mapper: consolidate builder and connection helpers

hscontrol/mapper/batcher.go

@@ -315,11 +315,7 @@ func (b *Batcher) AddNode(
 	initialMap, err := b.MapResponseFromChange(id, change.FullSelf(id))
 	if err != nil {
 		nlog.Error().Err(err).Msg("initial map generation failed")
-		nodeConn.removeConnectionByChannel(c)
-
-		if !nodeConn.hasActiveConnections() {
-			nodeConn.markDisconnected()
-		}
+		nodeConn.detach(c)
 
 		return fmt.Errorf("generating initial map for node %d: %w", id, err)
 	}
@@ -343,11 +339,7 @@ func (b *Batcher) AddNode(
 		nlog.Error().Err(ErrInitialMapSendTimeout).Msg("initial map send timeout")
 		nlog.Debug().Caller().Dur("timeout.duration", 5*time.Second). //nolint:mnd
 										Msg("initial map send timed out because channel was blocked or receiver not ready")
-		nodeConn.removeConnectionByChannel(c)
-
-		if !nodeConn.hasActiveConnections() {
-			nodeConn.markDisconnected()
-		}
+		nodeConn.detach(c)
 
 		return fmt.Errorf("%w for node %d", ErrInitialMapSendTimeout, id)
 	}

hscontrol/mapper/builder.go

@@ -61,6 +61,16 @@ func (b *MapResponseBuilder) hasErrors() bool {
 	return len(b.errs) > 0
 }
 
+// node looks up the requesting node, recording ErrNodeNotFoundMapper on miss.
+func (b *MapResponseBuilder) node() (types.NodeView, bool) {
+	nv, ok := b.mapper.state.GetNodeByID(b.nodeID)
+	if !ok {
+		b.addError(ErrNodeNotFoundMapper)
+	}
+
+	return nv, ok
+}
+
 // WithCapabilityVersion sets the capability version for the response.
 func (b *MapResponseBuilder) WithCapabilityVersion(capVer tailcfg.CapabilityVersion) *MapResponseBuilder {
 	b.capVer = capVer
@@ -69,9 +79,8 @@ func (b *MapResponseBuilder) WithCapabilityVersion(capVer tailcfg.CapabilityVers
 
 // WithSelfNode adds the requesting node to the response.
 func (b *MapResponseBuilder) WithSelfNode() *MapResponseBuilder {
-	nv, ok := b.mapper.state.GetNodeByID(b.nodeID)
+	nv, ok := b.node()
 	if !ok {
-		b.addError(ErrNodeNotFoundMapper)
 		return b
 	}
 
@@ -136,9 +145,8 @@ func (b *MapResponseBuilder) WithDebugConfig() *MapResponseBuilder {
 
 // WithSSHPolicy adds SSH policy configuration for the requesting node.
 func (b *MapResponseBuilder) WithSSHPolicy() *MapResponseBuilder {
-	node, ok := b.mapper.state.GetNodeByID(b.nodeID)
+	node, ok := b.node()
 	if !ok {
-		b.addError(ErrNodeNotFoundMapper)
 		return b
 	}
 
@@ -155,9 +163,8 @@ func (b *MapResponseBuilder) WithSSHPolicy() *MapResponseBuilder {
 
 // WithDNSConfig adds DNS configuration for the requesting node.
 func (b *MapResponseBuilder) WithDNSConfig() *MapResponseBuilder {
-	node, ok := b.mapper.state.GetNodeByID(b.nodeID)
+	node, ok := b.node()
 	if !ok {
-		b.addError(ErrNodeNotFoundMapper)
 		return b
 	}
 
@@ -168,9 +175,8 @@ func (b *MapResponseBuilder) WithDNSConfig() *MapResponseBuilder {
 
 // WithUserProfiles adds user profiles for the requesting node and given peers.
 func (b *MapResponseBuilder) WithUserProfiles(peers views.Slice[types.NodeView]) *MapResponseBuilder {
-	node, ok := b.mapper.state.GetNodeByID(b.nodeID)
+	node, ok := b.node()
 	if !ok {
-		b.addError(ErrNodeNotFoundMapper)
 		return b
 	}
 
@@ -185,9 +191,8 @@ func (b *MapResponseBuilder) WithUserProfiles(peers views.Slice[types.NodeView])
 // For autogroup:self policies, it returns per-node compiled rules.
 // For global policies, it returns the global filter reduced for this node.
 func (b *MapResponseBuilder) WithPacketFilters() *MapResponseBuilder {
-	node, ok := b.mapper.state.GetNodeByID(b.nodeID)
+	node, ok := b.node()
 	if !ok {
-		b.addError(ErrNodeNotFoundMapper)
 		return b
 	}
 

hscontrol/mapper/mapper.go

@@ -499,15 +499,9 @@ func (m *mapper) filterVisiblePeerPatches(
 		return nil
 	}
 
-	var filtered []*tailcfg.PeerChange
-
-	for _, patch := range patches {
-		if _, vis := visible[patch.NodeID]; vis {
-			filtered = append(filtered, patch)
-		}
-	}
-
-	return filtered
+	return filterByVisible(visible, patches, func(p *tailcfg.PeerChange) tailcfg.NodeID {
+		return p.NodeID
+	})
 }
 
 // filterVisibleNodes restricts a peer slice to the nodes the recipient can see
@@ -524,15 +518,27 @@ func (m *mapper) filterVisibleNodes(
 		return views.SliceOf([]types.NodeView{})
 	}
 
-	var filtered []types.NodeView
+	return views.SliceOf(filterByVisible(visible, peers.AsSlice(), func(p types.NodeView) tailcfg.NodeID {
+		return p.ID().NodeID()
+	}))
+}
 
-	for _, peer := range peers.All() {
-		if _, vis := visible[peer.ID().NodeID()]; vis {
-			filtered = append(filtered, peer)
+// filterByVisible keeps only the items whose key resolves to a NodeID present
+// in the visible set, preserving input order.
+func filterByVisible[T any](
+	visible map[tailcfg.NodeID]struct{},
+	items []T,
+	key func(T) tailcfg.NodeID,
+) []T {
+	var filtered []T
+
+	for _, it := range items {
+		if _, ok := visible[key(it)]; ok {
+			filtered = append(filtered, it)
 		}
 	}
 
-	return views.SliceOf(filtered)
+	return filtered
 }
 
 func writeDebugMapResponse(

hscontrol/mapper/node_conn.go

@@ -183,6 +183,16 @@ func (mc *multiChannelNodeConn) removeConnectionByChannel(c chan<- *tailcfg.MapR
 	return false
 }
 
+// detach removes the connection for the given channel and marks the node
+// disconnected if no active connections remain.
+func (mc *multiChannelNodeConn) detach(c chan<- *tailcfg.MapResponse) {
+	mc.removeConnectionByChannel(c)
+
+	if !mc.hasActiveConnections() {
+		mc.markDisconnected()
+	}
+}
+
 // hasActiveConnections checks if the node has any active connections.
 func (mc *multiChannelNodeConn) hasActiveConnections() bool {
 	mc.mutex.RLock()