Different versions of Rails have stored flash messages in different objects in the session, making it a pain to upgrade without nuking everyones session. The good ol' ActionDispatch::Session::SessionRestoreError making life difficult.

This gem was created because we wanted to be able to keep our users Rails 2 sessions working on Rails 3, and we figured as long as we're going to be doing crazy stuff we might as well go and use the far more sensible practice from Rails 4 of storing the flash as basic ruby types.

When using this gem on a Rails 2 or 3 app:

• Flash messages are stored as basic objects in the Rails 4 style.
• Flash messages in the Rails 2 format can be successfully decoded.
• Flash messages in the Rails 3 format can be successfully decoded.
• Flash messages in the Rails 4 format can be successfully decoded.

Additionally, on Rails 2 we include some patches for the SessionHash and CookieStore, in order to make them act more like their HashWithIndifferentAccess versions on Rails 3, so that your session_id can survive a trip to Rails 3 and back.

This actually makes it possible to bounce requests from a Rails 2 server, to a Rails 3 server and back again so long as both servers are using this gem. Very helpful when you're doing a big Rails 2 => 3 upgrade and want to run a few Rails 3 servers concurrently with your Rails 2 cluster to verify everything is fine and performance is acceptable without having to do the all-in switch.

Add this line to your application's Gemfile:

gem 'rails_4_session_flash_backport'

And then execute:

$ bundle

Or install it yourself as:

$ gem install rails_4_session_flash_backport

Copyright (c) 2012 Envato, Lucas Parry, chendo. See LICENSE.txt for further details.