tailscale/ipn/ipnlocal/node_backend_test.go

// Copyright (c) Tailscale Inc & contributors
// SPDX-License-Identifier: BSD-3-Clause

package ipnlocal

import (
	"context"
	"errors"
	"maps"
	"net/netip"
	"slices"
	"testing"
	"time"

	"tailscale.com/net/routecheck/peernode"
	"tailscale.com/tailcfg"
	"tailscale.com/tstest"
	"tailscale.com/types/key"
	"tailscale.com/types/netmap"
	"tailscale.com/types/views"
	"tailscale.com/util/dnsname"
	"tailscale.com/util/eventbus"
	"tailscale.com/util/mak"
	"tailscale.com/util/set"
)

func TestNodeBackendReadiness(t *testing.T) {
	nb := newNodeBackend(t.Context(), tstest.WhileTestRunningLogger(t), eventbus.New())

	// The node backend is not ready until [nodeBackend.ready] is called,
	// and [nodeBackend.Wait] should fail with [context.DeadlineExceeded].
	ctx, cancelCtx := context.WithTimeout(context.Background(), 100*time.Millisecond)
	defer cancelCtx()
	if err := nb.Wait(ctx); err != ctx.Err() {
		t.Fatalf("Wait: got %v; want %v", err, ctx.Err())
	}

	// Start a goroutine to wait for the node backend to become ready.
	waitDone := make(chan struct{})
	go func() {
		if err := nb.Wait(context.Background()); err != nil {
			t.Errorf("Wait: got %v; want nil", err)
		}
		close(waitDone)
	}()

	// Call [nodeBackend.ready] to indicate that the node backend is now ready.
	go nb.ready()

	// Once the backend is called, [nodeBackend.Wait] should return immediately without error.
	if err := nb.Wait(context.Background()); err != nil {
		t.Fatalf("Wait: got %v; want nil", err)
	}
	// And any pending waiters should also be unblocked.
	<-waitDone
}

func TestNodeBackendShutdown(t *testing.T) {
	nb := newNodeBackend(t.Context(), tstest.WhileTestRunningLogger(t), eventbus.New())

	shutdownCause := errors.New("test shutdown")

	// Start a goroutine to wait for the node backend to become ready.
	// This test expects it to block until the node backend shuts down
	// and then return the specified shutdown cause.
	waitDone := make(chan struct{})
	go func() {
		if err := nb.Wait(context.Background()); err != shutdownCause {
			t.Errorf("Wait: got %v; want %v", err, shutdownCause)
		}
		close(waitDone)
	}()

	// Call [nodeBackend.shutdown] to indicate that the node backend is shutting down.
	nb.shutdown(shutdownCause)

	// Calling it again is fine, but should not change the shutdown cause.
	nb.shutdown(errors.New("test shutdown again"))

	// After shutdown, [nodeBackend.Wait] should return with the specified shutdown cause.
	if err := nb.Wait(context.Background()); err != shutdownCause {
		t.Fatalf("Wait: got %v; want %v", err, shutdownCause)
	}
	// The context associated with the node backend should also be cancelled
	// and its cancellation cause should match the shutdown cause.
	if err := nb.Context().Err(); !errors.Is(err, context.Canceled) {
		t.Fatalf("Context.Err: got %v; want %v", err, context.Canceled)
	}
	if cause := context.Cause(nb.Context()); cause != shutdownCause {
		t.Fatalf("Cause: got %v; want %v", cause, shutdownCause)
	}
	// And any pending waiters should also be unblocked.
	<-waitDone
}

func TestNodeBackendReadyAfterShutdown(t *testing.T) {
	nb := newNodeBackend(t.Context(), tstest.WhileTestRunningLogger(t), eventbus.New())

	shutdownCause := errors.New("test shutdown")
	nb.shutdown(shutdownCause)
	nb.ready() // Calling ready after shutdown is a no-op, but should not panic, etc.
	if err := nb.Wait(context.Background()); err != shutdownCause {
		t.Fatalf("Wait: got %v; want %v", err, shutdownCause)
	}
}

func TestNodeBackendParentContextCancellation(t *testing.T) {
	ctx, cancelCtx := context.WithCancel(context.Background())
	nb := newNodeBackend(ctx, tstest.WhileTestRunningLogger(t), eventbus.New())

	cancelCtx()

	// Cancelling the parent context should cause [nodeBackend.Wait]
	// to return with [context.Canceled].
	if err := nb.Wait(context.Background()); !errors.Is(err, context.Canceled) {
		t.Fatalf("Wait: got %v; want %v", err, context.Canceled)
	}

	// And the node backend's context should also be cancelled.
	if err := nb.Context().Err(); !errors.Is(err, context.Canceled) {
		t.Fatalf("Context.Err: got %v; want %v", err, context.Canceled)
	}
}

func TestNodeBackendConcurrentReadyAndShutdown(t *testing.T) {
	nb := newNodeBackend(t.Context(), tstest.WhileTestRunningLogger(t), eventbus.New())

	// Calling [nodeBackend.ready] and [nodeBackend.shutdown] concurrently
	// should not cause issues, and [nodeBackend.Wait] should unblock,
	// but the result of [nodeBackend.Wait] is intentionally undefined.
	go nb.ready()
	go nb.shutdown(errors.New("test shutdown"))

	nb.Wait(context.Background())
}

func TestNodeBackendReachability(t *testing.T) {
	for _, tc := range []struct {
		name string

		// Cap sets [tailcfg.NodeAttrClientSideReachability] on the self
		// node.
		//
		// When disabled, the client relies on the control plane sending
		// an accurate peer.Online flag. When enabled, the client
		// ignores peer.Online and is forced to return true.
		cap bool
		// rchk sets [tailcfg.NodeAttrClientSideReachabilityRouteCheck]
		// on the self node.
		//
		// When enabled with [tailcfg.NodeAttrClientSideReachability]
		// above, the client ignores peer.Online and determines whether
		// it can reach the peer node using [routecheck] reports.
		rchk bool

		online bool
		pong   peernode.Reachability
		want   bool
	}{
		{
			name:   "disabled/offline",
			cap:    false,
			online: false,
			want:   false,
		},
		{
			name:   "disabled/online",
			cap:    false,
			online: true,
			want:   true,
		},
		{
			name:   "forced/offline",
			cap:    true,
			rchk:   false,
			online: false,
			want:   true,
		},
		{
			name:   "forced/online",
			cap:    true,
			rchk:   false,
			online: true,
			want:   true,
		},
		{
			name:   "routecheck/offline/needs-probe",
			cap:    true,
			rchk:   true,
			online: false,
			pong:   peernode.Unknown,
			want:   false,
		},
		{
			name:   "routecheck/offline/unreachable",
			cap:    true,
			rchk:   true,
			online: false,
			pong:   peernode.Unreachable,
			want:   false,
		},
		{
			name:   "routecheck/offline/reachable",
			cap:    true,
			rchk:   true,
			online: false,
			pong:   peernode.Reachable,
			want:   true,
		},
		{
			name:   "routecheck/online/needs-probe",
			cap:    true,
			rchk:   true,
			online: true,
			pong:   peernode.Unknown,
			want:   true,
		},
		{
			name:   "routecheck/online/unreachable",
			cap:    true,
			rchk:   true,
			online: true,
			pong:   peernode.Unreachable,
			want:   false,
		},
		{
			name:   "routecheck/online/reachable",
			cap:    true,
			rchk:   true,
			online: true,
			pong:   peernode.Reachable,
			want:   true,
		},
	} {
		t.Run(tc.name, func(t *testing.T) {
			self := &tailcfg.Node{
				ID:       1,
				StableID: "stable1",
				Name:     "self",
			}
			if tc.cap {
				mak.Set(&self.CapMap, tailcfg.NodeAttrClientSideReachability, nil)
			}
			if tc.rchk {
				mak.Set(&self.CapMap, tailcfg.NodeAttrClientSideReachabilityRouteCheck, nil)
			}

			peer := &tailcfg.Node{
				ID:       2,
				StableID: "stable2",
				Name:     "peer",
				Online:   &tc.online,
			}

			nb := newNodeBackend(t.Context(), tstest.WhileTestRunningLogger(t), eventbus.New())
			nb.netMap = &netmap.NetworkMap{
				SelfNode: self.View(),
				Peers:    []tailcfg.NodeView{peer.View()},
				// HACK: AllCaps is usually populated by Control
				AllCaps: set.SetOf(slices.Collect(maps.Keys(self.CapMap))),
			}

			got := nb.PeerIsReachable(routecheckReport(tc.pong), peer.View())
			if got != tc.want {
				t.Errorf("got %v, want %v", got, tc.want)
			}
		})
	}
}

type routecheckReport peernode.Reachability

var _ RouteCheckReport = *new(routecheckReport)

func (rp routecheckReport) IsReachable(_ tailcfg.NodeID) peernode.Reachability {
	return peernode.Reachability(rp)
}

func TestNodeBackendRouteManager(t *testing.T) {
	nb := newNodeBackend(t.Context(), tstest.WhileTestRunningLogger(t), eventbus.New())

	mkPeer := func(id tailcfg.NodeID, stableID tailcfg.StableNodeID, addr4 string, extra ...string) tailcfg.NodeView {
		n := &tailcfg.Node{
			ID:       id,
			StableID: stableID,
			Key:      key.NewNode().Public(),
			HomeDERP: 1, // required by the route manager's reachability filter
			Addresses: []netip.Prefix{
				netip.MustParsePrefix(addr4),
			},
		}
		n.AllowedIPs = append(n.AllowedIPs, n.Addresses...)
		for _, s := range extra {
			n.AllowedIPs = append(n.AllowedIPs, netip.MustParsePrefix(s))
		}
		return n.View()
	}
	wantPeerFor := func(ip string, want tailcfg.NodeView) {
		t.Helper()
		got, ok := nb.routeMgr.Outbound().Lookup(netip.MustParseAddr(ip))
		if !want.Valid() {
			if ok {
				t.Errorf("Outbound lookup %s = %v; want no match", ip, got)
			}
			return
		}
		if !ok || got.Key != want.Key() {
			t.Errorf("Outbound lookup %s = %v, %v; want %v", ip, got, ok, want.Key())
		}
	}

	p1 := mkPeer(1, "stable1", "100.64.0.1/32")
	p2 := mkPeer(2, "stable2", "100.64.0.2/32", "0.0.0.0/0", "::/0")

	// A full netmap populates the route manager.
	nb.SetNetMap(&netmap.NetworkMap{Peers: []tailcfg.NodeView{p1, p2}})
	wantPeerFor("100.64.0.1", p1)
	wantPeerFor("100.64.0.2", p2)
	wantPeerFor("8.8.8.8", tailcfg.NodeView{}) // exit node not selected

	// Selecting peer 2 as the exit node resolves its stable ID and
	// installs its /0 routes. The commit reports peer 2's allowed
	// prefixes as changed.
	if changed := nb.updateRouteManagerPrefs(routePrefs{ExitNodeID: "stable2", ExitNodeSelected: true}); len(changed) != 1 || changed[p2.Key()] == nil {
		t.Errorf("updateRouteManagerPrefs(exit=stable2) changed = %v; want just %v", changed, p2.Key())
	}
	wantPeerFor("8.8.8.8", p2)

	// A selected exit node that resolves to no current peer must
	// blackhole internet traffic, not fall back to "no exit node":
	// the default routes stay in the OS route set with no outbound
	// peer to carry them. Peer 2's allowed prefixes lose the /0s,
	// which the commit reports.
	if changed := nb.updateRouteManagerPrefs(routePrefs{ExitNodeID: "no-such-node", ExitNodeSelected: true}); len(changed) != 1 || changed[p2.Key()] == nil {
		t.Errorf("updateRouteManagerPrefs(exit=unresolved) changed = %v; want just %v", changed, p2.Key())
	}
	wantPeerFor("8.8.8.8", tailcfg.NodeView{})
	if !nb.routeMgr.OSRoutes().Get(netip.MustParsePrefix("0.0.0.0/0")) {
		t.Error("unresolved exit node: OSRoutes missing 0.0.0.0/0 blackhole route")
	}

	nb.updateRouteManagerPrefs(routePrefs{})
	wantPeerFor("8.8.8.8", tailcfg.NodeView{})
	if nb.routeMgr.OSRoutes().Get(netip.MustParsePrefix("0.0.0.0/0")) {
		t.Error("no exit node: OSRoutes unexpectedly contains 0.0.0.0/0")
	}

	// Incremental deltas: add peer 3, remove peer 1.
	p3 := mkPeer(3, "stable3", "100.64.0.3/32")
	deltaRes, handled := nb.UpdateNetmapDelta([]netmap.NodeMutation{
		netmap.NodeMutationUpsert{Node: p3},
		netmap.MakeNodeMutationRemove(1),
	})
	if !handled {
		t.Fatal("UpdateNetmapDelta not handled")
	}
	if changed := deltaRes.ChangedAllowedIPs; len(changed) != 2 || changed[p3.Key()] == nil {
		t.Errorf("UpdateNetmapDelta changed = %v; want entries for %v and %v", changed, p3.Key(), p1.Key())
	}
	if v, ok := deltaRes.ChangedAllowedIPs[p1.Key()]; !ok || v != nil {
		t.Errorf("UpdateNetmapDelta changed[%v] = %v, %v; want nil, true for removed peer", p1.Key(), v, ok)
	}
	wantPeerFor("100.64.0.3", p3)
	wantPeerFor("100.64.0.1", tailcfg.NodeView{})

	// A full netmap that drops a peer removes it from the route manager.
	nb.SetNetMap(&netmap.NetworkMap{Peers: []tailcfg.NodeView{p2}})
	wantPeerFor("100.64.0.3", tailcfg.NodeView{})
	wantPeerFor("100.64.0.2", p2)
}

// TestNodeBackendDiscoChanged exercises the full-netmap disco change
// detection: a peer whose disco key changes has restarted and needs its
// WireGuard session reset, unless the new key was already learned over
// TSMP (that is, over a working WireGuard session with the peer).
func TestNodeBackendDiscoChanged(t *testing.T) {
	nb := newNodeBackend(t.Context(), tstest.WhileTestRunningLogger(t), eventbus.New())

	nk := key.NewNode().Public()
	mkNetMap := func(disco key.DiscoPublic) *netmap.NetworkMap {
		n := &tailcfg.Node{
			ID:       1,
			Key:      nk,
			DiscoKey: disco,
			HomeDERP: 1,
		}
		return &netmap.NetworkMap{Peers: []tailcfg.NodeView{n.View()}}
	}
	newDisco := func() key.DiscoPublic { return key.NewDisco().Public() }

	// A brand-new peer is not a disco change.
	d1 := newDisco()
	if got := nb.SetNetMap(mkNetMap(d1)); len(got) != 0 {
		t.Errorf("SetNetMap(new peer) discoChanged = %v; want none", got)
	}

	// A changed disco key requires a session reset.
	d2 := newDisco()
	if got := nb.SetNetMap(mkNetMap(d2)); !slices.Contains(got, nk) {
		t.Errorf("SetNetMap(changed disco) discoChanged = %v; want %v", got, nk)
	}

	// An unchanged disco key does not.
	if got := nb.SetNetMap(mkNetMap(d2)); len(got) != 0 {
		t.Errorf("SetNetMap(same disco) discoChanged = %v; want none", got)
	}

	// A change already learned via TSMP is suppressed...
	d3 := newDisco()
	nb.recordTSMPLearnedDisco(nk, d3)
	if got := nb.SetNetMap(mkNetMap(d3)); len(got) != 0 {
		t.Errorf("SetNetMap(TSMP-learned disco) discoChanged = %v; want none", got)
	}

	// ...but the TSMP entry is consumed, so the next change resets again.
	d4 := newDisco()
	if got := nb.SetNetMap(mkNetMap(d4)); !slices.Contains(got, nk) {
		t.Errorf("SetNetMap(after TSMP entry consumed) discoChanged = %v; want %v", got, nk)
	}

	// A TSMP-learned key that doesn't match the netmap's new key still
	// resets the session and bumps the mismatch metric.
	before := metricTSMPLearnedKeyMismatch.Value()
	nb.recordTSMPLearnedDisco(nk, newDisco())
	d5 := newDisco()
	if got := nb.SetNetMap(mkNetMap(d5)); !slices.Contains(got, nk) {
		t.Errorf("SetNetMap(TSMP mismatch) discoChanged = %v; want %v", got, nk)
	}
	if delta := metricTSMPLearnedKeyMismatch.Value() - before; delta != 1 {
		t.Errorf("metricTSMPLearnedKeyMismatch delta = %d; want 1", delta)
	}

	// Removing the peer garbage-collects its TSMP entry: after the peer
	// comes back, a change to the once-recorded key is a normal reset.
	d6 := newDisco()
	nb.recordTSMPLearnedDisco(nk, d6)
	nb.SetNetMap(&netmap.NetworkMap{})
	nb.SetNetMap(mkNetMap(d5))
	if got := nb.SetNetMap(mkNetMap(d6)); !slices.Contains(got, nk) {
		t.Errorf("SetNetMap(after TSMP entry GC) discoChanged = %v; want %v", got, nk)
	}

	// Transitions to or from a zero disco key never reset.
	if got := nb.SetNetMap(mkNetMap(key.DiscoPublic{})); len(got) != 0 {
		t.Errorf("SetNetMap(to zero disco) discoChanged = %v; want none", got)
	}
	if got := nb.SetNetMap(mkNetMap(d1)); len(got) != 0 {
		t.Errorf("SetNetMap(from zero disco) discoChanged = %v; want none", got)
	}
}

// TestNodeBackendDiscoChangedDelta is like TestNodeBackendDiscoChanged
// but for the incremental path: disco changes arriving as
// [netmap.NodeMutationUpsert] deltas.
func TestNodeBackendDiscoChangedDelta(t *testing.T) {
	nb := newNodeBackend(t.Context(), tstest.WhileTestRunningLogger(t), eventbus.New())

	mkNode := func(k key.NodePublic, disco key.DiscoPublic) tailcfg.NodeView {
		return (&tailcfg.Node{ID: 1, Key: k, DiscoKey: disco, HomeDERP: 1}).View()
	}
	newDisco := func() key.DiscoPublic { return key.NewDisco().Public() }
	apply := func(muts ...netmap.NodeMutation) set.Set[key.NodePublic] {
		t.Helper()
		deltaRes, handled := nb.UpdateNetmapDelta(muts)
		if !handled {
			t.Fatal("UpdateNetmapDelta not handled")
		}
		return deltaRes.DiscoChanged
	}

	nk := key.NewNode().Public()
	d1 := newDisco()
	nb.SetNetMap(&netmap.NetworkMap{Peers: []tailcfg.NodeView{mkNode(nk, d1)}})

	// An upserted peer with a changed disco key needs a session reset.
	d2 := newDisco()
	if got := apply(netmap.NodeMutationUpsert{Node: mkNode(nk, d2)}); !got.Contains(nk) {
		t.Errorf("upsert(changed disco) discoChanged = %v; want %v", got, nk)
	}

	// An unchanged disco key does not.
	if got := apply(netmap.NodeMutationUpsert{Node: mkNode(nk, d2)}); len(got) != 0 {
		t.Errorf("upsert(same disco) discoChanged = %v; want none", got)
	}

	// A change already learned via TSMP is suppressed.
	d3 := newDisco()
	nb.recordTSMPLearnedDisco(nk, d3)
	if got := apply(netmap.NodeMutationUpsert{Node: mkNode(nk, d3)}); len(got) != 0 {
		t.Errorf("upsert(TSMP-learned disco) discoChanged = %v; want none", got)
	}

	// A node key rotation replaces the WireGuard peer outright, so no
	// disco-based reset is reported.
	nk2 := key.NewNode().Public()
	if got := apply(netmap.NodeMutationUpsert{Node: mkNode(nk2, newDisco())}); len(got) != 0 {
		t.Errorf("upsert(rotated node key) discoChanged = %v; want none", got)
	}

	// Removing the peer garbage-collects its TSMP entry: after the peer
	// comes back, a change to the once-recorded key is a normal reset.
	d4 := newDisco()
	nb.recordTSMPLearnedDisco(nk2, d4)
	apply(netmap.MakeNodeMutationRemove(1))
	apply(netmap.NodeMutationUpsert{Node: mkNode(nk2, newDisco())})
	if got := apply(netmap.NodeMutationUpsert{Node: mkNode(nk2, d4)}); !got.Contains(nk2) {
		t.Errorf("upsert(after TSMP entry GC) discoChanged = %v; want %v", got, nk2)
	}
}

func TestNodeBackendRouteManagerExtras(t *testing.T) {
	nb := newNodeBackend(t.Context(), tstest.WhileTestRunningLogger(t), eventbus.New())

	n := &tailcfg.Node{
		ID:       1,
		Key:      key.NewNode().Public(),
		HomeDERP: 1,
		Addresses: []netip.Prefix{
			netip.MustParsePrefix("100.64.0.1/32"),
		},
	}
	n.AllowedIPs = n.Addresses
	p1 := n.View()
	nb.SetNetMap(&netmap.NetworkMap{Peers: []tailcfg.NodeView{p1}})

	transit := netip.MustParsePrefix("fe80::1234/128")
	extrasFor := func(k key.NodePublic) views.Slice[netip.Prefix] {
		if k == p1.Key() {
			return views.SliceOf([]netip.Prefix{transit})
		}
		return views.Slice[netip.Prefix]{}
	}

	// Installing extras reports the peer's allowed prefixes as
	// changed and adds the transit IP to the outbound table.
	changed := nb.updateRouteManagerExtras(extrasFor)
	if len(changed) != 1 || !slices.Contains(changed[p1.Key()], transit) {
		t.Errorf("updateRouteManagerExtras changed = %v; want %v including %v", changed, p1.Key(), transit)
	}
	if pr, ok := nb.routeMgr.Outbound().Lookup(transit.Addr()); !ok || pr.Key != p1.Key() {
		t.Errorf("Outbound lookup %v = %v, %v; want %v", transit.Addr(), pr, ok, p1.Key())
	}
	if nb.routeMgr.OSRoutes().Get(transit) {
		t.Errorf("OSRoutes contains %v; extras must not reach the OS route set", transit)
	}

	// An unchanged hook result is a no-op.
	if changed := nb.updateRouteManagerExtras(extrasFor); changed != nil {
		t.Errorf("unchanged extras reported changes: %v", changed)
	}

	// A hook that no longer returns extras removes them.
	changed = nb.updateRouteManagerExtras(func(key.NodePublic) views.Slice[netip.Prefix] {
		return views.Slice[netip.Prefix]{}
	})
	if len(changed) != 1 {
		t.Errorf("clearing extras changed = %v; want just %v", changed, p1.Key())
	}
	if _, ok := nb.routeMgr.Outbound().Lookup(transit.Addr()); ok {
		t.Errorf("Outbound still routes %v after extras cleared", transit.Addr())
	}
}

// Tests the live MagicDNS lookup methods backing
// [resolver.MagicDNSHosts]: forward, reverse, and subdomain-cap
// lookups must serve from the node indexes and stay correct across
// netmap deltas without any full Hosts map rebuild.
func TestNodeBackendMagicDNSHosts(t *testing.T) {
	nb := newNodeBackend(t.Context(), tstest.WhileTestRunningLogger(t), eventbus.New())

	self := &tailcfg.Node{
		ID:        1,
		Name:      "self.example.ts.net.",
		Addresses: []netip.Prefix{netip.MustParsePrefix("100.64.0.1/32")},
	}
	p1 := &tailcfg.Node{
		ID:   2,
		Key:  key.NewNode().Public(),
		Name: "p1.example.ts.net.",
		Addresses: []netip.Prefix{
			netip.MustParsePrefix("100.64.0.2/32"),
			netip.MustParsePrefix("fd7a:115c:a1e0::2/128"),
		},
		CapMap: tailcfg.NodeCapMap{tailcfg.NodeAttrDNSSubdomainResolve: nil},
	}
	nb.SetNetMap(&netmap.NetworkMap{
		SelfNode: self.View(),
		Peers:    []tailcfg.NodeView{p1.View()},
	})

	wantHost := func(fqdn dnsname.FQDN, want ...netip.Addr) {
		t.Helper()
		ips, ok := nb.magicDNSHostAddrs(fqdn)
		if len(want) == 0 {
			if ok {
				t.Errorf("magicDNSHostAddrs(%q) = %v; want no match", fqdn, ips)
			}
			return
		}
		if !ok || !slices.Equal(ips, want) {
			t.Errorf("magicDNSHostAddrs(%q) = %v, %v; want %v", fqdn, ips, ok, want)
		}
	}

	// The self node has IPv4, so the peer's IPv6 address is
	// filtered out (issue 1152).
	wantHost("p1.example.ts.net.", netip.MustParseAddr("100.64.0.2"))
	wantHost("self.example.ts.net.", netip.MustParseAddr("100.64.0.1"))
	wantHost("unknown.example.ts.net.")

	if fqdn, ok := nb.magicDNSPTR(netip.MustParseAddr("100.64.0.2")); !ok || fqdn != "p1.example.ts.net." {
		t.Errorf("magicDNSPTR(100.64.0.2) = %q, %v; want p1's name", fqdn, ok)
	}
	if got, want := nb.magicDNSSubdomainHost("p1.example.ts.net."), true; got != want {
		t.Errorf("magicDNSSubdomainHost(p1) = %v; want %v", got, want)
	}
	if got, want := nb.magicDNSSubdomainHost("self.example.ts.net."), false; got != want {
		t.Errorf("magicDNSSubdomainHost(self) = %v; want %v", got, want)
	}

	// Removing the peer via a delta drops its records.
	if _, handled := nb.UpdateNetmapDelta([]netmap.NodeMutation{netmap.MakeNodeMutationRemove(2)}); !handled {
		t.Fatal("UpdateNetmapDelta not handled")
	}
	wantHost("p1.example.ts.net.")
	if fqdn, ok := nb.magicDNSPTR(netip.MustParseAddr("100.64.0.2")); ok {
		t.Errorf("magicDNSPTR(100.64.0.2) after removal = %q; want no match", fqdn)
	}

	// Adding a peer via a delta serves it immediately.
	p3 := &tailcfg.Node{
		ID:        3,
		Key:       key.NewNode().Public(),
		Name:      "p3.example.ts.net.",
		Addresses: []netip.Prefix{netip.MustParsePrefix("100.64.0.3/32")},
	}
	if _, handled := nb.UpdateNetmapDelta([]netmap.NodeMutation{netmap.NodeMutationUpsert{Node: p3.View()}}); !handled {
		t.Fatal("UpdateNetmapDelta not handled")
	}
	wantHost("p3.example.ts.net.", netip.MustParseAddr("100.64.0.3"))
}