From 27fe7a447b0ee61b5bb3380e1b1858b679b3fd9c Mon Sep 17 00:00:00 2001
From: MV Shiva Prasad <okshiva@google.com>
Date: Thu, 7 Aug 2025 12:54:06 +0530
Subject: [PATCH 1/2] xds: xdsClient caches transient error for new watchers

---
 .../main/java/io/grpc/xds/client/XdsClientImpl.java  | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/xds/src/main/java/io/grpc/xds/client/XdsClientImpl.java b/xds/src/main/java/io/grpc/xds/client/XdsClientImpl.java
index d3384cbbe4e..bd5fcbfee00 100644
--- a/xds/src/main/java/io/grpc/xds/client/XdsClientImpl.java
+++ b/xds/src/main/java/io/grpc/xds/client/XdsClientImpl.java
@@ -676,6 +676,8 @@ private final class ResourceSubscriber<T extends ResourceUpdate> {
     private ResourceMetadata metadata;
     @Nullable
     private String errorDescription;
+    @Nullable
+    private Status lastError;
 
     ResourceSubscriber(XdsResourceType<T> type, String resource) {
       syncContext.throwIfNotInThisSynchronizationContext();
@@ -712,11 +714,16 @@ void addWatcher(ResourceWatcher<T> watcher, Executor watcherExecutor) {
       watchers.put(watcher, watcherExecutor);
       T savedData = data;
       boolean savedAbsent = absent;
+      Status savedError = lastError;
       watcherExecutor.execute(() -> {
         if (errorDescription != null) {
           watcher.onError(Status.INVALID_ARGUMENT.withDescription(errorDescription));
           return;
         }
+        if (savedError != null) {
+          watcher.onError(savedError);
+          return;
+        }
         if (savedData != null) {
           notifyWatcher(watcher, savedData);
         } else if (savedAbsent) {
@@ -808,6 +815,7 @@ void onData(ParsedResource<T> parsedResource, String version, long updateTime,
       this.metadata = ResourceMetadata
           .newResourceMetadataAcked(parsedResource.getRawResource(), version, updateTime);
       absent = false;
+      lastError = null;
       if (resourceDeletionIgnored) {
         logger.log(XdsLogLevel.FORCE_INFO, "xds server {0}: server returned new version "
                 + "of resource for which we previously ignored a deletion: type {1} name {2}",
@@ -857,6 +865,7 @@ void onAbsent(@Nullable ProcessingTracker processingTracker, ServerInfo serverIn
       if (!absent) {
         data = null;
         absent = true;
+        lastError = null;
         metadata = serverInfo.resourceTimerIsTransientError()
             ? ResourceMetadata.newResourceMetadataTimeout()
             : ResourceMetadata.newResourceMetadataDoesNotExist();
@@ -894,6 +903,9 @@ void onError(Status error, @Nullable ProcessingTracker tracker) {
       Status errorAugmented = Status.fromCode(error.getCode())
           .withDescription(description + "nodeID: " + bootstrapInfo.node().getId())
           .withCause(error.getCause());
+      this.lastError = errorAugmented;
+      this.data = null;
+      this.absent = false;
 
       for (ResourceWatcher<T> watcher : watchers.keySet()) {
         if (tracker != null) {

From 033a4b10360e7bca9fe88f0613e3c8600cebf543 Mon Sep 17 00:00:00 2001
From: MV Shiva Prasad <okshiva@google.com>
Date: Fri, 8 Aug 2025 21:09:12 +0530
Subject: [PATCH 2/2] address comments

---
 xds/src/main/java/io/grpc/xds/client/XdsClientImpl.java | 2 --
 1 file changed, 2 deletions(-)

diff --git a/xds/src/main/java/io/grpc/xds/client/XdsClientImpl.java b/xds/src/main/java/io/grpc/xds/client/XdsClientImpl.java
index bd5fcbfee00..4c6823f844a 100644
--- a/xds/src/main/java/io/grpc/xds/client/XdsClientImpl.java
+++ b/xds/src/main/java/io/grpc/xds/client/XdsClientImpl.java
@@ -904,8 +904,6 @@ void onError(Status error, @Nullable ProcessingTracker tracker) {
           .withDescription(description + "nodeID: " + bootstrapInfo.node().getId())
           .withCause(error.getCause());
       this.lastError = errorAugmented;
-      this.data = null;
-      this.absent = false;
 
       for (ResourceWatcher<T> watcher : watchers.keySet()) {
         if (tracker != null) {