handle_conditional_get!

# File actionpack/lib/action_controller/response.rb, line 184
      def handle_conditional_get!
        if etag? || last_modified?
          set_conditional_cache_control!
        elsif nonempty_ok_response?
          self.etag = body

          if request && request.etag_matches?(etag)
            self.status = '304 Not Modified'
            self.body = ''
          end

          set_conditional_cache_control!
        end
      end