[sync] Add store version to model type store backend

components/sync/model_impl/model_type_store_backend.cc

Index: components/sync/model_impl/model_type_store_backend.cc
diff --git a/components/sync/model_impl/model_type_store_backend.cc b/components/sync/model_impl/model_type_store_backend.cc
index 564bbd3dbe6f038513657d10f539e2cec2b12be4..d3bc8ecacf4568c43e036b9c6cddd6286ba83c83 100644
--- a/components/sync/model_impl/model_type_store_backend.cc
+++ b/components/sync/model_impl/model_type_store_backend.cc
@@ -8,6 +8,7 @@
 
 #include "base/files/file_path.h"
 #include "base/memory/ptr_util.h"
+#include "components/sync/protocol/model_type_store_schema_descriptor.pb.h"
 #include "third_party/leveldatabase/env_chromium.h"
 #include "third_party/leveldatabase/src/helpers/memenv/memenv.h"
 #include "third_party/leveldatabase/src/include/leveldb/db.h"
@@ -18,8 +19,13 @@
 #include "third_party/leveldatabase/src/include/leveldb/status.h"
 #include "third_party/leveldatabase/src/include/leveldb/write_batch.h"
 
+using sync_pb::ModelTypeStoreSchemaDescriptor;
+
 namespace syncer {
 
+const int64_t kLatestSchemaVersion = 1;
+const char kDBSchemaDescriptorRecordId[] = "_mts_schema_descriptor";
+
 // static
 base::LazyInstance<ModelTypeStoreBackend::BackendMap>
     ModelTypeStoreBackend::backend_map_ = LAZY_INSTANCE_INITIALIZER;
@@ -80,6 +86,19 @@ ModelTypeStore::Result ModelTypeStoreBackend::Init(
     return ModelTypeStore::Result::UNSPECIFIED_ERROR;
   }
   db_.reset(db_raw);
+
+  ModelTypeStoreSchemaDescriptor current_descriptor;
+  if (!GetStoreDescriptor(&current_descriptor)) {
+    return ModelTypeStore::Result::UNSPECIFIED_ERROR;
+  }
+
+  if (current_descriptor.version_number() < kLatestSchemaVersion) {
+    ModelTypeStoreSchemaDescriptor desired_descriptor;
+    desired_descriptor.set_version_number(kLatestSchemaVersion);
+    if (!Migrate(current_descriptor, desired_descriptor)) {
+      return ModelTypeStore::Result::UNSPECIFIED_ERROR;
+    }
+  }
   return ModelTypeStore::Result::SUCCESS;
 }
 
@@ -99,8 +118,7 @@ ModelTypeStore::Result ModelTypeStoreBackend::ReadRecordsWithPrefix(
     key = prefix + id;
     leveldb::Status status = db_->Get(read_options, key, &value);
     if (status.ok()) {
-      // TODO(pavely): Use emplace_back instead of push_back once it is allowed.
-      record_list->push_back(ModelTypeStore::Record(id, value));
+      record_list->emplace_back(id, value);
     } else if (status.IsNotFound()) {
       missing_id_list->push_back(id);
     } else {
@@ -124,9 +142,7 @@ ModelTypeStore::Result ModelTypeStoreBackend::ReadAllRecordsWithPrefix(
     if (!key.starts_with(prefix_slice))
       break;
     key.remove_prefix(prefix_slice.size());
-    // TODO(pavely): Use emplace_back instead of push_back once it is allowed.
-    record_list->push_back(
-        ModelTypeStore::Record(key.ToString(), iter->value().ToString()));
+    record_list->emplace_back(key.ToString(), iter->value().ToString());
   }
   return iter->status().ok() ? ModelTypeStore::Result::SUCCESS
                              : ModelTypeStore::Result::UNSPECIFIED_ERROR;
@@ -142,4 +158,44 @@ ModelTypeStore::Result ModelTypeStoreBackend::WriteModifications(
                      : ModelTypeStore::Result::UNSPECIFIED_ERROR;
 }
 
+bool ModelTypeStoreBackend::GetStoreDescriptor(
+    ModelTypeStoreSchemaDescriptor* schema_descriptor) {
+  DCHECK(db_);
+  leveldb::ReadOptions read_options;
+  read_options.verify_checksums = true;
+  std::string value;
+  leveldb::Status status =
+      db_->Get(read_options, kDBSchemaDescriptorRecordId, &value);
+  if (status.IsNotFound()) {
+    schema_descriptor->set_version_number(0);
+    return true;
+  } else if (!status.ok()) {
+    return false;
+  }
+  return schema_descriptor->ParseFromString(value);
+}
+
+bool ModelTypeStoreBackend::Migrate(
+    const ModelTypeStoreSchemaDescriptor& current_descriptor,
+    const ModelTypeStoreSchemaDescriptor& desired_descriptor) {
+  DCHECK(db_);
+  int64_t current_version = current_descriptor.version_number();
+  if (current_version == 0) {
+    if (Migrate0To1()) {
+      current_version = 1;
+    }
+  }
+  return current_version == desired_descriptor.version_number();
+}
+
+bool ModelTypeStoreBackend::Migrate0To1() {
+  DCHECK(db_);
+  ModelTypeStoreSchemaDescriptor schema_descriptor;
+  schema_descriptor.set_version_number(1);
+  leveldb::Status status =
+      db_->Put(leveldb::WriteOptions(), kDBSchemaDescriptorRecordId,
+               schema_descriptor.SerializeAsString());
+  return status.ok();
+}
+
 }  // namespace syncer