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contracts/src/IRollup.sol

@@ -174,6 +174,11 @@ interface IRollup {
      */
     function currentRequiredStake() external view returns (uint256);
 
+    /**
+     * @return confirmedBlockNum size of inbox confirmed
+     */
+    function confirmedBlockNum() external view returns (uint256);
+
     /**
      * @notice Requires that the first unresolved assertion is confirmable. Otherwise, reverts.
      * This is exposed as a utility function to validators.

contracts/src/ISequencerInbox.sol

@@ -36,10 +36,10 @@ interface ISequencerInbox is IDAProvider {
     /// @dev Thrown when sequencer tries to append an empty batch
     error EmptyBatch();
 
-    /// @dev Thrown when underflow occurs reading txBatch
+    /// @dev Thrown when underflow occurs reading txBatchData
     error TxBatchDataUnderflow();
 
-    /// @dev Thrown when overflow occurs reading txBatch
+    /// @dev Thrown when overflow occurs reading txBatchData
     error TxBatchDataOverflow();
 
     /// @dev Thrown when a transaction batch has an incorrect version

contracts/src/Rollup.sol

@@ -171,6 +171,11 @@ contract Rollup is RollupBase {
         return baseStakeAmount;
     }
 
+    /// @inheritdoc IRollup
+    function confirmedBlockNum() public view override returns (uint256) {
+        return assertions[lastConfirmedAssertionID].blockNum;
+    }
+
     /// @inheritdoc IRollup
     function getStaker(address addr) external view override returns (Staker memory) {
         return stakers[addr];

contracts/test/SequencerInbox.t.sol

@@ -94,9 +94,10 @@ contract SequencerInboxTest is SequencerBaseSetup {
         seqIn.appendTxBatch(hex"00");
     }
 
-    function test_appendTxBatch_emptyBatch_succeeds() public {
+    function test_appendTxBatch_invalidVersion_reverts() public {
+        vm.expectRevert(ISequencerInbox.TxBatchVersionIncorrect.selector);
         vm.prank(sequencerAddress);
-        seqIn.appendTxBatch(hex"00");
+        seqIn.appendTxBatch(hex"01"); // version 0 is the only valid version
     }
 
     //////////////////////////////

services/sidecar/rollup/derivation/batch_builder.go

@@ -2,6 +2,7 @@ package derivation
 
 import (
 	"bytes"
+	"errors"
 	"fmt"
 	"io"
 	"math/big"
@@ -16,7 +17,7 @@ type batchBuilder struct {
 	maxBatchSize uint64
 
 	pendingBlocks  []DerivationBlock
-	builtBatchData *[]byte
+	builtBatchData []byte
 
 	lastAppended types.BlockID
 }
@@ -70,7 +71,7 @@ func (b *batchBuilder) Reset(lastAppended types.BlockID) {
 
 // This short-circuits the build process if a batch is
 // already built and `Advance` hasn't been called.
-func (b *batchBuilder) Build() (*[]byte, error) {
+func (b *batchBuilder) Build() ([]byte, error) {
 	if b.builtBatchData != nil {
 		return b.builtBatchData, nil
 	}
@@ -86,7 +87,7 @@ func (b *batchBuilder) Build() (*[]byte, error) {
 		return nil, fmt.Errorf("failed to encode batch: %w", err)
 	}
 
-	b.builtBatchData = &batchData
+	b.builtBatchData = batchData
 	return b.builtBatchData, nil
 }
 
@@ -95,6 +96,10 @@ func (b *batchBuilder) Advance() {
 }
 
 func (b *batchBuilder) serializeToAttrs() (*BatchAttributes, error) {
+	if len(b.pendingBlocks) == 0 {
+		return nil, errors.New("no pending blocks")
+	}
+
 	var (
 		block  DerivationBlock
 		idx    int
@@ -122,7 +127,7 @@ func (b *batchBuilder) serializeToAttrs() (*BatchAttributes, error) {
 	}
 	// Construct batch attributes.
 	attrs := &BatchAttributes{firstL2BlockNumber, blocks}
-	log.Info("Serialized l2 blocks", "first", firstL2BlockNumber, "last", b.pendingBlocks[idx].BlockNumber())
+	log.Info("Serialized l2 blocks", "first", firstL2BlockNumber, "last", block.BlockNumber())
 	// Advance queue.
 	b.pendingBlocks = b.pendingBlocks[idx+1:]
 	log.Trace("Advanced pending blocks", "len", len(b.pendingBlocks))

services/sidecar/rollup/derivation/derivation_block.go

@@ -61,12 +61,17 @@ func BlocksFromData(calldata []any) ([]DerivationBlock, error) {
 	}
 
 	txBatchVersion := txBatchData[0]
-	if txBatchVersion != TxBatchVersion() {
-		return nil, &DecodeTxBatchError{fmt.Sprintf("invalid tx batch version")}
+	switch txBatchVersion {
+	case 0:
+		return blocksFromV0Data(txBatchData[1:])
+	default:
+		return nil, &DecodeTxBatchError{fmt.Sprintf("invalid tx batch version: {%d}", txBatchVersion)}
 	}
+}
 
+func blocksFromV0Data(v0Data []byte) ([]DerivationBlock, error) {
 	var decodedBatch BatchAttributes
-	if err := rlp.Decode(bytes.NewReader(txBatchData[:1]), &decodedBatch); err != nil {
+	if err := rlp.Decode(bytes.NewReader(v0Data), &decodedBatch); err != nil {
 		return nil, err
 	}
 

services/sidecar/rollup/rpc/bridge/serialization.go

@@ -51,7 +51,7 @@ func UnpackAppendTxBatchInput(tx *types.Transaction) ([]any, error) {
 	return serializationUtil.inboxAbi.Methods[AppendTxBatchFnName].Inputs.Unpack(tx.Data()[MethodNumBytes:])
 }
 
-func packAppendTxBatchInput(txBatchData *[]byte) ([]byte, error) {
+func packAppendTxBatchInput(txBatchData []byte) ([]byte, error) {
 	return serializationUtil.inboxAbi.Pack(AppendTxBatchFnName, txBatchData)
 }
 

services/sidecar/rollup/rpc/bridge/tx_mgr.go

@@ -33,9 +33,9 @@ func NewTxManager(txMgr EthTxManager, cfg bridgeConfig) (*TxManager, error) {
 
 func (m *TxManager) AppendTxBatch(
 	ctx context.Context,
-	txBatch *[]byte,
+	txBatchData []byte,
 ) (*types.Receipt, error) {
-	data, err := packAppendTxBatchInput(txBatch)
+	data, err := packAppendTxBatchInput(txBatchData)
 	if err != nil {
 		return nil, err
 	}

services/sidecar/rollup/services/disseminator/interface.go

@@ -21,15 +21,15 @@ type BuildPayloadResponse = engine.ForkChoiceResponse
 type BatchBuilder interface {
 	Append(block derivation.DerivationBlock, header derivation.HeaderRef) error
 	LastAppended() types.BlockID
-	Build() (*[]byte, error)
+	Build() ([]byte, error)
 	Advance()
 	Reset(lastAppended types.BlockID)
 }
 
 type TxManager interface {
 	AppendTxBatch(
 		ctx context.Context,
-		batchData *[]byte,
+		txBatchData []byte,
 	) (*ethTypes.Receipt, error)
 }