perform_action

# File actionpack/lib/action_controller/base.rb, line 1251
      def perform_action
        if action_methods.include?(action_name)
          send(action_name)
          default_render unless performed?
        elsif respond_to? :method_missing
          method_missing action_name
          default_render unless performed?
        elsif template_exists?
          default_render
        else
          raise UnknownAction, "No action responded to #{action_name}. Actions: #{action_methods.sort.to_sentence}", caller
        end
      end