ipn, wgengine/magicsock: add ipn.Prefs.DisableDERP bool

Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>

ipn/local.go

@@ -167,8 +167,10 @@ func (b *LocalBackend) Start(opts Options) error {
 	b.notify = opts.Notify
 	b.netMapCache = nil
 	persist := b.prefs.Persist
+	wantDERP := !b.prefs.DisableDERP
 	b.mu.Unlock()
 
+	b.e.SetDERPEnabled(wantDERP)
 	b.updateFilter(nil)
 
 	var err error

ipn/prefs.go

@@ -53,6 +53,9 @@ type Prefs struct {
 	// TODO(danderson): remove?
 	NotepadURLs bool
 
+	// DisableDERP prevents DERP from being used.
+	DisableDERP bool
+
 	// The Persist field is named 'Config' in the file for backward
 	// compatibility with earlier versions.
 	// TODO(apenwarr): We should move this out of here, it's not a pref.
@@ -99,6 +102,7 @@ func (p *Prefs) Equals(p2 *Prefs) bool {
 		p.CorpDNS == p2.CorpDNS &&
 		p.WantRunning == p2.WantRunning &&
 		p.NotepadURLs == p2.NotepadURLs &&
+		p.DisableDERP == p2.DisableDERP &&
 		p.UsePacketFilter == p2.UsePacketFilter &&
 		compareIPNets(p.AdvertiseRoutes, p2.AdvertiseRoutes) &&
 		p.Persist.Equals(p2.Persist)

ipn/prefs_test.go

@@ -20,7 +20,7 @@ func fieldsOf(t reflect.Type) (fields []string) {
 }
 
 func TestPrefsEqual(t *testing.T) {
-	prefsHandles := []string{"ControlURL", "RouteAll", "AllowSingleHosts", "CorpDNS", "WantRunning", "UsePacketFilter", "AdvertiseRoutes", "NotepadURLs", "Persist"}
+	prefsHandles := []string{"ControlURL", "RouteAll", "AllowSingleHosts", "CorpDNS", "WantRunning", "UsePacketFilter", "AdvertiseRoutes", "NotepadURLs", "DisableDERP", "Persist"}
 	if have := fieldsOf(reflect.TypeOf(Prefs{})); !reflect.DeepEqual(have, prefsHandles) {
 		t.Errorf("Prefs.Equal check might be out of sync\nfields: %q\nhandled: %q\n",
 			have, prefsHandles)