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<?php
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// This file is part of Moodle - http://moodle.org/
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//
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// Moodle is free software: you can redistribute it and/or modify
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// it under the terms of the GNU General Public License as published by
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// the Free Software Foundation, either version 3 of the License, or
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// (at your option) any later version.
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//
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// Moodle is distributed in the hope that it will be useful,
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// but WITHOUT ANY WARRANTY; without even the implied warranty of
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// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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// GNU General Public License for more details.
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//
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// You should have received a copy of the GNU General Public License
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// along with Moodle. If not, see <http://www.gnu.org/licenses/>.
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/**
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* V4 UUID generator.
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*
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* @package core
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* @copyright 2019 Matteo Scaramuccia <moodle@matteoscaramuccia.com>
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* @license http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
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*/
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namespace core;
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use Exception;
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defined('MOODLE_INTERNAL') || die();
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/**
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* V4 UUID generator class.
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*
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* @package core
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* @copyright 2019 Matteo Scaramuccia <moodle@matteoscaramuccia.com>
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* @license http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
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*/
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class uuid {
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/**
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* Generate a V4 UUID using PECL UUID extension.
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* @see https://github.com/php/pecl-networking-uuid PECL uuid
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* @see https://tools.ietf.org/html/rfc4122
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*
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* @return string|bool The UUID when PECL UUID extension is available;
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* otherwise, false.
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*/
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protected static function generate_uuid_via_pecl_uuid_extension() {
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$uuid = false;
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// Check if PECL uuid extension has been actually installed.
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if (function_exists('\uuid_time')) {
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// Set V4 version.
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$uuid = \uuid_create(UUID_TYPE_RANDOM);
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}
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return $uuid;
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}
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/**
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* Generate a V4 UUID using PHP 7+ features.
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*
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* @see https://www.php.net/manual/en/function.random-bytes.php
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* @see https://tools.ietf.org/html/rfc4122
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*
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* @return string|bool The UUID when random_bytes() function is available;
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* otherwise, false when missing the sources of randomness used by random_bytes().
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*/
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protected static function generate_uuid_via_random_bytes() {
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$uuid = false;
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// If none of the sources of randomness are available,
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// then an Exception will be thrown.
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try {
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$data = random_bytes(16);
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$data[6] = chr((ord($data[6]) & 0x0f) | 0x40); // Set version to 0100.
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$data[8] = chr((ord($data[8]) & 0x3f) | 0x80); // Set bits 6-7 to 10.
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$uuid = vsprintf('%s%s-%s-%s-%s-%s%s%s', str_split(bin2hex($data), 4));
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} catch (Exception $e) {
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// Could not generate a random string. Is this OS secure?
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$uuid = false;
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}
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return $uuid;
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}
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/**
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* Generate a V4 UUID.
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*
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* Unique is hard. Very hard. Attempt to use the PECL UUID function if available, and if not then revert to
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* constructing the uuid using random_bytes or mt_rand.
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*
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* It is important that this token is not solely based on time as this could lead
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* to duplicates in a clustered environment (especially on VMs due to poor time precision).
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*
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* UUIDs are just 128 bits long but with different supported versions (RFC 4122), mainly two:
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* - V1: the goal is uniqueness, at the cost of anonymity since it is coupled to the host generating it, via its MAC address.
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* - V4: the goal is randomness, at the cost of (rare) collisions.
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* Here, the V4 type is the preferred choice.
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*
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* The format is:
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* xxxxxxxx-xxxx-4xxx-Yxxx-xxxxxxxxxxxx
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* where x is any hexadecimal digit and Y is a random choice from 8, 9, a, or b.
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*
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* @see https://tools.ietf.org/html/rfc4122
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*
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* @return string The V4 UUID.
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*/
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public static function generate() {
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// Try PHP UUID extensions first.
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$uuid = self::generate_uuid_via_pecl_uuid_extension();
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// Fall back to better random features, when possible.
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if (empty($uuid)) {
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$uuid = self::generate_uuid_via_random_bytes();
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}
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// Finally, create it with the available randomness.
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if (empty($uuid)) {
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// Fallback uuid generation based on:
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// "http://www.php.net/manual/en/function.uniqid.php#94959".
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$uuid = sprintf('%04x%04x-%04x-%04x-%04x-%04x%04x%04x',
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// 32 bits for "time_low".
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mt_rand(0, 0xffff), mt_rand(0, 0xffff),
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// 16 bits for "time_mid".
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mt_rand(0, 0xffff),
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// 16 bits for "time_hi_and_version",
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// four most significant bits holds version number 4.
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mt_rand(0, 0x0fff) | 0x4000,
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// 16 bits, 8 bits for "clk_seq_hi_res",
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// 8 bits for "clk_seq_low",
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// two most significant bits holds zero and one for variant DCE1.1.
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mt_rand(0, 0x3fff) | 0x8000,
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// 48 bits for "node".
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mt_rand(0, 0xffff), mt_rand(0, 0xffff), mt_rand(0, 0xffff));
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}
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return trim($uuid);
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}
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}
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