Sessions

Kohana provides classes that make it easy to work with both cookies and sessions. At a high level both sessions and cookies provide the same functionality. They allow the developer to store temporary or persistent information about a specific client for later retrieval, usually to make something persistent between requests.

Sessions should be used for storing temporary or private data. Very sensitive data should be stored using the [Session] class with the “database” or “native” adapters. When using the “cookie” adapter, the session should always be encrypted.

[!!] For more information on best practices with session variables see the seven deadly sins of sessions.

Storing, Retrieving, and Deleting Data

[Cookie] and [Session] provide a very similar API for storing data. The main difference between them is that sessions are accessed using an object, and cookies are accessed using a static class.

Accessing the session instance is done using the [Session::instance] method:

// Get the session instance
$session = Session::instance();

When using sessions, you can also get all of the current session data using the [Session::as_array] method:

// Get all of the session data as an array
$data = $session->as_array();

You can also use this to overload the $_SESSION global to get and set data in a way more similar to standard PHP:

// Overload $_SESSION with the session data
$_SESSION =& $session->as_array();

// Set session data
$_SESSION[$key] = $value;

Storing Data

Storing session or cookie data is done using the set method:

// Set session data
$session->set($key, $value);
// Or
Session::instance()->set($key, $value);

// Store a user id
$session->set('user_id', 10);

Retrieving Data

Getting session or cookie data is done using the get method:

// Get session data
$data = $session->get($key, $default_value);

// Get the user id
$user = $session->get('user_id');

Deleting Data

Deleting session or cookie data is done using the delete method:

// Delete session data
$session->delete($key);


// Delete the user id
$session->delete('user_id');

Session Configuration

Always check these settings before making your application live, as many of them will have a direct affect on the security of your application.

Session Adapters

When creating or accessing an instance of the [Session] class you can decide which session adapter or driver you wish to use. The session adapters that are available to you are:

Native

Stores session data in the default location for your web server. The storage location is defined by session.save_path in php.ini or defined by ini_set.

Database

Stores session data in a database table using the [Session_Database] class. Requires the [Database] module to be enabled.

Cookie

Stores session data in a cookie using the [Cookie] class. Sessions will have a 4KB limit when using this adapter, and should be encrypted.

The default adapter can be set by changing the value of [Session::$default]. The default adapter is “native”.

To access a Session using the default adapter, simply call [Session::instance()]. To access a Session using something other than the default, pass the adapter name to instance(), for example: Session::instance('cookie')

Session Adapter Settings

You can apply configuration settings to each of the session adapters by creating a session config file at APPPATH/config/session.php. The following sample configuration file defines all the settings for each adapter:

[!!] As with cookies, a “lifetime” setting of “0” means that the session will expire when the browser is closed.

return array(
    'native' => array(
        'name' => 'session_name',
        'lifetime' => 43200,
    ),
    'cookie' => array(
        'name' => 'cookie_name',
        'encrypted' => TRUE,
        'lifetime' => 43200,
    ),
    'database' => array(
        'name' => 'cookie_name',
        'encrypted' => TRUE,
        'lifetime' => 43200,
        'group' => 'default',
        'table' => 'table_name',
        'columns' => array(
            'session_id'  => 'session_id',
    		'last_active' => 'last_active',
    		'contents'    => 'contents'
        ),
        'gc' => 500,
    ),
);

Native Adapter

Cookie Adapter

Database Adapter

Table Schema

You will need to create the session storage table in the database. This is the default schema:

CREATE TABLE  `sessions` (
    `session_id` VARCHAR(24) NOT NULL,
    `last_active` INT UNSIGNED NOT NULL,
    `contents` TEXT NOT NULL,
    PRIMARY KEY (`session_id`),
    INDEX (`last_active`)
) ENGINE = MYISAM;

Table Columns

You can change the column names to match an existing database schema when connecting to a legacy session table. The default value is the same as the key value.

session_id

the name of the “id” column

last_active

UNIX timestamp of the last time the session was updated

contents

session data stored as a serialized string, and optionally encrypted