ShareCode PHP hạn chế tấn công DDOS

<?php
error_reporting(E_ALL ^ E_WARNING);
define('ROOTPATH', dirname(__FILE__) . DIRECTORY_SEPARATOR);
class core
{
    public static $ip; // Biến địa chỉ IP
    public static $ip_via_proxy = 0; // Biến địa chỉ IP tĩnh
    public static $ip_count = array(); // Đếm số địa chỉ IP
 
    private $flood_chk = 1; // Enabling - Disabling IP in flood
    private $flood_interval = '60'; // The time interval in seconds
    private $flood_limit = '120'; // The number of requests allowed per interval
 
    function __construct()
    {
        $ip = ip2long($_SERVER['REMOTE_ADDR']) or die('Invalid IP');
        self::$ip = sprintf("%u", $ip);
 
        if (isset($_SERVER['HTTP_X_FORWARDED_FOR']) && preg_match_all('#\d{1,3}\.\d{1,3}\.\d{1,3}\.\d{1,3}#s', $_SERVER['HTTP_X_FORWARDED_FOR'], $vars)) {
            foreach ($vars[0] AS $var) {
                $ip_via_proxy = ip2long($var);
                if ($ip_via_proxy && $ip_via_proxy != $ip && !preg_match('#^(10|172\.16|192\.168)\.#', $var)) {
                    self::$ip_via_proxy = sprintf("%u", $ip_via_proxy);
                    break;
                }
            }
        }
 
        $this->ip_flood();
    }
 
    function ip_flood()
    {
        if ($this->flood_chk) {
            $file = ROOTPATH . 'files/system/cache/ip_flood.dat';
            $tmp = array();
            $requests = 1;
            if (!file_exists($file)) $in = fopen($file, "w+");
            else $in = fopen($file, "r+");
            flock($in, LOCK_EX) or die("Cannot flock ANTIFLOOD file.");
            $now = time();
            while ($block = fread($in, 8)) {
                $arr = unpack("Lip/Ltime", $block);
                if (($now - $arr['time']) > $this->flood_interval) continue;
                if ($arr['ip'] == self::$ip) $requests++;
                $tmp[] = $arr;
                self::$ip_count[] = $arr['ip'];
            }
            fseek($in, 0);
            ftruncate($in, 0);
            for ($i = 0; $i < count($tmp); $i++) fwrite($in, pack('LL', $tmp[$i]['ip'], $tmp[$i]['time']));
            fwrite($in, pack('LL', self::$ip, $now));
            fclose($in);
            if ($requests > $this->flood_limit) {
                die('FLOOD: exceeded limit of allowed requests');
            }
        }
    }
}
new core;
?>

self::$ip_count[] = $arr['ip'];