From 43c91c8161f041fd4f0ee45a7660d9344f2a509d Mon Sep 17 00:00:00 2001
From: "copilot-swe-agent[bot]" <198982749+Copilot@users.noreply.github.com>
Date: Sat, 1 Nov 2025 08:42:24 +0000
Subject: [PATCH] Fix Domain() to return BaseDomain instead of ServerURL
 hostname

Co-authored-by: kradalby <98431+kradalby@users.noreply.github.com>
---
 hscontrol/mapper/builder_test.go |  9 +++++----
 hscontrol/types/config.go        | 12 ++++--------
 2 files changed, 9 insertions(+), 12 deletions(-)

diff --git a/hscontrol/mapper/builder_test.go b/hscontrol/mapper/builder_test.go
index 978b2c0e..f36a120b 100644
--- a/hscontrol/mapper/builder_test.go
+++ b/hscontrol/mapper/builder_test.go
@@ -57,10 +57,10 @@ func TestMapResponseBuilder_WithCapabilityVersion(t *testing.T) {
 }
 
 func TestMapResponseBuilder_WithDomain(t *testing.T) {
-	domain := "test.example.com"
+	baseDomain := "internal.example.com"
 	cfg := &types.Config{
-		ServerURL:  "https://test.example.com",
-		BaseDomain: domain,
+		ServerURL:  "https://headscale.external.com",
+		BaseDomain: baseDomain,
 	}
 
 	mockState := &state.State{}
@@ -74,7 +74,8 @@ func TestMapResponseBuilder_WithDomain(t *testing.T) {
 	builder := m.NewMapResponseBuilder(nodeID).
 		WithDomain()
 
-	assert.Equal(t, domain, builder.resp.Domain)
+	// Domain should be the BaseDomain (internal tailnet domain), not ServerURL hostname
+	assert.Equal(t, baseDomain, builder.resp.Domain)
 	assert.False(t, builder.hasErrors())
 }
 
diff --git a/hscontrol/types/config.go b/hscontrol/types/config.go
index 732b4d5a..dfd069a1 100644
--- a/hscontrol/types/config.go
+++ b/hscontrol/types/config.go
@@ -246,15 +246,11 @@ func validatePKCEMethod(method string) error {
 	return nil
 }
 
-// Domain returns the hostname/domain part of the ServerURL.
-// If the ServerURL is not a valid URL, it returns the BaseDomain.
+// Domain returns the base domain for the tailnet.
+// This is the domain used for MagicDNS and displayed in Tailscale clients
+// as the network name.
 func (c *Config) Domain() string {
-	u, err := url.Parse(c.ServerURL)
-	if err != nil {
-		return c.BaseDomain
-	}
-
-	return u.Hostname()
+	return c.BaseDomain
 }
 
 // LoadConfig prepares and loads the Headscale configuration into Viper.