code: func (serv *v2MetadataService) GetMetadata(diffID layer.DiffID) ([]V2Metadata, error) {
  	if serv.store == nil {
  		return nil, errors.New("no metadata storage")
  	}
  	jsonBytes, err := serv.store.Get(serv.diffIDNamespace(), serv.diffIDKey(diffID))
  	if err != nil {
  		return nil, err
  	}
  
  	var metadata []V2Metadata
  	if err := json.Unmarshal(jsonBytes, &metadata); err != nil {
  		return nil, err
  	}
  
  	return metadata, nil
  }
docs: // GetMetadata finds the metadata associated with a layer DiffID.