# File lib/responders/http_cache_responder.rb, line 24
    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