ImplicitHeadMiddleware and ImplicitOptionsMiddleware

Expressive offers middleware for implicitly supporting HEAD and OPTIONS requests. The HTTP/1.1 specifications indicate that all server implementations must support HEAD requests for any given URI, and that they should support OPTIONS requests. To make this possible, we have added features to our routing layer, and middleware that can detect implicit support for these methods (i.e., the route was not registered explicitly with the method).

Both middleware detailed here are provided in the zend-expressive-router package.

ImplicitHeadMiddleware

Zend\Expressive\Router\Middleware\ImplicitHeadMiddleware provides support for handling HEAD requests to routed middleware when the route does not explicitly allow for the method. It should be registered between the routing and dispatch middleware.

The zend-expressive-router package provides a factory for creating an instance, and registers it by default via its configuration provider.

If you want to provide a response instance with additional headers or a custom status code, you will need to provide your own factory.

Within your application pipeline, add the middleware between the routing and dispatch middleware, generally immediately following the routing middleware:

$app->pipe(RouteMiddleware::class);
$app->pipe(ImplicitHeadMiddleware::class);
// ...
$app->pipe(DispatchMiddleware::class);

(Note: if you used the Expressive skeleton, this middleware is likely already in your pipeline.)

When in place, it will do the following:

  • If the request method is HEAD, AND
  • the request composes a RouteResult attribute, AND
  • the route result indicates a routing failure due to HTTP method used, THEN
  • the middleware will return a response.

In all other cases, it returns the result of delegating to the next middleware layer.

When the middleware decides it can answer the request, one of two things may occur. First, if the route does not support the GET method, then the middleware returns an empty response. However, if GET is supported, it will dispatch the next layer, but with a GET request instead of HEAD; additionally, it will inject the returned response with an empty response body before returning it.

Detecting forwarded requests

When the next layer is dispatched, the request will have an additional attribute, Zend\Expressive\Router\Middleware\ImplicitHeadMiddleware::FORWARDED_HTTP_METHOD_ATTRIBUTE, with a value of HEAD. As such, you can check for this value in order to vary the headers returned if desired.

ImplicitOptionsMiddleware

Zend\Expressive\Router\Middleware\ImplicitOptionsMiddleware provides support for handling OPTIONS requests to routed middleware when the route does not explicitly allow for the method. Like the ImplicitHeadMiddleware, it should be registered between the routing and dispatch middleware.

The zend-expressive-router package provides a factory for creating an instance, and registers it by default via its configuration provider.

If you want to provide a response instance with additional headers or a custom status code, you will need to provide your own factory.

Within your application pipeline, add the middleware between the routing and dispatch middleware, generally immediately following the routing middleware or ImplicitHeadMiddleware:

$app->pipe(RouteMiddleware::class);
$app->pipe(ImplicitOptionsMiddleware::class);
// ...
$app->pipe(DispatchMiddleware::class);

(Note: if you used the Expressive skeleton, this middleware is likely already in your pipeline.)

When in place, it will do the following:

  • If the request method is OPTIONS, AND
  • the request composes a RouteResult attribute, AND
  • the route result indicates a routing failure due to HTTP method used, THEN
  • the middleware will return a 200 response with an Allow header indicating methods the route allows.

In all other cases, it returns the result of delegating to the next middleware layer.

One thing to note: the allowed methods reported by the route and/or route result, and returned via the Allow header, may vary based on router implementation. In most cases, it should be an aggregate of all routes using the same path specification; however, it could be only the methods supported explicitly by the matched route.

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