Merge pull request #3802 from ethereum-optimism/driver-status-api

op-node: get block with sync status, make finalization more safe

op-e2e/actions/l1_replica.go

@@ -177,8 +177,16 @@ func (s *L1Replica) L1Client(t Testing, cfg *rollup.Config) *sources.L1Client {
 // ActL1FinalizeNext finalizes the next block, which must be marked as safe before doing so (see ActL1SafeNext).
 func (s *L1Replica) ActL1FinalizeNext(t Testing) {
 	safe := s.l1Chain.CurrentSafeBlock()
-	finalizedNum := s.l1Chain.CurrentFinalizedBlock().NumberU64()
-	if safe.NumberU64() <= finalizedNum {
+	safeNum := uint64(0)
+	if safe != nil {
+		safeNum = safe.NumberU64()
+	}
+	finalized := s.l1Chain.CurrentFinalizedBlock()
+	finalizedNum := uint64(0)
+	if finalized != nil {
+		finalizedNum = finalized.NumberU64()
+	}
+	if safeNum <= finalizedNum {
 		t.InvalidAction("need to move forward safe block before moving finalized block")
 		return
 	}
@@ -192,7 +200,11 @@ func (s *L1Replica) ActL1FinalizeNext(t Testing) {
 // ActL1SafeNext marks the next unsafe block as safe.
 func (s *L1Replica) ActL1SafeNext(t Testing) {
 	safe := s.l1Chain.CurrentSafeBlock()
-	next := s.l1Chain.GetBlockByNumber(safe.NumberU64() + 1)
+	safeNum := uint64(0)
+	if safe != nil {
+		safeNum = safe.NumberU64()
+	}
+	next := s.l1Chain.GetBlockByNumber(safeNum + 1)
 	if next == nil {
 		t.InvalidAction("if head of chain is marked as safe then there's no next block")
 		return

op-e2e/actions/l2_batcher.go

@@ -7,15 +7,16 @@ import (
 	"io"
 	"math/big"
 
-	"github.com/ethereum-optimism/optimism/op-node/eth"
-	"github.com/ethereum-optimism/optimism/op-node/rollup"
-	"github.com/ethereum-optimism/optimism/op-node/rollup/derive"
 	"github.com/ethereum/go-ethereum/common"
 	"github.com/ethereum/go-ethereum/core"
 	"github.com/ethereum/go-ethereum/core/types"
 	"github.com/ethereum/go-ethereum/log"
 	"github.com/ethereum/go-ethereum/params"
 	"github.com/stretchr/testify/require"
+
+	"github.com/ethereum-optimism/optimism/op-node/eth"
+	"github.com/ethereum-optimism/optimism/op-node/rollup"
+	"github.com/ethereum-optimism/optimism/op-node/rollup/derive"
 )
 
 type SyncStatusAPI interface {
@@ -149,8 +150,8 @@ func (s *L2Batcher) ActL2BatchSubmit(t Testing) {
 	data.WriteByte(derive.DerivationVersion0)
 	// subtract one, to account for the version byte
 	if err := s.l2ChannelOut.OutputFrame(data, s.l2BatcherCfg.MaxL1TxSize-1); err == io.EOF {
+		s.l2ChannelOut = nil
 		s.l2Submitting = false
-		// there may still be some data to submit
 	} else if err != nil {
 		s.l2Submitting = false
 		t.Fatalf("failed to output channel data to frame: %v", err)

op-e2e/actions/l2_batcher_test.go

@@ -4,12 +4,14 @@ import (
 	"math/big"
 	"testing"
 
+	"github.com/ethereum/go-ethereum/common"
 	"github.com/ethereum/go-ethereum/core/types"
 	"github.com/ethereum/go-ethereum/log"
 	"github.com/ethereum/go-ethereum/params"
 	"github.com/stretchr/testify/require"
 
 	"github.com/ethereum-optimism/optimism/op-e2e/e2eutils"
+	"github.com/ethereum-optimism/optimism/op-node/eth"
 	"github.com/ethereum-optimism/optimism/op-node/testlog"
 )
 
@@ -87,3 +89,108 @@ func TestBatcher(gt *testing.T) {
 	require.False(t, isPending)
 	require.NotNil(t, vTx)
 }
+
+func TestL2Finalization(gt *testing.T) {
+	t := NewDefaultTesting(gt)
+	dp := e2eutils.MakeDeployParams(t, defaultRollupTestParams)
+	sd := e2eutils.Setup(t, dp, defaultAlloc)
+	log := testlog.Logger(t, log.LvlDebug)
+	miner, engine, sequencer := setupSequencerTest(t, sd, log)
+
+	sequencer.ActL2PipelineFull(t)
+
+	// build an empty L1 block (#1), mark it as justified
+	miner.ActEmptyBlock(t)
+	miner.ActL1SafeNext(t) // #0 -> #1
+
+	// sequencer builds L2 chain, up to and including a block that has the new L1 block as origin
+	sequencer.ActL1HeadSignal(t)
+	sequencer.ActBuildToL1Head(t)
+
+	sequencer.ActL2PipelineFull(t)
+	sequencer.ActL1SafeSignal(t)
+	require.Equal(t, uint64(1), sequencer.SyncStatus().SafeL1.Number)
+
+	// build another L1 block (#2), mark it as justified. And mark previous justified as finalized.
+	miner.ActEmptyBlock(t)
+	miner.ActL1SafeNext(t)     // #1 -> #2
+	miner.ActL1FinalizeNext(t) // #0 -> #1
+	sequencer.ActL1HeadSignal(t)
+	sequencer.ActBuildToL1Head(t)
+
+	// continue to build L2 chain referencing the new L1 blocks
+	sequencer.ActL2PipelineFull(t)
+	sequencer.ActL1FinalizedSignal(t)
+	sequencer.ActL1SafeSignal(t)
+	require.Equal(t, uint64(2), sequencer.SyncStatus().SafeL1.Number)
+	require.Equal(t, uint64(1), sequencer.SyncStatus().FinalizedL1.Number)
+	require.Equal(t, uint64(0), sequencer.SyncStatus().FinalizedL2.Number, "L2 block has to be included on L1 before it can be finalized")
+
+	batcher := NewL2Batcher(log, sd.RollupCfg, &BatcherCfg{
+		MinL1TxSize: 0,
+		MaxL1TxSize: 128_000,
+		BatcherKey:  dp.Secrets.Batcher,
+	}, sequencer.RollupClient(), miner.EthClient(), engine.EthClient())
+
+	heightToSubmit := sequencer.SyncStatus().UnsafeL2.Number
+
+	batcher.ActSubmitAll(t)
+	// confirm batch on L1, block #3
+	miner.ActL1StartBlock(12)(t)
+	miner.ActL1IncludeTx(dp.Addresses.Batcher)(t)
+	miner.ActL1EndBlock(t)
+
+	// read the batch
+	sequencer.ActL2PipelineFull(t)
+	require.Equal(t, uint64(0), sequencer.SyncStatus().FinalizedL2.Number, "Batch must be included in finalized part of L1 chain for L2 block to finalize")
+
+	// build some more L2 blocks, so there is an unsafe part again that hasn't been submitted yet
+	sequencer.ActL1HeadSignal(t)
+	sequencer.ActBuildToL1Head(t)
+
+	// submit those blocks too, block #4
+	batcher.ActSubmitAll(t)
+	miner.ActL1StartBlock(12)(t)
+	miner.ActL1IncludeTx(dp.Addresses.Batcher)(t)
+	miner.ActL1EndBlock(t)
+
+	// add some more L1 blocks #5, #6
+	miner.ActEmptyBlock(t)
+	miner.ActEmptyBlock(t)
+
+	// and more unsafe L2 blocks
+	sequencer.ActL1HeadSignal(t)
+	sequencer.ActBuildToL1Head(t)
+
+	// move safe/finalize markers: finalize the L1 chain block with the first batch, but not the second
+	miner.ActL1SafeNext(t)     // #2 -> #3
+	miner.ActL1SafeNext(t)     // #3 -> #4
+	miner.ActL1FinalizeNext(t) // #1 -> #2
+	miner.ActL1FinalizeNext(t) // #2 -> #3
+
+	sequencer.ActL2PipelineFull(t)
+	sequencer.ActL1FinalizedSignal(t)
+	sequencer.ActL1SafeSignal(t)
+	sequencer.ActL1HeadSignal(t)
+	require.Equal(t, uint64(6), sequencer.SyncStatus().HeadL1.Number)
+	require.Equal(t, uint64(4), sequencer.SyncStatus().SafeL1.Number)
+	require.Equal(t, uint64(3), sequencer.SyncStatus().FinalizedL1.Number)
+	require.Equal(t, heightToSubmit, sequencer.SyncStatus().FinalizedL2.Number, "finalized L2 blocks in first batch")
+
+	// need to act with the engine on the signals still
+	sequencer.ActL2PipelineFull(t)
+
+	engCl := engine.EngineClient(t, sd.RollupCfg)
+	engBlock, err := engCl.L2BlockRefByLabel(t.Ctx(), eth.Finalized)
+	require.NoError(t, err)
+	require.Equal(t, heightToSubmit, engBlock.Number, "engine finalizes what rollup node finalizes")
+
+	// Now try to finalize block 4, but with a bad/malicious alternative hash.
+	// If we get this false signal, we shouldn't finalize the L2 chain.
+	altBlock4 := sequencer.SyncStatus().SafeL1
+	altBlock4.Hash = common.HexToHash("0xdead")
+	sequencer.derivation.Finalize(altBlock4)
+	sequencer.ActL2PipelineFull(t)
+	require.Equal(t, uint64(3), sequencer.SyncStatus().FinalizedL1.Number)
+	require.Equal(t, heightToSubmit, sequencer.SyncStatus().FinalizedL2.Number, "unknown/bad finalized L1 blocks are ignored")
+}

op-e2e/actions/l2_engine.go

@@ -175,7 +175,7 @@ func (e *L2Engine) ActL2IncludeTx(from common.Address) Action {
 			e.l2GasPool, e.l2BuildingState, e.l2BuildingHeader, tx, &e.l2BuildingHeader.GasUsed, *e.l2Chain.GetVMConfig())
 		if err != nil {
 			e.l2TxFailed = append(e.l2TxFailed, tx)
-			t.Fatalf("failed to apply transaction to L1 block (tx %d): %v", len(e.l2Transactions), err)
+			t.Fatalf("failed to apply transaction to L2 block (tx %d): %v", len(e.l2Transactions), err)
 		}
 		e.l2Receipts = append(e.l2Receipts, receipt)
 		e.l2Transactions = append(e.l2Transactions, tx)

op-e2e/actions/l2_verifier.go

@@ -118,13 +118,14 @@ func (s *L2Verifier) L2Unsafe() eth.L2BlockRef {
 
 func (s *L2Verifier) SyncStatus() *eth.SyncStatus {
 	return &eth.SyncStatus{
-		CurrentL1:   s.derivation.Origin(),
-		HeadL1:      s.l1State.L1Head(),
-		SafeL1:      s.l1State.L1Safe(),
-		FinalizedL1: s.l1State.L1Finalized(),
-		UnsafeL2:    s.L2Unsafe(),
-		SafeL2:      s.L2Safe(),
-		FinalizedL2: s.L2Finalized(),
+		CurrentL1:          s.derivation.Origin(),
+		CurrentL1Finalized: s.derivation.FinalizedL1(),
+		HeadL1:             s.l1State.L1Head(),
+		SafeL1:             s.l1State.L1Safe(),
+		FinalizedL1:        s.l1State.L1Finalized(),
+		UnsafeL2:           s.L2Unsafe(),
+		SafeL2:             s.L2Safe(),
+		FinalizedL2:        s.L2Finalized(),
 	}
 }
 
@@ -160,15 +161,16 @@ func (s *L2Verifier) ActL1HeadSignal(t Testing) {
 }
 
 func (s *L2Verifier) ActL1SafeSignal(t Testing) {
-	head, err := s.l1.L1BlockRefByLabel(t.Ctx(), eth.Safe)
+	safe, err := s.l1.L1BlockRefByLabel(t.Ctx(), eth.Safe)
 	require.NoError(t, err)
-	s.l1State.HandleNewL1SafeBlock(head)
+	s.l1State.HandleNewL1SafeBlock(safe)
 }
 
 func (s *L2Verifier) ActL1FinalizedSignal(t Testing) {
-	head, err := s.l1.L1BlockRefByLabel(t.Ctx(), eth.Finalized)
+	finalized, err := s.l1.L1BlockRefByLabel(t.Ctx(), eth.Finalized)
 	require.NoError(t, err)
-	s.l1State.HandleNewL1FinalizedBlock(head)
+	s.l1State.HandleNewL1FinalizedBlock(finalized)
+	s.derivation.Finalize(finalized)
 }
 
 // ActL2PipelineStep runs one iteration of the L2 derivation pipeline

op-node/eth/sync_status.go

@@ -3,10 +3,18 @@ package eth
 // SyncStatus is a snapshot of the driver.
 // Values may be zeroed if not yet initialized.
 type SyncStatus struct {
-	// CurrentL1 is the block that the derivation process is currently at,
-	// this may not be fully derived into L2 data yet.
+	// CurrentL1 is the L1 block that the derivation process is currently at in the inner-most stage.
+	// This may not be fully derived into L2 data yet.
+	// The safe L2 blocks were produced/included fully from the L1 chain up to and including this L1 block.
 	// If the node is synced, this matches the HeadL1, minus the verifier confirmation distance.
 	CurrentL1 L1BlockRef `json:"current_l1"`
+	// CurrentL1Finalized is the L1 block that the derivation process is currently accepting as finalized
+	// in the inner-most stage,
+	// This may not be fully derived into L2 data yet.
+	// The finalized L2 blocks were produced/included fully from the L1 chain up to and including this L1 block.
+	// This may lag behind the FinalizedL1 when the FinalizedL1 could not yet be verified
+	// to be canonical w.r.t. the currently derived L2 chain. It may be zeroed if no block could be verified yet.
+	CurrentL1Finalized L1BlockRef `json:"current_l1_finalized"`
 	// HeadL1 is the perceived head of the L1 chain, no confirmation distance.
 	// The head is not guaranteed to build on the other L1 sync status fields,
 	// as the node may be in progress of resetting to adapt to a L1 reorg.

op-node/rollup/derive/engine_queue.go

@@ -72,7 +72,7 @@ type EngineQueue struct {
 	// This update may repeat if the engine returns a temporary error.
 	needForkchoiceUpdate bool
 
-	finalizedL1 eth.BlockID
+	finalizedL1 eth.L1BlockRef
 
 	safeAttributes []*eth.PayloadAttributes
 	unsafePayloads PayloadsQueue // queue of unsafe payloads, ordered by ascending block number, may have gaps
@@ -83,7 +83,7 @@ type EngineQueue struct {
 	engine Engine
 	prev   NextAttributesProvider
 
-	origin eth.L1BlockRef // only used for pipeline resets
+	origin eth.L1BlockRef // updated on resets, and whenever we read from the previous stage.
 
 	metrics   Metrics
 	l1Fetcher L1Fetcher
@@ -106,6 +106,7 @@ func NewEngineQueue(log log.Logger, cfg *rollup.Config, engine Engine, metrics M
 	}
 }
 
+// Origin identifies the L1 chain (incl.) that included and/or produced all the safe L2 blocks.
 func (eq *EngineQueue) Origin() eth.L1BlockRef {
 	return eq.origin
 }
@@ -134,9 +135,28 @@ func (eq *EngineQueue) AddSafeAttributes(attributes *eth.PayloadAttributes) {
 	eq.safeAttributes = append(eq.safeAttributes, attributes)
 }
 
-func (eq *EngineQueue) Finalize(l1Origin eth.BlockID) {
-	eq.finalizedL1 = l1Origin
-	eq.tryFinalizeL2()
+func (eq *EngineQueue) Finalize(l1Origin eth.L1BlockRef) {
+	if l1Origin.Number < eq.finalizedL1.Number {
+		eq.log.Error("ignoring old L1 finalized block signal! Is the L1 provider corrupted?", "prev_finalized_l1", eq.finalizedL1, "signaled_finalized_l1", l1Origin)
+		return
+	}
+	// Perform a safety check: the L1 finalization signal is only accepted if we previously processed the L1 block.
+	// This prevents a corrupt L1 provider from tricking us in recognizing a L1 block inconsistent with the L1 chain we are on.
+	// Missing a finality signal due to empty buffer is fine, it will finalize when the buffer is filled again.
+	for _, fd := range eq.finalityData {
+		if fd.L1Block == l1Origin.ID() {
+			eq.finalizedL1 = l1Origin
+			eq.tryFinalizeL2()
+			return
+		}
+	}
+	eq.log.Warn("ignoring finalization signal for unknown L1 block, waiting for new L1 blocks in buffer", "prev_finalized_l1", eq.finalizedL1, "signaled_finalized_l1", l1Origin)
+}
+
+// FinalizedL1 identifies the L1 chain (incl.) that included and/or produced all the finalized L2 blocks.
+// This may return a zeroed ID if no finalization signals have been seen yet.
+func (eq *EngineQueue) FinalizedL1() eth.L1BlockRef {
+	return eq.finalizedL1
 }
 
 func (eq *EngineQueue) Finalized() eth.L2BlockRef {
@@ -167,6 +187,7 @@ func (eq *EngineQueue) Step(ctx context.Context) error {
 	}
 	outOfData := false
 	if len(eq.safeAttributes) == 0 {
+		eq.origin = eq.prev.Origin()
 		if next, err := eq.prev.NextAttributes(ctx, eq.safeHead); err == io.EOF {
 			outOfData = true
 		} else if err != nil {
@@ -191,7 +212,7 @@ func (eq *EngineQueue) Step(ctx context.Context) error {
 // and then marks the latest fully derived L2 block from this as finalized,
 // or defaults to the current finalized L2 block.
 func (eq *EngineQueue) tryFinalizeL2() {
-	if eq.finalizedL1 == (eth.BlockID{}) {
+	if eq.finalizedL1 == (eth.L1BlockRef{}) {
 		return // if no L1 information is finalized yet, then skip this
 	}
 	// default to keep the same finalized block
@@ -200,6 +221,7 @@ func (eq *EngineQueue) tryFinalizeL2() {
 	for _, fd := range eq.finalityData {
 		if fd.L2Block.Number > finalizedL2.Number && fd.L1Block.Number <= eq.finalizedL1.Number {
 			finalizedL2 = fd.L2Block
+			eq.needForkchoiceUpdate = true
 		}
 	}
 	eq.finalized = finalizedL2
@@ -214,11 +236,11 @@ func (eq *EngineQueue) postProcessSafeL2() {
 		eq.finalityData = append(eq.finalityData[:0], eq.finalityData[1:finalityLookback]...)
 	}
 	// remember the last L2 block that we fully derived from the given finality data
-	if len(eq.finalityData) == 0 || eq.finalityData[len(eq.finalityData)-1].L1Block.Number < eq.prev.Origin().Number {
+	if len(eq.finalityData) == 0 || eq.finalityData[len(eq.finalityData)-1].L1Block.Number < eq.origin.Number {
 		// append entry for new L1 block
 		eq.finalityData = append(eq.finalityData, FinalityData{
 			L2Block: eq.safeHead,
-			L1Block: eq.prev.Origin().ID(),
+			L1Block: eq.origin.ID(),
 		})
 	} else {
 		// if it's a now L2 block that was derived from the same latest L1 block, then just update the entry
@@ -233,7 +255,7 @@ func (eq *EngineQueue) logSyncProgress(reason string) {
 		"l2_safe", eq.safeHead,
 		"l2_unsafe", eq.unsafeHead,
 		"l2_time", eq.unsafeHead.Time,
-		"l1_derived", eq.prev.Origin(),
+		"l1_derived", eq.origin,
 	)
 }
 

op-node/rollup/derive/engine_queue_test.go

@@ -250,7 +250,7 @@ func TestEngineQueue_Finalize(t *testing.T) {
 	eq.postProcessSafeL2()
 
 	// let's finalize D (current L1), from which we fully derived C1 (it was safe head), but not D0 (included in E)
-	eq.Finalize(refD.ID())
+	eq.Finalize(refD)
 
 	require.Equal(t, refC1, eq.Finalized(), "C1 was included in finalized D, and should now be finalized")
 

op-node/rollup/derive/pipeline.go

@@ -5,9 +5,10 @@ import (
 	"fmt"
 	"io"
 
+	"github.com/ethereum/go-ethereum/log"
+
 	"github.com/ethereum-optimism/optimism/op-node/eth"
 	"github.com/ethereum-optimism/optimism/op-node/rollup"
-	"github.com/ethereum/go-ethereum/log"
 )
 
 type Metrics interface {
@@ -30,13 +31,14 @@ type ResetableStage interface {
 }
 
 type EngineQueueStage interface {
+	FinalizedL1() eth.L1BlockRef
 	Finalized() eth.L2BlockRef
 	UnsafeL2Head() eth.L2BlockRef
 	SafeL2Head() eth.L2BlockRef
 	Origin() eth.L1BlockRef
 	SetUnsafeHead(head eth.L2BlockRef)
 
-	Finalize(l1Origin eth.BlockID)
+	Finalize(l1Origin eth.L1BlockRef)
 	AddSafeAttributes(attributes *eth.PayloadAttributes)
 	AddUnsafePayload(payload *eth.ExecutionPayload)
 	Step(context.Context) error
@@ -97,14 +99,22 @@ func (dp *DerivationPipeline) Reset() {
 	dp.resetting = 0
 }
 
+// Origin is the L1 block of the inner-most stage of the derivation pipeline,
+// i.e. the L1 chain up to and including this point included and/or produced all the safe L2 blocks.
 func (dp *DerivationPipeline) Origin() eth.L1BlockRef {
 	return dp.eng.Origin()
 }
 
-func (dp *DerivationPipeline) Finalize(l1Origin eth.BlockID) {
+func (dp *DerivationPipeline) Finalize(l1Origin eth.L1BlockRef) {
 	dp.eng.Finalize(l1Origin)
 }
 
+// FinalizedL1 is the L1 finalization of the inner-most stage of the derivation pipeline,
+// i.e. the L1 chain up to and including this point included and/or produced all the finalized L2 blocks.
+func (dp *DerivationPipeline) FinalizedL1() eth.L1BlockRef {
+	return dp.eng.FinalizedL1()
+}
+
 func (dp *DerivationPipeline) Finalized() eth.L2BlockRef {
 	return dp.eng.Finalized()
 }

op-node/rollup/driver/driver.go

@@ -39,6 +39,7 @@ type L2Chain interface {
 	derive.Engine
 	L2BlockRefByLabel(ctx context.Context, label eth.BlockLabel) (eth.L2BlockRef, error)
 	L2BlockRefByHash(ctx context.Context, l2Hash common.Hash) (eth.L2BlockRef, error)
+	L2BlockRefByNumber(ctx context.Context, num uint64) (eth.L2BlockRef, error)
 }
 
 type DerivationPipeline interface {
@@ -46,7 +47,8 @@ type DerivationPipeline interface {
 	Step(ctx context.Context) error
 	SetUnsafeHead(head eth.L2BlockRef)
 	AddUnsafePayload(payload *eth.ExecutionPayload)
-	Finalize(ref eth.BlockID)
+	Finalize(ref eth.L1BlockRef)
+	FinalizedL1() eth.L1BlockRef
 	Finalized() eth.L2BlockRef
 	SafeL2Head() eth.L2BlockRef
 	UnsafeL2Head() eth.L2BlockRef
@@ -92,7 +94,7 @@ func NewDriver(driverCfg *Config, cfg *rollup.Config, l2 L2Chain, l1 L1Chain, ne
 		l1State:          l1State,
 		derivation:       derivationPipeline,
 		idleDerivation:   false,
-		syncStatusReq:    make(chan chan eth.SyncStatus, 10),
+		stateReq:         make(chan chan struct{}),
 		forceReset:       make(chan chan struct{}, 10),
 		config:           cfg,
 		driverConfig:     driverCfg,

op-node/rollup/driver/state.go

@@ -30,8 +30,8 @@ type Driver struct {
 	// When the derivation pipeline is waiting for new data to do anything
 	idleDerivation bool
 
-	// Requests for sync status. Synchronized with event loop to avoid reading an inconsistent sync status.
-	syncStatusReq chan chan eth.SyncStatus
+	// Requests to block the event loop for synchronous execution to avoid reading an inconsistent state
+	stateReq chan chan struct{}
 
 	// Upon receiving a channel in this channel, the derivation pipeline is forced to be reset.
 	// It tells the caller that the reset occurred by closing the passed in channel.
@@ -300,7 +300,7 @@ func (s *Driver) eventLoop() {
 			// no step, justified L1 information does not do anything for L2 derivation or status
 		case newL1Finalized := <-s.l1FinalizedSig:
 			s.l1State.HandleNewL1FinalizedBlock(newL1Finalized)
-			s.derivation.Finalize(newL1Finalized.ID())
+			s.derivation.Finalize(newL1Finalized)
 			reqStep() // we may be able to mark more L2 data as finalized now
 		case <-delayedStepReq:
 			delayedStepReq = nil
@@ -342,16 +342,8 @@ func (s *Driver) eventLoop() {
 				stepAttempts = 0
 				reqStep() // continue with the next step if we can
 			}
-		case respCh := <-s.syncStatusReq:
-			respCh <- eth.SyncStatus{
-				CurrentL1:   s.derivation.Origin(),
-				HeadL1:      s.l1State.L1Head(),
-				SafeL1:      s.l1State.L1Safe(),
-				FinalizedL1: s.l1State.L1Finalized(),
-				UnsafeL2:    s.derivation.UnsafeL2Head(),
-				SafeL2:      s.derivation.SafeL2Head(),
-				FinalizedL2: s.derivation.Finalized(),
-			}
+		case respCh := <-s.stateReq:
+			respCh <- struct{}{}
 		case respCh := <-s.forceReset:
 			s.log.Warn("Derivation pipeline is manually reset")
 			s.derivation.Reset()
@@ -381,18 +373,48 @@ func (s *Driver) ResetDerivationPipeline(ctx context.Context) error {
 	}
 }
 
+// syncStatus returns the current sync status, and should only be called synchronously with
+// the driver event loop to avoid retrieval of an inconsistent status.
+func (s *Driver) syncStatus() *eth.SyncStatus {
+	return &eth.SyncStatus{
+		CurrentL1:          s.derivation.Origin(),
+		CurrentL1Finalized: s.derivation.FinalizedL1(),
+		HeadL1:             s.l1State.L1Head(),
+		SafeL1:             s.l1State.L1Safe(),
+		FinalizedL1:        s.l1State.L1Finalized(),
+		UnsafeL2:           s.derivation.UnsafeL2Head(),
+		SafeL2:             s.derivation.SafeL2Head(),
+		FinalizedL2:        s.derivation.Finalized(),
+	}
+}
+
+// SyncStatus blocks the driver event loop and captures the syncing status.
+// If the event loop is too busy and the context expires, a context error is returned.
 func (s *Driver) SyncStatus(ctx context.Context) (*eth.SyncStatus, error) {
-	respCh := make(chan eth.SyncStatus, 1)
+	wait := make(chan struct{})
 	select {
+	case s.stateReq <- wait:
+		resp := s.syncStatus()
+		<-wait
+		return resp, nil
 	case <-ctx.Done():
 		return nil, ctx.Err()
-	case s.syncStatusReq <- respCh:
-		select {
-		case <-ctx.Done():
-			return nil, ctx.Err()
-		case resp := <-respCh:
-			return &resp, nil
-		}
+	}
+}
+
+// BlockRefWithStatus blocks the driver event loop and captures the syncing status,
+// along with an L2 block reference by number consistent with that same status.
+// If the event loop is too busy and the context expires, a context error is returned.
+func (s *Driver) BlockRefWithStatus(ctx context.Context, num uint64) (eth.L2BlockRef, *eth.SyncStatus, error) {
+	wait := make(chan struct{})
+	select {
+	case s.stateReq <- wait:
+		resp := s.syncStatus()
+		ref, err := s.l2.L2BlockRefByNumber(ctx, num)
+		<-wait
+		return ref, resp, err
+	case <-ctx.Done():
+		return eth.L2BlockRef{}, nil, ctx.Err()
 	}
 }