code: func NewFileStorage(caURL *url.URL) (Storage, error) {
  	return &FileStorage{
  		Path:      filepath.Join(storageBasePath, caURL.Host),
  		nameLocks: make(map[string]*sync.WaitGroup),
  	}, nil
  }
docs: // NewFileStorage is a StorageConstructor function that creates a new
  // Storage instance backed by the local disk. The resulting Storage
  // instance is guaranteed to be non-nil if there is no error.