Rails3, Rack and "Where did my Metal go?"

Our Rails3 (beta4) application had one route mapped in config/routes to a Sinatra app, by means of the following route:

match '/foo', :to => EndPointApp, :as => :endpoint

The route was being defined to run as a Sinatra Application

require 'sinatra'
class EndPointApp < Sinatra::Application
  post '/foo' do
    ...
  end
end

This was working mostly fine, but it was returning Set-Cookie header with the standard Rails sessions cookie, which in this case was preventing the client of this endpoint from successfully interpreting the result. As I could do nothing about the client side, I had to remove Set-Cookie from the headers, but only for this end-point and obviously not from the entire app. This proved to be somewhat more complicated than I had hoped, so let me share the solution here in hopes it might save someone else an hour or two.

First, I ran "rake middleware" and observed the following Rack stack:

use ActionDispatch::Static
use Rack::Lock
use ActiveSupport::Cache::Strategy::LocalCache
use Rack::Runtime
use Rails::Rack::Logger
use ActionDispatch::ShowExceptions
use ActionDispatch::RemoteIp
use Rack::Sendfile
use ActionDispatch::Callbacks
use ActiveRecord::ConnectionAdapters::ConnectionManagement
use ActiveRecord::QueryCache
use ActionDispatch::Cookies
use ActionDispatch::Session::CookieStore
use ActionDispatch::Flash
use ActionDispatch::ParamsParser
use Rack::MethodOverride
use ActionDispatch::Head
run Kigster::Application.routes

As can be immediately seen from here, the routes execute very last after Session::CookieStore already wrapped the request. OK, so looks like I need to bypass the routes somehow, and so I started to look at Rails::Metal, which is supposed to run before all other processing.

Once I started to look for Rails::Metal, I realized pretty quickly that I am missing metal generator:

> rails g metal
Could not find generator metal.

After a few more rounds of digging around, it turns out that in Rails3 Beta4 Rails::Metal has been completely removed, because it is no longer needed in a Rack environment.

So I had convert my Sinatra module to a Rack module, and insert it into the Rack middleware stack before the Cookie/Sessions:

require File.expand_path('../../../config/environment',  __FILE__) unless defined?(Rails)

module Kigster
  class EndPoint
    def initialize(app)
      @app = app
    end
    def call(env)
      if env["PATH_INFO"] =~ /^foo/
        process_request(env)
      else
        @app.call(env)
      end
    end

    private
    def process_request(env) 
       req = Rack::Request.new(env)
       params = req.params
       # do stuff
       [ 200, 
         { "Content-Type"   => "text/html", 
           "Content-Length" => "0" }, 
         [""]   
       ]
    end
  end
end

I had add the following to my config/application.rb to enable this Rack module, and have it run before the ActionDispatch::Session::CookieStore:

# config/application.rb
# require the file directly
require File.join(File.dirname(__FILE__), '../app/metal/kigster_endpoint')
....
module Kigster
  class Application < Rails::Application
    config.middleware.insert_after Rails::Rack::Logger, 
                                   Kigster::EndPoint
  end
end

Now my handler executes before the session, and the result does not include Set-Cookie header.

Any other suggestions on how to make this any simpler, or more correct are as always welcome!