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<?php

/**
 * Returns the IP of the user.
 *
 * @return string|false
 */
function getIP() {
    foreach (array('HTTP_CLIENT_IP', 'HTTP_X_FORWARDED_FOR', 'HTTP_X_FORWARDED', 'HTTP_X_CLUSTER_CLIENT_IP', 'HTTP_FORWARDED_FOR', 'HTTP_FORWARDED', 'REMOTE_ADDR') as $key) {
        $val = filter_input(INPUT_SERVER, $key);

        if (empty($val)) {
            continue;
        }

        $ips = array_map('trim', explode(',', $val));

        foreach ($ips as $ip) {
            if (filter_var($ip, FILTER_VALIDATE_IP, FILTER_FLAG_NO_PRIV_RANGE | FILTER_FLAG_NO_RES_RANGE) !== false) {
                return $ip;
            }
        }
    }

    return false;
}