How to embed a Sinatra app inside a Rails app through a plugin (not Metal)

gistfile1.rb

script/generate plugin HelloWorld

# vendor/plugins/hello_world/init.rb
Rails.configuration.gem "sinatra"
Rails.configuration.middleware.insert_before("ActionController::Failsafe", "HelloWorld")

# vendor/plugins/hello_world/lib/hello_world.rb
# your sinatra app goes here...
require 'sinatra/base'
class HelloWorld < Sinatra::Base
  get "/hello" do
    "Hello World!"
  end
  #this hackeration is required for sinatra to be a nice rack citizen
  error 404 do
    @app.call(env)
  end
end

Under what circumstances and versions is the 'hackeration' actually necessary? In the version I'm running (Sinatra 1.0 based), if I use three middleware modules written this way, then 'halt 404, "foobar"' from my application, I'll get 2^3 - 1 (yes, 7) retries of the application URL handler. In addition, if I log something before the call on line 16, I never see that log message in any normal routing context.

@cobbr2 I'm not entirely sure this is required anymore. This is old 2.3.x stuff... not sure if it's useful in rails 3 or even newer versions of rack and sinatra. I wrote this pre-sinatra 1.0