ADODB Session Management Manual


body, td {
/*font-family: Arial, Helvetica, sans-serif;*/
font-size: 11pt;
}
pre {
font-size: 9pt;
background-color: #EEEEEE; padding: .5em; margin: 0px;
}
.toplink {
font-size: 8pt;
}



ADODB Session 2 Management Manual

V4.92a 29 Aug 2006 (c) 2000-2006 John Lim (jlim#natsoft.com.my)

This software is dual licensed using BSD-Style and
LGPL. This means you can use it in compiled proprietary and commercial
products.
Useful ADOdb links: Download
  Other Docs

Introduction
This document discusses the newer session handler adodb-session2.php. If
you have used the older adodb-session.php, then be forewarned that you will
need to alter your session table format. Otherwise everything is backward
compatible.
Here are the older
docs for
adodb-session.php.
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
session_register($variable_name). 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.
This is a distributed memory based caching system suitable for storing session
information.

The Improved Session Handler
In ADOdb 4.91, we added a new session handler, in adodb-session2.php.
It features the following improvements:

Fully supports server farms using a new database table format. The
previous version used the web server time for timestamps, which can cause problems
on a system with multiple web servers with possibly inconsistent
times. The new version uses the database server time instead for all timestamps.
The older database table format is obsolete. The database table must be modified
to support storage of the database server time mentioned above. Also the field
named DATA has been changed to SESSDATA. In some databases, DATA is a reserved
word.
The functions dataFieldName() and syncSeconds() is obsolete.


Usage is


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#$_SESSION['AVAR'] += 1;print "<p>\$_SESSION['AVAR']={$_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. If you want to override it:


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 defaultadodb-cryptsession2.php : Use this if you want to store encrypted session data in the databaseadodb-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();

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( )


To use a encrypted sessions, simply replace the file adodb-session2.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
1. Create this table in your database. Here is the MySQL version:

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 DEFAULT '',
PRIMARY KEY ( sesskey ) ,
INDEX sess2_expiry( expiry ),
INDEX sess2_expireref( expireref )
)

For PostgreSQL, use:
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 );
Here is the Oracle definition, which 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
$USERID is passed in as the first parameter, eg. NotifyFn($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.

1. You can then write a session monitor, scanning expireref to see
who is currently logged on.

2. 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.
3. You can scan the sessions table to ensure no user
can be logged in twice. Useful for security reasons.

Compression/Encryption Schemes
Since ADOdb 4.05, thanks to Ross Smith, 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: adodb_session_regenerate_id()
Dynamically change the current session id with a newly generated one and update
database. 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('path/to/adodb/session/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 still supported:
$ADODB_SESSION_DRIVER='mysql';
$ADODB_SESSION_CONNECT='localhost';
$ADODB_SESSION_USER ='root';
$ADODB_SESSION_PWD ='abc';
$ADODB_SESSION_DB ='phplens';

include('path/to/adodb/session/adodb-session2.php');
In the above example, the only things you need to change in your code to upgrade
is

your session table format to the new one.
the include file from adodb-session.php to adodb-session2.php.

More Info
Also see the core ADOdb documentation. And if
you are interested in the obsolete adodb-session.php, see old
session documentation.