sync: Attempt to recover from directory corruption

sync/syncable/directory_backing_store_unittest.cc

Index: sync/syncable/directory_backing_store_unittest.cc
diff --git a/sync/syncable/directory_backing_store_unittest.cc b/sync/syncable/directory_backing_store_unittest.cc
index 25aca638a8453b5da43fa7591f240581aa093ded..0a1cc3db7e79977725bcfdbd5f10f12cb4607728 100644
--- a/sync/syncable/directory_backing_store_unittest.cc
+++ b/sync/syncable/directory_backing_store_unittest.cc
@@ -2083,22 +2083,37 @@ TEST_F(DirectoryBackingStoreTest, ModelTypeIds) {
   }
 }
 
-// TODO(109668): This had to be disabled because the latest API will
-// intentionally crash when a database is this badly corrupted.
-TEST_F(DirectoryBackingStoreTest, DISABLED_Corruption) {
+// This is a whitebox test intended to exercise the code path where the on-disk
+// directory load code decides to delete the current directory and start fresh.
+//
+// Unfortunately, there's no way to tell that this code path is actually
+// exercised by the test.  If the directory failed to detect the corruption, the
+// result would look exactly the same from this level of abstraction.
+//
+// This is considered "minor" corruption because the database recreation is
+// expected to succeed.  The alternative, where recreation does not succeed (ie.
+// due to read-only file system), is not tested here.
+TEST_F(DirectoryBackingStoreTest, MinorCorruption) {
   {
     scoped_ptr<OnDiskDirectoryBackingStore> dbs(
         new OnDiskDirectoryBackingStore(GetUsername(), GetDatabasePath()));
-    EXPECT_TRUE(LoadAndIgnoreReturnedData(dbs.get()));
+    EXPECT_EQ(OPENED, LoadAndIgnoreReturnedData(dbs.get()));
+  }
+
+  // Corrupt the root node.
+  {
+    sql::Connection connection;
+    ASSERT_TRUE(connection.Open(GetDatabasePath()));
+    ASSERT_TRUE(connection.Execute(
+            "UPDATE metas SET parent_id='bogus' WHERE id = 'r';"));
   }
-  std::string bad_data("BAD DATA");
-  EXPECT_TRUE(file_util::WriteFile(GetDatabasePath(), bad_data.data(),
-                                   bad_data.size()));
+
   {
     scoped_ptr<OnDiskDirectoryBackingStore> dbs(
         new OnDiskDirectoryBackingStore(GetUsername(), GetDatabasePath()));
+    dbs->AllowFailureForTest();
 
-    EXPECT_FALSE(LoadAndIgnoreReturnedData(dbs.get()));
+    EXPECT_EQ(OPENED, LoadAndIgnoreReturnedData(dbs.get()));
   }
 }