gRPC-Web support

[dflemstr]

I'd like to use tower with the gRPC-Web protocol.

Some use-cases that I'm thinking about in order of priority:

• Create a server in Rust that can be used by existing gRPC-Web client implementations (e.g. from browsers/node.js and Typescript)
• Create a client in Rust that can be compiled to WebAssembly (and interop via for example stdweb and the Webpack native wasm loader) and used in the browser.
• Support multiplexing ordinary gRPC and gRPC-Web on the same port.
• Nice-to-have: Support multiplexing some other web service (e.g. static file server) for requests that are not gRPC or gRPC-Web.

I'd like to discuss how to do this in a nice way. Here's what I was (maybe naïvely) thinking:

• Create tower-grpc-web containing a struct GrpcWebService that wraps another tower::Service using http::Request and http::Response, and transparently changes the encoding on the fly. This can then be used with tower-grpc generated clients/servers directly.
• Create support for tower+HTTP/1
• Build some tower glue to the WhatWG fetch API
• Create a multiplexer that can bind a single port and dispatch to different tower::Services depending on if the request is HTTP/1 or HTTP/2 and depending on headers like Content-Type.

Does this sound sane? Are there any existing components I could leverage? Is there a smarter way to do this?

[carllerche]

Yeah, it sounds roughly sane. I don't know that much about the grpc-web protocol. I also am not entirely sure what the fetch API is in practice.

If you want to experiment with something, maybe try a spike in an external repo and we can go from there.

[dflemstr]

Just to update this issue, I'm still working on this but am stuck fixing lower-level components such as the compiler support for wasm interacting with webpack. If anybody else is reading this issue, please ping me if you are interested in helping out!

[ghost]

+1 from me.
I use the improbable one with golang and would jump onto a rust version in an instant.

[ghost]

Btw the scope is sane. It's exactly what I do in golang currently.
Golangs wasm is still a bit rough around the edges, but the rust wasm is pretty solid, so it's definitely worthwhile pursuing this

[johanbrandhorst]

Just chiming in that I've thought about doing this asynchronously but that it would be cool to contribute to an existing effort. I've got a pretty good idea of how the gRPC-Web protocol works and how to use the Fetch API with it, but I'm very inexperienced with Rust. Please let me know how I can help!

[johanbrandhorst]

I don't think it's worthwhile implementing a wrapper around the Improbable grpc-web client, just write the whole thing in WASM, it's not really a large amount of logic and you can probably copy most of it from the open source client.

[lalomartins]

I'm not sure where the talk about WASM is coming from, that's IMO out of scope — we don't need a new grpc-web client-side implementation and if we did it would have little to do with tower. As I understand it the idea here is to add support for the server side grpc-web protocol to tower, so that I can write a server in Rust with tower and that server will support both regular grpc clients and grpc-web clients.

Edit: ok, the original request does talk about both. But I think if a client-side WASM implementation is wanted at all, it should probably be a separate ticket or even a separate project.

[johanbrandhorst]

Great, thanks for the clarification. I understand the distinction. In any case @dflemstr, please reach out (@JohanBrandhorst on twitter) because I'd love to collaborate on a client implementation. The server side, again, should be fairly trivial and translatable from the Improbable gRPC-Web proxy.

[dflemstr]

@johanbrandhorst I decided to spend my time on other things while waiting for the tower ecosystem to mature a bit before spending more time on this. Maybe now is a good time to continue.

What I would like to have is a detailed understanding of how to translate a gRPC-Web request to gRPC and vice versa. Right now there is only the Go reference implementation which is a bit hard to follow (it mutates request objects here and there and has an interesting way of stashing away request trailers etc).

Given that we have that, a tower wrapper should be easy to add.

I am also interested in a client implementation, that can be compiled to WASM for use client side. This enables a lot of code sharing between server and client which is quite nice.

[mash-graz]

a working implementation of gRPC-web in rust would be indeed very useful, but more satisfying support for twirp (= http1.1 protobuf+json fallback for simple browser access) in tower could be even more desirable.

[johanbrandhorst]

@mash-graz I think that could be covered under a separate issue.

[mash-graz]

@johanbrandhorst done! => #185

[micfan]

I have just tested this "unofficial" grpc-web repo, it move far than the official grpc-web. The improbable-eng/grpc-web can work with Golang gRPC server.

A WSAM Rust client runing in Browser, connecting to server via HTTP2, exposing API to JS/TS... I'm frustrated, that is a huge project

[johanbrandhorst]

As mentioned in hyperium/tonic#31, I've created a sandbox repo to play around with prototyping this: https://github.com/johanbrandhorst/rust-grpc-web-wasm-test. It's currently just a Go gRPC server with the gRPC-Web proxy, the idea is that we can manually try to implement a first pass on a Rust WASM client. See the README for more information.