Wrap large IndexedDB values into Blobs before writing to LevelDB.

third_party/WebKit/Source/modules/indexeddb/IDBRequestLoader.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 IDBRequestLoader_h
+#define IDBRequestLoader_h
+
+#include "core/fileapi/FileReaderLoaderClient.h"
+#include "platform/wtf/PassRefPtr.h"
+#include "platform/wtf/RefPtr.h"
+#include "platform/wtf/Vector.h"
+
+#include <memory>
+
+namespace blink {
+
+class FileReaderLoader;
+class IDBRequestQueueItem;
+class IDBRequest;
+class IDBValue;
+
+// Loads IndexedDB values that have been wrapped in Blobs by IDBValueWrapper.
+//
+// An IDBRequestLoader unwraps the result of a single IDBRequest. While most
+// IndexedDB requests result in a single value, getAll() in IDBObjectStore and

[jsbell, 2017/05/15 23:37:38]

Should we add a TODO to handle fetches of multiple values in parallel batches?

[pwnall, 2017/05/19 18:27:34]

Done.
I added it in the .cpp file. The loader API will not change, so readers who only
intend to cover the header shouldn't see the TODO.

+// IDBIndex results in an array of values. In the interest of simplicity,
+// IDBRequestLoader only knows how to unwrap an array of values, even though
+// most of the time the array will consist of a single element. This design
+// assumes that the overhead of creating and destroying a Vector is much smaller
+// than the IPC overhead required to load the Blob data into the renderer.
+class IDBRequestLoader : public FileReaderLoaderClient {
+ public:
+  // Creates a loader that will unwrap IDBValues received by a IDBRequest.
+  //
+  // result_values must be kept alive until the loader calls
+  // IDBRequestQueueItem::MarkReady().
+  IDBRequestLoader(IDBRequestQueueItem*,
+                   Vector<RefPtr<IDBValue>>* result_values);
+
+  ~IDBRequestLoader() override;
+
+  static bool NeedsUnwrapping(IDBValue*);

[jsbell, 2017/05/15 23:37:38]

If we drop the use of these methods then IDBRequestQueueItem is the only user of
this class. It could move to being an nested class, but it's big enough that
it's own file is probably better.

[pwnall, 2017/05/19 18:27:34]

Ack.

Also, the loader will grow in size and complexity when we implement special
treatment for WASM chunks.

+  static bool NeedUnwrapping(const Vector<RefPtr<IDBValue>>&);
+
+  // Start unwrapping values.
+  //
+  // When the unwrapping completes, the loader will call MarkReady() on the
+  // request queue item.
+  void Start();
+
+  // FileReaderLoaderClient implementaton.
+  void DidStartLoading() override;
+  void DidReceiveDataForClient(const char* data, unsigned data_length) override;
+  void DidFinishLoading() override;
+  void DidFail(FileError::ErrorCode) override;
+
+ private:
+  // Starts unwrapping the next wrapped IDBValue.
+  //
+  // If no more wrapped IDBValues are found, this calls the IDBRequest
+  // callbacks.
+  void StartNextValue();
+
+  void ReportSuccess();
+  void ReportError();
+
+  std::unique_ptr<FileReaderLoader> loader_;
+
+  // Transaction result queue item for the IDBRequest.
+  //
+  // The IDBRequestQueueItem owns this loader.
+  IDBRequestQueueItem* queue_item_;
+
+  // All the values that will be passed back to the IDBRequest.
+  Vector<RefPtr<IDBValue>>* const values_;

[jsbell, 2017/05/15 23:37:38]

Comment on who owns this. (it's implied in the constructor, but wouldn't hurt to
say it here too)

[pwnall, 2017/05/19 18:27:34]

Done.

+
+  // Buffer used to unwrap an IDBValue.
+  Vector<char> wrapped_data_;
+
+  // The value being currently unwrapped.
+  Vector<RefPtr<IDBValue>>::iterator current_value_;
+};
+
+}  // namespace blink
+
+#endif  // IDBRequestLoader_h