error_pages.rst

.. index::
   single: Controller; Customize error pages
   single: Error pages

How to Customize Error Pages

In Symfony applications, all errors are treated as exceptions, no matter if they are just a 404 Not Found error or a fatal error triggered by throwing some exception in your code.

In the :doc:`development environment </configuration/environments>`, Symfony catches all the exceptions and displays a special exception page with lots of debug information to help you quickly discover the root problem:

Since these pages contain a lot of sensitive internal information, Symfony won't display them in the production environment. Instead, it'll show a simple and generic error page:

Error pages for the production environment can be customized in different ways depending on your needs:

1. If you just want to change the contents and styles of the error pages to match the rest of your application, :ref:`override the default error templates <use-default-exception-controller>`;
2. If you also want to tweak the logic used by Symfony to generate error pages, :ref:`override the default exception controller <custom-exception-controller>`;
3. If you need total control of exception handling to execute your own logic :ref:`use the kernel.exception event <use-kernel-exception-event>`.

Overriding the Default Error Templates

When the error page loads, an internal :class:`Symfony\\Bundle\\TwigBundle\\Controller\\ExceptionController` is used to render a Twig template to show the user.

This controller uses the HTTP status code, the request format and the following logic to determine the template filename:

1. Look for a template for the given format and status code (like error404.json.twig or error500.html.twig);
2. If the previous template doesn't exist, discard the status code and look for a generic template for the given format (like error.json.twig or error.xml.twig);
3. If none of the previous template exist, fall back to the generic HTML template (error.html.twig).

To override these templates, rely on the standard Symfony method for :ref:`overriding templates that live inside a bundle <override-templates>` and put them in the templates/bundles/TwigBundle/Exception/ directory.

A typical project that returns HTML and JSON pages, might look like this:

templates/
└─ bundles/
   └─ TwigBundle/
      └─ Exception/
         ├─ error404.html.twig
         ├─ error403.html.twig
         ├─ error.html.twig      # All other HTML errors (including 500)
         ├─ error404.json.twig
         ├─ error403.json.twig
         └─ error.json.twig      # All other JSON errors (including 500)

Example 404 Error Template

To override the 404 error template for HTML pages, create a new error404.html.twig template located at templates/bundles/TwigBundle/Exception/:

{# templates/bundles/TwigBundle/Exception/error404.html.twig #}
{% extends 'base.html.twig' %}

{% block body %}
    <h1>Page not found</h1>

    <p>
        The requested page couldn't be located. Checkout for any URL
        misspelling or <a href="{{ path('homepage') }}">return to the homepage</a>.
    </p>
{% endblock %}

In case you need them, the ExceptionController passes some information to the error template via the status_code and status_text variables that store the HTTP status code and message respectively.

Tip

You can customize the status code by implementing :class:`Symfony\\Component\\HttpKernel\\Exception\\HttpExceptionInterface` and its required getStatusCode() method. Otherwise, the status_code will default to 500.

Note

The exception pages shown in the development environment can be customized in the same way as error pages. Create a new exception.html.twig template for the standard HTML exception page or exception.json.twig for the JSON exception page.

Testing Error Pages during Development

While you're in the development environment, Symfony shows the big exception page instead of your shiny new customized error page. So, how can you see what it looks like and debug it?

Fortunately, the default ExceptionController allows you to preview your error pages during development.

To use this feature, you need to load some special routes provided by TwigBundle (if the application uses :doc:`Symfony Flex </setup/flex>` they are loaded automatically when installing Twig support):

.. configuration-block::

    .. code-block:: yaml

        # config/routes/dev/twig.yaml
        _errors:
            resource: '@TwigBundle/Resources/config/routing/errors.xml'
            prefix:   /_error

    .. code-block:: xml

        <!-- config/routes/dev/twig.xml -->
        <?xml version="1.0" encoding="UTF-8" ?>
        <routes xmlns="http://symfony.com/schema/routing"
            xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
            xsi:schemaLocation="http://symfony.com/schema/routing
                http://symfony.com/schema/routing/routing-1.0.xsd">

            <import resource="@TwigBundle/Resources/config/routing/errors.xml"
                prefix="/_error" />
        </routes>

    .. code-block:: php

        // config/routes/dev/twig.php
        use Symfony\Component\Routing\RouteCollection;

        $routes = new RouteCollection();
        $routes->addCollection(
            $loader->import('@TwigBundle/Resources/config/routing/errors.xml')
        );
        $routes->addPrefix("/_error");

        return $routes;

With this route added, you can use URLs like these to preview the error page for a given status code as HTML or for a given status code and format.

http://localhost/index.php/_error/{statusCode}
http://localhost/index.php/_error/{statusCode}.{format}

Overriding the Default ExceptionController

If you need a little more flexibility beyond just overriding the template, then you can change the controller that renders the error page. For example, you might need to pass some additional variables into your template.

To do this, simply create a new controller anywhere in your application and set the :ref:`twig.exception_controller <config-twig-exception-controller>` configuration option to point to it:

.. configuration-block::

    .. code-block:: yaml

        # config/packages/twig.yaml
        twig:
            exception_controller: App\Controller\ExceptionController::showException

    .. code-block:: xml

        <!-- config/packages/twig.xml -->
        <?xml version="1.0" encoding="UTF-8" ?>
        <container xmlns="http://symfony.com/schema/dic/services"
            xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
            xmlns:twig="http://symfony.com/schema/dic/twig"
            xsi:schemaLocation="http://symfony.com/schema/dic/services
                http://symfony.com/schema/dic/services/services-1.0.xsd
                http://symfony.com/schema/dic/twig
                http://symfony.com/schema/dic/twig/twig-1.0.xsd">

            <twig:config>
                <twig:exception-controller>App\Controller\ExceptionController::showException</twig:exception-controller>
            </twig:config>

        </container>

    .. code-block:: php

        // config/packages/twig.php
        $container->loadFromExtension('twig', array(
            'exception_controller' => 'App\Controller\ExceptionController::showException',
            // ...
        ));

The :class:`Symfony\\Component\\HttpKernel\\EventListener\\ExceptionListener` class used by the TwigBundle as a listener of the kernel.exception event creates the request that will be dispatched to your controller. In addition, your controller will be passed two parameters:

exception

A :class:`\\Symfony\\Component\\Debug\\Exception\\FlattenException` instance created from the exception being handled.

logger

A :class:`\\Symfony\\Component\\HttpKernel\\Log\\DebugLoggerInterface` instance which may be null in some circumstances.

Instead of creating a new exception controller from scratch you can, of course, also extend the default :class:`Symfony\\Bundle\\TwigBundle\\Controller\\ExceptionController`. In that case, you might want to override one or both of the showAction() and findTemplate() methods. The latter one locates the template to be used.

Note

In case of extending the :class:`Symfony\\Bundle\\TwigBundle\\Controller\\ExceptionController` you may configure a service to pass the Twig environment and the debug flag to the constructor.

.. configuration-block::

    .. code-block:: yaml

        # config/services.yaml
        services:
            _defaults:
                # ... be sure autowiring is enabled
                autowire: true
            # ...

            App\Controller\CustomExceptionController:
                public: true
                arguments:
                    $debug: '%kernel.debug%'

    .. code-block:: xml

        <!-- config/services.xml -->
        <?xml version="1.0" encoding="UTF-8" ?>
        <container xmlns="http://symfony.com/schema/dic/services"
            xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
            xsi:schemaLocation="http://symfony.com/schema/dic/services
                http://symfony.com/schema/dic/services/services-1.0.xsd">

            <services>
                <!-- ... be sure autowiring is enabled -->
                <defaults autowire="true" />
                <!-- ... -->

                <service id="App\Controller\CustomExceptionController" public="true">
                    <argument key="$debug">%kernel.debug%</argument>
                </service>
            </services>

        </container>

    .. code-block:: php

        // config/services.php
        use App\Controller\CustomExceptionController;

        $container->autowire(CustomExceptionController::class)
            ->setArgument('$debug', '%kernel.debug%');

Tip

The :ref:`error page preview <testing-error-pages>` also works for your own controllers set up this way.

Working with the kernel.exception Event

When an exception is thrown, the :class:`Symfony\\Component\\HttpKernel\\HttpKernel` class catches it and dispatches a kernel.exception event. This gives you the power to convert the exception into a Response in a few different ways.

Working with this event is actually much more powerful than what has been explained before, but also requires a thorough understanding of Symfony internals. Suppose that your code throws specialized exceptions with a particular meaning to your application domain.

:doc:`Writing your own event listener </event_dispatcher>` for the kernel.exception event allows you to have a closer look at the exception and take different actions depending on it. Those actions might include logging the exception, redirecting the user to another page or rendering specialized error pages.

Note

If your listener calls setResponse() on the :class:`Symfony\\Component\\HttpKernel\\Event\\GetResponseForExceptionEvent`, event, propagation will be stopped and the response will be sent to the client.

This approach allows you to create centralized and layered error handling: instead of catching (and handling) the same exceptions in various controllers time and again, you can have just one (or several) listeners deal with them.

Tip

See :class:`Symfony\\Component\\Security\\Http\\Firewall\\ExceptionListener` class code for a real example of an advanced listener of this type. This listener handles various security-related exceptions that are thrown in your application (like :class:`Symfony\\Component\\Security\\Core\\Exception\\AccessDeniedException`) and takes measures like redirecting the user to the login page, logging them out and other things.