From 228a82f178ec97f470a12ea9998e0c93f59b2458 Mon Sep 17 00:00:00 2001
From: James Tucker <james@tailscale.com>
Date: Wed, 1 Nov 2023 11:38:44 -0700
Subject: [PATCH] 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      |  6 ++++++
 ipn/ipnlocal/local_test.go | 22 ++++++++++++++++++++++
 ipn/ipnlocal/peerapi.go    |  2 +-
 tailcfg/tailcfg.go         | 16 ++++++++++------
 4 files changed, 39 insertions(+), 7 deletions(-)

diff --git a/ipn/ipnlocal/local.go b/ipn/ipnlocal/local.go
index 17f23e0f1..886f6ead0 100644
--- a/ipn/ipnlocal/local.go
+++ b/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
 }
 
diff --git a/ipn/ipnlocal/local_test.go b/ipn/ipnlocal/local_test.go
index 1ac51ce58..c9e511cc0 100644
--- a/ipn/ipnlocal/local_test.go
+++ b/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")
diff --git a/ipn/ipnlocal/peerapi.go b/ipn/ipnlocal/peerapi.go
index 3f5b0beaf..0a7471f19 100644
--- a/ipn/ipnlocal/peerapi.go
+++ b/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 += "."
diff --git a/tailcfg/tailcfg.go b/tailcfg/tailcfg.go
index 3fb7d70ab..54f3b24f7 100644
--- a/tailcfg/tailcfg.go
+++ b/tailcfg/tailcfg.go
@@ -624,11 +624,12 @@ func (h *Hostinfo) CheckRequestTags() error {
 type ServiceProto string
 
 const (
-	TCP        = ServiceProto("tcp")
-	UDP        = ServiceProto("udp")
-	PeerAPI4   = ServiceProto("peerapi4")
-	PeerAPI6   = ServiceProto("peerapi6")
-	PeerAPIDNS = ServiceProto("peerapi-dns-proxy")
+	TCP          = ServiceProto("tcp")
+	UDP          = ServiceProto("udp")
+	PeerAPI4     = ServiceProto("peerapi4")
+	PeerAPI6     = ServiceProto("peerapi6")
+	PeerAPIDNS   = ServiceProto("peerapi-dns-proxy")
+	AppConnector = ServiceProto("app-connector")
 )
 
 // Service represents a service running on a node.
@@ -645,10 +646,13 @@ type Service struct {
 	//     * "peerapi6": peerapi is available on IPv6; Port is the
 	//        port number that the peerapi is running on the
 	//        node's Tailscale IPv6 address.
-	//     * "peerapi-dns": the local peerapi service supports
+	//     * "peerapi-dns-proxy": the local peerapi service supports
 	//        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
+	//        available. For this service, the Port number is
+	//        really the version number of the service.
 	Proto ServiceProto
 
 	// Port is the port number.