Wrap large IndexedDB values into Blobs before writing to LevelDB.

third_party/WebKit/Source/modules/indexeddb/IDBValueWrapper.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/IDBValueWrapper.h"
+
+#include <utility>
+
+#include "bindings/core/v8/ScriptValue.h"
+#include "bindings/core/v8/SerializationTag.h"
+#include "bindings/core/v8/SerializedScriptValue.h"
+#include "bindings/modules/v8/V8BindingForModules.h"
+#include "core/fileapi/Blob.h"
+#include "modules/indexeddb/IDBRequest.h"
+#include "platform/wtf/text/WTFString.h"
+
+namespace blink {
+
+IDBValueWrapper::IDBValueWrapper(v8::Isolate* isolate,
+                                 v8::Local<v8::Value> value,
+                                 bool write_wasm_to_stream,
+                                 ExceptionState& exception_state) {
+  SerializedScriptValue::SerializeOptions options;
+  options.blob_info = &blob_info_;
+  options.for_storage = true;
+  options.write_wasm_to_stream = write_wasm_to_stream;
+
+  serialized_value_ = SerializedScriptValue::Serialize(isolate, value, options,
+                                                       exception_state);
+
+#if DCHECK_IS_ON()
+  if (exception_state.HadException())
+    had_exception_ = true;
+#endif  // DCHECK_IS_ON()
+}
+
+void IDBValueWrapper::Clone(ScriptState* script_state, ScriptValue* clone) {
+#if DCHECK_IS_ON()
+  DCHECK(!had_exception_)
+      << "Clone() called on wrapper with serialization exception";
+  DCHECK(!wrap_called_) << "Clone() called after WrapIfBiggerThan()";
+#endif  // DCHECK_IS_ON()
+  *clone = DeserializeScriptValue(script_state, serialized_value_.Get(),
+                                  &blob_info_);
+}
+
+void IDBValueWrapper::WriteVarint(unsigned value, Vector<char>& output) {
+  // Writes an unsigned integer as a base-128 varint.
+  // The number is written, 7 bits at a time, from the least significant to
+  // the most significant 7 bits. Each byte, except the last, has the MSB set.
+  // See also https://developers.google.com/protocol-buffers/docs/encoding
+  do {
+    output.push_back((value & 0x7F) | 0x80);
+    value >>= 7;
+  } while (value);
+  output.back() &= 0x7F;
+}
+
+void IDBValueWrapper::WriteAsciiString(const String& value,
+                                       Vector<char>& output) {
+  DCHECK(value.Is8Bit() && value.ContainsOnlyASCII());
+
+  IDBValueWrapper::WriteVarint(value.length(), output);
+  output.Append(value.Characters8(), value.length());
+}
+
+bool IDBValueWrapper::WrapIfBiggerThan(unsigned max_bytes) {
+#if DCHECK_IS_ON()
+  DCHECK(!had_exception_)
+      << "WrapIfBiggerThan() called on wrapper with serialization exception";
+  DCHECK(!wrap_called_)
+      << "WrapIfBiggerThan() called twice on the same wrapper";
+  wrap_called_ = true;
+#endif  // DCHECK_IS_ON()
+
+  serialized_value_->ToWireBytes(wire_bytes_);
+  if (wire_bytes_.size() <= max_bytes)

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

Check the accessible buffer instead of wire bytes, before serializing to wire
bytes. Then we don't have to do that for every value :P

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

I still need to serialize, even if no wrapping happens. ExtractWireBytes() is
called unconditionally, and it needs to return what gets written to LevelDB.

I copied & adapted some of the CL's commit message to the IDBValueWrapper class
docs. Does this help clarify things?

+    return false;
+
+  // TODO(pwnall): The MIME type should probably be an atomic string.
+  String mime_type(kWrapMimeType);
+  Blob* wrapper =

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

Add a TODO & bug to use CreateBuilder in WebBlobRegistry
https://cs.chromium.org/chromium/src/third_party/WebKit/public/platform/WebBl...

To create the blob, as this does another memcpy.

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

Done.

+      Blob::Create(reinterpret_cast<unsigned char*>(wire_bytes_.data()),
+                   wire_bytes_.size(), mime_type);
+
+  wrapper_handle_ = std::move(wrapper->GetBlobDataHandle());

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

Do we need this to be a separate handle? Can we just add this to blob_info_?

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

IIUC, WebBlobInfo is a struct that wraps the fields that I'm passing in here. It
doesn't manage a browser-side reference to the Blob, like BlobDataHandle does.
So I need to hang onto the BlobDataHandle here and return it in
ExtractBlobDataHandles(), so IDBObjectStore::put() can pass it to the backend.

+  blob_info_.emplace_back(wrapper_handle_->Uuid(), wrapper_handle_->GetType(),
+                          wrapper->size());
+
+  wire_bytes_.clear();
+
+  // Version 17 of SSV always writes a V8 envelope after the Blink envelope, so
+  // its output starts with 0xFF 0x11 0xFF. Therefore, we can use 0xFF 0x11 0xvv
+  // as an escape prefix, for 0x00 <= 0xvv < 0xFF.
+  wire_bytes_.push_back(kVersionTag);
+  wire_bytes_.push_back(17);
+  wire_bytes_.push_back(1);
+  IDBValueWrapper::WriteVarint(wrapper->size(), wire_bytes_);
+  IDBValueWrapper::WriteAsciiString(wrapper->Uuid(), wire_bytes_);
+  return true;
+}
+
+void IDBValueWrapper::ExtractBlobDataHandles(
+    Vector<RefPtr<BlobDataHandle>>* blob_data_handles) {
+  for (const auto& kvp : serialized_value_->BlobDataHandles())
+    blob_data_handles->push_back(kvp.value);
+  if (wrapper_handle_)
+    blob_data_handles->push_back(std::move(wrapper_handle_));
+}
+
+PassRefPtr<SharedBuffer> IDBValueWrapper::ExtractWireBytes() {
+#if DCHECK_IS_ON()
+  DCHECK(!had_exception_)
+      << "ExtractWireBytes() called on wrapper with serialization exception";
+#endif  // DCHECK_IS_ON()
+
+  return SharedBuffer::AdoptVector(wire_bytes_);
+}
+
+}  // namespace blink