Streaming the contents of an em-http-request in a Rails response

gistfile1.rb

  def stream
    @path = request[:path]
    puts "1) grabbing the output"
    already_called = false
    self.response_body = work_around_double_call_bug { |resp, output|
      return if already_called
      already_called = true

      puts "3) output grabbed: #{output}. Requesting Drobpox..."
      dropbox_session.stream @path do |em_http_req|
        req_fiber = Fiber.current
        puts "4) Setting the EM callbacks..."
        em_http_req.headers { |data|
          puts "6) Got the headers"
          headers['Content-Type']   = data['CONTENT_TYPE']
          headers['Content-Length'] = data['CONTENT_LENGTH']
        }
        em_http_req.stream { |chunk|
          print '>'
          output.write chunk
        }
        
        em_http_req.callback { |res|
          puts "8) Finished receiving data #{res}"
          req_fiber.resume(:error)
        }
        em_http_req.errback  { |err| req_fiber.resume(:error) }

        puts "5) Pausing there !"
        Fiber.yield
        puts "9) All clear !"
      end
    }
    puts "2) Finished the Request"
  end

  private 


  # To circumvent this Rails bug: 
  # https://rails.lighthouseapp.com/projects/8994-ruby-on-rails/tickets/4554-render-text-proc-regression#ticket-4554-15
  def work_around_double_call_bug &block
    already_called = false
    proc do |*args|
      yield *args unless already_called
      already_called = true
    end
  end