appc: add RouteInfo struct and persist it to StateStore

Lays the groundwork for the ability to persist app connectors discovered
routes, which will allow us to stop advertising routes for a domain if
the app connector no longer monitors that domain.

Updates #11008
Signed-off-by: Fran Bull <fran@tailscale.com>

appc/appconnector.go

@@ -36,6 +36,19 @@ type RouteAdvertiser interface {
 	UnadvertiseRoute(...netip.Prefix) error
 }
 
+// RouteInfo is a data structure used to persist the in memory state of an AppConnector
+// so that we can know, even after a restart, which routes came from ACLs and which were
+// learned from domains.
+type RouteInfo struct {
+	// Control is the routes from the 'routes' section of an app connector acl.
+	Control []netip.Prefix `json:",omitempty"`
+	// Domains are the routes discovered by observing DNS lookups for configured domains.
+	Domains map[string][]netip.Addr `json:",omitempty"`
+	// Wildcards are the configured DNS lookup domains to observe. When a DNS query matches Wildcards,
+	// its result is added to Domains.
+	Wildcards []string `json:",omitempty"`
+}
+
 // AppConnector is an implementation of an AppConnector that performs
 // its function as a subsystem inside of a tailscale node. At the control plane
 // side App Connector routing is configured in terms of domains rather than IP

ipn/ipnlocal/local.go

@@ -6210,6 +6210,43 @@ func (b *LocalBackend) UnadvertiseRoute(toRemove ...netip.Prefix) error {
 	return err
 }
 
+// namespace a key with the profile manager's current profile key, if any
+func namespaceKeyForCurrentProfile(pm *profileManager, key ipn.StateKey) ipn.StateKey {
+	return pm.CurrentProfile().Key + "||" + key
+}
+
+const routeInfoStateStoreKey ipn.StateKey = "_routeInfo"
+
+func (b *LocalBackend) storeRouteInfo(ri *appc.RouteInfo) error {
+	b.mu.Lock()
+	defer b.mu.Unlock()
+	if b.pm.CurrentProfile().ID == "" {
+		return nil
+	}
+	key := namespaceKeyForCurrentProfile(b.pm, routeInfoStateStoreKey)
+	bs, err := json.Marshal(ri)
+	if err != nil {
+		return err
+	}
+	return b.pm.WriteState(key, bs)
+}
+
+func (b *LocalBackend) readRouteInfoLocked() (*appc.RouteInfo, error) {
+	if b.pm.CurrentProfile().ID == "" {
+		return &appc.RouteInfo{}, nil
+	}
+	key := namespaceKeyForCurrentProfile(b.pm, routeInfoStateStoreKey)
+	bs, err := b.pm.Store().ReadState(key)
+	ri := &appc.RouteInfo{}
+	if err != nil {
+		return nil, err
+	}
+	if err := json.Unmarshal(bs, ri); err != nil {
+		return nil, err
+	}
+	return ri, nil
+}
+
 // seamlessRenewalEnabled reports whether seamless key renewals are enabled
 // (i.e. we saw our self node with the SeamlessKeyRenewal attr in a netmap).
 // This enables beta functionality of renewing node keys without breaking

ipn/ipnlocal/local_test.go

@@ -3454,3 +3454,66 @@ func TestEnableAutoUpdates(t *testing.T) {
 		t.Fatalf("disabling auto-updates: got error: %v", err)
 	}
 }
+
+func TestReadWriteRouteInfo(t *testing.T) {
+	// set up a backend with more than one profile
+	b := newTestBackend(t)
+	prof1 := ipn.LoginProfile{ID: "id1", Key: "key1"}
+	prof2 := ipn.LoginProfile{ID: "id2", Key: "key2"}
+	b.pm.knownProfiles["id1"] = &prof1
+	b.pm.knownProfiles["id2"] = &prof2
+	b.pm.currentProfile = &prof1
+
+	// set up routeInfo
+	ri1 := &appc.RouteInfo{}
+	ri1.Wildcards = []string{"1"}
+
+	ri2 := &appc.RouteInfo{}
+	ri2.Wildcards = []string{"2"}
+
+	// read before write
+	readRi, err := b.readRouteInfoLocked()
+	if readRi != nil {
+		t.Fatalf("read before writing: want nil, got %v", readRi)
+	}
+	if err != ipn.ErrStateNotExist {
+		t.Fatalf("read before writing: want %v, got %v", ipn.ErrStateNotExist, err)
+	}
+
+	// write the first routeInfo
+	if err := b.storeRouteInfo(ri1); err != nil {
+		t.Fatal(err)
+	}
+
+	// write the other routeInfo as the other profile
+	if err := b.pm.SwitchProfile("id2"); err != nil {
+		t.Fatal(err)
+	}
+	if err := b.storeRouteInfo(ri2); err != nil {
+		t.Fatal(err)
+	}
+
+	// read the routeInfo of the first profile
+	if err := b.pm.SwitchProfile("id1"); err != nil {
+		t.Fatal(err)
+	}
+	readRi, err = b.readRouteInfoLocked()
+	if err != nil {
+		t.Fatal(err)
+	}
+	if !slices.Equal(readRi.Wildcards, ri1.Wildcards) {
+		t.Fatalf("read prof1 routeInfo wildcards:  want %v, got %v", ri1.Wildcards, readRi.Wildcards)
+	}
+
+	// read the routeInfo of the second profile
+	if err := b.pm.SwitchProfile("id2"); err != nil {
+		t.Fatal(err)
+	}
+	readRi, err = b.readRouteInfoLocked()
+	if err != nil {
+		t.Fatal(err)
+	}
+	if !slices.Equal(readRi.Wildcards, ri2.Wildcards) {
+		t.Fatalf("read prof2 routeInfo wildcards:  want %v, got %v", ri2.Wildcards, readRi.Wildcards)
+	}
+}