[Sync] Implements the loopback sync server.

components/sync/engine_impl/loopback_server/loopback_server.cc

Index: components/sync/engine_impl/loopback_server/loopback_server.cc
diff --git a/components/sync/test/fake_server/fake_server.cc b/components/sync/engine_impl/loopback_server/loopback_server.cc
similarity index 50%
copy from components/sync/test/fake_server/fake_server.cc
copy to components/sync/engine_impl/loopback_server/loopback_server.cc
index 66b720a6b06c40e359d76a7ac4c1d0f7553e8f3f..ef701df388764d1e214a5a27655260a578f109eb 100644
--- a/components/sync/test/fake_server/fake_server.cc
+++ b/components/sync/engine_impl/loopback_server/loopback_server.cc
@@ -1,53 +1,58 @@
-// Copyright 2014 The Chromium Authors. All rights reserved.
+// Copyright 2016 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 "components/sync/test/fake_server/fake_server.h"
+#include "components/sync/engine_impl/loopback_server/loopback_server.h"
+
+#include <stdint.h>
 
 #include <algorithm>
 #include <limits>
+#include <memory>
 #include <set>
+#include <string>
 #include <utility>
+#include <vector>
 
+#include "base/files/file_util.h"
 #include "base/guid.h"
 #include "base/logging.h"
+#include "base/rand_util.h"
 #include "base/stl_util.h"
 #include "base/strings/string_number_conversions.h"
 #include "base/strings/string_util.h"
 #include "base/strings/stringprintf.h"
 #include "base/synchronization/lock.h"
-#include "components/sync/test/fake_server/bookmark_entity.h"
-#include "components/sync/test/fake_server/permanent_entity.h"
-#include "components/sync/test/fake_server/tombstone_entity.h"
-#include "components/sync/test/fake_server/unique_client_entity.h"
+#include "components/sync/base/model_type.h"
+#include "components/sync/engine_impl/loopback_server/persistent_bookmark_entity.h"
+#include "components/sync/engine_impl/loopback_server/persistent_permanent_entity.h"
+#include "components/sync/engine_impl/loopback_server/persistent_tombstone_entity.h"
+#include "components/sync/engine_impl/loopback_server/persistent_unique_client_entity.h"
 #include "net/base/net_errors.h"
 #include "net/http/http_status_code.h"
 
 using std::string;
 using std::vector;
+
 using syncer::GetModelType;
 using syncer::GetModelTypeFromSpecifics;
 using syncer::ModelType;
 using syncer::ModelTypeSet;
 
-namespace fake_server {
+namespace syncer {
 
-class FakeServerEntity;
+class LoopbackServerEntity;
 
 namespace {
 
-// The default keystore key.
-static const char kDefaultKeystoreKey[] = "1111111111111111";
+static const int kCurrentLoopbackServerProtoVersion = 1;
+static const int kKeystoreKeyLenght = 16;
 
-// Properties of the bookmark bar permanent folder.
+// Properties of the bookmark bar permanent folders.
 static const char kBookmarkBarFolderServerTag[] = "bookmark_bar";
 static const char kBookmarkBarFolderName[] = "Bookmark Bar";
-
-// Properties of the other bookmarks permanent folder.
 static const char kOtherBookmarksFolderServerTag[] = "other_bookmarks";
 static const char kOtherBookmarksFolderName[] = "Other Bookmarks";
-
-// Properties of the synced bookmarks permanent folder.
 static const char kSyncedBookmarksFolderServerTag[] = "synced_bookmarks";
 static const char kSyncedBookmarksFolderName[] = "Synced Bookmarks";
 
@@ -83,7 +88,7 @@ class UpdateSieve {
 
   // Determines whether the server should send an |entity| to the client as
   // part of a GetUpdatesResponse.
-  bool ClientWantsItem(const FakeServerEntity& entity) const {
+  bool ClientWantsItem(const LoopbackServerEntity& entity) const {
     int64_t version = entity.GetVersion();
     if (version <= min_version_) {
       return false;
@@ -92,7 +97,7 @@ class UpdateSieve {
     }
 
     ModelTypeToVersionMap::const_iterator it =
-        request_from_version_.find(entity.model_type());
+        request_from_version_.find(entity.GetModelType());
 
     return it == request_from_version_.end() ? false : it->second < version;
   }
@@ -134,7 +139,6 @@ std::unique_ptr<UpdateSieve> UpdateSieve::Create(
       bool parsed = base::StringToInt64(marker.token(), &version);
       CHECK(parsed) << "Unable to parse progress marker token.";
     }
-
     ModelType model_type =
         syncer::GetModelTypeFromSpecificsFieldNumber(marker.data_type_id());
     request_from_version[model_type] = version;
@@ -147,40 +151,37 @@ std::unique_ptr<UpdateSieve> UpdateSieve::Create(
       new UpdateSieve(request_from_version, min_version));
 }
 
-// Returns whether |entity| is deleted or permanent.
-bool IsDeletedOrPermanent(const FakeServerEntity& entity) {
-  return entity.IsDeleted() || entity.IsPermanent();
-}
-
 }  // namespace
 
-FakeServer::FakeServer()
-    : version_(0),
-      store_birthday_(0),
-      authenticated_(true),
-      error_type_(sync_pb::SyncEnums::SUCCESS),
-      alternate_triggered_errors_(false),
-      request_counter_(0),
-      network_enabled_(true),
-      weak_ptr_factory_(this) {
+LoopbackServer::LoopbackServer(const base::FilePath& persistent_file)
+    : version_(0), store_birthday_(0), persistent_file_(persistent_file) {
   Init();
 }
 
-FakeServer::~FakeServer() {}
+LoopbackServer::~LoopbackServer() {}
 
-void FakeServer::Init() {
-  keystore_keys_.push_back(kDefaultKeystoreKey);
+void LoopbackServer::Init() {
+  if (LoadStateFromFile(persistent_file_))
+    return;
+
+  keystore_keys_.push_back(GenerateNewKeystoreKey());
 
   const bool create_result = CreateDefaultPermanentItems();
   DCHECK(create_result) << "Permanent items were not created successfully.";
 }
 
-bool FakeServer::CreatePermanentBookmarkFolder(const std::string& server_tag,
-                                               const std::string& name) {
+std::string LoopbackServer::GenerateNewKeystoreKey() const {
+  // TODO(pastarmovj): Check if true random bytes is ok or alpha-nums is needed?
+  return base::RandBytesAsString(kKeystoreKeyLenght);
+}
+
+bool LoopbackServer::CreatePermanentBookmarkFolder(
+    const std::string& server_tag,
+    const std::string& name) {
   DCHECK(thread_checker_.CalledOnValidThread());
-  std::unique_ptr<FakeServerEntity> entity =
-      PermanentEntity::Create(syncer::BOOKMARKS, server_tag, name,
-                              ModelTypeToRootTag(syncer::BOOKMARKS));
+  std::unique_ptr<LoopbackServerEntity> entity =
+      PersistentPermanentEntity::Create(syncer::BOOKMARKS, server_tag, name,
+                                        ModelTypeToRootTag(syncer::BOOKMARKS));
   if (!entity)
     return false;
 
@@ -188,7 +189,7 @@ bool FakeServer::CreatePermanentBookmarkFolder(const std::string& server_tag,
   return true;
 }
 
-bool FakeServer::CreateDefaultPermanentItems() {
+bool LoopbackServer::CreateDefaultPermanentItems() {
   // Permanent folders are always required for Bookmarks (hierarchical
   // structure) and Nigori (data stored in permanent root folder).
   ModelTypeSet permanent_folder_types =
@@ -198,8 +199,8 @@ bool FakeServer::CreateDefaultPermanentItems() {
        it.Inc()) {
     ModelType model_type = it.Get();
 
-    std::unique_ptr<FakeServerEntity> top_level_entity =
-        PermanentEntity::CreateTopLevel(model_type);
+    std::unique_ptr<LoopbackServerEntity> top_level_entity =
+        PersistentPermanentEntity::CreateTopLevel(model_type);
     if (!top_level_entity) {
       return false;
     }
@@ -218,37 +219,21 @@ bool FakeServer::CreateDefaultPermanentItems() {
   return true;
 }
 
-void FakeServer::UpdateEntityVersion(FakeServerEntity* entity) {
+void LoopbackServer::UpdateEntityVersion(LoopbackServerEntity* entity) {
   entity->SetVersion(++version_);
 }
 
-void FakeServer::SaveEntity(std::unique_ptr<FakeServerEntity> entity) {
+void LoopbackServer::SaveEntity(std::unique_ptr<LoopbackServerEntity> entity) {
   UpdateEntityVersion(entity.get());
-  entities_[entity->id()] = std::move(entity);
+  entities_[entity->GetId()] = std::move(entity);
 }
 
-void FakeServer::HandleCommand(const string& request,
-                               const base::Closure& completion_closure,
-                               int* error_code,
-                               int* response_code,
-                               std::string* response) {
+void LoopbackServer::HandleCommand(
+    const string& request,
+    HttpResponse::ServerConnectionCode* server_status,
+    int64_t* response_code,
+    std::string* response) {
   DCHECK(thread_checker_.CalledOnValidThread());
-  if (!network_enabled_) {
-    *error_code = net::ERR_FAILED;
-    *response_code = net::ERR_FAILED;
-    *response = string();
-    completion_closure.Run();
-    return;
-  }
-  request_counter_++;
-
-  if (!authenticated_) {
-    *error_code = 0;
-    *response_code = net::HTTP_UNAUTHORIZED;
-    *response = string();
-    completion_closure.Run();
-    return;
-  }
 
   sync_pb::ClientToServerMessage message;
   bool parsed = message.ParseFromString(request);
@@ -259,23 +244,14 @@ void FakeServer::HandleCommand(const string& request,
   if (message.has_store_birthday() &&
       message.store_birthday() != GetStoreBirthday()) {
     response_proto.set_error_code(sync_pb::SyncEnums::NOT_MY_BIRTHDAY);
-  } else if (error_type_ != sync_pb::SyncEnums::SUCCESS &&
-             ShouldSendTriggeredError()) {
-    response_proto.set_error_code(error_type_);
-  } else if (triggered_actionable_error_.get() && ShouldSendTriggeredError()) {
-    sync_pb::ClientToServerResponse_Error* error =
-        response_proto.mutable_error();
-    error->CopyFrom(*(triggered_actionable_error_.get()));
   } else {
     bool success = false;
     switch (message.message_contents()) {
       case sync_pb::ClientToServerMessage::GET_UPDATES:
-        last_getupdates_message_ = message;
         success = HandleGetUpdatesRequest(message.get_updates(),
                                           response_proto.mutable_get_updates());
         break;
       case sync_pb::ClientToServerMessage::COMMIT:
-        last_commit_message_ = message;
         success = HandleCommitRequest(message.commit(),
                                       message.invalidator_client_id(),
                                       response_proto.mutable_commit());
@@ -286,20 +262,16 @@ void FakeServer::HandleCommand(const string& request,
         success = true;
         break;
       default:
-        *error_code = net::ERR_NOT_IMPLEMENTED;
-        *response_code = 0;
+        *server_status = HttpResponse::SYNC_SERVER_ERROR;
+        *response_code = net::ERR_NOT_IMPLEMENTED;
         *response = string();
-        completion_closure.Run();
         return;
     }
 
     if (!success) {
-      // TODO(pvalenzuela): Add logging here so that tests have more info about
-      // the failure.
-      *error_code = net::ERR_FAILED;
-      *response_code = 0;
+      *server_status = HttpResponse::SYNC_SERVER_ERROR;
+      *response_code = net::ERR_FAILED;
       *response = string();
-      completion_closure.Run();
       return;
     }
 
@@ -308,30 +280,15 @@ void FakeServer::HandleCommand(const string& request,
 
   response_proto.set_store_birthday(GetStoreBirthday());
 
-  *error_code = 0;
+  *server_status = HttpResponse::SERVER_CONNECTION_OK;
   *response_code = net::HTTP_OK;
   *response = response_proto.SerializeAsString();
-  completion_closure.Run();
-}
 
-bool FakeServer::GetLastCommitMessage(sync_pb::ClientToServerMessage* message) {
-  if (!last_commit_message_.has_commit())
-    return false;
-
-  message->CopyFrom(last_commit_message_);
-  return true;
+  // TODO(pastarmovj): This should be done asynchronously.
+  SaveStateToFile(persistent_file_);
 }
 
-bool FakeServer::GetLastGetUpdatesMessage(
-    sync_pb::ClientToServerMessage* message) {
-  if (!last_getupdates_message_.has_get_updates())
-    return false;
-
-  message->CopyFrom(last_getupdates_message_);
-  return true;
-}
-
-bool FakeServer::HandleGetUpdatesRequest(
+bool LoopbackServer::HandleGetUpdatesRequest(
     const sync_pb::GetUpdatesMessage& get_updates,
     sync_pb::GetUpdatesResponse* response) {
   // TODO(pvalenzuela): Implement batching instead of sending all information
@@ -352,7 +309,7 @@ bool FakeServer::HandleGetUpdatesRequest(
   int64_t max_response_version = 0;
   for (EntityMap::const_iterator it = entities_.begin(); it != entities_.end();
        ++it) {
-    const FakeServerEntity& entity = *it->second;
+    const LoopbackServerEntity& entity = *it->second;
     if (sieve->ClientWantsItem(entity)) {
       sync_pb::SyncEntity* response_entity = response->add_entries();
       entity.SerializeAsProto(response_entity);
@@ -360,7 +317,7 @@ bool FakeServer::HandleGetUpdatesRequest(
       max_response_version =
           std::max(max_response_version, response_entity->version());
 
-      if (entity.model_type() == syncer::NIGORI) {
+      if (entity.GetModelType() == syncer::NIGORI) {
         send_encryption_keys_based_on_nigori =
             response_entity->specifics().nigori().passphrase_type() ==
             sync_pb::NigoriSpecifics::KEYSTORE_PASSPHRASE;
@@ -380,7 +337,7 @@ bool FakeServer::HandleGetUpdatesRequest(
   return true;
 }
 
-string FakeServer::CommitEntity(
+string LoopbackServer::CommitEntity(
     const sync_pb::SyncEntity& client_entity,
     sync_pb::CommitResponse_EntryResponse* entry_response,
     const string& client_guid,
@@ -389,51 +346,52 @@ string FakeServer::CommitEntity(
     return string();
   }
 
-  std::unique_ptr<FakeServerEntity> entity;
+  std::unique_ptr<LoopbackServerEntity> entity;
   if (client_entity.deleted()) {
-    entity = TombstoneEntity::Create(client_entity.id_string(),
-                                     client_entity.client_defined_unique_tag());
+    entity = PersistentTombstoneEntity::Create(client_entity);
     DeleteChildren(client_entity.id_string());
   } else if (GetModelType(client_entity) == syncer::NIGORI) {
     // NIGORI is the only permanent item type that should be updated by the
     // client.
     EntityMap::const_iterator iter = entities_.find(client_entity.id_string());
     CHECK(iter != entities_.end());
-    entity = PermanentEntity::CreateUpdatedNigoriEntity(client_entity,
-                                                        *iter->second);
+    entity = PersistentPermanentEntity::CreateUpdatedNigoriEntity(
+        client_entity, *iter->second);
   } else if (client_entity.has_client_defined_unique_tag()) {
-    entity = UniqueClientEntity::Create(client_entity);
+    entity = PersistentUniqueClientEntity::Create(client_entity);
   } else {
     // TODO(pvalenzuela): Validate entity's parent ID.
     EntityMap::const_iterator iter = entities_.find(client_entity.id_string());
     if (iter != entities_.end()) {
-      entity = BookmarkEntity::CreateUpdatedVersion(client_entity,
-                                                    *iter->second, parent_id);
+      entity = PersistentBookmarkEntity::CreateUpdatedVersion(
+          client_entity, *iter->second, parent_id);
     } else {
-      entity = BookmarkEntity::CreateNew(client_entity, parent_id, client_guid);
+      entity = PersistentBookmarkEntity::CreateNew(client_entity, parent_id,
+                                                   client_guid);
     }
   }
 
   if (!entity) {
-    // TODO(pvalenzuela): Add logging so that it is easier to determine why
-    // creation failed.
+    LOG(ERROR) << "No server entity was created for client entity with type: "
+               << GetModelType(client_entity)
+               << " and ID: " << client_entity.id_string() << ".";
     return string();
   }
 
-  const std::string id = entity->id();
+  const std::string id = entity->GetId();
   SaveEntity(std::move(entity));
   BuildEntryResponseForSuccessfulCommit(id, entry_response);
   return id;
 }
 
-void FakeServer::BuildEntryResponseForSuccessfulCommit(
+void LoopbackServer::BuildEntryResponseForSuccessfulCommit(
     const std::string& entity_id,
     sync_pb::CommitResponse_EntryResponse* entry_response) {
   EntityMap::const_iterator iter = entities_.find(entity_id);
   CHECK(iter != entities_.end());
-  const FakeServerEntity& entity = *iter->second;
+  const LoopbackServerEntity& entity = *iter->second;
   entry_response->set_response_type(sync_pb::CommitResponse::SUCCESS);
-  entry_response->set_id_string(entity.id());
+  entry_response->set_id_string(entity.GetId());
 
   if (entity.IsDeleted()) {
     entry_response->set_version(entity.GetVersion() + 1);
@@ -443,7 +401,8 @@ void FakeServer::BuildEntryResponseForSuccessfulCommit(
   }
 }
 
-bool FakeServer::IsChild(const string& id, const string& potential_parent_id) {
+bool LoopbackServer::IsChild(const string& id,
+                             const string& potential_parent_id) {
   EntityMap::const_iterator iter = entities_.find(id);
   if (iter == entities_.end()) {
     // We've hit an ID (probably the imaginary root entity) that isn't stored
@@ -451,7 +410,7 @@ bool FakeServer::IsChild(const string& id, const string& potential_parent_id) {
     return false;
   }
 
-  const FakeServerEntity& entity = *iter->second;
+  const LoopbackServerEntity& entity = *iter->second;
   if (entity.GetParentId() == potential_parent_id)
     return true;
 
@@ -459,24 +418,26 @@ bool FakeServer::IsChild(const string& id, const string& potential_parent_id) {
   return IsChild(entity.GetParentId(), potential_parent_id);
 }
 
-void FakeServer::DeleteChildren(const string& id) {
-  std::vector<std::unique_ptr<FakeServerEntity>> tombstones;
+void LoopbackServer::DeleteChildren(const string& id) {
+  std::vector<sync_pb::SyncEntity> tombstones;
   // Find all the children of id.
-  for (const auto& entity : entities_) {
+  for (auto& entity : entities_) {
     if (IsChild(entity.first, id)) {
-      tombstones.push_back(TombstoneEntity::Create(
-          entity.first, entity.second->client_defined_unique_tag()));
+      sync_pb::SyncEntity proto;
+      entity.second->SerializeAsProto(&proto);
+      tombstones.emplace_back(proto);
     }
   }
 
   for (auto& tombstone : tombstones) {
-    SaveEntity(std::move(tombstone));
+    SaveEntity(PersistentTombstoneEntity::Create(tombstone));
   }
 }
 
-bool FakeServer::HandleCommitRequest(const sync_pb::CommitMessage& commit,
-                                     const std::string& invalidator_client_id,
-                                     sync_pb::CommitResponse* response) {
+bool LoopbackServer::HandleCommitRequest(
+    const sync_pb::CommitMessage& commit,
+    const std::string& invalidator_client_id,
+    sync_pb::CommitResponse* response) {
   std::map<string, string> client_to_server_ids;
   string guid = commit.cache_guid();
   ModelTypeSet committed_model_types;
@@ -506,110 +467,13 @@ bool FakeServer::HandleCommitRequest(const sync_pb::CommitMessage& commit,
 
     EntityMap::const_iterator iter = entities_.find(entity_id);
     CHECK(iter != entities_.end());
-    committed_model_types.Put(iter->second->model_type());
-  }
-
-  for (auto& observer : observers_)
-    observer.OnCommit(invalidator_client_id, committed_model_types);
-
-  return true;
-}
-
-std::unique_ptr<base::DictionaryValue>
-FakeServer::GetEntitiesAsDictionaryValue() {
-  DCHECK(thread_checker_.CalledOnValidThread());
-  std::unique_ptr<base::DictionaryValue> dictionary(
-      new base::DictionaryValue());
-
-  // Initialize an empty ListValue for all ModelTypes.
-  ModelTypeSet all_types = ModelTypeSet::All();
-  for (ModelTypeSet::Iterator it = all_types.First(); it.Good(); it.Inc()) {
-    dictionary->Set(ModelTypeToString(it.Get()), new base::ListValue());
-  }
-
-  for (EntityMap::const_iterator it = entities_.begin(); it != entities_.end();
-       ++it) {
-    const FakeServerEntity& entity = *it->second;
-    if (IsDeletedOrPermanent(entity)) {
-      // Tombstones are ignored as they don't represent current data. Folders
-      // are also ignored as current verification infrastructure does not
-      // consider them.
-      continue;
-    }
-    base::ListValue* list_value;
-    if (!dictionary->GetList(ModelTypeToString(entity.model_type()),
-                             &list_value)) {
-      return std::unique_ptr<base::DictionaryValue>();
-    }
-    // TODO(pvalenzuela): Store more data for each entity so additional
-    // verification can be performed. One example of additional verification
-    // is checking the correctness of the bookmark hierarchy.
-    list_value->AppendString(entity.GetName());
-  }
-
-  return dictionary;
-}
-
-std::vector<sync_pb::SyncEntity> FakeServer::GetSyncEntitiesByModelType(
-    ModelType model_type) {
-  std::vector<sync_pb::SyncEntity> sync_entities;
-  DCHECK(thread_checker_.CalledOnValidThread());
-  for (EntityMap::const_iterator it = entities_.begin(); it != entities_.end();
-       ++it) {
-    const FakeServerEntity& entity = *it->second;
-    if (!IsDeletedOrPermanent(entity) && entity.model_type() == model_type) {
-      sync_pb::SyncEntity sync_entity;
-      entity.SerializeAsProto(&sync_entity);
-      sync_entities.push_back(sync_entity);
-    }
-  }
-  return sync_entities;
-}
-
-void FakeServer::InjectEntity(std::unique_ptr<FakeServerEntity> entity) {
-  DCHECK(thread_checker_.CalledOnValidThread());
-  SaveEntity(std::move(entity));
-}
-
-bool FakeServer::ModifyEntitySpecifics(
-    const std::string& id,
-    const sync_pb::EntitySpecifics& updated_specifics) {
-  EntityMap::const_iterator iter = entities_.find(id);
-  if (iter == entities_.end() ||
-      iter->second->model_type() !=
-          GetModelTypeFromSpecifics(updated_specifics)) {
-    return false;
-  }
-
-  FakeServerEntity* entity = iter->second.get();
-  entity->SetSpecifics(updated_specifics);
-  UpdateEntityVersion(entity);
-  return true;
-}
-
-bool FakeServer::ModifyBookmarkEntity(
-    const std::string& id,
-    const std::string& parent_id,
-    const sync_pb::EntitySpecifics& updated_specifics) {
-  EntityMap::const_iterator iter = entities_.find(id);
-  if (iter == entities_.end() ||
-      iter->second->model_type() != syncer::BOOKMARKS ||
-      GetModelTypeFromSpecifics(updated_specifics) != syncer::BOOKMARKS) {
-    return false;
+    committed_model_types.Put(iter->second->GetModelType());
   }
 
-  BookmarkEntity* entity = static_cast<BookmarkEntity*>(iter->second.get());
-
-  entity->SetParentId(parent_id);
-  entity->SetSpecifics(updated_specifics);
-  if (updated_specifics.has_bookmark()) {
-    entity->SetName(updated_specifics.bookmark().title());
-  }
-  UpdateEntityVersion(entity);
   return true;
 }
 
-void FakeServer::ClearServerData() {
+void LoopbackServer::ClearServerData() {
   DCHECK(thread_checker_.CalledOnValidThread());
   entities_.clear();
   keystore_keys_.clear();
@@ -617,113 +481,76 @@ void FakeServer::ClearServerData() {
   Init();
 }
 
-void FakeServer::SetAuthenticated() {
+std::string LoopbackServer::GetStoreBirthday() const {
   DCHECK(thread_checker_.CalledOnValidThread());
-  authenticated_ = true;
-}
-
-void FakeServer::SetUnauthenticated() {
-  DCHECK(thread_checker_.CalledOnValidThread());
-  authenticated_ = false;
+  return base::Int64ToString(store_birthday_);
 }
 
-bool FakeServer::TriggerError(const sync_pb::SyncEnums::ErrorType& error_type) {
+void LoopbackServer::SerializeState(sync_pb::LoopbackServerProto* proto) const {
   DCHECK(thread_checker_.CalledOnValidThread());
-  if (triggered_actionable_error_.get()) {
-    DVLOG(1) << "Only one type of error can be triggered at any given time.";
-    return false;
-  }
-
-  error_type_ = error_type;
-  return true;
-}
 
-bool FakeServer::TriggerActionableError(
-    const sync_pb::SyncEnums::ErrorType& error_type,
-    const string& description,
-    const string& url,
-    const sync_pb::SyncEnums::Action& action) {
-  DCHECK(thread_checker_.CalledOnValidThread());
-  if (error_type_ != sync_pb::SyncEnums::SUCCESS) {
-    DVLOG(1) << "Only one type of error can be triggered at any given time.";
-    return false;
+  proto->set_version(kCurrentLoopbackServerProtoVersion);
+  proto->set_store_birthday(store_birthday_);
+  proto->set_last_version_assigned(version_);
+  for (const auto& key : keystore_keys_)
+    proto->add_keystore_keys(key);
+  for (const auto& entity : entities_) {
+    auto* new_entity = proto->mutable_entities()->Add();
+    entity.second->SerializeAsLoopbackServerEntity(new_entity);
   }
-
-  sync_pb::ClientToServerResponse_Error* error =
-      new sync_pb::ClientToServerResponse_Error();
-  error->set_error_type(error_type);
-  error->set_error_description(description);
-  error->set_url(url);
-  error->set_action(action);
-  triggered_actionable_error_.reset(error);
-  return true;
 }
 
-bool FakeServer::EnableAlternatingTriggeredErrors() {
+bool LoopbackServer::DeSerializeState(
+    const sync_pb::LoopbackServerProto& proto) {
   DCHECK(thread_checker_.CalledOnValidThread());
-  if (error_type_ == sync_pb::SyncEnums::SUCCESS &&
-      !triggered_actionable_error_.get()) {
-    DVLOG(1) << "No triggered error set. Alternating can't be enabled.";
-    return false;
+  CHECK_EQ(proto.version(), kCurrentLoopbackServerProtoVersion);
+
+  store_birthday_ = proto.store_birthday();
+  version_ = proto.last_version_assigned();
+  for (int i = 0; i < proto.keystore_keys_size(); ++i)
+    keystore_keys_.push_back(proto.keystore_keys(i));
+  for (int i = 0; i < proto.entities_size(); ++i) {
+    entities_[proto.entities(i).entity().id_string()] =
+        LoopbackServerEntity::CreateEntityFromProto(proto.entities(i));
   }
 
-  alternate_triggered_errors_ = true;
-  // Reset the counter so that the the first request yields a triggered error.
-  request_counter_ = 0;
   return true;
 }
 
-bool FakeServer::ShouldSendTriggeredError() const {
-  if (!alternate_triggered_errors_)
-    return true;
-
-  // Check that the counter is odd so that we trigger an error on the first
-  // request after alternating is enabled.
-  return request_counter_ % 2 != 0;
-}
-
-void FakeServer::AddObserver(Observer* observer) {
-  DCHECK(thread_checker_.CalledOnValidThread());
-  observers_.AddObserver(observer);
-}
-
-void FakeServer::RemoveObserver(Observer* observer) {
-  DCHECK(thread_checker_.CalledOnValidThread());
-  observers_.RemoveObserver(observer);
-}
+// Saves all entities and server state to a protobuf file in |filename|.
+bool LoopbackServer::SaveStateToFile(const base::FilePath& filename) const {
+  sync_pb::LoopbackServerProto proto;
+  SerializeState(&proto);
 
-void FakeServer::EnableNetwork() {
-  DCHECK(thread_checker_.CalledOnValidThread());
-  network_enabled_ = true;
+  std::string serialized = proto.SerializeAsString();
+  int result = base::WriteFile(filename, serialized.data(), serialized.size());
+  return result == static_cast<int>(serialized.size());
 }
 
-void FakeServer::DisableNetwork() {
-  DCHECK(thread_checker_.CalledOnValidThread());
-  network_enabled_ = false;
-}
-
-std::string FakeServer::GetBookmarkBarFolderId() const {
-  DCHECK(thread_checker_.CalledOnValidThread());
-  for (EntityMap::const_iterator it = entities_.begin(); it != entities_.end();
-       ++it) {
-    FakeServerEntity* entity = it->second.get();
-    if (entity->GetName() == kBookmarkBarFolderName && entity->IsFolder() &&
-        entity->model_type() == syncer::BOOKMARKS) {
-      return entity->id();
+// Loads all entities and server state from a protobuf file in |filename|.
+bool LoopbackServer::LoadStateFromFile(const base::FilePath& filename) {
+  if (base::PathExists(filename)) {
+    std::string serialized;
+    if (base::ReadFileToString(filename, &serialized)) {
+      sync_pb::LoopbackServerProto proto;
+      if (serialized.length() > 0 && proto.ParseFromString(serialized)) {
+        DeSerializeState(proto);
+        return true;
+      } else {
+        LOG(ERROR) << "Loopback sync can not parse the persistent state file.";
+        return false;
+      }
+    } else {
+      // TODO(pastarmovj): Try to understand what is the issue e.g. file already
+      // open, no access rights etc. and decide if better course of action is
+      // available instead of giving up and wiping the global state on the next
+      // write.
+      LOG(ERROR) << "Loopback sync can not read the persistent state file.";
+      return false;
     }
   }
-  NOTREACHED() << "Bookmark Bar entity not found.";
-  return "";
-}
-
-base::WeakPtr<FakeServer> FakeServer::AsWeakPtr() {
-  DCHECK(thread_checker_.CalledOnValidThread());
-  return weak_ptr_factory_.GetWeakPtr();
-}
-
-std::string FakeServer::GetStoreBirthday() const {
-  DCHECK(thread_checker_.CalledOnValidThread());
-  return base::Int64ToString(store_birthday_);
+  LOG(WARNING) << "Loopback sync persistent state file does not exist.";
+  return false;
 }
 
-}  // namespace fake_server
+}  // namespace syncer