$_SERVER

function http()
{
return (isset($_SERVER[‘HTTPS‘]) && (strtolower($_SERVER[‘HTTPS‘]) != ‘off‘)) ? ‘https://‘ : ‘http://‘;
}

function get_domain()
{
/* 协议 */
$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;
}

$_SERVER

原文：https://www.cnblogs.com/hehexu/p/9941529.html