delay_proxy.rb

require 'webrick'
require 'webrick/httpproxy'

# How to test it
#
# In a terminal:
# $ ruby delay_proxy.rb
#
# In another terminal:
# $ http_proxy=http://localhost:8001 curl http://www.google.it
#
$chunk_size = 10
# the proxy port
$port = 8001

class DelayIO
  def initialize(res)
    # TODO split the data into tokens with the sleep "<!-- sleep xyx -->" in order to build
    # the data chunks to send in intervals.
    @data = res.body
  end

  def readpartial(maxlen, outbuf)
    # TODO return the data in chunks with a sleep in between them
    # in this example we just split data into fixed chunks
    sleep 1
    # send data
    outbuf << "#{@data[0, $chunk_size]}\n"
    # remove processed data
    @data = @data[$chunk_size - 1, @data.length - 1]
  end

  def bytesize
    [@data.length, $chunk_size].min
  end

  def close
    # noop
    # not a real IO socket
  end
end

handler = proc do |req, res|
  res.chunked = true
  # this is a hack to force the chunk size
  res.instance_variable_set('@buffer_size', $chunk_size)
  res.body = DelayIO.new(res)
end

# start an http proxy on $port
proxy = WEBrick::HTTPProxyServer.new(Port: $port, ProxyContentHandler: handler)
proxy.start