Wrap large IndexedDB values into Blobs before writing to LevelDB.

third_party/WebKit/Source/modules/indexeddb/IDBValueWrapping.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/IDBValueWrapping.h"
+
+#include <utility>
+
+#include "bindings/core/v8/ScriptValue.h"
+#include "bindings/core/v8/serialization/SerializationTag.h"
+#include "bindings/modules/v8/V8BindingForModules.h"
+#include "core/fileapi/Blob.h"
+#include "modules/indexeddb/IDBRequest.h"
+#include "modules/indexeddb/IDBValue.h"
+#include "platform/blob/BlobData.h"
+#include "platform/wtf/text/WTFString.h"
+
+namespace blink {
+
+namespace {
+
+// V8 values are stored on disk by IndexedDB using the format implemented in
+// SerializedScriptValue (SSV). The wrapping detection logic in
+// IDBValueUnwrapper::IsWrapped() must be able to distinguish between SSV byte
+// sequences produced and byte sequences expressing the fact that an IDBValue
+// has been wrapped and requires post-processing.
+//
+// The detection logic takes advantage of the highly regular structure around
+// SerializedScriptValue. A version 17 byte sequence always starts with the
+// following four bytes:
+//
+// 1) 0xFF - kVersionTag
+// 2) 0x11 - Blink wrapper version, 17
+// 3) 0xFF - kVersionTag
+// 4) 0x0D - V8 serialization version, currently 13, doesn't matter
+//
+// It follows that SSV will never produce byte sequences starting with 0xFF,
+// 0x11, and any value except for 0xFF. If the SSV format changes, the version
+// will have to be bumped.
+
+// The SSV format version whose encoding hole is (ab)used for wrapping.
+const static uint8_t kRequiresProcessingSSVPseudoVersion = 17;
+
+// Identifies IndexedDB values that were wrapped in Blobs. The wrapper has the
+// following format:
+//
+// 1) 0xFF - kVersionTag
+// 2) 0x11 - kRequiresProcessingSSVPseudoVersion
+// 3) 0x01 - kBlobWrappedValue
+// 4) varint - Blob size
+// 5) varint - the offset of the SSV-wrapping Blob in the IDBValue list of Blobs
+//             (should always be the last Blob)
+const static uint8_t kBlobWrappedValue = 1;
+
+}  // namespace
+
+IDBValueWrapper::IDBValueWrapper(
+    v8::Isolate* isolate,
+    v8::Local<v8::Value> value,
+    SerializedScriptValue::SerializeOptions::WasmSerializationPolicy
+        wasm_policy,
+    ExceptionState& exception_state) {
+  SerializedScriptValue::SerializeOptions options;
+  options.blob_info = &blob_info_;
+  options.for_storage = SerializedScriptValue::kForStorage;
+  options.wasm_policy = wasm_policy;
+
+  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_) << __FUNCTION__
+                          << " 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;
+}
+
+bool IDBValueWrapper::WrapIfBiggerThan(unsigned max_bytes) {
+#if DCHECK_IS_ON()
+  DCHECK(!had_exception_) << __FUNCTION__
+                          << " called on wrapper with serialization exception";
+  DCHECK(!wrap_called_) << __FUNCTION__ << " called twice on the same wrapper";
+  wrap_called_ = true;
+#endif  // DCHECK_IS_ON()
+
+  serialized_value_->ToWireBytes(wire_bytes_);
+  if (wire_bytes_.size() <= max_bytes)
+    return false;
+
+  // TODO(pwnall): The MIME type should probably be an atomic string.
+  String mime_type(kWrapMimeType);
+  // TODO(crbug.com/721516): Use WebBlobRegistry::CreateBuilder instead of
+  //                         Blob::Create to avoid a buffer copy.
+  Blob* wrapper =
+      Blob::Create(reinterpret_cast<unsigned char*>(wire_bytes_.data()),
+                   wire_bytes_.size(), mime_type);
+
+  wrapper_handle_ = wrapper->GetBlobDataHandle();
+  blob_info_.emplace_back(wrapper_handle_->Uuid(), wrapper_handle_->GetType(),
+                          wrapper->size());
+
+  wire_bytes_.clear();
+
+  wire_bytes_.push_back(kVersionTag);
+  wire_bytes_.push_back(kRequiresProcessingSSVPseudoVersion);
+  wire_bytes_.push_back(kBlobWrappedValue);
+  IDBValueWrapper::WriteVarint(wrapper->size(), wire_bytes_);
+  IDBValueWrapper::WriteVarint(serialized_value_->BlobDataHandles().size(),
+                               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_));
+}
+
+RefPtr<SharedBuffer> IDBValueWrapper::ExtractWireBytes() {
+#if DCHECK_IS_ON()
+  DCHECK(!had_exception_) << __FUNCTION__
+                          << " called on wrapper with serialization exception";
+#endif  // DCHECK_IS_ON()
+
+  return SharedBuffer::AdoptVector(wire_bytes_);
+}
+
+IDBValueUnwrapper::IDBValueUnwrapper() {
+  Reset();
+}
+
+bool IDBValueUnwrapper::IsWrapped(IDBValue* value) {
+  DCHECK(value);
+
+  uint8_t header[3];
+  if (!value->data_ || value->data_->size() < sizeof(header))
+    return false;
+
+  value->data_->GetPartAsBytes(header, static_cast<size_t>(0), sizeof(header));
+  return header[0] == kVersionTag &&
+         header[1] == kRequiresProcessingSSVPseudoVersion &&
+         header[2] == kBlobWrappedValue;
+}
+
+bool IDBValueUnwrapper::IsWrapped(const Vector<RefPtr<IDBValue>>& values) {
+  for (const auto& value : values) {
+    if (IsWrapped(value.Get()))
+      return true;
+  }
+  return false;
+}
+
+RefPtr<IDBValue> IDBValueUnwrapper::Unwrap(
+    IDBValue* wrapped_value,
+    RefPtr<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 IDBValue::Create(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;
+
+  if (!ReadVarint(blob_size_))
+    return Reset();
+
+  unsigned blob_offset;
+  if (!ReadVarint(blob_offset))
+    return Reset();
+
+  size_t value_blob_count = value->blob_data_->size();
+  if (!value_blob_count || blob_offset != value_blob_count - 1)
+    return Reset();
+
+  blob_handle_ = value->blob_data_->back();
+  if (blob_handle_->size() != blob_size_)
+    return Reset();
+
+  return true;
+}
+
+RefPtr<BlobDataHandle> IDBValueUnwrapper::WrapperBlobHandle() {
+  DCHECK(blob_handle_);
+
+  return std::move(blob_handle_);
+}
+
+bool IDBValueUnwrapper::ReadVarint(unsigned& value) {
+  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;
+}
+
+}  // namespace blink