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Table of Contents
Session Management
The original session management routines that use adodb-session.inc.php
are deprecated as of ADOdb version 5.20, and will be removed in ADOdb Version 6.0.0. For information on upgrading from the original version, see Here
Introduction
ADOdb session management extends the standard functionality of PHP sessions, by allowing the normal session data seen to be stored in a database itself. There are numerous ways that this method enhances the default behavior
- Simplified clean-up at end of session life
- Easy analysis of session data
- Simple session termination
- Session data can be manipulated by external programs
- Encryption of session data
- Allows implementation of session termination callbacks
- Session data can be retained if used with load balancing servers
Why Session Variables in a Database?
We store state information specific to a user or web client in session variables. These session variables persist throughout a session, as the user moves from page to page.
To use session variables, call session_start() at the beginning of your web page, before your HTTP headers are sent. Then for every variable you want to keep alive for the duration of the session, call variable you want to keep alive for the duration of the session, use $_SESSION['variablename']
. By default, the session handler will keep track of the session by using a cookie. You can save objects or arrays in session variables also.
The default method of storing sessions is to store it in a file. However if you have special needs such as you:
- Have multiple web servers that need to share session info
- Need to do special processing of each session
- Require notification when a session expires
The ADOdb session handler provides you with the above additional capabilities by storing the session information as records in a database table that can be shared across multiple servers.
These records will be garbage collected based on the php.ini [session] timeout settings. You can register a notification function to notify you when the record has expired and is about to be freed by the garbage collector.
An alternative to using a database backed session handler is to use Memcached Setup. This is a distributed memory based caching system suitable for storing session information.
Usage
include_once "adodb/session/adodb-session2.php"; ADOdb_Session::config($driver, $host, $user, $password, $database,$options=false); session_start(); /* * Test session vars, the following should increment on refresh */ if (!isset($_SESSION['AVAR'])) $_SESSION['AVAR'] = 0; $_SESSION['AVAR'] += 1; print "<p>\$_SESSION['AVAR']={$_SESSION['AVAR']}</p>";
When the session is created in session_start( ), the global variable $ADODB_SESS_CONN
holds the connection object.
The default name of the table is sessions2.
Overriding Table Name Defaults
include_once "adodb/session/adodb-session2.php"; $options['table'] = 'mytablename'; ADOdb_Session::config($driver, $host, $user, $password, $database,$options); session_start();
ADOdb Session Handler Features
- Ability to define a notification function that is called when a session expires. Typically used to detect session logout and release global resources.
- Optimization of database writes. We crc32 the session data and only perform an update to the session data if there is a data change.
- Support for large amounts of session data with CLOBs (see adodb-session-clob2.php). Useful for Oracle.
- Support for encrypted session data, see adodb-cryptsession2.php. Enabling encryption is simply a matter of including adodb-cryptsession2.php instead of adodb-session2.php.
Session Handler Files
There are 3 session management files that you can use:
adodb-session2.php : The default adodb-cryptsession2.php : Use this if you want to store encrypted session data in the database adodb-session-clob2.php : Use this if you are storing DATA in clobs and you are NOT using oci8 driver
Usage Examples
To force non-persistent connections, call persist()
first before session_start()
:
include_once "adodb/session/adodb-session2.php"; $driver = 'mysql'; $host = 'localhost'; $user = 'auser'; $pwd = 'secret'; $database = 'sessiondb'; ADOdb_Session::config($driver, $host, $user, $password, $database, $options=false); ADOdb_session::Persist($connectMode=false); session_start();
DSN Support
using DSN support so you can set other options such as port number:
include_once "adodb/session/adodb-session2.php"; $dsn = 'mysql://root:pwd@localhost/mydb?persist=1&port=5654'; ADOdb_Session::config($dsn, '', '', ''); session_start();
The parameter to the persist( )
method sets the connection mode. You can pass the following:
$connectMode | Connection Method |
---|---|
true | PConnect() |
false | Connect() |
'N' | NConnect() |
'P' | PConnect() |
'C' | Connect() |
Using Encrypted Sessions
To use a encrypted sessions, replace the file adodb-session2.php
with adodb-cryptsession2.php
:
include 'adodb/session/adodb-cryptsession2.php'; $driver = 'mysql'; $host = 'localhost'; $user = 'auser'; $pwd = 'secret'; $database = 'sessiondb'; ADOdb_Session::config($driver, $host, $user, $password, $database,$options=false); adodb_sess_open(false,false,$connectMode=false); session_start();
And the same technique for adodb-session-clob2.php:
include 'adodb/session/adodb-session2-clob2.php'; $driver = 'oci8'; $host = 'localhost'; $user = 'auser'; $pwd = 'secret'; $database = 'sessiondb'; ADOdb_Session::config($driver, $host, $user, $password, $database,$options=false); adodb_sess_open(false,false,$connectMode=false); session_start();
Installation
Create this table in your database.
MySQL
CREATE TABLE sessions2( sesskey VARCHAR( 64 ) NOT NULL DEFAULT '', expiry DATETIME NOT NULL , expireref VARCHAR( 250 ) DEFAULT '', created DATETIME NOT NULL , modified DATETIME NOT NULL , sessdata LONGTEXT, PRIMARY KEY ( sesskey ) , INDEX sess2_expiry( expiry ), INDEX sess2_expireref( expireref ) )
PostgreSQL
CREATE TABLE sessions2( sesskey VARCHAR( 64 ) NOT NULL DEFAULT '', expiry TIMESTAMP NOT NULL , expireref VARCHAR( 250 ) DEFAULT '', created TIMESTAMP NOT NULL , modified TIMESTAMP NOT NULL , sessdata TEXT DEFAULT '', PRIMARY KEY ( sesskey ) ); create INDEX sess2_expiry on sessions2( expiry ); create INDEX sess2_expireref on sessions2 ( expireref );
Oracle
This definition uses a CLOB for the SESSDATA field:
CREATE TABLE SESSIONS2 ( SESSKEY VARCHAR2(48 BYTE) NOT NULL, EXPIRY DATE NOT NULL, EXPIREREF VARCHAR2(200 BYTE), CREATED DATE NOT NULL, MODIFIED DATE NOT NULL, SESSDATA CLOB, PRIMARY KEY(SESSKEY) );
CREATE INDEX SESS2_EXPIRY ON SESSIONS2(EXPIRY); CREATE INDEX SESS2_EXPIREREF ON SESSIONS2(EXPIREREF);
We need to use a CLOB here because for text greater than 4000 bytes long, Oracle requires you to use the CLOB data type. If you are using the oci8 driver, ADOdb will automatically enable CLOB handling. So you can use either adodb-session2.php
or adodb-session-clob2.php
- in this case it doesn't matter.
Notifications
You can receive notification when your session is cleaned up by the session garbage collector or when you call session_destroy().
PHP's session extension will automatically run a special garbage collection function based on your php.ini session.cookie_lifetime and session.gc_probability settings. This will in turn call adodb's garbage collection function, which can be setup to do notification.
PHP Session --> ADOdb Session --> Find all recs --> Send --> Delete queued GC Function GC Function to be deleted notification records executed at called by for all recs random time Session Extension queued for deletion
When a session is created, we need to store a value in the session record (in the EXPIREREF field), typically the userid of the session. Later when the session has expired, just before the record is deleted, we reload the EXPIREREF field and call the notification function with the value of EXPIREREF, which is the userid of the person being logged off.
ADOdb uses a global variable $ADODB_SESSION_EXPIRE_NOTIFY that you must predefine before session start to store the notification configuration. $ADODB_SESSION_EXPIRE_NOTIFY is an array with 2 elements, the first being the name of the session variable you would like to store in the EXPIREREF field, and the 2nd is the notification function's name.
For example, suppose we want to be notified when a user's session has expired, based on the userid. When the user logs in, we store the id in the global session variable $USERID. The function name is NotifyFn
.
So we define (before session_start() is called):
$ADODB_SESSION_EXPIRE_NOTIFY = array('USERID','NotifyFn');
And when the NotifyFn is called (when the session expires), the $EXPIREREF
holding the user id is passed in as the first parameter, e.g. NotifyFn($userid, $sesskey)
. The session key (which is the primary key of the record in the sessions table) is the 2nd parameter.
Here is an example of a Notification function that deletes some records in the database and temporary files:
function NotifyFn($expireref, $sesskey) { global $ADODB_SESS_CONN; # the session connection object $user = $ADODB_SESS_CONN->qstr($expireref); $ADODB_SESS_CONN->Execute("delete from shopping_cart where user=$user"); system("rm /work/tmpfiles/$expireref/*"); }
NOTE 1: If you have register_globals disabled in php.ini, then you will have to manually set the EXPIREREF. e.g.
$GLOBALS['USERID'] = GetUserID(); $ADODB_SESSION_EXPIRE_NOTIFY = array('USERID','NotifyFn');
NOTE 2: If you want to change the EXPIREREF after the session record has been created, you will need to modify any session variable to force a database record update.
Neat Notification Tricks
ExpireRef normally holds the user id of the current session.
- You can then write a session monitor, scanning expireref to see who is currently logged on.
- If you delete the sessions record for a specific user, eg.
delete from sessions where expireref = '$USER
' then the user is logged out. Useful for ejecting someone from a site. - You can scan the sessions table to ensure no user can be logged in twice. Useful for security reasons.
Compression/Encryption Schemes
Multiple encryption and compression schemes are supported. Currently, supported are:
- MD5Crypt (crypt.inc.php)
- MCrypt
- Secure (Horde's emulation of MCrypt, if MCrypt module is not available.)
- GZip
- BZip2
These are stackable. E.g.
ADODB_Session::filter(new ADODB_Compress_Bzip2()); ADODB_Session::filter(new ADODB_Encrypt_MD5());
will compress and then encrypt the record in the database.
Session Cookie Regeneration
The method adodb_session_regenerate_id()
will dynamically change the current session id with a newly generated one and update database. This currently only works with cookies. Useful to improve security by reducing the risk of session-hijacking. See this article on Session Fixation for more info on the theory behind this feature.
Usage
include 'adodb/adodb-session2.php'; session_start(); /* * Approximately every 10 page loads, reset cookie for safety. * This is extremely simplistic example, better * to regenerate only when the user logs in or changes * user privilege levels. */ if ((rand()%10) == 0) adodb_session_regenerate_id();
This function calls session_regenerate_id()
internally or simulates it if the function does not exist.
Vacuum/Optimize Database
During session garbage collection, if postgresql is detected, ADOdb can be set to run VACUUM. If mysql is detected, then optimize database could be called.You can turn this on or off using:
$turnOn = true; # or false ADODB_Session::optimize($turnOn);
The default is optimization is disabled.
Backwards Compatability
The older method of connecting to ADOdb using global variables is now deprecated, and will be removed in ADOdb version 6.0:
$ADODB_SESSION_DRIVER='mysql'; $ADODB_SESSION_CONNECT='localhost'; $ADODB_SESSION_USER ='root'; $ADODB_SESSION_PWD ='abc'; $ADODB_SESSION_DB ='phplens'; include 'adodb/adodb-session.php';