Stream request hangs until first message

[wngr]

Thanks for updating the library for proper stream support!

I'm building a gRPC client, that works both on native and on the web platform. I stumbled across the following bug:

#[wasm_bindgen_test]
async fn test_echo_pending() {
    let mut client = EchoClient::default();
    // The future below will only resolve once the server returns a first message.
    client
        .echo_stream(EchoRequest {
            message: "SILENCE!".to_string(),
        })
        .await
        .expect("success stream response")
        .into_inner();
}

This behaviour is different from using tonic::transport::Channel.

Reproducer can be found at https://github.com/devashishdxt/tonic-web-wasm-client/commit/1036c3f3dc316240f7e11a36ae0c4626c7758fbd.

[wngr]

So it seems the request returns indeed does return a 200 (so no problem with this library per se nor with tonic-web; developer console), but the Promise returned by the fetch call is still pending:

fetch("http://localhost:50051/echo.Echo/EchoStream", {
  "headers": {
    "accept": "application/grpc-web+proto",
    "accept-language": "en-GB,en",
    "content-type": "application/grpc-web+proto",
    "sec-fetch-dest": "empty",
    "sec-fetch-mode": "cors",
    "sec-fetch-site": "cross-site",
    "sec-gpc": "1",
    "x-grpc-web": "1"
  },
  "referrer": "http://127.0.0.1:8000/",
  "referrerPolicy": "strict-origin-when-cross-origin",
  "body": "\u0000\u0000\u0000\u0000\n\n\bSILENCE!",
  "method": "POST",
  "mode": "cors",
  "credentials": "omit"
});

That's .. unexpected?

[devashishdxt]

If the promise returned by the fetch call is pending until first message is received, there's very little we can do here. I'll look into it over the weekend.

[devashishdxt]

Also, in the code that you published, you need to register a Waker when you return Poll::Pending so that your async runtime can start polling that future once it is ready. Current implementation will hang forever.

[devashishdxt]

Closing this issue