Detect network interface change and restart the service when detected

netstatus/netstatus.go

@@ -0,0 +1,80 @@
+package netstatus
+
+import (
+	"context"
+	"net"
+	"reflect"
+	"sync"
+	"time"
+)
+
+type Change struct{}
+
+var handlers struct {
+	sync.Mutex
+	c []chan<- Change
+}
+
+var cancel context.CancelFunc
+var lastInterfaces []net.Interface
+
+// Notify sends a Change to c any time the network interfaces status change.
+func Notify(c chan<- Change) {
+	handlers.Lock()
+	defer handlers.Unlock()
+	if handlers.c == nil {
+		go startChecker()
+	}
+	handlers.c = append(handlers.c, c)
+}
+
+// Stop unsubscribes from network interfaces change notification.
+func Stop(c chan<- Change) {
+	handlers.Lock()
+	defer handlers.Unlock()
+	var newC = make([]chan<- Change, 0, len(handlers.c)-1)
+	for _, ch := range handlers.c {
+		if ch != c {
+			newC = append(newC, c)
+		}
+	}
+	handlers.c = newC
+	if len(handlers.c) == 0 && cancel != nil {
+		cancel()
+		cancel = nil
+	}
+}
+
+func broadcast(c Change) {
+	handlers.Lock()
+	defer handlers.Unlock()
+	for _, ch := range handlers.c {
+		ch <- c
+	}
+}
+
+func startChecker() {
+	tick := time.NewTicker(30 * time.Second)
+	defer tick.Stop()
+	var ctx context.Context
+	ctx, cancel = context.WithCancel(context.Background())
+	defer cancel()
+	changed() // init
+	for {
+		select {
+		case <-tick.C:
+			if changed() {
+				broadcast(Change{})
+			}
+		case <-ctx.Done():
+			break
+		}
+	}
+}
+
+func changed() bool {
+	interfaces, _ := net.Interfaces()
+	changed := !reflect.DeepEqual(lastInterfaces, interfaces)
+	lastInterfaces = interfaces
+	return changed
+}

service.go

@@ -17,6 +17,7 @@ import (
 
 	cflag "github.com/nextdns/nextdns/flag"
 	"github.com/nextdns/nextdns/mdns"
+	"github.com/nextdns/nextdns/netstatus"
 	"github.com/nextdns/nextdns/proxy"
 	"github.com/nextdns/nextdns/resolver"
 	"github.com/nextdns/nextdns/resolver/endpoint"
@@ -54,6 +55,11 @@ func (p *proxySvc) Start(s service.Service) (err error) {
 	return nil
 }
 
+func (p *proxySvc) Restart() error {
+	p.Stop(nil)
+	return p.Start(nil)
+}
+
 func (p *proxySvc) Stop(s service.Service) error {
 	if p.stop != nil {
 		p.stop()
@@ -213,6 +219,16 @@ func svc(cmd string) error {
 		if *reportClientInfo {
 			setupClientReporting(p, conf)
 		}
+		go func() {
+			netChange := make(chan netstatus.Change)
+			netstatus.Notify(netChange)
+			for range netChange {
+				_ = log.Info("Network change detected, restarting")
+				if err := p.Restart(); err != nil {
+					_ = log.Errorf("Restart failed: %v", err)
+				}
+			}
+		}()
 		return s.Run()
 	default:
 		panic("unknown cmd: " + cmd)