/lib/Sabre/DAV/UUIDUtil.php

<?php

namespace Sabre\DAV;

/**
 * UUID Utility
 *
 * This class has static methods to generate and validate UUID's.
 * UUIDs are used a decent amount within various *DAV standards, so it made
 * sense to include it.
 *
 * @copyright Copyright (C) 2007-2013 fruux GmbH (https://fruux.com/).
 * @author Evert Pot (http://evertpot.com/)
 * @license http://code.google.com/p/sabredav/wiki/License Modified BSD License
 */
class UUIDUtil {

    /**
     * Returns a pseudo-random v4 UUID
     *
     * This function is based on a comment by Andrew Moore on php.net
     *
     * @see http://www.php.net/manual/en/function.uniqid.php#94959
     * @return string
     */
    static function getUUID() {

        return sprintf( '%04x%04x-%04x-%04x-%04x-%04x%04x%04x',
            // 32 bits for "time_low"
            mt_rand( 0, 0xffff ), mt_rand( 0, 0xffff ),

            // 16 bits for "time_mid"
            mt_rand( 0, 0xffff ),

            // 16 bits for "time_hi_and_version",
            // four most significant bits holds version number 4
            mt_rand( 0, 0x0fff ) | 0x4000,

            // 16 bits, 8 bits for "clk_seq_hi_res",
            // 8 bits for "clk_seq_low",
            // two most significant bits holds zero and one for variant DCE1.1
            mt_rand( 0, 0x3fff ) | 0x8000,

            // 48 bits for "node"
            mt_rand( 0, 0xffff ), mt_rand( 0, 0xffff ), mt_rand( 0, 0xffff )
        );
    }

    /**
     * Checks if a string is a valid UUID.
     *
     * @param string $uuid
     * @return bool
     */
    static function validateUUID($uuid) {

        return preg_match(
            '/^[a-f0-9]{8}-[a-f0-9]{4}-[a-f0-9]{4}-[a-f0-9]{4}-[a-f0-9]{12}$/i',
            $uuid
        ) == true;

    }

}