arc: Register media files to MediaProvider.

chrome/browser/chromeos/arc/arc_downloads_watcher_service.cc

+// Copyright 2016 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "chrome/browser/chromeos/arc/arc_downloads_watcher_service.h"
+
+#include <memory>
+#include <utility>
+
+#include "base/callback.h"
+#include "base/files/file_enumerator.h"
+#include "base/files/file_path.h"
+#include "base/files/file_path_watcher.h"
+#include "base/memory/ptr_util.h"
+#include "base/time/time.h"
+#include "chrome/browser/download/download_prefs.h"
+#include "chrome/browser/profiles/profile_manager.h"
+#include "chrome/common/chrome_paths.h"
+#include "components/arc/arc_bridge_service.h"
+#include "content/public/browser/browser_thread.h"
+#include "mojo/public/cpp/bindings/array.h"
+
+using content::BrowserThread;
+
+// Mapping from Android file paths to last modified timestamps.
+using TimestampMap = std::map<base::FilePath, base::Time>;
+
+static const base::FilePath::CharType kAndroidDownloadDir[] =
+    FILE_PATH_LITERAL("/storage/emulated/0/Download");
+
+namespace arc {
+
+namespace {
+
+// Compares two TimestampMaps and returns the list of file paths added/removed
+// or whose timestamp have changed.
+std::vector<base::FilePath> CollectChangedPaths(
+    const TimestampMap& timestamp_map_a,
+    const TimestampMap& timestamp_map_b) {
+  std::vector<base::FilePath> changed_paths;
+
+  TimestampMap::const_iterator iter_a = timestamp_map_a.begin();
+  TimestampMap::const_iterator iter_b = timestamp_map_b.begin();
+  while (iter_a != timestamp_map_a.end() && iter_b != timestamp_map_b.end()) {
+    if (iter_a->first == iter_b->first) {
+      if (iter_a->second != iter_b->second) {
+        changed_paths.emplace_back(iter_a->first);
+      }
+      ++iter_a;
+      ++iter_b;
+    } else if (iter_a->first < iter_b->first) {
+      changed_paths.emplace_back(iter_a->first);
+      ++iter_a;
+    } else {  // iter_a->first > iter_b->first
+      changed_paths.emplace_back(iter_b->first);
+      ++iter_b;
+    }
+  }
+
+  while (iter_a != timestamp_map_a.end()) {
+    changed_paths.emplace_back(iter_a->first);
+    ++iter_a;
+  }
+  while (iter_b != timestamp_map_b.end()) {
+    changed_paths.emplace_back(iter_b->first);
+    ++iter_b;
+  }
+
+  return changed_paths;
+}
+
+}  // namespace
+
+// The core part of ArcDownloadsWatcherService to watch for file changes in
+// Downloads directory.
+class ArcDownloadsWatcherService::DownloadsWatcher {
+ public:
+  using Callback =
+      base::Callback<void(const std::vector<base::FilePath>& paths)>;
+
+  explicit DownloadsWatcher(const Callback& callback);
+  ~DownloadsWatcher();
+
+  // Starts watching Downloads directory.
+  void Start();
+
+ private:
+  // Called by base::FilePathWatcher to notify file changes.
+  void OnFilePathChanged(const base::FilePath& path, bool error);
+
+  // Scans files under |downloads_dir_| recursively and builds a map from file
+  // paths (in Android filesystem) to last modified timestamps.
+  TimestampMap BuildTimestampMap() const;
+
+  Callback callback_;
+  base::FilePath downloads_dir_;
+  std::unique_ptr<base::FilePathWatcher> watcher_;
+  TimestampMap last_timestamp_map_;
+
+  // Note: This should remain the last member so it'll be destroyed and
+  // invalidate the weak pointers before any other members are destroyed.
+  base::WeakPtrFactory<DownloadsWatcher> weak_ptr_factory_;
+
+  DISALLOW_COPY_AND_ASSIGN(DownloadsWatcher);
+};
+
+ArcDownloadsWatcherService::DownloadsWatcher::DownloadsWatcher(
+    const Callback& callback)
+    : callback_(callback), weak_ptr_factory_(this) {
+  DCHECK_CURRENTLY_ON(BrowserThread::UI);
+
+  downloads_dir_ = DownloadPrefs(ProfileManager::GetActiveUserProfile())
+                       .GetDefaultDownloadDirectoryForProfile()
+                       .StripTrailingSeparators();
+}
+
+ArcDownloadsWatcherService::DownloadsWatcher::~DownloadsWatcher() {
+  DCHECK_CURRENTLY_ON(BrowserThread::FILE);
+}
+
+void ArcDownloadsWatcherService::DownloadsWatcher::Start() {
+  DCHECK_CURRENTLY_ON(BrowserThread::FILE);
+
+  // Initialize with the current timestamp map and avoid initial notification.
+  // It is not needed since MediaProvider scans whole storage area on boot.
+  last_timestamp_map_ = BuildTimestampMap();
+
+  watcher_.reset(new base::FilePathWatcher());

[Luis Héctor Chávez, 2016/05/20 15:18:59]

nit: watcher_ = base::MakeUnique<FilePathWatcher>();

[Shuhei Takahashi, 2016/05/24 08:46:33]

Done.

+  // On Linux, base::FilePathWatcher::Watch() always returns true.
+  watcher_->Watch(downloads_dir_, true,
+                  base::Bind(&DownloadsWatcher::OnFilePathChanged,
+                             weak_ptr_factory_.GetWeakPtr()));
+}
+
+void ArcDownloadsWatcherService::DownloadsWatcher::OnFilePathChanged(
+    const base::FilePath& path,
+    bool error) {
+  // On Linux, |error| is always false. Also, |path| is always the same path
+  // as one given to FilePathWatcher::Watch().
+  DCHECK_CURRENTLY_ON(BrowserThread::FILE);
+
+  TimestampMap current_timestamp_map = BuildTimestampMap();
+
+  std::vector<base::FilePath> changed_paths =
+      CollectChangedPaths(last_timestamp_map_, current_timestamp_map);
+
+  last_timestamp_map_ = std::move(current_timestamp_map);
+
+  callback_.Run(changed_paths);
+}
+
+TimestampMap ArcDownloadsWatcherService::DownloadsWatcher::BuildTimestampMap()
+    const {
+  DCHECK(!downloads_dir_.EndsWithSeparator());
+  TimestampMap timestamp_map;
+
+  // Enumerate normal files only; directories and symlinks are skipped.
+  base::FileEnumerator enumerator(downloads_dir_, true,
+                                  base::FileEnumerator::FILES);
+  for (;;) {

[Luis Héctor Chávez, 2016/05/20 15:18:59]

nit: for (const base::FilePath& cros_path = enumerator.Next();
          !cros_path.empty();
          cros_path = enumerator.Next())

seems to be more idiomatic.

[Shuhei Takahashi, 2016/05/24 08:46:33]

Done, but I made |cros_path| non-reference to permit re-assignment.

+    const base::FilePath& cros_path = enumerator.Next();
+    if (cros_path.empty()) {
+      break;
+    }
+    // Android file path can be obtained by replacing |downloads_dir_| prefix
+    // with |kAndroidDownloadDir|.
+    const base::FilePath& android_path =
+        base::FilePath(kAndroidDownloadDir)
+            .Append(
+                cros_path.value().substr(downloads_dir_.value().length() + 1));
+    const base::FileEnumerator::FileInfo& info = enumerator.GetInfo();
+    timestamp_map[android_path] = info.GetLastModifiedTime();
+  }
+  return timestamp_map;
+}
+
+ArcDownloadsWatcherService::ArcDownloadsWatcherService(
+    ArcBridgeService* bridge_service)
+    : ArcService(bridge_service), weak_ptr_factory_(this) {
+  DCHECK_CURRENTLY_ON(BrowserThread::UI);
+  arc_bridge_service()->AddObserver(this);
+}
+
+ArcDownloadsWatcherService::~ArcDownloadsWatcherService() {
+  DCHECK_CURRENTLY_ON(BrowserThread::UI);
+  arc_bridge_service()->RemoveObserver(this);
+  StopWatchDownloads();
+  DCHECK(!watcher_.get());
+}
+
+void ArcDownloadsWatcherService::OnFileSystemInstanceReady() {
+  DCHECK_CURRENTLY_ON(BrowserThread::UI);
+  StartWatchDownloads();
+}
+
+void ArcDownloadsWatcherService::OnFileSystemInstanceClosed() {
+  DCHECK_CURRENTLY_ON(BrowserThread::UI);
+  StopWatchDownloads();
+}
+
+void ArcDownloadsWatcherService::StartWatchDownloads() {
+  DCHECK_CURRENTLY_ON(BrowserThread::UI);
+  StopWatchDownloads();
+  DCHECK(!watcher_.get());
+  watcher_.reset(new DownloadsWatcher(
+      base::Bind(&ArcDownloadsWatcherService::OnDownloadsChanged,
+                 weak_ptr_factory_.GetWeakPtr())));
+  BrowserThread::PostTask(
+      BrowserThread::FILE, FROM_HERE,
+      base::Bind(&DownloadsWatcher::Start, base::Unretained(watcher_.get())));
+}
+
+void ArcDownloadsWatcherService::StopWatchDownloads() {
+  DCHECK_CURRENTLY_ON(BrowserThread::UI);
+  if (watcher_.get()) {
+    BrowserThread::DeleteSoon(BrowserThread::FILE, FROM_HERE,
+                              watcher_.release());
+  }
+}
+
+void ArcDownloadsWatcherService::OnDownloadsChanged(
+    const std::vector<base::FilePath>& paths) {
+  DCHECK_CURRENTLY_ON(BrowserThread::FILE);
+
+  auto instance = arc_bridge_service()->file_system_instance();
+  if (!instance) {
+    return;
+  }
+
+  mojo::Array<mojo::String> mojo_paths(paths.size());
+  for (int i = 0; i < paths.size(); ++i) {
+    mojo_paths[i] = paths[i].value();
+  }
+  instance->RequestMediaScan(std::move(mojo_paths));
+}
+
+}  // namespace arc