code: func (si *SnapshotInfo) GetSnapshotID() string {
  	if strings.IndexByte(si.AuthServiceURL, ',') != -1 {
  		panic(fmt.Errorf("forbidden symbol ',' in URL %q", si.AuthServiceURL))
  	}
  	return fmt.Sprintf("v1,%s,%d", si.AuthServiceURL, si.Rev)
  }
docs: // GetSnapshotID returns datastore ID of the corresponding Snapshot entity.