PHP 获取当前网址协议（各种服务器通用）

PHP 获取当前网址协议 (HTTP/HTTPS)

if(isset($_SERVER['HTTP_X_CLIENT_SCHEME'])){
    $scheme = $_SERVER['HTTP_X_CLIENT_SCHEME'] . '://';
}elseif(isset($_SERVER['REQUEST_SCHEME'])){
    $scheme = $_SERVER['REQUEST_SCHEME'] . '://';
}else{
    $scheme = 'http://';
}
echo $scheme; // http:// or https://