multi: prevent nil panics in stop methods.

With this PR we might call the stop method even when the start
method of a subsystem did not successfully finish therefore we
need to make sure we guard the stop methods for potential panics
if some variables are not initialized in the contructors of the
subsystems.

chainntnfs/bitcoindnotify/bitcoind.go

@@ -151,7 +151,12 @@ func (b *BitcoindNotifier) Stop() error {
 
 		close(epochClient.epochChan)
 	}
-	b.txNotifier.TearDown()
+
+	// The txNotifier is only initialized in the start method therefore we
+	// need to make sure we don't access a nil pointer here.
+	if b.txNotifier != nil {
+		b.txNotifier.TearDown()
+	}
 
 	// Stop the mempool notifier.
 	b.memNotifier.TearDown()

chainntnfs/neutrinonotify/neutrino.go

@@ -152,7 +152,12 @@ func (n *NeutrinoNotifier) Stop() error {
 
 		close(epochClient.epochChan)
 	}
-	n.txNotifier.TearDown()
+
+	// The txNotifier is only initialized in the start method therefore we
+	// need to make sure we don't access a nil pointer here.
+	if n.txNotifier != nil {
+		n.txNotifier.TearDown()
+	}
 
 	return nil
 }

chanfitness/chaneventstore.go

@@ -226,7 +226,10 @@ func (c *ChannelEventStore) Stop() error {
 
 	// Stop the ticker after the goroutine reading from it has exited, to
 	// avoid a race.
-	c.cfg.FlapCountTicker.Stop()
+	if c.cfg.FlapCountTicker == nil {
+		return fmt.Errorf("ChannelEventStore FlapCountTicker not " +
+			"initialized")
+	}
 
 	log.Debugf("ChannelEventStore shutdown complete")
 

discovery/gossiper.go

@@ -753,7 +753,11 @@ func (d *AuthenticatedGossiper) stop() {
 	log.Debug("Authenticated Gossiper is stopping")
 	defer log.Debug("Authenticated Gossiper stopped")
 
-	d.blockEpochs.Cancel()
+	// `blockEpochs` is only initialized in the start routine so we make
+	// sure we don't panic here.
+	if d.blockEpochs != nil {
+		d.blockEpochs.Cancel()
+	}
 
 	d.syncMgr.Stop()
 

htlcswitch/interceptable_switch.go

@@ -242,7 +242,11 @@ func (s *InterceptableSwitch) Stop() error {
 	close(s.quit)
 	s.wg.Wait()
 
-	s.blockEpochStream.Cancel()
+	// We need to check whether the start routine run and initialized the
+	// `blockEpochStream`.
+	if s.blockEpochStream != nil {
+		s.blockEpochStream.Cancel()
+	}
 
 	log.Debug("InterceptableSwitch shutdown complete")
 

invoices/invoiceregistry.go

@@ -261,6 +261,11 @@ func (i *InvoiceRegistry) Stop() error {
 	log.Info("InvoiceRegistry shutting down...")
 	defer log.Debug("InvoiceRegistry shutdown complete")
 
+	if i.expiryWatcher == nil {
+		return fmt.Errorf("InvoiceRegistry expiryWatcher not " +
+			"initialized")
+	}
+
 	i.expiryWatcher.Stop()
 
 	close(i.quit)

server.go

@@ -2107,6 +2107,9 @@ func (s *server) Start() error {
 			}
 		}
 
+		// chanSubSwapper must be started after the `channelNotifier`
+		// because it depends on channel events as a synchronization
+		// point.
 		cleanup = cleanup.add(s.chanSubSwapper.Stop)
 		if err := s.chanSubSwapper.Start(); err != nil {
 			startErr = err