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session_start> <session_set_cookie_params
[edit] Last updated: Sat, 12 May 2012

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session_set_save_handler

(PHP 4, PHP 5)

session_set_save_handlerSets 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
}

$handler = new MySessionHandler();
session_set_save_handler($handlertrue);
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->savePath0777);
        }

        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



session_start> <session_set_cookie_params
[edit] Last updated: Sat, 12 May 2012
 
add a note add a note User Contributed Notes session_set_save_handler
Rusty X 06-Mar-2012 09:39
It is important to understand that PHP's default file-based session handling LOCKS the session file, inherently allowing ONLY ONE thread handling any given session at a time.
When you implement a DB-backed session storage and you do not do any locking, you may run into situations where more than one thread is serving the same session, and you may LOSE DATA because the second thread will overwrite any session changes done by the first thread.
You should therefore think about locking the session somehow if you want to have the exact same behavior as with the default file-based implementation. For example, with InnoDB you could do a SELECT ... FOR UPDATE, or you can use the GET_LOCK() function.
balazsbotond at gmail dot com 13-Nov-2011 04:36
It is important to note that autoload handlers don't work inside the read, write, etc. functions, so you have to explicitly require_once all classes you use there.
pavelc at users dot sourceforge dot net 11-Jul-2011 04:21
I write a class that unites whole handler functionality. It's not even needed to save instances of this class in variables. Just add a row:
<?php
new SessionSaveHandler();
?>
and the handler will rule the sessions ;-)
<?php

class SessionSaveHandler {
    protected
$savePath;
    protected
$sessionName;

    public function
__construct() {
       
session_set_save_handler(
            array(
$this, "open"),
            array(
$this, "close"),
            array(
$this, "read"),
            array(
$this, "write"),
            array(
$this, "destroy"),
            array(
$this, "gc")
        );
    }

    public function
open($savePath, $sessionName) {
       
$this->savePath = $savePath;
       
$this->sessionName = $sessionName;
        return
true;
    }

    public function
close() {
       
// your code if any
       
return true;
    }

    public function
read($id) {
       
// your code
   
}

    public function
write($id, $data) {
       
// your code
   
}

    public function
destroy($id) {
       
// your code
   
}

    public function
gc($maxlifetime) {
       
// your code
   
}
}

new
SessionSaveHandler();

?>
lukas.starecek 23-May-2011 05:12
I have solved problem with session handler, which needs some other objects (for example DB access object), with register_shutdown_function. Just calling

<?php

register_shutdown_function
('session_write_close');

?>

solved my problem. Shutdown functions are called before object destructors.

If you use class for session handling (my prefered way), you can call register_shutdown_function in constructor and you must not mess your code in another place.

Example:

<?php

class SessionHandler {

    protected
$_db;

    public function
__construct(PDO $db) {
       
$this->_db = $db;
       
register_shutdown_function('session_write_close');
    }
   
    function
open($save_path, $session_name) {
    }
   
    function
close() {
    }
   
    function
read($id) {
    }

    function
write($id, $sess_data) {
    }

    function
destroy($id) {
    }

    function
gc($maxlifetime) {
    }
}

?>
frank at interactinet dot com 22-Mar-2011 01:37
I had trouble with committing session data.
To "commit and continue" without closing your session, put this at the top of your "write" method:

<?php

$id
= session_id();
session_write_close();
session_id($id);
session_start();

?>

Note that ANY time php generates a new session id, it is not automatically updated in a database. This can be helpful:

<?php

public function resetSessionId()
{
   
$old = session_id();
   
session_regenerate_id();
   
$new = session_id();
   
SessionHandler::regenerate_id($old,$new);
}

public function
regenerate_id($old,$new)
{
   
$db = mysqli->connect(...);

   
$db->query('UPDATE sessions SET session_id = \''.$db->escape_string($new).'\'
    WHERE session_id = \''
.$db->escape_string($old).'\'');
}
?>
dummynick at gmail dot com 24-May-2010 08:37
I was getting Fatal error: Exception thrown without a stack frame and it took days to figure out the reason. I am using memcache to store sessions and in my custom class I use Memcache class in write method.

I put the code in the write method inside try-catch block and it solved my problem.
newton at tricko dot com dot br 19-Feb-2010 08:46
I have been done with session problems creating a new and my own session system.

This is very simple, bellow the class file, a good pratice is include these file as your first line:

<?php
 
class SessionDB {
    private
$data=null;
    private
$session_id=null;
    private
$minutes_to_expire=3600; // TIME TO MAINTAIN DATA ON DB
   
   
public function __construct(){
      global
$SESSION;
     
      if (isset(
$_COOKIE['session_id'])){
       
$this->session_id = $_COOKIE['session_id'];
      } else {
       
       
$this->session_id = md5(microtime().rand(1,9999999999999999999999999)); // GENERATE A RANDOM ID
       
       
setcookie('session_id',$this->session_id);
       
       
$sql = "INSERT INTO `tb_session_db` (`session_id`, `updated_on`) VALUES ('{$this->session_id}', NOW())";
       
mysql_query($sql);
      }
     
     
$sql = "SELECT `value` FROM `tb_session_db` WHERE `session_id`='{$this->session_id}'";
     
$query = mysql_query($sql);
     
     
$this->data = unserialize(mysql_result($query, 0, 'value'));
     
$SESSION = $this->data;
    }
   
    private function
expire(){
     
$date_to_delete = date("Y-m-d H:i:s", time()-60*$this->minutes_to_expire);
     
$sql = "DELETE FROM `tb_session_db` WHERE `update_on` <= '$date_to_delete'";
     
mysql_query($sql);
    }
   
    public function
__destruct(){
      global
$SESSION;
     
     
$this->data = serialize($SESSION);
     
     
$sql = "UPDATE `tb_session_db` SET `value`='{$this->data}', `updated_on`=NOW() WHERE `session_id`='{$this->session_id}'";
     
mysql_query($sql);
     
     
$this->expire();
    }
  }
 
/*
TABLE STRUCTURE
  CREATE TABLE IF NOT EXISTS `tb_session_db` (
    `session_id` varchar(32) NOT NULL,
    `value` blob,
    `updated_on` datetime DEFAULT NULL,
    PRIMARY KEY (`session_id`)
  ) ENGINE=MyISAM DEFAULT CHARSET=latin1;
*/
?>

With this file included, connected to MySQL database who has the table `tb_session_db` I can easy do that into my config file:

<?php
 
require_once('session_db.php');
 
   
define('MYSQL_HOST','mysql.example.com');
   
define('MYSQL_USER','.......');
   
define('MYSQL_PASS','.......');
   
define('MYSQL_BASE','.......');
   
   
mysql_connect(MYSQL_HOST, MYSQL_USER, MYSQL_PASS) or die('Cannot connect');
   
mysql_select_db(MYSQL_BASE) or die('Cannot select DB');
   
mysql_set_charset('utf8_general_ci');
   
 
$SESSION = null;
  global
$SESSION;
 
$session_db = new SessionDB();
?>

To use $SESSION on a function/class method, you must call:
global $SESSION

For who will not work with this over classes or functions, it is a very simple/fast way to work!
bart2yk at yahoo dot com 22-Jan-2010 01:57
You can call the session_write in db object destructor to be shore that you still have a connection to mysql and the session is write.
joel the usual at sign then purerave.com 04-Dec-2009 10:53
When storing sessions in a DB, it's usually beneficial to use an existing custom DB object, but this creates problems with the latest version of PHP 5.3.1. This used to work fine on PHP 5.2.x (Linux and Windows).

The problem now is that session_write_close() is not automatically called when execution ends, but rather after all the objects have been destructed, including the DB object!

There are two ways around this, either manually calling session_write_close() at the end of your script(s), or not using the DB object.

I'm sure this is the intended behavior from the beginning.
skds1433 at hotmail dot com 02-Aug-2009 03:21
I pulled a really stupid move. If you are trying to debug your garbage collector, make sure you call the following >>> BEFORE <<< "session_start":

<?php
ini_set
('session.gc_probability', 100);
ini_set('session.gc_divisor', 100);
?>

I was sure it was a bug in PHP, but turned out (like 99% of the time) to be me own fault.
foddex at foddex dot net 08-Jun-2009 01:01
A quick note for people having problems storing binary session data. Using prepared statements solves all your quote-related issues! Start reading here http://php.net/manual/en/mysqli-stmt.prepare.php for more information!
yangqingrong at gmail dot com 21-Apr-2009 09:44
session_set_save_handler is used before session_start.if your session is setted as auto start. it will return FALSE value.so you need add session_write_close() before session_set_save_handler to cancel the session's auto start.it  likes this:

<?php
/*
qq:290359552
*/
session_write_close(); //cancel the session's auto start,important

function open()
{
   ...
}
....
session_set_save_handler( ... );
session_start();
?>
harald at hholzer at 13-Mar-2009 10:40
after spending 8 hours to find out whats going on..

just for the records, because php.net ignore the real world out there:

debian 5 installs by default the php-suhosin module, which changes the behavior of session_set_save_handler read/write function.

on calling the session write function the session data will be encrypted, and the returning string from the read function are decrypted and verified.

the encrypted data is no more compatible with session_encode/session_decode.

and breaks by default, subdomain handling and multiple host setups where different document roots are used.

for futher information look at:
http://www.hardened-php.net/suhosin/configuration.html

session sample data (debian 4):
test|s:3:"sdf";

session sample data (debian 5, with php-suhosin):
3GdlPEGr2kYgRFDs-pUSoKomZ4fN7r5BM5oKOCMsWNc...

i thing the suhosin patch should report a warning in case of invalid session data, to get a clue whats going wrong.
e dot sand at elisand dot com 04-Mar-2009 11:42
The "binary" data that is in the session data appears to surround class/object names, and if you pass your session data through a function to sanitize it for SQL injection, you may indeed run in to problems.

For example, using the PDO::quote() function to prepare the data for injection (in my case for SQLite3), it was stopping short as soon as it encountered the first bit of binary data, causing my session information to be corrupted.

This change *must* have happened somewhere in the 5.2 series, because I just started encountering this problem recently on a code base that had been tested & working on earlier versions of PHP 5.2.

This may in fact be a bug - I have not yet checked... but beware, and perhaps using base64 to encode/decode your session data is a good thing to do just to be sure (though you are now left unable to visually inspect serialized session information at the storage level which is a rather big problem for on-the-fly debugging of sessions).
anonymous at anonymous dot org 06-Oct-2008 12:11
if you simply append the information from session variables every time you'll have many multiples for variables each time they are changed. a simple way to do this is explode the data twice to seperate the variable name from the other relevant information and foreach() check against the stored set. here is a little bit of a mess i wrote to do it.
assuming stored session variables in both database and passed through function:

<?php
$buffer
= array();
$buffer = explode('|',$sessiondata);
$buf1 = array();
$buf2 = array();
$finalbuff = '';
foreach(
$buffer as $i){
   
$i = explode(';',$i);
    foreach(
$i as $b){
       
array_push($buf1,$b);
    }
}
$buffer = explode('|',$result['data']);
foreach(
$buffer as $i){ $i = explode(';',$i); foreach($i as $b){ array_push($buf2,$b);}}
$z = 0;
$x = 0;
while(
$buf2[$z]){
    while(
$buf1[$x]){
        if(
$buf2[$z] == $buf1[$x]){
           
$buf2[($z+1)] = $buf1[($x+1)];
        }
       
$x+=2;
    }
   
$z+=2;
}
foreach(
$buf2 as $i){ $finalbuff .= $i; }
?>

$sessiondata is the variable passed through the function and $result['data'] is the data stored in an sql database.
james at dunmore dot me dot uk 13-Aug-2008 06:31
If your using database session handler and your database is in UTF8, but you happen to have a script running in IS0-8859 that tries to put symbols such as £ signs into the database - then the session will corrupt and data will go missing.

You can either - make sure you never put special characters into the session, or - more helpful, do this in your 'write' function

<?php

public static function write( $key, $val )
        {
           
$val = utf8_encode( $val );
           
           
$val = preg_replace( '!s:(\d+):"(.*?)";!se', "'s:'.strlen('$2').':\"$2\";'", $val );

              
//......

?>

probably an overhead on this, but less overhead than loosing data.

You could also use WDDX for storing sessions I suppose
tomas at slax dot org 08-Jul-2008 07:00
Regarding the SAPIs: The warning mentioned in function's description (that the Current working directory is changed with some SAPIs) is very important.

It means that if your callback 'write' function needs to write to a file in current directory, it will not find it. You have to use absolute path and not rely upon the current working directory.

I thought this warning applies only to some strange environments like Windows, but it happens exactly on Linux + Apache 2.2 + PHP 5.
anddriga at gmail dot com 09-May-2008 10:44
Some PHP code for memcached session handler.

<?php
class SessionHadler
{
    private static
$lifetime = 0;

    public static function
open()
    {
       
self::$lifetime = ini_get('session.gc_maxlifetime');
       
        return
true;
    }
   
    public static function
read($id)
    {
        return
memcached::get("sessions/{$id}");
    }
   
    public static function
write($id, $data)
    {
        return
memcached::set("sessions/{$id}", $data, self::$lifetime);
    }
   
    public static function
destroy($id)
    {
        return
memcached::delete("sessions/{$id}");
    }
   
    private function
__construct(){}
    public static function
gc(){ return true; }
    public static function
close(){    return true; }
    public function
__destruct()
    {
       
session_write_close();
    }
}
?>
james at enginecreative dot co dot uk 06-Apr-2008 03:22
With regards to db session handling:

Remember if you use the REPLACE INTO method to have your session key as the primary key otherwise you will end up with duplicate records in your table.

http://dev.mysql.com/doc/refman/5.0/en/replace.html
james dot ellis at gmail dot com 04-Apr-2008 03:39
When writing your own session handler, particularly database session handlers, play close attention to garbage cleanup and how it could affect server load.

To pick a round number example:

If you have 1000 requests per minute on session enabled pages, everyone needs a session started but the session garbage cleanup does not need to run every request. Doing so would cause unrequired queries on the database server.

In this example, setting your probability/divisor to 1/1000 would be sufficient to clean up old sessions at a minimum once a minute. If you don't need that kind of granularity, increase the gc divisor.

Finding the tradeoff between clearing up old sessions and server load is the important aspect here.
maria at junkies dot jp 09-Dec-2007 06:51
blow example and ta summary of these comments.
and using the simple native functions of mysql.

<?php
class Session
{

   
/**
     * a database connection resource
     * @var resource
     */
   
private $_sess_db;

   
/**
     * Open the session
     * @return bool
     */
   
public function open() {

        if (
$this->_sess_db = mysql_connect(SESSION_DB_HOST,
                                           
SESSION_DB_USER,
                                           
SESSION_DB_PASS)) {
            return
mysql_select_db(SESSION_DB_DATABASE, $this->_sess_db);
        }
        return
false;

    }

   
/**
     * Close the session
     * @return bool
     */
   
public function close() {

        return
mysql_close($this->_sess_db);

    }

   
/**
     * Close the session
     * @return bool
     */
   
public function close() {

        return
mysql_close($this->_sess_db);

    }

   
/**
     * Read the session
     * @param int session id
     * @return string string of the sessoin
     */
   
public function read($id) {

       
$id = mysql_real_escape_string($id);
       
$sql = sprintf("SELECT `data` FROM `sessions` " .
                      
"WHERE id = '%s'", $id);
        if (
$result = mysql_query($sql, $this->_sess_db)) {
            if (
mysql_num_rows($result)) {
               
$record = mysql_fetch_assoc($result);
                return
$record['data'];
            }
        }
        return
'';

    }

   
/**
     * Write the session
     * @param int session id
     * @param string data of the session
     */
   
public function write($id, $data) {

       
$sql = sprintf("REPLACE INTO `sessions` VALUES('%s', '%s', '%s')",
                      
mysql_real_escape_string($id),
                      
mysql_real_escape_string($data),
                      
mysql_real_escape_string(time()));
        return
mysql_query($sql, $this->_sess_db);

    }

   
/**
     * Destoroy the session
     * @param int session id
     * @return bool
     */
   
public function destroy($id) {

       
$sql = sprintf("DELETE FROM `sessions` WHERE `id` = '%s'", $id);
        return
mysql_query($sql, $this->_sess_db);

}

   
/**
     * Garbage Collector
     * @param int life time (sec.)
     * @return bool
     * @see session.gc_divisor      100
     * @see session.gc_maxlifetime 1440
     * @see session.gc_probability    1
     * @usage execution rate 1/100
     *        (session.gc_probability/session.gc_divisor)
     */
   
public function gc($max) {

       
$sql = sprintf("DELETE FROM `sessions` WHERE `timestamp` < '%s'",
                      
mysql_real_escape_string(time() - $max));
        return
mysql_query($sql, $this->_sess_db);

    }

}

//ini_set('session.gc_probability', 50);
ini_set('session.save_handler', 'user');

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

// below sample main

session_start();
session_regenerate_id(true);

if (isset(
$_SESSION['counter'])) {
   
$_SESSION['counter']++;
} else {
   
$_SESSION['counter'] = 1;
}

?>
mixailo at mercenaries dot ru 11-Oct-2007 04:55
It is useful to use MEMORY storage engine in MySQL while handling sessions.
http://dev.mysql.com/doc/refman/5.0/en/memory-storage-engine.html
james at dunmore dot me dot uk 11-Oct-2007 08:52
I think it is very important here to stress that the WRITE method should use UPDATE+INSERT (or mysql specific REPLACE).

There is example code "out there" that uses just UPDATE for the write method, in which case, when session_regenerate_id is called, session data is lost (as an update would fail, as the key has changed).

I've just wasted a whole day due to this (I know I should have thought it through / RTFM, but it is an easy trap to fall into).
Colin 08-Mar-2007 12:10
When using a custom session handler, if the first callback function (sessOpen in my case) finds no session id, one is set by the time the second argument (sessRead in my case) is called.
matt at openflows dot org 19-Sep-2006 05:02
Note that for security reasons the Debian and Ubuntu distributions of php do not call _gc to remove old sessions, but instead run /etc/cron.d/php*, which check the value of session.gc_maxlifetime in php.ini and delete the session files in /var/lib/php*.  This is all fine, but it means if you write your own session handlers you'll need to explicitly call your _gc function yourself.  A good place to do this is in your _close function, like this:

<?php
function _close() {
   
_gc(get_cfg_var("session.gc_maxlifetime"));
  
// rest of function goes here
}
?>
information at saunderswebsolutions dot com 16-Aug-2006 11:56
Note that if session.auto_start is set to On in the php.ini, your session_set_save_handler will return false as the session has already been initialized.

If you are finding that your code works OK on one machine but doesn't work on another, check to see if session.auto_start is set to On
sneakyimp AT hotmail DOT com 04-Aug-2006 09:20
the behavior, return values, and exact time of calling for these functions is pretty poorly documented here.  i thought folks might like to know that:

1) calling session_start() triggers PHP to first call your open function and then call your read function before resuming with the code immediately following your session_start() call.

2) calling session_id('some_value') within your open function WILL NOT SET THE SESSION COOKIE (at least not on my setup - PHP 4.4.1).  Assuming you defined some function to validate a session id called my_func(), you might want to do something like this in your open function:

<?php
 
function _open($save_path, $session_name) {
   
// check for session id
   
$sess_id = session_id();
    if (empty(
$sess_id) || !myfunc($sess_id)) {
     
//session_id is INVALID - generating new
     
$new_id = md5(uniqid("some random seed here"));
     
session_id($new_id);
     
setcookie(session_name(),
                   
$new_id,
                   
0,
                   
"/",
                   
".mydomain.com");
      }

    return
true;
  }
// _open()
?>
mjohnson at pitsco dot com 28-Mar-2006 11:04
With regards to the read handler, the docs say:

  "Read function must return string value always to make save
  handler work as expected. Return empty string if there is no
  data to read."

I can't emphasize this enough. I just spent half a day trying to figure out why my sessions weren't storing any information. I was blithely returning the results of a query on the database from the read handler. Since there was no match for the new ID, the result was NULL. Since it wasn't a string, sessions were essentially disabled. So, the safe thing might be something like this:

<?php
function sessRead($id)
{
   
// Look up data
   
$results = getStuff($id);
   
   
// Make sure it's a string
   
settype($results, 'string');
    return
$results;
}
?>

Of course, you can do whatever you want with it. But, no matter what, make sure you return a string.

HTH,
Michael
stalker at ruun dot de 03-Jan-2006 07:25
object- and mysql-based session-handler, requires the following table:

CREATE TABLE `ws_sessions` (
  `session_id` varchar(255) binary NOT NULL default '',
  `session_expires` int(10) unsigned NOT NULL default '0',
  `session_data` text,
  PRIMARY KEY  (`session_id`)
) TYPE=InnoDB;

<?php
class session {
   
// session-lifetime
   
var $lifeTime;
   
// mysql-handle
   
var $dbHandle;
    function
open($savePath, $sessName) {
      
// get session-lifetime
      
$this->lifeTime = get_cfg_var("session.gc_maxlifetime");
      
// open database-connection
      
$dbHandle = @mysql_connect("server","user","password");
      
$dbSel = @mysql_select_db("database",$dbHandle);
      
// return success
      
if(!$dbHandle || !$dbSel)
           return
false;
      
$this->dbHandle = $dbHandle;
       return
true;
    }
    function
close() {
       
$this->gc(ini_get('session.gc_maxlifetime'));
       
// close database-connection
       
return @mysql_close($this->dbHandle);
    }
    function
read($sessID) {
       
// fetch session-data
       
$res = mysql_query("SELECT session_data AS d FROM ws_sessions
                            WHERE session_id = '
$sessID'
                            AND session_expires > "
.time(),$this->dbHandle);
       
// return data or an empty string at failure
       
if($row = mysql_fetch_assoc($res))
            return
$row['d'];
        return
"";
    }
    function
write($sessID,$sessData) {
       
// new session-expire-time
       
$newExp = time() + $this->lifeTime;
       
// is a session with this id in the database?
       
$res = mysql_query("SELECT * FROM ws_sessions
                            WHERE session_id = '
$sessID'",$this->dbHandle);
       
// if yes,
       
if(mysql_num_rows($res)) {
           
// ...update session-data
           
mysql_query("UPDATE ws_sessions
                         SET session_expires = '
$newExp',
                         session_data = '
$sessData'
                         WHERE session_id = '
$sessID'",$this->dbHandle);
           
// if something happened, return true
           
if(mysql_affected_rows($this->dbHandle))
                return
true;
        }
       
// if no session-data was found,
       
else {
           
// create a new row
           
mysql_query("INSERT INTO ws_sessions (
                         session_id,
                         session_expires,
                         session_data)
                         VALUES(
                         '
$sessID',
                         '
$newExp',
                         '
$sessData')",$this->dbHandle);
           
// if row was created, return true
           
if(mysql_affected_rows($this->dbHandle))
                return
true;
        }
       
// an unknown error occured
       
return false;
    }
    function
destroy($sessID) {
       
// delete session-data
       
mysql_query("DELETE FROM ws_sessions WHERE session_id = '$sessID'",$this->dbHandle);
       
// if session was deleted, return true,
       
if(mysql_affected_rows($this->dbHandle))
            return
true;
       
// ...else return false
       
return false;
    }
    function
gc($sessMaxLifeTime) {
       
// delete old sessions
       
mysql_query("DELETE FROM ws_sessions WHERE session_expires < ".time(),$this->dbHandle);
       
// return affected rows
       
return mysql_affected_rows($this->dbHandle);
    }
}
$session = new session();
session_set_save_handler(array(&$session,"open"),
                         array(&
$session,"close"),
                         array(&
$session,"read"),
                         array(&
$session,"write"),
                         array(&
$session,"destroy"),
                         array(&
$session,"gc"));
session_start();
// etc...
?>
bachir 04-Dec-2005 10:48
php doesn't make any checks about PHPSESSID cookie format, it is then important to verify cookie format before making any sql request.

if your read session request is :
SELECT DataValue FROM sessions WHERE SessionID='$aKey'

this generic cookie could succeed to access others session: PHPSESSID=1' OR SessionID LIKE '%>>

for safety, you can make this verification before sql request:
if (! preg_match('/^([0-9a-f]{32})$/i',$aKey)) return NULL;

hope this can be helpful
ccav at maxbaud dot net 21-Aug-2005 04:35
Ok, after much hairpulling, I've figured out a successful way to store objects in a session using a postgresql savehandler.

<?php
function write ($id, $sess_data)
{
  global
$sql// my global db connection object
 
$sess_data = @pg_escape_bytea(serialize($sess_id)); //works with any type
 
$sql->Query("delete from sessions where sessionid = '$id'"); // delete old session record
 
$sql->Query("insert into sessions (sessionid,datavalue) values ('$id', '$sess_data')");  //insert into session table
 
return true;
}

function
read ($id)
{
  global
$sql;
 
$result=$sql->Query("select * from sessions where sessionid = '$id'");
  if (
$sql->rows==1) {
   
$row=$sql->Fetch(0);
   
$rval = unserialize(@pg_unescape_bytea($sql->data[2]));
    return
$rval;
  } else {
    return
"";
  }
}
?>

Make the datavalue column (the one used to store the actual session data) in the sessions table type bytea.

The problem apparently lies in the PHP serialize for objects, where there is a CR/LF inserted between the object id and the property array.  The CR/LF isn't escaped, and causes a fit for postgresql.

Any data type in PHP can be serialized, so there's no need to distinguish between types.

The object is fully restored, with methods.
niklas at removethisandthedot dot bivald dot com 15-Jul-2005 05:29
Many people are using session_set_save_handler to store the session in a session database, which ofcourse is both valid and smart since it (could) increas security.

What many people forgets, is that session ids can easily be edited by a user as he see fit (by editing a session_cookie for example*)

* If you like to play around to test your site, check Add n edit Cookies extension for firefox.

This might not be a big deal when saving them in a file, since the worst thing that may happen is that the user losts his session and a new one is generated. But when saving to an DB it is*. One should never trust that the server itself add slashes and escapes other vital characters.

* A google search for "SQL Injection" gives 716 000 hits.

Example code, none working:
<?PHP

   
function read ($session_id)
    {
       
$sql        = mysql_query("SELECT * FROM mysessions WHERE session_id=$session_id");
       
$data= mysql_fetch_array($sql);

        }
    }

?>

Is obviously flawed. Since setting our session ID to "; drop mysessions; " would create serious problems.

A more suitable approch would be, something in the lines of:

Example code, none working:
<?PHP

   
function read ($session_id)
    {

  
// ( Code by php.net )
  
if (get_magic_quotes_gpc()) {
      
$session_id = stripslashes($session_id);
   }
  
// Quote if not integer
  
if (!is_numeric($session_id)) {
      
$session_id = mysql_real_escape_string($session_id);
   }

       
$sql        = mysql_query("SELECT * FROM mysessions WHERE session_id=$session_id");
       
$fieldarray = mysql_fetch_array($sql);

        }
    }

?>

I quick checked different sample codes and tutorials and none of them actually escaped session ids.

That's my two cents for too night,
Niklas
korvus at kgstudios dot net 11-Jun-2005 05:34
It seems when you call 'session_name()', php loads the session id automatically from GET ( if the index exists ) and passes it to the 'read' callback method correctly, but the 'write' callback is invoked twice: first the auto-generated session id, then the custom session id

So be aware of what queries you execute inside the callback .. I got crazy because I used a MySQL 'REPLACE' statement to agilize, and I spent a lot of hours trying to understand why 2 rows instead of 1 were being affected ( the first id was inserting, the second updating )

I hope this helps!
Robert Chapin 06-May-2005 02:09
Session authentication is not meant to be part of the session handlers.

These handlers only read and write the session data itself, and will not allow you to call the vital function session_regenerate_id().

To add extra authentication routines, call them after session_start returns control.  DO NOT put them in your 'open' or 'read' handlers.

Enjoy,
-- Miqro
oliver at teqneers dot de 03-Feb-2005 03:44
For some people it might be important to know, that if the standard session handler has been overwritten with session_set_save_handler, no locking is working anymore (between session_read and session_write). The following might happen:

script "A" start         .
read session data        .
.                        script "B" start
.                        read session data
running (30secs)         add session data
.                        write sesion data
.                        script "B" stop
write session data       .
script "A" stop          .

If a script "A" runs for a long time (say 30secs) the same user might start another script "B", which also uses a session. Script "B" will start and read session data, even though script "A" is still running. Because script "B" is much faster it will finish its work and write back its session data before script "A" has ended. Now script "A" ends and overwrites all of script "B"'s session data. If you DON'T use session_set_save_handler, this cannot happend, because in this case, PHP will not start script "B" until script "A" ends.
Balu 19-Sep-2004 03:26
If a session is closed the save-handlers seem to be resetted (in PHP 4.1.2 they are), so you need to run session_set_save_handler() again after e.g. running session_write_close() and restarting the session with session_start();
dolan at unt dot edu 09-Jun-2004 01:23
This is an LDAP implementation that I wrote which works just fine for me.  This assumes you've got some global variables with your host and other info.  It also uses a custom error function which I have not defined here.  Also, it assumes your LDAP server is set up with correct permissions, objectclass, and all that.  I used an octet string in LDAP to hold the session data.  I had to manually wrap some of this so be careful with cutting and pasting.

<?php
$sessconn
=null;
//Custom session handling stored in local LDAP
function ldap_sess_open($save_path,$session_name) {
    global
$infohost,$infoport,$infodn,$infopw,$sessconn;
   
$sessconn=@ldap_connect($infohost,$infoport);
    if(!@
ldap_bind($sessconn,$infodn,$infopw)) {
   
setError("Failed to open session.");
    return
false;
    }
    return
true;
}

function
ldap_sess_close() {
    global
$sessconn;
    @
ldap_close($sessconn);
    return
true;
}

function
ldap_sess_read($id) {
    global
$sessconn;
   
$sr=@ldap_search($sessconn,'ou=sessions,o=Company',
"(cn=$id)");
   
$info=@ldap_get_entries($sessconn,$sr);
    if(
$info['count']>0)
    return
$info[0]['session'][0];
    else
    return
"";
}

function
ldap_sess_write($id,$sess_data) {
    global
$sessconn;
   
$update=array();
   
$update['objectClass']=array('phpsession','top');
   
$update['session']=$sess_data;
   
$dn="cn=$id,ou=sessions,o=Company";
    @
ldap_delete($sessconn,$dn);
    @
ldap_add($sessconn,$dn,$update);
    return
true;
}

function
ldap_sess_destroy($id) {
    global
$sessconn;
   
$dn="cn=$id,ou=sessions,o=Company";
    @
ldap_delete($sessconn,$dn);
    return
true;
}

function
ldap_sess_gc($maxlifetime) {
    global
$sessconn;
   
$sr=@ldap_search($sessconn,'ou=sessions,o=Company',
'(objectClass=phpsession)',array('+','cn'));
   
$info=@ldap_get_entries($sessconn,$sr);
    if(
$info['count']>0) {
    for(
$i=0;$i<$info['count'];$i++) {
       
$id=$info[$i]['cn'][0];
       
$dn="cn=$id,ou=sessions,o=Company";
       
$modified=stamp2local($info[$i]['modifytimestamp'][0]);
        if((
time()-$modified)>=$maxlifetime)
        @
ldap_delete($sessconn,$dn);
    }
    }
    return
true;
}

//converts my LDAP timestamps over to Unix timestamps
function stamp2local($ldapstamp) {
   
$year=substr($ldapstamp,0,4);
   
$month=substr($ldapstamp,4,2);
   
$day=substr($ldapstamp,6,2);
   
$hour=substr($ldapstamp,8,2);
   
$minute=substr($ldapstamp,10,2);
   
$stamp=gmmktime($hour,$minute,0,$month,$day,$year);
    return
$stamp;
}

//Use this so that if your LDAP server goes down people can still
//retain sessions the normal way
$checkds=@ldap_connect($infohost,$infoport);
if(@
ldap_bind($checkds,$infodn,$infopw)) {
   
session_set_save_handler("ldap_sess_open","ldap_sess_close",
"ldap_sess_read","ldap_sess_write","ldap_sess_destroy",
"ldap_sess_gc");
}
@
ldap_close($checkds);
?>
tonanbarbarian at hotmail dot com 03-Dec-2003 10:30
I found the need to have a garbage collection function run with my sessions so I had to write my own session handler.

I took the example code above but found that it had a problem, it does not open the session file exclusively.
This means that if you have a frameset where 2 pages are accessing the session at the same time and both modify the session only the last page to finish processing will have its session data saved. The first page will have all of its session data overwritten.

So here is a modified version of a file session handler in PHP that has file locking. (Not supported on FAT or NFS apparently)

<?php
$sess_save_path
= $sess_session_name = $fp=null;
function
open ($save_path, $session_name) {
  global
$sess_save_path, $sess_session_name;
      
 
$sess_save_path = $save_path;
 
$sess_session_name = $session_name;
  return(
true);
}

function
close() {
  global
$fp;
 
flock($fp, LOCK_UN);
 
fclose($fp);
 
$fp=null;
  return(
true);
}

function
read ($id) {
  global
$sess_save_path, $sess_session_name, $fp;

 
$sess_file = "$sess_save_path/sess_$id";
  if (
$fp = @fopen($sess_file, "r+")) {
   
flock($fp, LOCK_EX);
   
$sess_data = fread($fp, filesize($sess_file));
    return(
$sess_data);
  } else {
    return(
""); // Must return "" here.
 
}

}

function
write ($id, $sess_data) {
  global
$sess_save_path, $sess_session_name, $fp;

 
$sess_file = "$sess_save_path/sess_$id";
  if (!empty(
$fp)) {
   
fseek($fp,0);
    return(
fwrite($fp, $sess_data));
  } elseif (
$fp = @fopen($sess_file, "w")) {
   
flock($fp, LOCK_EX);
    return(
fwrite($fp, $sess_data));
  } else {
    return(
false);
  }
}

function
destroy ($id) {
  global
$sess_save_path, $sess_session_name;
      
 
$sess_file = "$sess_save_path/sess_$id";
  return(@
unlink($sess_file));
}

function
gc ($maxlifetime) {
    global
$sess_save_path, $sess_session_name;
      
 
$sess_file = "$sess_save_path/sess_$id";
  return
true;
}

session_set_save_handler ("open", "close", "read", "write", "destroy", "gc");
?>

enjoy
coco at digitalco2 dot com 23-Nov-2003 03:59
When using mySQL for your session handling functions, don't forget to call mysql_select_db() to change the database if you are using a separate database for your session data. Call mysql_select_db() INSIDE every handler function that accesses the database, since if you write session data after accessing another database, it will not change the database to your session database, and therefore, not write the session data.
ivo at magstudio dot net 25-Nov-2002 07:08
Just a few words to explain some troubles while using session_set_save_handler(). It appears that internally PHP calls session management functions in this order: open(), read(), write(), close(). Close() function is called even if you does not make a call to sesison_start(), perhaps for some reasons like cleaning.
   If you try to redefine these functions and call sessions_set_save_handler() but something doesn't work, (in my case the ssion data hasn't been written) it's a good idea to debug them in the order they are called. They doesn't produce error output to browser but you can use print or echo.
   Shortly, if your write() function doesn't work as expected take a look for errors in previous functions - open() and read().
   I hope that this will help to save someone few hours debugging.
spam at skurrilo dot de 08-May-2002 04:16
You can't use the session autostart feature with

session.save_handler = user

set in your php.ini. Use instead the auto_prepend_file directive in the php.ini and point it to your save_handler with an session_start() at the end.

 
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