server_push_multiple_content_type.rb

require 'rubygems'
require 'sinatra'
require 'open-uri'

# doesn't work on thin and webrick                                                                                                                                                                               
set :server, 'mongrel'

get '/' do
  boundary = 'ThisRandomString'
  response['Content-Type'] = 'multipart/x-mixed-replace;boundary=' + boundary

  PushResponse.new(boundary, 1) do
    if rand > 0.5
      ['text/plain', rand.to_s]
    else
      ['image/png', open('http://buycheapviagraonlinenow.com/tmp/87aacdf4_500.png').read]
    end
  end
end

class PushResponse
  def initialize(boundary, interval, &block)
    @boundary = boundary
    @interval = interval
    @block = block
  end

  def each
    yield "--#{@boundary}\n"

    loop do
      content_type, content = @block.call
      yield "Content-Type: #{content_type}\n\n" + content + "\n--#{@boundary}\n"
      sleep @interval
    end
  end
end