Wrap large IndexedDB values into Blobs before writing to LevelDB.

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

+// 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.
+
+#include "modules/indexeddb/IDBValueUnwrapper.h"
+
+#include <memory>
+#include <utility>
+
+#include "bindings/core/v8/SerializationTag.h"
+#include "modules/indexeddb/IDBValue.h"
+#include "modules/indexeddb/IDBValueWrapper.h"
+#include "platform/blob/BlobData.h"
+#include "platform/wtf/text/WTFString.h"
+
+namespace blink {
+
+IDBValueUnwrapper::IDBValueUnwrapper() {
+  Reset();
+}
+
+bool IDBValueUnwrapper::IsWrapped(IDBValue* value) {
+  DCHECK(value);
+  if (!value->data_ || value->data_->size() < 3)
+    return false;
+
+  uint8_t header[3];
+  value->data_->GetPartAsBytes(header, static_cast<size_t>(0), sizeof(header));
+  return header[0] == kVersionTag && header[1] == 17 && header[2] == 1;
+}
+
+PassRefPtr<IDBValue> IDBValueUnwrapper::CreateUnwrapped(
+    IDBValue* wrapped_value,
+    PassRefPtr<SharedBuffer> wrapper_blob_content) {
+  DCHECK(wrapped_value);
+  DCHECK(wrapped_value->data_);
+  DCHECK_GT(wrapped_value->blob_info_->size(), 0U);
+  DCHECK_EQ(wrapped_value->blob_info_->size(),
+            wrapped_value->blob_data_->size());
+
+  // Create an IDBValue with the same blob information, minus the last blob.
+  unsigned blob_count = wrapped_value->BlobInfo()->size() - 1;
+  std::unique_ptr<Vector<RefPtr<BlobDataHandle>>> blob_data =
+      WTF::MakeUnique<Vector<RefPtr<BlobDataHandle>>>();
+  blob_data->ReserveCapacity(blob_count);
+  std::unique_ptr<Vector<WebBlobInfo>> blob_info =
+      WTF::MakeUnique<Vector<WebBlobInfo>>();
+  blob_info->ReserveCapacity(blob_count);
+
+  for (unsigned i = 0; i < blob_count; ++i) {
+    blob_data->push_back((*wrapped_value->blob_data_)[i]);
+    blob_info->push_back((*wrapped_value->blob_info_)[i]);
+  }
+
+  return AdoptRef(new IDBValue(std::move(wrapper_blob_content),
+                               std::move(blob_data), std::move(blob_info)));
+}
+
+bool IDBValueUnwrapper::Parse(IDBValue* value) {
+  // Fast path that avoids unnecessary dynamic allocations.
+  if (!IDBValueUnwrapper::IsWrapped(value))
+    return false;
+
+  const uint8_t* data = reinterpret_cast<const uint8_t*>(value->data_->Data());
+  end_ = data + value->data_->size();
+  current_ = data + 3;
+
+  String blob_uuid;
+  if (!ReadVarint(blob_size_))
+    return Reset();
+  if (!ReadAsciiString(blob_uuid))
+    return Reset();
+
+  blob_handle_ = value->blob_data_->back();
+
+  // TODO(pwnall): Blobs seem to get different UUIDs when they're resurrected?
+  //               If this is true, stashing the UUID is useless.
+  if (blob_handle_->size() != blob_size_)
+    return Reset();
+
+  return true;
+}
+
+PassRefPtr<BlobDataHandle> IDBValueUnwrapper::WrapperBlobHandle() {
+  DCHECK(blob_handle_);
+
+  return std::move(blob_handle_);
+}
+
+bool IDBValueUnwrapper::ReadVarint(unsigned& value) {

[dmurph, 2017/05/04 22:27:07]

There must be a library method for this... maybe it's only here?
https://cs.chromium.org/chromium/src/content/browser/indexed_db/indexed_db_le...

[pwnall, 2017/05/11 23:54:24]

As far as I know, there isn't. Please correct me if I'm wrong, so I don't have
to write tests :)

The code you pointed to in the browser. The varint encoding/decoding in the
renderer that I know of is in SSV, but we moved it from Blink to V8. This code
is lifted & adapted from V8.

+  value = 0;
+  unsigned shift = 0;
+  bool has_another_byte;
+  do {
+    if (current_ >= end_)
+      return false;
+
+    if (shift >= sizeof(unsigned) * 8)
+      return false;
+    uint8_t byte = *current_;
+    ++current_;
+    value |= static_cast<unsigned>(byte & 0x7F) << shift;
+    shift += 7;
+
+    has_another_byte = byte & 0x80;
+  } while (has_another_byte);
+  return true;
+}
+
+bool IDBValueUnwrapper::ReadAsciiString(String& value) {
+  unsigned length;
+  if (!ReadVarint(length))
+    return false;
+
+  if (end_ - current_ < length)
+    return false;
+  String output(current_, length);
+  value.swap(output);
+  current_ += length;
+  return true;
+}
+
+}  // namespace blink