code: def connection_open(self) -> None:
          
          # 4.1. The WebSocket Connection is Established.
          assert self.state is State.CONNECTING
          self.state = State.OPEN
          logger.debug("%s - state = OPEN", self.side)
          # Start the task that receives incoming WebSocket messages.
          self.transfer_data_task = self.loop.create_task(self.transfer_data())
          # Start the task that sends pings at regular intervals.
          self.keepalive_ping_task = self.loop.create_task(self.keepalive_ping())
          # Start the task that eventually closes the TCP connection.
          self.close_connection_task = self.loop.create_task(self.close_connection())
docs: Callback when the WebSocket opening handshake completes.
  
          Enter the OPEN state and start the data transfer phase.