<?php
/**
 * Retrieves the best guess of the client's actual IP address.
 * Takes into account numerous HTTP proxy headers due to variations
 * in how different ISPs handle IP addresses in headers between hops.
 *
 * Source: https://gist.github.com/cballou/2201933
 *
 */
function get_ip_address() {
	// check for shared internet/ISP IP
	if (!empty($_SERVER['HTTP_CLIENT_IP']) && validate_ip($_SERVER['HTTP_CLIENT_IP'])) {
		return $_SERVER['HTTP_CLIENT_IP'];
	}

	// check for IPs passing through proxies
	if (!empty($_SERVER['HTTP_X_FORWARDED_FOR'])) {
		// check if multiple ips exist in var
		if (strpos($_SERVER['HTTP_X_FORWARDED_FOR'], ',') !== false) {
			$iplist = explode(',', $_SERVER['HTTP_X_FORWARDED_FOR']);
			foreach ($iplist as $ip) {
				if (validate_ip($ip))
					return $ip;
			}
		} else {
			if (validate_ip($_SERVER['HTTP_X_FORWARDED_FOR']))
				return $_SERVER['HTTP_X_FORWARDED_FOR'];
		}
	}
	if (!empty($_SERVER['HTTP_X_FORWARDED']) && validate_ip($_SERVER['HTTP_X_FORWARDED']))
		return $_SERVER['HTTP_X_FORWARDED'];
	if (!empty($_SERVER['HTTP_X_CLUSTER_CLIENT_IP']) && validate_ip($_SERVER['HTTP_X_CLUSTER_CLIENT_IP']))
		return $_SERVER['HTTP_X_CLUSTER_CLIENT_IP'];
	if (!empty($_SERVER['HTTP_FORWARDED_FOR']) && validate_ip($_SERVER['HTTP_FORWARDED_FOR']))
		return $_SERVER['HTTP_FORWARDED_FOR'];
	if (!empty($_SERVER['HTTP_FORWARDED']) && validate_ip($_SERVER['HTTP_FORWARDED']))
		return $_SERVER['HTTP_FORWARDED'];

	// return unreliable ip since all else failed
	return $_SERVER['REMOTE_ADDR'];
}

/**
 * Ensures an ip address is both a valid IP and does not fall within
 * a private network range.
 *
 * Source: https://gist.github.com/cballou/2201933
 *
 */
function validate_ip($ip) {
	if (strtolower($ip) === 'unknown')
		return false;

	// generate ipv4 network address
	$ip = ip2long($ip);

	// if the ip is set and not equivalent to 255.255.255.255
	if ($ip !== false && $ip !== -1) {
		// make sure to get unsigned long representation of ip
		// due to discrepancies between 32 and 64 bit OSes and
		// signed numbers (ints default to signed in PHP)
		$ip = sprintf('%u', $ip);
		// do private network range checking
		if ($ip >= 0 && $ip <= 50331647) return false;
		if ($ip >= 167772160 && $ip <= 184549375) return false;
		if ($ip >= 2130706432 && $ip <= 2147483647) return false;
		if ($ip >= 2851995648 && $ip <= 2852061183) return false;
		if ($ip >= 2886729728 && $ip <= 2887778303) return false;
		if ($ip >= 3221225984 && $ip <= 3221226239) return false;
		if ($ip >= 3232235520 && $ip <= 3232301055) return false;
		if ($ip >= 4294967040) return false;
	}
	return true;
}