tailcfg,ipn/ipnlocal: add hostinfo field to replace service entry

Updates tailscale/corp#15437
Signed-off-by: James Tucker <james@tailscale.com>

ipn/ipnlocal/local.go

@@ -1544,6 +1544,7 @@ func (b *LocalBackend) Start(opts ipn.Options) error {
 	hostinfo.FrontendLogID = opts.FrontendLogID
 	hostinfo.Userspace.Set(b.sys.IsNetstack())
 	hostinfo.UserspaceRouter.Set(b.sys.IsNetstackRouter())
+	hostinfo.AppConnector.Set(b.appConnector != nil)
 	b.logf.JSON(1, "Hostinfo", hostinfo)
 
 	// TODO(apenwarr): avoid the need to reinit controlclient.
@@ -3270,6 +3271,11 @@ func (b *LocalBackend) blockEngineUpdates(block bool) {
 // b.mu must be held.
 func (b *LocalBackend) reconfigAppConnectorLocked(nm *netmap.NetworkMap, prefs ipn.PrefsView) {
 	const appConnectorCapName = "tailscale.com/app-connectors"
+	defer func() {
+		if b.hostinfo != nil {
+			b.hostinfo.AppConnector.Set(b.appConnector != nil)
+		}
+	}()
 
 	if !prefs.AppConnector().Advertise {
 		var old *appc.AppConnector

ipn/ipnlocal/local_test.go

@@ -1263,6 +1263,9 @@ func TestReconfigureAppConnector(t *testing.T) {
 	if !foundAppConnectorService {
 		t.Fatalf("expected app connector service")
 	}
+	if v, _ := b.hostinfo.AppConnector.Get(); !v {
+		t.Fatalf("expected app connector service")
+	}
 
 	// disable the connector in order to assert that the service is removed
 	b.EditPrefs(&ipn.MaskedPrefs{
@@ -1288,6 +1291,9 @@ func TestReconfigureAppConnector(t *testing.T) {
 	if foundAppConnectorService {
 		t.Fatalf("expected no app connector service")
 	}
+	if v, _ := b.hostinfo.AppConnector.Get(); v {
+		t.Fatalf("expected no app connector service")
+	}
 }
 
 func hasAppConnectorService(b *LocalBackend) bool {

tailcfg/tailcfg.go

@@ -629,6 +629,7 @@ const (
 	PeerAPI4   = ServiceProto("peerapi4")
 	PeerAPI6   = ServiceProto("peerapi6")
 	PeerAPIDNS = ServiceProto("peerapi-dns-proxy")
+	// Deprecated: use the field on HostInfo instead.
 	AppConnector = ServiceProto("app-connector")
 )
 
@@ -650,9 +651,9 @@ type Service struct {
 	//        being a DNS proxy (when the node is an exit
 	//        node). For this service, the Port number is really
 	//        the version number of the service.
-	//     * "app-connector": the local app-connector service is
+	//     * "app-connector": (deprecated) the local app-connector
-	//        available. For this service, the Port number is
+	//        service is available. For this service, the Port number
-	//        really the version number of the service.
+	//        is really the version number of the service.
 	Proto ServiceProto
 
 	// Port is the port number.
@@ -748,6 +749,7 @@ type Hostinfo struct {
 	Cloud           string         `json:",omitempty"`
 	Userspace       opt.Bool       `json:",omitempty"` // if the client is running in userspace (netstack) mode
 	UserspaceRouter opt.Bool       `json:",omitempty"` // if the client's subnet router is running in userspace (netstack) mode
+	AppConnector    opt.Bool       `json:",omitempty"` // if the client is running the app-connector service
 
 	// Location represents geographical location data about a
 	// Tailscale host. Location is optional and only set if

tailcfg/tailcfg_clone.go

@@ -177,6 +177,7 @@ var _HostinfoCloneNeedsRegeneration = Hostinfo(struct {
 	Cloud           string
 	Userspace       opt.Bool
 	UserspaceRouter opt.Bool
+	AppConnector    opt.Bool
 	Location        *Location
 }{})
 

tailcfg/tailcfg_test.go

@@ -17,6 +17,7 @@ import (
 
 	. "tailscale.com/tailcfg"
 	"tailscale.com/types/key"
+	"tailscale.com/types/opt"
 	"tailscale.com/types/ptr"
 	"tailscale.com/util/must"
 )
@@ -64,6 +65,7 @@ func TestHostinfoEqual(t *testing.T) {
 		"Cloud",
 		"Userspace",
 		"UserspaceRouter",
+		"AppConnector",
 		"Location",
 	}
 	if have := fieldsOf(reflect.TypeOf(Hostinfo{})); !reflect.DeepEqual(have, hiHandles) {
@@ -228,6 +230,16 @@ func TestHostinfoEqual(t *testing.T) {
 			&Hostinfo{App: "golink"},
 			true,
 		},
+		{
+			&Hostinfo{AppConnector: opt.Bool("true")},
+			&Hostinfo{AppConnector: opt.Bool("true")},
+			true,
+		},
+		{
+			&Hostinfo{AppConnector: opt.Bool("true")},
+			&Hostinfo{AppConnector: opt.Bool("false")},
+			false,
+		},
 	}
 	for i, tt := range tests {
 		got := tt.a.Equal(tt.b)

tailcfg/tailcfg_view.go

@@ -317,6 +317,7 @@ func (v HostinfoView) SSH_HostKeys() views.Slice[string]      { return views.Sli
 func (v HostinfoView) Cloud() string                          { return v.ж.Cloud }
 func (v HostinfoView) Userspace() opt.Bool                    { return v.ж.Userspace }
 func (v HostinfoView) UserspaceRouter() opt.Bool              { return v.ж.UserspaceRouter }
+func (v HostinfoView) AppConnector() opt.Bool                 { return v.ж.AppConnector }
 func (v HostinfoView) Location() *Location {
 	if v.ж.Location == nil {
 		return nil
@@ -363,6 +364,7 @@ var _HostinfoViewNeedsRegeneration = Hostinfo(struct {
 	Cloud           string
 	Userspace       opt.Bool
 	UserspaceRouter opt.Bool
+	AppConnector    opt.Bool
 	Location        *Location
 }{})