code: func (s *ChainService) GetBlockHeight(hash *chainhash.Hash) (int32, error) {
  	_, height, err := s.BlockHeaders.FetchHeader(hash)
  	if err != nil {
  		return 0, err
  	}
  	return int32(height), nil
  }
docs: // GetBlockHeight gets the height of a block by its hash. An error is returned
  // if the given block hash is unknown.