http_cache_responder.rb
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	module Responders
	# Set HTTP Last-Modified headers based on the given resource. It's used only
	# on API behavior (to_format) and is useful for a client to check in the server
	# if a resource changed after a specific date or not.
	#
	# This is not usually not used in html requests because pages contains a lot
	# information besides the resource information, as current_user, flash messages,
	# widgets... that are better handled with other strategies, as fragment caches and
	# the digest of the body.
	#
	module HttpCacheResponder
	def initialize(controller, resources, options={})
	super
	@http_cache = options.delete(:http_cache)
	end

	def to_format
	return if do_http_cache? && do_http_cache!
	super
	end

	protected

	def do_http_cache!
	timestamp = resources.map do \|resource\|
	resource.updated_at.try(:utc) if resource.respond_to?(:updated_at)
	end.compact.max

	controller.response.last_modified \|\|= timestamp if timestamp

	head :not_modified if fresh = request.fresh?(controller.response)
	fresh
	end

	def do_http_cache?
	get? && @http_cache != false && ActionController::Base.perform_caching &&
	persisted? && resourceful? && resource.respond_to?(:updated_at)
	end

	def persisted?
	resource.respond_to?(:persisted?) ? resource.persisted? : true
	end
	end
	end