def host(self) -> str:
        """
        获取 host + port, 如果开启 proxy 开关。使用 X-Forwarded-Host 头
        """
        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