[Sync] Introduce AttachmentStoreForSync class

sync/api/attachments/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_API_ATTACHMENTS_ATTACHMENT_STORE_H_
 #define SYNC_API_ATTACHMENTS_ATTACHMENT_STORE_H_
 
 #include "base/callback.h"
 #include "base/memory/ref_counted.h"
 #include "base/memory/scoped_ptr.h"
 #include "sync/api/attachments/attachment.h"
 #include "sync/api/attachments/attachment_id.h"
 #include "sync/api/attachments/attachment_metadata.h"
 #include "sync/base/sync_export.h"
 
 namespace base {
 class FilePath;
 class SequencedTaskRunner;
 }  // namespace base
 
 namespace syncer {
 
+class AttachmentStoreBackend;
+class AttachmentStoreForSync;
 class AttachmentStoreFrontend;
-class AttachmentStoreBackend;
 
 // AttachmentStore is a place to locally store and access Attachments.
 //
 // AttachmentStore class is an interface exposed to data type and
 // AttachmentService code.
 // It also contains factory methods for default attachment store
 // implementations.
 // Destroying this object does not necessarily cancel outstanding async
 // operations. If you need cancel like semantics, use WeakPtr in the callbacks.
 class SYNC_EXPORT AttachmentStore {
  public:
   // TODO(maniscalco): Consider udpating Read and Write methods to support
   // resumable transfers (bug 353292).
 
   // The result status of an attachment store operation.
   // Do not re-order or delete these entries; they are used in a UMA histogram.
   enum Result {
     SUCCESS = 0,            // No error, all completed successfully.
     UNSPECIFIED_ERROR = 1,  // An unspecified error occurred for >= 1 item.
     STORE_INITIALIZATION_FAILED = 2,  // AttachmentStore initialization failed.
     // When adding a value here, you must increment RESULT_SIZE below.
   };
   static const int RESULT_SIZE =
       10;  // Size of the Result enum; used for histograms.
 
   // Each attachment can have references from sync or model type. Tracking these
   // references is needed for lifetime management of attachment, it can only be
   // deleted from the store when it doesn't have references.
-  enum AttachmentReferrer {
+  enum Component {
     MODEL_TYPE,
     SYNC,
   };
 
   typedef base::Callback<void(const Result&)> InitCallback;
   typedef base::Callback<void(const Result&,
                               scoped_ptr<AttachmentMap>,
                               scoped_ptr<AttachmentIdList>)> ReadCallback;
   typedef base::Callback<void(const Result&)> WriteCallback;
   typedef base::Callback<void(const Result&)> DropCallback;
@@ skipping 50 matching lines @@
 
   // Asynchronously reads metadata for all attachments in the store.
   //
   // |callback| will be invoked when finished. If any of the metadata entries
   // could not be read, |callback|'s Result will be UNSPECIFIED_ERROR.
   void ReadAllMetadata(const ReadMetadataCallback& callback);
 
   // Given current AttachmentStore (this) creates separate AttachmentStore that
   // will be used by sync components (AttachmentService). Resulting
   // AttachmentStore is backed by the same frontend/backend.
-  scoped_ptr<AttachmentStore> CreateAttachmentStoreForSync() const;
+  scoped_ptr<AttachmentStoreForSync> CreateAttachmentStoreForSync() const;
 
   // Creates an AttachmentStore backed by in-memory implementation of attachment
   // store. For now frontend lives on the same thread as backend.
   static scoped_ptr<AttachmentStore> CreateInMemoryStore();
 
   // Creates an AttachmentStore backed by on-disk implementation of attachment
   // store. Opens corresponding leveldb database located at |path|. All backend
   // operations are scheduled to |backend_task_runner|. Opening attachment store
   // is asynchronous, once it finishes |callback| will be called on the thread
   // that called CreateOnDiskStore. Calling Read/Write/Drop before
   // initialization completed is allowed.  Later if initialization fails these
   // operations will fail with STORE_INITIALIZATION_FAILED error.
   static scoped_ptr<AttachmentStore> CreateOnDiskStore(
       const base::FilePath& path,
       const scoped_refptr<base::SequencedTaskRunner>& backend_task_runner,
       const InitCallback& callback);
 
   // Creates set of AttachmentStore/AttachmentStoreFrontend instances for tests
   // that provide their own implementation of AttachmentstoreBackend for
   // mocking.
   static scoped_ptr<AttachmentStore> CreateMockStoreForTest(
       scoped_ptr<AttachmentStoreBackend> backend);
 
+ protected:
+  AttachmentStore(const scoped_refptr<AttachmentStoreFrontend>& frontend,
+                  Component component);
+
+  const scoped_refptr<AttachmentStoreFrontend>& frontend() { return frontend_; }
+
  private:
-  AttachmentStore(const scoped_refptr<AttachmentStoreFrontend>& frontend,
-                  AttachmentReferrer referrer);
-
   scoped_refptr<AttachmentStoreFrontend> frontend_;
   // Modification operations with attachment store will be performed on behalf
-  // of |referrer_|.
-  const AttachmentReferrer referrer_;
+  // of |component_|.
+  const Component component_;
 
   DISALLOW_COPY_AND_ASSIGN(AttachmentStore);
 };
 
+// AttachmentStoreForSync extends AttachmentStore and provides additional
+// functions necessary for AttachmentService. These are needed when
+// AttachmentService writes attachment on behalf of model type after download
+// and takes reference on attachment for the duration of upload.
+// Model type implementation shouldn't use this interface.
+class AttachmentStoreForSync : public AttachmentStore {
+ public:
+  // Asynchronously adds reference from sync to attachments.
+  void SetSyncReference(const AttachmentIdList& ids);
+
+  // Asynchronously drops sync reference from attachments.
+  void DropSyncReference(const AttachmentIdList& ids);
+
+ private:
+  friend class AttachmentStore;
+  AttachmentStoreForSync(const scoped_refptr<AttachmentStoreFrontend>& frontend,
+                         Component consumer_component,
+                         Component sync_component);
+
+  // |sync_component_| is passed to frontend when sync related operations are
+  // perfromed.
+  const Component sync_component_;
+
+  DISALLOW_COPY_AND_ASSIGN(AttachmentStoreForSync);
+};
+
 }  // namespace syncer
 
 #endif  // SYNC_API_ATTACHMENTS_ATTACHMENT_STORE_H_