sync: use progress markers instead of timestamps during GetUpdates

chrome/browser/sync/syncable/directory_backing_store.cc

Index: chrome/browser/sync/syncable/directory_backing_store.cc
diff --git a/chrome/browser/sync/syncable/directory_backing_store.cc b/chrome/browser/sync/syncable/directory_backing_store.cc
index feefd91b7e6a3dc9deb189d46f19bd9247124b1d..d6e74c77f39d7ef05bd635feb250fe7fbfb00721 100644
--- a/chrome/browser/sync/syncable/directory_backing_store.cc
+++ b/chrome/browser/sync/syncable/directory_backing_store.cc
@@ -44,7 +44,7 @@ static const string::size_type kUpdateStatementBufferSize = 2048;
 
 // Increment this version whenever updating DB tables.
 extern const int32 kCurrentDBVersion;  // Global visibility for our unittest.
-const int32 kCurrentDBVersion = 74;
+const int32 kCurrentDBVersion = 75;
 
 namespace {
 
@@ -411,11 +411,13 @@ bool DirectoryBackingStore::SaveChanges(
     for (int i = FIRST_REAL_MODEL_TYPE; i < MODEL_TYPE_COUNT; ++i) {
       SQLStatement op;
       op.prepare(dbhandle, "INSERT OR REPLACE INTO models (model_id, "
-      "last_download_timestamp, initial_sync_ended) VALUES ( ?, ?, ?)");
+      "progress_marker, initial_sync_ended) VALUES ( ?, ?, ?)");
       // We persist not ModelType but rather a protobuf-derived ID.
       string model_id = ModelTypeEnumToModelId(ModelTypeFromInt(i));
+      string progress_marker;
+      info.download_progress[i].SerializeToString(&progress_marker);
       op.bind_blob(0, model_id.data(), model_id.length());
-      op.bind_int64(1, info.last_download_timestamp[i]);
+      op.bind_blob(1, progress_marker.data(), progress_marker.length());
       op.bind_bool(2, info.initial_sync_ended[i]);
 
       if (!(SQLITE_DONE == op.step() &&
@@ -473,11 +475,18 @@ DirOpenResult DirectoryBackingStore::InitializeTables() {
       version_on_disk = 73;
   }
 
+  // Version 74 added state for the autofill migration.
   if (version_on_disk == 73) {
     if (MigrateVersion73To74())
       version_on_disk = 74;
   }
 
+  // Version 75 migrated from int64-based timestamps to per-datatype tokens.
+  if (version_on_disk == 74) {
+    if (MigrateVersion74To75())
+      version_on_disk = 75;
+  }
+
   // If one of the migrations requested it, drop columns that aren't current.
   // It's only safe to do this after migrating all the way to the current
   // version.
@@ -606,14 +615,14 @@ bool DirectoryBackingStore::LoadInfo(Directory::KernelLoadInfo* info) {
   {
     SQLStatement query;
     query.prepare(load_dbhandle_,
-        "SELECT model_id, last_download_timestamp, initial_sync_ended "
+        "SELECT model_id, progress_marker, initial_sync_ended "
         "FROM models");
     while (SQLITE_ROW == query.step()) {
-      string model_id;
-      query.column_blob_as_string(0, &model_id);
-      ModelType type = ModelIdToModelTypeEnum(model_id);
+      ModelType type = ModelIdToModelTypeEnum(query.column_blob(0),
+                                              query.column_bytes(0));
       if (type != UNSPECIFIED) {
-        info->kernel_info.last_download_timestamp[type] = query.column_int64(1);
+        info->kernel_info.download_progress[type].ParseFromArray(
+            query.column_blob(1), query.column_bytes(1));
         info->kernel_info.initial_sync_ended[type] = query.column_bool(2);
       }
     }
@@ -709,14 +718,15 @@ void DirectoryBackingStore::DropAllTables() {
   SafeDropTable("share_version");
   SafeDropTable("extended_attributes");
   SafeDropTable("models");
+  SafeDropTable("temp_models");
   needs_column_refresh_ = false;
 }
 
 // static
 ModelType DirectoryBackingStore::ModelIdToModelTypeEnum(
-    const string& model_id) {
+    const void* data, int size) {
   sync_pb::EntitySpecifics specifics;
-  if (!specifics.ParseFromString(model_id))
+  if (!specifics.ParseFromArray(data, size))
     return syncable::UNSPECIFIED;
   return syncable::GetModelTypeFromSpecifics(specifics);
 }
@@ -900,7 +910,7 @@ bool DirectoryBackingStore::MigrateVersion68To69() {
 // were removed from the share_info table.  They were replaced by
 // the 'models' table, which has these values on a per-datatype basis.
 bool DirectoryBackingStore::MigrateVersion70To71() {
-  if (SQLITE_DONE != CreateModelsTable())
+  if (SQLITE_DONE != CreateV71ModelsTable())
     return false;
 
   // Move data from the old share_info columns to the new models table.
@@ -950,12 +960,15 @@ bool DirectoryBackingStore::MigrateVersion70To71() {
 }
 
 bool DirectoryBackingStore::MigrateVersion71To72() {
+  // Version 72 removed a table 'extended_attributes', whose
+  // contents didn't matter.
   SafeDropTable("extended_attributes");
   SetVersion(72);
   return true;
 }
 
 bool DirectoryBackingStore::MigrateVersion72To73() {
+  // Version 73 added one column to the table 'share_info': notification_state
   int result =
       ExecQuery(load_dbhandle_,
                 "ALTER TABLE share_info ADD COLUMN notification_state BLOB");
@@ -966,6 +979,13 @@ bool DirectoryBackingStore::MigrateVersion72To73() {
 }
 
 bool DirectoryBackingStore::MigrateVersion73To74() {
+  // Version 74 added the following columns to the table 'share_info':
+  //   autofill_migration_state
+  //   bookmarks_added_during_autofill_migration
+  //   autofill_migration_time
+  //   autofill_entries_added_during_migration
+  //   autofill_profiles_added_during_migration
+
   int result =
       ExecQuery(load_dbhandle_,
                 "ALTER TABLE share_info ADD COLUMN autofill_migration_state "
@@ -1008,6 +1028,60 @@ bool DirectoryBackingStore::MigrateVersion73To74() {
   return true;
 }
 
+bool DirectoryBackingStore::MigrateVersion74To75() {
+  // In version 74, there was a table 'models':
+  //     blob model_id (entity specifics, primary key)
+  //     int last_download_timestamp
+  //     boolean initial_sync_ended
+  // In version 75, we deprecated the integer-valued last_download_timestamp,
+  // using insted a protobuf-valued progress_marker field:
+  //     blob progress_marker
+  // The progress_marker values are initialized from the value of
+  // last_download_timestamp, thereby preserving the download state.
+
+  // Move aside the old table and create a new empty one at the current schema.
+  if (SQLITE_DONE != ExecQuery(load_dbhandle_,
+          "ALTER TABLE models RENAME TO temp_models")) {
+    return false;
+  }
+  if (!CreateModelsTable())
+    return false;
+
+  SQLStatement query;
+  query.prepare(load_dbhandle_,
+      "SELECT model_id, last_download_timestamp, initial_sync_ended "
+      "FROM temp_models");
+  while (SQLITE_ROW == query.step()) {
+    ModelType type = ModelIdToModelTypeEnum(query.column_blob(0),
+                                            query.column_bytes(0));
+    if (type != UNSPECIFIED) {
+      // Set the |timestamp_token_for_migration| on a new
+      // DataTypeProgressMarker, using the old value of last_download_timestamp.
+      // The server will turn this into a real token on our behalf the next
+      // time we check for updates.
+      sync_pb::DataTypeProgressMarker progress_marker;
+      progress_marker.set_data_type_id(
+          GetExtensionFieldNumberFromModelType(type));
+      progress_marker.set_timestamp_token_for_migration(query.column_int64(1));
+      std::string progress_blob;
+      progress_marker.SerializeToString(&progress_blob);
+
+      SQLStatement update;
+      update.prepare(load_dbhandle_, "INSERT INTO models (model_id, "
+          "progress_marker, initial_sync_ended) VALUES (?, ?, ?)");
+      update.bind_blob(0, query.column_blob(0), query.column_bytes(0));
+      update.bind_blob(1, progress_blob.data(), progress_blob.length());
+      update.bind_bool(2, query.column_bool(2));
+      if (SQLITE_DONE != update.step())
+        return false;
+    }
+  }
+  // Drop the old table.
+  SafeDropTable("temp_models");
+
+  SetVersion(75);
+  return true;
+}
 
 int DirectoryBackingStore::CreateTables() {
   VLOG(1) << "First run, creating tables";
@@ -1106,14 +1180,26 @@ int DirectoryBackingStore::CreateMetasTable(bool is_temporary) {
   return ExecQuery(load_dbhandle_, query.c_str());
 }
 
+int DirectoryBackingStore::CreateV71ModelsTable() {
+  // This is an old schema for the Models table, used from versions 71 to 74.
+  return ExecQuery(load_dbhandle_,
+      "CREATE TABLE models ("
+      "model_id BLOB primary key, "
+      "last_download_timestamp INT, "
+      // Gets set if the syncer ever gets updates from the
+      // server and the server returns 0.  Lets us detect the
+      // end of the initial sync.
+      "initial_sync_ended BOOLEAN default 0)");
+}
+
 int DirectoryBackingStore::CreateModelsTable() {
-  // This is the current schema for the Models table, from version 71
+  // This is the current schema for the Models table, from version 75
   // onward.  If you change the schema, you'll probably want to double-check
-  // the use of this function in the v70-v71 migration.
+  // the use of this function in the v74-v75 migration.
   return ExecQuery(load_dbhandle_,
       "CREATE TABLE models ("
       "model_id BLOB primary key, "
-      "last_download_timestamp INT, "
+      "progress_marker BLOB, "
       // Gets set if the syncer ever gets updates from the
       // server and the server returns 0.  Lets us detect the
       // end of the initial sync.
@@ -1124,9 +1210,8 @@ int DirectoryBackingStore::CreateShareInfoTable(bool is_temporary) {
   const char* name = is_temporary ? "temp_share_info" : "share_info";
   string query = "CREATE TABLE ";
   query.append(name);
-  // This is the current schema for the ShareInfo table, from version 71
-  // onward.  If you change the schema, you'll probably want to double-check
-  // the use of this function in the v70-v71 migration.
+  // This is the current schema for the ShareInfo table, from version 74
+  // onward.
   query.append(" ("
       "id TEXT primary key, "
       "name TEXT, "
@@ -1151,9 +1236,7 @@ int DirectoryBackingStore::CreateShareInfoTableVersion71(
   const char* name = is_temporary ? "temp_share_info" : "share_info";
   string query = "CREATE TABLE ";
   query.append(name);
-  // This is the current schema for the ShareInfo table, from version 71
-  // onward.  If you change the schema, you'll probably want to double-check
-  // the use of this function in the v70-v71 migration.
+  // This is the schema for the ShareInfo table used from versions 71 to 72.
   query.append(" ("
       "id TEXT primary key, "
       "name TEXT, "