ipn/ipnlocal, types: plumb tailnet display name cap through to network profile (#17045)

Updates tailscale/corp#30456

Signed-off-by: Nick O'Neill <nick@tailscale.com>

ipn/ipnlocal/local.go

@@ -1650,12 +1650,18 @@ func (b *LocalBackend) SetControlClientStatus(c controlclient.Client, st control
 		prefsChanged = true
 	}
 
+	// If the tailnet's display name has changed, update prefs.
+	if st.NetMap != nil && st.NetMap.TailnetDisplayName() != b.pm.CurrentProfile().NetworkProfile().DisplayName {
+		prefsChanged = true
+	}
+
 	// Perform all mutations of prefs based on the netmap here.
 	if prefsChanged {
 		// Prefs will be written out if stale; this is not safe unless locked or cloned.
 		if err := b.pm.SetPrefs(prefs.View(), ipn.NetworkProfile{
 			MagicDNSName: curNetMap.MagicDNSSuffix(),
 			DomainName:   curNetMap.DomainName(),
+			DisplayName:  curNetMap.TailnetDisplayName(),
 		}); err != nil {
 			b.logf("Failed to save new controlclient state: %v", err)
 		}
@@ -1716,6 +1722,7 @@ func (b *LocalBackend) SetControlClientStatus(c controlclient.Client, st control
 			if err := b.pm.SetPrefs(p, ipn.NetworkProfile{
 				MagicDNSName: st.NetMap.MagicDNSSuffix(),
 				DomainName:   st.NetMap.DomainName(),
+				DisplayName:  st.NetMap.TailnetDisplayName(),
 			}); err != nil {
 				b.logf("Failed to save new controlclient state: %v", err)
 			}
@@ -6185,6 +6192,7 @@ func (b *LocalBackend) resolveExitNode() (changed bool) {
 	if err := b.pm.SetPrefs(prefs.View(), ipn.NetworkProfile{
 		MagicDNSName: nm.MagicDNSSuffix(),
 		DomainName:   nm.DomainName(),
+		DisplayName:  nm.TailnetDisplayName(),
 	}); err != nil {
 		b.logf("failed to save exit node changes: %v", err)
 	}

ipn/ipnlocal/node_backend.go

@@ -168,6 +168,7 @@ func (nb *nodeBackend) NetworkProfile() ipn.NetworkProfile {
 		// These are ok to call with nil netMap.
 		MagicDNSName: nb.netMap.MagicDNSSuffix(),
 		DomainName:   nb.netMap.DomainName(),
+		DisplayName:  nb.netMap.TailnetDisplayName(),
 	}
 }
 

ipn/prefs.go

@@ -988,6 +988,7 @@ type WindowsUserID string
 type NetworkProfile struct {
 	MagicDNSName string
 	DomainName   string
+	DisplayName  string
 }
 
 // RequiresBackfill returns whether this object does not have all the data

types/netmap/netmap.go

@@ -252,6 +252,22 @@ func (nm *NetworkMap) DomainName() string {
 	return nm.Domain
 }
 
+// TailnetDisplayName returns the admin-editable name contained in
+// NodeAttrTailnetDisplayName. If the capability is not present it
+// returns an empty string.
+func (nm *NetworkMap) TailnetDisplayName() string {
+	if nm == nil || !nm.SelfNode.Valid() {
+		return ""
+	}
+
+	tailnetDisplayNames, err := tailcfg.UnmarshalNodeCapViewJSON[string](nm.SelfNode.CapMap(), tailcfg.NodeAttrTailnetDisplayName)
+	if err != nil || len(tailnetDisplayNames) == 0 {
+		return ""
+	}
+
+	return tailnetDisplayNames[0]
+}
+
 // HasSelfCapability reports whether nm.SelfNode contains capability c.
 //
 // It exists to satisify an unused (as of 2025-01-04) interface in the logknob package.