check for gaps in block numbers and throw if found during migration

op-chain-ops/cmd/celo-migrate/ancients.go

@@ -144,6 +144,9 @@ func readAncientBlocks(ctx context.Context, freezer *rawdb.Freezer, startBlock,
 func transformBlocks(ctx context.Context, in <-chan RLPBlockRange, out chan<- RLPBlockRange) error {
 	// Transform blocks from the in channel and send them to the out channel
 	defer close(out)
+
+	prevBlockNumber := uint64(0)
+
 	for blockRange := range in {
 		select {
 		case <-ctx.Done():
@@ -152,6 +155,11 @@ func transformBlocks(ctx context.Context, in <-chan RLPBlockRange, out chan<- RL
 			for i := range blockRange.hashes {
 				blockNumber := blockRange.start + uint64(i)
 
+				if blockNumber != 0 && blockNumber != prevBlockNumber+1 {
+					return fmt.Errorf("Gap found between ancient blocks numbered %d and %d. Please delete the target directory and repeat the migration with an uncorrupted source directory.", prevBlockNumber, blockNumber)
+				}
+				prevBlockNumber = blockNumber
+
 				newHeader, err := transformHeader(blockRange.headers[i])
 				if err != nil {
 					return fmt.Errorf("can't transform header: %w", err)

op-chain-ops/cmd/celo-migrate/non-ancients.go

@@ -75,11 +75,18 @@ func migrateNonAncientsDb(newDB ethdb.Database, lastBlock, numAncients, batchSiz
 		}
 	}
 
+	prevBlockNumber := uint64(numAncients - 1)
+
 	for i := numAncients; i <= lastBlock; i += batchSize {
 		numbersHash := rawdb.ReadAllHashesInRange(newDB, i, i+batchSize-1)
 
 		log.Info("Processing Block Range", "process", "non-ancients", "from", i, "to(inclusve)", i+batchSize-1, "count", len(numbersHash))
 		for _, numberHash := range numbersHash {
+			if numberHash.Number != 0 && numberHash.Number != prevBlockNumber+1 {
+				return 0, fmt.Errorf("Gap found between non-ancient blocks numbered %d and %d. Please delete the target directory and repeat the migration with an uncorrupted source directory.", prevBlockNumber, numberHash.Number)
+			}
+			prevBlockNumber = numberHash.Number
+
 			if err := migrateNonAncientBlock(numberHash.Number, numberHash.Hash, newDB); err != nil {
 				return 0, err
 			}