before_sending

# File actionpack/lib/action_dispatch/http/response.rb, line 440
    def before_sending
      # Normally we've already committed by now, but it's possible
      # (e.g., if the controller action tries to read back its own
      # response) to get here before that. In that case, we must force
      # an "early" commit: we're about to freeze the headers, so this is
      # our last chance.
      commit! unless committed?

      headers.freeze
      request.commit_cookie_jar! unless committed?
    end