refactored_err.go

type FailingStorage struct{}
func (f *FailingStorage) Add(k, v string) (err error) {
	return errors.New("now we fail")
}

var s = NewSafeStorage(&FailingStorage{})
func handleAdd(w http.ResponseWriter, r *http.Request) {
	key := r.Host
	value := r.Method

	if err := s.Add(key, value); err != nil {
		http.Error(w, e, http.StatusInternalServerError)
		return
	}
}