feat: fix panic on empty Events array in etcd watch response (#36)

Author: hsluoyz

go.mod

@@ -4,6 +4,5 @@ go 1.16
 
 require (
 	github.com/casbin/casbin/v2 v2.30.2
-	go.etcd.io/etcd/api/v3 v3.5.0
 	go.etcd.io/etcd/client/v3 v3.5.0
 )

watcher.go

@@ -164,6 +164,14 @@ func (w *Watcher) Update() error {
 func (w *Watcher) startWatch() error {
 	watcher := w.client.Watch(context.Background(), w.keyName)
 	for res := range watcher {
+		// Skip progress notifications
+		if res.IsProgressNotify() {
+			continue
+		}
+		// Skip empty events
+		if len(res.Events) == 0 {
+			continue
+		}
 		t := res.Events[0]
 		if t.IsCreate() || t.IsModify() {
 			w.lock.RLock()