code: async def read(self):
          
          try:
              data = await self._stream_reader.readuntil(self.SEPARATOR)
          except asyncio.IncompleteReadError:
              self.connection_lost()
          else:
              query = self.decoder(data)
              if self.debug:
                  access_logger.info("get query: {}".format(
                      query
                  ), extra=self._extra)
              return query
docs: 读取请求,并转化为python的字典结构.如果读入了EOF,那么触发回调函数connection_lost.