Receive latest block hash from admin_stopSequencer

Pass block hash to admin_startSequencer

op-e2e/actions/l2_verifier.go

@@ -113,12 +113,12 @@ func (s *l2VerifierBackend) ResetDerivationPipeline(ctx context.Context) error {
 	return nil
 }
 
-func (s *l2VerifierBackend) StartSequencer(ctx context.Context) error {
+func (s *l2VerifierBackend) StartSequencer(ctx context.Context, blockHash common.Hash) error {
 	return nil
 }
 
-func (s *l2VerifierBackend) StopSequencer(ctx context.Context) error {
-	return errors.New("stopping the L2Verifier sequencer is not supported")
+func (s *l2VerifierBackend) StopSequencer(ctx context.Context) (common.Hash, error) {
+	return common.Hash{}, errors.New("stopping the L2Verifier sequencer is not supported")
 }
 
 func (s *L2Verifier) L2Finalized() eth.L2BlockRef {

op-e2e/system_test.go

@@ -1153,7 +1153,8 @@ func TestStopStartSequencer(t *testing.T) {
 
 	ctx, cancel := context.WithTimeout(context.Background(), 5*time.Second)
 	defer cancel()
-	err = nodeRPC.CallContext(ctx, nil, "admin_stopSequencer")
+	blockHash := common.Hash{}
+	err = nodeRPC.CallContext(ctx, &blockHash, "admin_stopSequencer")
 	require.Nil(t, err, "Error stopping sequencer")
 
 	blockBefore = latestBlock(t, l2Seq)
@@ -1163,7 +1164,7 @@ func TestStopStartSequencer(t *testing.T) {
 
 	ctx, cancel = context.WithTimeout(context.Background(), 5*time.Second)
 	defer cancel()
-	err = nodeRPC.CallContext(ctx, nil, "admin_startSequencer")
+	err = nodeRPC.CallContext(ctx, nil, "admin_startSequencer", blockHash)
 	require.Nil(t, err, "Error starting sequencer")
 
 	blockBefore = latestBlock(t, l2Seq)

op-node/node/api.go

@@ -26,8 +26,8 @@ type driverClient interface {
 	SyncStatus(ctx context.Context) (*eth.SyncStatus, error)
 	BlockRefWithStatus(ctx context.Context, num uint64) (eth.L2BlockRef, *eth.SyncStatus, error)
 	ResetDerivationPipeline(context.Context) error
-	StartSequencer(context.Context) error
-	StopSequencer(context.Context) error
+	StartSequencer(ctx context.Context, blockHash common.Hash) error
+	StopSequencer(context.Context) (common.Hash, error)
 }
 
 type rpcMetrics interface {
@@ -53,13 +53,13 @@ func (n *adminAPI) ResetDerivationPipeline(ctx context.Context) error {
 	return n.dr.ResetDerivationPipeline(ctx)
 }
 
-func (n *adminAPI) StartSequencer(ctx context.Context) error {
+func (n *adminAPI) StartSequencer(ctx context.Context, blockHash common.Hash) error {
 	recordDur := n.m.RecordRPCServerRequest("admin_startSequencer")
 	defer recordDur()
-	return n.dr.StartSequencer(ctx)
+	return n.dr.StartSequencer(ctx, blockHash)
 }
 
-func (n *adminAPI) StopSequencer(ctx context.Context) error {
+func (n *adminAPI) StopSequencer(ctx context.Context) (common.Hash, error) {
 	recordDur := n.m.RecordRPCServerRequest("admin_stopSequencer")
 	defer recordDur()
 	return n.dr.StopSequencer(ctx)

op-node/node/server_test.go

@@ -219,10 +219,10 @@ func (c *mockDriverClient) ResetDerivationPipeline(ctx context.Context) error {
 	return c.Mock.MethodCalled("ResetDerivationPipeline").Get(0).(error)
 }
 
-func (c *mockDriverClient) StartSequencer(ctx context.Context) error {
+func (c *mockDriverClient) StartSequencer(ctx context.Context, blockHash common.Hash) error {
 	return c.Mock.MethodCalled("StartSequencer").Get(0).(error)
 }
 
-func (c *mockDriverClient) StopSequencer(ctx context.Context) error {
-	return c.Mock.MethodCalled("StopSequencer").Get(0).(error)
+func (c *mockDriverClient) StopSequencer(ctx context.Context) (common.Hash, error) {
+	return c.Mock.MethodCalled("StopSequencer").Get(0).(common.Hash), nil
 }

op-node/rollup/driver/driver.go

@@ -97,8 +97,8 @@ func NewDriver(driverCfg *Config, cfg *rollup.Config, l2 L2Chain, l1 L1Chain, ne
 		idleDerivation:   false,
 		stateReq:         make(chan chan struct{}),
 		forceReset:       make(chan chan struct{}, 10),
-		startSequencer:   make(chan chan struct{}, 10),
-		stopSequencer:    make(chan chan struct{}, 10),
+		startSequencer:   make(chan hashAndErrorChannel, 10),
+		stopSequencer:    make(chan chan hashAndError, 10),
 		config:           cfg,
 		driverConfig:     driverCfg,
 		done:             make(chan struct{}),

op-node/rollup/driver/state.go

 package driver
 
 import (
+	"bytes"
 	"context"
 	"encoding/json"
 	"errors"
@@ -9,6 +10,7 @@ import (
 	gosync "sync"
 	"time"
 
+	"github.com/ethereum/go-ethereum/common"
 	"github.com/ethereum/go-ethereum/log"
 
 	"github.com/ethereum-optimism/optimism/op-node/eth"
@@ -42,13 +44,13 @@ type Driver struct {
 	// It tells the caller that the reset occurred by closing the passed in channel.
 	forceReset chan chan struct{}
 
-	// Upon receiving a channel in this channel, the sequencer is started.
-	// It tells the caller that the sequencer started by closing the passed in channel.
-	startSequencer chan chan struct{}
+	// Upon receiving a hash in this channel, the sequencer is started at the given hash.
+	// It tells the caller that the sequencer started by closing the passed in channel (or returning an error).
+	startSequencer chan hashAndErrorChannel
 
 	// Upon receiving a channel in this channel, the sequencer is stopped.
-	// It tells the caller that the sequencer stopped by closing the passed in channel.
-	stopSequencer chan chan struct{}
+	// It tells the caller that the sequencer stopped by returning the latest sequenced L2 block hash.
+	stopSequencer chan chan hashAndError
 
 	// Rollup config: rollup chain configuration
 	config *rollup.Config
@@ -375,15 +377,26 @@ func (s *Driver) eventLoop() {
 			s.derivation.Reset()
 			s.metrics.RecordPipelineReset()
 			close(respCh)
-		case respCh := <-s.startSequencer:
-			s.log.Info("Sequencer has been started")
-			s.driverConfig.SequencerEnabled = true
-			sequencingPlannedOnto = eth.BlockID{}
-			close(respCh)
+		case resp := <-s.startSequencer:
+			unsafeHead := s.derivation.UnsafeL2Head().Hash
+			if s.driverConfig.SequencerEnabled {
+				resp.err <- errors.New("sequencer already running")
+			} else if !bytes.Equal(unsafeHead[:], resp.hash[:]) {
+				resp.err <- fmt.Errorf("block hash does not match: head %s, received %s", unsafeHead.String(), resp.hash.String())
+			} else {
+				s.log.Info("Sequencer has been started")
+				s.driverConfig.SequencerEnabled = true
+				sequencingPlannedOnto = eth.BlockID{}
+				close(resp.err)
+			}
 		case respCh := <-s.stopSequencer:
-			s.log.Warn("Sequencer has been stopped")
-			s.driverConfig.SequencerEnabled = false
-			close(respCh)
+			if !s.driverConfig.SequencerEnabled {
+				respCh <- hashAndError{err: errors.New("sequencer not running")}
+			} else {
+				s.log.Warn("Sequencer has been stopped")
+				s.driverConfig.SequencerEnabled = false
+				respCh <- hashAndError{hash: s.derivation.UnsafeL2Head().Hash}
+			}
 		case <-s.done:
 			return
 		}
@@ -408,32 +421,35 @@ func (s *Driver) ResetDerivationPipeline(ctx context.Context) error {
 	}
 }
 
-func (s *Driver) StartSequencer(ctx context.Context) error {
-	respCh := make(chan struct{}, 1)
+func (s *Driver) StartSequencer(ctx context.Context, blockHash common.Hash) error {
+	h := hashAndErrorChannel{
+		hash: blockHash,
+		err:  make(chan error, 1),
+	}
 	select {
 	case <-ctx.Done():
 		return ctx.Err()
-	case s.startSequencer <- respCh:
+	case s.startSequencer <- h:
 		select {
 		case <-ctx.Done():
 			return ctx.Err()
-		case <-respCh:
-			return nil
+		case e := <-h.err:
+			return e
 		}
 	}
 }
 
-func (s *Driver) StopSequencer(ctx context.Context) error {
-	respCh := make(chan struct{}, 1)
+func (s *Driver) StopSequencer(ctx context.Context) (common.Hash, error) {
+	respCh := make(chan hashAndError, 1)
 	select {
 	case <-ctx.Done():
-		return ctx.Err()
+		return common.Hash{}, ctx.Err()
 	case s.stopSequencer <- respCh:
 		select {
 		case <-ctx.Done():
-			return ctx.Err()
-		case <-respCh:
-			return nil
+			return common.Hash{}, ctx.Err()
+		case he := <-respCh:
+			return he.hash, he.err
 		}
 	}
 }
@@ -502,3 +518,13 @@ func (s *Driver) snapshot(event string) {
 		"l2Safe", deferJSONString{s.derivation.SafeL2Head()},
 		"l2FinalizedHead", deferJSONString{s.derivation.Finalized()})
 }
+
+type hashAndError struct {
+	hash common.Hash
+	err  error
+}
+
+type hashAndErrorChannel struct {
+	hash common.Hash
+	err  chan error
+}