Bradezone

We all know CakePHP is the bee’s knees for developing web applications, but what’s not so hot is Cake’s handling of error pages. Most developers discover soon enough that they can customize their error pages, most commonly the 404 “not found” page, by creating an appropriately named file, e.g. error404.ctp, within the views/errors folder. Easy peasy, right? Sure, but lurking in the bowels of Cake’s code is a significantly more obscure problem that manifests itself in various ways. Simply put, CakePHP fails to load components and does not run the beforeFilter() function of the AppController, deviating from its normal page-loading process. This can lead to utterly maddening behavior if you do anything important in beforeFilter(), which would be almost always.

An application I’m developing at work runs critical code in beforeFilter() that checks if a user is logged in and uses the results to set the website title and which links appear in the main menu. So you could say that’s fairly important. But on my error pages, Cake would conveniently display no title or main menu whatsoever. Because no debugging messages were displayed, I thought the issue might have been a minor case of a different layout file being used for error pages. But after a thorough combing of Cake’s library code, I discovered the ugly truth within the cake/libs/error.php file: the CakeErrorController class, which is used by the accompanying ErrorHandler class, never calls the beforeFilter() function. This contrasts with the Dispatcher class in cake/dispatcher.php that is responsible for most normal pages—this code eventually runs beforeFilter() within the controller’s _invoke() function, but before that it also calls the controller’s constructClasses() function, which turned out to be a critical part of my solution to this now unwieldy problem.

After attempting several ways of making the error pages run my beforeFilter() code, I found that simply adding $this->beforeFilter(); as the last line of the CakeErrorController constructor seemed to work. The problem with doing this, however, is that I had to change a core file within Cake. As my fellow developers know, this is not an option, so I had to make it work from within my own code. But luckily I was on the right track: the constructor inherits from the AppController constructor, which I was free to modify. So within my application’s app_controller.php file, I added a constructor and copied the code from CakeErrorController, making sure to add my call to beforeFilter() at the end. Amazingly it seemed to work, so I then proceeded to see which lines I could safely comment out, until I was left with just a few lines of code. The constructClasses() function in particular seems to be Cake’s succinct way of loading the components used by the application. After testing several normal pages and error pages alike, I feel fairly confident that I have solved my initial problem. Here’s the code I added to app_controller.php:

function __construct() {
    parent::__construct();
    if ($this->name == 'CakeError') {
        $this->constructClasses();
        $this->beforeFilter();
    }
}

Since I was forced to put the code in the main AppController class, some side effects may exist: beforeFilter() is potentially called twice on standard pages and perhaps earlier than normal. From what I can tell, this doesn’t affect the application’s performance or behavior. So hopefully this solution will help other CakePHP developers who want their error pages to behave as expected. But surely I am not alone in hoping that future versions of CakePHP will make this workaround unnecessary.

UPDATE: I tweaked the code to include an explicit check for CakeErrorController before running the extra lines of code in the constructor. I found a fail case that had to do with adding new users via the Auth component—new passwords were being hashed twice. So this new snippet should successfully eliminate the possibility of code running twice needlessly.

Posted on Thursday, May 21st, 2009 at 6:59 pm in Web Stuff.
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