Session Library
***************

The Session class permits you maintain a user’s “state” and track
their activity while they browse your site.

CodeIgniter comes with a few session storage drivers:

   * files (default; file-system based)

   * database

   * redis

   * memcached

In addition, you may create your own, custom session drivers based on
other kinds of storage, while still taking advantage of the features
of the Session class.

* Using the Session Class

  * Initializing a Session

  * How do Sessions work?

    * A note about concurrency

  * What is Session Data?

  * Retrieving Session Data

  * Adding Session Data

  * Removing Session Data

  * Flashdata

  * Tempdata

  * Destroying a Session

  * Accessing session metadata

  * Session Preferences

  * Session Drivers

    * Files Driver

      * Bonus Tip

    * Database Driver

    * Redis Driver

    * Memcached Driver

      * Bonus Tip

    * Custom Drivers

* Class Reference


Using the Session Class
=======================


Initializing a Session
----------------------

Sessions will typically run globally with each page load, so the
Session class should either be initialized in your controller
constructors, or it can be auto-loaded by the system. For the most
part the session class will run unattended in the background, so
simply initializing the class will cause it to read, create, and
update sessions when necessary.

To initialize the Session class manually in your controller
constructor, use the "$this->load->library()" method:

   $this->load->library('session');

Once loaded, the Sessions library object will be available using:

   $this->session

Important:

  Because the Loader Class is instantiated by CodeIgniter’s base
  controller, make sure to call "parent::__construct()" before trying
  to load a library from inside a controller constructor.


How do Sessions work?
---------------------

When a page is loaded, the session class will check to see if valid
session cookie is sent by the user’s browser. If a sessions cookie
does **not** exist (or if it doesn’t match one stored on the server or
has expired) a new session will be created and saved.

If a valid session does exist, its information will be updated. With
each update, the session ID may be regenerated if configured to do so.

It’s important for you to understand that once initialized, the
Session class runs automatically. There is nothing you need to do to
cause the above behavior to happen. You can, as you’ll see below, work
with session data, but the process of reading, writing, and updating a
session is automatic.

Note:

  Under CLI, the Session library will automatically halt itself, as
  this is a concept based entirely on the HTTP protocol.


A note about concurrency
~~~~~~~~~~~~~~~~~~~~~~~~

Unless you’re developing a website with heavy AJAX usage, you can skip
this section. If you are, however, and if you’re experiencing
performance issues, then this note is exactly what you’re looking for.

Sessions in previous versions of CodeIgniter didn’t implement locking,
which meant that two HTTP requests using the same session could run
exactly at the same time. To use a more appropriate technical term -
requests were non-blocking.

However, non-blocking requests in the context of sessions also means
unsafe, because modifications to session data (or session ID
regeneration) in one request can interfere with the execution of a
second, concurrent request. This detail was at the root of many issues
and the main reason why CodeIgniter 3.0 has a completely re-written
Session library.

Why are we telling you this? Because it is likely that after trying to
find the reason for your performance issues, you may conclude that
locking is the issue and therefore look into how to remove the locks …

DO NOT DO THAT! Removing locks would be **wrong** and it will cause
you more problems!

Locking is not the issue, it is a solution. Your issue is that you
still have the session open, while you’ve already processed it and
therefore no longer need it. So, what you need is to close the session
for the current request after you no longer need it.

Long story short - call "session_write_close()" once you no longer
need anything to do with session variables.


What is Session Data?
---------------------

Session data is simply an array associated with a particular session
ID (cookie).

If you’ve used sessions in PHP before, you should be familiar with
PHP’s $_SESSION superglobal (if not, please read the content on that
link).

CodeIgniter gives access to its session data through the same means,
as it uses the session handlers’ mechanism provided by PHP. Using
session data is as simple as manipulating (read, set and unset values)
the "$_SESSION" array.

In addition, CodeIgniter also provides 2 special types of session data
that are further explained below: flashdata and tempdata.

Note:

  In previous versions, regular session data in CodeIgniter was
  referred to as ‘userdata’. Have this in mind if that term is used
  elsewhere in the manual. Most of it is written to explain how the
  custom ‘userdata’ methods work.


Retrieving Session Data
-----------------------

Any piece of information from the session array is available through
the "$_SESSION" superglobal:

   $_SESSION['item']

Or through the magic getter:

   $this->session->item

And for backwards compatibility, through the "userdata()" method:

   $this->session->userdata('item');

Where item is the array key corresponding to the item you wish to
fetch. For example, to assign a previously stored ‘name’ item to the
"$name" variable, you will do this:

   $name = $_SESSION['name'];

   // or:

   $name = $this->session->name

   // or:

   $name = $this->session->userdata('name');

Note:

  The "userdata()" method returns NULL if the item you are trying to
  access does not exist.

If you want to retrieve all of the existing userdata, you can simply
omit the item key (magic getter only works for properties):

   $_SESSION

   // or:

   $this->session->userdata();


Adding Session Data
-------------------

Let’s say a particular user logs into your site. Once authenticated,
you could add their username and e-mail address to the session, making
that data globally available to you without having to run a database
query when you need it.

You can simply assign data to the "$_SESSION" array, as with any other
variable. Or as a property of "$this->session".

Alternatively, the old method of assigning it as “userdata” is also
available. That however passing an array containing your new data to
the "set_userdata()" method:

   $this->session->set_userdata($array);

Where "$array" is an associative array containing your new data.
Here’s an example:

   $newdata = array(
           'username'  => 'johndoe',
           'email'     => 'johndoe@some-site.com',
           'logged_in' => TRUE
   );

   $this->session->set_userdata($newdata);

If you want to add userdata one value at a time, "set_userdata()" also
supports this syntax:

   $this->session->set_userdata('some_name', 'some_value');

If you want to verify that a session value exists, simply check with
"isset()":

   // returns FALSE if the 'some_name' item doesn't exist or is NULL,
   // TRUE otherwise:
   isset($_SESSION['some_name'])

Or you can call "has_userdata()":

   $this->session->has_userdata('some_name');


Removing Session Data
---------------------

Just as with any other variable, unsetting a value in "$_SESSION" can
be done through "unset()":

   unset($_SESSION['some_name']);

   // or multiple values:

   unset(
           $_SESSION['some_name'],
           $_SESSION['another_name']
   );

Also, just as "set_userdata()" can be used to add information to a
session, "unset_userdata()" can be used to remove it, by passing the
session key. For example, if you wanted to remove ‘some_name’ from
your session data array:

   $this->session->unset_userdata('some_name');

This method also accepts an array of item keys to unset:

   $array_items = array('username', 'email');

   $this->session->unset_userdata($array_items);

Note:

  In previous versions, the "unset_userdata()" method used to accept
  an associative array of "key => 'dummy value'" pairs. This is no
  longer supported.


Flashdata
---------

CodeIgniter supports “flashdata”, or session data that will only be
available for the next request, and is then automatically cleared.

This can be very useful, especially for one-time informational, error
or status messages (for example: “Record 2 deleted”).

It should be noted that flashdata variables are regular session vars,
only marked in a specific way under the ‘__ci_vars’ key (please don’t
touch that one, you’ve been warned).

To mark an existing item as “flashdata”:

   $this->session->mark_as_flash('item');

If you want to mark multiple items as flashdata, simply pass the keys
as an array:

   $this->session->mark_as_flash(array('item', 'item2'));

To add flashdata:

   $_SESSION['item'] = 'value';
   $this->session->mark_as_flash('item');

Or alternatively, using the "set_flashdata()" method:

   $this->session->set_flashdata('item', 'value');

You can also pass an array to "set_flashdata()", in the same manner as
"set_userdata()".

Reading flashdata variables is the same as reading regular session
data through "$_SESSION":

   $_SESSION['item']

Important:

  The "userdata()" method will NOT return flashdata items.

However, if you want to be sure that you’re reading “flashdata” (and
not any other kind), you can also use the "flashdata()" method:

   $this->session->flashdata('item');

Or to get an array with all flashdata, simply omit the key parameter:

   $this->session->flashdata();

Note:

  The "flashdata()" method returns NULL if the item cannot be found.

If you find that you need to preserve a flashdata variable through an
additional request, you can do so using the "keep_flashdata()" method.
You can either pass a single item or an array of flashdata items to
keep.

   $this->session->keep_flashdata('item');
   $this->session->keep_flashdata(array('item1', 'item2', 'item3'));


Tempdata
--------

CodeIgniter also supports “tempdata”, or session data with a specific
expiration time. After the value expires, or the session expires or is
deleted, the value is automatically removed.

Similarly to flashdata, tempdata variables are regular session vars
that are marked in a specific way under the ‘__ci_vars’ key (again,
don’t touch that one).

To mark an existing item as “tempdata”, simply pass its key and expiry
time (in seconds!) to the "mark_as_temp()" method:

   // 'item' will be erased after 300 seconds
   $this->session->mark_as_temp('item', 300);

You can mark multiple items as tempdata in two ways, depending on
whether you want them all to have the same expiry time or not:

   // Both 'item' and 'item2' will expire after 300 seconds
   $this->session->mark_as_temp(array('item', 'item2'), 300);

   // 'item' will be erased after 300 seconds, while 'item2'
   // will do so after only 240 seconds
   $this->session->mark_as_temp(array(
           'item'  => 300,
           'item2' => 240
   ));

To add tempdata:

   $_SESSION['item'] = 'value';
   $this->session->mark_as_temp('item', 300); // Expire in 5 minutes

Or alternatively, using the "set_tempdata()" method:

   $this->session->set_tempdata('item', 'value', 300);

You can also pass an array to "set_tempdata()":

   $tempdata = array('newuser' => TRUE, 'message' => 'Thanks for joining!');

   $this->session->set_tempdata($tempdata, NULL, $expire);

Note:

  If the expiration is omitted or set to 0, the default time-to-live
  value of 300 seconds (or 5 minutes) will be used.

To read a tempdata variable, again you can just access it through the
"$_SESSION" superglobal array:

   $_SESSION['item']

Important:

  The "userdata()" method will NOT return tempdata items.

Or if you want to be sure that you’re reading “tempdata” (and not any
other kind), you can also use the "tempdata()" method:

   $this->session->tempdata('item');

And of course, if you want to retrieve all existing tempdata:

   $this->session->tempdata();

Note:

  The "tempdata()" method returns NULL if the item cannot be found.

If you need to remove a tempdata value before it expires, you can
directly unset it from the "$_SESSION" array:

   unset($_SESSION['item']);

However, this won’t remove the marker that makes this specific item to
be tempdata (it will be invalidated on the next HTTP request), so if
you intend to reuse that same key in the same request, you’d want to
use "unset_tempdata()":

   $this->session->unset_tempdata('item');


Destroying a Session
--------------------

To clear the current session (for example, during a logout), you may
simply use either PHP’s session_destroy() function, or the
"sess_destroy()" method. Both will work in exactly the same way:

   session_destroy();

   // or

   $this->session->sess_destroy();

Note:

  This must be the last session-related operation that you do during
  the same request. All session data (including flashdata and
  tempdata) will be destroyed permanently and functions will be
  unusable during the same request after you destroy the session.


Accessing session metadata
--------------------------

In previous CodeIgniter versions, the session data array included 4
items by default: ‘session_id’, ‘ip_address’, ‘user_agent’,
‘last_activity’.

This was due to the specifics of how sessions worked, but is now no
longer necessary with our new implementation. However, it may happen
that your application relied on these values, so here are alternative
methods of accessing them:

   * session_id: "session_id()"

   * ip_address: "$_SERVER['REMOTE_ADDR']"

   * user_agent: "$this->input->user_agent()" (unused by sessions)

   * last_activity: Depends on the storage, no straightforward way.
     Sorry!


Session Preferences
-------------------

CodeIgniter will usually make everything work out of the box. However,
Sessions are a very sensitive component of any application, so some
careful configuration must be done. Please take your time to consider
all of the options and their effects.

You’ll find the following Session related preferences in your
**application/config/config.php** file:

+------------------------------+-----------------+------------------------------------------+----------------------------------------------------------------------------------------------+
| Preference                   | Default         | Options                                  | Description                                                                                  |
|==============================|=================|==========================================|==============================================================================================|
| **sess_driver**              | files           | files/database/redis/memcached/*custom*  | The session storage driver to use.                                                           |
+------------------------------+-----------------+------------------------------------------+----------------------------------------------------------------------------------------------+
| **sess_cookie_name**         | ci_session      | [A-Za-z_-] characters only               | The name used for the session cookie.                                                        |
+------------------------------+-----------------+------------------------------------------+----------------------------------------------------------------------------------------------+
| **sess_samesite**            | ci_session      | ‘Lax’, ‘Strict’ or ‘None’                | SameSite attribute value for session cookies. Defaults to "session.cookie_samesite" on PHP   |
|                              |                 |                                          | 7.3+ or ‘Lax’ if not present at all.                                                         |
+------------------------------+-----------------+------------------------------------------+----------------------------------------------------------------------------------------------+
| **sess_expiration**          | 7200 (2 hours)  | Time in seconds (integer)                | The number of seconds you would like the session to last. If you would like a non-expiring   |
|                              |                 |                                          | session (until browser is closed) set the value to zero: 0                                   |
+------------------------------+-----------------+------------------------------------------+----------------------------------------------------------------------------------------------+
| **sess_save_path**           | NULL            | None                                     | Specifies the storage location, depends on the driver being used.                            |
+------------------------------+-----------------+------------------------------------------+----------------------------------------------------------------------------------------------+
| **sess_match_ip**            | FALSE           | TRUE/FALSE (boolean)                     | Whether to validate the user’s IP address when reading the session cookie. Note that some    |
|                              |                 |                                          | ISPs dynamically changes the IP, so if you want a non-expiring session you will likely set   |
|                              |                 |                                          | this to FALSE.                                                                               |
+------------------------------+-----------------+------------------------------------------+----------------------------------------------------------------------------------------------+
| **sess_time_to_update**      | 300             | Time in seconds (integer)                | This option controls how often the session class will regenerate itself and create a new     |
|                              |                 |                                          | session ID. Setting it to 0 will disable session ID regeneration.                            |
+------------------------------+-----------------+------------------------------------------+----------------------------------------------------------------------------------------------+
| **sess_regenerate_destroy**  | FALSE           | TRUE/FALSE (boolean)                     | Whether to destroy session data associated with the old session ID when auto-regenerating    |
|                              |                 |                                          | the session ID. When set to FALSE, the data will be later deleted by the garbage collector.  |
+------------------------------+-----------------+------------------------------------------+----------------------------------------------------------------------------------------------+

Note:

  As a last resort, the Session library will try to fetch PHP’s
  session related INI settings, as well as legacy CI settings such as
  ‘sess_expire_on_close’ when any of the above is not configured.
  However, you should never rely on this behavior as it can cause
  unexpected results or be changed in the future. Please configure
  everything properly.

In addition to the values above, the cookie and native drivers apply
the following configuration values shared by the Input and Security
classes:

+--------------------+-----------------+-----------------------------------------------------------------------------+
| Preference         | Default         | Description                                                                 |
|====================|=================|=============================================================================|
| **cookie_domain**  | ‘’              | The domain for which the session is applicable                              |
+--------------------+-----------------+-----------------------------------------------------------------------------+
| **cookie_path**    | /               | The path to which the session is applicable                                 |
+--------------------+-----------------+-----------------------------------------------------------------------------+
| **cookie_secure**  | FALSE           | Whether to create the session cookie only on encrypted (HTTPS) connections  |
+--------------------+-----------------+-----------------------------------------------------------------------------+

Note:

  The ‘cookie_httponly’ setting doesn’t have an effect on sessions.
  Instead the HttpOnly parameter is always enabled, for security
  reasons. Additionally, the ‘cookie_prefix’ setting is completely
  ignored.


Session Drivers
---------------

As already mentioned, the Session library comes with 4 drivers, or
storage engines, that you can use:

   * files

   * database

   * redis

   * memcached

By default, the Files Driver will be used when a session is
initialized, because it is the most safe choice and is expected to
work everywhere (virtually every environment has a file system).

However, any other driver may be selected via the
"$config['sess_driver']" line in your
**application/config/config.php** file, if you chose to do so. Have it
in mind though, every driver has different caveats, so be sure to get
yourself familiar with them (below) before you make that choice.

In addition, you may also create and use Custom Drivers, if the ones
provided by default don’t satisfy your use case.

Note:

  In previous CodeIgniter versions, a different, “cookie driver” was
  the only option and we have received negative feedback on not
  providing that option. While we do listen to feedback from the
  community, we want to warn you that it was dropped because it is
  **unsafe** and we advise you NOT to try to replicate it via a custom
  driver.


Files Driver
~~~~~~~~~~~~

The ‘files’ driver uses your file system for storing session data.

It can safely be said that it works exactly like PHP’s own default
session implementation, but in case this is an important detail for
you, have it mind that it is in fact not the same code and it has some
limitations (and advantages).

To be more specific, it doesn’t support PHP’s directory level and mode
formats used in session.save_path, and it has most of the options
hard-coded for safety. Instead, only absolute paths are supported for
"$config['sess_save_path']".

Another important thing that you should know, is to make sure that you
don’t use a publicly-readable or shared directory for storing your
session files. Make sure that *only you* have access to see the
contents of your chosen *sess_save_path* directory. Otherwise, anybody
who can do that, can also steal any of the current sessions (also
known as “session fixation” attack).

On UNIX-like operating systems, this is usually achieved by setting
the 0700 mode permissions on that directory via the *chmod* command,
which allows only the directory’s owner to perform read and write
operations on it. But be careful because the system user *running* the
script is usually not your own, but something like ‘www-data’ instead,
so only setting those permissions will probable break your
application.

Instead, you should do something like this, depending on your
environment

   mkdir /<path to your application directory>/sessions/
   chmod 0700 /<path to your application directory>/sessions/
   chown www-data /<path to your application directory>/sessions/


Bonus Tip
"""""""""

Some of you will probably opt to choose another session driver because
file storage is usually slower. This is only half true.

A very basic test will probably trick you into believing that an SQL
database is faster, but in 99% of the cases, this is only true while
you only have a few current sessions. As the sessions count and server
loads increase - which is the time when it matters - the file system
will consistently outperform almost all relational database setups.

In addition, if performance is your only concern, you may want to look
into using tmpfs, (warning: external resource), which can make your
sessions blazing fast.


Database Driver
~~~~~~~~~~~~~~~

The ‘database’ driver uses a relational database such as MySQL or
PostgreSQL to store sessions. This is a popular choice among many
users, because it allows the developer easy access to the session data
within an application - it is just another table in your database.

However, there are some conditions that must be met:

   * Only your **default** database connection (or the one that you
     access as "$this->db" from your controllers) can be used.

   * You must have the Query Builder enabled.

   * You can NOT use a persistent connection.

   * You can NOT use a connection with the *cache_on* setting enabled.

In order to use the ‘database’ session driver, you must also create
this table that we already mentioned and then set it as your
"$config['sess_save_path']" value. For example, if you would like to
use ‘ci_sessions’ as your table name, you would do this:

   $config['sess_driver'] = 'database';
   $config['sess_save_path'] = 'ci_sessions';

Note:

  If you’ve upgraded from a previous version of CodeIgniter and you
  don’t have ‘sess_save_path’ configured, then the Session library
  will look for the old ‘sess_table_name’ setting and use it instead.
  Please don’t rely on this behavior as it will get removed in the
  future.

And then of course, create the database table …

For MySQL:

   CREATE TABLE IF NOT EXISTS `ci_sessions` (
           `id` varchar(128) NOT NULL,
           `ip_address` varchar(45) NOT NULL,
           `timestamp` int(10) unsigned DEFAULT 0 NOT NULL,
           `data` blob NOT NULL,
           KEY `ci_sessions_timestamp` (`timestamp`)
   );

For PostgreSQL:

   CREATE TABLE "ci_sessions" (
           "id" varchar(128) NOT NULL,
           "ip_address" varchar(45) NOT NULL,
           "timestamp" bigint DEFAULT 0 NOT NULL,
           "data" text DEFAULT '' NOT NULL
   );

   CREATE INDEX "ci_sessions_timestamp" ON "ci_sessions" ("timestamp");

You will also need to add a PRIMARY KEY **depending on your
‘sess_match_ip’ setting**. The examples below work both on MySQL and
PostgreSQL:

   // When sess_match_ip = TRUE
   ALTER TABLE ci_sessions ADD PRIMARY KEY (id, ip_address);

   // When sess_match_ip = FALSE
   ALTER TABLE ci_sessions ADD PRIMARY KEY (id);

   // To drop a previously created primary key (use when changing the setting)
   ALTER TABLE ci_sessions DROP PRIMARY KEY;

Important:

  Only MySQL and PostgreSQL databases are officially supported, due to
  lack of advisory locking mechanisms on other platforms. Using
  sessions without locks can cause all sorts of problems, especially
  with heavy usage of AJAX, and we will not support such cases. Use
  "session_write_close()" after you’ve done processing session data if
  you’re having performance issues.


Redis Driver
~~~~~~~~~~~~

Note:

  Since Redis doesn’t have a locking mechanism exposed, locks for this
  driver are emulated by a separate value that is kept for up to 300
  seconds.

Redis is a storage engine typically used for caching and popular
because of its high performance, which is also probably your reason to
use the ‘redis’ session driver.

The downside is that it is not as ubiquitous as relational databases
and requires the phpredis PHP extension to be installed on your
system, and that one doesn’t come bundled with PHP. Chances are,
you’re only be using the ‘redis’ driver only if you’re already both
familiar with Redis and using it for other purposes.

Just as with the ‘files’ and ‘database’ drivers, you must also
configure the storage location for your sessions via the
"$config['sess_save_path']" setting. The format here is a bit
different and complicated at the same time. It is best explained by
the *phpredis* extension’s README file, so we’ll simply link you to
it:

   https://github.com/phpredis/phpredis#php-session-handler

Warning:

  CodeIgniter’s Session library does NOT use the actual ‘redis’
  "session.save_handler". Take note **only** of the path format in the
  link above.

For the most common case however, a simple "host:port" pair should be
sufficient:

   $config['sess_driver'] = 'redis';
   $config['sess_save_path'] = 'tcp://localhost:6379';


Memcached Driver
~~~~~~~~~~~~~~~~

Note:

  Since Memcache doesn’t have a locking mechanism exposed, locks for
  this driver are emulated by a separate value that is kept for up to
  300 seconds.

The ‘memcached’ driver is very similar to the ‘redis’ one in all of
its properties, except perhaps for availability, because PHP’s
Memcached extension is distributed via PECL and some Linux
distrubutions make it available as an easy to install package.

Other than that, and without any intentional bias towards Redis,
there’s not much different to be said about Memcached - it is also a
popular product that is usually used for caching and famed for its
speed.

However, it is worth noting that the only guarantee given by Memcached
is that setting value X to expire after Y seconds will result in it
being deleted after Y seconds have passed (but not necessarily that it
won’t expire earlier than that time). This happens very rarely, but
should be considered as it may result in loss of sessions.

The "$config['sess_save_path']" format is fairly straightforward here,
being just a "host:port" pair:

   $config['sess_driver'] = 'memcached';
   $config['sess_save_path'] = 'localhost:11211';


Bonus Tip
"""""""""

Multi-server configuration with an optional *weight* parameter as the
third colon-separated (":weight") value is also supported, but we have
to note that we haven’t tested if that is reliable.

If you want to experiment with this feature (on your own risk), simply
separate the multiple server paths with commas:

   // localhost will be given higher priority (5) here,
   // compared to 192.0.2.1 with a weight of 1.
   $config['sess_save_path'] = 'localhost:11211:5,192.0.2.1:11211:1';


Custom Drivers
~~~~~~~~~~~~~~

You may also create your own, custom session drivers. However, have it
in mind that this is typically not an easy task, as it takes a lot of
knowledge to do it properly.

You need to know not only how sessions work in general, but also how
they work specifically in PHP, how the underlying storage mechanism
works, how to handle concurrency, avoid deadlocks (but NOT through
lack of locks) and last but not least - how to handle the potential
security issues, which is far from trivial.

Long story short - if you don’t know how to do that already in raw
PHP, you shouldn’t be trying to do it within CodeIgniter either.
You’ve been warned.

If you only want to add some extra functionality to your sessions,
just extend the base Session class, which is a lot more easier. Read
the Creating Libraries article to learn how to do that.

Now, to the point - there are three general rules that you must follow
when creating a session driver for CodeIgniter:

   * Put your driver’s file under
     **application/libraries/Session/drivers/** and follow the naming
     conventions used by the Session class.

     For example, if you were to create a ‘dummy’ driver, you would
     have a "Session_dummy_driver" class name, that is declared in
     *application/libraries/Session/drivers/Session_dummy_driver.php*.

   * Extend the "CI_Session_driver" class.

     This is just a basic class with a few internal helper methods. It
     is also extendable like any other library, if you really need to
     do that, but we are not going to explain how … if you’re familiar
     with how class extensions/overrides work in CI, then you already
     know how to do it. If not, well, you shouldn’t be doing it in the
     first place.

   * Implement the SessionHandlerInterface interface.

     Note:

       You may notice that "SessionHandlerInterface" is provided by
       PHP since version 5.4.0. CodeIgniter will automatically declare
       the same interface if you’re running an older PHP version.

     The link will explain why and how.

So, based on our ‘dummy’ driver example above, you’d end up with
something like this:

   // application/libraries/Session/drivers/Session_dummy_driver.php:

   class CI_Session_dummy_driver extends CI_Session_driver implements SessionHandlerInterface
   {

           public function __construct(&$params)
           {
                   // DO NOT forget this
                   parent::__construct($params);

                   // Configuration & other initializations
           }

           public function open($save_path, $name)
           {
                   // Initialize storage mechanism (connection)
           }

           public function read($session_id)
           {
                   // Read session data (if exists), acquire locks
           }

           public function write($session_id, $session_data)
           {
                   // Create / update session data (it might not exist!)
           }

           public function close()
           {
                   // Free locks, close connections / streams / etc.
           }

           public function destroy($session_id)
           {
                   // Call close() method & destroy data for current session (order may differ)
           }

           public function gc($maxlifetime)
           {
                   // Erase data for expired sessions
           }

   }

If you’ve done everything properly, you can now set your *sess_driver*
configuration value to ‘dummy’ and use your own driver.
Congratulations!


Class Reference
===============

class CI_Session

   userdata([$key = NULL])

      Parameters:
         * **$key** ("mixed") – Session item key or NULL

      Returns:
         Value of the specified item key, or an array of all userdata

      Return type:
         "mixed"

      Gets the value for a specific "$_SESSION" item, or an array of
      all “userdata” items if not key was specified.

      Note:

        This is a legacy method kept only for backwards compatibility
        with older applications. You should directly access
        "$_SESSION" instead.

   all_userdata()

      Returns:
         An array of all userdata

      Return type:
         "array"

      Returns an array containing all “userdata” items.

      Note:

        This method is DEPRECATED. Use "userdata()" with no parameters
        instead.

   &get_userdata()

      Returns:
         A reference to "$_SESSION"

      Return type:
         "array"

      Returns a reference to the "$_SESSION" array.

      Note:

        This is a legacy method kept only for backwards compatibility
        with older applications.

   has_userdata($key)

      Parameters:
         * **$key** ("string") – Session item key

      Returns:
         TRUE if the specified key exists, FALSE if not

      Return type:
         "bool"

      Checks if an item exists in "$_SESSION".

      Note:

        This is a legacy method kept only for backwards compatibility
        with older applications. It is just an alias for
        "isset($_SESSION[$key])" - please use that instead.

   set_userdata($data[, $value = NULL])

      Parameters:
         * **$data** ("mixed") – An array of key/value pairs to set as
           session data, or the key for a single item

         * **$value** ("mixed") – The value to set for a specific
           session item, if $data is a key

      Return type:
         "void"

      Assigns data to the "$_SESSION" superglobal.

      Note:

        This is a legacy method kept only for backwards compatibility
        with older applications.

   unset_userdata($key)

      Parameters:
         * **$key** ("mixed") – Key for the session data item to
           unset, or an array of multiple keys

      Return type:
         "void"

      Unsets the specified key(s) from the "$_SESSION" superglobal.

      Note:

        This is a legacy method kept only for backwards compatibility
        with older applications. It is just an alias for
        "unset($_SESSION[$key])" - please use that instead.

   mark_as_flash($key)

      Parameters:
         * **$key** ("mixed") – Key to mark as flashdata, or an array
           of multiple keys

      Returns:
         TRUE on success, FALSE on failure

      Return type:
         "bool"

      Marks a "$_SESSION" item key (or multiple ones) as “flashdata”.

   get_flash_keys()

      Returns:
         Array containing the keys of all “flashdata” items.

      Return type:
         "array"

      Gets a list of all "$_SESSION" that have been marked as
      “flashdata”.

   unmark_flash($key)

      Parameters:
         * **$key** ("mixed") – Key to be un-marked as flashdata, or
           an array of multiple keys

      Return type:
         "void"

      Unmarks a "$_SESSION" item key (or multiple ones) as
      “flashdata”.

   flashdata([$key = NULL])

      Parameters:
         * **$key** ("mixed") – Flashdata item key or NULL

      Returns:
         Value of the specified item key, or an array of all flashdata

      Return type:
         "mixed"

      Gets the value for a specific "$_SESSION" item that has been
      marked as “flashdata”, or an array of all “flashdata” items if
      no key was specified.

      Note:

        This is a legacy method kept only for backwards compatibility
        with older applications. You should directly access
        "$_SESSION" instead.

   keep_flashdata($key)

      Parameters:
         * **$key** ("mixed") – Flashdata key to keep, or an array of
           multiple keys

      Returns:
         TRUE on success, FALSE on failure

      Return type:
         "bool"

      Retains the specified session data key(s) as “flashdata” through
      the next request.

      Note:

        This is a legacy method kept only for backwards compatibility
        with older applications. It is just an alias for the
        "mark_as_flash()" method.

   set_flashdata($data[, $value = NULL])

      Parameters:
         * **$data** ("mixed") – An array of key/value pairs to set as
           flashdata, or the key for a single item

         * **$value** ("mixed") – The value to set for a specific
           session item, if $data is a key

      Return type:
         "void"

      Assigns data to the "$_SESSION" superglobal and marks it as
      “flashdata”.

      Note:

        This is a legacy method kept only for backwards compatibility
        with older applications.

   mark_as_temp($key[, $ttl = 300])

      Parameters:
         * **$key** ("mixed") – Key to mark as tempdata, or an array
           of multiple keys

         * **$ttl** ("int") – Time-to-live value for the tempdata, in
           seconds

      Returns:
         TRUE on success, FALSE on failure

      Return type:
         "bool"

      Marks a "$_SESSION" item key (or multiple ones) as “tempdata”.

   get_temp_keys()

      Returns:
         Array containing the keys of all “tempdata” items.

      Return type:
         "array"

      Gets a list of all "$_SESSION" that have been marked as
      “tempdata”.

   unmark_temp($key)

      Parameters:
         * **$key** ("mixed") – Key to be un-marked as tempdata, or an
           array of multiple keys

      Return type:
         "void"

      Unmarks a "$_SESSION" item key (or multiple ones) as “tempdata”.

   tempdata([$key = NULL])

      Parameters:
         * **$key** ("mixed") – Tempdata item key or NULL

      Returns:
         Value of the specified item key, or an array of all tempdata

      Return type:
         "mixed"

      Gets the value for a specific "$_SESSION" item that has been
      marked as “tempdata”, or an array of all “tempdata” items if no
      key was specified.

      Note:

        This is a legacy method kept only for backwards compatibility
        with older applications. You should directly access
        "$_SESSION" instead.

   set_tempdata($data[, $value = NULL])

      Parameters:
         * **$data** ("mixed") – An array of key/value pairs to set as
           tempdata, or the key for a single item

         * **$value** ("mixed") – The value to set for a specific
           session item, if $data is a key

         * **$ttl** ("int") – Time-to-live value for the tempdata
           item(s), in seconds

      Return type:
         "void"

      Assigns data to the "$_SESSION" superglobal and marks it as
      “tempdata”.

      Note:

        This is a legacy method kept only for backwards compatibility
        with older applications.

   sess_regenerate([$destroy = FALSE])

      Parameters:
         * **$destroy** ("bool") – Whether to destroy session data

      Return type:
         "void"

      Regenerate session ID, optionally destroying the current
      session’s data.

      Note:

        This method is just an alias for PHP’s native
        session_regenerate_id() function.

   sess_destroy()

      Return type:
         "void"

      Destroys the current session.

      Note:

        This must be the *last* session-related function that you
        call. All session data will be lost after you do that.

      Note:

        This method is just an alias for PHP’s native
        session_destroy() function.

   __get($key)

      Parameters:
         * **$key** ("string") – Session item key

      Returns:
         The requested session data item, or NULL if it doesn’t exist

      Return type:
         "mixed"

      A magic method that allows you to use "$this->session->item"
      instead of "$_SESSION['item']", if that’s what you prefer.

      It will also return the session ID by calling "session_id()" if
      you try to access "$this->session->session_id".

   __set($key, $value)

      Parameters:
         * **$key** ("string") – Session item key

         * **$value** ("mixed") – Value to assign to the session item
           key

      Returns:
         void

      A magic method that allows you to assign items to "$_SESSION" by
      accessing them as "$this->session" properties:

         $this->session->foo = 'bar';

         // Results in:
         // $_SESSION['foo'] = 'bar';
