Support `permessage-deflate` for websockets

[stopachka]

Hey team!

I've been using ring-undertow-adapter and it's been great! One feature we needed recently, is to enable permessage-deflate for websockets. To do this, we patched ring.adapter.undertow/ws-request like so:

(defn ws-request [^HttpServerExchange exchange ^IPersistentMap headers ^WebSocketConnectionCallback callback]
  (let [handler (->  (WebSocketProtocolHandshakeHandler. callback)
                     (.addExtension (PerMessageDeflateHandshake. true 6)))]
    (when headers
      (set-headers (.getResponseHeaders exchange) headers))
    (.handleRequest handler exchange)))

This resulted in quite a nice perf bump for slow connections.

Would you be interested in upstreaming some option for permessage-deflate? Happy to pop in a PR. Maybe we can include this as an option in the :undertow/websocket map.

[nikolap]

Hey! This looks good, thanks for the improvement. I'd like the idea of it as a param. Would you be interested in pushing a PR for it?