Original rack-flash as well as rack-flash3 forcibly changes the key names to symbols. Unfortunately this does not work if the session storage is backed by something that does not support symbols (i.e. Redis). rack-flash4 addresses this problem by converting the keys to strings, so you can use things like flash['error'] and it will behave as expected.

Treeder forked the original Rack::Flash and patched its issues, see https://github.com/treeder/rack-flash

However, when not using Sinatra, the code still won't work. This patches that in the Patch_rack_builder_call branch.

flash[:notice] = "You can stop rolling your own now."

Simple flash hash implementation for Rack apps.

View the RDoc.

Here's how to use it.

gem 'rack-flash3'

You can access flash entries via env['x-rack.flash']. You can treat it either like a regular flash hash:

env['x-rack.flash'][:notice] = 'You have logged out.'

Or you can pass the :accessorize option to declare your flash types. Each of these will have accessors defined on the flash object:

use Rack::Flash, :accessorize => [:notice, :error]

# Set a flash entry
env['x-rack.flash'].notice = 'You have logged out.'

# Get a flash entry
env['x-rack.flash'].notice # => 'You have logged out.'

# Set a a flash entry for only the current request
env['x-rack.flash'].notice! 'You have logged out.'

Sample rack app:

get = proc { |env|
  [200, {},
    env['x-rack.flash'].notice || 'No flash set. Try going to /set'
  ]
}

set = proc { |env|
  env['x-rack.flash'].notice = 'Hey, the flash was set!'
  [302, {'Location' => '/'},
    'You are being redirected.'
  ]
}

builder = Rack::Builder.new do
  use Rack::Session::Cookie
  use Rack::Flash, :accessorize => true

  map('/set') { run set }
  map('/')    { run get }
end

Rack::Handler::Mongrel.run builder, :Port => 9292

If you're using Sinatra, you can use the flash hash just like in Rails:

require 'sinatra/base'
require 'rack-flash'

class MyApp < Sinatra::Base
  enable :sessions
  use Rack::Flash

  post '/set-flash' do
    # Set a flash entry
    flash[:notice] = "Thanks for signing up!"
    
    # Get a flash entry
    flash[:notice] # => "Thanks for signing up!"
    
    # Set a flash entry for only the current request
    flash.now[:notice] = "Thanks for signing up!"
  end
end

If you've got any ideas on how to simplify access to the flash hash for vanilla Rack apps, let me know. It still feels a bit off to me.

By default Rack::Flash has slightly different behavior than Rails in that it doesn't delete entries until they are used. If you want entries to be cleared even if they are not ever accessed, you can use the :sweep option:

use Rack::Flash, :sweep => true

This will sweep stale flash entries, whether or not you actually use them.