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<?php
/**
 * CodeIgniter
 *
 * An open source application development framework for PHP
 *
 * This content is released under the MIT License (MIT)
 *
 * Copyright (c) 2014 - 2016, British Columbia Institute of Technology
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in
 * all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
 * THE SOFTWARE.
 *
 * @package     CodeIgniter
 * @author      EllisLab Dev Team
 * @copyright   Copyright (c) 2008 - 2014, EllisLab, Inc. (https://ellislab.com/)
 * @copyright   Copyright (c) 2014 - 2016, British Columbia Institute of Technology (http://bcit.ca/)
 * @license     http://opensource.org/licenses/MIT      MIT License
 * @link        https://codeigniter.com
 * @since       Version 3.0.0
 * @filesource
 */
defined('BASEPATH') OR exit('No direct script access allowed');

/**
 * CodeIgniter Session Redis Driver
 *
 * @package     CodeIgniter
 * @subpackage  Libraries
 * @category    Sessions
 * @author      Andrey Andreev
 * @link        https://codeigniter.com/user_guide/libraries/sessions.html
 */
class CI_Session_redis_driver extends CI_Session_driver implements SessionHandlerInterface {

        /**
         * phpRedis instance
         *
         * @var resource
         */
        protected $_redis;

        /**
         * Key prefix
         *
         * @var string
         */
        protected $_key_prefix = 'ci_session:';

        /**
         * Lock key
         *
         * @var string
         */
        protected $_lock_key;

        /**
         * Key exists flag
         *
         * @var bool
         */
        protected $_key_exists = FALSE;

        // ------------------------------------------------------------------------

        /**
         * Class constructor
         *
         * @param       array   $params Configuration parameters
         * @return      void
         */
        public function __construct(&$params)
        {
                parent::__construct($params);

                if (empty($this->_config['save_path']))
                {
                        log_message('error', 'Session: No Redis save path configured.');
                }
                elseif (preg_match('#(?:tcp://)?([^:?]+)(?:\:(\d+))?(\?.+)?#', $this->_config['save_path'], $matches))
                {
                        isset($matches[3]) OR $matches[3] = ''; // Just to avoid undefined index notices below
                        $this->_config['save_path'] = array(
                                'host' => $matches[1],
                                'port' => empty($matches[2]) ? NULL : $matches[2],
                                'password' => preg_match('#auth=([^\s&]+)#', $matches[3], $match) ? $match[1] : NULL,
                                'database' => preg_match('#database=(\d+)#', $matches[3], $match) ? (int) $match[1] : NULL,
                                'timeout' => preg_match('#timeout=(\d+\.\d+)#', $matches[3], $match) ? (float) $match[1] : NULL
                        );

                        preg_match('#prefix=([^\s&]+)#', $matches[3], $match) && $this->_key_prefix = $match[1];
                }
                else
                {
                        log_message('error', 'Session: Invalid Redis save path format: '.$this->_config['save_path']);
                }

                if ($this->_config['match_ip'] === TRUE)
                {
                        $this->_key_prefix .= $_SERVER['REMOTE_ADDR'].':';
                }
        }

        // ------------------------------------------------------------------------

        /**
         * Open
         *
         * Sanitizes save_path and initializes connection.
         *
         * @param       string  $save_path      Server path
         * @param       string  $name           Session cookie name, unused
         * @return      bool
         */
        public function open($save_path, $name)
        {
                if (empty($this->_config['save_path']))
                {
                        return $this->_fail();
                }

                $redis = new Redis();
                if ( ! $redis->connect($this->_config['save_path']['host'], $this->_config['save_path']['port'], $this->_config['save_path']['timeout']))
                {
                        log_message('error', 'Session: Unable to connect to Redis with the configured settings.');
                }
                elseif (isset($this->_config['save_path']['password']) && ! $redis->auth($this->_config['save_path']['password']))
                {
                        log_message('error', 'Session: Unable to authenticate to Redis instance.');
                }
                elseif (isset($this->_config['save_path']['database']) && ! $redis->select($this->_config['save_path']['database']))
                {
                        log_message('error', 'Session: Unable to select Redis database with index '.$this->_config['save_path']['database']);
                }
                else
                {
                        $this->_redis = $redis;
                        return $this->_success;
                }

                return $this->_fail();
        }

        // ------------------------------------------------------------------------

        /**
         * Read
         *
         * Reads session data and acquires a lock
         *
         * @param       string  $session_id     Session ID
         * @return      string  Serialized session data
         */
        public function read($session_id)
        {
                if (isset($this->_redis) && $this->_get_lock($session_id))
                {
                        // Needed by write() to detect session_regenerate_id() calls
                        $this->_session_id = $session_id;

                        $session_data = $this->_redis->get($this->_key_prefix.$session_id);

                        is_string($session_data)
                                ? $this->_key_exists = TRUE
                                : $session_data = '';

                        $this->_fingerprint = md5($session_data);
                        return $session_data;
                }

                return $this->_fail();
        }

        // ------------------------------------------------------------------------

        /**
         * Write
         *
         * Writes (create / update) session data
         *
         * @param       string  $session_id     Session ID
         * @param       string  $session_data   Serialized session data
         * @return      bool
         */
        public function write($session_id, $session_data)
        {
                if ( ! isset($this->_redis))
                {
                        return $this->_fail();
                }
                // Was the ID regenerated?
                elseif ($session_id !== $this->_session_id)
                {
                        if ( ! $this->_release_lock() OR ! $this->_get_lock($session_id))
                        {
                                return $this->_fail();
                        }

                        $this->_key_exists = FALSE;
                        $this->_session_id = $session_id;
                }

                if (isset($this->_lock_key))
                {
                        $this->_redis->setTimeout($this->_lock_key, 300);
                        if ($this->_fingerprint !== ($fingerprint = md5($session_data)) OR $this->_key_exists === FALSE)
                        {
                                if ($this->_redis->set($this->_key_prefix.$session_id, $session_data, $this->_config['expiration']))
                                {
                                        $this->_fingerprint = $fingerprint;
                                        $this->_key_exists = TRUE;
                                        return $this->_success;
                                }

                                return $this->_fail();
                        }

                        return ($this->_redis->setTimeout($this->_key_prefix.$session_id, $this->_config['expiration']))
                                ? $this->_success
                                : $this->_fail();
                }

                return $this->_fail();
        }

        // ------------------------------------------------------------------------

        /**
         * Close
         *
         * Releases locks and closes connection.
         *
         * @return      bool
         */
        public function close()
        {
                if (isset($this->_redis))
                {
                        try {
                                if ($this->_redis->ping() === '+PONG')
                                {
                                        $this->_release_lock();
                                        if ($this->_redis->close() === FALSE)
                                        {
                                                return $this->_fail();
                                        }
                                }
                        }
                        catch (RedisException $e)
                        {
                                log_message('error', 'Session: Got RedisException on close(): '.$e->getMessage());
                        }

                        $this->_redis = NULL;
                        return $this->_success;
                }

                return $this->_success;
        }

        // ------------------------------------------------------------------------

        /**
         * Destroy
         *
         * Destroys the current session.
         *
         * @param       string  $session_id     Session ID
         * @return      bool
         */
        public function destroy($session_id)
        {
                if (isset($this->_redis, $this->_lock_key))
                {
                        if (($result = $this->_redis->delete($this->_key_prefix.$session_id)) !== 1)
                        {
                                log_message('debug', 'Session: Redis::delete() expected to return 1, got '.var_export($result, TRUE).' instead.');
                        }

                        $this->_cookie_destroy();
                        return $this->_success;
                }

                return $this->_fail();
        }

        // ------------------------------------------------------------------------

        /**
         * Garbage Collector
         *
         * Deletes expired sessions
         *
         * @param       int     $maxlifetime    Maximum lifetime of sessions
         * @return      bool
         */
        public function gc($maxlifetime)
        {
                // Not necessary, Redis takes care of that.
                return $this->_success;
        }

        // ------------------------------------------------------------------------

        /**
         * Get lock
         *
         * Acquires an (emulated) lock.
         *
         * @param       string  $session_id     Session ID
         * @return      bool
         */
        protected function _get_lock($session_id)
        {
                // PHP 7 reuses the SessionHandler object on regeneration,
                // so we need to check here if the lock key is for the
                // correct session ID.
                if ($this->_lock_key === $this->_key_prefix.$session_id.':lock')
                {
                        return $this->_redis->setTimeout($this->_lock_key, 300);
                }

                // 30 attempts to obtain a lock, in case another request already has it
                $lock_key = $this->_key_prefix.$session_id.':lock';
                $attempt = 0;
                do
                {
                        if (($ttl = $this->_redis->ttl($lock_key)) > 0)
                        {
                                sleep(1);
                                continue;
                        }

                        if ( ! $this->_redis->setex($lock_key, 300, time()))
                        {
                                log_message('error', 'Session: Error while trying to obtain lock for '.$this->_key_prefix.$session_id);
                                return FALSE;
                        }

                        $this->_lock_key = $lock_key;
                        break;
                }
                while (++$attempt < 30);

                if ($attempt === 30)
                {
                        log_message('error', 'Session: Unable to obtain lock for '.$this->_key_prefix.$session_id.' after 30 attempts, aborting.');
                        return FALSE;
                }
                elseif ($ttl === -1)
                {
                        log_message('debug', 'Session: Lock for '.$this->_key_prefix.$session_id.' had no TTL, overriding.');
                }

                $this->_lock = TRUE;
                return TRUE;
        }

        // ------------------------------------------------------------------------

        /**
         * Release lock
         *
         * Releases a previously acquired lock
         *
         * @return      bool
         */
        protected function _release_lock()
        {
                if (isset($this->_redis, $this->_lock_key) && $this->_lock)
                {
                        if ( ! $this->_redis->delete($this->_lock_key))
                        {
                                log_message('error', 'Session: Error while trying to free lock for '.$this->_lock_key);
                                return FALSE;
                        }

                        $this->_lock_key = NULL;
                        $this->_lock = FALSE;
                }

                return TRUE;
        }

}