Create a strict order in ReadingListSpecifics

components/reading_list/ios/reading_list_store.h

 // 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.
 
 #ifndef COMPONENTS_READING_LIST_IOS_READING_LIST_STORE_H_
 #define COMPONENTS_READING_LIST_IOS_READING_LIST_STORE_H_
 
 #include "base/threading/non_thread_safe.h"
 #include "components/reading_list/ios/reading_list_model_storage.h"
 #include "components/reading_list/ios/reading_list_store_delegate.h"
@@ skipping 54 matching lines @@
 
   // Apply changes from the sync server locally.
   // Please note that |entity_changes| might have fewer entries than
   // |metadata_change_list| in case when some of the data changes are filtered
   // out, or even be empty in case when a commit confirmation is processed and
   // only the metadata needs to persisted.
   syncer::SyncError ApplySyncChanges(
       std::unique_ptr<syncer::MetadataChangeList> metadata_change_list,
       syncer::EntityChangeList entity_changes) override;
 
+  // Returns whether entries respect a strict order for sync and if |rhs| can be
+  // submitted to sync after |lhs| has been received.
+  // The order should ensure that there is no sync loop in sync and should be
+  // submitted to sync in strictly increasing order.
+  // Entries are in increasing order if all the fields respect increasing order.
+  // - URL must be the same.
+  // - title must verify rhs.title.compare(lhs.title) >= 0

[pavely, 2016/12/07 19:16:06]

I don't really understand why title is taken into account for comparison. What
if in the future chrome allows to rename articles and user shortens title? Will
it be rejected by other clients?

[Olivier, 2016/12/08 08:04:07]

At the moment, title cannot be changed, so the only conflict can appear if one
device does have a title and the other does not.
If we add the possibility to change the title, we will need to set a new field
like "last_title_change_timestamp" to handle conflicts.

+  // - rhs.creation_time_us >= lhs.creation_time_us
+  // - rhs.update_time_us >= lhs.update_time_us
+  // - if rhs.update_time_us > lhs.update_time_us, rhs.state can be anything.
+  // - if rhs.update_time_us == lhs.update_time_us, rhs.state >= lhs.state in
+  //          the order UNSEEN, UNREAD, READ.
+  static bool CompareEntriesForSync(const sync_pb::ReadingListSpecifics& lhs,
+                                    const sync_pb::ReadingListSpecifics& rhs);
+
   // Asynchronously retrieve the corresponding sync data for |storage_keys|.
   void GetData(StorageKeyList storage_keys, DataCallback callback) override;
 
   // Asynchronously retrieve all of the local sync data.
   void GetAllData(DataCallback callback) override;
 
   // Get or generate a client tag for |entity_data|. This must be the same tag
   // that was/would have been generated in the SyncableService/Directory world
   // for backward compatibility with pre-USS clients. The only time this
   // theoretically needs to be called is on the creation of local data, however
@@ skipping 43 matching lines @@
   std::unique_ptr<syncer::ModelTypeStore> store_;
   ReadingListModel* model_;
   ReadingListStoreDelegate* delegate_;
   StoreFactoryFunction create_store_callback_;
 
   int pending_transaction_count_;
   std::unique_ptr<syncer::ModelTypeStore::WriteBatch> batch_;
 };
 
 #endif  // COMPONENTS_READING_LIST_IOS_READING_LIST_STORE_H_