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/Allocator.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
+// 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 {
+  USING_FAST_MALLOC(IDBRequestLoader);
+
+ public:
+  // Creates a loader that will unwrap IDBValues received by a IDBRequest.
+  //
+  // result_values must be kept alive until the loader calls
+  // IDBRequestQueueItem::OnResultLoadComplete().
+  IDBRequestLoader(IDBRequestQueueItem*,
+                   Vector<RefPtr<IDBValue>>* result_values);
+
+  ~IDBRequestLoader() override;
+
+  // Start unwrapping values.
+  //
+  // When the unwrapping completes, the loader will call OnResultLoadComplete()
+  // on the request queue item.
+  void Start();
+  // Halt the process of unwrapping values, if possible.
+  void Cancel();
+
+  // 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 ReportSuccess(), which
+  // ends up calling IDBRequestQueueItem::OnResultLoadComplete().
+  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.
+  //
+  // The Vector is owned by the IDBRequestLoader owner, which is currently a
+  // IDBRequestQueueItem.
+  Vector<RefPtr<IDBValue>>* const values_;
+
+  // 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