From 4dd66b9cdb7d3ddb74db216aaea5cae54d63acb3 Mon Sep 17 00:00:00 2001
From: Gauri Kalra <kalragauri@google.com>
Date: Tue, 14 Jul 2026 06:27:36 +0000
Subject: [PATCH] fix(storage): prevent indefinite hang when calling Close() on
 async appendable uploads

---
 .../storage/internal/async/writer_connection_impl.cc | 12 +++++++++++-
 .../internal/async/writer_connection_impl_test.cc    | 10 ++++++++++
 .../storage/tests/async_client_integration_test.cc   |  2 +-
 3 files changed, 22 insertions(+), 2 deletions(-)

diff --git a/google/cloud/storage/internal/async/writer_connection_impl.cc b/google/cloud/storage/internal/async/writer_connection_impl.cc
index 3acafa12d7dd8..a27ea4fbc3070 100644
--- a/google/cloud/storage/internal/async/writer_connection_impl.cc
+++ b/google/cloud/storage/internal/async/writer_connection_impl.cc
@@ -225,7 +225,17 @@ future<Status> AsyncWriterConnectionImpl::OnClose(std::size_t upload_size,
         HandleFinishAfterError("Expected Finish() error after non-ok Write()"));
   }
   offset_ += upload_size;
-  return Finish().then([](auto f) { return f.get(); });
+  std::unique_lock<std::mutex> lk(mu_);
+  auto impl = impl_;
+  lk.unlock();
+  return impl->Read()
+      .then([this](auto f) { return OnQuery(f.get()); })
+      .then([this](auto g) {
+        auto status = g.get();
+        if (!status) return make_ready_future(std::move(status).status());
+        return Finish();
+      })
+      .then([](auto f) { return f.get(); });
 }
 
 future<StatusOr<google::storage::v2::Object>>
diff --git a/google/cloud/storage/internal/async/writer_connection_impl_test.cc b/google/cloud/storage/internal/async/writer_connection_impl_test.cc
index 03ecf7699cc2c..906ec74480614 100644
--- a/google/cloud/storage/internal/async/writer_connection_impl_test.cc
+++ b/google/cloud/storage/internal/async/writer_connection_impl_test.cc
@@ -850,6 +850,12 @@ TEST(AsyncWriterConnectionTest, CloseEmpty) {
                   "test-only-algo");
         return sequencer.PushBack("Write");
       });
+  EXPECT_CALL(*mock, Read).WillOnce([&] {
+    return sequencer.PushBack("Read").then([](auto f) {
+      if (!f.get()) return absl::optional<Response>();
+      return absl::make_optional(Response{});
+    });
+  });
   EXPECT_CALL(*mock, Finish).WillOnce([&] {
     return sequencer.PushBack("Finish").then([](auto f) {
       if (f.get()) return Status{};
@@ -867,6 +873,10 @@ TEST(AsyncWriterConnectionTest, CloseEmpty) {
   ASSERT_THAT(next.second, "Write");
   next.first.set_value(true);
 
+  next = sequencer.PopFrontWithName();
+  ASSERT_THAT(next.second, "Read");
+  next.first.set_value(true);
+
   next = sequencer.PopFrontWithName();
   ASSERT_THAT(next.second, "Finish");
   next.first.set_value(true);
diff --git a/google/cloud/storage/tests/async_client_integration_test.cc b/google/cloud/storage/tests/async_client_integration_test.cc
index 6827ec4ec8f57..e383aeee30f14 100644
--- a/google/cloud/storage/tests/async_client_integration_test.cc
+++ b/google/cloud/storage/tests/async_client_integration_test.cc
@@ -810,7 +810,7 @@ TEST_F(AsyncClientIntegrationTest, ResumeAppendableObjectUpload) {
     token = *std::move(p);
   }
 
-  writer.Close();
+  ASSERT_STATUS_OK(writer.Close().get());
 
   // Reset the existing writer and resume the upload.
   writer = AsyncWriter();