pre_controller clashes with post_controller_constructor - php

Question

I want to check if the user has permission to access to the URL (controller/method) combination. It should check before any method called in called controller and method belongs to it.
As far as I understand, the hook should be pre_controller for the logic above but when I use it, I think it clashes with post_controller_constructor shown below. If I use post_controller instead then it works but this time logic is compromised.
How can I solve this problem?
Thanks
CONFIG/HOOKS
//Used to authenticate user session to decide whether to authenticate site or not
$hook['post_controller_constructor'] =
array(
'class' => 'site_authentication',
'function' => 'authenticate',
'filename' => 'site_authentication.php',
'filepath' => 'hooks',
'params' => null
);
//Used to authenticate permitted controllers
$hook['pre_controller'] =
array(
'class' => 'permitted_controllers',
'function' => 'authenticate',
'filename' => 'permitted_controllers.php',
'filepath' => 'hooks',
'params' => null
);
APPLICATION/HOOKS
//This works fine
class site_authentication
{
private $CI;
public function __construct()
{
$this->CI =& get_instance();
}
public function authenticate()
{
if (! $this->CI->session->userdata('site'))
{
redirect('to error page');
}
$user_session = $this->CI->session->userdata('site');
//Some more stuff here
}
}
//This doesn't work with pre_controller
class permitted_controllers
{
private $CI;
public function __construct()
{
$this->CI =& get_instance();
}
public function authenticate()
{
$user_session = $this->CI->session->userdata('site');
//Url is set here, ignore syntax error below
$url = $this->CI->uri->segment(1) . 2 . 3;
if (! in_array($url, $user_session['controllers']))
{
redirect('to error page');
}
}
}
If I combine them two, they work fine under post_controller_constructor but they won't work separately?
$hook['post_controller_constructor'] [] =
array(
'class' => 'site_authentication',
'function' => 'authenticate',
'filename' => 'site_authentication.php',
'filepath' => 'hooks',
'params' => null
);
$hook['post_controller_constructor'] [] =
array(
'class' => 'permitted_controllers',
'function' => 'authenticate',
'filename' => 'permitted_controllers.php',
'filepath' => 'hooks',
'params' => null
);

Answer 1

pre_controller hook is run before the super object has been constructed, so it is not a viable option for hooking into CI's normal syntax (such as $this->db->query()).
I'd suggest creating a base controller (aka MY_Controller or some other name) and adding the permission check to its constructor. Then, each controller that should run the permissions check will then extend MY_Controller instead of CI_Controller. Here's Phil Sturgeon's classic article about base controllers.
Hooks are called on every page load. If you don't need to check permissions somewhere, you need to either add that logic to your hook, or add logic somewhere else to try and disable it. Not very extendable. Using a base controller, adding the permission check is as simple as extending a different class.

Answer 2

The pre_controller hook executes before the super object has been fully constructed read more here