Wrap large IndexedDB values into Blobs before writing to LevelDB.

third_party/WebKit/Source/modules/indexeddb/IDBValueUnwrapper.h

+// Copyright 2017 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.
+
+#ifndef IDBValueUnwrapper_h
+#define IDBValueUnwrapper_h
+
+#include "platform/SharedBuffer.h"
+#include "platform/wtf/PassRefPtr.h"

[jsbell, 2017/05/08 22:08:01]

We prefer std::move() of RefPtr now. (Trade off between matching surrounding
code vs. new style. Whatever ends up being more readable for now.)

[pwnall, 2017/05/11 23:54:25]

Mostly done.

I also removed the PassRefPtr instances I had introduced in IDBRequest.

I couldn't remove AdoptRef in IDBValueUnwrapper::CreateUnwrapped(). I kept
hitting a DCHECK for !adoption_is_required_ at RefCounted.h:46. I skimmed
through RefCounted / RefPtr / PassRefPtr, and I couldn't find an adoption
mechanism that doesn't rely on PassRefPtr. Sigh.

+#include "platform/wtf/RefPtr.h"
+#include "platform/wtf/Vector.h"
+#include "public/platform/WebBlobInfo.h"
+
+namespace WTF {
+class String;
+}
+
+namespace blink {
+
+class BlobDataHandle;
+class IDBValue;
+class SharedBuffer;
+
+// Logic for unwrapping large IndexedDB values from Blobs.
+class IDBValueUnwrapper {
+ public:
+  // Wrapper for an IndexedDB value.

[jsbell, 2017/05/08 22:08:01]

More details?

[pwnall, 2017/05/11 23:54:25]

Done.
I added more details to the top of the class. I think that explains the
constructor.

+  //
+  // The serialization process can throw an exception. The caller is responsible

[jsbell, 2017/05/08 22:08:01]

Comment doesn't apply to unwrapper

[pwnall, 2017/05/11 23:54:25]

Done.
Thanks for catching!

+  // for checking exception_state.
+  IDBValueUnwrapper();
+
+  // Checks whether a IDBValue's data was wrapped in a Blob.
+  static bool IsWrapped(IDBValue*);
+
+  // Pieces together an unwrapped IDBValue from a wrapped value and Blob data.
+  static PassRefPtr<IDBValue> CreateUnwrapped(
+      IDBValue* wrapped_value,
+      PassRefPtr<SharedBuffer> wrapper_blob_content);
+
+  // Parses the wrapper Blob information from a wrapped IDBValue.
+  //
+  // Returns true for success, and false for failure. Failure can mean that the
+  // given value was not a wrapped IDBValue, or that the value bytes were
+  // corrupted.
+  bool Parse(IDBValue*);
+
+  // Returns the size of the Blob obtained by the last Unwrap() call.
+  //
+  // Should only be called after a successful result from Unwrap().
+  inline unsigned WrapperBlobSize() const {
+    DCHECK(end_);
+    return blob_size_;
+  }
+
+  // Returns a handle to the Blob obtained by the last Unwrap() call.
+  //
+  // Should only be called exactly once after a successful result from Unwrap().
+  PassRefPtr<BlobDataHandle> WrapperBlobHandle();
+
+ private:
+  // Used to deserialize the wrapped value.
+  bool ReadVarint(unsigned& value);
+  bool ReadAsciiString(String& value);
+
+  // Resets
+  inline bool Reset() {
+#if DCHECK_IS_ON()
+    blob_handle_.Clear();
+    current_ = nullptr;
+    end_ = nullptr;
+#endif  // DCHECK_IS_ON()
+    return false;
+  }
+
+  // Deserialization cursor in the SharedBuffer of the IDBValue being unwrapped.
+  const uint8_t* current_;
+
+  // Smallest invalid position_ value.
+  const uint8_t* end_;
+
+  // The size of the Blob holding the data for the last unwrapped IDBValue.
+  unsigned blob_size_;
+
+  // Handle to the Blob holding the data for the last unwrapped IDBValue.
+  RefPtr<BlobDataHandle> blob_handle_;
+};
+
+}  // namespace blink
+
+#endif  // IDBValueWrapper_h

[jsbell, 2017/05/08 22:08:01]

nit: missing "Un"

[pwnall, 2017/05/11 23:54:25]

Done.