server.rb

#
# s3_store.rb
#
require "em-synchrony"
require "em-synchrony/em-http"

class S3Store
  def initialize(uri)
    @uri    = uri
  end

  def get
    http = EventMachine::HttpRequest.new(@uri).aget
    finish = proc { env.chunked_stream_close } # undefined local variable or method `env'
    http.stream { |chunk| yield chunk }
    http.callback &finish
    http.errback &finish
  end
end

#
# server.rb
#
require 'goliath'
require 'json'

class GetImage < Goliath::API

  def response(env)
    store = S3Store.new('http://dl.dropbox.com/u/3528102/10.iso') #10mb file

    EM.next_tick do
      store.get { |chunk| env.chunked_stream_send chunk }
    end

    headers = {'Content-Type' => 'application/octet-stream', 'X-Stream' => 'Goliath'}
    chunked_streaming_response(200, headers)
  end
end

class Server < Goliath::API

  get '/image', GetImage
end