Middleware API

Drupal 8/9/10 has a Middleware API that it adopted from the broader PHP community. This one-liner from their project page captures it well:

Symfony's HttpKernelInterface provides a solid interface, which makes creating and sharing framework-agnostic HTTP filters a breeze!

So, StackPHP:

1. builds on top of Symfony's HttpKernelInterface
2. is a convention for composing HttpKernelInterface middlewares.

That's it!

Dependency Injection

The Drupal\Core\DependencyInjection\Compiler\StackedKernelPass compiler pass implicitly prepends the inner kernel as first constructor argument of the middleware. Thus, you do not need to define arguments in your modules *.services.yml definition for the middleware unless your middleware depends on another registered service.

Caution

Middlewares run on every request. Effectively, the Middleware API is the equivalent of Drupal 7's hook_boot(). So, make sure they run at the appropriate time (i.e. the appropriate order), and ensure they do as little I/O as possible. Because every request will be impacted. Add one slow StackPHP middleware, and the entire Drupal 8+ site will be slow!

Examples

You can find lots of examples at https://github.com/stackphp/stackphp.com/blob/master/source/middlewares.....

Drupal core

In Drupal core, the following concepts are implemented via StackPHP middlewares:

1. Internal page cache ( \Drupal\page_cache\StackMiddleware\PageCache)
2. content negotiation (\Drupal\Core\StackMiddleware\NegotiationMiddleware)
3. reverse proxy support (\Drupal\Core\StackMiddleware\ReverseProxyMiddleware)
4. session handling (\Drupal\Core\StackMiddleware\Session)

Drupal Contributed Modules (example list)

1. Rate Limiter (Rate Limiting Service for API consumption)
2. Redirect after login
3. Firewall (on Request)
4. Shield

3rd Party Github Hosted

1. CORS-Drupal8 (https://github.com/dmouse/cors-drupal8)

See also

• https://github.com/stackphp
• core committer concern: https://www.drupal.org/node/1869548#comment-11287753