Clear the send queue when the other peer closes the connection

[lpinca]

Description

permessage-deflate is enabled and one of the peer has queued data waiting for it to be compressed, framed and sent over the connection. Meanwhile, the other peer closes the connection. What should we do?

Currently the data processing keeps going as nothing happened and the callback of each enqueued send operation, if any, is invoked with an error when trying to write to the closed socket (after the 'close' event). This a waste of computational power. There is no reason to compress, frame, and try to send the data if we know beforehand that the socket is closed.

One way to work around the issue is to remove the enqueued send operations after invoking their callback with an error and before emitting the 'close' event.
The issue happens when a message is already being compressed so the queue should be cleared when compression completes.

Thoughts?

Reproducible in:

version: >=0.6.0
Node.js version(s): all
OS version(s): all

Steps to reproduce:

const crypto = require('crypto');
const WebSocket = require('ws');

const wss = new WebSocket.Server({
  perMessageDeflate: { threshold: 0 },
  port: 3000
}, () => {
  const ws = new WebSocket('ws://localhost:3000');

  ws.on('open', () => {
    setTimeout(() => ws.terminate(), 10);
  });
});

wss.on('connection', (ws) => {
  ws.on('close', () => console.log('close'));

  const data = crypto.randomBytes(1024);

  for (let i = 0; i < 1024; i++) {
    ws.send(data, (err) => {
      if (err) console.log(err);
    });
  }
});