Merge pull request #2060 from OffchainLabs/allow-empty-forwarder

Allow the TxForwarder to be empty

execution/gethexec/forwarder.go

@@ -151,7 +151,7 @@ func (f *TxForwarder) PublishTransaction(inctx context.Context, tx *types.Transa
 		if err == nil || !f.tryNewForwarderErrors.MatchString(err.Error()) {
 			return err
 		}
-		log.Info("error forwarding transaction to a backup target", "target", f.targets[pos], "err", err)
+		log.Warn("error forwarding transaction to a backup target", "target", f.targets[pos], "err", err)
 	}
 	return errors.New("failed to publish transaction to any of the forwarding targets")
 }
@@ -161,7 +161,9 @@ const maxHealthTimeout = 10 * time.Second
 
 // CheckHealth returns health of the highest priority forwarding target
 func (f *TxForwarder) CheckHealth(inctx context.Context) error {
-	if !f.enabled.Load() {
+	// If f.enabled is true, len(f.rpcClients) should always be greater than zero,
+	// but better safe than sorry.
+	if !f.enabled.Load() || len(f.rpcClients) == 0 {
 		return ErrNoSequencer
 	}
 	f.healthMutex.Lock()
@@ -205,8 +207,6 @@ func (f *TxForwarder) Initialize(inctx context.Context) error {
 	f.targets = targets
 	if len(f.rpcClients) > 0 {
 		f.enabled.Store(true)
-	} else if lastError == nil {
-		return errors.New("no non-empty forwarding targets specified")
 	} else {
 		return lastError
 	}
@@ -232,6 +232,14 @@ func (f *TxForwarder) Started() bool {
 	return true
 }
 
+// Returns the URL of the first forwarding target, or an empty string if none are set.
+func (f *TxForwarder) PrimaryTarget() string {
+	if len(f.targets) == 0 {
+		return ""
+	}
+	return f.targets[0]
+}
+
 type TxDropper struct{}
 
 func NewTxDropper() *TxDropper {

execution/gethexec/sequencer.go

@@ -487,17 +487,17 @@ func (s *Sequencer) CheckHealth(ctx context.Context) error {
 func (s *Sequencer) ForwardTarget() string {
 	s.activeMutex.Lock()
 	defer s.activeMutex.Unlock()
-	if s.forwarder == nil || len(s.forwarder.targets) == 0 {
+	if s.forwarder == nil {
 		return ""
 	}
-	return s.forwarder.targets[0]
+	return s.forwarder.PrimaryTarget()
 }
 
 func (s *Sequencer) ForwardTo(url string) error {
 	s.activeMutex.Lock()
 	defer s.activeMutex.Unlock()
 	if s.forwarder != nil {
-		if len(s.forwarder.targets) > 0 && s.forwarder.targets[0] == url {
+		if s.forwarder.PrimaryTarget() == url {
 			log.Warn("attempted to update sequencer forward target with existing target", "url", url)
 			return nil
 		}