mirror of
https://github.com/moodle/moodle.git
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f8e2383bdd
There is an edge case whereby redis will fail to accept connections on the first try but retrying the connection seems to make it work Included in this commit: * Retry functionality in the session init
434 lines
15 KiB
PHP
434 lines
15 KiB
PHP
<?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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* Redis based session handler.
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*
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* @package core
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* @copyright 2015 Russell Smith <mr-russ@smith2001.net>
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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\session;
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use RedisException;
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defined('MOODLE_INTERNAL') || die();
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/**
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* Redis based session handler.
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*
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* The default Redis session handler does not handle locking in 2.2.7, so we have written a php session handler
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* that uses locking. The places where locking is used was modeled from the memcached code that is used in Moodle
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* https://github.com/php-memcached-dev/php-memcached/blob/master/php_memcached_session.c
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*
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* @package core
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* @copyright 2016 Russell Smith
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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 redis extends handler {
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/** @var string $host save_path string */
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protected $host = '';
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/** @var int $port The port to connect to */
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protected $port = 6379;
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/** @var string $auth redis password */
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protected $auth = '';
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/** @var int $database the Redis database to store sesions in */
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protected $database = 0;
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/** @var array $servers list of servers parsed from save_path */
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protected $prefix = '';
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/** @var int $acquiretimeout how long to wait for session lock in seconds */
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protected $acquiretimeout = 120;
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/** @var int $serializer The serializer to use */
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protected $serializer = \Redis::SERIALIZER_PHP;
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/**
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* @var int $lockexpire how long to wait in seconds before expiring the lock automatically
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* so that other requests may continue execution, ignored if PECL redis is below version 2.2.0.
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*/
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protected $lockexpire;
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/** @var Redis Connection */
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protected $connection = null;
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/** @var array $locks List of currently held locks by this page. */
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protected $locks = array();
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/** @var int $timeout How long sessions live before expiring. */
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protected $timeout;
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/**
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* Create new instance of handler.
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*/
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public function __construct() {
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global $CFG;
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if (isset($CFG->session_redis_host)) {
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$this->host = $CFG->session_redis_host;
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}
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if (isset($CFG->session_redis_port)) {
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$this->port = (int)$CFG->session_redis_port;
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}
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if (isset($CFG->session_redis_auth)) {
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$this->auth = $CFG->session_redis_auth;
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}
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if (isset($CFG->session_redis_database)) {
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$this->database = (int)$CFG->session_redis_database;
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}
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if (isset($CFG->session_redis_prefix)) {
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$this->prefix = $CFG->session_redis_prefix;
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}
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if (isset($CFG->session_redis_acquire_lock_timeout)) {
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$this->acquiretimeout = (int)$CFG->session_redis_acquire_lock_timeout;
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}
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if (!empty($CFG->session_redis_serializer_use_igbinary) && defined('\Redis::SERIALIZER_IGBINARY')) {
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$this->serializer = \Redis::SERIALIZER_IGBINARY; // Set igbinary serializer if phpredis supports it.
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}
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// The following configures the session lifetime in redis to allow some
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// wriggle room in the user noticing they've been booted off and
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// letting them log back in before they lose their session entirely.
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$updatefreq = empty($CFG->session_update_timemodified_frequency) ? 20 : $CFG->session_update_timemodified_frequency;
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$this->timeout = $CFG->sessiontimeout + $updatefreq + MINSECS;
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$this->lockexpire = $CFG->sessiontimeout;
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if (isset($CFG->session_redis_lock_expire)) {
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$this->lockexpire = (int)$CFG->session_redis_lock_expire;
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}
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}
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/**
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* Start the session.
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*
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* @return bool success
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*/
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public function start() {
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$result = parent::start();
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return $result;
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}
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/**
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* Init session handler.
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*/
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public function init() {
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if (!extension_loaded('redis')) {
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throw new exception('sessionhandlerproblem', 'error', '', null, 'redis extension is not loaded');
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}
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if (empty($this->host)) {
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throw new exception('sessionhandlerproblem', 'error', '', null,
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'$CFG->session_redis_host must be specified in config.php');
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}
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// The session handler requires a version of Redis with the SETEX command (at least 2.0).
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$version = phpversion('Redis');
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if (!$version or version_compare($version, '2.0') <= 0) {
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throw new exception('sessionhandlerproblem', 'error', '', null, 'redis extension version must be at least 2.0');
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}
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$this->connection = new \Redis();
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$result = session_set_save_handler(array($this, 'handler_open'),
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array($this, 'handler_close'),
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array($this, 'handler_read'),
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array($this, 'handler_write'),
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array($this, 'handler_destroy'),
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array($this, 'handler_gc'));
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if (!$result) {
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throw new exception('redissessionhandlerproblem', 'error');
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}
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// MDL-59866: Add retries for connections (up to 5 times) to make sure it goes through.
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$counter = 1;
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$maxnumberofretries = 5;
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while ($counter <= $maxnumberofretries) {
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try {
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$delay = rand(100000, 500000);
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// One second timeout was chosen as it is long for connection, but short enough for a user to be patient.
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if (!$this->connection->connect($this->host, $this->port, 1, null, $delay)) {
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throw new RedisException('Unable to connect to host.');
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}
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if ($this->auth !== '') {
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if (!$this->connection->auth($this->auth)) {
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throw new RedisException('Unable to authenticate.');
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}
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}
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if (!$this->connection->setOption(\Redis::OPT_SERIALIZER, $this->serializer)) {
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throw new RedisException('Unable to set Redis PHP Serializer option.');
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}
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if ($this->prefix !== '') {
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// Use custom prefix on sessions.
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if (!$this->connection->setOption(\Redis::OPT_PREFIX, $this->prefix)) {
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throw new RedisException('Unable to set Redis Prefix option.');
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}
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}
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if ($this->database !== 0) {
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if (!$this->connection->select($this->database)) {
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throw new RedisException('Unable to select Redis database '.$this->database.'.');
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}
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}
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$this->connection->ping();
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return true;
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} catch (RedisException $e) {
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$logstring = "Failed to connect (try {$counter} out of {$maxnumberofretries}) to redis ";
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$logstring .= "at {$this->host}:{$this->port}, error returned was: {$e->getMessage()}";
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// @codingStandardsIgnoreStart
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error_log($logstring);
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// @codingStandardsIgnoreEnd
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}
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$counter++;
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// Introduce a random sleep between 100ms and 500ms.
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usleep(rand(100000, 500000));
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}
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// We have exhausted our retries, time to give up.
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return false;
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}
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/**
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* Update our session search path to include session name when opened.
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*
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* @param string $savepath unused session save path. (ignored)
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* @param string $sessionname Session name for this session. (ignored)
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* @return bool true always as we will succeed.
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*/
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public function handler_open($savepath, $sessionname) {
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return true;
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}
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/**
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* Close the session completely. We also remove all locks we may have obtained that aren't expired.
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*
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* @return bool true on success. false on unable to unlock sessions.
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*/
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public function handler_close() {
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try {
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foreach ($this->locks as $id => $expirytime) {
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if ($expirytime > $this->time()) {
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$this->unlock_session($id);
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}
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unset($this->locks[$id]);
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}
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} catch (RedisException $e) {
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error_log('Failed talking to redis: '.$e->getMessage());
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return false;
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}
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return true;
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}
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/**
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* Read the session data from storage
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*
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* @param string $id The session id to read from storage.
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* @return string The session data for PHP to process.
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*
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* @throws RedisException when we are unable to talk to the Redis server.
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*/
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public function handler_read($id) {
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try {
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$this->lock_session($id);
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$sessiondata = $this->connection->get($id);
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if ($sessiondata === false) {
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$this->unlock_session($id);
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return '';
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}
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$this->connection->expire($id, $this->timeout);
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} catch (RedisException $e) {
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error_log('Failed talking to redis: '.$e->getMessage());
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throw $e;
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}
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return $sessiondata;
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}
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/**
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* Write the serialized session data to our session store.
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*
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* @param string $id session id to write.
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* @param string $data session data
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* @return bool true on write success, false on failure
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*/
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public function handler_write($id, $data) {
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if (is_null($this->connection)) {
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// The session has already been closed, don't attempt another write.
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error_log('Tried to write session: '.$id.' before open or after close.');
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return false;
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}
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// We do not do locking here because memcached doesn't. Also
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// PHP does open, read, destroy, write, close. When a session doesn't exist.
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// There can be race conditions on new sessions racing each other but we can
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// address that in the future.
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try {
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$this->connection->setex($id, $this->timeout, $data);
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} catch (RedisException $e) {
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error_log('Failed talking to redis: '.$e->getMessage());
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return false;
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}
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return true;
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}
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/**
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* Handle destroying a session.
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*
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* @param string $id the session id to destroy.
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* @return bool true if the session was deleted, false otherwise.
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*/
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public function handler_destroy($id) {
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try {
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$this->connection->del($id);
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$this->unlock_session($id);
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} catch (RedisException $e) {
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error_log('Failed talking to redis: '.$e->getMessage());
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return false;
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}
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return true;
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}
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/**
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* Garbage collect sessions. We don't we any as Redis does it for us.
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*
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* @param integer $maxlifetime All sessions older than this should be removed.
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* @return bool true, as Redis handles expiry for us.
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*/
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public function handler_gc($maxlifetime) {
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return true;
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}
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/**
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* Unlock a session.
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*
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* @param string $id Session id to be unlocked.
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*/
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protected function unlock_session($id) {
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if (isset($this->locks[$id])) {
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$this->connection->del($id.".lock");
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unset($this->locks[$id]);
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}
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}
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/**
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* Obtain a session lock so we are the only one using it at the moent.
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*
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* @param string $id The session id to lock.
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* @return bool true when session was locked, exception otherwise.
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* @throws exception When we are unable to obtain a session lock.
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*/
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protected function lock_session($id) {
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$lockkey = $id.".lock";
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$haslock = isset($this->locks[$id]) && $this->time() < $this->locks[$id];
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$startlocktime = $this->time();
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/* To be able to ensure sessions don't write out of order we must obtain an exclusive lock
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* on the session for the entire time it is open. If another AJAX call, or page is using
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* the session then we just wait until it finishes before we can open the session.
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*/
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while (!$haslock) {
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$haslock = $this->connection->setnx($lockkey, '1');
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if (!$haslock) {
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usleep(rand(100000, 1000000));
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if ($this->time() > $startlocktime + $this->acquiretimeout) {
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// This is a fatal error, better inform users.
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// It should not happen very often - all pages that need long time to execute
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// should close session immediately after access control checks.
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error_log('Cannot obtain session lock for sid: '.$id.' within '.$this->acquiretimeout.
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'. It is likely another page has a long session lock, or the session lock was never released.');
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throw new exception("Unable to obtain session lock");
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}
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} else {
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$this->locks[$id] = $this->time() + $this->lockexpire;
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$this->connection->expire($lockkey, $this->lockexpire);
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return true;
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}
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}
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}
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/**
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* Return the current time.
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*
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* @return int the current time as a unixtimestamp.
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*/
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protected function time() {
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return time();
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}
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/**
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* Check the backend contains data for this session id.
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*
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* Note: this is intended to be called from manager::session_exists() only.
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*
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* @param string $sid
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* @return bool true if session found.
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*/
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public function session_exists($sid) {
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if (!$this->connection) {
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return false;
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}
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try {
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return $this->connection->exists($sid);
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} catch (RedisException $e) {
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return false;
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}
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}
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/**
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* Kill all active sessions, the core sessions table is purged afterwards.
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*/
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public function kill_all_sessions() {
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global $DB;
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if (!$this->connection) {
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return;
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}
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$rs = $DB->get_recordset('sessions', array(), 'id DESC', 'id, sid');
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foreach ($rs as $record) {
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$this->handler_destroy($record->sid);
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}
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$rs->close();
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}
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/**
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* Kill one session, the session record is removed afterwards.
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*
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* @param string $sid
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*/
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public function kill_session($sid) {
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if (!$this->connection) {
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return;
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}
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$this->handler_destroy($sid);
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}
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}
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