flash_session_cookie.rb

# This is a Rack Middleware to fix the missing Cookie bug in Flash. 
# It is inspired by http://thewebfellas.com/blog/2008/12/22/flash-uploaders-rails-cookie-based-sessions-and-csrf-rack-middleware-to-the-rescue

# Just load this middleware and add something like this to your session_store initializer: 
# ActionController::Dispatcher.middleware.use FlashSessionCookie, "_app_session_id"

class FlashSessionCookie
  def initialize(app, session_key = '_session_id')
    @app = app
    @session_key = session_key
  end

  def call(env)
    if env['HTTP_USER_AGENT'] =~ /^(Adobe|Shockwave) Flash/
      request = Rack::Request.new(env)
      if request.POST.include?(@session_key)
        env['HTTP_COOKIE'] = [ @session_key, request.POST[ @session_key ] ].join('=').freeze
      end
    end
    @app.call(env)
  end
end