PHP IP Fix behind Reverse Proxies (CloudFlare and Varnish)

ip_fix.php

<?php
// fix CloudFlare/Varnish IPs
function transform_cf(&$ip){
	if(!isset($_SERVER['HTTP_CF_CONNECTING_IP']))
		return;

	$cf_cidrs = array(
		"103.21.244.0/22",
		"103.22.200.0/22",
		"103.31.4.0/22",
		"104.16.0.0/12",
		"108.162.192.0/18",
		"141.101.64.0/18",
		"162.158.0.0/15",
		"172.64.0.0/13",
		"173.245.48.0/20",
		"188.114.96.0/20",
		"190.93.240.0/20",
		"197.234.240.0/22",
		"198.41.128.0/17",
		"199.27.128.0/21",
		
		// IPv6 not supported yet...
	);

	foreach($cf_cidrs as $cidr){
		list($subnet, $mask) = explode('/', $cidr);
		// this works for IPv4, but not IPv6
		if (/*!$mask ||*/ ip2long($ip) >> $mask == ip2long($subnet) >> $mask){
			$ip = $_SERVER['HTTP_CF_CONNECTING_IP'];
			return; // break;
		}
	}
	// no change
}

function transform_varnish(&$ip){
	// Again, IPv6 doesn't work here...
	$ipl = ip2long($ip);
	if(!($ipl >> 24 == 10 || // 10.0.0.0/8
		$ipl >> 24 == 127 || // 127.0.0.0/8
		$ipl >> 20 == 0xAC1 || // 172.16.0.0/12
		$ipl >> 16 == 0xC0A8 // 192.168.0.0/16
		))
		return;

	if(isset($_SERVER['HTTP_X_REMOTE_ADDR']))
		$ip = $_SERVER['HTTP_X_REMOTE_ADDR'];

	elseif(isset($_SERVER['HTTP_X_FORWARDED_FOR']))
		$ip = explode(', ', $_SERVER['HTTP_X_FORWARDED_FOR'])[0];

	// no change
}

transform_varnish($_SERVER['REMOTE_ADDR']); // local Varnish
transform_cf($_SERVER['REMOTE_ADDR']); // CloudFlare