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// Copyright 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/syncer_util.h"
#include <stdint.h>
#include <algorithm>
#include <set>
#include <string>
#include <vector>
#include "base/base64.h"
#include "base/location.h"
#include "base/metrics/histogram.h"
#include "base/rand_util.h"
#include "base/strings/string_number_conversions.h"
#include "sync/engine/conflict_resolver.h"
#include "sync/engine/syncer_proto_util.h"
#include "sync/engine/syncer_types.h"
#include "sync/internal_api/public/base/attachment_id_proto.h"
#include "sync/internal_api/public/base/model_type.h"
#include "sync/internal_api/public/base/unique_position.h"
#include "sync/protocol/bookmark_specifics.pb.h"
#include "sync/protocol/password_specifics.pb.h"
#include "sync/protocol/sync.pb.h"
#include "sync/syncable/directory.h"
#include "sync/syncable/entry.h"
#include "sync/syncable/model_neutral_mutable_entry.h"
#include "sync/syncable/mutable_entry.h"
#include "sync/syncable/syncable_changes_version.h"
#include "sync/syncable/syncable_model_neutral_write_transaction.h"
#include "sync/syncable/syncable_proto_util.h"
#include "sync/syncable/syncable_read_transaction.h"
#include "sync/syncable/syncable_util.h"
#include "sync/syncable/syncable_write_transaction.h"
#include "sync/util/cryptographer.h"
#include "sync/util/time.h"
namespace syncer {
using syncable::CHANGES_VERSION;
using syncable::Directory;
using syncable::Entry;
using syncable::GET_BY_HANDLE;
using syncable::GET_BY_ID;
using syncable::ID;
using syncable::Id;
syncable::Id FindLocalIdToUpdate(
syncable::BaseTransaction* trans,
const sync_pb::SyncEntity& update) {
// Expected entry points of this function:
// SyncEntity has NOT been applied to SERVER fields.
// SyncEntity has NOT been applied to LOCAL fields.
// DB has not yet been modified, no entries created for this update.
const std::string& client_id = trans->directory()->cache_guid();
const syncable::Id& update_id = SyncableIdFromProto(update.id_string());
if (update.has_client_defined_unique_tag() &&
!update.client_defined_unique_tag().empty()) {
// When a server sends down a client tag, the following cases can occur:
// 1) Client has entry for tag already, ID is server style, matches
// 2) Client has entry for tag already, ID is server, doesn't match.
// 3) Client has entry for tag already, ID is local, (never matches)
// 4) Client has no entry for tag
// Case 1, we don't have to do anything since the update will
// work just fine. Update will end up in the proper entry, via ID lookup.
// Case 2 - Happens very rarely due to lax enforcement of client tags
// on the server, if two clients commit the same tag at the same time.
// When this happens, we pick the lexically-least ID and ignore all other
// items.
// Case 3 - We need to replace the local ID with the server ID so that
// this update gets targeted at the correct local entry; we expect conflict
// resolution to occur.
// Case 4 - Perfect. Same as case 1.
syncable::Entry local_entry(trans, syncable::GET_BY_CLIENT_TAG,
// The SyncAPI equivalent of this function will return !good if IS_DEL.
// The syncable version will return good even if IS_DEL.
// TODO(chron): Unit test the case with IS_DEL and make sure.
if (local_entry.good()) {
if (local_entry.GetId().ServerKnows()) {
if (local_entry.GetId() != update_id) {
// Case 2.
LOG(WARNING) << "Duplicated client tag.";
if (local_entry.GetId() < update_id) {
// Signal an error; drop this update on the floor. Note that
// we don't server delete the item, because we don't allow it to
// exist locally at all. So the item will remain orphaned on
// the server, and we won't pay attention to it.
return syncable::Id();
// Target this change to the existing local entry; later,
// we'll change the ID of the local entry to update_id
// if needed.
return local_entry.GetId();
} else {
// Case 3: We have a local entry with the same client tag.
// We should change the ID of the local entry to the server entry.
// This will result in an server ID with base version == 0, but that's
// a legal state for an item with a client tag. By changing the ID,
// update will now be applied to local_entry.
DCHECK(0 == local_entry.GetBaseVersion() ||
CHANGES_VERSION == local_entry.GetBaseVersion());
return local_entry.GetId();
} else if (update.has_originator_cache_guid() &&
update.originator_cache_guid() == client_id) {
// If a commit succeeds, but the response does not come back fast enough
// then the syncer might assume that it was never committed.
// The server will track the client that sent up the original commit and
// return this in a get updates response. When this matches a local
// uncommitted item, we must mutate our local item and version to pick up
// the committed version of the same item whose commit response was lost.
// There is however still a race condition if the server has not
// completed the commit by the time the syncer tries to get updates
// again. To mitigate this, we need to have the server time out in
// a reasonable span, our commit batches have to be small enough
// to process within our HTTP response "assumed alive" time.
// We need to check if we have an entry that didn't get its server
// id updated correctly. The server sends down a client ID
// and a local (negative) id. If we have a entry by that
// description, we should update the ID and version to the
// server side ones to avoid multiple copies of the same thing.
syncable::Id client_item_id = syncable::Id::CreateFromClientString(
syncable::Entry local_entry(trans, GET_BY_ID, client_item_id);
// If it exists, then our local client lost a commit response. Use
// the local entry.
if (local_entry.good() && !local_entry.GetIsDel()) {
int64_t old_version = local_entry.GetBaseVersion();
int64_t new_version = update.version();
DCHECK_LE(old_version, 0);
DCHECK_GT(new_version, 0);
// Otherwise setting the base version could cause a consistency failure.
// An entry should never be version 0 and SYNCED.
// Just a quick sanity check.
DVLOG(1) << "Reuniting lost commit response IDs. server id: "
<< update_id << " local id: " << local_entry.GetId()
<< " new version: " << new_version;
return local_entry.GetId();
} else if (update.has_server_defined_unique_tag() &&
!update.server_defined_unique_tag().empty()) {
// The client creates type root folders with a local ID on demand when a
// progress marker for the given type is initially set.
// The server might also attempt to send a type root folder for the same
// type (during the transition period until support for root folders is
// removed for new client versions).
// TODO(stanisc): remove this once the transition to
// implicit root folders on the server is done.
syncable::Entry local_entry(trans, syncable::GET_BY_SERVER_TAG,
if (local_entry.good() && !local_entry.GetId().ServerKnows()) {
DCHECK(local_entry.GetId() != update_id);
return local_entry.GetId();
// Fallback: target an entry having the server ID, creating one if needed.
return update_id;
UpdateAttemptResponse AttemptToUpdateEntry(
syncable::WriteTransaction* const trans,
syncable::MutableEntry* const entry,
Cryptographer* cryptographer) {
if (!entry->GetIsUnappliedUpdate())
return SUCCESS; // No work to do.
syncable::Id id = entry->GetId();
const sync_pb::EntitySpecifics& specifics = entry->GetServerSpecifics();
ModelType type = GetModelTypeFromSpecifics(specifics);
// Only apply updates that we can decrypt. If we can't decrypt the update, it
// is likely because the passphrase has not arrived yet. Because the
// passphrase may not arrive within this GetUpdates, we can't just return
// conflict, else we try to perform normal conflict resolution prematurely or
// the syncer may get stuck. As such, we return CONFLICT_ENCRYPTION, which is
// treated as an unresolvable conflict. See the description in syncer_types.h.
// This prevents any unsynced changes from commiting and postpones conflict
// resolution until all data can be decrypted.
if (specifics.has_encrypted() &&
!cryptographer->CanDecrypt(specifics.encrypted())) {
// We can't decrypt this node yet.
DVLOG(1) << "Received an undecryptable "
<< ModelTypeToString(entry->GetServerModelType())
<< " update, returning conflict_encryption.";
} else if (specifics.has_password() &&
entry->GetUniqueServerTag().empty()) {
// Passwords use their own legacy encryption scheme.
const sync_pb::PasswordSpecifics& password = specifics.password();
if (!cryptographer->CanDecrypt(password.encrypted())) {
DVLOG(1) << "Received an undecryptable password update, returning "
<< "conflict_encryption.";
if (!entry->GetServerIsDel()) {
syncable::Id new_parent = entry->GetServerParentId();
if (!new_parent.IsNull()) {
// Perform this step only if the parent is specified.
// The unset parent means that the implicit type root would be used.
Entry parent(trans, GET_BY_ID, new_parent);
// A note on non-directory parents:
// We catch most unfixable tree invariant errors at update receipt time,
// however we deal with this case here because we may receive the child
// first then the illegal parent. Instead of dealing with it twice in
// different ways we deal with it once here to reduce the amount of code
// and potential errors.
if (!parent.good() || parent.GetIsDel() || !parent.GetIsDir()) {
DVLOG(1) << "Entry has bad parent, returning conflict_hierarchy.";
if (entry->GetParentId() != new_parent) {
if (!entry->GetIsDel() && !IsLegalNewParent(trans, id, new_parent)) {
DVLOG(1) << "Not updating item " << id
<< ", illegal new parent (would cause loop).";
} else {
// new_parent is unset.
} else if (entry->GetIsDir()) {
Directory::Metahandles handles;
trans->directory()->GetChildHandlesById(trans, id, &handles);
if (!handles.empty()) {
// If we have still-existing children, then we need to deal with
// them before we can process this change.
DVLOG(1) << "Not deleting directory; it's not empty " << *entry;
if (entry->GetIsUnsynced()) {
DVLOG(1) << "Skipping update, returning conflict for: " << id
<< " ; it's unsynced.";
if (specifics.has_encrypted()) {
DVLOG(2) << "Received a decryptable "
<< ModelTypeToString(entry->GetServerModelType())
<< " update, applying normally.";
} else {
DVLOG(2) << "Received an unencrypted "
<< ModelTypeToString(entry->GetServerModelType())
<< " update, applying normally.";
UpdateLocalDataFromServerData(trans, entry);
return SUCCESS;
std::string GetUniqueBookmarkTagFromUpdate(const sync_pb::SyncEntity& update) {
if (!update.has_originator_cache_guid() ||
!update.has_originator_client_item_id()) {
LOG(ERROR) << "Update is missing requirements for bookmark position."
<< " This is a server bug.";
return UniquePosition::RandomSuffix();
return syncable::GenerateSyncableBookmarkHash(
update.originator_cache_guid(), update.originator_client_item_id());
UniquePosition GetUpdatePosition(const sync_pb::SyncEntity& update,
const std::string& suffix) {
if (!(SyncerProtoUtil::ShouldMaintainPosition(update))) {
return UniquePosition::CreateInvalid();
} else if (update.has_unique_position()) {
UniquePosition proto_position =
if (proto_position.IsValid()) {
return proto_position;
// Now, there are two cases hit here.
// 1. Did not receive unique_position for this update.
// 2. Received unique_position, but it is invalid(ex. empty).
// And we will create a valid position for this two cases.
if (update.has_position_in_parent()) {
return UniquePosition::FromInt64(update.position_in_parent(), suffix);
} else {
LOG(ERROR) << "No position information in update. This is a server bug.";
return UniquePosition::FromInt64(0, suffix);
namespace {
// Helper to synthesize a new-style sync_pb::EntitySpecifics for use locally,
// when the server speaks only the old sync_pb::SyncEntity_BookmarkData-based
// protocol.
void UpdateBookmarkSpecifics(const std::string& singleton_tag,
const std::string& url,
const std::string& favicon_bytes,
syncable::ModelNeutralMutableEntry* local_entry) {
// In the new-style protocol, the server no longer sends bookmark info for
// the "google_chrome" folder. Mimic that here.
if (singleton_tag == "google_chrome")
sync_pb::EntitySpecifics pb;
sync_pb::BookmarkSpecifics* bookmark = pb.mutable_bookmark();
if (!url.empty())
if (!favicon_bytes.empty())
void UpdateBookmarkPositioning(
const sync_pb::SyncEntity& update,
syncable::ModelNeutralMutableEntry* local_entry) {
// Update our unique bookmark tag. In many cases this will be identical to
// the tag we already have. However, clients that have recently upgraded to
// versions that support unique positions will have incorrect tags. See the
// v86 migration logic in for more information.
// Both the old and new values are unique to this element. Applying this
// update will not risk the creation of conflicting unique tags.
std::string bookmark_tag = GetUniqueBookmarkTagFromUpdate(update);
if (UniquePosition::IsValidSuffix(bookmark_tag)) {
// Update our position.
UniquePosition update_pos =
GetUpdatePosition(update, local_entry->GetUniqueBookmarkTag());
if (update_pos.IsValid()) {
} // namespace
void UpdateServerFieldsFromUpdate(
syncable::ModelNeutralMutableEntry* target,
const sync_pb::SyncEntity& update,
const std::string& name) {
if (update.deleted()) {
if (target->GetServerIsDel()) {
// If we already think the item is server-deleted, we're done.
// Skipping these cases prevents our committed deletions from coming
// back and overriding subsequent undeletions. For non-deleted items,
// the version number check has a similar effect.
// Mark entry as unapplied update first to ensure journaling the deletion.
// The server returns very lightweight replies for deletions, so we don't
// clobber a bunch of fields on delete.
if (!target->GetUniqueClientTag().empty()) {
// Items identified by the client unique tag are undeletable; when
// they're deleted, they go back to version 0.
} else {
// Otherwise, fake a server version by bumping the local number.
std::max(target->GetServerVersion(), target->GetBaseVersion()) + 1);
DCHECK_EQ(target->GetId(), SyncableIdFromProto(update.id_string()))
<< "ID Changing not supported here";
if (SyncerProtoUtil::ShouldMaintainHierarchy(update)) {
} else {
if (update.has_server_defined_unique_tag()) {
const std::string& tag = update.server_defined_unique_tag();
if (update.has_client_defined_unique_tag()) {
const std::string& tag = update.client_defined_unique_tag();
// Store the datatype-specific part as a protobuf.
if (update.has_specifics()) {
DCHECK_NE(GetModelType(update), UNSPECIFIED)
<< "Storing unrecognized datatype in sync database.";
} else if (update.has_bookmarkdata()) {
// Legacy protocol response for bookmark data.
const sync_pb::SyncEntity::BookmarkData& bookmark = update.bookmarkdata();
if (SyncerProtoUtil::ShouldMaintainPosition(update)) {
UpdateBookmarkPositioning(update, target);
// We only mark the entry as unapplied if its version is greater than the
// local data. If we're processing the update that corresponds to one of our
// commit we don't apply it as time differences may occur.
if (update.version() > target->GetBaseVersion()) {
// Creates a new Entry iff no Entry exists with the given id.
void CreateNewEntry(syncable::ModelNeutralWriteTransaction *trans,
const syncable::Id& id) {
syncable::Entry entry(trans, GET_BY_ID, id);
if (!entry.good()) {
syncable::ModelNeutralMutableEntry new_entry(
// This function is called on an entry when we can update the user-facing data
// from the server data.
void UpdateLocalDataFromServerData(
syncable::WriteTransaction* trans,
syncable::MutableEntry* entry) {
DVLOG(2) << "Updating entry : " << *entry;
// Start by setting the properties that determine the model_type.
// Clear the previous server specifics now that we're applying successfully.
// This strange dance around the IS_DEL flag avoids problems when setting
// the name.
// TODO(chron): Is this still an issue? Unit test this codepath.
if (entry->GetServerIsDel()) {
} else {
VerifyCommitResult ValidateCommitEntry(syncable::Entry* entry) {
syncable::Id id = entry->GetId();
if (id == entry->GetParentId()) {
CHECK(id.IsRoot()) << "Non-root item is self parenting." << *entry;
// If the root becomes unsynced it can cause us problems.
LOG(ERROR) << "Root item became unsynced " << *entry;
if (entry->IsRoot()) {
LOG(ERROR) << "Permanent item became unsynced " << *entry;
if (entry->GetIsDel() && !entry->GetId().ServerKnows()) {
// Drop deleted uncommitted entries.
return VERIFY_OK;
void MarkDeletedChildrenSynced(
syncable::Directory* dir,
syncable::BaseWriteTransaction* trans,
std::set<syncable::Id>* deleted_folders) {
// There's two options here.
// 1. Scan deleted unsynced entries looking up their pre-delete tree for any
// of the deleted folders.
// 2. Take each folder and do a tree walk of all entries underneath it.
// #2 has a lower big O cost, but writing code to limit the time spent inside
// the transaction during each step is simpler with 1. Changing this decision
// may be sensible if this code shows up in profiling.
if (deleted_folders->empty())
Directory::Metahandles handles;
dir->GetUnsyncedMetaHandles(trans, &handles);
if (handles.empty())
Directory::Metahandles::iterator it;
for (it = handles.begin() ; it != handles.end() ; ++it) {
syncable::ModelNeutralMutableEntry entry(trans, GET_BY_HANDLE, *it);
if (!entry.GetIsUnsynced() || !entry.GetIsDel())
syncable::Id id = entry.GetParentId();
while (id != trans->root_id()) {
if (deleted_folders->find(id) != deleted_folders->end()) {
// We've synced the deletion of this deleted entries parent.
Entry parent(trans, GET_BY_ID, id);
if (!parent.good() || !parent.GetIsDel())
id = parent.GetParentId();
VerifyResult VerifyNewEntry(
const sync_pb::SyncEntity& update,
syncable::Entry* target,
const bool deleted) {
if (target->good()) {
// Not a new update.
if (deleted) {
// Deletion of an item we've never seen can be ignored.
// Assumes we have an existing entry; check here for updates that break
// consistency rules.
VerifyResult VerifyUpdateConsistency(
syncable::ModelNeutralWriteTransaction* trans,
const sync_pb::SyncEntity& update,
const bool deleted,
const bool is_directory,
ModelType model_type,
syncable::ModelNeutralMutableEntry* target) {
const syncable::Id& update_id = SyncableIdFromProto(update.id_string());
// If the update is a delete, we don't really need to worry at this stage.
if (deleted)
if (model_type == UNSPECIFIED) {
// This update is to an item of a datatype we don't recognize. The server
// shouldn't have sent it to us. Throw it on the ground.
if (target->GetServerVersion() > 0) {
// Then we've had an update for this entry before.
if (is_directory != target->GetServerIsDir() ||
model_type != target->GetServerModelType()) {
if (target->GetIsDel()) { // If we've deleted the item, we don't care.
} else {
LOG(ERROR) << "Server update doesn't agree with previous updates. ";
LOG(ERROR) << " Entry: " << *target;
LOG(ERROR) << " Update: "
<< SyncerProtoUtil::SyncEntityDebugString(update);
if (!deleted && (target->GetId() == update_id) &&
(target->GetServerIsDel() ||
(!target->GetIsUnsynced() && target->GetIsDel() &&
target->GetBaseVersion() > 0))) {
// An undelete. The latter case in the above condition is for
// when the server does not give us an update following the
// commit of a delete, before undeleting.
// Undeletion is common for items that reuse the client-unique tag.
VerifyResult result = VerifyUndelete(trans, update, target);
if (VERIFY_UNDECIDED != result)
return result;
if (target->GetBaseVersion() > 0) {
// We've committed this update in the past.
if (is_directory != target->GetIsDir() ||
model_type != target->GetModelType()) {
LOG(ERROR) << "Server update doesn't agree with committed item. ";
LOG(ERROR) << " Entry: " << *target;
LOG(ERROR) << " Update: "
<< SyncerProtoUtil::SyncEntityDebugString(update);
if (target->GetId() == update_id) {
if (target->GetServerVersion() > update.version()) {
LOG(WARNING) << "We've already seen a more recent version.";
LOG(WARNING) << " Entry: " << *target;
LOG(WARNING) << " Update: "
<< SyncerProtoUtil::SyncEntityDebugString(update);
// Assumes we have an existing entry; verify an update that seems to be
// expressing an 'undelete'
VerifyResult VerifyUndelete(syncable::ModelNeutralWriteTransaction* trans,
const sync_pb::SyncEntity& update,
syncable::ModelNeutralMutableEntry* target) {
// TODO(nick): We hit this path for items deleted items that the server
// tells us to re-create; only deleted items with positive base versions
// will hit this path. However, it's not clear how such an undeletion
// would actually succeed on the server; in the protocol, a base
// version of 0 is required to undelete an object. This codepath
// should be deprecated in favor of client-tag style undeletion
// (where items go to version 0 when they're deleted), or else
// removed entirely (if this type of undeletion is indeed impossible).
DVLOG(1) << "Server update is attempting undelete. " << *target
<< "Update:" << SyncerProtoUtil::SyncEntityDebugString(update);
// Move the old one aside and start over. It's too tricky to get the old one
// back into a state that would pass CheckTreeInvariants().
if (target->GetIsDel()) {
if (target->GetUniqueClientTag().empty())
LOG(WARNING) << "Doing move-aside undeletion on client-tagged item.";
if (update.version() < target->GetServerVersion()) {
LOG(WARNING) << "Update older than current server version for "
<< *target << " Update:"
<< SyncerProtoUtil::SyncEntityDebugString(update);
return VERIFY_SUCCESS; // Expected in new sync protocol.
} // namespace syncer