blob: d91d0eb1b4537f1b78c77643cc29aab9f7485e3f [file] [log] [blame]
// Copyright 2013 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/process_updates_util.h"
#include <stddef.h>
#include <stdint.h>
#include <string>
#include "base/location.h"
#include "base/metrics/sparse_histogram.h"
#include "sync/engine/syncer_proto_util.h"
#include "sync/engine/syncer_types.h"
#include "sync/engine/syncer_util.h"
#include "sync/internal_api/public/sessions/update_counters.h"
#include "sync/syncable/directory.h"
#include "sync/syncable/model_neutral_mutable_entry.h"
#include "sync/syncable/syncable_model_neutral_write_transaction.h"
#include "sync/syncable/syncable_proto_util.h"
#include "sync/syncable/syncable_util.h"
#include "sync/util/cryptographer.h"
#include "sync/util/data_type_histogram.h"
namespace syncer {
using sessions::StatusController;
using syncable::GET_BY_ID;
namespace {
// This function attempts to determine whether or not this update is genuinely
// new, or if it is a reflection of one of our own commits.
// There is a known inaccuracy in its implementation. If this update ends up
// being applied to a local item with a different ID, we will count the change
// as being a non-reflection update. Fortunately, the server usually updates
// our IDs correctly in its commit response, so a new ID during GetUpdate should
// be rare.
// The only scenarios I can think of where this might happen are:
// - We commit a new item to the server, but we don't persist the
// server-returned new ID to the database before we shut down. On the GetUpdate
// following the next restart, we will receive an update from the server that
// updates its local ID.
// - When two attempts to create an item with identical UNIQUE_CLIENT_TAG values
// collide at the server. I have seen this in testing. When it happens, the
// test server will send one of the clients a response to upate its local ID so
// that both clients will refer to the item using the same ID going forward. In
// this case, we're right to assume that the update is not a reflection.
// For more information, see FindLocalIdToUpdate().
bool UpdateContainsNewVersion(syncable::BaseTransaction *trans,
const sync_pb::SyncEntity &update) {
int64_t existing_version = -1; // The server always sends positive versions.
syncable::Entry existing_entry(trans, GET_BY_ID,
if (existing_entry.good())
existing_version = existing_entry.GetBaseVersion();
if (!existing_entry.good() && update.deleted()) {
// There are several possible explanations for this. The most common cases
// will be first time sync and the redelivery of deletions we've already
// synced, accepted, and purged from our database. In either case, the
// update is useless to us. Let's count them all as "not new", even though
// that may not always be entirely accurate.
return false;
if (existing_entry.good() &&
!existing_entry.GetUniqueClientTag().empty() &&
existing_entry.GetIsDel() &&
update.deleted()) {
// Unique client tags will have their version set to zero when they're
// deleted. The usual version comparison logic won't be able to detect
// reflections of these items. Instead, we assume any received tombstones
// are reflections. That should be correct most of the time.
return false;
return existing_version < update.version();
// In the event that IDs match, but tags differ AttemptReuniteClient tag
// will have refused to unify the update.
// We should not attempt to apply it at all since it violates consistency
// rules.
VerifyResult VerifyTagConsistency(
const sync_pb::SyncEntity& entry,
const syncable::ModelNeutralMutableEntry& same_id) {
if (entry.has_client_defined_unique_tag() &&
entry.client_defined_unique_tag() !=
same_id.GetUniqueClientTag()) {
// Checks whether or not an update is fit for processing.
// The answer may be "no" if the update appears invalid, or it's not releveant
// (ie. a delete for an item we've never heard of), or other reasons.
VerifyResult VerifyUpdate(
syncable::ModelNeutralWriteTransaction* trans,
const sync_pb::SyncEntity& entry,
ModelType requested_type) {
syncable::Id id = SyncableIdFromProto(entry.id_string());
VerifyResult result = VERIFY_FAIL;
const bool deleted = entry.has_deleted() && entry.deleted();
const bool is_directory = IsFolder(entry);
const ModelType model_type = GetModelType(entry);
if (!id.ServerKnows()) {
LOG(ERROR) << "Illegal negative id in received updates";
return result;
const std::string name = SyncerProtoUtil::NameFromSyncEntity(entry);
if (name.empty() && !deleted) {
LOG(ERROR) << "Zero length name in non-deleted update";
return result;
syncable::ModelNeutralMutableEntry same_id(trans, GET_BY_ID, id);
result = VerifyNewEntry(entry, &same_id, deleted);
ModelType placement_type = !deleted ? GetModelType(entry)
: same_id.good() ? same_id.GetModelType() : UNSPECIFIED;
if (VERIFY_UNDECIDED == result) {
result = VerifyTagConsistency(entry, same_id);
if (VERIFY_UNDECIDED == result) {
if (deleted) {
// For deletes the server could send tombostones for items that
// the client did not request. If so ignore those items.
if (IsRealDataType(placement_type) && requested_type != placement_type) {
result = VERIFY_SKIP;
} else {
// If we have an existing entry, we check here for updates that break
// consistency rules.
if (VERIFY_UNDECIDED == result) {
result = VerifyUpdateConsistency(trans, entry, deleted,
is_directory, model_type, &same_id);
if (VERIFY_UNDECIDED == result)
result = VERIFY_SUCCESS; // No news is good news.
return result; // This might be VERIFY_SUCCESS as well
// Returns true if the entry is still ok to process.
bool ReverifyEntry(syncable::ModelNeutralWriteTransaction* trans,
const sync_pb::SyncEntity& entry,
syncable::ModelNeutralMutableEntry* same_id) {
const bool deleted = entry.has_deleted() && entry.deleted();
const bool is_directory = IsFolder(entry);
const ModelType model_type = GetModelType(entry);
return VERIFY_SUCCESS == VerifyUpdateConsistency(trans,
// Process a single update. Will avoid touching global state.
// If the update passes a series of checks, this function will copy
// the SyncEntity's data into the SERVER side of the syncable::Directory.
void ProcessUpdate(
const sync_pb::SyncEntity& update,
const Cryptographer* cryptographer,
syncable::ModelNeutralWriteTransaction* const trans) {
const syncable::Id& server_id = SyncableIdFromProto(update.id_string());
const std::string name = SyncerProtoUtil::NameFromSyncEntity(update);
// Look to see if there's a local item that should recieve this update,
// maybe due to a duplicate client tag or a lost commit response.
syncable::Id local_id = FindLocalIdToUpdate(trans, update);
// FindLocalEntryToUpdate has veto power.
if (local_id.IsNull()) {
return; // The entry has become irrelevant.
CreateNewEntry(trans, local_id);
// We take a two step approach. First we store the entries data in the
// server fields of a local entry and then move the data to the local fields
syncable::ModelNeutralMutableEntry target_entry(trans, GET_BY_ID, local_id);
// We need to run the Verify checks again; the world could have changed
// since we last verified.
if (!ReverifyEntry(trans, update, &target_entry)) {
return; // The entry has become irrelevant.
// If we're repurposing an existing local entry with a new server ID,
// change the ID now, after we're sure that the update can succeed.
if (local_id != server_id) {
ChangeEntryIDAndUpdateChildren(trans, &target_entry, server_id);
// When IDs change, versions become irrelevant. Forcing BASE_VERSION
// to zero would ensure that this update gets applied, but would indicate
// creation or undeletion if it were committed that way. Instead, prefer
// forcing BASE_VERSION to entry.version() while also forcing
// IS_UNAPPLIED_UPDATE to true. If the item is UNSYNCED, it's committable
// from the new state; it may commit before the conflict resolver gets
// a crack at it.
if (target_entry.GetIsUnsynced() || target_entry.GetBaseVersion() > 0) {
// If either of these conditions are met, then we can expect valid client
// fields for this entry. When BASE_VERSION is positive, consistency is
// enforced on the client fields at update-application time. Otherwise,
// we leave the BASE_VERSION field alone; it'll get updated the first time
// we successfully apply this update.
// Force application of this update, no matter what.
// If this is a newly received undecryptable update, and the only thing that
// has changed are the specifics, store the original decryptable specifics,
// (on which any current or future local changes are based) before we
// overwrite SERVER_SPECIFICS.
// MTIME, CTIME, and NON_UNIQUE_NAME are not enforced.
bool position_matches = false;
if (target_entry.ShouldMaintainPosition() && !update.deleted()) {
std::string update_tag = GetUniqueBookmarkTagFromUpdate(update);
if (UniquePosition::IsValidSuffix(update_tag)) {
position_matches = GetUpdatePosition(update, update_tag).Equals(
} else {
} else {
// If this item doesn't care about positions, then set this flag to true.
position_matches = true;
if (!update.deleted() && !target_entry.GetServerIsDel() &&
(SyncableIdFromProto(update.parent_id_string()) ==
target_entry.GetServerParentId()) &&
position_matches &&
update.has_specifics() && update.specifics().has_encrypted() &&
!cryptographer->CanDecrypt(update.specifics().encrypted())) {
sync_pb::EntitySpecifics prev_specifics =
// We only store the old specifics if they were decryptable and applied and
// there is no BASE_SERVER_SPECIFICS already. Else do nothing.
if (!target_entry.GetIsUnappliedUpdate() &&
target_entry.GetBaseServerSpecifics())) &&
(!prev_specifics.has_encrypted() ||
cryptographer->CanDecrypt(prev_specifics.encrypted()))) {
DVLOG(2) << "Storing previous server specifcs: "
<< prev_specifics.SerializeAsString();
} else if (IsRealDataType(GetModelTypeFromSpecifics(
target_entry.GetBaseServerSpecifics()))) {
// We have a BASE_SERVER_SPECIFICS, but a subsequent non-specifics-only
// change arrived. As a result, we can't use the specifics alone to detect
// changes, so we clear BASE_SERVER_SPECIFICS.
UpdateServerFieldsFromUpdate(&target_entry, update, name);
} // namespace
void ProcessDownloadedUpdates(
syncable::Directory* dir,
syncable::ModelNeutralWriteTransaction* trans,
ModelType type,
const SyncEntityList& applicable_updates,
sessions::StatusController* status,
UpdateCounters* counters) {
for (SyncEntityList::const_iterator update_it = applicable_updates.begin();
update_it != applicable_updates.end(); ++update_it) {
DCHECK_EQ(type, GetModelType(**update_it));
if (!UpdateContainsNewVersion(trans, **update_it)) {
if ((*update_it)->deleted()) {
VerifyResult verify_result = VerifyUpdate(trans, **update_it, type);
if (verify_result != VERIFY_SUCCESS && verify_result != VERIFY_UNDELETE)
ProcessUpdate(**update_it, dir->GetCryptographer(trans), trans);
if ((*update_it)->ByteSize() > 0) {
void ExpireEntriesByVersion(syncable::Directory* dir,
syncable::ModelNeutralWriteTransaction* trans,
ModelType type,
int64_t version_watermark) {
syncable::Directory::Metahandles handles;
dir->GetMetaHandlesOfType(trans, type, &handles);
for (size_t i = 0; i < handles.size(); ++i) {
syncable::ModelNeutralMutableEntry entry(trans, syncable::GET_BY_HANDLE,
if (!entry.good() || !entry.GetId().ServerKnows() ||
entry.GetUniqueServerTag() == ModelTypeToRootTag(type) ||
entry.GetIsUnappliedUpdate() || entry.GetIsUnsynced() ||
entry.GetIsDel() || entry.GetServerIsDel() ||
entry.GetBaseVersion() >= version_watermark) {
// Mark entry as unapplied update first to ensure journaling the deletion.
// Mark entry as deleted by server.
} // namespace syncer