xds: not cancel and restart RDS watch on the same LDS update (#3619)

xds/internal/client/client_watchers_service.go

@@ -62,6 +62,7 @@ type serviceUpdateWatcher struct {
 
 	mu        sync.Mutex
 	closed    bool
+	rdsName   string
 	rdsCancel func()
 }
 
@@ -82,6 +83,12 @@ func (w *serviceUpdateWatcher) handleLDSResp(update ldsUpdate, err error) {
 		return
 	}
 
+	if w.rdsName == update.routeName {
+		// If the new routeName is same as the previous, don't cancel and
+		// restart the RDS watch.
+		return
+	}
+	w.rdsName = update.routeName
 	if w.rdsCancel != nil {
 		w.rdsCancel()
 	}

xds/internal/client/client_watchers_service_test.go

@@ -337,3 +337,49 @@ func (s) TestServiceWatchWithClientClose(t *testing.T) {
 		t.Fatal(cbErr)
 	}
 }
+
+// TestServiceNotCancelRDSOnSameLDSUpdate covers the case that if the second LDS
+// update contains the same RDS name as the previous, the RDS watch isn't
+// canceled and restarted.
+func (s) TestServiceNotCancelRDSOnSameLDSUpdate(t *testing.T) {
+	v2ClientCh, cleanup := overrideNewXDSV2Client()
+	defer cleanup()
+
+	c, err := New(clientOpts(testXDSServer))
+	if err != nil {
+		t.Fatalf("failed to create client: %v", err)
+	}
+	defer c.Close()
+
+	v2Client := <-v2ClientCh
+
+	serviceUpdateCh := testutils.NewChannel()
+	c.WatchService(testLDSName, func(update ServiceUpdate, err error) {
+		serviceUpdateCh.Send(serviceUpdateErr{u: update, err: err})
+	})
+
+	wantUpdate := ServiceUpdate{Cluster: testCDSName}
+
+	<-v2Client.addWatches[ldsURL]
+	v2Client.r.newLDSUpdate(map[string]ldsUpdate{
+		testLDSName: {routeName: testRDSName},
+	})
+	<-v2Client.addWatches[rdsURL]
+	v2Client.r.newRDSUpdate(map[string]rdsUpdate{
+		testRDSName: {clusterName: testCDSName},
+	})
+
+	if u, err := serviceUpdateCh.Receive(); err != nil || u != (serviceUpdateErr{wantUpdate, nil}) {
+		t.Errorf("unexpected serviceUpdate: %v, error receiving from channel: %v", u, err)
+	}
+
+	// Another LDS update with a the same RDS_name.
+	v2Client.r.newLDSUpdate(map[string]ldsUpdate{
+		testLDSName: {routeName: testRDSName},
+	})
+	select {
+	case <-v2Client.removeWatches[rdsURL]:
+		t.Fatalf("unexpected rds watch cancel")
+	case <-time.After(time.Second):
+	}
+}