Add a Restore() method to ValueStore and make StorageAPI use it

chrome/browser/value_store/leveldb_value_store.cc

Index: chrome/browser/value_store/leveldb_value_store.cc
diff --git a/chrome/browser/value_store/leveldb_value_store.cc b/chrome/browser/value_store/leveldb_value_store.cc
index 043bcb3d1915f4e3a316f871d9ff06f47aa8f1cb..b795b6b9d71dfa50be3834abfb31486a6aa80a0e 100644
--- a/chrome/browser/value_store/leveldb_value_store.cc
+++ b/chrome/browser/value_store/leveldb_value_store.cc
@@ -269,6 +269,55 @@ ValueStore::WriteResult LeveldbValueStore::Clear() {
   return MakeWriteResult(changes.Pass());
 }
 
+bool LeveldbValueStore::Restore() {
+  DCHECK(BrowserThread::CurrentlyOn(BrowserThread::FILE));
+
+  ReadResult result = Get();
+  std::string previous_key;
+  while (result->IsCorrupted()) {
+    // If we don't have a specific corrupted key, or we've tried and failed to
+    // clear this specific key, or we fail to restore the key, then wipe the
+    // whole database.
+    if (!result->error().key.get() || *result->error().key == previous_key ||
+        !RestoreKey(*result->error().key)) {
+      DeleteDbFile();
+      result = Get();
+      break;
+    }
+
+    // Otherwise, re-Get() the database to check if there is still any
+    // corruption.
+    previous_key = *result->error().key;
+    result = Get();
+  }
+
+  // If we still have an error, it means we've tried deleting the database file,
+  // and failed. There's nothing more we can do.
+  return !result->IsCorrupted();

[not at google - send to devlin, 2014/02/19 21:25:29]

I guess another complication with all this is if invalid keys make it into sync
or policy. I'm not sure how all of this would behave, particularly if we're
going to go and turn around and restore the data.

i'll add it to the list of things to look into later.

[Devlin, 2014/02/19 23:12:28]

Yeah...

I don't think that we can get a corrupted key _from_ a local copy of sync
storage to the cloud's copy of sync storage, because it relies on Get() to do so
(which would fail if it's corrupt).  But if the cloud version gets corrupted,
we're going to have a bad time.

+}
+
+bool LeveldbValueStore::RestoreKey(const std::string& key) {
+  DCHECK(BrowserThread::CurrentlyOn(BrowserThread::FILE));
+
+  ReadResult result = Get(key);
+  if (result->IsCorrupted()) {
+    leveldb::WriteBatch batch;
+    batch.Delete(key);
+    scoped_ptr<ValueStore::Error> error = WriteToDb(&batch);
+    // If we can't delete the key, the restore failed.
+    if (error.get())
+      return false;
+    result = Get(key);
+  }
+
+  // The restore succeeded if there is no corruption error.
+  return !result->IsCorrupted();
+}
+
+bool LeveldbValueStore::WriteToDbForTest(leveldb::WriteBatch* batch) {
+  return !WriteToDb(batch).get();
+}
+
 scoped_ptr<ValueStore::Error> LeveldbValueStore::EnsureDbIsOpen() {
   DCHECK(BrowserThread::CurrentlyOn(BrowserThread::FILE));