Add BackgroundDownloader for Mac

Implement a background CRX downloader for Mac using NSURLSession's
background transfer capabilities. This is intended to work similarly
to the BITS-backed downloader on Windows.

Downloads started by this implementation can continue even if Chrome
is suspended/terminated and can persist through network errors,
reboots, etc.

When the downloader is instantiated, MacOS may notify it of downloads
which were completed in the background. Thus, a cache of unclaimed
downloads is maintained.


Low-Coverage-Reason: TRIVIAL_CHANGE changes to chrome_component_updater_configurator.cc and crx_downloader_factory.cc are trivial
Bug: 1493709
Change-Id: Ief188e6769a846486e1b558469fdfcfe0b12f566
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4973235
Reviewed-by: Avi Drissman <avi@chromium.org>
Commit-Queue: Noah Rose Ledesma <noahrose@google.com>
Reviewed-by: Sorin Jianu <sorin@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1216377}

chrome/browser/component_updater/chrome_component_updater_configurator.cc

@@ -91,6 +91,8 @@ class ChromeConfigurator : public update_client::Configurator {
  private:
   friend class base::RefCountedThreadSafe<ChromeConfigurator>;
 
+  absl::optional<base::FilePath> GetBackgroundDownloaderCache() const;
+
   ConfiguratorImpl configurator_impl_;
   raw_ptr<PrefService>
       pref_service_;  // This member is not owned by this class.
@@ -191,8 +193,8 @@ ChromeConfigurator::GetNetworkFetcherFactory() {
 scoped_refptr<update_client::CrxDownloaderFactory>
 ChromeConfigurator::GetCrxDownloaderFactory() {
   if (!crx_downloader_factory_) {
-    crx_downloader_factory_ =
-        update_client::MakeCrxDownloaderFactory(GetNetworkFetcherFactory());
+    crx_downloader_factory_ = update_client::MakeCrxDownloaderFactory(
+        GetNetworkFetcherFactory(), GetBackgroundDownloaderCache());
   }
   return crx_downloader_factory_;
 }
@@ -268,6 +270,16 @@ absl::optional<base::FilePath> ChromeConfigurator::GetCrxCachePath() const {
                 : absl::nullopt;
 }
 
+// TODO(crbug/1496582): Consolidate the cache path getters.
+absl::optional<base::FilePath>
+ChromeConfigurator::GetBackgroundDownloaderCache() const {
+  base::FilePath path;
+  bool result = base::PathService::Get(chrome::DIR_USER_DATA, &path);
+  return result ? absl::optional<base::FilePath>(
+                      path.AppendASCII("download_cache"))
+                : absl::nullopt;
+}
+
 }  // namespace
 
 scoped_refptr<update_client::Configurator>

components/component_updater/component_updater_command_line_config_policy.cc

@@ -39,19 +39,20 @@ const char kSwitchDisableDeltaUpdates[] = "disable-delta-updates";
 // value is in seconds.
 const char kInitialDelay[] = "initial-delay";
 
-#if BUILDFLAG(IS_WIN)
+#if BUILDFLAG(IS_MAC) || BUILDFLAG(IS_WIN)
 // Disables background downloads.
 const char kSwitchDisableBackgroundDownloads[] = "disable-background-downloads";
-#endif  // BUILDFLAG(IS_WIN)
+#endif  // BUILDFLAG(IS_MAC) || BUILDFLAG(IS_WIN)
 
 // If there is an element of |vec| of the form |test|=.*, returns the right-
 // hand side of that assignment. Otherwise, returns an empty string.
 // The right-hand side may contain additional '=' characters, allowing for
 // further nesting of switch arguments.
 std::string GetSwitchArgument(const std::vector<std::string>& vec,
                               const char* test) {
-  if (vec.empty())
+  if (vec.empty()) {
     return std::string();
+  }
   for (auto it = vec.begin(); it != vec.end(); ++it) {
     const std::size_t found = it->find("=");
     if (found != std::string::npos) {
@@ -76,7 +77,7 @@ ComponentUpdaterCommandLineConfigPolicy::
       cmdline->GetSwitchValueASCII(switches::kComponentUpdater), ",",
       base::KEEP_WHITESPACE, base::SPLIT_WANT_NONEMPTY);
 
-#if BUILDFLAG(IS_WIN)
+#if BUILDFLAG(IS_MAC) || BUILDFLAG(IS_WIN)
   background_downloads_enabled_ =
       !base::Contains(switch_values, kSwitchDisableBackgroundDownloads);
 #else
@@ -98,8 +99,9 @@ ComponentUpdaterCommandLineConfigPolicy::
   const std::string initial_delay =
       GetSwitchArgument(switch_values, kInitialDelay);
   double initial_delay_seconds = 0;
-  if (base::StringToDouble(initial_delay, &initial_delay_seconds))
+  if (base::StringToDouble(initial_delay, &initial_delay_seconds)) {
     initial_delay_ = base::Seconds(initial_delay_seconds);
+  }
 }
 
 bool ComponentUpdaterCommandLineConfigPolicy::BackgroundDownloadsEnabled()

components/update_client/BUILD.gn

@@ -174,6 +174,14 @@ static_library("update_client") {
     "//url",
   ]
 
+  if (is_mac) {
+    sources += [
+      "background_downloader_mac.h",
+      "background_downloader_mac.mm",
+    ]
+    frameworks = [ "Foundation.framework" ]
+  }
+
   if (is_win) {
     sources += [
       "background_downloader_win.cc",
@@ -286,6 +294,10 @@ source_set("unit_tests") {
     if (is_win) {
       sources += [ "background_downloader_win_unittest.cc" ]
     }
+
+    if (is_mac) {
+      sources += [ "background_downloader_mac_unittest.cc" ]
+    }
   }
 
   deps = [

components/update_client/background_downloader_mac.h

@@ -0,0 +1,80 @@
+// Copyright 2023 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_BACKGROUND_DOWNLOADER_MAC_H_
+#define COMPONENTS_UPDATE_CLIENT_BACKGROUND_DOWNLOADER_MAC_H_
+
+#include "base/files/file_path.h"
+#include "base/functional/callback_forward.h"
+#include "base/gtest_prod_util.h"
+#include "base/memory/ref_counted.h"
+#include "base/memory/scoped_refptr.h"
+#include "base/memory/weak_ptr.h"
+#include "base/sequence_checker.h"
+#include "base/task/sequenced_task_runner.h"
+#include "components/update_client/crx_downloader.h"
+
+namespace update_client {
+namespace {
+// TODO(crbug.com/1493709): The session identifier might need to be more complex
+// to accommodate multiple Chrome processes.
+static constexpr char kDefaultBackgroundSessionId[] = "CrxDownloader";
+}  // namespace
+
+class BackgroundDownloaderSharedSession
+    : public base::RefCountedThreadSafe<BackgroundDownloaderSharedSession> {
+ public:
+  using OnDownloadCompleteCallback = base::RepeatingCallback<void(
+      bool,
+      const update_client::CrxDownloader::Result&,
+      const update_client::CrxDownloader::DownloadMetrics&)>;
+
+  virtual void DoStartDownload(
+      const GURL& url,
+      OnDownloadCompleteCallback on_download_complete_callback) = 0;
+
+  // Cancel all download tasks and invalidates this session. Future calls to
+  // DoStartDownload will fail until the session is recreated.
+  virtual void InvalidateAndCancel() = 0;
+
+ protected:
+  friend class base::RefCountedThreadSafe<BackgroundDownloaderSharedSession>;
+  virtual ~BackgroundDownloaderSharedSession() = default;
+};
+
+class BackgroundDownloader : public CrxDownloader {
+ public:
+  BackgroundDownloader(
+      scoped_refptr<CrxDownloader> successor,
+      scoped_refptr<BackgroundDownloaderSharedSession> shared_session,
+      scoped_refptr<base::SequencedTaskRunner> background_sequence_);
+
+ private:
+  friend class BackgroundDownloaderTest;
+  friend class BackgroundDownloaderCrashingClientTest;
+  FRIEND_TEST_ALL_PREFIXES(BackgroundDownloaderTest, ConcurrentDownloaders);
+
+  // Overrides for CrxDownloader.
+  ~BackgroundDownloader() override;
+  base::OnceClosure DoStartDownload(const GURL& url) override;
+
+  base::OnceClosure DoStartDownload(
+      const GURL& url,
+      BackgroundDownloaderSharedSession::OnDownloadCompleteCallback);
+
+  SEQUENCE_CHECKER(sequence_checker_);
+  scoped_refptr<BackgroundDownloaderSharedSession> shared_session_;
+  scoped_refptr<base::SequencedTaskRunner> background_sequence_;
+  base::WeakPtrFactory<BackgroundDownloader> weak_ptr_factory_{this};
+};
+
+scoped_refptr<BackgroundDownloaderSharedSession>
+MakeBackgroundDownloaderSharedSession(
+    scoped_refptr<base::SequencedTaskRunner> background_sequence,
+    const base::FilePath& download_cache,
+    const std::string& session_identifier = kDefaultBackgroundSessionId);
+
+}  // namespace update_client
+
+#endif  // COMPONENTS_UPDATE_CLIENT_BACKGROUND_DOWNLOADER_MAC_H_