mediaview: Support watchers in ArcDocumentsProviderRoot.

chrome/browser/chromeos/arc/fileapi/arc_documents_provider_root.h

Index: chrome/browser/chromeos/arc/fileapi/arc_documents_provider_root.h
diff --git a/chrome/browser/chromeos/arc/fileapi/arc_documents_provider_root.h b/chrome/browser/chromeos/arc/fileapi/arc_documents_provider_root.h
index fd8f8807e3b3ac777b6b68b4a91e35f4d1777311..de752e580a5ae92c5ba1d0cc4e135ae3b7da5ec0 100644
--- a/chrome/browser/chromeos/arc/fileapi/arc_documents_provider_root.h
+++ b/chrome/browser/chromeos/arc/fileapi/arc_documents_provider_root.h
@@ -5,6 +5,8 @@
 #ifndef CHROME_BROWSER_CHROMEOS_ARC_FILEAPI_ARC_DOCUMENTS_PROVIDER_ROOT_H_
 #define CHROME_BROWSER_CHROMEOS_ARC_FILEAPI_ARC_DOCUMENTS_PROVIDER_ROOT_H_
 
+#include <stdint.h>
+
 #include <map>
 #include <string>
 #include <vector>
@@ -12,10 +14,14 @@
 #include "base/callback_forward.h"
 #include "base/files/file_path.h"
 #include "base/macros.h"
+#include "base/memory/ref_counted.h"
 #include "base/memory/weak_ptr.h"
 #include "base/optional.h"
+#include "chrome/browser/chromeos/arc/fileapi/arc_file_system_operation_runner.h"
+#include "chrome/browser/chromeos/arc/fileapi/arc_file_system_operation_runner_util.h"
 #include "components/arc/common/file_system.mojom.h"
 #include "storage/browser/fileapi/async_file_util.h"
+#include "storage/browser/fileapi/watcher_manager.h"
 
 class GURL;
 
@@ -26,16 +32,19 @@ namespace arc {
 // All methods must be called on the IO thread.
 // If this object is deleted while there are in-flight operations, callbacks
 // for those operations will be never called.
-class ArcDocumentsProviderRoot {
+class ArcDocumentsProviderRoot : public ArcFileSystemOperationRunner::Observer {
  public:
   using GetFileInfoCallback = storage::AsyncFileUtil::GetFileInfoCallback;
   using ReadDirectoryCallback = storage::AsyncFileUtil::ReadDirectoryCallback;
+  using ChangeType = storage::WatcherManager::ChangeType;
+  using WatcherCallback = base::Callback<void(ChangeType type)>;
+  using StatusCallback = base::Callback<void(base::File::Error error)>;
   using ResolveToContentUrlCallback =
       base::Callback<void(const GURL& content_url)>;
 
   ArcDocumentsProviderRoot(const std::string& authority,
                            const std::string& root_document_id);
-  ~ArcDocumentsProviderRoot();
+  ~ArcDocumentsProviderRoot() override;
 
   // Queries information of a file just like AsyncFileUtil.GetFileInfo().
   void GetFileInfo(const base::FilePath& path,
@@ -46,6 +55,56 @@ class ArcDocumentsProviderRoot {
   void ReadDirectory(const base::FilePath& path,
                      const ReadDirectoryCallback& callback);
 
+  // Installs a document watcher.
+  //
+  // It is not allowed to install multiple watchers at the same file path;
+  // if attempted, duplicated requests will fail.
+  //
+  // Currently, watchers can be installed only on directories, and only
+  // directory content changes are notified. The result of installing a watcher
+  // to a non-directory in unspecified.
+  //
+  // NOTES ABOUT CORRECTNESS AND CONSISTENCY:
+  //
+  // Document watchers are not always correct and they may miss some updates or
+  // even notify incorrect update events for several reasons, such as:
+  //
+  //   - Directory moves: Currently a watcher will misbehave if the watched
+  //     directory is moved to another location. This is acceptable for now
+  //     since we whitelist MediaDocumentsProvider only.
+  //   - Duplicated file name handling in this class: The same reason as
+  //     directory moves. This may happen even with MediaDocumentsProvider,
+  //     but the chance will not be very high.
+  //   - File system operation races: For example, an watcher can be installed
+  //     to a non-directory in a race condition.
+  //   - Broken DocumentsProviders: For example, we get no notification if a
+  //     document provider does not call setNotificationUri().
+  //
+  // However, consistency of installed watchers is guaranteed. That is, after
+  // a watcher is installed on a file path X, an attempt to uninstall a watcher
+  // at X will always success.

[dcheng, 2017/03/03 09:40:56]

Nit: success => succeed

[Shuhei Takahashi, 2017/03/03 10:12:11]

Oops, I always make this mistake :)

+  //
+  // Unfortunately it is too difficult (or maybe theoretically impossible) to
+  // implement a perfect Android document watcher which never misses document
+  // updates. So the current implementation gives up correctness, but instead
+  // focuses on following two goals:
+  //
+  //   1. Keep the implementation simple, rather than trying hard to catch
+  //      race conditions or minor cases. Even if we return wrong results, the
+  //      worst consequence is just that users do not see the latest contents
+  //      until they refresh UI.
+  //
+  //   2. Keep consistency of installed watchers so that the caller can avoid
+  //      dangling watchers.
+  void AddWatcher(const base::FilePath& path,
+                  const WatcherCallback& watcher_callback,
+                  const StatusCallback& callback);
+
+  // Uninstalls a document watcher.
+  // See the documentation of AddWatcher() above.
+  void RemoveWatcher(const base::FilePath& path,
+                     const StatusCallback& callback);
+
   // Resolves a file path into a content:// URL pointing to the file
   // on DocumentsProvider. Returns URL that can be passed to
   // ArcContentFileSystemFileSystemReader to read the content.
@@ -53,6 +112,9 @@ class ArcDocumentsProviderRoot {
   void ResolveToContentUrl(const base::FilePath& path,
                            const ResolveToContentUrlCallback& callback);
 
+  // ArcFileSystemOperationRunner::Observer overrides:
+  void OnWatchersCleared() override;
+
  private:
   // Thin representation of a document in documents provider.
   struct ThinDocument {
@@ -82,6 +144,17 @@ class ArcDocumentsProviderRoot {
       base::File::Error error,
       NameToThinDocumentMap mapping);
 
+  void AddWatcherWithDocumentId(const base::FilePath& path,
+                                const WatcherCallback& watcher_callback,
+                                const StatusCallback& callback,
+                                const std::string& document_id);
+  void OnWatcherAdded(const base::FilePath& path,
+                      const StatusCallback& callback,
+                      int64_t watcher_id);
+  void OnWatcherAddedButRemoved(const StatusCallback& callback, bool success);
+
+  void OnWatcherRemoved(const StatusCallback& callback, bool success);
+
   void ResolveToContentUrlWithDocumentId(
       const ResolveToContentUrlCallback& callback,
       const std::string& document_id);
@@ -110,6 +183,25 @@ class ArcDocumentsProviderRoot {
 
   const std::string authority_;
   const std::string root_document_id_;
+
+  // Map from a file path to a watcher ID.
+  //
+  // A watcher can be "orphan" when watchers are cleared as notified by
+  // OnWatchersCleared() callback. Such watchers are still tracked here,
+  // but they are not known by the remote service, so they are represented
+  // by the invalid watcher ID (-1).
+  //
+  // Note that we do not use a document ID as a key here to guarantee that
+  // a watch installed by AddWatcher() can be always identified in
+  // RemoveWatcher() with the same file path specified.
+  // See the documentation of AddWatcher() for more details.
+  std::map<base::FilePath, int64_t> path_to_watcher_id_;
+
+  // Can be null if this instance is not observing ArcFileSystemOperationRunner.
+  // Observation is started on the first call of AddWatcher().
+  scoped_refptr<file_system_operation_runner_util::ObserverIOThreadWrapper>
+      observer_wrapper_;
+
   base::WeakPtrFactory<ArcDocumentsProviderRoot> weak_ptr_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(ArcDocumentsProviderRoot);