mapper: send change instead of full update (#2775)

hscontrol/mapper/batcher.go

@@ -88,16 +88,9 @@ func generateMapResponse(nodeID types.NodeID, version tailcfg.CapabilityVersion,
 			// TODO(kradalby): This can potentially be a peer update of the old and new subnet router.
 			mapResp, err = mapper.fullMapResponse(nodeID, version)
 		} else {
-			// CRITICAL FIX: Read actual online status from NodeStore when available,
-			// fall back to deriving from change type for unit tests or when NodeStore is empty
-			var onlineStatus bool
-			if node, found := mapper.state.GetNodeByID(c.NodeID); found && node.IsOnline().Valid() {
-				// Use actual NodeStore status when available (production case)
-				onlineStatus = node.IsOnline().Get()
-			} else {
-				// Fall back to deriving from change type (unit test case or initial setup)
-				onlineStatus = c.Change == change.NodeCameOnline
-			}
+			// Trust the change type for online/offline status to avoid race conditions
+			// between NodeStore updates and change processing
+			onlineStatus := c.Change == change.NodeCameOnline
 
 			mapResp, err = mapper.peerChangedPatchResponse(nodeID, []*tailcfg.PeerChange{
 				{
@@ -108,11 +101,33 @@ func generateMapResponse(nodeID types.NodeID, version tailcfg.CapabilityVersion,
 		}
 
 	case change.NodeNewOrUpdate:
-		mapResp, err = mapper.fullMapResponse(nodeID, version)
+		// If the node is the one being updated, we send a self update that preserves peer information
+		// to ensure the node sees changes to its own properties (e.g., hostname/DNS name changes)
+		// without losing its view of peer status during rapid reconnection cycles
+		if c.IsSelfUpdate(nodeID) {
+			mapResp, err = mapper.selfMapResponse(nodeID, version)
+		} else {
+			mapResp, err = mapper.peerChangeResponse(nodeID, version, c.NodeID)
+		}
 
 	case change.NodeRemove:
 		mapResp, err = mapper.peerRemovedResponse(nodeID, c.NodeID)
 
+	case change.NodeKeyExpiry:
+		// If the node is the one whose key is expiring, we send a "full" self update
+		// as nodes will ignore patch updates about themselves (?).
+		if c.IsSelfUpdate(nodeID) {
+			mapResp, err = mapper.selfMapResponse(nodeID, version)
+			// mapResp, err = mapper.fullMapResponse(nodeID, version)
+		} else {
+			mapResp, err = mapper.peerChangedPatchResponse(nodeID, []*tailcfg.PeerChange{
+				{
+					NodeID:    c.NodeID.NodeID(),
+					KeyExpiry: c.NodeExpiry,
+				},
+			})
+		}
+
 	default:
 		// The following will always hit this:
 		// change.Full, change.Policy

hscontrol/mapper/batcher_test.go

@@ -1028,7 +1028,9 @@ func TestBatcherWorkQueueBatching(t *testing.T) {
 
 			// Add multiple changes rapidly to test batching
 			batcher.AddWork(change.DERPSet)
-			batcher.AddWork(change.KeyExpiry(testNodes[1].n.ID))
+			// Use a valid expiry time for testing since test nodes don't have expiry set
+			testExpiry := time.Now().Add(24 * time.Hour)
+			batcher.AddWork(change.KeyExpiry(testNodes[1].n.ID, testExpiry))
 			batcher.AddWork(change.DERPSet)
 			batcher.AddWork(change.NodeAdded(testNodes[1].n.ID))
 			batcher.AddWork(change.DERPSet)
@@ -1278,7 +1280,9 @@ func TestBatcherWorkerChannelSafety(t *testing.T) {
 
 					// Add node-specific work occasionally
 					if i%10 == 0 {
-						batcher.AddWork(change.KeyExpiry(testNode.n.ID))
+						// Use a valid expiry time for testing since test nodes don't have expiry set
+						testExpiry := time.Now().Add(24 * time.Hour)
+						batcher.AddWork(change.KeyExpiry(testNode.n.ID, testExpiry))
 					}
 
 					// Rapid removal creates race between worker and removal
@@ -1493,7 +1497,9 @@ func TestBatcherConcurrentClients(t *testing.T) {
 					if i%7 == 0 && len(allNodes) > 0 {
 						// Node-specific changes using real nodes
 						node := allNodes[i%len(allNodes)]
-						batcher.AddWork(change.KeyExpiry(node.n.ID))
+						// Use a valid expiry time for testing since test nodes don't have expiry set
+						testExpiry := time.Now().Add(24 * time.Hour)
+						batcher.AddWork(change.KeyExpiry(node.n.ID, testExpiry))
 					}
 
 					// Small delay to allow some batching

hscontrol/mapper/builder.go

@@ -28,6 +28,7 @@ type debugType string
 
 const (
 	fullResponseDebug   debugType = "full"
+	selfResponseDebug   debugType = "self"
 	patchResponseDebug  debugType = "patch"
 	removeResponseDebug debugType = "remove"
 	changeResponseDebug debugType = "change"
@@ -68,24 +69,17 @@ func (b *MapResponseBuilder) WithCapabilityVersion(capVer tailcfg.CapabilityVers
 
 // WithSelfNode adds the requesting node to the response.
 func (b *MapResponseBuilder) WithSelfNode() *MapResponseBuilder {
-	nodeView, ok := b.mapper.state.GetNodeByID(b.nodeID)
+	nv, ok := b.mapper.state.GetNodeByID(b.nodeID)
 	if !ok {
 		b.addError(errors.New("node not found"))
 		return b
 	}
 
-	// Always use batcher's view of online status for self node
-	// The batcher respects grace periods for logout scenarios
-	node := nodeView.AsStruct()
-	// if b.mapper.batcher != nil {
-	// 	node.IsOnline = ptr.To(b.mapper.batcher.IsConnected(b.nodeID))
-	// }
-
 	_, matchers := b.mapper.state.Filter()
 	tailnode, err := tailNode(
-		node.View(), b.capVer, b.mapper.state,
+		nv, b.capVer, b.mapper.state,
 		func(id types.NodeID) []netip.Prefix {
-			return policy.ReduceRoutes(node.View(), b.mapper.state.GetNodePrimaryRoutes(id), matchers)
+			return policy.ReduceRoutes(nv, b.mapper.state.GetNodePrimaryRoutes(id), matchers)
 		},
 		b.mapper.cfg)
 	if err != nil {

hscontrol/mapper/mapper.go

@@ -158,6 +158,26 @@ func (m *mapper) fullMapResponse(
 		Build()
 }
 
+func (m *mapper) selfMapResponse(
+	nodeID types.NodeID,
+	capVer tailcfg.CapabilityVersion,
+) (*tailcfg.MapResponse, error) {
+	ma, err := m.NewMapResponseBuilder(nodeID).
+		WithDebugType(selfResponseDebug).
+		WithCapabilityVersion(capVer).
+		WithSelfNode().
+		Build()
+	if err != nil {
+		return nil, err
+	}
+
+	// Set the peers to nil, to ensure the node does not think
+	// its getting a new list.
+	ma.Peers = nil
+
+	return ma, err
+}
+
 func (m *mapper) derpMapResponse(
 	nodeID types.NodeID,
 ) (*tailcfg.MapResponse, error) {
@@ -190,7 +210,6 @@ func (m *mapper) peerChangeResponse(
 	return m.NewMapResponseBuilder(nodeID).
 		WithDebugType(changeResponseDebug).
 		WithCapabilityVersion(capVer).
-		WithSelfNode().
 		WithUserProfiles(peers).
 		WithPeerChanges(peers).
 		Build()