Proyectos de Subversion Moodle

<?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/>.

/**

 * Memcached based session handler.

 *

 * @package    core

 * @copyright  2013 Petr Skoda {@link http://skodak.org}

 * @license    http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later

 */

namespace core\session;

defined('MOODLE_INTERNAL') || die();

/**

 * Memcached based session handler.

 *

 * @package    core

 * @copyright  2013 Petr Skoda {@link http://skodak.org}

 * @license    http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later

 */

class memcached extends handler {

    /** @var string $savepath save_path string  */

    protected $savepath;

    /** @var array $servers list of servers parsed from save_path */

    protected $servers;

    /** @var string $prefix session key prefix  */

    protected $prefix;

    /** @var int $acquiretimeout how long to wait for session lock */

    protected $acquiretimeout = 120;

    /**

     * @var int $lockexpire how long to wait before expiring the lock so that other requests

     * may continue execution, ignored if PECL memcached is below version 2.2.0.

     */

    protected $lockexpire = 7200;

    /**

     * @var integer $lockretrysleep Used for memcached 3.x (PHP7), the amount of time to

     * sleep between attempts to acquire the session lock. Mimics the deprecated config

     * memcached.sess_lock_wait.

     */

    protected $lockretrysleep = 150;

    /**

     * Create new instance of handler.

     */

    public function __construct() {

        global $CFG;

        if (empty($CFG->session_memcached_save_path)) {

            $this->savepath = '';

        } else {

            $this->savepath =  $CFG->session_memcached_save_path;

        }

        if (empty($this->savepath)) {

            $this->servers = array();

        } else {

            $this->servers = self::connection_string_to_memcache_servers($this->savepath);

        }

        if (empty($CFG->session_memcached_prefix)) {

            $this->prefix = ini_get('memcached.sess_prefix');

        } else {

            $this->prefix = $CFG->session_memcached_prefix;

        }

        if (!empty($CFG->session_memcached_acquire_lock_timeout)) {

            $this->acquiretimeout = (int)$CFG->session_memcached_acquire_lock_timeout;

        }

        if (!empty($CFG->session_memcached_lock_expire)) {

            $this->lockexpire = (int)$CFG->session_memcached_lock_expire;

        }

        if (!empty($CFG->session_memcached_lock_retry_sleep)) {

            $this->lockretrysleep = (int)$CFG->session_memcached_lock_retry_sleep;

        }

    }

    /**

     * Start the session.

     * @return bool success

     */

    public function start() {

        ini_set('memcached.sess_locking', $this->requires_write_lock() ? '1' : '0');

        // NOTE: memcached before 2.2.0 expires session locks automatically after max_execution_time,

        //       this leads to major difference compared to other session drivers that timeout

        //       and stop the second request execution instead.

        $default = ini_get('max_execution_time');

        set_time_limit($this->acquiretimeout);

        $isnewsession = empty($_COOKIE[session_name()]);

        $starttimer = microtime(true);

        $result = parent::start();

        // If session_start returned TRUE, but it took as long

        // as the timeout value, and the $_SESSION returned is

        // empty when should not have been (isnewsession false)

        // then assume it did timeout and is invalid.

        // Add 1 second to elapsed time to account for inexact

        // timings in php_memcached_session.c.

        // @TODO Remove this check when php-memcached is fixed

        // to return false after key lock acquisition timeout.

        if (!$isnewsession && $result && count($_SESSION) == 0

            && (microtime(true) - $starttimer + 1) >= floatval($this->acquiretimeout)) {

            $result = false;

        }

        set_time_limit($default);

        return $result;

    }

    /**

     * Init session handler.

     */

    public function init() {

        if (!extension_loaded('memcached')) {

            throw new exception('sessionhandlerproblem', 'error', '', null, 'memcached extension is not loaded');

        }

        $version = phpversion('memcached');

        if (!$version or version_compare($version, '2.0') < 0) {

            throw new exception('sessionhandlerproblem', 'error', '', null, 'memcached extension version must be at least 2.0');

        }

        if (empty($this->savepath)) {

            throw new exception('sessionhandlerproblem', 'error', '', null, '$CFG->session_memcached_save_path must be specified in config.php');

        }

        ini_set('session.save_handler', 'memcached');

        ini_set('session.save_path', $this->savepath);

        ini_set('memcached.sess_prefix', $this->prefix);

        ini_set('memcached.sess_lock_expire', $this->lockexpire);

        if (version_compare($version, '3.0.0-dev') >= 0) {

            // With memcached 3.x (PHP 7) we configure the max retries to make and the time to sleep between each retry.

            // There are two sleep config values, an initial and a max value.

            // After each attempt the memcached module adjusts the sleep value to be the lesser of the configured max

            // value, or 2X the previous value.

            // With default memcached.ini configs (5, 1s, 2s) the result is only 5 attempts to lock over 9 sec.

            // To mimic the behavior of the 2.2.x module so we get more attempts and much more frequently, config both

            // sleep values to the old default value of 150 msec (making it constant) and calculate number of retries

            // using the existing Moodle config $CFG->session_memcached_acquire_lock_timeout.

            // Doing this so admins configure session lock attempt timeout in familiar terms, and more straight-forward

            // to detect if lock attempt timeout has occurred in start().

            // If _min and _max values are not equal, the actual lock acquire timeout will not be the expected

            // configured value in $CFG->session_memcached_acquire_lock_timeout; this will cause session data loss when

            // failure to acquire the lock is not detected.

            ini_set('memcached.sess_lock_wait_min', $this->lockretrysleep);

            ini_set('memcached.sess_lock_wait_max', $this->lockretrysleep);

            ini_set('memcached.sess_lock_retries', (int)(($this->acquiretimeout * 1000) / $this->lockretrysleep) + 1);

        } else {

            // With memcached 2.2.x we configure max time to attempt lock, and accept default value (in memcached.ini)

            // for sleep time between each attempt (usually 150 msec), then memcached calculates the max number of

            // retries to make.

            ini_set('memcached.sess_lock_max_wait', $this->acquiretimeout);

        }

    }

    /**

     * 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->servers) {

            return false;

        }

        // Go through the list of all servers because

        // we do not know where the session handler put the

        // data.

        foreach ($this->servers as $server) {

            list($host, $port) = $server;

            $memcached = new \Memcached();

            $memcached->addServer($host, $port);

            $value = $memcached->get($this->prefix . $sid);

            $memcached->quit();

            if ($value !== false) {

                return true;

            }

        }

        return false;

    }

    /**

     * Kill all active sessions, the core sessions table is

     * purged afterwards.

     */

    public function kill_all_sessions() {

        global $DB;

        if (!$this->servers) {

            return;

        }

        // Go through the list of all servers because

        // we do not know where the session handler put the

        // data.

        $memcacheds = array();

        foreach ($this->servers as $server) {

            list($host, $port) = $server;

            $memcached = new \Memcached();

            $memcached->addServer($host, $port);

            $memcacheds[] = $memcached;

        }

        // Note: this can be significantly improved by fetching keys from memcached,

        //       but we need to make sure we are not deleting somebody else's sessions.

        $rs = $DB->get_recordset('sessions', array(), 'id DESC', 'id, sid');

        foreach ($rs as $record) {

            foreach ($memcacheds as $memcached) {

                $memcached->delete($this->prefix . $record->sid);

            }

        }

        $rs->close();

        foreach ($memcacheds as $memcached) {

            $memcached->quit();

        }

    }

    /**

     * Kill one session, the session record is removed afterwards.

     * @param string $sid

     */

    public function kill_session($sid) {

        if (!$this->servers) {

            return;

        }

        // Go through the list of all servers because

        // we do not know where the session handler put the

        // data.

        foreach ($this->servers as $server) {

            list($host, $port) = $server;

            $memcached = new \Memcached();

            $memcached->addServer($host, $port);

            $memcached->delete($this->prefix . $sid);

            $memcached->quit();

        }

    }

    /**

     * Convert a connection string to an array of servers.

     *

     * "abc:123, xyz:789" to

     *  [

     *      ['abc', '123'],

     *      ['xyz', '789'],

     *  ]

     *

     * @param   string  $str save_path value containing memcached connection string

     * @return  array[]

     */

    protected static function connection_string_to_memcache_servers(string $str): array {

        $servers = [];

        $parts   = explode(',', $str);

        foreach ($parts as $part) {

            $part = trim($part);

            $pos  = strrpos($part, ':');

            if ($pos !== false) {

                $host = substr($part, 0, $pos);

                $port = substr($part, ($pos + 1));

            } else {

                $host = $part;

                $port = 11211;

            }

            $servers[] = [$host, $port];

        }

        return $servers;

    }

}