Front Controller Pattern

What is the Front Controller Pattern?

The Front Controller pattern handles all incoming requests through a single entry point, which dispatches to appropriate handlers.

All Requests → FrontController → Router → Action Controller → Response

Benefits

1. Centralized control: One point for authentication, logging, error handling
2. URL routing: Single place to map URLs to handlers
3. Security: Cross-cutting concerns handled in one place
4. Extensibility: Interceptors can modify the dispatch chain

Magento's FrontController

namespace Magento\Framework\App;

class FrontController
{
    public function __construct(
        private array $routers,
        private ManagerInterface $eventManager,
        private AppInterface $app
    ) {}

    public function dispatch(RequestInterface $request): ResponseInterface
    {
        // 1. Check if already dispatched (prevent double dispatch)
        if ($this->app->isDispatched()) {
            return $this->app->getResponse();
        }

        // 2. Fire event (plugins can modify request)
        $this->eventManager->dispatch('controller_action_predispatch', [
            'request' => $request,
        ]);

        // 3. Try each router until one matches
        $routerFound = false;
        foreach ($this->routers as $router) {
            $actionInstance = $router->match($request);
            if ($actionInstance !== null) {
                $routerFound = true;
                break;
            }
        }

        if (!$routerFound) {
            // No router matched → 404
            return $this->prepareNotFoundResponse();
        }

        // 4. Execute the action
        $result = $actionInstance->dispatch($request);

        // 5. Return response
        return $result;
    }
}

Router Interface

namespace Magento\Framework\App\Router\Action\ListInterface;

interface ActionListInterface
{
    public function getActionClass($routeName, $routeModule);
}

// Standard router resolves:
// frontName → module → controller → action
// catalog → Magento_Catalog → Product → View
// = Magento\Catalog\Controller\Product\View

Action Controller Dispatch

namespace Magento\Framework\App\Action;

abstract class Action
{
    public function dispatch(RequestInterface $request): ResponseInterface
    {
        $this->request = $request;
        $this->_eventPrefix = $this->getRequest()->getRouteName();

        // Fire pre-dispatch event
        $this->_eventManager->dispatch(
            'controller_action_predispatch_' . $this->getRequest()->getFullActionName(),
            ['controller_action' => $this]
        );

        // Execute the action (implemented by subclass)
        $result = $this->execute();

        // Fire post-dispatch event
        $this->_eventManager->dispatch(
            'controller_action_postdispatch_' . $this->getRequest()->getFullActionName(),
            ['controller_action' => $this]
        );

        return $result;
    }

    abstract public function execute();
}

Request Object

namespace Magento\Framework\App\Request;

class Http implements RequestInterface
{
    // Get all parameters
    public function getParams(): array

    // Get specific parameter
    public function getParam(string $key, $default = null)

    // Set parameter
    public function setParam(string $key, $value): Http

    // Get HTTP method
    public function getMethod(): string

    // Get request URI
    public function getRequestUri(): string

    // Get action name (from URL)
    public function getActionName(): string

    // Get controller name (from URL)
    public function getControllerName(): string

    // Get module name (from URL)
    public function getModuleName(): string

    // Get full action name: module_controller_action
    public function getFullActionName(): string
}

// Usage in controller:
$productId = $this->getRequest()->getParam('id');
$page = $this->getRequest()->getParam('p', 1);
$search = $this->getRequest()->getParam('q');

Response Object

namespace Magento\Framework\App\Response;

class Http implements ResponseInterface
{
    // Set HTTP status code
    public function setStatusCode(int $code): Http

    // Set response header
    public function setHeader(string $name, string $value, bool $replace = false): Http

    // Set response body
    public function setBody(string $content): Http

    // Set redirect URL
    public function setRedirect(string $url, int $code = 302): Http

    // Send response to client
    public function sendResponse(): void
}

// Usage:
$this->getResponse()->setStatusCode(404);
$this->getResponse()->setHeader('Content-Type', 'application/json');
$this->getResponse()->setBody(json_encode(['error' => 'Not found']));

Intercepting the Dispatch Process

<!-- etc/di.xml -->
<config>
    <type name="Magento\Framework\App\FrontController">
        <plugin name="vendor_dispatch_log"
                type="Vendor\Module\Plugin\FrontControllerPlugin"
                sortOrder="10"/>
    </type>
</config>

namespace Vendor\Module\Plugin;

class FrontControllerPlugin
{
    public function __construct(
        private \Psr\Log\LoggerInterface $logger
    ) {}

    // Before dispatch: log all requests
    public function beforeDispatch(
        \Magento\Framework\App\FrontController $subject,
        \Magento\Framework\App\RequestInterface $request
    ): void {
        $this->logger->info('Request dispatched', [
            'uri' => $request->getRequestUri(),
            'method' => $request->getMethod(),
            'route' => $request->getRouteName(),
        ]);
    }

    // After dispatch: log response time
    public function afterDispatch(
        \Magento\Framework\App\FrontController $subject,
        $result
    ) {
        $this->logger->info('Dispatch completed', [
            'status' => $result->getStatusCode(),
        ]);
        return $result; // Must return the result!
    }
}

Around Dispatch: Modify Request

public function aroundDispatch(
    \Magento\Framework\App\FrontController $subject,
    callable $proceed,
    \Magento\Framework\App\RequestInterface $request
) {
    // Before: modify request
    if ($request->getParam('force_ssl') && !$request->isSecure()) {
        // Force HTTPS
        return $this->redirect->redirect($request, 'https://' . $request->getHttpHost() . $request->getRequestUri());
    }

    // Call original dispatch
    $result = $proceed($request);

    // After: modify response
    $result->setHeader('X-Custom-Header', 'value');

    return $result;
}

Controller-Level Plugins

<!-- Plugin on specific controller -->
<type name="Magento\Catalog\Controller\Product\View">
    <plugin name="vendor_product_view_log"
            type="Vendor\Module\Plugin\ProductViewPlugin"/>
</type>

public function beforeExecute(\Magento\Catalog\Controller\Product\View $subject)
{
    // Runs before Product\View::execute()
    $productId = $subject->getRequest()->getParam('id');
    $this->logger->info('Product view: ' . $productId);
}

public function afterExecute(\Magento\Catalog\Controller\Product\View $subject, $result)
{
    // Runs after Product\View::execute()
    $this->analytics->trackPageView('product', $productId);
    return $result;
}