Improving Rack

So this is an experiment and proof of concept to see if we could improve Rack without losing compatibility.

Core Goal

• Compatibility. But new features would only be available with new API.
• Compatibility is handled via Rack::Builder2
• Better encapsulation (Stop Rack::Request.new(env) all the way down)
• Easier streaming (mainly targeting HTTP/2)
• Remove Rack internal complexity (enough of respond_to? check and BodyProxy)

Current Implementation

• Old middleware and application should work as if
• New middleware could take the advantage of new SPEC (process_request(req, res) for now)
• If no old middleware were trying to walk through the response body (e.g. Rack::ContentLength), the call stack from application wouldn't see middleware around. (now it's iterating rather than stacking)
• Old middleware would suffer from some performance penalty due to the new compatibility layer. Move to the new API to restore performance.

Next Goal

• Access full response for new middleware (maybe via callback or buffer)
• Streaming for new middleware

See Also

• Rack 2.0, or Rack for the Future
• Yesod's Web Application Interface, source.

type Application = Request -> (Response -> IO ResponseReceived) ->
                   IO ResponseReceived

type Middleware = Application -> Application