gRPC-web Cloud Run issue

To run this example:

Open index.html in your browser.

What it shows

The gRPC-web client running on this page does requests every 500ms to https://grpc-web-test-envoy-snpekwsqaa-ez.a.run.app. This Cloud Run app runs an Envoy proxy with a gRPC web filter pointing to another Cloud Run app (https://grpc-web-test-snpekwsqaa-ez.a.run.app) that runs a regular gRPC server built from the Dockerfile in this repository. This demo demonstrates that only some requests return the correct response code/message, namely the expected error invalid input.

browser

    => Regular HTTP

        Envoy proxy (https://grpc-web-test-envoy-snpekwsqaa-ez.a.run.app)

            => HTTP2 (gRPC traffic)

                gRPC server (https://grpc-web-test-snpekwsqaa-ez.a.run.app)

            <= Response (with AND without `Content-Length: 0`)

    <= Valid response only if `Content-Length: 0` header is NOT present

result (screenshot from browser inspect console tab):

Client URL update instructions

To update the browser client to point to another host like localhost or another Cloud Run instance, do the following.

Update the HOST variable in client.js to the new URL.

Run the following from the project folder:

npm install
npx webpack

Counterexample

This problem does not happen for a TLS server not on Cloud Run. To demonstrate, use server-ssl.js to run the server locally with the envoy config pointing at server host.

The local Envoy server is just to showcase the problem. The response has been inspected and comes in empty, i.e. the problem is not caused by Envoy.