
+                (true, true) => {
+                    return Ok(()).into();
+                }
+                (false, _) => {
+                    ready!(self.rest.poll_ready(cx))?;
+                    self.rest_ready = false;
+                }
+                (_, false) => {
+                    ready!(self.grpc.poll_ready(cx))?;
+                    self.grpc_ready = true;
+                }
+            }
+        }
+    }
+
+    fn call(&mut self, req: Request<Body>) -> Self::Future {
+        if is_grpc_request(&req) {
+            self.grpc_ready = false;
+            let future = self.grpc.call(req);
+            Box::pin(async move {
+                let res = future.await?;
+                Ok(res.into_response())
+            })
+        } else {
+            self.rest_ready = false;
+            let future = self.rest.call(req);
+            Box::pin(async move {
+                let res = future.await?;
+                Ok(res.into_response())
+            })
+        }
+    }
+}
+
+fn is_grpc_request<B>(req: &Request<B>) -> bool {
+    req.headers()
+        .get("content-type")
+        .map(|content_type| content_type.as_bytes())
+        .filter(|content_type| content_type.starts_with(b"application/grpc"))
+        .is_some()
+}