app: fix sigint hanging

When the node notifier was replaced with batcher, we removed
its closing, but forgot to add the batchers so it was never
stopping node connections and waiting forever.

Fixes #2751

Signed-off-by: Kristoffer Dalby <kristoffer@tailscale.com>

hscontrol/mapper/batcher_lockfree.go

@@ -153,7 +153,7 @@ func (b *LockFreeBatcher) Start() {
 func (b *LockFreeBatcher) Close() {
 	if b.cancel != nil {
 		b.cancel()
-		b.cancel = nil // Prevent multiple calls
+		b.cancel = nil
 	}
 
 	// Only close workCh once
@@ -163,10 +163,15 @@ func (b *LockFreeBatcher) Close() {
 	default:
 		close(b.workCh)
 	}
+
+	// Close the underlying channels supplying the data to the clients.
+	b.nodes.Range(func(nodeID types.NodeID, conn *multiChannelNodeConn) bool {
+		conn.close()
+		return true
+	})
 }
 
 func (b *LockFreeBatcher) doWork() {
-
 	for i := range b.workers {
 		go b.worker(i + 1)
 	}
@@ -184,17 +189,18 @@ func (b *LockFreeBatcher) doWork() {
 			// Clean up nodes that have been offline for too long
 			b.cleanupOfflineNodes()
 		case <-b.ctx.Done():
+			log.Info().Msg("batcher context done, stopping to feed workers")
 			return
 		}
 	}
 }
 
 func (b *LockFreeBatcher) worker(workerID int) {
-
 	for {
 		select {
 		case w, ok := <-b.workCh:
 			if !ok {
+				log.Debug().Int("worker.id", workerID).Msgf("worker channel closing, shutting down worker %d", workerID)
 				return
 			}
 
@@ -213,7 +219,7 @@ func (b *LockFreeBatcher) worker(workerID int) {
 					if result.err != nil {
 						b.workErrors.Add(1)
 						log.Error().Err(result.err).
-							Int("workerID", workerID).
+							Int("worker.id", workerID).
 							Uint64("node.id", w.nodeID.Uint64()).
 							Str("change", w.c.Change.String()).
 							Msg("failed to generate map response for synchronous work")
@@ -223,7 +229,7 @@ func (b *LockFreeBatcher) worker(workerID int) {
 
 					b.workErrors.Add(1)
 					log.Error().Err(result.err).
-						Int("workerID", workerID).
+						Int("worker.id", workerID).
 						Uint64("node.id", w.nodeID.Uint64()).
 						Msg("node not found for synchronous work")
 				}
@@ -248,13 +254,14 @@ func (b *LockFreeBatcher) worker(workerID int) {
 				if err != nil {
 					b.workErrors.Add(1)
 					log.Error().Err(err).
-						Int("workerID", workerID).
+						Int("worker.id", workerID).
 						Uint64("node.id", w.c.NodeID.Uint64()).
 						Str("change", w.c.Change.String()).
 						Msg("failed to apply change")
 				}
 			}
 		case <-b.ctx.Done():
+			log.Debug().Int("workder.id", workerID).Msg("batcher context is done, exiting worker")
 			return
 		}
 	}
@@ -336,6 +343,7 @@ func (b *LockFreeBatcher) processBatchedChanges() {
 }
 
 // cleanupOfflineNodes removes nodes that have been offline for too long to prevent memory leaks.
+// TODO(kradalby): reevaluate if we want to keep this.
 func (b *LockFreeBatcher) cleanupOfflineNodes() {
 	cleanupThreshold := 15 * time.Minute
 	now := time.Now()
@@ -477,6 +485,15 @@ func newMultiChannelNodeConn(id types.NodeID, mapper *mapper) *multiChannelNodeC
 	}
 }
 
+func (mc *multiChannelNodeConn) close() {
+	mc.mutex.Lock()
+	defer mc.mutex.Unlock()
+
+	for _, conn := range mc.connections {
+		close(conn.c)
+	}
+}
+
 // addConnection adds a new connection.
 func (mc *multiChannelNodeConn) addConnection(entry *connectionEntry) {
 	mutexWaitStart := time.Now()
@@ -530,6 +547,10 @@ func (mc *multiChannelNodeConn) getActiveConnectionCount() int {
 
 // send broadcasts data to all active connections for the node.
 func (mc *multiChannelNodeConn) send(data *tailcfg.MapResponse) error {
+	if data == nil {
+		return nil
+	}
+
 	mc.mutex.Lock()
 	defer mc.mutex.Unlock()
 
@@ -597,6 +618,10 @@ func (mc *multiChannelNodeConn) send(data *tailcfg.MapResponse) error {
 
 // send sends data to a single connection entry with timeout-based stale connection detection.
 func (entry *connectionEntry) send(data *tailcfg.MapResponse) error {
+	if data == nil {
+		return nil
+	}
+
 	// Use a short timeout to detect stale connections where the client isn't reading the channel.
 	// This is critical for detecting Docker containers that are forcefully terminated
 	// but still have channels that appear open.

hscontrol/mapper/batcher_test.go

@@ -1361,7 +1361,11 @@ func TestBatcherConcurrentClients(t *testing.T) {
 				go func(nodeID types.NodeID, channel chan *tailcfg.MapResponse) {
 					for {
 						select {
-						case data := <-channel:
+						case data, ok := <-channel:
+							if !ok {
+								// Channel was closed, exit gracefully
+								return
+							}
 							if valid, reason := validateUpdateContent(data); valid {
 								tracker.recordUpdate(
 									nodeID,
@@ -1419,24 +1423,28 @@ func TestBatcherConcurrentClients(t *testing.T) {
 							ch := make(chan *tailcfg.MapResponse, SMALL_BUFFER_SIZE)
 
 							churningChannelsMutex.Lock()
-
 							churningChannels[nodeID] = ch
-
 							churningChannelsMutex.Unlock()
+
 							batcher.AddNode(nodeID, ch, tailcfg.CapabilityVersion(100))
 
 							// Consume updates to prevent blocking
 							go func() {
 								for {
 									select {
-									case data := <-ch:
+									case data, ok := <-ch:
+										if !ok {
+											// Channel was closed, exit gracefully
+											return
+										}
 										if valid, _ := validateUpdateContent(data); valid {
 											tracker.recordUpdate(
 												nodeID,
 												1,
 											) // Use 1 as update size since we have MapResponse
 										}
-									case <-time.After(20 * time.Millisecond):
+									case <-time.After(500 * time.Millisecond):
+										// Longer timeout to prevent premature exit during heavy load
 										return
 									}
 								}