[client] Check wginterface instead of engine ctx (#2676)

Moving code to ensure wgInterface is gone right after context is
cancelled/stop in the off chance that on next retry the backoff
operation is permanently cancelled and interface is abandoned without
destroying.

client/internal/connect.go

@@ -269,12 +269,6 @@ 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()
@@ -294,6 +288,15 @@ func (c *ConnectClient) run(
 		}
 
 		<-engineCtx.Done()
+		c.engineMutex.Lock()
+		if c.engine != nil && c.engine.wgInterface != nil {
+			log.Infof("ensuring %s is removed, Netbird engine context cancelled", c.engine.wgInterface.Name())
+			if err := c.engine.Stop(); err != nil {
+				log.Errorf("Failed to stop engine: %v", err)
+			}
+			c.engine = nil
+		}
+		c.engineMutex.Unlock()
 		c.statusRecorder.ClientTeardown()
 
 		backOff.Reset()

client/internal/engine.go

@@ -251,6 +251,13 @@ func (e *Engine) Stop() error {
 	}
 	log.Info("Network monitor: stopped")
 
+	// stop/restore DNS first so dbus and friends don't complain because of a missing interface
+	e.stopDNSServer()
+
+	if e.routeManager != nil {
+		e.routeManager.Stop()
+	}
+
 	err := e.removeAllPeers()
 	if err != nil {
 		return fmt.Errorf("failed to remove all peers: %s", err)
@@ -1116,18 +1123,12 @@ func (e *Engine) close() {
 		}
 	}
 
-	// stop/restore DNS first so dbus and friends don't complain because of a missing interface
-	e.stopDNSServer()
-
-	if e.routeManager != nil {
-		e.routeManager.Stop()
-	}
-
 	log.Debugf("removing Netbird interface %s", e.config.WgIfaceName)
 	if e.wgInterface != nil {
 		if err := e.wgInterface.Close(); err != nil {
 			log.Errorf("failed closing Netbird interface %s %v", e.config.WgIfaceName, err)
 		}
+		e.wgInterface = nil
 	}
 
 	if !isNil(e.sshServer) {
@@ -1395,7 +1396,7 @@ func (e *Engine) startNetworkMonitor() {
 			}
 
 			// Set a new timer to debounce rapid network changes
-			debounceTimer = time.AfterFunc(1*time.Second, func() {
+			debounceTimer = time.AfterFunc(2*time.Second, func() {
 				// This function is called after the debounce period
 				mu.Lock()
 				defer mu.Unlock()
@@ -1426,17 +1427,18 @@ func (e *Engine) addrViaRoutes(addr netip.Addr) (bool, netip.Prefix, error) {
 }
 
 func (e *Engine) stopDNSServer() {
+	if e.dnsServer == nil {
+		return
+	}
+	e.dnsServer.Stop()
+	e.dnsServer = nil
 	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.