Routing and Dispatch Middleware

Within Expressive, we differentiate routing from dispatching. Routing is the act of matching a request to middleware; this typically involves inspecting the path and HTTP method used, but may also consider aspects such as headers, protocol, and more. Dispatching occurs after routing; it examines the results of routing, processing the middleware matched.

Expressive goes so far as to separate the two actions into separate middleware. This is done to allow additional middleware to execute between them. For example, as you'll learn in the next two chapters, we can look for routing failures and answer HEAD and OPTIONS requests, or return a 405 Method Not Allowed status without ever hitting the dispatch middleware. When you read about the UrlHelper, you'll discover it has associated middleware that can receive the results of routing in order to facilitate URI generation. Keeping the two actions separated as distinct middleware provides a ton of power and flexibility in building your applications.

We provide two middleware around these actions, each in the Zend\Expressive\Router\Middleware namespace and provided by the zendframework/zend-expressive-router package:

  • RouteMiddleware, which consumes a router in order to route a request.

  • DispatchMiddleware, which dispatches the route result.

RouteMiddleware

Zend\Expressive\Router\Middleware\RouteMiddleware receives a Zend\Expressive\Router\RouterInterface instance to its constructor. When it is processed, it passes the request to the router in order to receive a Zend\Expressive\Router\RouteResult instance.

When the result indicates a match, the middleware creates an updated request instance that includes each of the route match parameters as attributes.

Regardless of the result, it will create an updated request instance that includes the result as the attribute Zend\Expressive\Router\RouteResult.

It then invokes the handler; all later middleware can then access the route result using:

$result = $request->getAttribute(\Zend\Expressive\Router\RouteResult::class);

DispatchMiddleware

Zend\Expressive\Router\Middleware\DispatchMiddleware defines only the process() method required by the PSR-15 MiddlewareInterface. Internally, it:

  • checks for a RouteResult in the request, AND
  • processes it, passing the request and handler.

If there is no RouteResult, it delegates to the handler without doing anything else.

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