code: func (pdb *protoWatcher) Watch(resp func(datasync.ProtoWatchResp), closeChan chan string, keys ...string) error {
  	err := pdb.watcher.Watch(func(msg keyval.BytesWatchResp) {
  		resp(NewWatchResp(pdb.serializer, msg))
  	}, closeChan, keys...)
  	if err != nil {
  		return err
  	}
  	return nil
  }
docs: // Watch watches for changes in datastore.
  // <resp> callback is used for delivery of watch events.