很简单，就是一个函数。

<?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;
}