heroku_rack - static asset middleware

original_static_assets_middleware.rb

module Heroku
  class StaticAssetsMiddleware
  	def initialize(app)
  		@app = app
  	end

  	def call(env)
  		# call returns an array containing [response code, header, Rack::Response]
  		reply = @app.call(env)

  		reply = cache_static_asset(reply)

  		reply
  	end

  	def cache_static_asset(reply)
  		return reply unless can_cache?(reply)

  		status, headers, response = reply

  		# static files are cacheable for 12hrs
  		headers['Cache-Control'] = 'public, max-age=43200'

  		build_new_reply(status, headers, response)
  	end

  	def can_cache?(reply)
  		response = reply[2]
  		status = reply[0]
  		response.kind_of?(Rack::File) and status.to_i == 200
  	end

  	def build_new_reply(status, headers, response)
  		headers.delete('Etag') if headers.has_key?('Etag')
  		[ status, headers, response ]
  	end
  end
end

static_assets_middleware.rb

# For rails - place this file in an initializer
# Override heroku_rack - StaticAssetsMiddleware to extend default Cache-Control header
# See this thread --> http://groups.google.com/group/heroku/browse_thread/thread/607f0dc9a3979e1b

module Heroku
  class StaticAssetsMiddleware
    def cache_static_asset(reply)
      return reply unless can_cache?(reply)

      status, headers, response = reply

      # static files are cacheable for ...
      headers['Cache-Control'] = 'public, max-age=0'
      #headers['Cache-Control'] = 'public, max-age=43200' # 12 hours - Heroku default
      #headers['Cache-Control'] = 'public, max-age=31556926' # 1 year

      build_new_reply(status, headers, response)
    end
  end
end