code: func nextNode(it iterator.Iterator) *Node {
  	for end := false; !end; end = !it.Next() {
  		id, rest := splitNodeKey(it.Key())
  		if string(rest) != dbDiscoverRoot {
  			continue
  		}
  		return mustDecodeNode(id[:], it.Value())
  	}
  	return nil
  }
docs: // reads the next node record from the iterator, skipping over other
  // database entries.