I have found over the course of several hours debugging that the referenced articles found on numerous Google searches as well as a significant subset of Stack Overflow answers such as here, here and here all provide invalid or outdated information.
Things that can cause [critical] issues with saving session data to a database:
-
While all the examples online state that you can “fill” the
session_set_save_handler, none of them state that you must also set theregister_shutdown_function('session_write_close')too (reference). -
Several (older) guides refer to an outdated SQL Database structure, and should not be used. The database structure that you need for saving session data to the database is:
id/access/data. That’s it. no need for various extra timestamp columns as I’ve seen on a few “guides” and examples.- Several of the older guides also have outdated MySQL syntax such as
DELETE * FROM ...
- Several of the older guides also have outdated MySQL syntax such as
-
The class [made in my question] must implement the
SessionHandlerInterface. I have seen guides (referenced above) that give the implementation ofsessionHandlerwhich is not a suitable interface. Perhaps previous versions of PHP had a slightly different method (probably <5.4). -
The session class methods must return the values set out by the PHP manual. Again, probably inherited from pre-5.4 PHP but two guides I read stated that
class->openreturns the row to be read, whereas the PHP manual states that it needs to returntrueorfalseonly. -
This is the cause of my Original Issue: I was using custom session names (actually id’s as session names and session id’s are the same thing!) as per this very good StackOverflow post and this was generating a session name that was 128 characters long. As the session name is the sole key that is needed to be cracked to compromise a session and take over with a session hijacking then a longer name/id is a very good thing.
- But, this caused an issue because MySQL was silently slicing the session id down to just 32 characters instead of 128, so it was never able to find the session data in the database. This was a completely silent issue (maybe due to my database connection class not throwing warnings of such things). But this is the one to watch out for. If you have any issues with retrieving sessions from a database first check is that the full session id can be stored in the field provided.
So with all that out of the way there are some extra details to add as well:
The PHP manual page (linked above) shows an unsuitable pile of lines for a class object:
$handler = new MySessionHandler(); session_set_save_handler($handler, true); session_start();
Whereas it works just as well if you put this in the class constructor:
class MySessionHandler implements SessionHandlerInterface {
private $database = null;
public function __construct(){
$this->database = new Database(whatever);
// Set handler to overide SESSION
session_set_save_handler(
array($this, "open"),
array($this, "close"),
array($this, "read"),
array($this, "write"),
array($this, "destroy"),
array($this, "gc")
);
register_shutdown_function('session_write_close');
session_start();
}
...
}
This means that to then start a session on your output page all you need is:
<?php
require "path/to/sessionhandler.class.php";
new MySessionHandler();
//Bang session has been setup and started and works
For reference the complete Session communication class is as follows, this works with PHP 5.6 (and probably 7 but not tested on 7 yet)
<?php
/***
* Created by PhpStorm.
***/
class MySessionHandler implements SessionHandlerInterface {
private $database = null;
public function __construct($sessionDBconnectionUrl){
/***
* Just setting up my own database connection. Use yours as you need.
***/
require_once "class.database.include.php";
$this->database = new DatabaseObject($sessionDBconnectionUrl);
// Set handler to overide SESSION
session_set_save_handler(
array($this, "open"),
array($this, "close"),
array($this, "read"),
array($this, "write"),
array($this, "destroy"),
array($this, "gc")
);
register_shutdown_function('session_write_close');
session_start();
}
/**
* Open
*/
public function open($savepath, $id){
// If successful
$this->database->getSelect("SELECT `data` FROM sessions WHERE id = ? LIMIT 1",$id,TRUE);
if($this->database->selectRowsFoundCounter() == 1){
// Return True
return true;
}
// Return False
return false;
}
/**
* Read
*/
public function read($id)
{
// Set query
$readRow = $this->database->getSelect('SELECT `data` FROM sessions WHERE id = ? LIMIT 1', $id,TRUE);
if ($this->database->selectRowsFoundCounter() > 0) {
return $readRow['data'];
} else {
return '';
}
}
/**
* Write
*/
public function write($id, $data)
{
// Create time stamp
$access = time();
// Set query
$dataReplace[0] = $id;
$dataReplace[1] = $access;
$dataReplace[2] = $data;
if ($this->database->noReturnQuery('REPLACE INTO sessions(id,access,`data`) VALUES (?, ?, ?)', $dataReplace)) {
return true;
} else {
return false;
}
}
/**
* Destroy
*/
public function destroy($id)
{
// Set query
if ($this->database->noReturnQuery('DELETE FROM sessions WHERE id = ? LIMIT 1', $id)) {
return true;
} else {
return false;
}
}
/**
* Close
*/
public function close(){
// Close the database connection
if($this->database->dbiLink->close){
// Return True
return true;
}
// Return False
return false;
}
/**
* Garbage Collection
*/
public function gc($max)
{
// Calculate what is to be deemed old
$old = time() - $max;
if ($this->database->noReturnQuery('DELETE FROM sessions WHERE access < ?', $old)) {
return true;
} else {
return false;
}
}
public function __destruct()
{
$this->close();
}
}
Usage: As shown just above the class code text.