Middleware

Table of contents

Raindeer doesn't use Rack or a traditional middleware API. A middleware is just a pipeline, and in Raindeer everything is a pipeline already. Intercepting the request or response layer can be done in a few different ways. Below they are listed in the order in which they are executed.

Events

1. Boot File

Edit config/boot.rb to set things up before or after require 'raindeer/boot'.

2. BootEvent [CANDIDATE]

To intercept Raindeer's own boot process, BootEvent provides a more formal API.

Ordered Actions:

  1. :before_boot
  2. :load_config
  3. :load_providers
  4. :load_app
  5. :after_boot

3. RequestEvent

Say you want to authenticate, log or redirect before every request, then RequestEvent.define is the answer. We do it this way to minimise per-request overhead; if you're handling thousands of requests then you don't want to be processing nice tasty RouteEvents before denying access or issuing redirects.

Low::Events::RequestEvent.define do |observers|
  observers = [MyLogger, MyAuthenticator, *observers]
end

These additional observers will receive a :render/:receive/HTTP_VERB action, so add a corresponding method to those nodes/custom classes and return LowNode.render(event:), ResponseEvent or nil.

Tip

Event observers should only be redefined once, so keep them in a central location. Example: app/events/request_event

4. RouteEvent

Because you can listen to "mid-nodes" along a route, you can observe '/' with a side_effect action/method to intercept every routed request.

5. WildcardEvent

The router's unmatched requests will not be routed, but a WildcardEvent will then be called.

6. StatusEvent

Observe Status[404] or similar for when nothing above returns a non-nil reponse.

Pipeline Data Flow

Events are Push-based (trigger event) and Pull-based (return value). Code that triggers an event receives the output of that event, which may be the output of another sub event and so on.