xds: Don't cache rdsName in XdsDepManager

We can easily compute the rdsName and avoiding the state means we don't
need to override onResourceDoesNotExist() to keep the cache in-sync with
the config.

Author: ejona86

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

@@ -566,7 +566,6 @@ private interface RdsUpdateSupplier {
 
   private class LdsWatcher extends XdsWatcherBase<XdsListenerResource.LdsUpdate>
       implements RdsUpdateSupplier {
-    String rdsName;
 
     private LdsWatcher(String resourceName) {
       super(XdsListenerResource.getInstance(), resourceName);
@@ -581,43 +580,36 @@ public void onChanged(XdsListenerResource.LdsUpdate update) {
 
       HttpConnectionManager httpConnectionManager = update.httpConnectionManager();
       List<VirtualHost> virtualHosts;
-      String rdsName;
       if (httpConnectionManager == null) {
         // TCP listener. Unsupported config
         virtualHosts = Collections.emptyList(); // Not null, to not delegate to RDS
-        rdsName = null;
       } else {
         virtualHosts = httpConnectionManager.virtualHosts();
-        rdsName = httpConnectionManager.rdsName();
       }
-
       if (virtualHosts != null) {
-        // No RDS watcher since we are getting RDS updates via LDS
         updateRoutes(virtualHosts);
-        this.rdsName = null;
-      } else {
-        this.rdsName = rdsName;
+      }
+
+      String rdsName = getRdsName(update);
+      if (rdsName != null) {
         addRdsWatcher(rdsName);
       }
 
       setData(update);
       maybePublishConfig();
     }
 
-    @Override
-    public void onResourceDoesNotExist(String resourceName) {
-      if (cancelled) {
-        return;
+    private String getRdsName(XdsListenerResource.LdsUpdate update) {
+      HttpConnectionManager httpConnectionManager = update.httpConnectionManager();
+      if (httpConnectionManager == null) {
+        // TCP listener. Unsupported config
+        return null;
       }
-
-      checkArgument(resourceName().equals(resourceName), "Resource name does not match");
-      setDataAsStatus(Status.UNAVAILABLE.withDescription(
-          toContextString() + " does not exist" + nodeInfo()));
-      rdsName = null;
-      maybePublishConfig();
+      return httpConnectionManager.rdsName();
     }
 
-    private RdsWatcher getRdsWatcher(WatcherTracer tracer) {
+    private RdsWatcher getRdsWatcher(XdsListenerResource.LdsUpdate update, WatcherTracer tracer) {
+      String rdsName = getRdsName(update);
       if (rdsName == null) {
         return null;
       }
@@ -636,7 +628,7 @@ public RdsUpdateSupplier getRouteSource(WatcherTracer tracer) {
       if (virtualHosts != null) {
         return this;
       }
-      RdsWatcher rdsWatcher = getRdsWatcher(tracer);
+      RdsWatcher rdsWatcher = getRdsWatcher(getData().getValue(), tracer);
       assert rdsWatcher != null;
       return rdsWatcher;
     }