docs: def open(self):
          """ method which is called every time a new client connects """
          print 'Connection opened.'
          
          # retrieve user_id if specified
          user_id = self.get_argument("user_id", None)
          # add client to list of connected clients
          self.add_client(user_id)
          # welcome message
          self.send_message("Welcome to nodeshot websocket server.")
          # new client connected message
          client_count = len(self.get_clients().keys())
          new_client_message = 'New client connected, now we have %d %s!' % (client_count, 'client' if client_count <= 1 else 'clients')
          # broadcast new client connected message to all connected clients
          self.broadcast(new_client_message)
          
          print self.channels['private']