Request Handling

TYPO3 CMS has implemented PSR-15 for handling incoming HTTP requests. The implementation within TYPO3 is often called “Middlewares”, as PSR-15 consists of two interfaces where one is called Middleware .

Basic concept

The most important information is available at https://www.php-fig.org/psr/psr-15/ and https://www.php-fig.org/psr/psr-15/meta/ where the standard itself is explained.

The idea is to use PSR-7 Request and Response as a base, and wrap the execution with middlewares which implement PSR-15 . PSR-15 will receive the incoming request and return the created response. Within PSR-15 multiple request handlers and middlewares can be executed. Each of them can adjust the request and response.

TYPO3 implementation

TYPO3 has implemented the PSR-15 approach in the following way:

../../_images/flow-of-middleware-execution.svg

Figure 1-1: Application flow

  1. TYPO3 will create a PSR-7 request.
  2. TYPO3 will collect and sort all configured PSR-15 middlewares.
  3. TYPO3 will convert all middlewares to PSR-15 request handlers.
  4. TYPO3 will call the first middleware with request and the next middleware.
  5. Each middleware is processed, see request-handling-middleware .
  6. In the end each middleware has to return a PSR-7 response.
  7. This response is passed back to the execution flow.

Middlewares

Each middleware has to implement the PSR-15 MiddlewareInterface :

namespace Psr\Http\Server;

use Psr\Http\Message\ResponseInterface;
use Psr\Http\Message\ServerRequestInterface;

/**
 * Participant in processing a server request and response
 *
 * An HTTP middleware component participates in processing an HTTP message:
 * by acting on the request, generating the response, or forwarding the
 * request to a subsequent middleware and possibly acting on its response.
 */
interface MiddlewareInterface
{
    /**
     * Process an incoming server request
     *
     * Processes an incoming server request in order to produce a response.
     * If unable to produce the response itself, it may delegate to the provided
     * request handler to do so.
     */
    public function process(
        ServerRequestInterface $request,
        RequestHandlerInterface $handler
    ): ResponseInterface;
}

By doing so, the middleware can do one or multiple of the following:

  • Adjust the incoming request, e.g. add further information.
  • Create and return a PSR-7 response.
  • Call next request handler (which again can be a middleware).
  • Adjust response received from the next request handler.

Middleware examples

The following list shows typical use cases for middlewares.

Returning a custom response

This middleware will check whether TYPO3 is in maintenance mode and will return an unavailable response in that case. Otherwise the next middleware will be called, and its response is returned instead.

public function process(
    ServerRequestInterface $request,
    RequestHandlerInterface $handler
): ResponseInterface {
    if (/* if logic */) {
        return GeneralUtility::makeInstance(ErrorController::class)
            ->unavailableAction(
                $request,
                'This page is temporarily unavailable.'
            );
    }

    return $handler->handle($request);
}

Enriching the request

The current request can be extended with further information, e.g. the current resolved site and language could be attached to the request.

In order to do so, a new request is built with additional attributes, before calling the next request handler with the enhanced request.

public function process(
    ServerRequestInterface $request,
    RequestHandlerInterface $handler
): ResponseInterface {
    $routeResult = $this->matcher->matchRequest($request);

    $request = $request->withAttribute('site', $routeResult->getSite());
    $request = $request->withAttribute('language', $routeResult->getLanguage());

    return $handler->handle($request);
}

Enriching the response

This middleware will check the length of generated output, and add a header with this information to the response.

In order to do so, the next request handler is called. It will return the generated response, which can be enriched before it gets returned.

public function process(
    ServerRequestInterface $request,
    RequestHandlerInterface $handler
): ResponseInterface {
    $response = $handler->handle($request);

    if (/* if logic */) {
        $response = $response->withHeader(
            'Content-Length',
            (string)$response->getBody()->getSize()
        );
    }

    return $response;
}

Configuring middlewares

In order to implement a custom middleware, this middleware has to be configured. TYPO3 already provides some middlewares out of the box. Beside adding your own middlewares, it’s also possible to remove existing middlewares from the configuration.

The configuration is provided within Configuration/RequestMiddlewares.php of an extension:

return [
    'frontend' => [
        'middleware-identifier' => [
            'target' => \Vendor\ExtName\Middleware\ConcreteClass::class,
            'before' => [
                'another-middleware-identifier',
            ],
            'after' => [
                'yet-another-middleware-identifier',
            ],
        ],
    ],
    'backend' => [
        'middleware-identifier' => [
            'target' => \Vendor\ExtName\Middleware\AnotherConcreteClass::class,
            'before' => [
                'another-middleware-identifier',
            ],
            'after' => [
                'yet-another-middleware-identifier',
            ],
        ],
    ],
];

TYPO3 has multiple stacks where one middleware might only be necessary in one of them. Therefore the configuration defines the context on its first level to define the context. Within each context the middleware is registered as new subsection with an unique identifier as key.

The default stacks are: frontend and backend .

Each middleware consists of the following options:

target

PHP string

FQCN (=Fully Qualified Class Name) to use as middleware.

before

PHP Array

List of middleware identifiers. The middleware itself is executed before any other middleware within this array.

after

PHP Array

List of middleware identifiers. The middleware itself is executed after any other middleware within this array.

disabled

PHP boolean

Allows to disable specific middlewares.

Debugging

In order to see which middlewares are configured and to see the order of execution, TYPO3 offers a the menu entry HTTP Middlewares (PSR-15) within the “Configuration” module:

../../_images/ConfigurationMiddleware.png

Figure 1-2: TYPO3 configuration module listing configured middlewares.