Fix last continuous crosslink logic (#2316)

* Fix last continuous crosslink logic

* fix lint

* Add comment

core/blockchain.go

@@ -1866,38 +1866,29 @@ func (bc *BlockChain) ReadCrossLink(shardID uint32, blockNum uint64) (*types.Cro
 // This function will update the latest crosslink in the sense that
 // any previous block's crosslink is received up to this point
 // there is no missing hole between genesis to this crosslink of given shardID
-func (bc *BlockChain) LastContinuousCrossLink(batch rawdb.DatabaseWriter, cl types.CrossLink) error {
-	if !bc.Config().IsCrossLink(cl.Epoch()) {
+func (bc *BlockChain) LastContinuousCrossLink(batch rawdb.DatabaseWriter, shardID uint32) error {
+	if !bc.Config().IsCrossLink(bc.CurrentBlock().Epoch()) {
 		return errors.New("Trying to write last continuous cross link with epoch before cross link starting epoch")
 	}
 
-	cl0, err := bc.ReadShardLastCrossLink(cl.ShardID())
-	if cl0 == nil {
-		rawdb.WriteShardLastCrossLink(batch, cl.ShardID(), cl.Serialize())
-		return nil
-	}
-	if err != nil {
+	oldLink, err := bc.ReadShardLastCrossLink(shardID)
+	if oldLink == nil || err != nil {
 		return err
 	}
-	newCheckpoint := uint64(0)
-	for i := cl0.BlockNum() + 1; i < cl.BlockNum(); i++ {
-		tmp, err := bc.ReadCrossLink(cl.ShardID(), i)
-		if err != nil || tmp == nil {
-			newCheckpoint = i - 1
+	newLink := oldLink
+	// Starting from last checkpoint, keeping reading immediate next crosslink until there is a gap
+	for i := oldLink.BlockNum() + 1; ; i++ {
+		tmp, err := bc.ReadCrossLink(shardID, i)
+		if err == nil && tmp != nil && tmp.BlockNum() == i {
+			newLink = tmp
+		} else {
 			break
 		}
-		if i == cl.BlockNum()-1 {
-			newCheckpoint = cl.BlockNum()
-		}
 	}
 
-	if newCheckpoint > 0 {
-		utils.Logger().Debug().Msgf("LastContinuousCrossLink: latest checkpoint blockNum %d", newCheckpoint)
-		cln, err := bc.ReadCrossLink(cl.ShardID(), newCheckpoint)
-		if err != nil {
-			return err
-		}
-		return rawdb.WriteShardLastCrossLink(batch, cln.ShardID(), cln.Serialize())
+	if newLink.BlockNum() > oldLink.BlockNum() {
+		utils.Logger().Debug().Msgf("LastContinuousCrossLink: latest checkpoint blockNum %d", newLink.BlockNum())
+		return rawdb.WriteShardLastCrossLink(batch, shardID, newLink.Serialize())
 	}
 	return nil
 }

core/offchain.go

@@ -164,13 +164,21 @@ func (bc *BlockChain) CommitOffChainData(
 			if err := bc.WriteCrossLinks(batch, types.CrossLinks{crossLink}); err == nil {
 				utils.Logger().Info().Uint64("blockNum", crossLink.BlockNum()).Uint32("shardID", crossLink.ShardID()).Msg("[insertChain/crosslinks] Cross Link Added to Beaconchain")
 			}
-			bc.LastContinuousCrossLink(batch, crossLink)
+
+			cl0, _ := bc.ReadShardLastCrossLink(crossLink.ShardID())
+			if cl0 == nil {
+				rawdb.WriteShardLastCrossLink(batch, crossLink.ShardID(), crossLink.Serialize())
+			}
 		}
 
 		//clean/update local database cache after crosslink inserted into blockchain
 		num, err := bc.DeleteCommittedFromPendingCrossLinks(*crossLinks)
 		utils.Logger().Debug().Msgf("DeleteCommittedFromPendingCrossLinks, crosslinks in header %d,  pending crosslinks: %d, error: %+v", len(*crossLinks), num, err)
 	}
+	// Roll up latest crosslinks
+	for i := uint32(0); i < shard.Schedule.InstanceForEpoch(epoch).NumShards(); i++ {
+		bc.LastContinuousCrossLink(batch, i)
+	}
 
 	if bc.CurrentHeader().ShardID() == shard.BeaconChainShardID {
 		if bc.chainConfig.IsStaking(block.Epoch()) {

internal/params/config.go

@@ -37,7 +37,7 @@ var (
 	TestnetChainConfig = &ChainConfig{
 		ChainID:         TestnetChainID,
 		CrossTxEpoch:    big.NewInt(0),
-		CrossLinkEpoch:  big.NewInt(3),
+		CrossLinkEpoch:  big.NewInt(4),
 		StakingEpoch:    big.NewInt(4),
 		PreStakingEpoch: big.NewInt(2),
 		EIP155Epoch:     big.NewInt(0),
@@ -50,7 +50,7 @@ var (
 	PangaeaChainConfig = &ChainConfig{
 		ChainID:         PangaeaChainID,
 		CrossTxEpoch:    big.NewInt(0),
-		CrossLinkEpoch:  big.NewInt(2),
+		CrossLinkEpoch:  big.NewInt(3),
 		StakingEpoch:    big.NewInt(3),
 		PreStakingEpoch: big.NewInt(0),
 		EIP155Epoch:     big.NewInt(0),
@@ -62,9 +62,9 @@ var (
 	LocalnetChainConfig = &ChainConfig{
 		ChainID:         TestnetChainID,
 		CrossTxEpoch:    big.NewInt(0),
-		CrossLinkEpoch:  big.NewInt(3),
-		StakingEpoch:    big.NewInt(4),
-		PreStakingEpoch: big.NewInt(2),
+		CrossLinkEpoch:  big.NewInt(2),
+		StakingEpoch:    big.NewInt(2),
+		PreStakingEpoch: big.NewInt(0),
 		EIP155Epoch:     big.NewInt(0),
 		S3Epoch:         big.NewInt(0),
 		ReceiptLogEpoch: big.NewInt(0),