Add grpc-web proxy for non-http2 clients

[clevinson]

Create flag (enabled by default) to launch the grpc-web proxy for non-HTTP2 grpc web clients

Ref #5921

[alexanderbez]

What is a gRPC web proxy in this context and how does it differ from the gRPC HTTP gateway?

[ethanfrey]

I know this sounds like a nice feature to add, but I would be hesitant to add yet another server until there is a clear need (please link the client side project that cannot work without this). Every additional server is more ops overhead, as well as code maintenance.

grpc-web supports all modern browsers (since early 2019 or so) and uses HTTP/2.0. It does everything according to the grpc spec except client side streaming, which I doubt we use (and definitely would not be supported by the web proxy).

How about some explanation of concrete use cases here?

[amaury1093]

I think there's some confusion in the title, we are adding exactly the grpc-web you linked. Their README lists these 2 items:

• grpcweb: a go package that wraps a gRPC server
• grpcwebproxy: a standalone binary that wraps an arbitrary gRPC server

It's the first one that aleem's implementing in #8077. Somehow we still call it "proxy".

[amaury1093]

I wasn't aware HTTP2 was supported by 95% of browsers today. In this case, can a browser talk directly to a gRPC server (I thought no)? If yes, why do we even need grpc-web?

[ethanfrey]

Ah, re-reading the docs. Maybe that is needed for HTTP/2.0 as well.
I thought it was only needed for backwards compatibility.

I would be interesting to test this out sometime. With CosmJS, we use the grpc types but talk directly to tendermint rpc, as that is well defined and working since rc1 and before. We have no bandwidth to test out the grpc server with this, but if someone from your team does, you can probably use most of the types from it, and I'm sure you can get some pointers on discord.