php获取真实ip地址原理及实现

function get_real_ip(){
if(getenv("HTTP_CLIENT_IP") && strcasecmp(getenv("HTTP_CLIENT_IP"), "unknow")){
$ip = getenv("HTTP_CLIENT_IP");
}else if(getenv("HTTP_X_FORWARDED_FOR") && strcasecmp(getenv("HTTP_X_FORWARDED_FOR"), "unknow")){
$ip = getenv("HTTP_X_FORWARDED_FOR");
}else if(getenv("REMOTE_ADDR") && strcasecmp(getenv("REMOTE_ADDR"), "unknow")){
$ip = getenv("REMOTE_ADDR");
}else if(isset($_SERVER["REMOTE_ADDR"]) && $_SERVER["REMOTE_ADDR"] && strcasecmp($_SERVER["REMOTE_ADDR"],"unknow")){
$ip = $_SERVER["REMOTE_ADDR"];
}else{
$ip = "unknow";
}
return $ip;
}
echo get_real_ip();
?>