Client side support for http streaming

[siggisim]

Client side support for server-side grpc streaming over http.

This is behind a app.streaming_http_enabled flag.

If that flag is enabled, we'll do three things:

• We'll change our content-type from application/proto to application/grpc+proto
• We'll send proto messages as Length-Prefixed-Messages (see https://github.com/grpc/grpc/blob/master/doc/PROTOCOL-HTTP2.md)
• We'll read the response as a stream rather than just a single arraybuffer.

There is a TODO in there to support messages that come across chunks. This should be relatively straightforward to implement, but I haven't run into it in my testing - and would like to run into it before fixing.

Depends on: #5505

[bduffany]

How does this work in terms of the proto API? Will this let us write streaming RPC methods now or is there some additional codegen support needed? (IIRC the protobufjs codegen doesn't generate code for streaming APIs?)

[siggisim]

How does this work in terms of the proto API? Will this let us write streaming RPC methods now or is there some additional codegen support needed? (IIRC the protobufjs codegen doesn't generate code for streaming APIs?)

Here's an example:

    rpc_service.service.on("data", (response, method) => {
      // Todo probably check that you're dealing with the right method here
      console.log(response);
    });

    rpc_service.service.streamBuildLog(request);

We could probably do something fancy to make this nicer, but I don't think this is so bad.

[bduffany]

should this be return ? Seems like we'll do another fetch after this break, guessing that's not intended?

[siggisim]

Good catch, I am struggling with returns today lol.

I tested this a bunch without the fallback case at the bottom - and then added the fallback to support hiding this behind a flag, and guess I didn't notice the extra fetch.

[siggisim]

Fixed