L1 gas pricing: Don't post a batch if the only contents are a batch posting report

arbnode/batch_poster.go

@@ -7,10 +7,12 @@ import (
 	"bytes"
 	"context"
 	"fmt"
-	"github.com/offchainlabs/nitro/util/headerreader"
 	"math/big"
 	"time"
 
+	"github.com/offchainlabs/nitro/arbos"
+	"github.com/offchainlabs/nitro/util/headerreader"
+
 	"github.com/andybalholm/brotli"
 	"github.com/pkg/errors"
 	flag "github.com/spf13/pflag"
@@ -341,24 +343,30 @@ func (b *BatchPoster) maybePostSequencerBatch(ctx context.Context, timeSinceBatc
 		return nil, err
 	}
 	forcePostBatch := timeSinceBatchPosted >= b.config.MaxBatchPostInterval
+	haveUsefulMessage := false
 	for b.building.msgCount < msgCount {
 		msg, err := b.streamer.GetMessage(b.building.msgCount)
 		if err != nil {
 			log.Error("error getting message from streamer", "error", err)
 			break
 		}
+		if msg.Message.Header.Kind != arbos.L1MessageType_BatchPostingReport {
+			haveUsefulMessage = true
+		}
 		success, err := b.building.segments.AddMessage(&msg)
 		if err != nil {
 			log.Error("error adding message to batch", "error", err)
 			break
 		}
 		if !success {
-			forcePostBatch = true // this batch is full
+			// this batch is full
+			forcePostBatch = true
+			haveUsefulMessage = true
 			break
 		}
 		b.building.msgCount++
 	}
-	if !forcePostBatch {
+	if !forcePostBatch || !haveUsefulMessage {
 		// the batch isn't full yet and we've posted a batch recently
 		// don't post anything for now
 		return nil, nil

system_tests/block_validator_test.go

@@ -92,11 +92,25 @@ func testBlockValidatorSimple(t *testing.T, dasModeString string, expensiveTx bo
 		Fail(t, "Unexpected balance:", l2balance)
 	}
 
-	lastBlockHeader, err := l2clientB.HeaderByNumber(ctx, nil)
+	lastBlock, err := l2clientB.BlockByNumber(ctx, nil)
 	Require(t, err)
+	for {
+		usefulBlock := false
+		for _, tx := range lastBlock.Transactions() {
+			if tx.Type() != types.ArbitrumInternalTxType {
+				usefulBlock = true
+				break
+			}
+		}
+		if usefulBlock {
+			break
+		}
+		lastBlock, err = l2clientB.BlockByHash(ctx, lastBlock.ParentHash())
+		Require(t, err)
+	}
 	testDeadLine, _ := t.Deadline()
 	nodeA.StopAndWait()
-	if !nodeB.BlockValidator.WaitForBlock(lastBlockHeader.Number.Uint64(), time.Until(testDeadLine)-time.Second*10) {
+	if !nodeB.BlockValidator.WaitForBlock(lastBlock.NumberU64(), time.Until(testDeadLine)-time.Second*10) {
 		Fail(t, "did not validate all blocks")
 	}
 	nodeB.StopAndWait()

validator/challenge_manager.go

@@ -420,7 +420,7 @@ func (m *ChallengeManager) createInitialMachine(ctx context.Context, blockNum in
 	var batchInfo []BatchInfo
 	if tooFar {
 		// Just record the part of block creation before the message is read
-		_, preimages, readBatchInfo, err := RecordBlockCreation(ctx, m.blockchain, m.inboxReader, blockHeader, nil)
+		_, preimages, readBatchInfo, err := RecordBlockCreation(ctx, m.blockchain, m.inboxReader, blockHeader, nil, true)
 		if err != nil {
 			return err
 		}

validator/stateless_block_validator.go

@@ -13,6 +13,7 @@ import (
 	"github.com/ethereum/go-ethereum/common"
 	"github.com/ethereum/go-ethereum/core"
 	"github.com/ethereum/go-ethereum/core/rawdb"
+	"github.com/ethereum/go-ethereum/core/state"
 	"github.com/ethereum/go-ethereum/core/types"
 	"github.com/ethereum/go-ethereum/ethdb"
 	"github.com/ethereum/go-ethereum/log"
@@ -222,10 +223,26 @@ type BatchInfo struct {
 }
 
 // If msg is nil, this will record block creation up to the point where message would be accessed (for a "too far" proof)
-func RecordBlockCreation(ctx context.Context, blockchain *core.BlockChain, inboxReader InboxReaderInterface, prevHeader *types.Header, msg *arbstate.MessageWithMetadata) (common.Hash, map[common.Hash][]byte, []BatchInfo, error) {
-	recordingdb, chaincontext, recordingKV, err := arbitrum.PrepareRecording(blockchain, prevHeader)
-	if err != nil {
-		return common.Hash{}, nil, nil, err
+func RecordBlockCreation(ctx context.Context, blockchain *core.BlockChain, inboxReader InboxReaderInterface, prevHeader *types.Header, msg *arbstate.MessageWithMetadata, producePreimages bool) (common.Hash, map[common.Hash][]byte, []BatchInfo, error) {
+	var recordingdb *state.StateDB
+	var chaincontext core.ChainContext
+	var recordingKV *arbitrum.RecordingKV
+	var err error
+	if producePreimages {
+		recordingdb, chaincontext, recordingKV, err = arbitrum.PrepareRecording(blockchain, prevHeader)
+		if err != nil {
+			return common.Hash{}, nil, nil, err
+		}
+	} else {
+		var prevRoot common.Hash
+		if prevHeader != nil {
+			prevRoot = prevHeader.Root
+		}
+		recordingdb, err = blockchain.StateAt(prevRoot)
+		if err != nil {
+			return common.Hash{}, nil, nil, err
+		}
+		chaincontext = blockchain
 	}
 
 	chainConfig := blockchain.Config()
@@ -275,7 +292,13 @@ func RecordBlockCreation(ctx context.Context, blockchain *core.BlockChain, inbox
 		blockHash = block.Hash()
 	}
 
-	preimages, err := arbitrum.PreimagesFromRecording(chaincontext, recordingKV)
+	var preimages map[common.Hash][]byte
+	if recordingKV != nil {
+		preimages, err = arbitrum.PreimagesFromRecording(chaincontext, recordingKV)
+		if err != nil {
+			return common.Hash{}, nil, nil, err
+		}
+	}
 	return blockHash, preimages, readBatchInfo, err
 }
 
@@ -289,9 +312,9 @@ func BlockDataForValidation(ctx context.Context, blockchain *core.BlockChain, in
 		return
 	}
 
-	if prevHeader != nil && producePreimages {
+	if prevHeader != nil {
 		var blockhash common.Hash
-		blockhash, preimages, readBatchInfo, err = RecordBlockCreation(ctx, blockchain, inboxReader, prevHeader, &msg)
+		blockhash, preimages, readBatchInfo, err = RecordBlockCreation(ctx, blockchain, inboxReader, prevHeader, &msg, producePreimages)
 		if err != nil {
 			return
 		}
@@ -319,7 +342,7 @@ func SetMachinePreimageResolver(ctx context.Context, mach *ArbitratorMachine, pr
 	}
 
 	for _, batch := range batchInfo {
-		if arbstate.IsDASMessageHeaderByte(batch.Data[40]) {
+		if len(batch.Data) >= 41 && arbstate.IsDASMessageHeaderByte(batch.Data[40]) {
 			if das == nil {
 				log.Error("No DAS configured, but sequencer message found with DAS header")
 				if bc.Config().ArbitrumChainParams.DataAvailabilityCommittee {