fix #3581 synchronizer panic synchronizing from trusted node (#3582)

synchronizer/l2_sync/l2_shared/processor_trusted_batch_sync.go

@@ -171,6 +171,10 @@ func (s *ProcessorTrustedBatchSync) AddPostChecker(checker PostClosedBatchChecke
 
 // ProcessTrustedBatch processes a trusted batch and return the new state
 func (s *ProcessorTrustedBatchSync) ProcessTrustedBatch(ctx context.Context, trustedBatch *types.Batch, status TrustedState, dbTx pgx.Tx, debugPrefix string) (*TrustedState, error) {
+	if trustedBatch == nil {
+		log.Errorf("%s trustedBatch is nil, it never should be nil", debugPrefix)
+		return nil, fmt.Errorf("%s trustedBatch is nil, it never should be nil", debugPrefix)
+	}
 	log.Debugf("%s Processing trusted batch: %v", debugPrefix, trustedBatch.Number)
 	stateCurrentBatch, statePreviousBatch := s.GetCurrentAndPreviousBatchFromCache(&status)
 	if s.l1SyncChecker != nil {

synchronizer/l2_sync/l2_shared/trusted_batches_retrieve.go

@@ -109,6 +109,16 @@ func isSyncrhonizedTrustedState(lastTrustedStateBatchNumber uint64, latestSynced
 	return lastTrustedStateBatchNumber < latestSyncedBatch
 }
 
+func sanityCheckBatchReturnedByTrusted(batch *types.Batch, expectedBatchNumber uint64) error {
+	if batch == nil {
+		return fmt.Errorf("batch %d is nil", expectedBatchNumber)
+	}
+	if uint64(batch.Number) != expectedBatchNumber {
+		return fmt.Errorf("batch %d is not the expected batch %d", batch.Number, expectedBatchNumber)
+	}
+	return nil
+}
+
 func (s *TrustedBatchesRetrieve) syncTrustedBatchesToFrom(ctx context.Context, latestSyncedBatch uint64, lastTrustedStateBatchNumber uint64) error {
 	batchNumberToSync := max(latestSyncedBatch, s.firstBatchNumberToSync)
 	for batchNumberToSync <= lastTrustedStateBatchNumber {
@@ -120,6 +130,11 @@ func (s *TrustedBatchesRetrieve) syncTrustedBatchesToFrom(ctx context.Context, l
 			log.Warnf("%s failed to get batch %d from trusted state. Error: %v", debugPrefix, batchNumberToSync, err)
 			return err
 		}
+		err = sanityCheckBatchReturnedByTrusted(batchToSync, batchNumberToSync)
+		if err != nil {
+			log.Warnf("%s sanity check over Batch returned by Trusted-RPC failed: %v", debugPrefix, err)
+			return err
+		}
 
 		dbTx, err := s.state.BeginStateTransaction(ctx)
 		if err != nil {