Add skeleton code to wire Local- and Remote- file sync services

chrome/browser/sync_file_system/remote_change_processor.h

+// Copyright (c) 2012 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.
+
+#ifndef CHROME_BROWSER_SYNC_FILE_SYSTEM_REMOTE_CHANGE_PROCESSOR_H_
+#define CHROME_BROWSER_SYNC_FILE_SYSTEM_REMOTE_CHANGE_PROCESSOR_H_
+
+#include "base/basictypes.h"
+#include "base/callback_forward.h"
+#include "webkit/fileapi/syncable/sync_status_code.h"
+
+class FilePath;
+
+namespace fileapi {
+class FileChange;
+class FileChangeList;
+class FileSystemURL;
+}
+
+namespace sync_file_system {
+
+// Represents an interface to process one remote change and applies
+// it to the local file system.
+// This interface is to be implemented/backed by LocalSyncFileService.
+class RemoteChangeProcessor {
+ public:
+  typedef base::Callback<void(
+      fileapi::SyncStatusCode status,
+      fileapi::FileChangeList& change)> PrepareChangeCallback;
+  typedef base::Callback<void(fileapi::SyncStatusCode status)> StatusCallback;
+
+  RemoteChangeProcessor() {}
+  virtual ~RemoteChangeProcessor() {}
+
+  // This must be called before processing the change for the |url|.
+  // This tries to lock the target |url| and returns the local changes
+  // if any. (The change returned by the callback is to make a decision
+  // on conflict resolution, but NOT for applying local changes to the remote,
+  // which is supposed to be done by LocalChangeProcessor)

[tzik, 2012/10/22 12:28:19]

Should we invoke the callback soon, when we fail to acquire the lock? or store
the callback and invoke it after we acquire the lock?

I prefer returning fail immediately.

[kinuko, 2012/10/22 12:38:03]

I'm thinking about let it fail with an error like SYNC_STATUS_ERROR_SUSPENDED
immediately with the URL (so that the caller==SyncFileSystemService can register
the URL if necessary).

+  virtual void PrepareForProcessRemoteChange(
+      const fileapi::FileSystemURL& url,
+      const PrepareChangeCallback& callback) = 0;
+
+  // This is called to apply the remote |change|. If the change type is
+  // ADD_OR_UPDATE for a file, |local_path| needs to point to a
+  // local file path that contains the latest file image (e.g. a path
+  // to a temporary file which has the data downloaded from the server).
+  // This may fail with an error but should NOT result in a conflict
+  // (as we must have checked the change status in PrepareRemoteSync and
+  // have disabled any further writing).
+  virtual void ApplyRemoteChange(
+      const fileapi::FileChange& change,
+      const FilePath& local_path,
+      const fileapi::FileSystemURL& url,
+      const StatusCallback& callback) = 0;
+
+ private:
+  DISALLOW_COPY_AND_ASSIGN(RemoteChangeProcessor);
+};
+
+}  // namespace sync_file_system
+
+#endif  // CHROME_BROWSER_SYNC_FILE_SYSTEM_REMOTE_CHANGE_PROCESSOR_H_