A simple interface for storing and retrieving session data without the use of PHP's native session handling

3.2.0 2022-08-25 07:34 UTC

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Last update: 2024-03-25 11:17:04 UTC


A simple interface for storing and retrieving session data without the use of PHP's native session handling.

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If your project is using composer, simply require the package:

composer require kodus/session


This library provides a way of working with session data that promotes type safety and simplicity, without relying on PHP's native session handling.

Type safety is accomplished by gathering the session data into simple session model classes, whose attributes and methods can be type hinted, and storing instances of these in session, rather than storing values individually.

This approach requires an added amount of boilerplate code. The advantage of these session models easily outweighs the small amount of added workload of writing a small and simple data model.

Write operations to the session are deffered until the end of the request, when they are saved to the storage. This prevents broken session states as a result of critical errors.

Starting and ending sessions happens implicitly - for example, a session won't persist (and no session-cookie will be emitted) unless there is any data in the session; likewise, session will automatically terminate if session-data is cleared and/or the last session-model gets garbage-collected.

Session models

When storing data in session, the first step is to define your session model. You can think of a session model class as a container class for your session data.

A good example of a session model could be a user session model. Let's look at a user session, where both the ID and the full name of the user needs to be stored in session:

class UserSession implements SessionModel
    private $user_id;
    private $full_name;
    public function setUserID(int $user_id)
        $this->user_id = $user_id;
    public function getUserID(): int
        return $this->user_id ?: 0;
    public function setFullName(string $full_name)
        $this->full_name = $full_name;
    public function getFullName(): string
        return $this->full_name ?: "";
    public function isEmpty(): bool
        return empty($this->user_id) && empty($this->full_name);

These models should be encapsulated to the current domain. In other words, don't be tempted to collect all session data into a big "catch-all" session model.

The interface SessionModel only requires you to implement the method isEmpty(), so you can define you session models to your preferred style, as long as the following holds true:

  • Instances of SessionModel MUST be able to be serialized and deserialized by native PHP serialization functions without loss of data.

  • Instances of SessionModel MUST have a constructor method with no arguments, or default values for all constructor arguments.

It is strongly encouraged that implementations of SessionModel should only have attributes and methods specifically related to storing session data.

SessionModel::isEmpty(): bool: This method should only return true when a session models state is the same as when it was first constructed. When serializing the session models this is used for garbage collection, removing empty models from storage.


The interface Session defines a locator for your session models. You get session models for the current session by calling the get method.

The get() method returns a reference to the session model. All changes made to the instance are stored at the end of the request.

/** @var UserSession $user_session */
$user_session = $session->get(UserSession::class);

Session models are always available

Only one instance of a session model is available per session, and it is always available. If an instance of the session model was not stored in cache, a new instance will be created and returned by get().

This means you can assume that an instance of the session model is always available.

Deleting individual session models

Because session models are always available, you will never delete a session model directly.

Instead, your models must indicate via the SessionModel::isEmpty() method whether your model considers itself to be empty - if so, the Session Service will garbage-collect it at the end of the request.

If your individual session model can be "cleared", your model must define what that means - for example, the following model implementation supports a clear() method:

class UserSession implements SessionModel
    private $user_id;

    public function clear()

    public function isEmpty(): bool
        return empty($this->user_id);

    // ...

Clearing session state

You can clear an entire session, typically in a log-out controller/action:


Note that clearing the session will orphan any objects previously obtained via get().

Clearing the session also implicitly renews the session, as described below.

Renewing sessions

You can renew an existing session, typically in a log-in controller/action:


Renewing a session will retain the current session state, but changes the Session ID, and destroys the session data associated with the old Session ID.

Note that periodic renewal of the Session ID is not recommended - issuing a new Session ID should be done only after authentication, e.g. after successful validation of user-supplied login credentials over a secure connection.

Destroying a specific session

In rare cases, you may wish to destroy a specific session. For example, you may wish to forcibly destroy the active session of a user who has been blocked/banned from the site by an administrator.

You can do this by accessing the underlying SessionStorage implementation:


Note that this requires you to track the active Session ID for your users, which is outside the scope of this package - you could, for example, store the most recent Session ID in a column in your user-table in the database.

If you're using a dependency injection container, you should bootstrap the SessionStorage as a separate component, so you can access it independently of the SessionService.

Flash messages

A flash message is a message that can only be read once, e.g. notifications. With the session model concept this becomes a trivial task:

class Notifications implements SessionModel
    private $notifications = [];

    public function add(string $message)
        $this->notifications[] = $message;
    public function take()
        $notifications = $this->notifications;
        $this->notifications = [];
        return $notifications;

    public function isEmpty(): bool
        return count($this->notifications) == 0;


The package includes a PSR-15 compliant SessionMiddleware for easy integration of SessionService.

Either use this with your PSR-15 compatible middleware stack, or use it as reference for making custom middleware that integrates more deeply with the rest of your stack.

Put this near the top of your middleware stack - it will initialize the session state, then delegate unconditionally to the rest of your middleware stack, and finally commits any changes to session storage.

The request will be decorated with a SessionData instance, which can be obtained from the request, in lower layers of your middleware stack, using e.g. $request->getAttribute(SessionMiddleware::ATTRIBUTE_NAME).

Session Service

This section details how to integrate SessionService into your own stack.

To initialize a session (at the beginning of a request) use the beginSession() method, which returns an instance of SessionData, which represents the session state for the request you're processing.

SessionData implements Session, which defines the public facet of SessionData - type-hint against Session, for example, when providing this (e.g. via constructor-injection) to your controllers.

To commit changes to session state (at the end of a request) use the commitSession() method, which also adds a session cookie to a PSR-7 ResponseInterface instance.

Refer to SessionMiddleware for a working implementation of this pattern.

Storage Adapters

Customizing session storage is possible by implementing the SessionStorage interface.

Currently kodus/session comes with a SimpleCacheAdapter, which depends on an implementation of the PSR-16 cache interface for the physical storage of raw Session Data.

We recommend the ScrapBook package as a cache provider for SimpleCacheAdapter.


Here's an example of how to fully bootstrap all layers of the session abstraction, from a PDO database connection at the lowest level, over ScrapBook's SQLLite cache provider, to our PSR-16 Session Storage adapter, and finally to PSR-15 middleware:

use PDO;
use MatthiasMullie\Scrapbook\Adapters\SQLite;
use MatthiasMullie\Scrapbook\Psr16\SimpleCache;
use Kodus\Session\Adapters\SimpleCacheAdapter;
use Kodus\Session\SessionMiddleware;

$connection = new PDO('sqlite:cache.db');

$cache = new SimpleCache(new SQLite($connection));

$storage = new SimpleCacheAdapter($cache);

$service = new SessionService($storage);

$middleware = new SessionMiddleware($service);