sync: Improve handling of bad UniquePositions

Makes the client assign a valid position to incoming bookmarks if the
server has not populated the required fields.  This code should never be
triggered unless there is a bug in the server.  This risks reordering
users' bookmarks, but that's probably preferable to a crash.

Detects bookmarks that do not have valid position information during
database load.  If these corrupted bookmarks are detected, the entire
database is declared to be corrupt.  Sync will then re-download
all of the user's data, which should fix the problem.

BUG=367247

Review URL: https://codereview.chromium.org/278153002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@270308 0039d316-1c4b-4281-b951-d872f2087c98

3 files changed, 139 insertions, 9 deletions

diff --git a/sync/engine/syncer_util.cc b/sync/engine/syncer_util.cc
index 2235734..c7d93c1 100644
--- a/sync/engine/syncer_util.cc
+++ b/sync/engine/syncer_util.cc
@@ -12,6 +12,7 @@
 #include "base/base64.h"
 #include "base/location.h"
 #include "base/metrics/histogram.h"
+#include "base/rand_util.h"
 #include "base/strings/string_number_conversions.h"
 #include "sync/engine/conflict_resolver.h"
 #include "sync/engine/syncer_proto_util.h"
@@ -278,7 +279,9 @@ UpdateAttemptResponse AttemptToUpdateEntry(
 std::string GetUniqueBookmarkTagFromUpdate(const sync_pb::SyncEntity& update) {
   if (!update.has_originator_cache_guid() ||
       !update.has_originator_client_item_id()) {
-    return std::string();
+    LOG(ERROR) << "Update is missing requirements for bookmark position."
+               << " This is a server bug.";
+    return UniquePosition::RandomSuffix();
   }
 
   return syncable::GenerateSyncableBookmarkHash(
@@ -295,7 +298,8 @@ UniquePosition GetUpdatePosition(const sync_pb::SyncEntity& update,
   } else if (update.has_position_in_parent()) {
     return UniquePosition::FromInt64(update.position_in_parent(), suffix);
   } else {
-    return UniquePosition::CreateInvalid();
+    LOG(ERROR) << "No position information in update. This is a server bug.";
+    return UniquePosition::FromInt64(0, suffix);
   }
 }
 
@@ -341,10 +345,6 @@ void UpdateBookmarkPositioning(
       GetUpdatePosition(update, local_entry->GetUniqueBookmarkTag());
   if (update_pos.IsValid()) {
     local_entry->PutServerUniquePosition(update_pos);
-  } else {
-    // TODO(sync): This and other cases of unexpected input should be handled
-    // better.
-    NOTREACHED();
   }
 }
 
diff --git a/sync/engine/syncer_util.h b/sync/engine/syncer_util.h
index 575ab11..f39ad4b 100644
--- a/sync/engine/syncer_util.h
+++ b/sync/engine/syncer_util.h
@@ -12,6 +12,7 @@
 #include <string>
 #include <vector>
 
+#include "sync/base/sync_export.h"
 #include "sync/engine/syncer.h"
 #include "sync/engine/syncer_types.h"
 #include "sync/syncable/entry_kernel.h"
@@ -58,12 +59,14 @@ UpdateAttemptResponse AttemptToUpdateEntry(
 //
 // Will return an invalid position if no valid position can be constructed, or
 // if this type does not support positioning.
-UniquePosition GetUpdatePosition(const sync_pb::SyncEntity& update,
-                                 const std::string& suffix);
+SYNC_EXPORT_PRIVATE UniquePosition GetUpdatePosition(
+    const sync_pb::SyncEntity& update,
+    const std::string& suffix);
 
 // Fetch the cache_guid and item_id-based unique bookmark tag from an update.
 // Will return an empty string if someting unexpected happens.
-std::string GetUniqueBookmarkTagFromUpdate(const sync_pb::SyncEntity& update);
+SYNC_EXPORT_PRIVATE std::string GetUniqueBookmarkTagFromUpdate(
+    const sync_pb::SyncEntity& update);
 
 // Pass in name to avoid redundant UTF8 conversion.
 void UpdateServerFieldsFromUpdate(
diff --git a/sync/engine/syncer_util_unittest.cc b/sync/engine/syncer_util_unittest.cc
new file mode 100644
index 0000000..eec72ea
--- /dev/null
+++ b/sync/engine/syncer_util_unittest.cc
@@ -0,0 +1,127 @@
+// Copyright 2014 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 "sync/engine/syncer_util.h"
+
+#include "base/rand_util.h"
+#include "sync/internal_api/public/base/unique_position.h"
+#include "sync/protocol/sync.pb.h"
+#include "testing/gtest/include/gtest/gtest.h"
+
+namespace syncer {
+
+class GetUpdatePositionTest : public ::testing::Test {
+ public:
+  GetUpdatePositionTest() {
+    InitUpdate();
+
+    // Init test_position to some valid position value, but don't assign
+    // it to the update just yet.
+    std::string pos_suffix = UniquePosition::RandomSuffix();
+    test_position = UniquePosition::InitialPosition(pos_suffix);
+  }
+
+  void InitUpdate() {
+    update.set_id_string("I");
+    update.set_parent_id_string("P");
+    update.set_version(10);
+    update.set_mtime(100);
+    update.set_ctime(100);
+    update.set_deleted(false);
+    update.mutable_specifics()->mutable_bookmark()->set_title("Chrome");
+    update.mutable_specifics()->mutable_bookmark()->
+        set_url("https://www.chrome.com");
+  }
+
+  void InitSuffixIngredients() {
+    update.set_originator_cache_guid("CacheGUID");
+    update.set_originator_client_item_id("OrigID");
+  }
+
+  void InitProtoPosition() {
+    test_position.ToProto(update.mutable_unique_position());
+  }
+
+  void InitInt64Position(int64 pos_value) {
+    update.set_position_in_parent(pos_value);
+  }
+
+  sync_pb::SyncEntity update;
+  UniquePosition test_position;
+};
+
+// Generate a suffix from originator client GUID and client-assigned ID.  These
+// values should always be present in updates sent down to the client, and
+// combine to create a globally unique value.
+TEST_F(GetUpdatePositionTest, SuffixFromUpdate) {
+  InitSuffixIngredients();
+
+  // Expect suffix is valid and consistent.
+  std::string suffix1 = GetUniqueBookmarkTagFromUpdate(update);
+  std::string suffix2 = GetUniqueBookmarkTagFromUpdate(update);
+
+  EXPECT_EQ(suffix1, suffix2);
+  EXPECT_TRUE(UniquePosition::IsValidSuffix(suffix1));
+}
+
+// Receive an update without the ingredients used to make a consistent suffix.
+//
+// The server should never send us an update like this.  If it does,
+// that's a bug and it needs to be fixed.  Still, we'd like to not
+// crash and have fairly reasonable results in this scenario.
+TEST_F(GetUpdatePositionTest, SuffixFromRandom) {
+  // Intentonally do not call InitSuffixIngredients()
+
+  // Expect suffix is valid but inconsistent.
+  std::string suffix1 = GetUniqueBookmarkTagFromUpdate(update);
+  std::string suffix2 = GetUniqueBookmarkTagFromUpdate(update);
+
+  EXPECT_NE(suffix1, suffix2);
+  EXPECT_TRUE(UniquePosition::IsValidSuffix(suffix1));
+  EXPECT_TRUE(UniquePosition::IsValidSuffix(suffix2));
+}
+
+TEST_F(GetUpdatePositionTest, FromInt64) {
+  InitSuffixIngredients();
+  InitInt64Position(10);
+
+  std::string suffix = GetUniqueBookmarkTagFromUpdate(update);
+
+  // Expect the result is valid.
+  UniquePosition pos = GetUpdatePosition(update, suffix);
+  EXPECT_TRUE(pos.IsValid());
+
+  // Expect the position had some effect on ordering.
+  EXPECT_TRUE(pos.LessThan(
+      UniquePosition::FromInt64(11, UniquePosition::RandomSuffix())));
+}
+
+TEST_F(GetUpdatePositionTest, FromProto) {
+  InitSuffixIngredients();
+  InitInt64Position(10);
+
+  std::string suffix = GetUniqueBookmarkTagFromUpdate(update);
+
+  // The proto position is not set, so we should get one based on the int64.
+  // It should not match the proto we defined in the test harness.
+  UniquePosition int64_pos = GetUpdatePosition(update, suffix);
+  EXPECT_FALSE(int64_pos.Equals(test_position));
+
+  // Move the test harness' position value into the update proto.
+  // Expect that it takes precedence over the int64-based position.
+  InitProtoPosition();
+  UniquePosition pos = GetUpdatePosition(update, suffix);
+  EXPECT_TRUE(pos.Equals(test_position));
+}
+
+TEST_F(GetUpdatePositionTest, FromNothing) {
+  // Init none of the ingredients necessary to make a position.
+  // Verify we still generate a valid position locally.
+
+  std::string suffix = GetUniqueBookmarkTagFromUpdate(update);
+  UniquePosition pos = GetUpdatePosition(update, suffix);
+  EXPECT_TRUE(pos.IsValid());
+}
+
+}  // namespace syncer