Deal with nil LVH

After ethereum/execution-apis#254 the EL may
return  `nil` for LVH. Our current implementation would treat this as a
zero hash and thus mark all blocks since the merge block as INVALID

beacon-chain/blockchain/execution_engine.go

@@ -23,6 +23,8 @@ import (
 	"go.opencensus.io/trace"
 )
 
+var defaultLatestValidHash = bytesutil.ToBytes32([]byte{0xff})
+
 // notifyForkchoiceUpdateArg is the argument for the forkchoice update notification `notifyForkchoiceUpdate`.
 type notifyForkchoiceUpdateArg struct {
 	headState state.BeaconState
@@ -89,6 +91,9 @@ func (s *Service) notifyForkchoiceUpdate(ctx context.Context, arg *notifyForkcho
 		case powchain.ErrInvalidPayloadStatus:
 			newPayloadInvalidNodeCount.Inc()
 			headRoot := arg.headRoot
+			if len(lastValidHash) == 0 {
+				lastValidHash = defaultLatestValidHash[:]
+			}
 			invalidRoots, err := s.ForkChoicer().SetOptimisticToInvalid(ctx, headRoot, bytesutil.ToBytes32(headBlk.ParentRoot()), bytesutil.ToBytes32(lastValidHash))
 			if err != nil {
 				log.WithError(err).Error("Could not set head root to invalid")

beacon-chain/blockchain/execution_engine_test.go

@@ -344,6 +344,85 @@ func Test_NotifyForkchoiceUpdateRecursive_Protoarray(t *testing.T) {
 	require.Equal(t, true, fcs.HasNode(bre))
 }
 
+func Test_NotifyForkchoiceUpdate_NIlLVH(t *testing.T) {
+	ctx := context.Background()
+	beaconDB := testDB.SetupDB(t)
+
+	// Prepare blocks
+	ba := util.NewBeaconBlockBellatrix()
+	ba.Block.Body.ExecutionPayload.BlockNumber = 1
+	wba := util.SaveBlock(t, ctx, beaconDB, ba)
+	bra, err := wba.Block().HashTreeRoot()
+	require.NoError(t, err)
+
+	bb := util.NewBeaconBlockBellatrix()
+	bb.Block.Body.ExecutionPayload.BlockNumber = 2
+	wbb := util.SaveBlock(t, ctx, beaconDB, bb)
+	brb, err := wbb.Block().HashTreeRoot()
+	require.NoError(t, err)
+
+	bc := util.NewBeaconBlockBellatrix()
+	pc := [32]byte{'C'}
+	bc.Block.Body.ExecutionPayload.BlockHash = pc[:]
+	bc.Block.Body.ExecutionPayload.BlockNumber = 3
+	wbc := util.SaveBlock(t, ctx, beaconDB, bc)
+	brc, err := wbc.Block().HashTreeRoot()
+	require.NoError(t, err)
+
+	bd := util.NewBeaconBlockBellatrix()
+	pd := [32]byte{'D'}
+	bd.Block.Body.ExecutionPayload.BlockHash = pd[:]
+	bd.Block.Body.ExecutionPayload.BlockNumber = 4
+	bd.Block.ParentRoot = brc[:]
+	wbd := util.SaveBlock(t, ctx, beaconDB, bd)
+	brd, err := wbd.Block().HashTreeRoot()
+	require.NoError(t, err)
+
+	// Insert blocks into forkchoice
+	service := setupBeaconChain(t, beaconDB)
+	fcs := doublylinkedtree.New()
+	service.cfg.ForkChoiceStore = fcs
+	service.cfg.ProposerSlotIndexCache = cache.NewProposerPayloadIDsCache()
+
+	service.justifiedBalances.balances = []uint64{50, 100, 200}
+	require.NoError(t, err)
+	ojc := &ethpb.Checkpoint{Root: params.BeaconConfig().ZeroHash[:]}
+	ofc := &ethpb.Checkpoint{Root: params.BeaconConfig().ZeroHash[:]}
+	state, blkRoot, err := prepareForkchoiceState(ctx, 1, bra, [32]byte{}, [32]byte{'A'}, ojc, ofc)
+	require.NoError(t, err)
+	require.NoError(t, fcs.InsertNode(ctx, state, blkRoot))
+	state, blkRoot, err = prepareForkchoiceState(ctx, 2, brb, bra, [32]byte{'B'}, ojc, ofc)
+	require.NoError(t, err)
+	require.NoError(t, fcs.InsertNode(ctx, state, blkRoot))
+	state, blkRoot, err = prepareForkchoiceState(ctx, 3, brc, brb, [32]byte{'C'}, ojc, ofc)
+	require.NoError(t, err)
+	require.NoError(t, fcs.InsertNode(ctx, state, blkRoot))
+	state, blkRoot, err = prepareForkchoiceState(ctx, 4, brd, brc, [32]byte{'D'}, ojc, ofc)
+	require.NoError(t, err)
+	require.NoError(t, fcs.InsertNode(ctx, state, blkRoot))
+
+	// Prepare Engine Mock to return invalid LVH =  nil
+	service.cfg.ExecutionEngineCaller = &mockPOW.EngineClient{ErrForkchoiceUpdated: powchain.ErrInvalidPayloadStatus, OverrideValidHash: [32]byte{'C'}}
+	st, _ := util.DeterministicGenesisState(t, 1)
+	service.head = &head{
+		state: st,
+		block: wba,
+	}
+
+	require.NoError(t, beaconDB.SaveState(ctx, st, bra))
+	require.NoError(t, beaconDB.SaveGenesisBlockRoot(ctx, bra))
+	a := &notifyForkchoiceUpdateArg{
+		headState: st,
+		headBlock: wbd.Block(),
+		headRoot:  brd,
+	}
+	_, err = service.notifyForkchoiceUpdate(ctx, a)
+	require.Equal(t, true, IsInvalidBlock(err))
+	require.Equal(t, brd, InvalidBlockRoot(err))
+	require.Equal(t, brd, InvalidAncestorRoots(err)[0])
+	require.Equal(t, 1, len(InvalidAncestorRoots(err)))
+}
+
 //
 //
 //  A <- B <- C <- D