clientv3: handle non -1 watch ID on cancellation

Signed-off-by: Gyuho Lee <gyuhox@gmail.com>

clientv3/watch.go

@@ -367,7 +367,8 @@ func (w *watcher) closeStream(wgs *watchGrpcStream) {
 }
 
 func (w *watchGrpcStream) addSubstream(resp *pb.WatchResponse, ws *watcherStream) {
-	if resp.WatchId == -1 {
+	// check watch ID for backward compatibility (<= v3.3)
+	if resp.WatchId == -1 || (resp.Canceled && resp.CancelReason != "") {
 		// failed; no channel
 		close(ws.recvc)
 		return
@@ -453,6 +454,7 @@ func (w *watchGrpcStream) run() {
 		// Watch() requested
 		case wreq := <-w.reqc:
 			outc := make(chan WatchResponse, 1)
+			// TOOD: pass custom watch ID?
 			ws := &watcherStream{
 				initReq: *wreq,
 				id:      -1,
@@ -553,6 +555,7 @@ func (w *watchGrpcStream) dispatchEvent(pbresp *pb.WatchResponse) bool {
 	for i, ev := range pbresp.Events {
 		events[i] = (*Event)(ev)
 	}
+	// TODO: return watch ID?
 	wr := &WatchResponse{
 		Header:          *pbresp.Header,
 		Events:          events,