Decorator Middleware

A decorator middleware is a kind of middleware that always calls the next middleware in a chain.

HasCallbacks is a good example.

module ConvenientService
  module Common
    module Plugins
      module HasCallbacks
        class Middleware < Core::MethodChainMiddleware
          # ...
          def next(...)
            entity.callbacks.for([:before, method]).each { |callback| callback.call_in_context(entity) }

            original_value = chain.next(...)

            entity.callbacks.for([:after, method]).reverse_each { |callback| callback.call_in_context(entity, original_value) }

            original_value
          end
          # ...
        end
      end
    end
  end
end

It triggers before callbacks, then chain.next(...), and later after callbacks.

There are no conditionals that may skip chain.next(...) invocation.

That is why this middleware is considered decorator middleware.

In contrast, proxy middlewares may not call chain.next if needed.