ipn/ipnlocal,tailcfg: add AppConnector service to HostInfo when configured

Updates tailscale/corp#15437

Signed-off-by: James Tucker <james@tailscale.com>

ipn/ipnlocal/local.go

@@ -3166,6 +3166,12 @@ func (b *LocalBackend) peerAPIServicesLocked() (ret []tailcfg.Service) {
 			Port:  1, // version
 		})
 	}
+	if b.appConnector != nil {
+		ret = append(ret, tailcfg.Service{
+			Proto: tailcfg.AppConnector,
+			Port:  1, // version
+		})
+	}
 	return ret
 }
 

ipn/ipnlocal/local_test.go

@@ -1157,6 +1157,28 @@ func TestOfferingAppConnector(t *testing.T) {
 	}
 }
 
+func TestAppConnectorHostinfoService(t *testing.T) {
+	hasAppConnectorService := func(s []tailcfg.Service) bool {
+		for _, s := range s {
+			if s.Proto == tailcfg.AppConnector && s.Port == 1 {
+				return true
+			}
+		}
+		return false
+	}
+
+	b := newTestBackend(t)
+	b.mu.Lock()
+	defer b.mu.Unlock()
+	if hasAppConnectorService(b.peerAPIServicesLocked()) {
+		t.Fatal("unexpected app connector service")
+	}
+	b.appConnector = appc.NewEmbeddedAppConnector(t.Logf, nil)
+	if !hasAppConnectorService(b.peerAPIServicesLocked()) {
+		t.Fatal("expected app connector service")
+	}
+}
+
 func TestRouteAdvertiser(t *testing.T) {
 	b := newTestBackend(t)
 	testPrefix := netip.MustParsePrefix("192.0.0.8/32")

ipn/ipnlocal/peerapi.go

@@ -1003,7 +1003,7 @@ func dnsQueryForName(name, typStr string) []byte {
 	b := dnsmessage.NewBuilder(nil, dnsmessage.Header{
 		OpCode:           0, // query
 		RecursionDesired: true,
-		ID:               0,
+		ID:               1, // arbitrary, but 0 is rejected by some servers
 	})
 	if !strings.HasSuffix(name, ".") {
 		name += "."