Add upgrade event support

[hugmanrique]

This would make this library more similar to the HTTP Node API which would make switching to this lib much easier. The event callback has the following params:

• Response turbo-http object
• Socket turbo-net object
• Headers Map

I think having the request and response objects would be ideal. You can already grab the socket and the headers from the req object.

Here's the Node.js docs

[doesdev]

Based on some quick experimentation in hacking support in at the implementation level, it's a bit more complicated than this would suggest. the 3rd argument is actually a Buffer which, based on this, should be "the first packet of the upgraded stream".

But, I've not had much success hacking it in so far. Gonna mess around with it some more and report back if/when I get something working.

[doesdev]

Okay, through some hacking I did get WebSockets upgrade working with ws, with caveats. In addition to the server emitting an upgrade event here are the bits that I found needing to happen in order to make it work with ws.

• req.headers needs to be a plain ole object of header key values
• socket.write needs UTF-8 string support instead of just Buffer
• a couple methods need added to socket, namely setNoDelay and setTimeout
• I simply passed in Buffer.alloc(0) for argument 3 of the upgrade event emission

All of that results in being able to upgrade to WebSockets with ws. That by no means implies that anything I've done in these hacks would be expected to work with anything else or that it even works properly. It seems to work properly enough to pass my tests, but that doesn't mean what I did to get it working is anything near an actual solution.

If I am able to get to something I'm more confident about I'll do a PR (here and in turbo-net).

Here's what the hacky garbage I put together looks like:

function handleUpgrade (server, req, res) {
  if (req.getHeader('connection') !== 'Upgrade') return false
  req.headers = {}
  for (const [k, v] of req.getAllHeaders()) { req.headers[k] = v }

  const write = req.socket.write
  req.socket.write = function (d, len, cb) {
    return write.call(
      req.socket,
      Buffer.isBuffer(d) ? d : Buffer.from(d, 'utf8'),
      len,
      cb
    )
  }
  req.socket.setNoDelay = req.socket.setTimeout = () => {}

  server.emit('upgrade', req, req.socket, Buffer.alloc(0))
  return true
}

// somewhere in a request handler, which must also have access to the server object
function handleRequest (req, res) {
  if (handleUpgrade(server, req, res)) return
  // ...
}