htmlpurifier/library/HTMLPurifier/AttrDef/URI/IPv4.php

<?php

/**
 * Validates an IPv4 address
 * @author Feyd @ forums.devnetwork.net (public domain)
 */
class HTMLPurifier_AttrDef_URI_IPv4 extends HTMLPurifier_AttrDef
{

    /**
     * IPv4 regex, protected so that IPv6 can reuse it
     */
    protected $ip4;

    public function validate($aIP, $config, $context) {

        if (!$this->ip4) $this->_loadRegex();

        if (preg_match('#^' . $this->ip4 . '$#s', $aIP))
        {
                return $aIP;
        }

        return false;

    }

    /**
     * Lazy load function to prevent regex from being stuffed in
     * cache.
     */
    protected function _loadRegex() {
        $oct = '(?:25[0-5]|2[0-4][0-9]|1[0-9]{2}|[1-9][0-9]|[0-9])'; // 0-255
        $this->ip4 = "(?:{$oct}\\.{$oct}\\.{$oct}\\.{$oct})";
    }

}