xds:fix cancel xds watcher accidentally removes the url

Author: YifeiZhuang

xds/src/main/java/io/grpc/xds/XdsClientImpl.java

@@ -332,12 +332,13 @@ public void run() {
         if (!subscriber.isWatched()) {
           subscriber.cancelResourceWatch();
           resourceSubscribers.get(type).remove(resourceName);
-          subscribedResourceTypeUrls.remove(type.typeUrl());
           if (subscriber.xdsChannel != null) {
             subscriber.xdsChannel.adjustResourceSubscription(type);
           }
           if (resourceSubscribers.get(type).isEmpty()) {
             resourceSubscribers.remove(type);
+            subscribedResourceTypeUrls.remove(type.typeUrl());
+
           }
         }
       }

xds/src/test/java/io/grpc/xds/XdsClientImplTestBase.java

@@ -938,6 +938,33 @@ public void ldsResourceUpdated() {
     assertThat(channelForEmptyAuthority).isNull();
   }
 
+  @Test
+  public void ldsResourceUpdated_() {
+    DiscoveryRpcCall call = startResourceWatcher(XdsListenerResource.getInstance(), LDS_RESOURCE,
+        ldsResourceWatcher);
+    verifyResourceMetadataRequested(LDS, LDS_RESOURCE);
+
+    // Initial LDS response.
+    call.sendResponse(LDS, testListenerVhosts, VERSION_1, "0000");
+    call.verifyRequest(LDS, LDS_RESOURCE, VERSION_1, "0000", NODE);
+    verify(ldsResourceWatcher).onChanged(ldsUpdateCaptor.capture());
+    verifyGoldenListenerVhosts(ldsUpdateCaptor.getValue());
+    verifyResourceMetadataAcked(LDS, LDS_RESOURCE, testListenerVhosts, VERSION_1, TIME_INCREMENT);
+
+    xdsClient.watchXdsResource(XdsListenerResource.getInstance(),
+        LDS_RESOURCE + "1", ldsResourceWatcher);
+    xdsClient.cancelXdsResourceWatch(XdsListenerResource.getInstance(), LDS_RESOURCE + "1",ldsResourceWatcher);
+
+    // Updated LDS response.
+    Any testListenerVhosts2 = Any.pack(mf.buildListenerWithApiListener(LDS_RESOURCE,
+        mf.buildRouteConfiguration("new", mf.buildOpaqueVirtualHosts(VHOST_SIZE))));
+    call.sendResponse(LDS, testListenerVhosts2, VERSION_2, "0001");
+    call.verifyRequest(LDS, LDS_RESOURCE, VERSION_2, "0001", NODE);
+    verify(ldsResourceWatcher).onChanged(ldsUpdateCaptor.capture());
+    verifyGoldenListenerVhosts(ldsUpdateCaptor.getValue());
+    verifyResourceMetadataAcked(LDS, LDS_RESOURCE, testListenerVhosts2, VERSION_2, TIME_INCREMENT * 2);
+  }
+
   @Test
   public void ldsResourceUpdated_withXdstpResourceName() {
     BootstrapperImpl.enableFederation = true;