add helpers (#4972)

beacon-chain/blockchain/process_attestation_helpers.go

@@ -1,6 +1,7 @@
 package blockchain
 
 import (
+	"bytes"
 	"context"
 	"encoding/hex"
 	"fmt"
@@ -28,6 +29,23 @@ func (s *Service) getAttPreState(ctx context.Context, c *ethpb.Checkpoint) (*sta
 	if cachedState != nil {
 		return cachedState, nil
 	}
+	headRoot, err := s.HeadRoot(ctx)
+	if err != nil {
+		return nil, errors.Wrapf(err, "could not get head root")
+	}
+	if bytes.Equal(headRoot, c.Root) {
+		st, err := s.HeadState(ctx)
+		if err != nil {
+			return nil, errors.Wrapf(err, "could not get head state")
+		}
+		if err := s.checkpointState.AddCheckpointState(&cache.CheckpointState{
+			Checkpoint: c,
+			State:      st.Copy(),
+		}); err != nil {
+			return nil, errors.Wrap(err, "could not saved checkpoint state to cache")
+		}
+		return st, nil
+	}
 
 	baseState, err := s.beaconDB.State(ctx, bytesutil.ToBytes32(c.Root))
 	if err != nil {

beacon-chain/blockchain/process_block_helpers.go

@@ -58,8 +58,14 @@ func (s *Service) getBlockPreState(ctx context.Context, b *ethpb.BeaconBlock) (*
 // verifyBlkPreState validates input block has a valid pre-state.
 func (s *Service) verifyBlkPreState(ctx context.Context, b *ethpb.BeaconBlock) (*stateTrie.BeaconState, error) {
 	preState := s.initSyncState[bytesutil.ToBytes32(b.ParentRoot)]
-	var err error
 	if preState == nil {
+		headRoot, err := s.HeadRoot(ctx)
+		if err != nil {
+			return nil, errors.Wrapf(err, "could not get head root")
+		}
+		if bytes.Equal(headRoot, b.ParentRoot) {
+			return s.HeadState(ctx)
+		}
 		preState, err = s.beaconDB.State(ctx, bytesutil.ToBytes32(b.ParentRoot))
 		if err != nil {
 			return nil, errors.Wrapf(err, "could not get pre state for slot %d", b.Slot)