WebSocket permessage-deflate

[Mixfair]

• Julia 1.7.2
• HTTP.jl 0.9.17

Hi,

It would be great if HTTP.Websockets could support the permessage-deflate extension, which provides compression for websocket frames. It's described in RFC 7692 and is currently implemented client-side in browsers.

For example, endpoint:

using HTTP

url = "wss://stream.binance.com:9443/stream?streams=adausdt@depth20@100ms/btcusdt@depth20@100ms"
headers = [
   "sec-websocket-extensions" => "permessage-deflate",
]

HTTP.WebSockets.open(url, headers = headers) do ws
   while true
       data = readavailable(ws)
       println(String(data))
   end
end 

I have already implemented this feature locally with CodecZlib. If possible it would be great to see this feature by default

[quinnj]

Sigh.....I thought I'd at least get to do the 1.0 release w/ the overhauled WebSockets code that "actually works" before getting a request for this, but that's how it goes sometimes!

Yeah, I don't think this should be too hard to support with the redesigned WebSockets code on HTTP#master. I've been planning to do this as a post-1.0 task however since I it shouldn't involve any breaking changes, so it's easy to add as an enhancement for, e.g., 1.1 release.

@Mixfair, if you'd like to have a go at implementing this, I'd be happy to provide guidance!