gistfile1.rb

require 'sinatra/base'
require 'eventmachine'
require 'em-http-request'

EM.run do
  class App < Sinatra::Base

    helpers do
      def wait_for(&block)
        while block.call.nil?
          sleep(1.0 / 10)
        end
      end
    end

    get "/bar" do
      response = nil
      http = EventMachine::HttpRequest.new('https://www.google.dk/').get
      http.callback {
        response = http.response
      }
      wait_for { response }
      content_type :json
      [200, response.to_json]
    end

  end
  App.run!
end