判断用户是否使用代理的PHP代码

<?php
/*****************************************************
*
*    isProxy
*    check whether client is under Proxy or not
*    $_SERVER['HTTP_X_FORWARDED_FOR'] is pivotal here
*    if client is under Proxy, returns true
*    if client is not under Proxy, returns false
*    
*****************************************************/
 
function isProxy(){
    return (!empty($_SERVER['HTTP_X_FORWARDED_FOR'])) ? true : false;
}
?>