Middleware Stack

[HoneyryderChuck]

This proposes a basic spec for the middleware chain/stack, which is built within the Rack::Builder class (ivar @use).

A class implementing the middleware stack should implement both #useand #to_app,where:

• #use receives a middleware class, arguments and block;
• #to_app receives a rack app and returns the app chained with the middlewares.

This is an attempt to support #1111 , which proposes to replace the main rack builder app middleware stack with the rails application middleware object, removing the need to support 2 different middleware stacks.

[jeremyevans]

I think middleware stacks are something best handled by frameworks using rack as opposed to rack itself. I don't think think we want to add this feature to rack.