Routing Adapters

Routing

One fundamental feature of zend-expressive is that it provides mechanisms for implementing dynamic routing, a feature required in most modern web applications. As an example, you may want to allow matching both a resource, as well as individual items of that resource:

• /books might return a collection of books
• /books/zend-expressive might return the individual book identified by "zend-expressive".

Expressive does not provide routing on its own; you must choose a routing adapter that implements Zend\Expressive\Router\RouterInterface. The router is consumed by Zend\Expressive\Router\Middleware\RouteMiddleware as well as Zend\Expressive\Router\RouteCollector, the latter of which is composed in the Application instance. This allows you to choose the router with the capabilities that best match your own needs, while still providing a common abstraction for defining and aggregating routes and their related middleware.

Retrieving matched parameters

Routing enables the ability to match dynamic path segments (or other criteria). Typically, you will want access to the values matched. The routing middleware injects any matched parameters as returned by the underlying router into the request as attributes.

In the example above, let's assume the route was defined as /books/:id, where id is the name of the dynamic segment. This means that in the middleware invoked for this route, you can fetch the id attribute to discover what was matched:

$id = $request->getAttribute('id');

Retrieving the matched route

When routing is complete, the routing middleware injects a Zend\Expressive\Router\RouteResult instance as a request attribute, using that class name as the attribute name. The RouteResult instance provides you access to the following:

• Matching status via the methods $result->isSuccess(), $result->isFailure(), and $result->isMethodFailure() (indicating a path-based match that did not match an allowed HTTP method).
• Allowed HTTP methods, via $result->getAllowedMethods() (for either success or failure).
• The matched Zend\Expressive\Router\Route instance, via $result->getMatchedRoute() (successful matches only).
• The matched route name, via $result->getMatchedRouteName() (or via $result->getMatchedRoute()->getName(); successful matches only).
• Matched parameters, via $result->getMatchedParams() (as noted above, these are also each injected as discrete request attributes; successful matches only).

As an example, you could use middleware similar to the following to return a 403 response if routing was successful, but no Authorization header is present:

use Psr\Http\Server\RequestHandlerInterface;
use Zend\Diactoros\Response\EmptyResponse;
use Zend\Expressive\Router\RouteResult;

function ($request, RequestHandlerInterface $handler) use ($routesRequiringAuthorization, $validator) {
    if (! ($result = $request->getAttribute(RouteResult::class, false))) {
        // No route result present; delegate to next middleware
        return $handler->handle($request);
    }

    if (! in_array($result->getMatchedRouteName(), $routesRequiringAuthorization, true)) {
        // Not a route requiring authorization
        return $handler->handle($request);
    }

    $header = $request->getHeaderLine('Authorization');
    if (! $validator($header)) {
        return new EmptyResponse(403);
    }

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

Note that the first step is to determine if we have a RouteResult; if we do not have one, we should either delegate to the next middleware, or return some sort of response (generally a 404). In the case of Expressive, a later middleware will generate the 404 response for us, so we can safely delegate.

URI generation

Because routers have knowledge of the various paths they can match, they are also typically used within applications to generate URIs to other application resources. Expressive provides this capability in the RouterInterface, either delegating to the underlying router implementations or providing a compatible implementation of its own.

At it's most basic level, you call the generateUri() method with a route name and any substitutions you want to make:

$uri = $router->generateUri('book', ['id' => 'zend-expressive']);

Some routers may support providing options during URI generation. Starting in zend-expressive-router 2.0, which ships with Expressive starting with version 2.0, you may also pass a third argument to generateUri(), an array of router options:

$uri = $router->generateUri('book', ['id' => 'zend-expressive'], [
    'translator'  => $translator,
    'text_domain' => $currentLocale,
]);

Supported implementations

Expressive currently ships with adapters for the following routers:

• Aura.Router
• FastRoute
• zend-mvc Router