php 取得當前的域名 實現代碼

<?php

    /**
     * 取得當前的域名
     *
     * @access  public
     *
     * @return  string      當前的域名
     */
    function get_domain()
    {
        /* 協議 */
        $protocol = $this->http();
       
        /* 域名或IP地址 */ 
        if (isset($_SERVER['HTTP_X_FORWARDED_HOST']))
        {
            $host = $_SERVER['HTTP_X_FORWARDED_HOST'];
        }
        elseif (isset($_SERVER['HTTP_HOST']))
        {
            $host = $_SERVER['HTTP_HOST'];
        }
        else
        {
            /* 端口 */
            if (isset($_SERVER['SERVER_PORT']))
            {
                $port = ':' . $_SERVER['SERVER_PORT'];

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

            if (isset($_SERVER['SERVER_NAME']))
            {
                $host = $_SERVER['SERVER_NAME'] . $port;
            }
            elseif (isset($_SERVER['SERVER_ADDR']))
            {
                $host = $_SERVER['SERVER_ADDR'] . $port;
            }
        }

        return $protocol . $host;
    }
?>