4. Middleware

Radar for PHP

4. Middleware

Radar uses the Relay system for dispatching middleware. You can read more about middleware there.

To add Relay-compatible middleware entries to the queue, call the $adr->middle() method in web/index.php. Pass a class name as the only parameter to the method. The underlying dependency injection container will create an instance of that class so that Relay can call its __invoke() method.


Alternatively, pass:

  • An array of the form ['ClassName', 'method']. In this case, the underlying dependency injection container will create an instance of that class and call the specified method. The method should be Relay-compatible.

  • A new callable object with a Relay-compatible __invoke() method.

  • An anonymous function with a Relay-compatible signature.

4.1. Exception Handling

If middleware in the queue fails to catch an exception, the default Relay\Middleware\ExceptionHandler will catch it automatically. The ExceptionHandler will:

  • write the Exception message to a new Response object,
  • set a 500 HTTP status code on that new Response,
  • return the new Response to the previous middleware handler.

The ExceptionHandler should be placed after the ResponseSender middleware in the queue, so that the ResponseSender can then send the exceptional response.

4.2. Middleware And Domain Activity

You are going to be very tempted to place domain-related activity in your middleware, things like "checking to see if a user is authenticated" and so on. Resist this temptation. Middleware should only be about inspecting and modifying the request and response, not about handling domain elements. Middleware is not part of your core application; it is part of the HTTP user interface to that application.

One shorthand way of determining if you are doing domain work is this: if you have to touch a storage system of any sort, it's probably domain related. This includes things like starting a session, which uses some form of storage system to re-establish itself.

This may seem onerous, but remember: Radar is an HTTP-specific user interface wrapper around your core application. Anything that relates to authentication, authorization, database, disk, and so on are more properly part of your domain work, not the user- interface work related to the input and output related to that domain. All the data you need to work with the domain should come from the incoming request, and all the data you need to build a response should emit from the domain as a Payload.