ADODB Old Session Management Manual


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ADODB Session 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 documentation discusses the old adodb-session.php.
Here is the new documentation on the newer adodb-session2.php.
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.
Important Upgrade Notice: Since ADOdb 4.05, the session files
have been moved to its own folder, adodb/session. This is a rewrite
of the session code by Ross Smith. The old session code is in
adodb/session/old.
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-clob.php). Useful
for Oracle.
Support for encrypted session data, see
adodb-cryptsession.php. Enabling encryption is simply a matter of
including adodb-cryptsession.php instead of adodb-session.php.

Setup
There are 3 session management files that you can use:

adodb-session.php : The defaultadodb-session-clob.php : Use this if you are storing DATA in clobsadodb-cryptsession.php : Use this if you want to store encrypted session data in the database

Examples

include('adodb/adodb.inc.php'); $ADODB_SESSION_DRIVER='mysql'; $ADODB_SESSION_CONNECT='localhost'; $ADODB_SESSION_USER ='scott'; $ADODB_SESSION_PWD ='tiger'; $ADODB_SESSION_DB ='sessiondb'; include('adodb/session/adodb-session.php'); session_start(); # # Test session vars, the following should increment on refresh # $_SESSION['AVAR'] += 1; print "<p>\$_SESSION['AVAR']={$_SESSION['AVAR']}</p>";

To force non-persistent connections, call adodb_session_open() first before session_start():


include('adodb/adodb.inc.php'); $ADODB_SESSION_DRIVER='mysql'; $ADODB_SESSION_CONNECT='localhost'; $ADODB_SESSION_USER ='scott'; $ADODB_SESSION_PWD ='tiger'; $ADODB_SESSION_DB ='sessiondb'; include('adodb/session/adodb-session.php'); adodb_sess_open(false,false,false); session_start();

The 3rd parameter to adodb_sess_open($path, $sessname, $connectMode) sets the connection method. You can pass in 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-session.php:
include('adodb/adodb.inc.php'); $ADODB_SESSION_DRIVER='mysql'; $ADODB_SESSION_CONNECT='localhost'; $ADODB_SESSION_USER ='scott'; $ADODB_SESSION_PWD ='tiger'; $ADODB_SESSION_DB ='sessiondb'; include('adodb/session/adodb-cryptsession.php'); session_start();

And the same technique for adodb-session-clob.php:
include('adodb/adodb.inc.php'); $ADODB_SESSION_DRIVER='mysql'; $ADODB_SESSION_CONNECT='localhost'; $ADODB_SESSION_USER ='scott'; $ADODB_SESSION_PWD ='tiger'; $ADODB_SESSION_DB ='sessiondb'; include('adodb/session/adodb-session-clob.php'); session_start();

An alternative way to set persistant or non-persistent connections is to call the following function before session_start() is called.

ADODB_Session::persist('P'); # 'C' for non-persistent connections

Installation
1. Create this table in your database (MySQL syntax):

create table sessions (
SESSKEY char(32) not null,
EXPIRY int(11) unsigned not null,
EXPIREREF varchar(64),
DATA text not null,
primary key (sesskey)
);


You may want to rename the 'data' field to 'session_data' as
'data' appears to be a reserved word for one or more of the following:

ANSI SQL
IBM DB2
MS SQL Server
Postgres
SAP


If you do, then execute:

ADODB_Session::dataFieldName('session_data');

For the adodb-session-clob.php version, create this:

create table sessions ( SESSKEY char(32) not null, EXPIRY int(11) unsigned not null, EXPIREREF varchar(64), DATA CLOB, primary key (sesskey) );

2. Then define the following parameters. You can either modify this file, or define them before this file is included:
$ADODB_SESSION_DRIVER='database driver, eg. mysql or ibase'; $ADODB_SESSION_CONNECT='server to connect to'; $ADODB_SESSION_USER ='user'; $ADODB_SESSION_PWD ='password'; $ADODB_SESSION_DB ='database'; $ADODB_SESSION_TBL = 'sessions'; # setting this is optional

When the session is created, $ADODB_SESS_CONN holds the connection object. 3. Recommended is PHP 4.0.6 or later. There are documented session bugs in earlier versions of PHP.
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.

Using Oracle CLOBs
Suppose you are storing the DATA field in a CLOB:

CREATE TABLE sessions (
SESSKEY VARCHAR(32) NOT NULL,
EXPIRY NUMBER(16) NOT NULL,
EXPIREREF VARCHAR(64),
DATA CLOB,
PRIMARY KEY (sesskey)
);

Then your PHP code could look like this:

ADODB_SESSION_DRIVER='oci8';
$ADODB_SESSION_CONNECT=$tnsname;
$ADODB_SESSION_USER ='scott';
$ADODB_SESSION_PWD = 'tiger';
$ADODB_SESSION_DB ='';

$ADODB_SESSION_USE_LOBS = 'clob';
$ADODB_SESSION_TBL = 'sessions';

$ADODB_SESS_DEBUG=0;

include(ADODB_DIR.'/session/adodb-session.php');

ADODB_Session::persist('P'); # use 'C' for non-persistent connects

session_start();

Note that you can set persistance using ADODB_Session::persist('P').

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.
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:

$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-session.php');

session_start();
# 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 for optimization is it is disabled.
More Info
Also see the core ADOdb documentation.