[client] Ensure engine is stopped before starting it back (#2565)

Before starting a new instance of the engine, check if it is nil and stop the current instance

client/internal/connect.go

@@ -158,6 +158,7 @@ func (c *ConnectClient) run(
 	}
 
 	defer c.statusRecorder.ClientStop()
+	runningChanOpen := true
 	operation := func() error {
 		// if context cancelled we not start new backoff cycle
 		if c.isContextCancelled() {
@@ -267,6 +268,12 @@ func (c *ConnectClient) run(
 		checks := loginResp.GetChecks()
 
 		c.engineMutex.Lock()
+		if c.engine != nil && c.engine.ctx.Err() != nil {
+			log.Info("Stopping Netbird Engine")
+			if err := c.engine.Stop(); err != nil {
+				log.Errorf("Failed to stop engine: %v", err)
+			}
+		}
 		c.engine = NewEngineWithProbes(engineCtx, cancel, signalClient, mgmClient, relayManager, engineConfig, mobileDependency, c.statusRecorder, probes, checks)
 
 		c.engineMutex.Unlock()
@@ -279,9 +286,10 @@ func (c *ConnectClient) run(
 		log.Infof("Netbird engine started, the IP is: %s", peerConfig.GetAddress())
 		state.Set(StatusConnected)
 
-		if runningChan != nil {
+		if runningChan != nil && runningChanOpen {
 			runningChan <- nil
 			close(runningChan)
+			runningChanOpen = false
 		}
 
 		<-engineCtx.Done()

client/internal/engine.go

@@ -1115,10 +1115,7 @@ func (e *Engine) close() {
 	}
 
 	// stop/restore DNS first so dbus and friends don't complain because of a missing interface
-	if e.dnsServer != nil {
+	e.stopDNSServer()
-		e.dnsServer.Stop()
-		e.dnsServer = nil
-	}
 
 	if e.routeManager != nil {
 		e.routeManager.Stop()
@@ -1360,12 +1357,16 @@ func (e *Engine) probeTURNs() []relay.ProbeResult {
 }
 
 func (e *Engine) restartEngine() {
+	log.Info("restarting engine")
+	CtxGetState(e.ctx).Set(StatusConnecting)
+
 	if err := e.Stop(); err != nil {
 		log.Errorf("Failed to stop engine: %v", err)
 	}
-	if err := e.Start(); err != nil {
+
-		log.Errorf("Failed to start engine: %v", err)
+	_ = CtxGetState(e.ctx).Wrap(ErrResetConnection)
-	}
+	log.Infof("cancelling client, engine will be recreated")
+	e.clientCancel()
 }
 
 func (e *Engine) startNetworkMonitor() {
@@ -1387,6 +1388,7 @@ func (e *Engine) startNetworkMonitor() {
 			defer mu.Unlock()
 
 			if debounceTimer != nil {
+				log.Infof("Network monitor: detected network change, reset debounceTimer")
 				debounceTimer.Stop()
 			}
 
@@ -1396,7 +1398,7 @@ func (e *Engine) startNetworkMonitor() {
 				mu.Lock()
 				defer mu.Unlock()
 
-				log.Infof("Network monitor detected network change, restarting engine")
+				log.Infof("Network monitor: detected network change, restarting engine")
 				e.restartEngine()
 			})
 		})
@@ -1421,6 +1423,20 @@ func (e *Engine) addrViaRoutes(addr netip.Addr) (bool, netip.Prefix, error) {
 	return false, netip.Prefix{}, nil
 }
 
+func (e *Engine) stopDNSServer() {
+	err := fmt.Errorf("DNS server stopped")
+	nsGroupStates := e.statusRecorder.GetDNSStates()
+	for i := range nsGroupStates {
+		nsGroupStates[i].Enabled = false
+		nsGroupStates[i].Error = err
+	}
+	e.statusRecorder.UpdateDNSStates(nsGroupStates)
+	if e.dnsServer != nil {
+		e.dnsServer.Stop()
+		e.dnsServer = nil
+	}
+}
+
 // isChecksEqual checks if two slices of checks are equal.
 func isChecksEqual(checks []*mgmProto.Checks, oChecks []*mgmProto.Checks) bool {
 	return slices.EqualFunc(checks, oChecks, func(checks, oChecks *mgmProto.Checks) bool {