chanbackup: fix shutdown issue when backuper has not started yet

chanbackup/pubsub.go

@@ -7,6 +7,7 @@ import (
 	"net"
 	"os"
 	"sync"
+	"sync/atomic"
 
 	"github.com/btcsuite/btcd/wire"
 	"github.com/lightningnetwork/lnd/channeldb"
@@ -95,7 +96,12 @@ type ChannelNotifier interface {
 // be used to implement a system that always keeps the multi-chan backup file
 // on disk in a consistent state for safety purposes.
 type SubSwapper struct {
+	// started tracks whether the SubSwapper has been started and ensures
+	// it can only be started once.
 	started sync.Once
+
+	// stopped tracks whether the SubSwapper has been stopped and ensures
+	// it can only be stopped once.
 	stopped sync.Once
 
 	// backupState are the set of SCBs for all open channels we know of.
@@ -115,6 +121,11 @@ type SubSwapper struct {
 
 	quit chan struct{}
 	wg   sync.WaitGroup
+
+	// isActive tracks whether the SubSwapper is active and ready to receive
+	// messages. It is used to prevent manual updates from being sent to the
+	// SubSwapper after it has been stopped or not yet started.
+	isActive atomic.Bool
 }
 
 // NewSubSwapper creates a new instance of the SubSwapper given the starting
@@ -165,6 +176,7 @@ func (s *SubSwapper) Start() error {
 		if err := s.updateBackupFile(); err != nil {
 			startErr = fmt.Errorf("unable to refresh backup "+
 				"file: %v", err)
+
 			return
 		}
 
@@ -181,9 +193,13 @@ func (s *SubSwapper) Stop() error {
 		log.Infof("chanbackup.SubSwapper shutting down...")
 		defer log.Debug("chanbackup.SubSwapper shutdown complete")
 
+		// Mark the SubSwapper as not running.
+		s.isActive.Store(false)
+
 		close(s.quit)
 		s.wg.Wait()
 	})
+
 	return nil
 }
 
@@ -191,6 +207,11 @@ func (s *SubSwapper) Stop() error {
 // are processed in another goroutine. The method waits for the updates to be
 // fully processed and the file to be updated on-disk before returning.
 func (s *SubSwapper) ManualUpdate(singles []Single) error {
+	if !s.isActive.Load() {
+		return fmt.Errorf("swapper is not active, cannot perform " +
+			"manual update")
+	}
+
 	// Create the channel to send an error back. If the update handling
 	// and the subsequent file updating succeeds, nil is sent.
 	// The channel must have capacity of 1 to prevent Swapper blocking.
@@ -300,7 +321,8 @@ func (s *SubSwapper) updateBackupFile(closedChans ...wire.OutPoint) error {
 // backupFileUpdater is the primary goroutine of the SubSwapper which is
 // responsible for listening for changes to the channel, and updating the
 // persistent multi backup state with a new packed multi of the latest channel
-// state.
+// state. Once active, it will process subscription updates and manual updates
+// until the SubSwapper is stopped.
 func (s *SubSwapper) backupUpdater() {
 	// Ensure that once we exit, we'll cancel our active channel
 	// subscription.
@@ -309,6 +331,9 @@ func (s *SubSwapper) backupUpdater() {
 
 	log.Debugf("SubSwapper's backupUpdater is active!")
 
+	// Mark the SubSwapper as active.
+	s.isActive.Store(true)
+
 	for {
 		select {
 		// The channel state has been modified! We'll evaluate all