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/>.

/**

 * Database 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;

use SessionHandlerInterface;

/**

 * Database 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 database extends handler implements SessionHandlerInterface {

    /** @var \stdClass $record session record */

    protected $recordid = null;

    /** @var \moodle_database $database session database */

    protected $database = null;

    /** @var bool $failed session read/init failed, do not write back to DB */

    protected $failed = false;

    /** @var string $lasthash hash of the session data content */

    protected $lasthash = null;

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

    protected $acquiretimeout = 120;

    /**

     * Create new instance of handler.

     */

    public function __construct() {

        global $DB, $CFG;

        // Note: we store the reference here because we need to modify database in shutdown handler.

        $this->database = $DB;

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

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

        }

    }

    /**

     * Init session handler.

     */

    public function init() {

        if (!$this->database->session_lock_supported()) {

            throw new exception('sessionhandlerproblem', 'error', '', null, 'Database does not support session locking');

        }

        $result = session_set_save_handler($this);

        if (!$result) {

            throw new exception('dbsessionhandlerproblem', 'error');

        }

    }

    /**

     * 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) {

        // It was already checked in the calling code that the record in sessions table exists.

        return true;

    }

    /**

     * Kill all active sessions, the core sessions table is

     * purged afterwards.

     */

    public function kill_all_sessions() {

        // Nothing to do, the sessions table is cleared from core.

        return;

    }

    /**

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

     * @param string $sid

     */

    public function kill_session($sid) {

        // Nothing to do, the sessions table is purged afterwards.

        return;

    }

    /**

     * Open session handler.

     *

     * {@see http://php.net/manual/en/function.session-set-save-handler.php}

     *

     * @param string $path

     * @param string $name

     * @return bool success

     */

    public function open(string $path, string $name): bool {

        // Note: we use the already open database.

        return true;

    }

    /**

     * Close session handler.

     *

     * {@see http://php.net/manual/en/function.session-set-save-handler.php}

     *

     * @return bool success

     */

    public function close(): bool {

        if ($this->recordid) {

            try {

                $this->database->release_session_lock($this->recordid);

            } catch (\Exception $ex) {

                // Ignore any problems.

            }

        }

        $this->recordid = null;

        $this->lasthash = null;

        return true;

    }

    /**

     * Read session handler.

     *

     * {@see http://php.net/manual/en/function.session-set-save-handler.php}

     *

     * @param string $sid

     * @return string|false

     */

    public function read(string $sid): string|false {

        try {

            if (!$record = $this->database->get_record('sessions', array('sid'=>$sid), 'id')) {

                // Let's cheat and skip locking if this is the first access,

                // do not create the record here, let the manager do it after session init.

                $this->failed = false;

                $this->recordid = null;

                $this->lasthash = sha1('');

                return '';

            }

            if ($this->recordid and $this->recordid != $record->id) {

                error_log('Second session read with different record id detected, cannot read session');

                $this->failed = true;

                $this->recordid = null;

                return '';

            }

            if (!$this->recordid) {

                // Lock session if exists and not already locked.

                if ($this->requires_write_lock()) {

                    $this->database->get_session_lock($record->id, $this->acquiretimeout);

                }

                $this->recordid = $record->id;

            }

        } catch (\dml_sessionwait_exception $ex) {

            // 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.

            error_log('Cannot obtain session lock for sid: '.$sid);

            $this->failed = true;

            throw $ex;

        } catch (\Exception $ex) {

            // Do not rethrow exceptions here, this should not happen.

            error_log('Unknown exception when starting database session : '.$sid.' - '.$ex->getMessage());

            $this->failed = true;

            $this->recordid = null;

            return '';

        }

        // Finally read the full session data because we know we have the lock now.

        if (!$record = $this->database->get_record('sessions', array('id'=>$record->id), 'id, sessdata')) {

            // Ignore - something else just deleted the session record.

            $this->failed = true;

            $this->recordid = null;

            return '';

        }

        $this->failed = false;

        if (is_null($record->sessdata)) {

            $data = '';

            $this->lasthash = sha1('');

        } else {

            $data = base64_decode($record->sessdata);

            $this->lasthash = sha1($record->sessdata);

        }

        return $data;

    }

    /**

     * Write session handler.

     *

     * {@see http://php.net/manual/en/function.session-set-save-handler.php}

     *

     * NOTE: Do not write to output or throw any exceptions!

     *       Hopefully the next page is going to display nice error or it recovers...

     *

     * @param string $id

     * @param string $data

     * @return bool success

     */

    public function write(string $id, string $data): bool {

        if ($this->failed) {

            // Do not write anything back - we failed to start the session properly.

            return false;

        }

        // There might be some binary mess.

        $sessdata = base64_encode($data);

        $hash = sha1($sessdata);

        if ($hash === $this->lasthash) {

            return true;

        }

        try {

            if ($this->recordid) {

                $this->database->set_field('sessions', 'sessdata', $sessdata, ['id' => $this->recordid]);

            } else {

                // This happens in the first request when session record was just created in manager.

                $this->database->set_field('sessions', 'sessdata', $sessdata, ['sid' => $id]);

            }

        } catch (\Exception $ex) {

            // Do not rethrow exceptions here, this should not happen.

            // phpcs:ignore moodle.PHP.ForbiddenFunctions.FoundWithAlternative

            error_log(

                "Unknown exception when writing database session data : {$id} - " . $ex->getMessage(),

            );

        }

        return true;

    }

    /**

     * Destroy session handler.

     *

     * {@see http://php.net/manual/en/function.session-set-save-handler.php}

     *

     * @param string $id

     * @return bool success

     */

    public function destroy(string $id): bool {

        if (!$session = $this->database->get_record('sessions', ['sid' => $id], 'id, sid')) {

            if ($id == session_id()) {

                $this->recordid = null;

                $this->lasthash = null;

            }

            return true;

        }

        if ($this->recordid && ($session->id == $this->recordid)) {

            try {

                $this->database->release_session_lock($this->recordid);

            } catch (\Exception $ex) {

                // Ignore problems.

            }

            $this->recordid = null;

            $this->lasthash = null;

        }

        $this->database->delete_records('sessions', ['id' => $session->id]);

        return true;

    }

    /**

     * GC session handler.

     *

     * {@see http://php.net/manual/en/function.session-set-save-handler.php}

     *

     * @param int $max_lifetime moodle uses special timeout rules

     * @return bool success

     */

    // phpcs:ignore moodle.NamingConventions.ValidVariableName.VariableNameUnderscore

    public function gc(int $max_lifetime): int|false {

        // This should do something only if cron is not running properly...

        if (!$stalelifetime = ini_get('session.gc_maxlifetime')) {

            return false;

        }

        $params = ['purgebefore' => (time() - $stalelifetime)];

        $count = $this->database->count_records_select('sessions', 'userid = 0 AND timemodified < :purgebefore', $params);

        $this->database->delete_records_select('sessions', 'userid = 0 AND timemodified < :purgebefore', $params);

        return $count;

    }

}