get_ip_address.php

<?php
/**
 * Return the client's IP address.
 *
 * Returns the IP address if found, an empty string if not. The
 * output is santized via FILTER_VALIDATE_IP.
 *
 * The algorithm uses the HTTP_CLIENT_IP and HTTP_X_FORWARDED_FOR
 * globals to infer the IP address; if they are not available (as
 * it is the case in most cases), it uses the REMOTE_ADDR global.
 *
 * Do not use this function to grant access or privileges to
 * IP addresses, because the HTTP_CLIENT_IP and
 * HTTP_X_FORWARDED_FOR globals can be easily spoofed.
 *
 * On the other hand, the REMOTE_ADDR global is very difficult
 * to spoof. However, when the client is beyond a proxy, it isn't
 * necessarily the correct IP.
 *
 * See here for more details: http://stackoverflow.com/questions/
 * 3003145/how-to-get-the-client-ip-address-in-php
 *
 * Created by Guido W. Pettinari on 05.09.2016.
 * Latest version here:
 * https://gist.github.com/coccoinomane/4c420776dc16d80ea772aff06d3e1ef4
 */
function getClientIp ()
{

    if (isset($_SERVER['HTTP_CLIENT_IP']) && !empty($_SERVER['HTTP_CLIENT_IP'])) {

        $ip = $_SERVER['HTTP_CLIENT_IP'];

    } elseif (isset($_SERVER['HTTP_X_FORWARDED_FOR']) && !empty($_SERVER['HTTP_X_FORWARDED_FOR'])) {

        $ip = $_SERVER['HTTP_X_FORWARDED_FOR'];

    } elseif (isset($_SERVER['REMOTE_ADDR']) && !empty($_SERVER['REMOTE_ADDR'])) {

        $ip = $_SERVER['REMOTE_ADDR'];

    }
    else {
        
        return '';
        
    }

    return filter_var($ip, FILTER_VALIDATE_IP);

}