phpecshop获取端口的疑问

   if (isset($_SERVER[&＃039;SERVER_PORT&＃039;]))            {                $port = &＃039;:&＃039; . $_SERVER[&＃039;SERVER_PORT&＃039;];                if ((&＃039;:80&＃039; == $port && &＃039;http://&＃039; == $protocol) || (&＃039;:443&＃039; == $port && &＃039;                          https://&＃039; == $protocol))                {                    $port = &＃039;&＃039;;                }            }

其中

  if ((&＃039;:80&＃039; == $port && &＃039;http://&＃039; == $protocol) ||        (&＃039;:443&＃039; == $port && &＃039;https://&＃039; == $protocol))                {                    $port = &＃039;&＃039;;                }

这段代码的意思作用是什么？ 如果条件成立，为什么要把$port 设置为空？

整个函数的代码：

 function get_domain()    {        /* 协议 */        $protocol = $this->http();        /* 域名或IP地址 */        if (isset($_SERVER[&＃039;HTTP_X_FORWARDED_HOST&＃039;]))        {            $host = $_SERVER[&＃039;HTTP_X_FORWARDED_HOST&＃039;];        }        elseif (isset($_SERVER[&＃039;HTTP_HOST&＃039;]))        {            $host = $_SERVER[&＃039;HTTP_HOST&＃039;];        }        else        {            /* 端口 */            if (isset($_SERVER[&＃039;SERVER_PORT&＃039;]))            {                $port = &＃039;:&＃039; . $_SERVER[&＃039;SERVER_PORT&＃039;];                if ((&＃039;:80&＃039; == $port && &＃039;http://&＃039; == $protocol) || (&＃039;:443&＃039; == $port && &＃039;https://&＃039; == $protocol))                {                    $port = &＃039;&＃039;;                }            }            else            {                $port = &＃039;&＃039;;            }            if (isset($_SERVER[&＃039;SERVER_NAME&＃039;]))            {                $host = $_SERVER/本2文来源gao@.dai.ma.com搞@^&[email protected]搞gaodaima代码[&＃039;SERVER_NAME&＃039;] . $port;            }            elseif (isset($_SERVER[&＃039;SERVER_ADDR&＃039;]))            {                $host = $_SERVER[&＃039;SERVER_ADDR&＃039;] . $port;            }        }        return $protocol . $host;    }