tonic-web: proxy any kind of service

This allows applying the GrpcWebLayer to any kind of Service, not just ones that tonic generates. This makes it possible to use tonic-web as a grpc-web proxy to a gRPC server implemented in another language for example.

Author: bouk

tests/web/Cargo.toml

@@ -18,6 +18,8 @@ tonic-prost = { path = "../../tonic-prost" }
 
 [dev-dependencies]
 tonic-web = { path = "../../tonic-web" }
+tower-layer = "0.3"
+tower-service = "0.3"
 
 [build-dependencies]
 tonic-prost-build = { path = "../../tonic-prost-build" }

tests/web/tests/grpc_web.rs

@@ -42,6 +42,29 @@ async fn binary_request() {
     assert_eq!(&trailers[..], b"grpc-status:0\r\n");
 }
 
+#[tokio::test]
+async fn binary_request_reverse_proxy() {
+    let server_url = spawn_reverse_proxy().await;
+    let client = Client::builder(TokioExecutor::new()).build_http();
+
+    let req = build_request(server_url, "grpc-web", "grpc-web");
+    let res = client.request(req).await.unwrap();
+    let content_type = res.headers().get(header::CONTENT_TYPE).unwrap().clone();
+    let content_type = content_type.to_str().unwrap();
+
+    assert_eq!(res.status(), StatusCode::OK);
+    assert_eq!(content_type, "application/grpc-web+proto");
+
+    let (message, trailers) = decode_body(res.into_body(), content_type).await;
+    let expected = Output {
+        id: 1,
+        desc: "one".to_owned(),
+    };
+
+    assert_eq!(message, expected);
+    assert_eq!(&trailers[..], b"grpc-status:0\r\n");
+}
+
 #[tokio::test]
 async fn text_request() {
     let server_url = spawn().await;
@@ -84,6 +107,73 @@ async fn spawn() -> String {
     url
 }
 
+/// Spawn two servers, one serving the gRPC API and another acting as a grpc-web proxy
+async fn spawn_reverse_proxy() -> String {
+    use hyper_util::rt::TokioIo;
+    use hyper_util::client::legacy::Client;
+    use tower_layer::Layer;
+    use tower_service::Service;
+
+    // Set up gRPC service
+    let addr = SocketAddr::from(([127, 0, 0, 1], 0));
+    let listener = TcpListener::bind(addr).await.expect("listener");
+    let url = format!("http://{}", listener.local_addr().unwrap());
+    let listener_stream = TcpListenerStream::new(listener);
+
+    drop(tokio::spawn(async move {
+        Server::builder()
+            .add_service(TestServer::new(Svc))
+            .serve_with_incoming(listener_stream)
+            .await
+            .unwrap()
+    }));
+
+    // Set up proxy to the above service that applies tonic-web
+    let addr2 = SocketAddr::from(([127, 0, 0, 1], 0));
+    let http_client = Client::builder(TokioExecutor::new())
+        .http2_only(true)
+        .build_http();
+    let listener2 = TcpListener::bind(addr2).await.expect("listener");
+    let url2 = format!("http://{}", listener2.local_addr().unwrap());
+
+    let backend_url = url.clone();
+
+    drop(tokio::spawn(async move {
+        loop {
+            let (stream, _) = listener2.accept().await.unwrap();
+            let io = TokioIo::new(stream);
+            let client = http_client.clone();
+            let backend = backend_url.clone();
+
+            tokio::spawn(async move {
+                let svc = GrpcWebLayer::new().layer(client.clone());
+                let hyper_svc = hyper::service::service_fn(move |mut req: Request<Incoming>| {
+                    let mut svc = svc.clone();
+                    let backend = backend.clone();
+                    async move {
+                        // Rewrite URI to point to backend
+                        let path = req.uri().path_and_query().map(|pq| pq.as_str()).unwrap_or("/");
+                        let new_uri = format!("{}{}", backend, path).parse().unwrap();
+                        *req.uri_mut() = new_uri;
+
+                        let req = req.map(Body::new);
+                        svc.call(req).await
+                    }
+                });
+
+                if let Err(err) = hyper_util::server::conn::auto::Builder::new(TokioExecutor::new())
+                    .serve_connection(io, hyper_svc)
+                    .await
+                {
+                    eprintln!("Error serving connection: {:?}", err);
+                }
+            });
+        }
+    }));
+
+    url2
+}
+
 fn encode_body() -> Bytes {
     let input = Input {
         id: 1,

tonic-web/src/call.rs

@@ -1,4 +1,3 @@
-use std::fmt;
 use std::pin::Pin;
 use std::task::{ready, Context, Poll};
 
@@ -10,6 +9,8 @@ use pin_project::pin_project;
 use tokio_stream::Stream;
 use tonic::Status;
 
+use crate::BoxError;
+
 use self::content_types::*;
 
 // A grpc header is u8 (flag) + u32 (msg len)
@@ -158,11 +159,11 @@ impl<B> GrpcWebCall<B> {
     }
 }
 
-impl<B> GrpcWebCall<B>
+impl<B, D> GrpcWebCall<B>
 where
-    B: Body,
-    B::Data: Buf,
-    B::Error: fmt::Display,
+    B: Body<Data = D>,
+    B::Error: Into<BoxError> + Send,
+    D: Buf,
 {
     // Poll body for data, decoding (e.g. via Base64 if necessary) and returning frames
     // to the caller. If the caller is a client, it should look for trailers before
@@ -247,10 +248,11 @@ where
     }
 }
 
-impl<B> Body for GrpcWebCall<B>
+impl<B, D> Body for GrpcWebCall<B>
 where
-    B: Body,
-    B::Error: fmt::Display,
+    B: Body<Data = D>,
+    B::Error: Into<BoxError> + Send,
+    D: Buf,
 {
     type Data = Bytes;
     type Error = Status;
@@ -336,10 +338,11 @@ where
     }
 }
 
-impl<B> Stream for GrpcWebCall<B>
+impl<B, D> Stream for GrpcWebCall<B>
 where
-    B: Body,
-    B::Error: fmt::Display,
+    B: Body<Data = D>,
+    B::Error: Into<BoxError> + Send,
+    D: Buf,
 {
     type Item = Result<Frame<Bytes>, Status>;
 
@@ -372,7 +375,8 @@ impl Encoding {
     }
 }
 
-fn internal_error(e: impl std::fmt::Display) -> Status {
+fn internal_error(e: impl Into<BoxError> + Send) -> Status {
+    let e = e.into();
     Status::internal(format!("tonic-web: {e}"))
 }
 

tonic-web/src/layer.rs

@@ -1,22 +1,49 @@
-use super::GrpcWebService;
+use std::error::Error;
+
+use tonic::body::Body;
+use super::{BoxError, GrpcWebService};
 
 use tower_layer::Layer;
+use tower_service::Service;
 
 /// Layer implementing the grpc-web protocol.
-#[derive(Debug, Default, Clone)]
-pub struct GrpcWebLayer {
-    _priv: (),
+#[derive(Debug)]
+pub struct GrpcWebLayer<ResBody = Body> {
+    _markers: std::marker::PhantomData<fn() -> ResBody>,
+}
+
+impl<ResBody> Clone for GrpcWebLayer<ResBody> {
+    fn clone(&self) -> Self {
+        Self {
+            _markers: std::marker::PhantomData,
+        }
+    }
 }
 
-impl GrpcWebLayer {
+impl<ResBody> GrpcWebLayer<ResBody> {
     /// Create a new grpc-web layer.
-    pub fn new() -> GrpcWebLayer {
-        Self::default()
+    pub fn new() -> Self {
+        Self {
+            _markers: std::marker::PhantomData,
+        }
+    }
+}
+
+impl<ResBody> Default for GrpcWebLayer<ResBody> {
+    fn default() -> Self {
+        Self::new()
     }
 }
 
-impl<S> Layer<S> for GrpcWebLayer {
-    type Service = GrpcWebService<S>;
+impl<S, ResBody> Layer<S> for GrpcWebLayer<ResBody>
+where
+    S: Service<http::Request<Body>, Response = http::Response<ResBody>> + Send + 'static,
+    S::Future: Send + 'static,
+    S::Error: Into<BoxError> + Send,
+    ResBody: http_body::Body<Data = bytes::Bytes> + Send + 'static,
+    ResBody::Error: Error + Send + Sync + 'static,
+{
+    type Service = GrpcWebService<S, ResBody>;
 
     fn layer(&self, inner: S) -> Self::Service {
         GrpcWebService::new(inner)

tonic-web/src/lib.rs

@@ -80,7 +80,8 @@ mod client;
 mod layer;
 mod service;
 
-type BoxError = Box<dyn std::error::Error + Send + Sync>;
+/// Alias for a type-erased error type.
+pub type BoxError = Box<dyn std::error::Error + Send + Sync>;
 
 pub(crate) mod util {
     pub(crate) mod base64 {