code: func dbFetchHeaderByHash(dbTx database.Tx, hash *chainhash.Hash) (*wire.BlockHeader, error) {
  	headerBytes, err := dbTx.FetchBlockHeader(hash)
  	if err != nil {
  		return nil, err
  	}
  
  	var header wire.BlockHeader
  	err = header.Deserialize(bytes.NewReader(headerBytes))
  	if err != nil {
  		return nil, err
  	}
  
  	return &header, nil
  }
docs: // dbFetchHeaderByHash uses an existing database transaction to retrieve the
  // block header for the provided hash.