sync/engine/syncer_util.cc

   1 // Copyright 2012 The Chromium Authors. All rights reserved.
   2 // Use of this source code is governed by a BSD-style license that can be
   3 // found in the LICENSE file.
   4
   5 #include "sync/engine/syncer_util.h"
   6
   7 #include <algorithm>
   8 #include <set>
   9 #include <string>
  10 #include <vector>
  11
  12 #include "base/base64.h"
  13 #include "base/location.h"
  14 #include "base/metrics/histogram.h"
  15 #include "base/rand_util.h"
  16 #include "base/strings/string_number_conversions.h"
  17 #include "sync/engine/conflict_resolver.h"
  18 #include "sync/engine/syncer_proto_util.h"
  19 #include "sync/engine/syncer_types.h"
  20 #include "sync/internal_api/public/base/attachment_id_proto.h"
  21 #include "sync/internal_api/public/base/model_type.h"
  22 #include "sync/internal_api/public/base/unique_position.h"
  23 #include "sync/protocol/bookmark_specifics.pb.h"
  24 #include "sync/protocol/password_specifics.pb.h"
  25 #include "sync/protocol/sync.pb.h"
  26 #include "sync/syncable/directory.h"
  27 #include "sync/syncable/entry.h"
  28 #include "sync/syncable/model_neutral_mutable_entry.h"
  29 #include "sync/syncable/mutable_entry.h"
  30 #include "sync/syncable/syncable_changes_version.h"
  31 #include "sync/syncable/syncable_model_neutral_write_transaction.h"
  32 #include "sync/syncable/syncable_proto_util.h"
  33 #include "sync/syncable/syncable_read_transaction.h"
  34 #include "sync/syncable/syncable_util.h"
  35 #include "sync/syncable/syncable_write_transaction.h"
  36 #include "sync/util/cryptographer.h"
  37 #include "sync/util/time.h"
  38
  39 namespace syncer {
  40
  41 using syncable::BASE_SERVER_SPECIFICS;
  42 using syncable::BASE_VERSION;
  43 using syncable::CHANGES_VERSION;
  44 using syncable::CREATE_NEW_UPDATE_ITEM;
  45 using syncable::CTIME;
  46 using syncable::Directory;
  47 using syncable::Entry;
  48 using syncable::GET_BY_HANDLE;
  49 using syncable::GET_BY_ID;
  50 using syncable::ID;
  51 using syncable::IS_DEL;
  52 using syncable::IS_DIR;
  53 using syncable::IS_UNAPPLIED_UPDATE;
  54 using syncable::IS_UNSYNCED;
  55 using syncable::Id;
  56 using syncable::META_HANDLE;
  57 using syncable::MTIME;
  58 using syncable::MutableEntry;
  59 using syncable::NON_UNIQUE_NAME;
  60 using syncable::PARENT_ID;
  61 using syncable::SERVER_CTIME;
  62 using syncable::SERVER_IS_DEL;
  63 using syncable::SERVER_IS_DIR;
  64 using syncable::SERVER_MTIME;
  65 using syncable::SERVER_NON_UNIQUE_NAME;
  66 using syncable::SERVER_PARENT_ID;
  67 using syncable::SERVER_SPECIFICS;
  68 using syncable::SERVER_UNIQUE_POSITION;
  69 using syncable::SERVER_VERSION;
  70 using syncable::SPECIFICS;
  71 using syncable::SYNCER;
  72 using syncable::UNIQUE_BOOKMARK_TAG;
  73 using syncable::UNIQUE_CLIENT_TAG;
  74 using syncable::UNIQUE_POSITION;
  75 using syncable::UNIQUE_SERVER_TAG;
  76 using syncable::WriteTransaction;
  77
  78 syncable::Id FindLocalIdToUpdate(
  79     syncable::BaseTransaction* trans,
  80     const sync_pb::SyncEntity& update) {
  81   // Expected entry points of this function:
  82   // SyncEntity has NOT been applied to SERVER fields.
  83   // SyncEntity has NOT been applied to LOCAL fields.
  84   // DB has not yet been modified, no entries created for this update.
  85
  86   const std::string& client_id = trans->directory()->cache_guid();
  87   const syncable::Id& update_id = SyncableIdFromProto(update.id_string());
  88
  89   if (update.has_client_defined_unique_tag() &&
  90       !update.client_defined_unique_tag().empty()) {
  91     // When a server sends down a client tag, the following cases can occur:
  92     // 1) Client has entry for tag already, ID is server style, matches
  93     // 2) Client has entry for tag already, ID is server, doesn't match.
  94     // 3) Client has entry for tag already, ID is local, (never matches)
  95     // 4) Client has no entry for tag
  96
  97     // Case 1, we don't have to do anything since the update will
  98     // work just fine. Update will end up in the proper entry, via ID lookup.
  99     // Case 2 - Happens very rarely due to lax enforcement of client tags
 100     // on the server, if two clients commit the same tag at the same time.
 101     // When this happens, we pick the lexically-least ID and ignore all other
 102     // items.
 103     // Case 3 - We need to replace the local ID with the server ID so that
 104     // this update gets targeted at the correct local entry; we expect conflict
 105     // resolution to occur.
 106     // Case 4 - Perfect. Same as case 1.
 107
 108     syncable::Entry local_entry(trans, syncable::GET_BY_CLIENT_TAG,
 109                                 update.client_defined_unique_tag());
 110
 111     // The SyncAPI equivalent of this function will return !good if IS_DEL.
 112     // The syncable version will return good even if IS_DEL.
 113     // TODO(chron): Unit test the case with IS_DEL and make sure.
 114     if (local_entry.good()) {
 115       if (local_entry.GetId().ServerKnows()) {
 116         if (local_entry.GetId() != update_id) {
 117           // Case 2.
 118           LOG(WARNING) << "Duplicated client tag.";
 119           if (local_entry.GetId() < update_id) {
 120             // Signal an error; drop this update on the floor.  Note that
 121             // we don't server delete the item, because we don't allow it to
 122             // exist locally at all.  So the item will remain orphaned on
 123             // the server, and we won't pay attention to it.
 124             return syncable::Id();
 125           }
 126         }
 127         // Target this change to the existing local entry; later,
 128         // we'll change the ID of the local entry to update_id
 129         // if needed.
 130         return local_entry.GetId();
 131       } else {
 132         // Case 3: We have a local entry with the same client tag.
 133         // We should change the ID of the local entry to the server entry.
 134         // This will result in an server ID with base version == 0, but that's
 135         // a legal state for an item with a client tag.  By changing the ID,
 136         // update will now be applied to local_entry.
 137         DCHECK(0 == local_entry.GetBaseVersion() ||
 138                CHANGES_VERSION == local_entry.GetBaseVersion());
 139         return local_entry.GetId();
 140       }
 141     }
 142   } else if (update.has_originator_cache_guid() &&
 143       update.originator_cache_guid() == client_id) {
 144     // If a commit succeeds, but the response does not come back fast enough
 145     // then the syncer might assume that it was never committed.
 146     // The server will track the client that sent up the original commit and
 147     // return this in a get updates response. When this matches a local
 148     // uncommitted item, we must mutate our local item and version to pick up
 149     // the committed version of the same item whose commit response was lost.
 150     // There is however still a race condition if the server has not
 151     // completed the commit by the time the syncer tries to get updates
 152     // again. To mitigate this, we need to have the server time out in
 153     // a reasonable span, our commit batches have to be small enough
 154     // to process within our HTTP response "assumed alive" time.
 155
 156     // We need to check if we have an entry that didn't get its server
 157     // id updated correctly. The server sends down a client ID
 158     // and a local (negative) id. If we have a entry by that
 159     // description, we should update the ID and version to the
 160     // server side ones to avoid multiple copies of the same thing.
 161
 162     syncable::Id client_item_id = syncable::Id::CreateFromClientString(
 163         update.originator_client_item_id());
 164     DCHECK(!client_item_id.ServerKnows());
 165     syncable::Entry local_entry(trans, GET_BY_ID, client_item_id);
 166
 167     // If it exists, then our local client lost a commit response.  Use
 168     // the local entry.
 169     if (local_entry.good() && !local_entry.GetIsDel()) {
 170       int64 old_version = local_entry.GetBaseVersion();
 171       int64 new_version = update.version();
 172       DCHECK_LE(old_version, 0);
 173       DCHECK_GT(new_version, 0);
 174       // Otherwise setting the base version could cause a consistency failure.
 175       // An entry should never be version 0 and SYNCED.
 176       DCHECK(local_entry.GetIsUnsynced());
 177
 178       // Just a quick sanity check.
 179       DCHECK(!local_entry.GetId().ServerKnows());
 180
 181       DVLOG(1) << "Reuniting lost commit response IDs. server id: "
 182                << update_id << " local id: " << local_entry.GetId()
 183                << " new version: " << new_version;
 184
 185       return local_entry.GetId();
 186     }
 187   } else if (update.has_server_defined_unique_tag() &&
 188              !update.server_defined_unique_tag().empty()) {
 189     // The client creates type root folders with a local ID on demand when a
 190     // progress marker for the given type is initially set.
 191     // The server might also attempt to send a type root folder for the same
 192     // type (during the transition period until support for root folders is
 193     // removed for new client versions).
 194     // TODO(stanisc): crbug.com/438313: remove this once the transition to
 195     // implicit root folders on the server is done.
 196     syncable::Entry local_entry(trans, syncable::GET_BY_SERVER_TAG,
 197                                 update.server_defined_unique_tag());
 198     if (local_entry.good() && !local_entry.GetId().ServerKnows()) {
 199       DCHECK(local_entry.GetId() != update_id);
 200       return local_entry.GetId();
 201     }
 202   }
 203
 204   // Fallback: target an entry having the server ID, creating one if needed.
 205   return update_id;
 206 }
 207
 208 UpdateAttemptResponse AttemptToUpdateEntry(
 209     syncable::WriteTransaction* const trans,
 210     syncable::MutableEntry* const entry,
 211     Cryptographer* cryptographer) {
 212   CHECK(entry->good());
 213   if (!entry->GetIsUnappliedUpdate())
 214     return SUCCESS;  // No work to do.
 215   syncable::Id id = entry->GetId();
 216   const sync_pb::EntitySpecifics& specifics = entry->GetServerSpecifics();
 217   ModelType type = GetModelTypeFromSpecifics(specifics);
 218
 219   // Only apply updates that we can decrypt. If we can't decrypt the update, it
 220   // is likely because the passphrase has not arrived yet. Because the
 221   // passphrase may not arrive within this GetUpdates, we can't just return
 222   // conflict, else we try to perform normal conflict resolution prematurely or
 223   // the syncer may get stuck. As such, we return CONFLICT_ENCRYPTION, which is
 224   // treated as an unresolvable conflict. See the description in syncer_types.h.
 225   // This prevents any unsynced changes from commiting and postpones conflict
 226   // resolution until all data can be decrypted.
 227   if (specifics.has_encrypted() &&
 228       !cryptographer->CanDecrypt(specifics.encrypted())) {
 229     // We can't decrypt this node yet.
 230     DVLOG(1) << "Received an undecryptable "
 231              << ModelTypeToString(entry->GetServerModelType())
 232              << " update, returning conflict_encryption.";
 233     return CONFLICT_ENCRYPTION;
 234   } else if (specifics.has_password() &&
 235              entry->GetUniqueServerTag().empty()) {
 236     // Passwords use their own legacy encryption scheme.
 237     const sync_pb::PasswordSpecifics& password = specifics.password();
 238     if (!cryptographer->CanDecrypt(password.encrypted())) {
 239       DVLOG(1) << "Received an undecryptable password update, returning "
 240                << "conflict_encryption.";
 241       return CONFLICT_ENCRYPTION;
 242     }
 243   }
 244
 245   if (!entry->GetServerIsDel()) {
 246     syncable::Id new_parent = entry->GetServerParentId();
 247     if (!new_parent.IsNull()) {
 248       // Perform this step only if the parent is specified.
 249       // The unset parent means that the implicit type root would be used.
 250       Entry parent(trans, GET_BY_ID, new_parent);
 251       // A note on non-directory parents:
 252       // We catch most unfixable tree invariant errors at update receipt time,
 253       // however we deal with this case here because we may receive the child
 254       // first then the illegal parent. Instead of dealing with it twice in
 255       // different ways we deal with it once here to reduce the amount of code
 256       // and potential errors.
 257       if (!parent.good() || parent.GetIsDel() || !parent.GetIsDir()) {
 258         DVLOG(1) << "Entry has bad parent, returning conflict_hierarchy.";
 259         return CONFLICT_HIERARCHY;
 260       }
 261       if (entry->GetParentId() != new_parent) {
 262         if (!entry->GetIsDel() && !IsLegalNewParent(trans, id, new_parent)) {
 263           DVLOG(1) << "Not updating item " << id
 264                    << ", illegal new parent (would cause loop).";
 265           return CONFLICT_HIERARCHY;
 266         }
 267       }
 268     } else {
 269       // new_parent is unset.
 270       DCHECK(IsTypeWithClientGeneratedRoot(type));
 271     }
 272   } else if (entry->GetIsDir()) {
 273     Directory::Metahandles handles;
 274     trans->directory()->GetChildHandlesById(trans, id, &handles);
 275     if (!handles.empty()) {
 276       // If we have still-existing children, then we need to deal with
 277       // them before we can process this change.
 278       DVLOG(1) << "Not deleting directory; it's not empty " << *entry;
 279       return CONFLICT_HIERARCHY;
 280     }
 281   }
 282
 283   if (entry->GetIsUnsynced()) {
 284     DVLOG(1) << "Skipping update, returning conflict for: " << id
 285              << " ; it's unsynced.";
 286     return CONFLICT_SIMPLE;
 287   }
 288
 289   if (specifics.has_encrypted()) {
 290     DVLOG(2) << "Received a decryptable "
 291              << ModelTypeToString(entry->GetServerModelType())
 292              << " update, applying normally.";
 293   } else {
 294     DVLOG(2) << "Received an unencrypted "
 295              << ModelTypeToString(entry->GetServerModelType())
 296              << " update, applying normally.";
 297   }
 298
 299   UpdateLocalDataFromServerData(trans, entry);
 300
 301   return SUCCESS;
 302 }
 303
 304 std::string GetUniqueBookmarkTagFromUpdate(const sync_pb::SyncEntity& update) {
 305   if (!update.has_originator_cache_guid() ||
 306       !update.has_originator_client_item_id()) {
 307     LOG(ERROR) << "Update is missing requirements for bookmark position."
 308                << " This is a server bug.";
 309     return UniquePosition::RandomSuffix();
 310   }
 311
 312   return syncable::GenerateSyncableBookmarkHash(
 313       update.originator_cache_guid(), update.originator_client_item_id());
 314 }
 315
 316 UniquePosition GetUpdatePosition(const sync_pb::SyncEntity& update,
 317                                  const std::string& suffix) {
 318   DCHECK(UniquePosition::IsValidSuffix(suffix));
 319   if (!(SyncerProtoUtil::ShouldMaintainPosition(update))) {
 320     return UniquePosition::CreateInvalid();
 321   } else if (update.has_unique_position()) {
 322     return UniquePosition::FromProto(update.unique_position());
 323   } else if (update.has_position_in_parent()) {
 324     return UniquePosition::FromInt64(update.position_in_parent(), suffix);
 325   } else {
 326     LOG(ERROR) << "No position information in update. This is a server bug.";
 327     return UniquePosition::FromInt64(0, suffix);
 328   }
 329 }
 330
 331 namespace {
 332
 333 // Helper to synthesize a new-style sync_pb::EntitySpecifics for use locally,
 334 // when the server speaks only the old sync_pb::SyncEntity_BookmarkData-based
 335 // protocol.
 336 void UpdateBookmarkSpecifics(const std::string& singleton_tag,
 337                              const std::string& url,
 338                              const std::string& favicon_bytes,
 339                              syncable::ModelNeutralMutableEntry* local_entry) {
 340   // In the new-style protocol, the server no longer sends bookmark info for
 341   // the "google_chrome" folder.  Mimic that here.
 342   if (singleton_tag == "google_chrome")
 343     return;
 344   sync_pb::EntitySpecifics pb;
 345   sync_pb::BookmarkSpecifics* bookmark = pb.mutable_bookmark();
 346   if (!url.empty())
 347     bookmark->set_url(url);
 348   if (!favicon_bytes.empty())
 349     bookmark->set_favicon(favicon_bytes);
 350   local_entry->PutServerSpecifics(pb);
 351 }
 352
 353 void UpdateBookmarkPositioning(
 354     const sync_pb::SyncEntity& update,
 355     syncable::ModelNeutralMutableEntry* local_entry) {
 356   // Update our unique bookmark tag.  In many cases this will be identical to
 357   // the tag we already have.  However, clients that have recently upgraded to
 358   // versions that support unique positions will have incorrect tags.  See the
 359   // v86 migration logic in directory_backing_store.cc for more information.
 360   //
 361   // Both the old and new values are unique to this element.  Applying this
 362   // update will not risk the creation of conflicting unique tags.
 363   std::string bookmark_tag = GetUniqueBookmarkTagFromUpdate(update);
 364   if (UniquePosition::IsValidSuffix(bookmark_tag)) {
 365     local_entry->PutUniqueBookmarkTag(bookmark_tag);
 366   }
 367
 368   // Update our position.
 369   UniquePosition update_pos =
 370       GetUpdatePosition(update, local_entry->GetUniqueBookmarkTag());
 371   if (update_pos.IsValid()) {
 372     local_entry->PutServerUniquePosition(update_pos);
 373   }
 374 }
 375
 376 }  // namespace
 377
 378 void UpdateServerFieldsFromUpdate(
 379     syncable::ModelNeutralMutableEntry* target,
 380     const sync_pb::SyncEntity& update,
 381     const std::string& name) {
 382   if (update.deleted()) {
 383     if (target->GetServerIsDel()) {
 384       // If we already think the item is server-deleted, we're done.
 385       // Skipping these cases prevents our committed deletions from coming
 386       // back and overriding subsequent undeletions.  For non-deleted items,
 387       // the version number check has a similar effect.
 388       return;
 389     }
 390     // Mark entry as unapplied update first to ensure journaling the deletion.
 391     target->PutIsUnappliedUpdate(true);
 392     // The server returns very lightweight replies for deletions, so we don't
 393     // clobber a bunch of fields on delete.
 394     target->PutServerIsDel(true);
 395     if (!target->GetUniqueClientTag().empty()) {
 396       // Items identified by the client unique tag are undeletable; when
 397       // they're deleted, they go back to version 0.
 398       target->PutServerVersion(0);
 399     } else {
 400       // Otherwise, fake a server version by bumping the local number.
 401       target->PutServerVersion(
 402           std::max(target->GetServerVersion(), target->GetBaseVersion()) + 1);
 403     }
 404     return;
 405   }
 406
 407   DCHECK_EQ(target->GetId(), SyncableIdFromProto(update.id_string()))
 408       << "ID Changing not supported here";
 409   target->PutServerParentId(SyncableIdFromProto(update.parent_id_string()));
 410   target->PutServerNonUniqueName(name);
 411   target->PutServerVersion(update.version());
 412   target->PutServerCtime(ProtoTimeToTime(update.ctime()));
 413   target->PutServerMtime(ProtoTimeToTime(update.mtime()));
 414   target->PutServerIsDir(IsFolder(update));
 415   if (update.has_server_defined_unique_tag()) {
 416     const std::string& tag = update.server_defined_unique_tag();
 417     target->PutUniqueServerTag(tag);
 418   }
 419   if (update.has_client_defined_unique_tag()) {
 420     const std::string& tag = update.client_defined_unique_tag();
 421     target->PutUniqueClientTag(tag);
 422   }
 423   // Store the datatype-specific part as a protobuf.
 424   if (update.has_specifics()) {
 425     DCHECK_NE(GetModelType(update), UNSPECIFIED)
 426         << "Storing unrecognized datatype in sync database.";
 427     target->PutServerSpecifics(update.specifics());
 428   } else if (update.has_bookmarkdata()) {
 429     // Legacy protocol response for bookmark data.
 430     const sync_pb::SyncEntity::BookmarkData& bookmark = update.bookmarkdata();
 431     UpdateBookmarkSpecifics(update.server_defined_unique_tag(),
 432                             bookmark.bookmark_url(),
 433                             bookmark.bookmark_favicon(),
 434                             target);
 435   }
 436   target->PutServerAttachmentMetadata(
 437       CreateAttachmentMetadata(update.attachment_id()));
 438   if (SyncerProtoUtil::ShouldMaintainPosition(update)) {
 439     UpdateBookmarkPositioning(update, target);
 440   }
 441
 442   // We only mark the entry as unapplied if its version is greater than the
 443   // local data. If we're processing the update that corresponds to one of our
 444   // commit we don't apply it as time differences may occur.
 445   if (update.version() > target->GetBaseVersion()) {
 446     target->PutIsUnappliedUpdate(true);
 447   }
 448   DCHECK(!update.deleted());
 449   target->PutServerIsDel(false);
 450 }
 451
 452 // Creates a new Entry iff no Entry exists with the given id.
 453 void CreateNewEntry(syncable::ModelNeutralWriteTransaction *trans,
 454                     const syncable::Id& id) {
 455   syncable::Entry entry(trans, GET_BY_ID, id);
 456   if (!entry.good()) {
 457     syncable::ModelNeutralMutableEntry new_entry(
 458         trans,
 459         syncable::CREATE_NEW_UPDATE_ITEM,
 460         id);
 461   }
 462 }
 463
 464 // This function is called on an entry when we can update the user-facing data
 465 // from the server data.
 466 void UpdateLocalDataFromServerData(
 467     syncable::WriteTransaction* trans,
 468     syncable::MutableEntry* entry) {
 469   DCHECK(!entry->GetIsUnsynced());
 470   DCHECK(entry->GetIsUnappliedUpdate());
 471
 472   DVLOG(2) << "Updating entry : " << *entry;
 473   // Start by setting the properties that determine the model_type.
 474   entry->PutSpecifics(entry->GetServerSpecifics());
 475   // Clear the previous server specifics now that we're applying successfully.
 476   entry->PutBaseServerSpecifics(sync_pb::EntitySpecifics());
 477   entry->PutIsDir(entry->GetServerIsDir());
 478   // This strange dance around the IS_DEL flag avoids problems when setting
 479   // the name.
 480   // TODO(chron): Is this still an issue? Unit test this codepath.
 481   if (entry->GetServerIsDel()) {
 482     entry->PutIsDel(true);
 483   } else {
 484     entry->PutNonUniqueName(entry->GetServerNonUniqueName());
 485     entry->PutParentId(entry->GetServerParentId());
 486     entry->PutUniquePosition(entry->GetServerUniquePosition());
 487     entry->PutIsDel(false);
 488   }
 489
 490   entry->PutCtime(entry->GetServerCtime());
 491   entry->PutMtime(entry->GetServerMtime());
 492   entry->PutBaseVersion(entry->GetServerVersion());
 493   entry->PutIsDel(entry->GetServerIsDel());
 494   entry->PutIsUnappliedUpdate(false);
 495   entry->PutAttachmentMetadata(entry->GetServerAttachmentMetadata());
 496 }
 497
 498 VerifyCommitResult ValidateCommitEntry(syncable::Entry* entry) {
 499   syncable::Id id = entry->GetId();
 500   if (id == entry->GetParentId()) {
 501     CHECK(id.IsRoot()) << "Non-root item is self parenting." << *entry;
 502     // If the root becomes unsynced it can cause us problems.
 503     LOG(ERROR) << "Root item became unsynced " << *entry;
 504     return VERIFY_UNSYNCABLE;
 505   }
 506   if (entry->IsRoot()) {
 507     LOG(ERROR) << "Permanent item became unsynced " << *entry;
 508     return VERIFY_UNSYNCABLE;
 509   }
 510   if (entry->GetIsDel() && !entry->GetId().ServerKnows()) {
 511     // Drop deleted uncommitted entries.
 512     return VERIFY_UNSYNCABLE;
 513   }
 514   return VERIFY_OK;
 515 }
 516
 517 void MarkDeletedChildrenSynced(
 518     syncable::Directory* dir,
 519     syncable::BaseWriteTransaction* trans,
 520     std::set<syncable::Id>* deleted_folders) {
 521   // There's two options here.
 522   // 1. Scan deleted unsynced entries looking up their pre-delete tree for any
 523   //    of the deleted folders.
 524   // 2. Take each folder and do a tree walk of all entries underneath it.
 525   // #2 has a lower big O cost, but writing code to limit the time spent inside
 526   // the transaction during each step is simpler with 1. Changing this decision
 527   // may be sensible if this code shows up in profiling.
 528   if (deleted_folders->empty())
 529     return;
 530   Directory::Metahandles handles;
 531   dir->GetUnsyncedMetaHandles(trans, &handles);
 532   if (handles.empty())
 533     return;
 534   Directory::Metahandles::iterator it;
 535   for (it = handles.begin() ; it != handles.end() ; ++it) {
 536     syncable::ModelNeutralMutableEntry entry(trans, GET_BY_HANDLE, *it);
 537     if (!entry.GetIsUnsynced() || !entry.GetIsDel())
 538       continue;
 539     syncable::Id id = entry.GetParentId();
 540     while (id != trans->root_id()) {
 541       if (deleted_folders->find(id) != deleted_folders->end()) {
 542         // We've synced the deletion of this deleted entries parent.
 543         entry.PutIsUnsynced(false);
 544         break;
 545       }
 546       Entry parent(trans, GET_BY_ID, id);
 547       if (!parent.good() || !parent.GetIsDel())
 548         break;
 549       id = parent.GetParentId();
 550     }
 551   }
 552 }
 553
 554 VerifyResult VerifyNewEntry(
 555     const sync_pb::SyncEntity& update,
 556     syncable::Entry* target,
 557     const bool deleted) {
 558   if (target->good()) {
 559     // Not a new update.
 560     return VERIFY_UNDECIDED;
 561   }
 562   if (deleted) {
 563     // Deletion of an item we've never seen can be ignored.
 564     return VERIFY_SKIP;
 565   }
 566
 567   return VERIFY_SUCCESS;
 568 }
 569
 570 // Assumes we have an existing entry; check here for updates that break
 571 // consistency rules.
 572 VerifyResult VerifyUpdateConsistency(
 573     syncable::ModelNeutralWriteTransaction* trans,
 574     const sync_pb::SyncEntity& update,
 575     const bool deleted,
 576     const bool is_directory,
 577     ModelType model_type,
 578     syncable::ModelNeutralMutableEntry* target) {
 579
 580   CHECK(target->good());
 581   const syncable::Id& update_id = SyncableIdFromProto(update.id_string());
 582
 583   // If the update is a delete, we don't really need to worry at this stage.
 584   if (deleted)
 585     return VERIFY_SUCCESS;
 586
 587   if (model_type == UNSPECIFIED) {
 588     // This update is to an item of a datatype we don't recognize. The server
 589     // shouldn't have sent it to us.  Throw it on the ground.
 590     return VERIFY_SKIP;
 591   }
 592
 593   if (target->GetServerVersion() > 0) {
 594     // Then we've had an update for this entry before.
 595     if (is_directory != target->GetServerIsDir() ||
 596         model_type != target->GetServerModelType()) {
 597       if (target->GetIsDel()) {  // If we've deleted the item, we don't care.
 598         return VERIFY_SKIP;
 599       } else {
 600         LOG(ERROR) << "Server update doesn't agree with previous updates. ";
 601         LOG(ERROR) << " Entry: " << *target;
 602         LOG(ERROR) << " Update: "
 603                    << SyncerProtoUtil::SyncEntityDebugString(update);
 604         return VERIFY_FAIL;
 605       }
 606     }
 607
 608     if (!deleted && (target->GetId() == update_id) &&
 609         (target->GetServerIsDel() ||
 610          (!target->GetIsUnsynced() && target->GetIsDel() &&
 611           target->GetBaseVersion() > 0))) {
 612       // An undelete. The latter case in the above condition is for
 613       // when the server does not give us an update following the
 614       // commit of a delete, before undeleting.
 615       // Undeletion is common for items that reuse the client-unique tag.
 616       VerifyResult result = VerifyUndelete(trans, update, target);
 617       if (VERIFY_UNDECIDED != result)
 618         return result;
 619     }
 620   }
 621   if (target->GetBaseVersion() > 0) {
 622     // We've committed this update in the past.
 623     if (is_directory != target->GetIsDir() ||
 624         model_type != target->GetModelType()) {
 625       LOG(ERROR) << "Server update doesn't agree with committed item. ";
 626       LOG(ERROR) << " Entry: " << *target;
 627       LOG(ERROR) << " Update: "
 628                  << SyncerProtoUtil::SyncEntityDebugString(update);
 629       return VERIFY_FAIL;
 630     }
 631     if (target->GetId() == update_id) {
 632       if (target->GetServerVersion() > update.version()) {
 633         LOG(WARNING) << "We've already seen a more recent version.";
 634         LOG(WARNING) << " Entry: " << *target;
 635         LOG(WARNING) << " Update: "
 636                      << SyncerProtoUtil::SyncEntityDebugString(update);
 637         return VERIFY_SKIP;
 638       }
 639     }
 640   }
 641   return VERIFY_SUCCESS;
 642 }
 643
 644 // Assumes we have an existing entry; verify an update that seems to be
 645 // expressing an 'undelete'
 646 VerifyResult VerifyUndelete(syncable::ModelNeutralWriteTransaction* trans,
 647                             const sync_pb::SyncEntity& update,
 648                             syncable::ModelNeutralMutableEntry* target) {
 649   // TODO(nick): We hit this path for items deleted items that the server
 650   // tells us to re-create; only deleted items with positive base versions
 651   // will hit this path.  However, it's not clear how such an undeletion
 652   // would actually succeed on the server; in the protocol, a base
 653   // version of 0 is required to undelete an object.  This codepath
 654   // should be deprecated in favor of client-tag style undeletion
 655   // (where items go to version 0 when they're deleted), or else
 656   // removed entirely (if this type of undeletion is indeed impossible).
 657   CHECK(target->good());
 658   DVLOG(1) << "Server update is attempting undelete. " << *target
 659            << "Update:" << SyncerProtoUtil::SyncEntityDebugString(update);
 660   // Move the old one aside and start over.  It's too tricky to get the old one
 661   // back into a state that would pass CheckTreeInvariants().
 662   if (target->GetIsDel()) {
 663     if (target->GetUniqueClientTag().empty())
 664       LOG(WARNING) << "Doing move-aside undeletion on client-tagged item.";
 665     target->PutId(trans->directory()->NextId());
 666     target->PutUniqueClientTag(std::string());
 667     target->PutBaseVersion(CHANGES_VERSION);
 668     target->PutServerVersion(0);
 669     return VERIFY_SUCCESS;
 670   }
 671   if (update.version() < target->GetServerVersion()) {
 672     LOG(WARNING) << "Update older than current server version for "
 673                  << *target << " Update:"
 674                  << SyncerProtoUtil::SyncEntityDebugString(update);
 675     return VERIFY_SUCCESS;  // Expected in new sync protocol.
 676   }
 677   return VERIFY_UNDECIDED;
 678 }
 679
 680 }  // namespace syncer