fiber.rb

def read_body # Net::HTTPResponse#read_body
  yield "foo"; yield "bar"; yield "baz"
end

class R # A Rack Streaming response
  def initialize
    @l = lambda do |block|
      read_body do |chunk| # Net::HTTPResponse#read_body
        sleep(0.5)
        block.call(chunk)
      end
    end
  end

  def each(&block)
    @l.call(block)
  end
end

R.new.each do |chunk|
  puts chunk # Streaming!
end