op-e2e: Proof of concept for time travelling L1

op-e2e/fakepos.go

+package op_e2e
+
+import (
+	"time"
+
+	"github.com/ethereum-optimism/optimism/op-service/clock"
+	"github.com/ethereum/go-ethereum"
+	"github.com/ethereum/go-ethereum/beacon/engine"
+	"github.com/ethereum/go-ethereum/common"
+	"github.com/ethereum/go-ethereum/eth"
+	"github.com/ethereum/go-ethereum/eth/catalyst"
+	"github.com/ethereum/go-ethereum/event"
+	"github.com/ethereum/go-ethereum/log"
+)
+
+// fakePoS is a testing-only utility to attach to Geth,
+// to build a fake proof-of-stake L1 chain with fixed block time and basic lagging safe/finalized blocks.
+type fakePoS struct {
+	clock     clock.Clock
+	eth       *eth.Ethereum
+	log       log.Logger
+	blockTime uint64
+
+	finalizedDistance uint64
+	safeDistance      uint64
+
+	engineAPI *catalyst.ConsensusAPI
+	sub       ethereum.Subscription
+}
+
+func (f *fakePoS) Start() error {
+	if advancing, ok := f.clock.(*clock.AdvancingClock); ok {
+		advancing.Start()
+	}
+	f.sub = event.NewSubscription(func(quit <-chan struct{}) error {
+		// poll every half a second: enough to catch up with any block time when ticks are missed
+		t := f.clock.NewTicker(time.Second / 2)
+		for {
+			select {
+			case now := <-t.Ch():
+				chain := f.eth.BlockChain()
+				head := chain.CurrentBlock()
+				finalized := chain.CurrentFinalBlock()
+				if finalized == nil { // fallback to genesis if nothing is finalized
+					finalized = chain.Genesis().Header()
+				}
+				safe := chain.CurrentSafeBlock()
+				if safe == nil { // fallback to finalized if nothing is safe
+					safe = finalized
+				}
+				if head.Number.Uint64() > f.finalizedDistance { // progress finalized block, if we can
+					finalized = f.eth.BlockChain().GetHeaderByNumber(head.Number.Uint64() - f.finalizedDistance)
+				}
+				if head.Number.Uint64() > f.safeDistance { // progress safe block, if we can
+					safe = f.eth.BlockChain().GetHeaderByNumber(head.Number.Uint64() - f.safeDistance)
+				}
+				// start building the block as soon as we are past the current head time
+				if head.Time >= uint64(now.Unix()) {
+					continue
+				}
+				newBlockTime := head.Time + f.blockTime
+				if time.Unix(int64(newBlockTime), 0).Add(5 * time.Minute).Before(f.clock.Now()) {
+					// We're a long way behind, let's skip some blocks...
+					newBlockTime = uint64(f.clock.Now().Unix())
+				}
+				res, err := f.engineAPI.ForkchoiceUpdatedV1(engine.ForkchoiceStateV1{
+					HeadBlockHash:      head.Hash(),
+					SafeBlockHash:      safe.Hash(),
+					FinalizedBlockHash: finalized.Hash(),
+				}, &engine.PayloadAttributes{
+					Timestamp:             newBlockTime,
+					Random:                common.Hash{},
+					SuggestedFeeRecipient: head.Coinbase,
+				})
+				if err != nil {
+					f.log.Error("failed to start building L1 block", "err", err)
+					continue
+				}
+				if res.PayloadID == nil {
+					f.log.Error("failed to start block building", "res", res)
+					continue
+				}
+				// wait with sealing, if we are not behind already
+				delay := time.Unix(int64(newBlockTime), 0).Sub(f.clock.Now())
+				tim := f.clock.NewTimer(delay)
+				select {
+				case <-tim.Ch():
+					// no-op
+				case <-quit:
+					tim.Stop()
+					return nil
+				}
+				payload, err := f.engineAPI.GetPayloadV1(*res.PayloadID)
+				if err != nil {
+					f.log.Error("failed to finish building L1 block", "err", err)
+					continue
+				}
+				if _, err := f.engineAPI.NewPayloadV1(*payload); err != nil {
+					f.log.Error("failed to insert built L1 block", "err", err)
+					continue
+				}
+				if _, err := f.engineAPI.ForkchoiceUpdatedV1(engine.ForkchoiceStateV1{
+					HeadBlockHash:      payload.BlockHash,
+					SafeBlockHash:      safe.Hash(),
+					FinalizedBlockHash: finalized.Hash(),
+				}, nil); err != nil {
+					f.log.Error("failed to make built L1 block canonical", "err", err)
+					continue
+				}
+			case <-quit:
+				return nil
+			}
+		}
+	})
+	return nil
+}
+
+func (f *fakePoS) Stop() error {
+	f.sub.Unsubscribe()
+	if advancing, ok := f.clock.(*clock.AdvancingClock); ok {
+		advancing.Stop()
+	}
+	return nil
+}

op-e2e/faultproof_test.go

+package op_e2e
+
+import (
+	"context"
+	"testing"
+	"time"
+
+	"github.com/ethereum-optimism/optimism/op-e2e/e2eutils"
+	"github.com/stretchr/testify/require"
+)
+
+func TestTimeTravel(t *testing.T) {
+	InitParallel(t)
+
+	cfg := DefaultSystemConfig(t)
+	delete(cfg.Nodes, "verifier")
+	cfg.SupportL1TimeTravel = true
+	sys, err := cfg.Start()
+	require.Nil(t, err, "Error starting up system")
+	defer sys.Close()
+
+	l1Client := sys.Clients["l1"]
+	preTravel, err := l1Client.BlockByNumber(context.Background(), nil)
+	require.NoError(t, err)
+
+	sys.TimeTravelClock.AdvanceTime(24 * time.Hour)
+
+	// Check that the L1 chain reaches the new time reasonably quickly (ie without taking a week)
+	// It should be able to jump straight to the new time with just a single block
+	ctx, cancel := context.WithTimeout(context.Background(), 3*time.Minute)
+	defer cancel()
+	err = e2eutils.WaitFor(ctx, time.Second, func() (bool, error) {
+		postTravel, err := l1Client.BlockByNumber(context.Background(), nil)
+		if err != nil {
+			return false, err
+		}
+		diff := time.Duration(postTravel.Time()-preTravel.Time()) * time.Second
+		return diff.Hours() > 23, nil
+	})
+	require.NoError(t, err)
+}

op-e2e/geth.go

@@ -9,9 +9,9 @@ import (
 	"time"
 
 	"github.com/ethereum-optimism/optimism/op-node/rollup/derive"
+	"github.com/ethereum-optimism/optimism/op-service/clock"
 	"github.com/ethereum/go-ethereum"
 	"github.com/ethereum/go-ethereum/accounts/keystore"
-	"github.com/ethereum/go-ethereum/beacon/engine"
 	"github.com/ethereum/go-ethereum/cmd/utils"
 	"github.com/ethereum/go-ethereum/common"
 	"github.com/ethereum/go-ethereum/core"
@@ -21,7 +21,6 @@ import (
 	"github.com/ethereum/go-ethereum/eth/ethconfig"
 	"github.com/ethereum/go-ethereum/eth/tracers"
 	"github.com/ethereum/go-ethereum/ethclient"
-	"github.com/ethereum/go-ethereum/event"
 	"github.com/ethereum/go-ethereum/log"
 	"github.com/ethereum/go-ethereum/miner"
 	"github.com/ethereum/go-ethereum/node"
@@ -110,7 +109,7 @@ func waitForBlock(number *big.Int, client *ethclient.Client, timeout time.Durati
 	}
 }
 
-func initL1Geth(cfg *SystemConfig, genesis *core.Genesis, opts ...GethOption) (*node.Node, *eth.Ethereum, error) {
+func initL1Geth(cfg *SystemConfig, genesis *core.Genesis, c clock.Clock, opts ...GethOption) (*node.Node, *eth.Ethereum, error) {
 	ethConfig := &ethconfig.Config{
 		NetworkId: cfg.DeployConfig.L1ChainID,
 		Genesis:   genesis,
@@ -134,6 +133,7 @@ func initL1Geth(cfg *SystemConfig, genesis *core.Genesis, opts ...GethOption) (*
 
 	// Instead of running a whole beacon node, we run this fake-proof-of-stake sidecar that sequences L1 blocks using the Engine API.
 	l1Node.RegisterLifecycle(&fakePoS{
+		clock:     c,
 		eth:       l1Eth,
 		log:       log.Root(), // geth logger is global anyway. Would be nice to replace with a local logger though.
 		blockTime: cfg.DeployConfig.L1BlockTime,
@@ -146,104 +146,6 @@ func initL1Geth(cfg *SystemConfig, genesis *core.Genesis, opts ...GethOption) (*
 	return l1Node, l1Eth, nil
 }
 
-// fakePoS is a testing-only utility to attach to Geth,
-// to build a fake proof-of-stake L1 chain with fixed block time and basic lagging safe/finalized blocks.
-type fakePoS struct {
-	eth       *eth.Ethereum
-	log       log.Logger
-	blockTime uint64
-
-	finalizedDistance uint64
-	safeDistance      uint64
-
-	engineAPI *catalyst.ConsensusAPI
-	sub       ethereum.Subscription
-}
-
-func (f *fakePoS) Start() error {
-	f.sub = event.NewSubscription(func(quit <-chan struct{}) error {
-		// poll every half a second: enough to catch up with any block time when ticks are missed
-		t := time.NewTicker(time.Second / 2)
-		for {
-			select {
-			case now := <-t.C:
-				chain := f.eth.BlockChain()
-				head := chain.CurrentBlock()
-				finalized := chain.CurrentFinalBlock()
-				if finalized == nil { // fallback to genesis if nothing is finalized
-					finalized = chain.Genesis().Header()
-				}
-				safe := chain.CurrentSafeBlock()
-				if safe == nil { // fallback to finalized if nothing is safe
-					safe = finalized
-				}
-				if head.Number.Uint64() > f.finalizedDistance { // progress finalized block, if we can
-					finalized = f.eth.BlockChain().GetHeaderByNumber(head.Number.Uint64() - f.finalizedDistance)
-				}
-				if head.Number.Uint64() > f.safeDistance { // progress safe block, if we can
-					safe = f.eth.BlockChain().GetHeaderByNumber(head.Number.Uint64() - f.safeDistance)
-				}
-				// start building the block as soon as we are past the current head time
-				if head.Time >= uint64(now.Unix()) {
-					continue
-				}
-				res, err := f.engineAPI.ForkchoiceUpdatedV1(engine.ForkchoiceStateV1{
-					HeadBlockHash:      head.Hash(),
-					SafeBlockHash:      safe.Hash(),
-					FinalizedBlockHash: finalized.Hash(),
-				}, &engine.PayloadAttributes{
-					Timestamp:             head.Time + f.blockTime,
-					Random:                common.Hash{},
-					SuggestedFeeRecipient: head.Coinbase,
-				})
-				if err != nil {
-					f.log.Error("failed to start building L1 block", "err", err)
-					continue
-				}
-				if res.PayloadID == nil {
-					f.log.Error("failed to start block building", "res", res)
-					continue
-				}
-				// wait with sealing, if we are not behind already
-				delay := time.Until(time.Unix(int64(head.Time+f.blockTime), 0))
-				tim := time.NewTimer(delay)
-				select {
-				case <-tim.C:
-					// no-op
-				case <-quit:
-					tim.Stop()
-					return nil
-				}
-				payload, err := f.engineAPI.GetPayloadV1(*res.PayloadID)
-				if err != nil {
-					f.log.Error("failed to finish building L1 block", "err", err)
-					continue
-				}
-				if _, err := f.engineAPI.NewPayloadV1(*payload); err != nil {
-					f.log.Error("failed to insert built L1 block", "err", err)
-					continue
-				}
-				if _, err := f.engineAPI.ForkchoiceUpdatedV1(engine.ForkchoiceStateV1{
-					HeadBlockHash:      payload.BlockHash,
-					SafeBlockHash:      safe.Hash(),
-					FinalizedBlockHash: finalized.Hash(),
-				}, nil); err != nil {
-					f.log.Error("failed to make built L1 block canonical", "err", err)
-					continue
-				}
-			case <-quit:
-				return nil
-			}
-		}
-	})
-	return nil
-}
-
-func (f *fakePoS) Stop() error {
-	f.sub.Unsubscribe()
-	return nil
-}
-
 func defaultNodeConfig(name string, jwtPath string) *node.Config {
 	return &node.Config{
 		Name:        name,

op-e2e/setup.go

@@ -241,6 +241,9 @@ type SystemConfig struct {
 
 	// Target L1 tx size for the batcher transactions
 	BatcherTargetL1TxSizeBytes uint64
+
+	// SupportL1TimeTravel determines if the L1 node supports quickly skipping forward in time
+	SupportL1TimeTravel bool
 }
 
 type System struct {
@@ -258,6 +261,13 @@ type System struct {
 	L2OutputSubmitter *l2os.L2OutputSubmitter
 	BatchSubmitter    *bss.BatchSubmitter
 	Mocknet           mocknet.Mocknet
+
+	// TimeTravelClock is nil unless SystemConfig.SupportL1TimeTravel was set to true
+	// It provides access to the clock instance used by the L1 node. Calling TimeTravelClock.AdvanceBy
+	// allows tests to quickly time travel L1 into the future.
+	// Note that this time travel may occur in a single block, creating a very large difference in the Time
+	// on sequential blocks.
+	TimeTravelClock *clock.AdvancingClock
 }
 
 func (sys *System) NodeEndpoint(name string) string {
@@ -339,6 +349,12 @@ func (cfg SystemConfig) Start(_opts ...SystemConfigOption) (*System, error) {
 		}
 	}()
 
+	c := clock.SystemClock
+	if cfg.SupportL1TimeTravel {
+		sys.TimeTravelClock = clock.NewAdvancingClock(100 * time.Millisecond)
+		c = sys.TimeTravelClock
+	}
+
 	l1Genesis, err := genesis.BuildL1DeveloperGenesis(cfg.DeployConfig)
 	if err != nil {
 		return nil, err
@@ -412,7 +428,7 @@ func (cfg SystemConfig) Start(_opts ...SystemConfigOption) (*System, error) {
 	sys.RollupConfig = &defaultConfig
 
 	// Initialize nodes
-	l1Node, l1Backend, err := initL1Geth(&cfg, l1Genesis, cfg.GethOptions["l1"]...)
+	l1Node, l1Backend, err := initL1Geth(&cfg, l1Genesis, c, cfg.GethOptions["l1"]...)
 	if err != nil {
 		return nil, err
 	}

op-service/clock/advancing.go

+package clock
+
+import (
+	"sync/atomic"
+	"time"
+)
+
+type AdvancingClock struct {
+	*DeterministicClock
+	systemTime   Clock
+	ticker       Ticker
+	advanceEvery time.Duration
+	quit         chan interface{}
+	running      atomic.Bool
+
+	lastTick time.Time
+}
+
+// NewAdvancingClock creates a clock that, when started, advances at the same rate as the system clock but
+// can also be advanced arbitrary amounts using the AdvanceTime method.
+// Unlike the system clock, time does not progress smoothly but only increments when AdvancedTime is called or
+// approximately after advanceEvery duration has elapsed. When advancing based on the system clock, the total time
+// the system clock has advanced is added to the current time, preventing time differences from building up over time.
+func NewAdvancingClock(advanceEvery time.Duration) *AdvancingClock {
+	now := SystemClock.Now()
+	return &AdvancingClock{
+		DeterministicClock: NewDeterministicClock(now),
+		systemTime:         SystemClock,
+		advanceEvery:       advanceEvery,
+		quit:               make(chan interface{}),
+		lastTick:           now,
+	}
+}
+
+func (c *AdvancingClock) Start() {
+	if !c.running.CompareAndSwap(false, true) {
+		// Already running
+		return
+	}
+	c.ticker = c.systemTime.NewTicker(c.advanceEvery)
+	go func() {
+		for {
+			select {
+			case now := <-c.ticker.Ch():
+				c.onTick(now)
+			case <-c.quit:
+				return
+			}
+		}
+	}()
+}
+
+func (c *AdvancingClock) Stop() {
+	if !c.running.CompareAndSwap(true, false) {
+		// Already stopped
+		return
+	}
+	c.quit <- nil
+}
+
+func (c *AdvancingClock) onTick(now time.Time) {
+	if !now.After(c.lastTick) {
+		// Time hasn't progressed for some reason, so do nothing
+		return
+	}
+	// Advance time by however long it has been since the last update.
+	// Ensures we don't drift from system time by more and more over time
+	advanceBy := now.Sub(c.lastTick)
+	c.AdvanceTime(advanceBy)
+	c.lastTick = now
+}

op-service/clock/advancing_test.go

+package clock
+
+import (
+	"testing"
+	"time"
+
+	"github.com/stretchr/testify/require"
+)
+
+func TestAdvancingClock_AdvancesByTimeBetweenTicks(t *testing.T) {
+	clock, realTime := newTestAdvancingClock(1 * time.Second)
+	clock.Start()
+	defer clock.Stop()
+	eventTicker := clock.NewTicker(1 * time.Second)
+
+	start := clock.Now()
+	realTime.AdvanceTime(1 * time.Second)
+	require.Equal(t, start.Add(1*time.Second), <-eventTicker.Ch(), "should trigger events when advancing")
+	require.Equal(t, start.Add(1*time.Second), clock.Now(), "Should advance on single tick")
+
+	start = clock.Now()
+	realTime.AdvanceTime(15 * time.Second)
+	require.Equal(t, start.Add(15*time.Second), <-eventTicker.Ch(), "should trigger events when advancing")
+	require.Equal(t, start.Add(15*time.Second), clock.Now(), "Should advance by time between ticks")
+}
+
+func TestAdvancingClock_Stop(t *testing.T) {
+	clock, realTime := newTestAdvancingClock(1 * time.Second)
+	clock.Start()
+	defer clock.Stop()
+	eventTicker := clock.NewTicker(1 * time.Second)
+
+	// Stop the clock again
+	clock.Stop()
+
+	start := clock.Now()
+	realTime.AdvanceTime(15 * time.Second)
+
+	clock.Start()
+	// Trigger the next tick
+	realTime.AdvanceTime(1 * time.Second)
+	// Time advances by the whole time the clock was stopped
+	// Note: if events were triggered while the clock was stopped, this event would be for the wrong time
+	require.Equal(t, start.Add(16*time.Second), <-eventTicker.Ch(), "should trigger events again after restarting")
+	require.Equal(t, start.Add(16*time.Second), clock.Now(), "Should advance by time between ticks after restarting")
+}
+
+func newTestAdvancingClock(advanceEvery time.Duration) (*AdvancingClock, *DeterministicClock) {
+	systemTime := NewDeterministicClock(time.UnixMilli(1000))
+	clock := &AdvancingClock{
+		DeterministicClock: NewDeterministicClock(time.UnixMilli(5000)),
+		systemTime:         systemTime,
+		advanceEvery:       advanceEvery,
+		quit:               make(chan interface{}),
+		lastTick:           systemTime.Now(),
+	}
+	return clock, systemTime
+}

op-service/clock/deterministic.go

@@ -107,8 +107,12 @@ func (t *ticker) fire(now time.Time) bool {
 	if t.stopped {
 		return false
 	}
-	t.ch <- now
+	// Publish without blocking and only update due time if we publish successfully
+	select {
+	case t.ch <- now:
 		t.nextDue = now.Add(t.period)
+	default:
+	}
 	return true
 }
 

op-service/clock/deterministic_test.go

@@ -2,6 +2,7 @@ package clock
 
 import (
 	"context"
+	"sync"
 	"sync/atomic"
 	"testing"
 	"time"
@@ -156,6 +157,38 @@ func TestNewTicker(t *testing.T) {
 		require.Len(t, ticker.Ch(), 0, "should not fire until due again")
 	})
 
+	t.Run("SkipsFiringWhenProcessingIsSlow", func(t *testing.T) {
+		clock := NewDeterministicClock(time.UnixMilli(1000))
+		ticker := clock.NewTicker(5 * time.Second)
+
+		// Fire once to fill the channel queue
+		clock.AdvanceTime(5 * time.Second)
+		firstEventTime := clock.Now()
+
+		var startProcessing sync.WaitGroup
+		startProcessing.Add(1)
+		processedTicks := make(chan time.Time)
+		go func() {
+			startProcessing.Wait()
+			// Read two events then exit
+			for i := 0; i < 2; i++ {
+				event := <-ticker.Ch()
+				processedTicks <- event
+			}
+		}()
+
+		// Advance time further before processing of events has started
+		// Can't publish any further events to the channel but shouldn't block
+		clock.AdvanceTime(30 * time.Second)
+
+		// Allow processing to start
+		startProcessing.Done()
+		require.Equal(t, firstEventTime, <-processedTicks, "Should process first event")
+
+		clock.AdvanceTime(5 * time.Second)
+		require.Equal(t, clock.Now(), <-processedTicks, "Should skip to latest time")
+	})
+
 	t.Run("StopFiring", func(t *testing.T) {
 		clock := NewDeterministicClock(time.UnixMilli(1000))
 		ticker := clock.NewTicker(5 * time.Second)