Error & Exception Handling¶

Error & Exception Configuration¶

Error configuration is done in your application’s config/app.php file. By default CakePHP uses Cake\Error\ErrorTrap and Cake\Error\ExceptionTrap to handle both PHP errors and exceptions respectively. The error configuration allows you to customize error handling for your application. The following options are supported:

• errorLevel - int - The level of errors you are interested in capturing. Use the built-in PHP error constants, and bitmasks to select the level of error you are interested in. See Deprecation Warnings to disable deprecation warnings.

• trace - bool - Include stack traces for errors in log files. Stack traces will be included in the log after each error. This is helpful for finding where/when errors are being raised.

• exceptionRenderer - string - The class responsible for rendering uncaught exceptions. If you choose a custom class you should place the file for that class in src/Error. This class needs to implement a render() method.

• log - bool - When true, exceptions + their stack traces will be logged to Cake\Log\Log.

• skipLog - array - An array of exception classnames that should not be logged. This is useful to remove NotFoundExceptions or other common, but uninteresting log messages.

• extraFatalErrorMemory - int - Set to the number of megabytes to increase the memory limit by when a fatal error is encountered. This allows breathing room to complete logging or error handling.

• logger (prior to 4.4.0 use errorLogger) - Cake\Error\ErrorLoggerInterface - The class responsible for logging errors and unhandled exceptions. Defaults to Cake\Error\ErrorLogger.

• errorRenderer - Cake\Error\ErrorRendererInterface - The class responsible for rendering errors. Default is chosen based on PHP SAPI.

• ignoredDeprecationPaths - array - A list of glob compatible paths that deprecation errors should be ignored in. Added in 4.2.0

By default, PHP errors are displayed when debug is true, and logged when debug is false. The fatal error handler will be called independent of debug level or errorLevel configuration, but the result will be different based on debug level. The default behavior for fatal errors is show a page to internal server error (debug disabled) or a page with the message, file and line (debug enabled).

deprecationWarning('The example() method is deprecated. Use getExample() instead.');

Changing Exception Handling¶

Exception handling offers several ways to tailor how exceptions are handled. Each approach gives you different amounts of control over the exception handling process.

1. Listen to events This allows you to be notified through CakePHP events when errors and exceptions have been handled.

2. Custom error templates This allows you to change the rendered view templates as you would any other template in your application.

3. Custom ErrorController This allows you to control how exception pages are rendered.

4. Custom ExceptionRenderer This allows you to control how exception pages and logging are performed.

5. Create & register your own error handler This gives you complete control over how errors & exceptions are handled, logged and rendered.

Listen to Events¶

The ErrorTrap and ExceptionTrap handlers will trigger CakePHP events when they handle errors. You can listen to the Error.beforeRender event to be notified of PHP errors. The Exception.beforeRender event is dispatched when an exception is handled:

$errorTrap = new ErrorTrap(Configure::read('Error'));
$errorTrap->getEventManager()->on(
    'Error.beforeRender',
    function (EventInterface $event, PhpError $error) {
        // do your thing
    }
);

Within an Error.beforeRender handler you have a few options:

• Stop the event to prevent rendering.

• Return a string to skip rendering and use the provided string instead

Within an Exception.beforeRender handler you have a few options:

• Stop the event to prevent rendering.

• Set the exception data attribute with setData('exception', $err) to replace the exception that is being rendered.

• Return a response from the event listener to skip rendering and use the provided response instead.

Custom Error Templates¶

The default error handler renders all uncaught exceptions your application raises with the help of Cake\Error\ExceptionRenderer, and your application’s ErrorController.

The error page views are located at templates/Error/. All 4xx errors use the error400.php template, and 5xx errors use the error500.php. Your error templates will have the following variables available:

• message The exception message.

• code The exception code.

• url The request URL.

• error The exception object.

In debug mode if your error extends Cake\Core\Exception\CakeException the data returned by getAttributes() will be exposed as view variables as well.

// inside templates/Error/error400.php
$this->layout = 'my_error';

Custom ErrorController¶

The App\Controller\ErrorController class is used by CakePHP’s exception rendering to render the error page view and receives all the standard request life-cycle events. By modifying this class you can control which components are used and which templates are rendered.

If your application uses Prefix Routing you can create custom error controllers for each routing prefix. For example, if you had an Admin prefix. You could create the following class:

namespace App\Controller\Admin;

use App\Controller\AppController;
use Cake\Event\EventInterface;

class ErrorController extends AppController
{
    /**
     * beforeRender callback.
     *
     * @param \Cake\Event\EventInterface $event Event.
     * @return void
     */
    public function beforeRender(EventInterface $event)
    {
        $this->viewBuilder()->setTemplatePath('Error');
    }
}

This controller would only be used when an error is encountered in a prefixed controller, and allows you to define prefix specific logic/templates as needed.

Custom ExceptionRenderer¶

If you want to control the entire exception rendering and logging process you can use the Error.exceptionRenderer option in config/app.php to choose a class that will render exception pages. Changing the ExceptionRenderer is useful when you want to change the logic used to create an error controller, choose the error template, or control the overall rendering process.

Your custom exception renderer class should be placed in src/Error. Let’s assume our application uses App\Exception\MissingWidgetException to indicate a missing widget. We could create an exception renderer that renders specific error pages when this error is handled:

// In src/Error/AppExceptionRenderer.php
namespace App\Error;

use Cake\Error\ExceptionRenderer;

class AppExceptionRenderer extends ExceptionRenderer
{
    public function missingWidget($error)
    {
        $response = $this->controller->getResponse();

        return $response->withStringBody('Oops that widget is missing.');
    }
}

// In config/app.php
'Error' => [
    'exceptionRenderer' => 'App\Error\AppExceptionRenderer',
    // ...
],
// ...

The above would handle our MissingWidgetException, and allow us to provide custom display/handling logic for those application exceptions.

Exception rendering methods receive the handled exception as an argument, and should return a Response object. You can also implement methods to add additional logic when handling CakePHP errors:

// In src/Error/AppExceptionRenderer.php
namespace App\Error;

use Cake\Error\ExceptionRenderer;

class AppExceptionRenderer extends ExceptionRenderer
{
    public function notFound($error)
    {
        // Do something with NotFoundException objects.
    }
}

// in src/Error/AppExceptionRenderer
namespace App\Error;

use App\Controller\SuperCustomErrorController;
use Cake\Controller\Controller;
use Cake\Error\ExceptionRenderer;

class AppExceptionRenderer extends ExceptionRenderer
{
    protected function _getController(): Controller
    {
        return new SuperCustomErrorController();
    }
}

// in config/app.php
'Error' => [
    'exceptionRenderer' => 'App\Error\AppExceptionRenderer',
    // ...
],
// ...

Custom Error Logging¶

Error handlers use instances of Cake\Error\ErrorLoggingInterface to create log messages and log them to the appropriate place. You can replace the error logger using the Error.logger configure value. An example error logger:

namespace App\Error;

use Cake\Error\ErrorLoggerInterface;
use Cake\Error\PhpError;
use Psr\Http\Message\ServerRequestInterface;
use Throwable;

/**
 * Log errors and unhandled exceptions to `Cake\Log\Log`
 */
class ErrorLogger implements ErrorLoggerInterface
{
    /**
     * @inheritDoc
     */
    public function logError(
        PhpError $error,
        ?ServerRequestInterface $request,
        bool $includeTrace = false
    ): void {
        // Log PHP Errors
    }

    /**
     * @inheritDoc
     */
    public function logException(
        ?ServerRequestInterface $request,
        bool $includeTrace = false
    ): void {
        // Log exceptions.
    }
}

Prior to CakePHP 4.4.0, you should implement logMessage() and log(), and then replace the error logger using the Error.errorLogger configure value:

namespace App\Error;

use Cake\Error\ErrorLoggerInterface;
use Psr\Http\Message\ServerRequestInterface;
use Throwable;

/**
 * Log errors and unhandled exceptions to `Cake\Log\Log`
 */
class ErrorLogger implements ErrorLoggerInterface
{
    /**
     * @inheritDoc
     */
    public function logMessage($level, string $message, array $context = []): bool
    {
        // Log PHP Errors
    }

    public function log(Throwable $exception, ?ServerRequestInterface $request = null): bool
    {
        // Log exceptions.
    }
}

Custom Error Rendering¶

By default CakePHP ships with error renderers for both web and console environments. If however, you would like to replace the logic that renders errors you can create a class:

// src/Error/CustomErrorRenderer.php
namespace App\Error;

use Cake\Error\ErrorRendererInterface;
use Cake\Error\PhpError;

class CustomErrorRenderer implements ErrorRendererInterface
{
    public function write(string $out): void
    {
        // output the rendered error to the appropriate output stream
    }

    public function render(PhpError $error, bool $debug): string
    {
        // Convert the error into the output string.
    }
}

The constructor of your renderer will be passed an array of all the Error configuration.

Creating your own Application Exceptions¶

You can create your own application exceptions using any of the built in SPL exceptions, Exception itself, or Cake\Core\Exception\Exception. If your application contained the following exception:

use Cake\Core\Exception\CakeException;

class MissingWidgetException extends CakeException
{
}

You could provide nice development errors, by creating templates/Error/missing_widget.php. When in production mode, the above error would be treated as a 500 error and use the error500 template.

Exceptions that subclass Cake\Http\Exception\HttpException, will have their error code used as an HTTP status code if the error code is between 400 and 506.

The constructor for Cake\Core\Exception\CakeException allows you to pass in additional data. This additional data is interpolated into the the _messageTemplate. This allows you to create data rich exceptions, that provide more context around your errors:

use Cake\Core\Exception\CakeException;

class MissingWidgetException extends CakeException
{
    // Context data is interpolated into this format string.
    protected $_messageTemplate = 'Seems that %s is missing.';

    // You can set a default exception code as well.
    protected $_defaultCode = 404;
}

throw new MissingWidgetException(['widget' => 'Pointy']);

When rendered, this your view template would have a $widget variable set. If you cast the exception as a string or use its getMessage() method you will get Seems that Pointy is missing..

Built in Exceptions for CakePHP¶

use Cake\Http\Exception\NotFoundException;

public function view($id = null)
{
    $article = $this->Articles->findById($id)->first();
    if (empty($article)) {
        throw new NotFoundException(__('Article not found'));
    }
    $this->set('article', $article);
    $this->viewBuilder()->setOption('serialize', ['article']);
}

use Cake\Network\Exception\NotFoundException;

public function view($id = null)
{
    $article = $this->Articles->findById($id)->first();
    if (empty($article)) {
        throw new NotFoundException(__('Article not found'));
    }
    $this->set('article', 'article');
    $this->viewBuilder()->setOption('serialize', ['article']);
}

"The response MUST include an Allow header containing a list of valid
methods for the requested resource."

Creating your Own Error Handler¶

By replacing the error handler you can customize how PHP errors and exceptions that are not caught by middleware are handled. Error handlers are different for the HTTP and Console parts of your application.

To create an error handler for HTTP requests, you should extend Cake\Error\ErrorHandler. As an example, we could build a class called AppError to handle errors during HTTP requests:

// In src/Error/AppError.php
namespace App\Error;

use Cake\Error\ErrorHandler;
use Throwable;

class AppError extends ErrorHandler
{
    protected function _displayError(array $error, bool $debug): void
    {
        echo 'There has been an error!';
    }

    protected function _displayException(Throwable $exception): void
    {
        echo 'There has been an exception!';
    }
}

Then we can register our error handler as the PHP error handler:

// In config/bootstrap.php
use App\Error\AppError;

if (PHP_SAPI !== 'cli') {
    $errorHandler = new AppError();
    $errorHandler->register();
}

Finally, we can use our error handler in the ErrorHandlerMiddleware:

// in src/Application.php
public function middleware(MiddlewareQueue $middlewareQueue): MiddlewareQueue
{
    $error = new AppError(Configure::read('Error'));
    $middleware->add(new ErrorHandlerMiddleware($error));

    return $middleware;
}

For console error handling, you should extend Cake\Error\ConsoleErrorHandler instead:

// In /src/Error/AppConsoleErrorHandler.php
namespace App\Error;
use Cake\Error\ConsoleErrorHandler;

class AppConsoleErrorHandler extends ConsoleErrorHandler {

    protected function _displayException(Throwable $exception): void {
        parent::_displayException($exception);
        if (isset($exception->queryString)) {
            $this->_stderr->write('Query String: ' . $exception->queryString);
        }
    }

}

Then we can register our console error handler as the PHP error handler:

// In config/bootstrap.php
use App\Error\AppConsoleErrorHandler;
$isCli = PHP_SAPI === 'cli';
if ($isCli) {
    (new AppConsoleErrorHandler(Configure::read('Error')))->register();
}

ErrorHandler objects have a few methods you may want to implement:

• _displayError(array $error, bool $debug) is used when errors are triggered.

• _displayException(Throwable $exception) method is called when there is an uncaught exception.

• _logError($level, array $error) is called when there is an error to log.

• logException(Throwable $exception) is called when there is an exception to log.

// In src/Error/AppError.php
namespace App\Error;

use Cake\Error\BaseErrorHandler;

class AppError extends BaseErrorHandler
{
    // Other methods.

    public function handleFatalError(int $code, string $description, string $file, int $line): bool
    {
        echo 'A fatal error has happened';
    }
}