server_push_on_sinatra.rb

require 'rubygems'
require 'sinatra'

# 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, 'text/plain', 0.5) do
    rand.to_s
  end
end

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

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

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