The SessionHandler class

(PHP 5 >= 5.4.0)

Introduction

SessionHandler a special class that can be used to expose the current internal PHP session save handler by inheritance. There are six methods which wrap the six internal session save handler callbacks (open, close, read, write, destroy and gc). By default, this class will wrap whatever internal save handler is set as as defined by the session.save_handler configuration directive which is usually files by default. Other internal session save handlers are provided by PHP extensions such as SQLite (as sqlite), Memcache (as memcache), and Memcached (as memcached).

When a plain instance of SessionHandler is set as the save handler using session_set_save_handler() it will wrap the current save handlers. A class extending from SessionHandler allows you to override the methods or intercept or filter them by calls the parent class methods which ultimately wrap the interal PHP session handlers.

This allows you, for example, to intercept the read and write methods to encrypt/decrypt the session data and then pass the result to and from the parent class. Alternatively one might chose to entirely override a method like the garbage collection callback gc.

Because the SessionHandler wraps the current internal save handler methods, the above example of encryption can be applied to any internal save handler without having to know the internals of the handlers.

To use this class, first set the save handler you wish to expose using session.save_handler and then pass an instance of SessionHandler or one extending it to session_set_save_handler().

Please note the callback methods of this class are designed to be called internally by PHP and are not meant to be called from user-space code. The return values are equally processed internally by PHP. For more information on the session workflow, please refer session_set_save_handler().

Class synopsis

SessionHandler implements SessionHandlerInterface {
/* Methods */
public bool close ( void )
public bool destroy ( string $session_id )
public bool gc ( int $maxlifetime )
public bool open ( string $save_path , string $session_id )
public string read ( string $session_id )
public bool write ( string $session_id , string $session_data )
}
Warning

This class is designed to expose the current internal PHP session save handler, if you you want to write your own custom save handlers, please implement the SessionHandlerInterface interface instead of extending from SessionHandler.

Example #1 Using SessionHandler to add encryption to internal PHP save handlers.

<?php
class EncryptedSessionHandler extends SessionHandler
{
    private $key;

    public function __construct($key)
    {
        $this->key = $key;
    }

    public function read($id)
    {
        $data = parent::read($id);

        return mycrypt_decrypt(MCRYPT_3DES, $this->key, $data, MCRYPT_MODE_ECB);
    }

    public function write($id, $data)
    {
        $data = mcrypt_encrypt(MCRYPT_3DES, $this->key, $data, MCRYPT_MODE_ECB);

        return parent::write($id, $data);
    }
}

// we'll intercept the native 'files' handler, but will equally work
// with other internal native handlers like 'sqlite', 'memcache' or 'memcached'
// which are provided by PHP extensions.
ini_set('session.save_handler', 'files');
$handler = new EncryptedSessionHandler('mykey');
session_set_save_handler($handler, true);
session_start();

// proceed to set and retrieve values by key from $_SESSION

Note:

Since this class' methods are designed to be called internally by PHP as part of the normal session workflow, child class calls to parent methods (i.e. the actual internal native handlers) will return FALSE unless the session has actually been started (either automatically, or by explicit session_start(). This is important to consider when writing unit tests where the class methods might be invoked manually.

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