sync: Introduce control data types

sync/engine/conflict_util.cc

+// 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.
+
+#include "sync/engine/conflict_util.h"
+
+#include "sync/syncable/mutable_entry.h"
+
+namespace syncer {
+
+using syncable::BASE_VERSION;
+using syncable::IS_UNAPPLIED_UPDATE;
+using syncable::IS_UNSYNCED;
+using syncable::SERVER_VERSION;
+
+using syncable::MutableEntry;
+
+// Allow the server's changes to take precedence.
+// This will take effect during the next ApplyUpdates step.
+void IgnoreLocalChanges(MutableEntry* entry) {
+  DCHECK(entry->Get(IS_UNSYNCED));
+  DCHECK(entry->Get(IS_UNAPPLIED_UPDATE));
+  entry->Put(IS_UNSYNCED, false);
+}
+
+// Overwrite the server with our own value.
+// We will commit our local data, overwriting the server, at the next
+// opportunity.
+void OverwriteServerChanges(MutableEntry* entry) {
+  DCHECK(entry->Get(IS_UNSYNCED));
+  DCHECK(entry->Get(IS_UNAPPLIED_UPDATE));
+  entry->Put(BASE_VERSION, entry->Get(SERVER_VERSION));
+  entry->Put(IS_UNAPPLIED_UPDATE, false);
+}
+
+// Having determined that everything matches, we ignore the non-conflict.
+void IgnoreConflict(MutableEntry* entry) {
+  // If we didn't also unset IS_UNAPPLIED_UPDATE, then we would lose unsynced
+  // positional data from adjacent entries when the server update gets applied
+  // and the item is re-inserted into the PREV_ID/NEXT_ID linked list. This is
+  // primarily an issue because we commit after applying updates, and is most
+  // commonly seen when positional changes are made while a passphrase is
+  // required (and hence there will be many encryption conflicts).
+  DCHECK(entry->Get(IS_UNSYNCED));
+  DCHECK(entry->Get(IS_UNAPPLIED_UPDATE));
+  entry->Put(BASE_VERSION, entry->Get(SERVER_VERSION));
+  entry->Put(IS_UNAPPLIED_UPDATE, false);
+  entry->Put(IS_UNSYNCED, false);
+}
+
+}  // namespace syncer