Server-side streaming support clarification

[tsegismont]

Hi,

In different parts of the documentation, it is said that server-side streaming is only supported when grpcwebtext mode is used. What's the limitation exactly?

I'm asking because I'm currently working on an implementation of gRPC-Web for Vert.x and, during my testing, it seemed to work[1] in both modes.

Do you believe I did something wrong or is it not officially supported because of some limitations in complex cases?

Thank you,
Thomas

[1] Worked with the browser client + Envoy Proxy + Vertx gRPC backend, and browser client + Vertx gRPC-Web backend as well.

[sampajano]

@tsegismont Thanks so much for starting the discussion! It's a worthy discussion!

I checked with the original author of the library (@stanley-cheung). He mentioned that at the time of design (pre 2020), binary payload didn't work across browsers when Transfer-Encoding is set to chunked (which is what's used with server streaming RPCs).

Do you/we have reason to believe this is still the case, or it has changed since then?

[tsegismont]

If I understand correctly, the limitation doesn't come from the client or proxy implementation, but from lack of support from some browsers?

[sampajano]

Yes, that's how i've understood the statement..

Although i have not researched into the original rationale, nor have i verified in newer browser(s), so i cannot say how true it is..

If i have to guess, there's probably some grounds for the original rationales. So if we can find some original source(s), and reasons to believe that things have evolved since then, i'd have much higher confidence 😃

[tsegismont]

Agreed. If you can get a list of tested browsers from the original authors, that would be great. In this case, I would volunteer for a PR that updates the doc (and then users could chose to use server-side streaming with binary format if their website doesn't target the unsupported browsers).

[sampajano]

@tsegismont Thanks so much for offering for the change! Appreciate it! 😃

---

Although, i just did a quick test using the echo example, with the only change to the following config to use grpcweb instead of grpcwebtext:

grpc-web/net/grpc/gateway/docker/commonjs_client/Dockerfile

Lines 19 to 21 in a639b4c

	RUN protoc -I=. echo.proto \
	--js_out=import_style=commonjs:./commonjs-example \
	--grpc-web_out=import_style=commonjs,mode=grpcwebtext:./commonjs-example

And it seems that the whole stream body was received it at once..

I'm not sure yet if this is a limitation of our Envoy proxy or the JS client (seems like it shouldn't be the case since it's working for you?), but it doesn't appear to be working out of the box..

I need more debugging to understand what's truly going on, and verify if it's a browser/proxy limitation, or simply a bug, etc..