class DeferrableBody
  include EventMachine::Deferrable

  def call(body)
    body.each do |chunk|
      @body_callback.call(chunk)
    end
  end

  def each &block
    @body_callback = block
  end
end

app = proc do |env|
  body = DeferrableBody.new

  EventMachine::next_tick do
    env["async.callback"].call [200,
                                {"Content-Type" => "text/html"},
                                body]
  end

  EventMachine::add_timer(1) do
     body.call ["Hello, world!"]
     body.succeed
  end

  [-1, {}, []]
end

run app