Session Functions
PHP Manual

session_set_save_handler

Sets user-level session storage functions

Description

bool session_set_save_handler ( callable $open , callable $close , callable $read , callable $write , callable $destroy , callable $gc )

Since PHP 5.4 it is possible to register the following prototype:

bool session_set_save_handler ( SessionHandlerInterface $sessionhandler [, bool $register_shutdown = true ] )

session_set_save_handler sets the user-level session storage functions which are used for storing and retrieving data associated with a session. This is most useful when a storage method other than those supplied by PHP sessions is preferred. i.e. Storing the session data in a local database.

Parameters

This function has two prototypes.

sessionhandler

An instance of a class implementing SessionHandlerInterface, such as SessionHandler, to register as the session handler. Since PHP 5.4 only.

register_shutdown

Register session_write_close as a register_shutdown_function function.

or
open(string $savePath, string $sessionName)

The open callback works like a constructor in classes and is executed when the session is being opened. It is the first callback function executed when the session is started automatically or manually with session_start. Return value is TRUE for success, FALSE for failure.

close()

The close callback works like a destructor in classes and is executed after the session write callback has been called. It is also invoked when session_write_close is called. Return value should be TRUE for success, FALSE for failure.

read(string $sessionId)

The read callback must always return a session encoded (serialized) string, or an empty string if there is no data to read.

This callback is called internally by PHP when the session starts or when session_start is called. Before this callback is invoked PHP will invoke the open callback.

The value this callback returns must be in exactly the same serialized format that was originally passed for storage to the write callback. The value returned will be unserialized automatically by PHP and used to populate the $_SESSION superglobal. While the data looks similar to serialize please note it is a different format which is speficied in the session.serialize_handler ini setting.

write(string $sessionId, string $data)

The write callback is called when the session needs to be saved and closed. This callback receives the current session ID a serialized version the $_SESSION superglobal. The serialization method used internally by PHP is specified in the session.serialize_handler ini setting.

The serialized session data passed to this callback should be stored against the passed session ID. When retrieving this data, the read callback must return the exact value that was originally passed to the write callback.

This callback is invoked when PHP shuts down or explicitly when session_write_close is called. Note that after executing this function PHP will internally execute the close callback.

Note:

The "write" handler is not executed until after the output stream is closed. Thus, output from debugging statements in the "write" handler will never be seen in the browser. If debugging output is necessary, it is suggested that the debug output be written to a file instead.

destroy($sessionId)

This callback is executed when a session is destroyed with session_destroy or with session_regenerate_id with the destroy parameter set to TRUE. Return value should be TRUE for success, FALSE for failure.

gc($lifetime)

The garbage collector callback is invoked internally by PHP periodically in order to purge old session data. The frequency is controlled by session.gc_probability and session.gc_divisor. The value of lifetime which is passed to this callback can be set in session.gc_maxlifetime. Return value should be TRUE for success, FALSE for failure.

Return Values

Returns TRUE on success or FALSE on failure.

Examples

Example #1 Custom session handler: see full code in SessionHandlerInterface synposis.

The following code is for PHP version 5.4.0 and above. We just show the invokation here, the full example can be seen in the SessionHandlerInterface synposis linked above.

Note we use the OOP prototype with session_set_save_handler and register the shutdown function using the function's parameter flag. This is generally advised when registering objects as session save handlers.

<?php
class MySessionHandler implements SessionHandlerInterface
{
    // implement interfaces here
}

$handler = new MySessionHandler();
session_set_save_handler($handler, true);
session_start();

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

Example #2 Custom session save handler using objects

The following code is for PHP versions less than 5.4.0.

The following example provides file based session storage similar to the PHP sessions default save handler files. This example could easily be extended to cover database storage using your favorite PHP supported database engine.

Note we additionally register the shutdown function session_write_close using register_shutdown_function under PHP less than 5.4.0. This is generally advised when registering objects as session save handlers under PHP less than 5.4.0.

<?php
class FileSessionHandler
{
    private $savePath;

    function open($savePath, $sessionName)
    {
        $this->savePath = $savePath;
        if (!is_dir($this->savePath)) {
            mkdir($this->savePath, 0777);
        }

        return true;
    }

    function close()
    {
        return true;
    }

    function read($id)
    {
        return (string)@file_get_contents("$this->savePath/sess_$id");
    }

    function write($id, $data)
    {
        return file_put_contents("$this->savePath/sess_$id", $data) === false ? false : true;
    }

    function destroy($id)
    {
        $file = "$this->savePath/sess_$id";
        if (file_exists($file)) {
            unlink($file);
        }

        return true;
    }

    function gc($maxlifetime)
    {
        foreach (glob("$this->savePath/sess_*") as $file) {
            if (filemtime($file) + $maxlifetime < time() && file_exists($file)) {
                unlink($file);
            }
        }

        return true;
    }
}

$handler = new FileSessionHandler();
session_set_save_handler(
    array($handler, 'open'),
    array($handler, 'close'),
    array($handler, 'read'),
    array($handler, 'write'),
    array($handler, 'destroy'),
    array($handler, 'gc')
    );

// the following prevents unexpected effects when using objects as save handlers
register_shutdown_function('session_write_close');

session_start();
// proceed to set and retrieve values by key from $_SESSION

Notes

Warning

When using objects as session save handlers, it is important to register the shutdown function with PHP to avoid unexpected side-effects from the way PHP internally destroys objects on shutdown and may prevent the write and close from being called. Typically you should register 'session_write_close' using the register_shutdown_function function.

As of PHP 5.4.0 you can use session_register_shutdown or simply use the 'register shutdown' flag when invoking session_set_save_handler using the OOP method and passing an instance that implements SessionHandlerInterface.

Warning

As of PHP 5.0.5 the write and close handlers are called after object destruction and therefore cannot use objects or throw exceptions. Exceptions are not able to be caught since will not be caught nor will any exception trace be displayed and the execution will just cease unexpectedly. The object destructors can however use sessions.

It is possible to call session_write_close from the destructor to solve this chicken and egg problem but the most reliable way is to register the shutdown function as described above.

Warning

Current working directory is changed with some SAPIs if session is closed in the script termination. It is possible to close the session earlier with session_write_close.

Changelog

Version Description
5.4.0 Added SessionHandlerInterface for implementing session handlers and SessionHandler to expose internal PHP session handlers.

See Also