Merge pull request #2375 from OffchainLabs/dangerous_batch_poster

[NIT-1290] batch poster dangerous config: AllowPostingFirstBatchWhenSequencerMessageCountMismatch

arbnode/batch_poster.go

@@ -111,6 +111,7 @@ type BatchPoster struct {
 
 	batchReverted        atomic.Bool // indicates whether data poster batch was reverted
 	nextRevertCheckBlock int64       // the last parent block scanned for reverting batches
+	postedFirstBatch     bool        // indicates if batch poster has posted the first batch
 
 	accessList func(SequencerInboxAccs, AfterDelayedMessagesRead int) types.AccessList
 }
@@ -127,6 +128,10 @@ const (
 	l1BlockBoundIgnore
 )
 
+type BatchPosterDangerousConfig struct {
+	AllowPostingFirstBatchWhenSequencerMessageCountMismatch bool `koanf:"allow-posting-first-batch-when-sequencer-message-count-mismatch"`
+}
+
 type BatchPosterConfig struct {
 	Enable                             bool `koanf:"enable"`
 	DisableDapFallbackStoreDataOnChain bool `koanf:"disable-dap-fallback-store-data-on-chain" reload:"hot"`
@@ -156,6 +161,7 @@ type BatchPosterConfig struct {
 	L1BlockBoundBypass             time.Duration               `koanf:"l1-block-bound-bypass" reload:"hot"`
 	UseAccessLists                 bool                        `koanf:"use-access-lists" reload:"hot"`
 	GasEstimateBaseFeeMultipleBips arbmath.Bips                `koanf:"gas-estimate-base-fee-multiple-bips"`
+	Dangerous                      BatchPosterDangerousConfig  `koanf:"dangerous"`
 
 	gasRefunder  common.Address
 	l1BlockBound l1BlockBound
@@ -1265,7 +1271,37 @@ func (b *BatchPoster) maybePostSequencerBatch(ctx context.Context) (bool, error)
 		}
 	}
 
-	data, kzgBlobs, err := b.encodeAddBatch(new(big.Int).SetUint64(batchPosition.NextSeqNum), batchPosition.MessageCount, b.building.msgCount, sequencerMsg, b.building.segments.delayedMsg, b.building.use4844)
+	prevMessageCount := batchPosition.MessageCount
+	if b.config().Dangerous.AllowPostingFirstBatchWhenSequencerMessageCountMismatch && !b.postedFirstBatch {
+		// AllowPostingFirstBatchWhenSequencerMessageCountMismatch can be used when the
+		// message count stored in batch poster's database gets out
+		// of sync with the sequencerReportedSubMessageCount stored in the parent chain.
+		//
+		// An example of when this out of sync issue can happen:
+		// 1. Batch poster is running fine, but then it shutdowns for more than 24h.
+		// 2. While the batch poster is down, someone sends a transaction to the parent chain
+		// smart contract to move a message from the delayed inbox to the main inbox.
+		// This will not update sequencerReportedSubMessageCount in the parent chain.
+		// 3. When batch poster starts again, the inbox reader will update the
+		// message count that is maintained in the batch poster's database to be equal to
+		// (sequencerReportedSubMessageCount that is stored in parent chain) +
+		// (the amount of delayed messages that were moved from the delayed inbox to the main inbox).
+		// At this moment the message count stored on batch poster's database gets out of sync with
+		// the sequencerReportedSubMessageCount stored in the parent chain.
+
+		// When the first batch is posted, sequencerReportedSubMessageCount in
+		// the parent chain will be updated to be equal to the new message count provided
+		// by the batch poster, which will make this out of sync issue disappear.
+		// That is why this strategy is only applied for the first batch posted after
+		// startup.
+
+		// If prevMessageCount is set to zero, sequencer inbox's smart contract allows
+		// to post a batch even if sequencerReportedSubMessageCount is not equal
+		// to the provided prevMessageCount
+		prevMessageCount = 0
+	}
+
+	data, kzgBlobs, err := b.encodeAddBatch(new(big.Int).SetUint64(batchPosition.NextSeqNum), prevMessageCount, b.building.msgCount, sequencerMsg, b.building.segments.delayedMsg, b.building.use4844)
 	if err != nil {
 		return false, err
 	}
@@ -1306,6 +1342,7 @@ func (b *BatchPoster) maybePostSequencerBatch(ctx context.Context) (bool, error)
 	if err != nil {
 		return false, err
 	}
+	b.postedFirstBatch = true
 	log.Info(
 		"BatchPoster: batch sent",
 		"sequenceNumber", batchPosition.NextSeqNum,