all: fallback to br0 as nameserver if 127.0.0.1 is used

On Firewalla, lo interface is excluded in all dnsmasq settings of all
interfaces, to prevent conflicts. The one that ctrld adds in
dnsmasq_local directory could not work if there're multiple dnsmasq
configs for multiple interfaces (real example from an user who uses
VLAN in router setup).

Instead, if we detect 127.0.0.1 on Firewalla, fallback to "br0"
interface IP address instead.

cmd/ctrld/cli.go

@@ -982,6 +982,10 @@ func uninstall(p *prog, s service.Service) {
 	}
 	initLogging()
 	if doTasks(tasks) {
+		if err := router.PostUninstall(svcConfig); err != nil {
+			mainLog.Warn().Err(err).Msg("post uninstallation failed, please check system/service log for details error")
+			return
+		}
 		// Stop already reset DNS on router.
 		if router.Name() == "" {
 			p.resetDNS()

cmd/ctrld/prog.go

@@ -235,7 +235,23 @@ func (p *prog) setDNS() {
 		return
 	}
 	logger.Debug().Msg("setting DNS for interface")
-	if err := setDNS(netIface, []string{cfg.Listener["0"].IP}); err != nil {
+	ns := cfg.Listener["0"].IP
+	if router.Name() == router.Firewalla && ns == "127.0.0.1" {
+		// On Firewalla, the lo interface is excluded in all dnsmasq settings of all interfaces.
+		// Thus, we use "br0" as the nameserver in /etc/resolv.conf file.
+		logger.Warn().Msg("127.0.0.1 won't work on Firewalla")
+		if netIface, err := net.InterfaceByName("br0"); err == nil {
+			addrs, _ := netIface.Addrs()
+			for _, addr := range addrs {
+				if netIP, ok := addr.(*net.IPNet); ok && netIP.IP.To4() != nil {
+					logger.Warn().Msg("using br0 interface IP address as DNS server")
+					ns = netIP.IP.To4().String()
+					break
+				}
+			}
+		}
+	}
+	if err := setDNS(netIface, []string{ns}); err != nil {
 		logger.Error().Err(err).Msgf("could not set DNS for interface")
 		return
 	}