PHP 获取ip地址

public function getIP()
    {
        if (getenv("HTTP_CLIENT_IP"))
            $ip = getenv("HTTP_CLIENT_IP");
        else if(getenv("HTTP_X_FORWARDED_FOR"))
            $ip = getenv("HTTP_X_FORWARDED_FOR");
        else if(getenv("REMOTE_ADDR"))
            $ip = getenv("REMOTE_ADDR");
        else
            $ip = "UNKNOWN";
        return $ip;
    }