bug/feat: implement WebSocket::bufferedAmount / backpressure

[threepointone]

Hiya! I just noticed that bufferedAmount isn't implemented on WebSocket (https://developer.mozilla.org/en-US/docs/Web/API/WebSocket/bufferedAmount). It's not a perfect solution for backpressure, but it would be better than not having it at all.

In the future, what is your opinion on proposals like WebSocketStream? https://github.com/ricea/websocketstream-explainer/

[kentonv]

I think bufferedAmount could trivially be implemented to add up the size of all messages in outgoingMessages. cc @MellowYarker who did most of the recent WebSocket improvements.

WebSocketStream seems like a good idea, and given that it reuses the Streams API it might not be too difficult to implement? @jasnell might have an opinion. But I guess it's not a standard yet.

[jasnell]

Just spotted this, sorry for the late response. WebSocketStream is nicer and is definitely on my radar but I think it needs to bake a bit longer before we can safely consider it.

[rikka0w0]

Just spotted this, sorry for the late response. WebSocketStream is nicer and is definitely on my radar but I think it needs to bake a bit longer before we can safely consider it.

Also, I would suggest that, we should not only allow the use of new WebSocketStream() as a WebSocket client to connect to a remote server, but also allow the incoming request to be upgraded to a "WebSocketStream-pair". If we can somehow create a WebSocketStream out of a "WebSocket", that will be even better.