update_client: Introduce a helper function to make timeout callbacks.

This wrapper guarantees that the callback will eventually be called even
if the recipient of the callback forgets about it.

Bug: 402773563
Change-Id: I48d23681d8b570972537d40c56d03591edea4e85
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4282299
Auto-Submit: Joshua Pawlicki <waffles@chromium.org>
Commit-Queue: Joshua Pawlicki <waffles@chromium.org>
Reviewed-by: Sorin Jianu <sorin@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1431756}

components/update_client/BUILD.gn

@@ -136,6 +136,7 @@ static_library("update_client") {
     "task_traits.h",
     "task_update.cc",
     "task_update.h",
+    "timed_callback.h",
     "unpacker.cc",
     "unpacker.h",
     "unzipper.h",
@@ -296,6 +297,7 @@ source_set("unit_tests") {
     "protocol_serializer_json_unittest.cc",
     "protocol_serializer_unittest.cc",
     "request_sender_unittest.cc",
+    "timed_callback_unittest.cc",
     "unpacker_unittest.cc",
     "update_checker_unittest.cc",
     "update_client_unittest.cc",

components/update_client/timed_callback.h

@@ -0,0 +1,77 @@
+// Copyright 2025 The Chromium Authors
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef COMPONENTS_UPDATE_CLIENT_TIMED_CALLBACK_H_
+#define COMPONENTS_UPDATE_CLIENT_TIMED_CALLBACK_H_
+
+#include <memory>
+#include <utility>
+
+#include "base/cancelable_callback.h"
+#include "base/functional/callback.h"
+#include "base/functional/callback_helpers.h"
+#include "base/task/sequenced_task_runner.h"
+#include "base/time/time.h"
+
+namespace update_client {
+
+// MakeTimedCallback posts a task to run `callback` after `timeout` with
+// `timeout_args` on the current sequence, and returns a new callback to the
+// caller that also calls `callback`. The returned callback must only be run on
+// the current sequence.
+//
+// If the timeout occurs before the returned callback is
+// run, the returned callback does nothing. It is safe to discard the returned
+// callback in this case, or to call it.
+//
+// If the returned callback is run before the timeout, the timeout will do
+// nothing.
+//
+// In either case, `callback` is guaranteed to run exactly once.
+//
+// For example, given:
+//   void HandleDecryptedContents(std::optional<std::string> plaintext);
+//   decryptAsync(ciphertext, base::BindOnce(&HandleDecryptedContents));
+//
+// It's possible to add a 30-second timeout:
+//   void HandleDecryptedContents(std::optional<std::string> plaintext);
+//   decryptAsync(
+//       cipher,
+//       MakeTimedCallback(
+//           base::BindOnce(&HandleDecryptedContents),
+//           base::Seconds(30),
+//           std::nullopt));
+//
+template <typename ReturnType, typename... Args>
+base::OnceCallback<ReturnType(Args...)> MakeTimedCallback(
+    base::OnceCallback<ReturnType(Args...)> callback,
+    base::TimeDelta timeout,
+    Args... timeout_args) {
+  auto wrapper =
+      std::make_unique<base::CancelableOnceCallback<ReturnType(Args...)>>(
+          std::move(callback));
+  // Both callbacks must be constructed before either has a chance to run.
+  // `callback_1` will be run with the `timeout_args` after `timeout`.
+  // When either callback is run, they invalidate CancelableCallback's internal
+  // weak pointers, and the other callback becomes a no-op.
+  base::OnceCallback<ReturnType()> callback_1 =
+      base::BindOnce(wrapper->callback(), std::move(timeout_args)...);
+  base::OnceCallback<ReturnType(Args...)> callback_2 = wrapper->callback();
+
+  base::SequencedTaskRunner::GetCurrentDefault()->PostDelayedTask(
+      FROM_HERE,
+      base::BindOnce(
+          [](std::unique_ptr<base::CancelableOnceCallback<ReturnType(Args...)>>
+             /* wrapper */,  // This callback takes ownership of `wrapper`.
+             base::OnceCallback<ReturnType()> callback_1) {
+            std::move(callback_1).Run();
+          },
+          std::move(wrapper), std::move(callback_1)),
+      timeout);
+  return callback_2;
+}
+
+}  // namespace update_client
+
+#endif  // COMPONENTS_UPDATE_CLIENT_TIMED_CALLBACK_H_

components/update_client/timed_callback_unittest.cc

@@ -0,0 +1,62 @@
+// Copyright 2025 The Chromium Authors
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "components/update_client/timed_callback.h"
+
+#include <utility>
+
+#include "base/functional/callback.h"
+#include "base/run_loop.h"
+#include "base/task/sequenced_task_runner.h"
+#include "base/test/bind.h"
+#include "base/test/mock_callback.h"
+#include "base/test/task_environment.h"
+#include "base/time/time.h"
+#include "testing/gtest/include/gtest/gtest.h"
+
+namespace update_client {
+namespace {
+
+TEST(TimedCallbackTest, CallNoTimeout) {
+  base::test::TaskEnvironment task_environment;
+  base::MockOnceClosure mock;
+  EXPECT_CALL(mock, Run());
+  std::move(MakeTimedCallback(mock.Get(), base::Seconds(55))).Run();
+}
+
+TEST(TimedCallbackTest, TimeoutThenCall) {
+  base::test::TaskEnvironment task_environment;
+  base::MockOnceCallback<void(int)> mock;
+  base::RunLoop loop;
+  EXPECT_CALL(mock, Run(1));
+  base::OnceCallback<void(int)> callback = MakeTimedCallback(
+      base::BindOnce(mock.Get().Then(loop.QuitClosure())), base::Seconds(1), 1);
+  loop.Run();
+  std::move(callback).Run(2);  // Should have no effect.
+}
+
+TEST(TimedCallbackTest, CallThenTimeout) {
+  base::test::TaskEnvironment task_environment;
+  base::MockOnceClosure mock;
+  base::RunLoop loop;
+  EXPECT_CALL(mock, Run());
+  MakeTimedCallback(mock.Get(), base::Seconds(0)).Run();
+  base::SequencedTaskRunner::GetCurrentDefault()->PostDelayedTask(
+      FROM_HERE, loop.QuitClosure(), base::Milliseconds(10));
+  loop.Run();
+}
+
+TEST(TimedCallbackTest, MoveOnlyParameter) {
+  base::test::TaskEnvironment task_environment;
+  base::MockOnceClosure mock;
+  EXPECT_CALL(mock, Run());
+  std::move(MakeTimedCallback(base::BindOnce([](base::OnceClosure closure) {
+                                std::move(closure).Run();
+                              }),
+                              base::Seconds(55), base::BindOnce([] {})))
+      .Run(mock.Get());
+}
+
+}  // namespace
+}  // namespace update_client