Creating Middleware

To create middleware, write a callable capable of receiving minimally PSR-7 ServerRequest and Response objects, and a callback to call the next middleware in the chain. In your middleware, you can handle as much or as little of the request as you want, including delegating to other middleware in order to produce or return a response.

As an example, consider the following middleware which will use an external router to map the incoming request path to a handler; if unable to map the request, it returns processing to the next middleware.

use Interop\Http\ServerMiddleware\DelegateInterface;
use Interop\Http\ServerMiddleware\MiddlewareInterface;

function ($req, DelegateInterface $delegate) use ($router) {
    $path = $req->getUri()->getPath();

    // Route the path
    $route = $router->route($path);
    if (! $route) {
        return $delegate->process($req);

    /** @var MiddlewareInterface $handler */
    $handler = $route->getHandler();
    return $handler->process($req, $delegate);

Middleware written in this way can be any of the following:

  • Closures (as shown above)
  • Functions
  • Static class methods
  • PHP array callbacks (e.g., [ $dispatcher, 'dispatch' ], where $dispatcher is a class instance)
  • Invokable PHP objects (i.e., instances of classes implementing __invoke())
  • Objects implementing Interop\Http\ServerMiddleware\MiddlewareInterface

In all cases, if you wish to implement typehinting, the signature is:

function (
    Psr\Http\Message\ServerRequestInterface $request,
    Interop\Http\ServerMiddleware\DelegateInterface $delegate
) : Psr\Http\Message\ResponseInterface

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