---
tags: workflow
---

# Определение ParentRoot при создании блока
Для Altair & Phase0

// Build data required for creating a new beacon block, so this method can be shared across forks.
func (vs *Server) buildPhase0BlockData(ctx context.Context, req *ethpb.BlockRequest) (*blockData, error) {
	...
	// Retrieve the parent block as the current head of the canonical chain.
	parentRoot, err := vs.HeadFetcher.HeadRoot(ctx)
	...
	return &blockData{
		ParentRoot:        parentRoot,
		...
	}, nil
}

// HeadRoot returns the root of the head of the chain.
func (s *Service) HeadRoot(ctx context.Context) ([]byte, error) {

	if s.headRoot() != params.BeaconConfig().ZeroHash {
		r := s.headRoot()
		return r[:], nil
	}

	b, err := s.cfg.BeaconDB.HeadBlock(ctx)

	r, err := b.Block().HashTreeRoot()
	return r[:], nil
}

// This returns the head root.
func (s *Service) headRoot() [32]byte {
	if s.head == nil {
		return params.BeaconConfig().ZeroHash
	}
	return s.head.root
}

// HeadBlock returns the head block of the chain.
// If the head is nil from service struct,
// it will attempt to get the head block from DB.
func (s *Service) HeadBlock(ctx context.Context) (block.SignedBeaconBlock, error) {
	s.headLock.RLock()
	defer s.headLock.RUnlock()

	if s.hasHeadState() {
		return s.headBlock(), nil
	}

	return s.cfg.BeaconDB.HeadBlock(ctx)
}

// HeadBlock returns the latest canonical block in the Ethereum Beacon Chain.
func (s *Store) HeadBlock(ctx context.Context) (block.SignedBeaconBlock, error) {
	var headBlock block.SignedBeaconBlock
	err := s.db.View(func(tx *bolt.Tx) error {
		bkt := tx.Bucket(blocksBucket)
		headRoot := bkt.Get(headBlockRootKey)
		if headRoot == nil {
			return nil
		}
		enc := bkt.Get(headRoot)
		if enc == nil {
			return nil
		}
		var err error
		headBlock, err = unmarshalBlock(ctx, enc)
		return err
	})
	return headBlock, err
}