How about impl AsyncRead/AsyncWrite for WebSocket?

[najamelan]

Motivation

Would allow frontend and backend code to communicate in an abstract manner on an async Stream. It allows code reuse and prevents every application to have to implement this on top of the existing websocket api

Proposed Solution

Add impl AsyncRead/AsyncWrite to websocket

Alternatives

Allow upgrading an Http connection to an AsyncRead/AsyncWrite without websockets. I have no idea what the implementation of this would look like, and if it's even possible without websockets.

That being said, this alternative would be preferable I think. It means we don't need WS on the server either, just an upgraded http connection.

Additional Context

I kind of need this. If need be I don't mind attempting to implement this myself. If this is deemed a good solution, is there any mentoring possible to hint the way?

[alexcrichton]

Thanks for the report! I've transferred this over to the gloo repository here from the wasm-bindgen repository becaues the web_sys crate is intended to be a low level binding to web APIs, but this would be perfect for the gloo project!

[najamelan]

@alexcrichton ok, that's cool. Currently what I'm looking at is using the set_onmessage on a websocket. If I understand well, the way to do this is by using a wasm-bindgen::Closure to create the callback Function.

I would have to expose something that has connect( url ) and returns an async Stream... Does that sound like the right approach to you? Does that seem realistic or do you see some technical blockers for this?

I also wonder, if I understood well, data from javascript has to be copied into the wasm memory. Is there a way to avoid this extra copy on the data that comes in from the websocket?

[fitzgen]

See also https://github.com/rustwasm/gloo/issues/7

[najamelan]

I'm making good progress on this I think, but I need a bit of advice. There isn't all that much example code or docs for this stuff. I can build streams that yield MessageEvent, but then the only way I see from the docs to get the data out of there and in rust is by using into_serde. This will use json stringify... I doubt that's what we want. There seem to be ways to share memory pointers from javascript like with WebAssembly.Memory and such, but what is the best way to get a bytearray out of a websocket connection into rust with wasm-bindgen, wasm-pack? Do I just write custom javascript for this? Given that this is a rust library, how do we ship the js?

[najamelan]

Never mind, I found how to make a UInt8Array out of it and use copy_to. I suppose it is currently impossible to receive data directly in the wasm memory to avoid copying?

[alexcrichton]

In the spirit of abstraction it might be pretty cool to get a stream of MessageEvent structures from a websocket which could be further layered with abstractions to parse MessageEvent as JSON and things like that perhaps? I don't have too much of an opinion here, just some random thoughts!

I'm not too familiar with the websocket interface, but if you can specify a buffer to fill in then you can fill in wasm memory directly, otherwise you'll have to copy it in afterwards

[najamelan]

Currently I have a sink/stream working that takes and yields Vec<u8>. The code is clean, documented and I'm looking into the unit testing now. Next I will add a tokio AsyncRead and AsyncWrite onto that. Document and test that and put it on github as proof of concept for review (tonight or tomorrow). After review I'm sure there will be some more cleanup to be done and after that we can discuss adding extra features like a stream of MessageEvents, text messages (currently only does binary), ...

[najamelan]

Ok, it took a few days longer than I had hoped, but here it is:

https://github.com/najamelan/wasm_websocket_stream

It would be nice if people could review this code. There are review questions in the readme. Please open issues on the repository for review feedback.