exchange.rb

require 'sinatra/base'

module Sinatra
  module Exchange
    RESPONSE = Struct.new(:status, :headers, :body)
    
    def get_local(path, params={})
      r = env['operator'].call(
        env.merge(
          'SCRIPT_NAME' => '', 
          'PATH_INFO' => path, 
          'REQUEST_METHOD' => 'GET', 
          'QUERY_STRING' => params.collect {|k,v| "#{k}=#{v}"}.join('&')
        )
      )
      RESPONSE.new(*r)
    end  
  end
  
  helpers Exchange
end

class Foo < Sinatra::Base
  helpers Sinatra::Exchange
  
  get '/' do
    bar = get_local '/bar', fud: 'dud'
    "foo says: #{bar.body.join}"
  end
end

class Bar < Sinatra::Base
  get '/' do
    "I am here: #{url('/')}, with these params: #{params}"
  end
end

class Operator
  def initialize(app, key = 'operator')
    @app, @key = app, key
  end
        
  def call(env)
    @app.call env.merge(@key => @app)
  end
end

require 'rack/test'
require 'minitest/autorun'

describe 'App' do
  include Rack::Test::Methods
  
  def app
    Rack::Builder.new do
  
      use Operator

      map '/foo' do
        run Foo
      end
  
      map '/bar' do
        run Bar
      end
    end
  end
  
  it 'must return bar from foo' do
    get '/foo'
    last_response.body.must_equal 'foo says: I am here: http://example.org/bar/, with these params: {"fud"=>"dud"}'
  end
end

gistfile1.rb

require 'sinatra/base'

class TrackMiddleware
  def initialize(app, key = "track.middleware") @app, @key = app, key end
  def call(env) @app.call env.merge(@key => @app) end
end

class Foo < Sinatra::Base
  get '/' do
    env['track.middleware'].call(env.merge('SCRIPT_NAME' => '/', 'PATH_INFO' => '/bar'))
  end
end

class Bar < Sinatra::Base
  get '/' do
    'bar'
  end
end

builder = Rack::Builder.new do
  use TrackMiddleware
  
  map('/foo') { run Foo }
  map('/bar') { run Bar }
end

Rack::Handler::Thin.run builder