Gazelle/sections/tools/services/get_host.php

<?
if(isset($_SERVER['http_if_modified_since'])) {
	header("Status: 304 Not Modified");
	die();
}

header('Expires: '.date('D, d-M-Y H:i:s \U\T\C',time()+3600*24*120)); //120 days
header('Last-Modified: '.date('D, d-M-Y H:i:s \U\T\C',time()));

if(!check_perms('users_view_ips')) { die('Access denied.'); }

$Octets = explode(".", $_GET['ip']);
if(
	empty($_GET['ip']) ||
	!preg_match('/\d{1,3}\.\d{1,3}\.\d{1,3}\.\d{1,3}/', $_GET['ip']) ||
	$Octets[0] < 0 ||
	$Octets[0] > 255 ||
	$Octets[1] < 0 ||
	$Octets[1] > 255 ||
	$Octets[2] < 0 ||
	$Octets[2] > 255 ||
	$Octets[3] < 0 ||
	$Octets[3] > 255 ||
	$Octets[0] == 127 ||
	($Octets[0] == 192 && $Octets[1] == 168)
) {
	die('Invalid IP.');
}

$Host = Tools::lookup_ip($_GET['ip']);

if ($Host === '') {
	trigger_error("Tools::get_host_by_ajax() command failed with no output, ensure that the host command exists on your system and accepts the argument -W");
} elseif ($Host === false) {
	print 'Could not retrieve host.';
} else {
	print $Host;
}