Get a user's IP address, also if you are behind a proxy server

getIp.php

<?php

/**
 * Return the remote IP address, also if you are behind a proxy server
 */
function getIp()
{
    if (isset($_SERVER)) {

        if (isset($_SERVER["HTTP_X_FORWARDED_FOR"])) {
            return $_SERVER["HTTP_X_FORWARDED_FOR"];
        }

        if (isset($_SERVER["HTTP_CLIENT_IP"])) {
            return $_SERVER["HTTP_CLIENT_IP"];
        }

        return $_SERVER["REMOTE_ADDR"];
    }

    if (getenv('HTTP_X_FORWARDED_FOR')) {
        return getenv('HTTP_X_FORWARDED_FOR');
    }

    if (getenv('HTTP_CLIENT_IP')) {
        return getenv('HTTP_CLIENT_IP');
    }

    return getenv('REMOTE_ADDR');

}