Current File : /home/vacivi36/ava/lib/classes/session/redis.php
<?php
// This file is part of Moodle - http://moodle.org/
//
// Moodle is free software: you can redistribute it and/or modify
// it under the terms of the GNU General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// Moodle is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
// GNU General Public License for more details.
//
// You should have received a copy of the GNU General Public License
// along with Moodle. If not, see <http://www.gnu.org/licenses/>.
/**
* Redis based session handler.
*
* @package core
* @copyright 2015 Russell Smith <mr-russ@smith2001.net>
* @license http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
*/
namespace core\session;
use RedisException;
defined('MOODLE_INTERNAL') || die();
/**
* Redis based session handler.
*
* The default Redis session handler does not handle locking in 2.2.7, so we have written a php session handler
* that uses locking. The places where locking is used was modeled from the memcached code that is used in Moodle
* https://github.com/php-memcached-dev/php-memcached/blob/master/php_memcached_session.c
*
* @package core
* @copyright 2016 Russell Smith
* @license http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
*/
class redis extends handler {
/**
* Compressor: none.
*/
const COMPRESSION_NONE = 'none';
/**
* Compressor: PHP GZip.
*/
const COMPRESSION_GZIP = 'gzip';
/**
* Compressor: PHP Zstandard.
*/
const COMPRESSION_ZSTD = 'zstd';
/** @var string $host save_path string */
protected $host = '';
/** @var int $port The port to connect to */
protected $port = 6379;
/** @var string $auth redis password */
protected $auth = '';
/** @var int $database the Redis database to store sesions in */
protected $database = 0;
/** @var array $servers list of servers parsed from save_path */
protected $prefix = '';
/** @var int $acquiretimeout how long to wait for session lock in seconds */
protected $acquiretimeout = 120;
/** @var int $acquirewarn how long before warning when waiting for a lock in seconds */
protected $acquirewarn = null;
/** @var int $lockretry how long to wait between session lock attempts in ms */
protected $lockretry = 100;
/** @var int $serializer The serializer to use */
protected $serializer = \Redis::SERIALIZER_PHP;
/** @var int $compressor The compressor to use */
protected $compressor = self::COMPRESSION_NONE;
/** @var string $lasthash hash of the session data content */
protected $lasthash = null;
/**
* @var int $lockexpire how long to wait in seconds before expiring the lock automatically
* so that other requests may continue execution, ignored if PECL redis is below version 2.2.0.
*/
protected $lockexpire;
/** @var Redis Connection */
protected $connection = null;
/** @var array $locks List of currently held locks by this page. */
protected $locks = array();
/** @var int $timeout How long sessions live before expiring. */
protected $timeout;
/**
* Create new instance of handler.
*/
public function __construct() {
global $CFG;
if (isset($CFG->session_redis_host)) {
$this->host = $CFG->session_redis_host;
}
if (isset($CFG->session_redis_port)) {
$this->port = (int)$CFG->session_redis_port;
}
if (isset($CFG->session_redis_auth)) {
$this->auth = $CFG->session_redis_auth;
}
if (isset($CFG->session_redis_database)) {
$this->database = (int)$CFG->session_redis_database;
}
if (isset($CFG->session_redis_prefix)) {
$this->prefix = $CFG->session_redis_prefix;
}
if (isset($CFG->session_redis_acquire_lock_timeout)) {
$this->acquiretimeout = (int)$CFG->session_redis_acquire_lock_timeout;
}
if (isset($CFG->session_redis_acquire_lock_warn)) {
$this->acquirewarn = (int)$CFG->session_redis_acquire_lock_warn;
}
if (isset($CFG->session_redis_acquire_lock_retry)) {
$this->lockretry = (int)$CFG->session_redis_acquire_lock_retry;
}
if (!empty($CFG->session_redis_serializer_use_igbinary) && defined('\Redis::SERIALIZER_IGBINARY')) {
$this->serializer = \Redis::SERIALIZER_IGBINARY; // Set igbinary serializer if phpredis supports it.
}
// The following configures the session lifetime in redis to allow some
// wriggle room in the user noticing they've been booted off and
// letting them log back in before they lose their session entirely.
$updatefreq = empty($CFG->session_update_timemodified_frequency) ? 20 : $CFG->session_update_timemodified_frequency;
$this->timeout = $CFG->sessiontimeout + $updatefreq + MINSECS;
$this->lockexpire = $CFG->sessiontimeout;
if (isset($CFG->session_redis_lock_expire)) {
$this->lockexpire = (int)$CFG->session_redis_lock_expire;
}
if (isset($CFG->session_redis_compressor)) {
$this->compressor = $CFG->session_redis_compressor;
}
}
/**
* Start the session.
*
* @return bool success
*/
public function start() {
$result = parent::start();
return $result;
}
/**
* Init session handler.
*/
public function init() {
if (!extension_loaded('redis')) {
throw new exception('sessionhandlerproblem', 'error', '', null, 'redis extension is not loaded');
}
if (empty($this->host)) {
throw new exception('sessionhandlerproblem', 'error', '', null,
'$CFG->session_redis_host must be specified in config.php');
}
// The session handler requires a version of Redis with the SETEX command (at least 2.0).
$version = phpversion('Redis');
if (!$version or version_compare($version, '2.0') <= 0) {
throw new exception('sessionhandlerproblem', 'error', '', null, 'redis extension version must be at least 2.0');
}
$this->connection = new \Redis();
$result = session_set_save_handler(array($this, 'handler_open'),
array($this, 'handler_close'),
array($this, 'handler_read'),
array($this, 'handler_write'),
array($this, 'handler_destroy'),
array($this, 'handler_gc'));
if (!$result) {
throw new exception('redissessionhandlerproblem', 'error');
}
// MDL-59866: Add retries for connections (up to 5 times) to make sure it goes through.
$counter = 1;
$maxnumberofretries = 5;
while ($counter <= $maxnumberofretries) {
try {
$delay = rand(100, 500);
// One second timeout was chosen as it is long for connection, but short enough for a user to be patient.
if (!$this->connection->connect($this->host, $this->port, 1, null, $delay)) {
throw new RedisException('Unable to connect to host.');
}
if ($this->auth !== '') {
if (!$this->connection->auth($this->auth)) {
throw new RedisException('Unable to authenticate.');
}
}
if (!$this->connection->setOption(\Redis::OPT_SERIALIZER, $this->serializer)) {
throw new RedisException('Unable to set Redis PHP Serializer option.');
}
if ($this->prefix !== '') {
// Use custom prefix on sessions.
if (!$this->connection->setOption(\Redis::OPT_PREFIX, $this->prefix)) {
throw new RedisException('Unable to set Redis Prefix option.');
}
}
if ($this->database !== 0) {
if (!$this->connection->select($this->database)) {
throw new RedisException('Unable to select Redis database '.$this->database.'.');
}
}
return true;
} catch (RedisException $e) {
$logstring = "Failed to connect (try {$counter} out of {$maxnumberofretries}) to redis ";
$logstring .= "at {$this->host}:{$this->port}, error returned was: {$e->getMessage()}";
debugging($logstring);
}
$counter++;
// Introduce a random sleep between 100ms and 500ms.
usleep(rand(100000, 500000));
}
// We have exhausted our retries, time to give up.
if (isset($logstring)) {
throw new RedisException($logstring);
}
}
/**
* Update our session search path to include session name when opened.
*
* @param string $savepath unused session save path. (ignored)
* @param string $sessionname Session name for this session. (ignored)
* @return bool true always as we will succeed.
*/
public function handler_open($savepath, $sessionname) {
return true;
}
/**
* Close the session completely. We also remove all locks we may have obtained that aren't expired.
*
* @return bool true on success. false on unable to unlock sessions.
*/
public function handler_close() {
$this->lasthash = null;
try {
foreach ($this->locks as $id => $expirytime) {
if ($expirytime > $this->time()) {
$this->unlock_session($id);
}
unset($this->locks[$id]);
}
} catch (RedisException $e) {
error_log('Failed talking to redis: '.$e->getMessage());
return false;
}
return true;
}
/**
* Read the session data from storage
*
* @param string $id The session id to read from storage.
* @return string The session data for PHP to process.
*
* @throws RedisException when we are unable to talk to the Redis server.
*/
public function handler_read($id) {
try {
if ($this->requires_write_lock()) {
$this->lock_session($id);
}
$sessiondata = $this->uncompress($this->connection->get($id));
if ($sessiondata === false) {
if ($this->requires_write_lock()) {
$this->unlock_session($id);
}
$this->lasthash = sha1('');
return '';
}
$this->connection->expire($id, $this->timeout);
} catch (RedisException $e) {
error_log('Failed talking to redis: '.$e->getMessage());
throw $e;
}
$this->lasthash = sha1(base64_encode($sessiondata));
return $sessiondata;
}
/**
* Compresses session data.
*
* @param mixed $value
* @return string
*/
private function compress($value) {
switch ($this->compressor) {
case self::COMPRESSION_NONE:
return $value;
case self::COMPRESSION_GZIP:
return gzencode($value);
case self::COMPRESSION_ZSTD:
return zstd_compress($value);
default:
debugging("Invalid compressor: {$this->compressor}");
return $value;
}
}
/**
* Uncompresses session data.
*
* @param string $value
* @return mixed
*/
private function uncompress($value) {
if ($value === false) {
return false;
}
switch ($this->compressor) {
case self::COMPRESSION_NONE:
break;
case self::COMPRESSION_GZIP:
$value = gzdecode($value);
break;
case self::COMPRESSION_ZSTD:
$value = zstd_uncompress($value);
break;
default:
debugging("Invalid compressor: {$this->compressor}");
}
return $value;
}
/**
* Write the serialized session data to our session store.
*
* @param string $id session id to write.
* @param string $data session data
* @return bool true on write success, false on failure
*/
public function handler_write($id, $data) {
$hash = sha1(base64_encode($data));
// If the content has not changed don't bother writing.
if ($hash === $this->lasthash) {
return true;
}
if (is_null($this->connection)) {
// The session has already been closed, don't attempt another write.
error_log('Tried to write session: '.$id.' before open or after close.');
return false;
}
// We do not do locking here because memcached doesn't. Also
// PHP does open, read, destroy, write, close. When a session doesn't exist.
// There can be race conditions on new sessions racing each other but we can
// address that in the future.
try {
$data = $this->compress($data);
$this->connection->setex($id, $this->timeout, $data);
} catch (RedisException $e) {
error_log('Failed talking to redis: '.$e->getMessage());
return false;
}
return true;
}
/**
* Handle destroying a session.
*
* @param string $id the session id to destroy.
* @return bool true if the session was deleted, false otherwise.
*/
public function handler_destroy($id) {
$this->lasthash = null;
try {
$this->connection->del($id);
$this->unlock_session($id);
} catch (RedisException $e) {
error_log('Failed talking to redis: '.$e->getMessage());
return false;
}
return true;
}
/**
* Garbage collect sessions. We don't we any as Redis does it for us.
*
* @param integer $maxlifetime All sessions older than this should be removed.
* @return bool true, as Redis handles expiry for us.
*/
public function handler_gc($maxlifetime) {
return true;
}
/**
* Unlock a session.
*
* @param string $id Session id to be unlocked.
*/
protected function unlock_session($id) {
if (isset($this->locks[$id])) {
$this->connection->del($id.".lock");
unset($this->locks[$id]);
}
}
/**
* Obtain a session lock so we are the only one using it at the moment.
*
* @param string $id The session id to lock.
* @return bool true when session was locked, exception otherwise.
* @throws exception When we are unable to obtain a session lock.
*/
protected function lock_session($id) {
$lockkey = $id.".lock";
$haslock = isset($this->locks[$id]) && $this->time() < $this->locks[$id];
$startlocktime = $this->time();
/* To be able to ensure sessions don't write out of order we must obtain an exclusive lock
* on the session for the entire time it is open. If another AJAX call, or page is using
* the session then we just wait until it finishes before we can open the session.
*/
// Store the current host, process id and the request URI so it's easy to track who has the lock.
$hostname = gethostname();
if ($hostname === false) {
$hostname = 'UNKNOWN HOST';
}
$pid = getmypid();
if ($pid === false) {
$pid = 'UNKNOWN';
}
$uri = isset($_SERVER['REQUEST_URI']) ? $_SERVER['REQUEST_URI'] : 'unknown uri';
$whoami = "[pid {$pid}] {$hostname}:$uri";
$haswarned = false; // Have we logged a lock warning?
while (!$haslock) {
$haslock = $this->connection->setnx($lockkey, $whoami);
if ($haslock) {
$this->locks[$id] = $this->time() + $this->lockexpire;
$this->connection->expire($lockkey, $this->lockexpire);
return true;
}
if (!empty($this->acquirewarn) && !$haswarned && $this->time() > $startlocktime + $this->acquirewarn) {
// This is a warning to better inform users.
$whohaslock = $this->connection->get($lockkey);
// phpcs:ignore
error_log("Warning: Cannot obtain session lock for sid: $id within $this->acquirewarn seconds but will keep trying. " .
"It is likely another page ($whohaslock) has a long session lock, or the session lock was never released.");
$haswarned = true;
}
if ($this->time() > $startlocktime + $this->acquiretimeout) {
// This is a fatal error, better inform users.
// It should not happen very often - all pages that need long time to execute
// should close session immediately after access control checks.
$whohaslock = $this->connection->get($lockkey);
// phpcs:ignore
error_log("Error: Cannot obtain session lock for sid: $id within $this->acquiretimeout seconds. " .
"It is likely another page ($whohaslock) has a long session lock, or the session lock was never released.");
$acquiretimeout = format_time($this->acquiretimeout);
$lockexpire = format_time($this->lockexpire);
$a = (object)[
'id' => substr($id, 0, 10),
'acquiretimeout' => $acquiretimeout,
'whohaslock' => $whohaslock,
'lockexpire' => $lockexpire];
throw new exception("sessioncannotobtainlock", 'error', '', $a);
}
if ($this->time() < $startlocktime + 5) {
// We want a random delay to stagger the polling load. Ideally
// this delay should be a fraction of the average response
// time. If it is too small we will poll too much and if it is
// too large we will waste time waiting for no reason. 100ms is
// the default starting point.
$delay = rand($this->lockretry, (int)($this->lockretry * 1.1));
} else {
// If we don't get a lock within 5 seconds then there must be a
// very long lived process holding the lock so throttle back to
// just polling roughly once a second.
$delay = rand(1000, 1100);
}
usleep($delay * 1000);
}
}
/**
* Return the current time.
*
* @return int the current time as a unixtimestamp.
*/
protected function time() {
return time();
}
/**
* Check the backend contains data for this session id.
*
* Note: this is intended to be called from manager::session_exists() only.
*
* @param string $sid
* @return bool true if session found.
*/
public function session_exists($sid) {
if (!$this->connection) {
return false;
}
try {
return !empty($this->connection->exists($sid));
} catch (RedisException $e) {
return false;
}
}
/**
* Kill all active sessions, the core sessions table is purged afterwards.
*/
public function kill_all_sessions() {
global $DB;
if (!$this->connection) {
return;
}
$rs = $DB->get_recordset('sessions', array(), 'id DESC', 'id, sid');
foreach ($rs as $record) {
$this->handler_destroy($record->sid);
}
$rs->close();
}
/**
* Kill one session, the session record is removed afterwards.
*
* @param string $sid
*/
public function kill_session($sid) {
if (!$this->connection) {
return;
}
$this->handler_destroy($sid);
}
}
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