system/libraries/Session/Session_driver.php

<?php
/**
 * CodeIgniter
 *
 * An open source application development framework for PHP
 *
 * This content is released under the MIT License (MIT)
 *
 * Copyright (c) 2014 - 2018, 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 - 2018, 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 Driver Class
 *
 * @package	CodeIgniter
 * @subpackage	Libraries
 * @category	Sessions
 * @author	Andrey Andreev
 * @link	https://codeigniter.com/user_guide/libraries/sessions.html
 */
abstract class CI_Session_driver implements SessionHandlerInterface {

	protected $_config;

	/**
	 * Data fingerprint
	 *
	 * @var	bool
	 */
	protected $_fingerprint;

	/**
	 * Lock placeholder
	 *
	 * @var	mixed
	 */
	protected $_lock = FALSE;

	/**
	 * Read session ID
	 *
	 * Used to detect session_regenerate_id() calls because PHP only calls
	 * write() after regenerating the ID.
	 *
	 * @var	string
	 */
	protected $_session_id;

	/**
	 * Success and failure return values
	 *
	 * Necessary due to a bug in all PHP 5 versions where return values
	 * from userspace handlers are not handled properly. PHP 7 fixes the
	 * bug, so we need to return different values depending on the version.
	 *
	 * @see	https://wiki.php.net/rfc/session.user.return-value
	 * @var	mixed
	 */
	protected $_success, $_failure;

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

	/**
	 * Class constructor
	 *
	 * @param	array	$params	Configuration parameters
	 * @return	void
	 */
	public function __construct(&$params)
	{
		$this->_config =& $params;

		if (is_php('7'))
		{
			$this->_success = TRUE;
			$this->_failure = FALSE;
		}
		else
		{
			$this->_success = 0;
			$this->_failure = -1;
		}
	}

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

	/**
	 * PHP 5.x validate ID
	 *
	 * Enforces session.use_strict_mode on PHP 5.x (7+ does it by itself)
	 *
	 * @return	void
	 */
	public function php5_validate_id()
	{
		if (PHP_VERSION_ID < 70000 && isset($_COOKIE[$this->_config['cookie_name']]) && ! $this->validateId($_COOKIE[$this->_config['cookie_name']]))
		{
			unset($_COOKIE[$this->_config['cookie_name']]);
		}
	}

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

	/**
	 * Cookie destroy
	 *
	 * Internal method to force removal of a cookie by the client
	 * when session_destroy() is called.
	 *
	 * @return	bool
	 */
	protected function _cookie_destroy()
	{
		return setcookie(
			$this->_config['cookie_name'],
			NULL,
			1,
			$this->_config['cookie_path'],
			$this->_config['cookie_domain'],
			$this->_config['cookie_secure'],
			TRUE
		);
	}

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

	/**
	 * Get lock
	 *
	 * A dummy method allowing drivers with no locking functionality
	 * (databases other than PostgreSQL and MySQL) to act as if they
	 * do acquire a lock.
	 *
	 * @param	string	$session_id
	 * @return	bool
	 */
	protected function _get_lock($session_id)
	{
		$this->_lock = TRUE;
		return TRUE;
	}

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

	/**
	 * Release lock
	 *
	 * @return	bool
	 */
	protected function _release_lock()
	{
		if ($this->_lock)
		{
			$this->_lock = FALSE;
		}

		return TRUE;
	}

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

	/**
	 * Fail
	 *
	 * Drivers other than the 'files' one don't (need to) use the
	 * session.save_path INI setting, but that leads to confusing
	 * error messages emitted by PHP when open() or write() fail,
	 * as the message contains session.save_path ...
	 * To work around the problem, the drivers will call this method
	 * so that the INI is set just in time for the error message to
	 * be properly generated.
	 *
	 * @return	mixed
	 */
	protected function _fail()
	{
		ini_set('session.save_path', config_item('sess_save_path'));
		return $this->_failure;
	}
}