code: def connection_made(self, transport: asyncio.transports.Transport):
          
          self._transport = transport
          self._remote_host = self._transport.get_extra_info('peername')
          self._extra = {"client": str(self._remote_host)}
          self.connections.add(self)
  
          self._stream_reader = asyncio.StreamReader(loop=self._loop)
          self._stream_writer = asyncio.StreamWriter(transport, self,
                                                     self._stream_reader,
                                                     self._loop)
          super().connection_made(transport)
          if self.timeout:
              self._timeout_handler = self._loop.call_soon(
                  self.timeout_callback)
          self._handlertask = asyncio.ensure_future(self.query_handler())
          if self.debug:
              access_logger.info("connected", extra=self._extra)
docs: 连接建立起来触发的回调函数.
  
          用于设定一些参数,并将监听任务放入事件循环,如果设置了timeout,也会将timeout_callback放入事件循环
  
          Parameters:
              transport (asyncio.Transports): - 连接的传输对象