code: func (r *ResponseRecorder) CloseNotify() <-chan bool {
  	if cn, ok := r.ResponseWriter.(http.CloseNotifier); ok {
  		return cn.CloseNotify()
  	}
  	panic(NonCloseNotifierError{Underlying: r.ResponseWriter})
  }
docs: // CloseNotify implements http.CloseNotifier.
  // It just inherits the underlying ResponseWriter's CloseNotify method.