Add a WsSession#id or provide a way to set one

The way to track a WsSession feels a bit too primitive. Essentially you have to put the WsSession into a Map<WsSession, UUID> in order to do stuff like on disconnect of the socket perform cleanup of resources that may have been created during the session (keyed by incoming connection).

fun main(args: Array<String>) {
  val app = Javalin.create().port(7000)

  val connectionCount = AtomicInteger(0)
  val connected = hashMapOf<WsSession, UUID>()

  app.ws("/ws") { ws ->
    
    ws.onConnect { sess ->
      sess.idleTimeout = Duration.ofSeconds(5).toMillis()

      val clientId = UUID.randomUUID()
      val currentConnectionCount = connectionCount.incrementAndGet()
      connected += Pair(sess, clientId)

      logger.info("connection established 'client = {}'", clientId)
      logger.info("connection 'count = {}'", currentConnectionCount)
    }

    ws.onClose { sess, code, reason ->
      val currentConnectionCount = connectionCount.decrementAndGet()
      val clientId = connected[sess]

      // Imagine some cleanup logic here for the particular client. without a tracked ID that is impossible. 

      logger.info("connection closed 'client = {}', 'code = {}' 'reason = {}'", clientId, code, reason)
      logger.info("connection 'count = {}'", currentConnectionCount)
    }
  }

  app.start()
}

Possibly related to GH-104

[plombardi89]

Opened GH-120 to track dev progress

[tipsy]

Closed by #120