From 5c562116fc49ae8d88268a5a0e6b297cd855b12b Mon Sep 17 00:00:00 2001
From: kari-ts <135075563+kari-ts@users.noreply.github.com>
Date: Wed, 9 Apr 2025 16:49:33 -0700
Subject: [PATCH] ipnlocal: log when client reports new peerAPI ports (#15463)

Updates tailscale/tailscale#14393

Signed-off-by: kari-ts <kari@tailscale.com>
---
 ipn/ipnlocal/local.go | 25 +++++++++++++++++++++++++
 1 file changed, 25 insertions(+)

diff --git a/ipn/ipnlocal/local.go b/ipn/ipnlocal/local.go
index 7d69b884d..cf71b80fa 100644
--- a/ipn/ipnlocal/local.go
+++ b/ipn/ipnlocal/local.go
@@ -4844,9 +4844,34 @@ func (b *LocalBackend) doSetHostinfoFilterServices() {
 	c := len(hi.Services)
 	hi.Services = append(hi.Services[:c:c], peerAPIServices...)
 	hi.PushDeviceToken = b.pushDeviceToken.Load()
+
+	// Compare the expected ports from peerAPIServices to the actual ports in hi.Services.
+	expectedPorts := extractPeerAPIPorts(peerAPIServices)
+	actualPorts := extractPeerAPIPorts(hi.Services)
+	if expectedPorts != actualPorts {
+		b.logf("Hostinfo peerAPI ports changed: expected %v, got %v", expectedPorts, actualPorts)
+	}
+
 	cc.SetHostinfo(&hi)
 }
 
+type portPair struct {
+	v4, v6 uint16
+}
+
+func extractPeerAPIPorts(services []tailcfg.Service) portPair {
+	var p portPair
+	for _, s := range services {
+		switch s.Proto {
+		case "peerapi4":
+			p.v4 = s.Port
+		case "peerapi6":
+			p.v6 = s.Port
+		}
+	}
+	return p
+}
+
 // NetMap returns the latest cached network map received from
 // controlclient, or nil if no network map was received yet.
 func (b *LocalBackend) NetMap() *netmap.NetworkMap {