Multipart response in Ruby/Rack

Question

I want my server to send a multipart response (multipart/x-mixed-replace). I'd prefer some kind of solution using the Sinatra framework or a generic Rack app, but any example in ruby would be nice. Here's the equivalent of what I'm trying to do, in PHP:

<?php
  header('Content-type: multipart/x-mixed-replace;boundary="rn9012"');

  print "--rn9012\n";
  print "Content-type: application/xml\n\n";
  print "<?xml version='1.0'?>\n";
  print "<content>First Part</content>\n";
  print "--rn9012\n";
  flush();

  sleep(5);
  print "Content-type: application/xml\n\n";
  print "<?xml version='1.0'?>\n";
  print "<content>Second Part</content>\n";
  print "--rn9012--\n";

?>

Answer 1

You can probably use the out.flush method for this:

class TestController < ApplicationController
  def index
    render :text => lambda { |resp, out|
      out.puts 'start'
      out.flush
      10.times do
        out.puts '.'
        out.flush
        sleep 1
      end
      out.puts 'done'
    }
  end
end

However, keep in mind that if you're using Mongrel to serve your Ruby code (as many people using RoR do), you won't be able to stream at all.