Migrate startup URLs pref.

chrome/browser/prefs/pref_model_associator.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 "chrome/browser/prefs/pref_model_associator.h"
 
 #include "base/auto_reset.h"
 #include "base/json/json_reader.h"
 #include "base/json/json_string_value_serializer.h"
 #include "base/location.h"
@@ skipping 30 matching lines @@
     sync_pb::EntitySpecifics* specifics) {
   if (type == syncer::PRIORITY_PREFERENCES) {
     DCHECK(!specifics->has_preference());
     return specifics->mutable_priority_preference()->mutable_preference();
   } else {
     DCHECK(!specifics->has_priority_preference());
     return specifics->mutable_preference();
   }
 }
 
+// List of migrated preference name pairs. If a preference is migrated
+// (meaning renamed) adding the old and new preference names here will ensure
+// that the sync engine knows how to deal with the synced values coming in
+// with the old name. Preference migration itself doesn't happen here. It may
+// happen in session_startup_pref.cc.
+const struct MigratedPreferences {
+  const char* const old_name;
+  const char* const new_name;
+} kMigratedPreferences[] = {
+  { prefs::kURLsToRestoreOnStartupOld, prefs::kURLsToRestoreOnStartup },
+};
+
+std::string GetOldMigratedPreferenceName(const char* preference_name) {
+  for (size_t i = 0; i < arraysize(kMigratedPreferences); ++i) {
+    if (!strcmp(kMigratedPreferences[i].new_name, preference_name))
+      return kMigratedPreferences[i].old_name;
+  }
+  return std::string();
+}
+
+std::string GetNewMigratedPreferenceName(const char* old_preference_name) {
+  for (size_t i = 0; i < arraysize(kMigratedPreferences); ++i) {
+    if (!strcmp(kMigratedPreferences[i].old_name, old_preference_name))
+      return kMigratedPreferences[i].new_name;
+  }
+  return std::string();
+}
+
 }  // namespace
 
 PrefModelAssociator::PrefModelAssociator(syncer::ModelType type)
     : models_associated_(false),
       processing_syncer_changes_(false),
       pref_service_(NULL),
       type_(type) {
   DCHECK(CalledOnValidThread());
   DCHECK(type_ == PREFERENCES || type_ == PRIORITY_PREFERENCES);
 }
 
 PrefModelAssociator::~PrefModelAssociator() {
   DCHECK(CalledOnValidThread());
   pref_service_ = NULL;
 
   STLDeleteContainerPairSecondPointers(synced_pref_observers_.begin(),
                                        synced_pref_observers_.end());
   synced_pref_observers_.clear();
 }
 
 void PrefModelAssociator::InitPrefAndAssociate(
     const syncer::SyncData& sync_pref,
     const std::string& pref_name,
-    syncer::SyncChangeList* sync_changes) {
+    syncer::SyncChangeList* sync_changes,
+    SyncDataMap* migrated_preference_list) {
   const Value* user_pref_value = pref_service_->GetUserPrefValue(
       pref_name.c_str());
   VLOG(1) << "Associating preference " << pref_name;
 
+  // Set if a migrated pref name has been added to the synced_preferences_ list.
+  bool remembered_migrated_synced_preference = false;
+
   if (sync_pref.IsValid()) {
     const sync_pb::PreferenceSpecifics& preference = GetSpecifics(sync_pref);
-    DCHECK_EQ(pref_name, preference.name());
-
+    DCHECK(pref_name == preference.name() ||
+           (IsMigratedPreference(pref_name.c_str()) &&
+            preference.name() ==
+                GetOldMigratedPreferenceName(pref_name.c_str())));
     base::JSONReader reader;
     scoped_ptr<Value> sync_value(reader.ReadToValue(preference.value()));
     if (!sync_value.get()) {
       LOG(ERROR) << "Failed to deserialize preference value: "
                  << reader.GetErrorMessage();
       return;
     }
 
     if (user_pref_value) {
       // We have both server and local values. Merge them.
@@ skipping 15 matching lines @@
         pref_service_->Set(pref_name.c_str(), *new_value);
       }
 
       // If the merge resulted in an updated value, inform the syncer.
       if (!sync_value->Equals(new_value.get())) {
         syncer::SyncData sync_data;
         if (!CreatePrefSyncData(pref_name, *new_value, &sync_data)) {
           LOG(ERROR) << "Failed to update preference.";
           return;
         }
-        sync_changes->push_back(
+
+        if (IsMigratedPreference(pref_name.c_str())) {

[Bernhard Bauer, 2013/10/15 22:03:52]

This logic is fairly tricky. We should think about some way to make sure that
other pref migration code added in the future will also be handled here.

[robertshield, 2013/10/16 01:23:27]

It is more complex than I had hoped, but it is as future proof as I think it is
worth making it. Two types of future migration come to mind:

1) Migrating additional prefs using the same sync and merge strategy. As per the
comment on line 56, migrating new prefs using the same strategy will be quite
straightforward. 

2) Migrating prefs using different sync and merging rules. We don't currently
have plans to do this and given the complexity of this relatively simple
operation, it's unlikely that we'll pursue this further. I'd prefer not to
over-generalise this code until and unless such plans come about.

[Bernhard Bauer, 2013/10/16 15:13:33]

Sorry, I wasn't suggesting to change this code, but I just wanted to make sure
we also use this for future migrations. More of a note-to-self :)

[robertshield, 2013/10/16 15:50:08]

No worries, I got one less UMA macro expansion out of it, so it's all good :)

+          // This preference has been migrated from an old version that must be
+          // kept in sync on older versions of Chrome.
+          std::string old_pref_name =
+              GetOldMigratedPreferenceName(pref_name.c_str());
+
+          if (preference.name() == old_pref_name) {
+            DCHECK(migrated_preference_list);
+            // If the name the syncer has is the old pre-migration value, then
+            // it's possible the new migrated preference name hasn't been synced
+            // yet. In that case the SyncChange should be an ACTION_ADD rather
+            // than an ACTION_UPDATE. Defer the decision of whether to sync with
+            // ACTION_ADD or ACTION_UPDATE until the migrated_preferences phase.
+            if (migrated_preference_list)
+              (*migrated_preference_list)[pref_name] = sync_data;
+          } else {
+            DCHECK_EQ(preference.name(), pref_name);
+            sync_changes->push_back(
+                syncer::SyncChange(FROM_HERE,
+                                   syncer::SyncChange::ACTION_UPDATE,
+                                   sync_data));
+          }
+
+          syncer::SyncData old_sync_data;
+          if (!CreatePrefSyncData(old_pref_name, *new_value, &old_sync_data)) {
+            LOG(ERROR) << "Failed to update preference.";
+            return;
+          }
+          if (migrated_preference_list)
+            (*migrated_preference_list)[old_pref_name] = old_sync_data;
+
+          // Keep track of the name of the synced pref. This will be idempotent
+          // with the insertion of pref_name below when the migrated value has
+          // already been synced, not so when it has not.
+          synced_preferences_.insert(preference.name());
+          remembered_migrated_synced_preference = true;
+        } else {
+          sync_changes->push_back(
             syncer::SyncChange(FROM_HERE,
                                syncer::SyncChange::ACTION_UPDATE,
                                sync_data));
+        }
       }
     } else if (!sync_value->IsType(Value::TYPE_NULL)) {
       // Only a server value exists. Just set the local user value.
       pref_service_->Set(pref_name.c_str(), *sync_value);
     } else {
       LOG(WARNING) << "Sync has null value for pref " << pref_name.c_str();
     }
   } else if (user_pref_value) {
     // The server does not know about this preference and should be added
     // to the syncer's database.
     syncer::SyncData sync_data;
     if (!CreatePrefSyncData(pref_name, *user_pref_value, &sync_data)) {
       LOG(ERROR) << "Failed to update preference.";
       return;
     }
     sync_changes->push_back(
         syncer::SyncChange(FROM_HERE,
                            syncer::SyncChange::ACTION_ADD,
                            sync_data));
   } else {
     // This pref does not have a sync value but also does not have a user
     // controlled value (either it's a default value or it's policy controlled,
     // either way it's not interesting). We can ignore it. Once it gets changed,
     // we'll send the new user controlled value to the syncer.
     return;
   }
 
   // Make sure we add it to our list of synced preferences so we know what
   // the server is aware of.
-  synced_preferences_.insert(pref_name);
+  if (!remembered_migrated_synced_preference)
+    synced_preferences_.insert(pref_name);
   return;
 }
 
 syncer::SyncMergeResult PrefModelAssociator::MergeDataAndStartSyncing(
     syncer::ModelType type,
     const syncer::SyncDataList& initial_sync_data,
     scoped_ptr<syncer::SyncChangeProcessor> sync_processor,
     scoped_ptr<syncer::SyncErrorFactory> sync_error_factory) {
   DCHECK_EQ(type_, type);
   DCHECK(CalledOnValidThread());
   DCHECK(pref_service_);
   DCHECK(!sync_processor_.get());
   DCHECK(sync_processor.get());
   DCHECK(sync_error_factory.get());
   syncer::SyncMergeResult merge_result(type);
   sync_processor_ = sync_processor.Pass();
   sync_error_factory_ = sync_error_factory.Pass();
 
   syncer::SyncChangeList new_changes;
   std::set<std::string> remaining_preferences = registered_preferences_;
 
+  // Maintains a list of old migrated preference names that we wish to sync.
+  // Keep track of these in a list such that when the preference iteration
+  // loops below are complete we can go back and determine whether
+  SyncDataMap migrated_preference_list;
+
   // Go through and check for all preferences we care about that sync already
   // knows about.
   for (syncer::SyncDataList::const_iterator sync_iter =
            initial_sync_data.begin();
        sync_iter != initial_sync_data.end();
        ++sync_iter) {
     DCHECK_EQ(type_, sync_iter->GetDataType());
 
     const sync_pb::PreferenceSpecifics& preference = GetSpecifics(*sync_iter);
-    const std::string& sync_pref_name = preference.name();
+    std::string sync_pref_name = preference.name();
 
     if (remaining_preferences.count(sync_pref_name) == 0) {
-      // We're not syncing this preference locally, ignore the sync data.
-      // TODO(zea): Eventually we want to be able to have the syncable service
-      // reconstruct all sync data for it's datatype (therefore having
-      // GetAllSyncData be a complete representation). We should store this data
-      // somewhere, even if we don't use it.
-      continue;
+      if (IsOldMigratedPreference(sync_pref_name.c_str())) {
+        // This old pref name is not syncable locally anymore but we accept
+        // changes from other Chrome installs of previous versions and migrate
+        // them to the new name. Note that we will be merging any differences
+        // between the new and old values and sync'ing them back.
+        sync_pref_name = GetNewMigratedPreferenceName(sync_pref_name.c_str());
+      } else {
+        // We're not syncing this preference locally, ignore the sync data.
+        // TODO(zea): Eventually we want to be able to have the syncable service
+        // reconstruct all sync data for its datatype (therefore having
+        // GetAllSyncData be a complete representation). We should store this
+        // data somewhere, even if we don't use it.
+        continue;
+      }
+    } else {
+      remaining_preferences.erase(sync_pref_name);
     }
-
-    remaining_preferences.erase(sync_pref_name);
-    InitPrefAndAssociate(*sync_iter, sync_pref_name, &new_changes);
+    InitPrefAndAssociate(*sync_iter, sync_pref_name, &new_changes,
+                         &migrated_preference_list);
   }
 
   // Go through and build sync data for any remaining preferences.
   for (std::set<std::string>::iterator pref_name_iter =
           remaining_preferences.begin();
        pref_name_iter != remaining_preferences.end();
        ++pref_name_iter) {
-    InitPrefAndAssociate(syncer::SyncData(), *pref_name_iter, &new_changes);
+    InitPrefAndAssociate(syncer::SyncData(), *pref_name_iter, &new_changes,
+                         &migrated_preference_list);
+  }
+
+  // Now go over any migrated preference names and build sync data for them too.
+  for (SyncDataMap::const_iterator migrated_pref_iter =
+          migrated_preference_list.begin();
+       migrated_pref_iter != migrated_preference_list.end();
+       ++migrated_pref_iter) {
+    syncer::SyncChange::SyncChangeType change_type =
+        (synced_preferences_.count(migrated_pref_iter->first) == 0) ?
+            syncer::SyncChange::ACTION_ADD :
+            syncer::SyncChange::ACTION_UPDATE;
+    new_changes.push_back(
+        syncer::SyncChange(FROM_HERE, change_type, migrated_pref_iter->second));
   }
 
   // Push updates to sync.
   merge_result.set_error(
       sync_processor_->ProcessSyncChanges(FROM_HERE, new_changes));
   if (merge_result.error().IsSet())
     return merge_result;
 
   models_associated_ = true;
   pref_service_->OnIsSyncingChanged();
   return merge_result;
 }
 
 void PrefModelAssociator::StopSyncing(syncer::ModelType type) {
   DCHECK_EQ(type_, type);
   models_associated_ = false;
   sync_processor_.reset();
   sync_error_factory_.reset();
   pref_service_->OnIsSyncingChanged();
 }
 
 scoped_ptr<Value> PrefModelAssociator::MergePreference(
     const std::string& name,
     const Value& local_value,
     const Value& server_value) {
-  if (name == prefs::kURLsToRestoreOnStartup) {
+  // This function special cases preferences individually, so don't attempt
+  // to merge for all migrated values.
+  if (name == prefs::kURLsToRestoreOnStartup ||
+      name == prefs::kURLsToRestoreOnStartupOld) {
     return scoped_ptr<Value>(MergeListValues(local_value, server_value)).Pass();
   }
 
   if (name == prefs::kContentSettingsPatternPairs) {
     return scoped_ptr<Value>(
         MergeDictionaryValues(local_value, server_value)).Pass();
   }
 
   // If this is not a specially handled preference, server wins.
   return scoped_ptr<Value>(server_value.DeepCopy()).Pass();
@@ skipping 75 matching lines @@
       }
       // Note that for all other types we want to preserve the "to"
       // values so we do nothing here.
     } else {
       result->SetWithoutPathExpansion(it.key(), from_value->DeepCopy());
     }
   }
   return result;
 }
 
+// static
+bool PrefModelAssociator::IsMigratedPreference(const char* preference_name) {
+  return !GetOldMigratedPreferenceName(preference_name).empty();
+}
+
+// static
+bool PrefModelAssociator::IsOldMigratedPreference(
+    const char* old_preference_name) {
+  return !GetNewMigratedPreferenceName(old_preference_name).empty();
+}
+
 // Note: This will build a model of all preferences registered as syncable
 // with user controlled data. We do not track any information for preferences
 // not registered locally as syncable and do not inform the syncer of
 // non-user controlled preferences.
 syncer::SyncDataList PrefModelAssociator::GetAllSyncData(
     syncer::ModelType type)
     const {
   DCHECK_EQ(type_, type);
   syncer::SyncDataList current_data;
   for (PreferenceSet::const_iterator iter = synced_preferences_.begin();
@@ skipping 47 matching lines @@
     // TODO(zea): consider taking some further action such as erasing the bad
     // data.
     if (!value.get())
       continue;
 
     // It is possible that we may receive a change to a preference we do not
     // want to sync. For example if the user is syncing a Mac client and a
     // Windows client, the Windows client does not support
     // kConfirmToQuitEnabled. Ignore updates from these preferences.
     const char* pref_name = name.c_str();
+    std::string new_name;
+    // We migrated this preference name, so do as if the name had not changed.
+    if (IsOldMigratedPreference(pref_name)) {
+      new_name = GetNewMigratedPreferenceName(pref_name);
+      pref_name = new_name.c_str();
+    }
+
     if (!IsPrefRegistered(pref_name))
       continue;
 
     const PrefService::Preference* pref =
         pref_service_->FindPreference(pref_name);
     DCHECK(pref);
 
     // This will only modify the user controlled value store, which takes
     // priority over the default value but is ignored if the preference is
     // policy controlled.
@@ skipping 88 matching lines @@
   }
 
   base::AutoReset<bool> processing_changes(&processing_syncer_changes_, true);
 
   NotifySyncedPrefObservers(name, false /*from_sync*/);
 
   if (synced_preferences_.count(name) == 0) {
     // Not in synced_preferences_ means no synced data. InitPrefAndAssociate(..)
     // will determine if we care about its data (e.g. if it has a default value
     // and hasn't been changed yet we don't) and take care syncing any new data.
-    InitPrefAndAssociate(syncer::SyncData(), name, &changes);
+    InitPrefAndAssociate(syncer::SyncData(), name, &changes, NULL);
   } else {
     // We are already syncing this preference, just update it's sync node.
     syncer::SyncData sync_data;
     if (!CreatePrefSyncData(name, *preference->GetValue(), &sync_data)) {
       LOG(ERROR) << "Failed to update preference.";
       return;
     }
     changes.push_back(
         syncer::SyncChange(FROM_HERE,
                            syncer::SyncChange::ACTION_UPDATE,
                            sync_data));
+    // This preference has been migrated from an old version that must be kept
+    // in sync on older versions of Chrome.
+    if (IsMigratedPreference(name.c_str())) {
+      std::string old_pref_name = GetOldMigratedPreferenceName(name.c_str());
+      if (!CreatePrefSyncData(old_pref_name,
+                              *preference->GetValue(),
+                              &sync_data)) {
+        LOG(ERROR) << "Failed to update preference.";
+        return;
+      }
+
+      syncer::SyncChange::SyncChangeType change_type =
+          (synced_preferences_.count(old_pref_name) == 0) ?
+              syncer::SyncChange::ACTION_ADD :
+              syncer::SyncChange::ACTION_UPDATE;
+      changes.push_back(
+          syncer::SyncChange(FROM_HERE, change_type, sync_data));
+    }
   }
 
   syncer::SyncError error =
       sync_processor_->ProcessSyncChanges(FROM_HERE, changes);
 }
 
 void PrefModelAssociator::SetPrefService(PrefServiceSyncable* pref_service) {
   DCHECK(pref_service_ == NULL);
   pref_service_ = pref_service;
 }
 
 void PrefModelAssociator::NotifySyncedPrefObservers(const std::string& path,
                                                     bool from_sync) const {
   SyncedPrefObserverMap::const_iterator observer_iter =
       synced_pref_observers_.find(path);
   if (observer_iter == synced_pref_observers_.end())
     return;
   SyncedPrefObserverList* observers = observer_iter->second;
   FOR_EACH_OBSERVER(SyncedPrefObserver, *observers,
                     OnSyncedPrefChanged(path, from_sync));
 }