code: def host(self) -> str:
          
          host = cast(Optional[str], None)
          if self.proxy and 'X-Forwarded-Host' in self._headers:
              xhost = cast(Optional[str], self.get('X-Forwarded-Host'))
              if xhost is not None:
                  host = xhost.split(",")[0].strip()
          host = host or cast(str, self.get('Host'))
          return host
docs: 获取 host + port, 如果开启 proxy 开关。使用 X-Forwarded-Host 头