Introduce AttachmentStore metadata record

sync/internal_api/public/attachments/on_disk_attachment_store.h

 // Copyright 2014 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 SYNC_INTERNAL_API_PUBLIC_ATTACHMENTS_ON_DISK_ATTACHMENT_STORE_H_
 #define SYNC_INTERNAL_API_PUBLIC_ATTACHMENTS_ON_DISK_ATTACHMENT_STORE_H_
 
 #include "base/files/file_path.h"
 #include "base/memory/ref_counted.h"
 #include "base/threading/non_thread_safe.h"
 #include "sync/api/attachments/attachment.h"
 #include "sync/api/attachments/attachment_id.h"
 #include "sync/api/attachments/attachment_store.h"
 #include "sync/base/sync_export.h"
 
+namespace attachment_store_pb {
+class AttachmentStoreMetadata;
+}  // namespace attachment_store_pb
+
 namespace base {
 class SequencedTaskRunner;
 }  // namespace base
 
 namespace leveldb {
 class DB;
+class Status;
 }  // namespace leveldb
 
 namespace syncer {
 
 // On-disk implementation of AttachmentStore. Stores attachments in leveldb
 // database in |path| directory.
 class SYNC_EXPORT OnDiskAttachmentStore : public AttachmentStoreBase,
                                           public base::NonThreadSafe {
  public:
   // Constructs attachment store.
@@ skipping 10 matching lines @@
   virtual void Write(const AttachmentList& attachments,
                      const WriteCallback& callback) override;
   virtual void Drop(const AttachmentIdList& ids,
                     const DropCallback& callback) override;
 
   // Opens leveldb database at |path|. It will create directory and database if
   // it doesn't exist.
   Result OpenOrCreate(const base::FilePath& path);
 
  private:
-  std::string CreateDataKeyFromAttachmentId(const AttachmentId& attachment_id);
+  static leveldb::Status ReadStoreMetadata(

[maniscalco, 2014/10/21 21:41:03]

Light suggestion: unless you need them to be part of the class, consider moving
these functions to an anon namespace in the .cc file.

[pavely, 2014/10/24 20:42:55]

Done.

+      leveldb::DB* db,
+      attachment_store_pb::AttachmentStoreMetadata* metadata);
+  static leveldb::Status UpdateStoreMetadata(
+      leveldb::DB* db,
+      const attachment_store_pb::AttachmentStoreMetadata& metadata);
+  std::string MakeDataKeyFromAttachmentId(const AttachmentId& attachment_id);
 
   scoped_refptr<base::SequencedTaskRunner> callback_task_runner_;
   scoped_ptr<leveldb::DB> db_;
 };
 
 }  // namespace syncer
 
 #endif  // SYNC_INTERNAL_API_PUBLIC_ATTACHMENTS_ON_DISK_ATTACHMENT_STORE_H_