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::GetNullId();
 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   }
 188   // Fallback: target an entry having the server ID, creating one if needed.
 189   return update_id;
 190 }
 191
 192 UpdateAttemptResponse AttemptToUpdateEntry(
 193     syncable::WriteTransaction* const trans,
 194     syncable::MutableEntry* const entry,
 195     Cryptographer* cryptographer) {
 196   CHECK(entry->good());
 197   if (!entry->GetIsUnappliedUpdate())
 198     return SUCCESS;  // No work to do.
 199   syncable::Id id = entry->GetId();
 200   const sync_pb::EntitySpecifics& specifics = entry->GetServerSpecifics();
 201
 202   // Only apply updates that we can decrypt. If we can't decrypt the update, it
 203   // is likely because the passphrase has not arrived yet. Because the
 204   // passphrase may not arrive within this GetUpdates, we can't just return
 205   // conflict, else we try to perform normal conflict resolution prematurely or
 206   // the syncer may get stuck. As such, we return CONFLICT_ENCRYPTION, which is
 207   // treated as an unresolvable conflict. See the description in syncer_types.h.
 208   // This prevents any unsynced changes from commiting and postpones conflict
 209   // resolution until all data can be decrypted.
 210   if (specifics.has_encrypted() &&
 211       !cryptographer->CanDecrypt(specifics.encrypted())) {
 212     // We can't decrypt this node yet.
 213     DVLOG(1) << "Received an undecryptable "
 214              << ModelTypeToString(entry->GetServerModelType())
 215              << " update, returning conflict_encryption.";
 216     return CONFLICT_ENCRYPTION;
 217   } else if (specifics.has_password() &&
 218              entry->GetUniqueServerTag().empty()) {
 219     // Passwords use their own legacy encryption scheme.
 220     const sync_pb::PasswordSpecifics& password = specifics.password();
 221     if (!cryptographer->CanDecrypt(password.encrypted())) {
 222       DVLOG(1) << "Received an undecryptable password update, returning "
 223                << "conflict_encryption.";
 224       return CONFLICT_ENCRYPTION;
 225     }
 226   }
 227
 228   if (!entry->GetServerIsDel()) {
 229     syncable::Id new_parent = entry->GetServerParentId();
 230     Entry parent(trans, GET_BY_ID,  new_parent);
 231     // A note on non-directory parents:
 232     // We catch most unfixable tree invariant errors at update receipt time,
 233     // however we deal with this case here because we may receive the child
 234     // first then the illegal parent. Instead of dealing with it twice in
 235     // different ways we deal with it once here to reduce the amount of code and
 236     // potential errors.
 237     if (!parent.good() || parent.GetIsDel() || !parent.GetIsDir()) {
 238       DVLOG(1) <<  "Entry has bad parent, returning conflict_hierarchy.";
 239       return CONFLICT_HIERARCHY;
 240     }
 241     if (entry->GetParentId() != new_parent) {
 242       if (!entry->GetIsDel() && !IsLegalNewParent(trans, id, new_parent)) {
 243         DVLOG(1) << "Not updating item " << id
 244                  << ", illegal new parent (would cause loop).";
 245         return CONFLICT_HIERARCHY;
 246       }
 247     }
 248   } else if (entry->GetIsDir()) {
 249     Directory::Metahandles handles;
 250     trans->directory()->GetChildHandlesById(trans, id, &handles);
 251     if (!handles.empty()) {
 252       // If we have still-existing children, then we need to deal with
 253       // them before we can process this change.
 254       DVLOG(1) << "Not deleting directory; it's not empty " << *entry;
 255       return CONFLICT_HIERARCHY;
 256     }
 257   }
 258
 259   if (entry->GetIsUnsynced()) {
 260     DVLOG(1) << "Skipping update, returning conflict for: " << id
 261              << " ; it's unsynced.";
 262     return CONFLICT_SIMPLE;
 263   }
 264
 265   if (specifics.has_encrypted()) {
 266     DVLOG(2) << "Received a decryptable "
 267              << ModelTypeToString(entry->GetServerModelType())
 268              << " update, applying normally.";
 269   } else {
 270     DVLOG(2) << "Received an unencrypted "
 271              << ModelTypeToString(entry->GetServerModelType())
 272              << " update, applying normally.";
 273   }
 274
 275   UpdateLocalDataFromServerData(trans, entry);
 276
 277   return SUCCESS;
 278 }
 279
 280 std::string GetUniqueBookmarkTagFromUpdate(const sync_pb::SyncEntity& update) {
 281   if (!update.has_originator_cache_guid() ||
 282       !update.has_originator_client_item_id()) {
 283     LOG(ERROR) << "Update is missing requirements for bookmark position."
 284                << " This is a server bug.";
 285     return UniquePosition::RandomSuffix();
 286   }
 287
 288   return syncable::GenerateSyncableBookmarkHash(
 289       update.originator_cache_guid(), update.originator_client_item_id());
 290 }
 291
 292 UniquePosition GetUpdatePosition(const sync_pb::SyncEntity& update,
 293                                  const std::string& suffix) {
 294   DCHECK(UniquePosition::IsValidSuffix(suffix));
 295   if (!(SyncerProtoUtil::ShouldMaintainPosition(update))) {
 296     return UniquePosition::CreateInvalid();
 297   } else if (update.has_unique_position()) {
 298     return UniquePosition::FromProto(update.unique_position());
 299   } else if (update.has_position_in_parent()) {
 300     return UniquePosition::FromInt64(update.position_in_parent(), suffix);
 301   } else {
 302     LOG(ERROR) << "No position information in update. This is a server bug.";
 303     return UniquePosition::FromInt64(0, suffix);
 304   }
 305 }
 306
 307 namespace {
 308
 309 // Helper to synthesize a new-style sync_pb::EntitySpecifics for use locally,
 310 // when the server speaks only the old sync_pb::SyncEntity_BookmarkData-based
 311 // protocol.
 312 void UpdateBookmarkSpecifics(const std::string& singleton_tag,
 313                              const std::string& url,
 314                              const std::string& favicon_bytes,
 315                              syncable::ModelNeutralMutableEntry* local_entry) {
 316   // In the new-style protocol, the server no longer sends bookmark info for
 317   // the "google_chrome" folder.  Mimic that here.
 318   if (singleton_tag == "google_chrome")
 319     return;
 320   sync_pb::EntitySpecifics pb;
 321   sync_pb::BookmarkSpecifics* bookmark = pb.mutable_bookmark();
 322   if (!url.empty())
 323     bookmark->set_url(url);
 324   if (!favicon_bytes.empty())
 325     bookmark->set_favicon(favicon_bytes);
 326   local_entry->PutServerSpecifics(pb);
 327 }
 328
 329 void UpdateBookmarkPositioning(
 330     const sync_pb::SyncEntity& update,
 331     syncable::ModelNeutralMutableEntry* local_entry) {
 332   // Update our unique bookmark tag.  In many cases this will be identical to
 333   // the tag we already have.  However, clients that have recently upgraded to
 334   // versions that support unique positions will have incorrect tags.  See the
 335   // v86 migration logic in directory_backing_store.cc for more information.
 336   //
 337   // Both the old and new values are unique to this element.  Applying this
 338   // update will not risk the creation of conflicting unique tags.
 339   std::string bookmark_tag = GetUniqueBookmarkTagFromUpdate(update);
 340   if (UniquePosition::IsValidSuffix(bookmark_tag)) {
 341     local_entry->PutUniqueBookmarkTag(bookmark_tag);
 342   }
 343
 344   // Update our position.
 345   UniquePosition update_pos =
 346       GetUpdatePosition(update, local_entry->GetUniqueBookmarkTag());
 347   if (update_pos.IsValid()) {
 348     local_entry->PutServerUniquePosition(update_pos);
 349   }
 350 }
 351
 352 }  // namespace
 353
 354 void UpdateServerFieldsFromUpdate(
 355     syncable::ModelNeutralMutableEntry* target,
 356     const sync_pb::SyncEntity& update,
 357     const std::string& name) {
 358   if (update.deleted()) {
 359     if (target->GetServerIsDel()) {
 360       // If we already think the item is server-deleted, we're done.
 361       // Skipping these cases prevents our committed deletions from coming
 362       // back and overriding subsequent undeletions.  For non-deleted items,
 363       // the version number check has a similar effect.
 364       return;
 365     }
 366     // The server returns very lightweight replies for deletions, so we don't
 367     // clobber a bunch of fields on delete.
 368     target->PutServerIsDel(true);
 369     if (!target->GetUniqueClientTag().empty()) {
 370       // Items identified by the client unique tag are undeletable; when
 371       // they're deleted, they go back to version 0.
 372       target->PutServerVersion(0);
 373     } else {
 374       // Otherwise, fake a server version by bumping the local number.
 375       target->PutServerVersion(
 376           std::max(target->GetServerVersion(), target->GetBaseVersion()) + 1);
 377     }
 378     target->PutIsUnappliedUpdate(true);
 379     return;
 380   }
 381
 382   DCHECK_EQ(target->GetId(), SyncableIdFromProto(update.id_string()))
 383       << "ID Changing not supported here";
 384   target->PutServerParentId(SyncableIdFromProto(update.parent_id_string()));
 385   target->PutServerNonUniqueName(name);
 386   target->PutServerVersion(update.version());
 387   target->PutServerCtime(ProtoTimeToTime(update.ctime()));
 388   target->PutServerMtime(ProtoTimeToTime(update.mtime()));
 389   target->PutServerIsDir(IsFolder(update));
 390   if (update.has_server_defined_unique_tag()) {
 391     const std::string& tag = update.server_defined_unique_tag();
 392     target->PutUniqueServerTag(tag);
 393   }
 394   if (update.has_client_defined_unique_tag()) {
 395     const std::string& tag = update.client_defined_unique_tag();
 396     target->PutUniqueClientTag(tag);
 397   }
 398   // Store the datatype-specific part as a protobuf.
 399   if (update.has_specifics()) {
 400     DCHECK_NE(GetModelType(update), UNSPECIFIED)
 401         << "Storing unrecognized datatype in sync database.";
 402     target->PutServerSpecifics(update.specifics());
 403   } else if (update.has_bookmarkdata()) {
 404     // Legacy protocol response for bookmark data.
 405     const sync_pb::SyncEntity::BookmarkData& bookmark = update.bookmarkdata();
 406     UpdateBookmarkSpecifics(update.server_defined_unique_tag(),
 407                             bookmark.bookmark_url(),
 408                             bookmark.bookmark_favicon(),
 409                             target);
 410   }
 411   target->PutServerAttachmentMetadata(
 412       CreateAttachmentMetadata(update.attachment_id()));
 413   if (SyncerProtoUtil::ShouldMaintainPosition(update)) {
 414     UpdateBookmarkPositioning(update, target);
 415   }
 416
 417   target->PutServerIsDel(update.deleted());
 418   // We only mark the entry as unapplied if its version is greater than the
 419   // local data. If we're processing the update that corresponds to one of our
 420   // commit we don't apply it as time differences may occur.
 421   if (update.version() > target->GetBaseVersion()) {
 422     target->PutIsUnappliedUpdate(true);
 423   }
 424 }
 425
 426 // Creates a new Entry iff no Entry exists with the given id.
 427 void CreateNewEntry(syncable::ModelNeutralWriteTransaction *trans,
 428                     const syncable::Id& id) {
 429   syncable::Entry entry(trans, GET_BY_ID, id);
 430   if (!entry.good()) {
 431     syncable::ModelNeutralMutableEntry new_entry(
 432         trans,
 433         syncable::CREATE_NEW_UPDATE_ITEM,
 434         id);
 435   }
 436 }
 437
 438 // This function is called on an entry when we can update the user-facing data
 439 // from the server data.
 440 void UpdateLocalDataFromServerData(
 441     syncable::WriteTransaction* trans,
 442     syncable::MutableEntry* entry) {
 443   DCHECK(!entry->GetIsUnsynced());
 444   DCHECK(entry->GetIsUnappliedUpdate());
 445
 446   DVLOG(2) << "Updating entry : " << *entry;
 447   // Start by setting the properties that determine the model_type.
 448   entry->PutSpecifics(entry->GetServerSpecifics());
 449   // Clear the previous server specifics now that we're applying successfully.
 450   entry->PutBaseServerSpecifics(sync_pb::EntitySpecifics());
 451   entry->PutIsDir(entry->GetServerIsDir());
 452   // This strange dance around the IS_DEL flag avoids problems when setting
 453   // the name.
 454   // TODO(chron): Is this still an issue? Unit test this codepath.
 455   if (entry->GetServerIsDel()) {
 456     entry->PutIsDel(true);
 457   } else {
 458     entry->PutNonUniqueName(entry->GetServerNonUniqueName());
 459     entry->PutParentId(entry->GetServerParentId());
 460     entry->PutUniquePosition(entry->GetServerUniquePosition());
 461     entry->PutIsDel(false);
 462   }
 463
 464   entry->PutCtime(entry->GetServerCtime());
 465   entry->PutMtime(entry->GetServerMtime());
 466   entry->PutBaseVersion(entry->GetServerVersion());
 467   entry->PutIsDel(entry->GetServerIsDel());
 468   entry->PutIsUnappliedUpdate(false);
 469   entry->PutAttachmentMetadata(entry->GetServerAttachmentMetadata());
 470 }
 471
 472 VerifyCommitResult ValidateCommitEntry(syncable::Entry* entry) {
 473   syncable::Id id = entry->GetId();
 474   if (id == entry->GetParentId()) {
 475     CHECK(id.IsRoot()) << "Non-root item is self parenting." << *entry;
 476     // If the root becomes unsynced it can cause us problems.
 477     LOG(ERROR) << "Root item became unsynced " << *entry;
 478     return VERIFY_UNSYNCABLE;
 479   }
 480   if (entry->IsRoot()) {
 481     LOG(ERROR) << "Permanent item became unsynced " << *entry;
 482     return VERIFY_UNSYNCABLE;
 483   }
 484   if (entry->GetIsDel() && !entry->GetId().ServerKnows()) {
 485     // Drop deleted uncommitted entries.
 486     return VERIFY_UNSYNCABLE;
 487   }
 488   return VERIFY_OK;
 489 }
 490
 491 void MarkDeletedChildrenSynced(
 492     syncable::Directory* dir,
 493     syncable::BaseWriteTransaction* trans,
 494     std::set<syncable::Id>* deleted_folders) {
 495   // There's two options here.
 496   // 1. Scan deleted unsynced entries looking up their pre-delete tree for any
 497   //    of the deleted folders.
 498   // 2. Take each folder and do a tree walk of all entries underneath it.
 499   // #2 has a lower big O cost, but writing code to limit the time spent inside
 500   // the transaction during each step is simpler with 1. Changing this decision
 501   // may be sensible if this code shows up in profiling.
 502   if (deleted_folders->empty())
 503     return;
 504   Directory::Metahandles handles;
 505   dir->GetUnsyncedMetaHandles(trans, &handles);
 506   if (handles.empty())
 507     return;
 508   Directory::Metahandles::iterator it;
 509   for (it = handles.begin() ; it != handles.end() ; ++it) {
 510     syncable::ModelNeutralMutableEntry entry(trans, GET_BY_HANDLE, *it);
 511     if (!entry.GetIsUnsynced() || !entry.GetIsDel())
 512       continue;
 513     syncable::Id id = entry.GetParentId();
 514     while (id != trans->root_id()) {
 515       if (deleted_folders->find(id) != deleted_folders->end()) {
 516         // We've synced the deletion of this deleted entries parent.
 517         entry.PutIsUnsynced(false);
 518         break;
 519       }
 520       Entry parent(trans, GET_BY_ID, id);
 521       if (!parent.good() || !parent.GetIsDel())
 522         break;
 523       id = parent.GetParentId();
 524     }
 525   }
 526 }
 527
 528 VerifyResult VerifyNewEntry(
 529     const sync_pb::SyncEntity& update,
 530     syncable::Entry* target,
 531     const bool deleted) {
 532   if (target->good()) {
 533     // Not a new update.
 534     return VERIFY_UNDECIDED;
 535   }
 536   if (deleted) {
 537     // Deletion of an item we've never seen can be ignored.
 538     return VERIFY_SKIP;
 539   }
 540
 541   return VERIFY_SUCCESS;
 542 }
 543
 544 // Assumes we have an existing entry; check here for updates that break
 545 // consistency rules.
 546 VerifyResult VerifyUpdateConsistency(
 547     syncable::ModelNeutralWriteTransaction* trans,
 548     const sync_pb::SyncEntity& update,
 549     const bool deleted,
 550     const bool is_directory,
 551     ModelType model_type,
 552     syncable::ModelNeutralMutableEntry* target) {
 553
 554   CHECK(target->good());
 555   const syncable::Id& update_id = SyncableIdFromProto(update.id_string());
 556
 557   // If the update is a delete, we don't really need to worry at this stage.
 558   if (deleted)
 559     return VERIFY_SUCCESS;
 560
 561   if (model_type == UNSPECIFIED) {
 562     // This update is to an item of a datatype we don't recognize. The server
 563     // shouldn't have sent it to us.  Throw it on the ground.
 564     return VERIFY_SKIP;
 565   }
 566
 567   if (target->GetServerVersion() > 0) {
 568     // Then we've had an update for this entry before.
 569     if (is_directory != target->GetServerIsDir() ||
 570         model_type != target->GetServerModelType()) {
 571       if (target->GetIsDel()) {  // If we've deleted the item, we don't care.
 572         return VERIFY_SKIP;
 573       } else {
 574         LOG(ERROR) << "Server update doesn't agree with previous updates. ";
 575         LOG(ERROR) << " Entry: " << *target;
 576         LOG(ERROR) << " Update: "
 577                    << SyncerProtoUtil::SyncEntityDebugString(update);
 578         return VERIFY_FAIL;
 579       }
 580     }
 581
 582     if (!deleted && (target->GetId() == update_id) &&
 583         (target->GetServerIsDel() ||
 584          (!target->GetIsUnsynced() && target->GetIsDel() &&
 585           target->GetBaseVersion() > 0))) {
 586       // An undelete. The latter case in the above condition is for
 587       // when the server does not give us an update following the
 588       // commit of a delete, before undeleting.
 589       // Undeletion is common for items that reuse the client-unique tag.
 590       VerifyResult result = VerifyUndelete(trans, update, target);
 591       if (VERIFY_UNDECIDED != result)
 592         return result;
 593     }
 594   }
 595   if (target->GetBaseVersion() > 0) {
 596     // We've committed this update in the past.
 597     if (is_directory != target->GetIsDir() ||
 598         model_type != target->GetModelType()) {
 599       LOG(ERROR) << "Server update doesn't agree with committed item. ";
 600       LOG(ERROR) << " Entry: " << *target;
 601       LOG(ERROR) << " Update: "
 602                  << SyncerProtoUtil::SyncEntityDebugString(update);
 603       return VERIFY_FAIL;
 604     }
 605     if (target->GetId() == update_id) {
 606       if (target->GetServerVersion() > update.version()) {
 607         LOG(WARNING) << "We've already seen a more recent version.";
 608         LOG(WARNING) << " Entry: " << *target;
 609         LOG(WARNING) << " Update: "
 610                      << SyncerProtoUtil::SyncEntityDebugString(update);
 611         return VERIFY_SKIP;
 612       }
 613     }
 614   }
 615   return VERIFY_SUCCESS;
 616 }
 617
 618 // Assumes we have an existing entry; verify an update that seems to be
 619 // expressing an 'undelete'
 620 VerifyResult VerifyUndelete(syncable::ModelNeutralWriteTransaction* trans,
 621                             const sync_pb::SyncEntity& update,
 622                             syncable::ModelNeutralMutableEntry* target) {
 623   // TODO(nick): We hit this path for items deleted items that the server
 624   // tells us to re-create; only deleted items with positive base versions
 625   // will hit this path.  However, it's not clear how such an undeletion
 626   // would actually succeed on the server; in the protocol, a base
 627   // version of 0 is required to undelete an object.  This codepath
 628   // should be deprecated in favor of client-tag style undeletion
 629   // (where items go to version 0 when they're deleted), or else
 630   // removed entirely (if this type of undeletion is indeed impossible).
 631   CHECK(target->good());
 632   DVLOG(1) << "Server update is attempting undelete. " << *target
 633            << "Update:" << SyncerProtoUtil::SyncEntityDebugString(update);
 634   // Move the old one aside and start over.  It's too tricky to get the old one
 635   // back into a state that would pass CheckTreeInvariants().
 636   if (target->GetIsDel()) {
 637     if (target->GetUniqueClientTag().empty())
 638       LOG(WARNING) << "Doing move-aside undeletion on client-tagged item.";
 639     target->PutId(trans->directory()->NextId());
 640     target->PutUniqueClientTag(std::string());
 641     target->PutBaseVersion(CHANGES_VERSION);
 642     target->PutServerVersion(0);
 643     return VERIFY_SUCCESS;
 644   }
 645   if (update.version() < target->GetServerVersion()) {
 646     LOG(WARNING) << "Update older than current server version for "
 647                  << *target << " Update:"
 648                  << SyncerProtoUtil::SyncEntityDebugString(update);
 649     return VERIFY_SUCCESS;  // Expected in new sync protocol.
 650   }
 651   return VERIFY_UNDECIDED;
 652 }
 653
 654 }  // namespace syncer