feat(web): Add GrpcWebClientService (#1472)

This adds `grpc-web` support for clients in `tonic-web`. This is done by
reusing the server side encoding/decoding but wrapping it in different
directions.

examples/Cargo.toml

@@ -270,7 +270,7 @@ routeguide = ["dep:async-stream", "tokio-stream", "dep:rand", "dep:serde", "dep:
 reflection = ["dep:tonic-reflection"]
 autoreload = ["tokio-stream/net", "dep:listenfd"]
 health = ["dep:tonic-health"]
-grpc-web = ["dep:tonic-web", "dep:bytes", "dep:http", "dep:hyper", "dep:tracing-subscriber"]
+grpc-web = ["dep:tonic-web", "dep:bytes", "dep:http", "dep:hyper", "dep:tracing-subscriber", "dep:tower"]
 tracing = ["dep:tracing", "dep:tracing-subscriber"]
 hyper-warp = ["dep:either", "dep:tower", "dep:hyper", "dep:http", "dep:http-body", "dep:warp"]
 hyper-warp-multiplex = ["hyper-warp"]

examples/src/grpc-web/client.rs

@@ -1,74 +1,28 @@
-use bytes::{Buf, BufMut, Bytes, BytesMut};
-use hello_world::{HelloReply, HelloRequest};
-use http::header::{ACCEPT, CONTENT_TYPE};
+use hello_world::{greeter_client::GreeterClient, HelloRequest};
+use tonic_web::GrpcWebClientLayer;
 
 pub mod hello_world {
     tonic::include_proto!("helloworld");
 }
 
 #[tokio::main]
 async fn main() -> Result<(), Box<dyn std::error::Error>> {
-    let msg = HelloRequest {
-        name: "Bob".to_string(),
-    };
+    // Must use hyper directly...
+    let client = hyper::Client::builder().build_http();
 
-    // a good old http/1.1 request
-    let request = http::Request::builder()
-        .version(http::Version::HTTP_11)
-        .method(http::Method::POST)
-        .uri("http://127.0.0.1:3000/helloworld.Greeter/SayHello")
-        .header(CONTENT_TYPE, "application/grpc-web")
-        .header(ACCEPT, "application/grpc-web")
-        .body(hyper::Body::from(encode_body(msg)))
-        .unwrap();
+    let svc = tower::ServiceBuilder::new()
+        .layer(GrpcWebClientLayer::new())
+        .service(client);
 
-    let client = hyper::Client::new();
+    let mut client = GreeterClient::with_origin(svc, "http://127.0.0.1:3000".try_into()?);
 
-    let response = client.request(request).await.unwrap();
+    let request = tonic::Request::new(HelloRequest {
+        name: "Tonic".into(),
+    });
 
-    assert_eq!(
-        response.headers().get(CONTENT_TYPE).unwrap(),
-        "application/grpc-web+proto"
-    );
+    let response = client.say_hello(request).await?;
 
-    let body = response.into_body();
-    let reply = decode_body::<HelloReply>(body).await;
-
-    println!("REPLY={:?}", reply);
+    println!("RESPONSE={:?}", response);
 
     Ok(())
 }
-
-// one byte for the compression flag plus four bytes for the length
-const GRPC_HEADER_SIZE: usize = 5;
-
-fn encode_body<T>(msg: T) -> Bytes
-where
-    T: prost::Message,
-{
-    let msg_len = msg.encoded_len();
-    let mut buf = BytesMut::with_capacity(GRPC_HEADER_SIZE + msg_len);
-
-    // compression flag, 0 means "no compression"
-    buf.put_u8(0);
-    buf.put_u32(msg_len as u32);
-
-    msg.encode(&mut buf).unwrap();
-    buf.freeze()
-}
-
-async fn decode_body<T>(body: hyper::Body) -> T
-where
-    T: Default + prost::Message,
-{
-    let mut body = hyper::body::to_bytes(body).await.unwrap();
-
-    // ignore the compression flag
-    body.advance(1);
-
-    let len = body.get_u32();
-    #[allow(clippy::let_and_return)]
-    let msg = T::decode(&mut body.split_to(len as usize)).unwrap();
-
-    msg
-}