View file sys/inc/ajaxRequest.php

<?php
function isAjax()
{
    $server = getenv('HTTP_X_REQUESTED_WITH');
    $server = ($server !== false ? strtolower($server) : null);
    return $server === 'xmlhttprequest';
}

if (isAjax() === false)
    exit(header('Location: /'));
DEFINE('H', getenv('DOCUMENT_ROOT') . '/');
include_once H . 'sys/inc/start.php';
include_once H . 'sys/inc/sess.php';
include_once H . 'sys/inc/settings.php';
include_once H . 'sys/inc/db_connect.php';
header("Connection: close");
Header("Cache-Control: no-cache, must-revalidate"); // говорим браузеру что-бы он не кешировал эту страницу
Header("Pragma: no-cache");
header("Content-type: application/json");
$user = false;
// Определение юзера
if (isset($_SESSION['id_user']) && is_numeric($_SESSION['id_user'])) {
    $user = mysql_fetch_assoc(mysql_query("SELECT `id` FROM `user` WHERE `id` = '" . $_SESSION['id_user'] . "' LIMIT 1"));
}
if (empty($user) === true)
    exit(header('Location: /'));
?>