altmetric/mongo-session-handler

A PHP session handler backed by MongoDB.

v2.1.0 2017-06-28 12:41 UTC

README

A PHP session handler backed by MongoDB.

Current version: 2.1.0
Supported PHP versions: 5.4, 5.5, 5.6, 7

Note: This package depends on the MongoDB PHP driver extension (mongodb) and its companion PHP library. If you need to use the older, legacy driver (mongo), please see version 1.0.

Installation

$ composer require altmetric/mongo-session-handler:^2.1

Usage

<?php
use Altmetric\MongoSessionHandler;

$sessions = $mongoClient->someDB->sessions;
$handler = new MongoSessionHandler($sessions);

session_set_save_handler($handler);
session_set_cookie_params(0, '/', '.example.com', false, true);
session_name('my_session_name');
session_start();

API Documentation

public MongoSessionHandler::__construct(MongoDB\Collection $collection[, Psr\Log\LoggerInterface $logger])

$handler = new \Altmetric\MongoSessionHandler($client->db->sessions);
session_set_save_handler($handler);
session_start();

$handler = new \Altmetric\MongoSessionHandler($client->db->sessions, $logger);

Instantiate a new MongoDB session handler with the following arguments:

  • $collection: a MongoDB\Collection collection to use for session storage;
  • $logger: an optional PSR-3-compliant logger.

The given $collection will be populated with documents using the following schema:

This handler implements the SessionHandlerInterface meaning that it can be registered as a session handler with session_set_save_handler.

Expiring sessions

If you wish to clean up expired sessions using SessionHandlerInterface::gc, ensure that your session.gc_divisor, session.gc_probability and session.gc_maxlifetime settings are populated accordingly, e.g. the following settings in your php.ini mean that sessions that haven't been updated in over an hour have a 1% chance of being cleaned whenever someone starts a new session:

session.gc_probability = 1
session.gc_divisor = 100
session.gc_maxlifetime = 3600

In order to keep session cleaning fast, you should add an index on the last_accessed field of your session $collection, e.g.

db.sessions.createIndex({last_accessed: 1});

Concurrency

As MongoDB prior to 3.0 does not support document level locking, this session handler operates on a principle of Last Write Wins.

If a user of a session causes two simultaneous writes then you may end up with the following situation:

  1. Window A reads session value of ['foo' => 'bar'];
  2. Window B reads session value of ['foo' => 'bar'];
  3. Window B writes session value of ['foo' => 'baz'];
  4. Window A writes session value of ['foo' => 'quux'].

The session will now contain ['foo' => 'quux'] as it was the last successful write. This may be surprising if you're trying to increment some value in a session as it is not locked during reads and writes:

  1. Window A reads session value of ['count' => 0];
  2. Window B reads session value of ['count' => 0];
  3. Window B writes session value of ['count' => 1];
  4. Window A writes session value of ['count' => 1].

Acknowledgements

License

Copyright © 2015-2017 Altmetric LLP

Distributed under the MIT License.