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/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*-
* vim: set ts=8 sts=2 et sw=2 tw=80:
* This Source Code Form is subject to the terms of the Mozilla Public
* License, v. 2.0. If a copy of the MPL was not distributed with this
* file, You can obtain one at */
#ifndef js_StructuredClone_h
#define js_StructuredClone_h
#include "mozilla/Attributes.h"
#include "mozilla/BufferList.h"
#include "mozilla/MemoryReporting.h"
#include <stdint.h>
#include <utility>
#include "jstypes.h"
#include "js/AllocPolicy.h"
#include "js/RootingAPI.h"
#include "js/TypeDecls.h"
#include "js/Value.h"
#include "js/Vector.h"
* API for safe passing of structured data, HTML 2018 Feb 21 section 2.7.
* This is a serialization scheme for JS values, somewhat like JSON. It
* preserves some aspects of JS objects (strings, numbers, own data properties
* with string keys, array elements) but not others (methods, getters and
* setters, prototype chains). Unlike JSON, structured data:
* - can contain cyclic references.
* - handles Maps, Sets, and some other object types.
* - supports *transferring* objects of certain types from one realm to
* another, rather than cloning them.
* - is specified by a living standard, and continues to evolve.
* - is encoded in a nonstandard binary format, and is never exposed to Web
* content in its serialized form. It's used internally by the browser to
* send data from one thread/realm/domain to another, not across the
* network.
struct JSStructuredCloneReader;
struct JSStructuredCloneWriter;
* The structured-clone serialization format version number.
* When serialized data is stored as bytes, e.g. in your Firefox profile, later
* versions of the engine may have to read it. When you upgrade Firefox, we
* don't crawl through your whole profile converting all saved data from the
* previous version of the serialization format to the latest version. So it is
* normal to have data in old formats stored in your profile.
* The JS engine can *write* data only in the current format version.
* It can *read* any data written in the current version, and data written for
* DifferentProcess scope in earlier versions.
* ## When to bump this version number
* When making a change so drastic that the JS engine needs to know whether
* it's reading old or new serialized data in order to handle both correctly,
* increment this version number. Make sure the engine can still read all
* old data written with previous versions.
* If StructuredClone.cpp doesn't contain code that distinguishes between
* version 8 and version 9, there should not be a version 9.
* Do not increment for changes that only affect SameProcess encoding.
* Increment only for changes that would otherwise break old serialized data.
* Do not increment for new data types. (Rationale: Modulo bugs, older versions
* of the JS engine can already correctly throw errors when they encounter new,
* unrecognized features. A version number bump does not actually help them.)
namespace JS {
* Indicates the "scope of validity" of serialized data.
* Writing plain JS data produces an array of bytes that can be copied and
* read in another process or whatever. The serialized data is Plain Old Data.
* However, HTML also supports `Transferable` objects, which, when cloned, can
* be moved from the source object into the clone, like when you take a
* photograph of someone and it steals their soul.
* We support cloning and transferring objects of many types.
* For example, when we transfer an ArrayBuffer (within a process), we "detach"
* the ArrayBuffer, embed the raw buffer pointer in the serialized data, and
* later install it in a new ArrayBuffer in the destination realm. Ownership
* of that buffer memory is transferred from the original ArrayBuffer to the
* serialized data and then to the clone.
* This only makes sense within a single address space. When we transfer an
* ArrayBuffer to another process, the contents of the buffer must be copied
* into the serialized data. (The original ArrayBuffer is still detached,
* though, for consistency; in some cases the caller shouldn't know or care if
* the recipient is in the same process.)
* ArrayBuffers are actually a lucky case; some objects (like MessagePorts)
* can't reasonably be stored by value in serialized data -- it's pointers or
* nothing.
* So there is a tradeoff between scope of validity -- how far away the
* serialized data may be sent and still make sense -- and efficiency or
* features. The read and write algorithms therefore take an argument of this
* type, allowing the user to control those trade-offs.
enum class StructuredCloneScope : uint32_t {
* The most restrictive scope, with greatest efficiency and features.
* When writing, this means: The caller promises that the serialized data
* will **not** be shipped off to a different process or stored in a
* database. However, it may be shipped to another thread. It's OK to
* produce serialized data that contains pointers to data that is safe to
* send across threads, such as array buffers. In Rust terms, the
* serialized data will be treated as `Send` but not `Copy`.
* When reading, this means: Accept transferred objects and buffers
* (pointers). The caller promises that the serialized data was written
* using this API (otherwise, the serialized data may contain bogus
* pointers, leading to undefined behavior).
* Starts from 1 because there used to be a SameProcessSameThread enum value
* of 0 and these values are encoded into the structured serialization format
* as part of the SCTAG_HEADER, and IndexedDB persists the representation to
* disk.
SameProcess = 1,
* When writing, this means we're writing for an audience in a different
* process. Produce serialized data that can be sent to other processes,
* bitwise copied, or even stored as bytes in a database and read by later
* versions of Firefox years from now. The HTML5 spec refers to this as
* "ForStorage" as in StructuredSerializeForStorage, though we use
* DifferentProcess for IPC as well as storage.
* Transferable objects are limited to ArrayBuffers, whose contents are
* copied into the serialized data (rather than just writing a pointer).
* When reading, this means: Do not accept pointers.
* Handle a backwards-compatibility case with IndexedDB (bug 1434308): when
* reading, this means to treat legacy SameProcess data as if it were
* DifferentProcess.
* Do not use this for writing; use DifferentProcess instead.
* Existing code wants to be able to create an uninitialized
* JSStructuredCloneData without knowing the scope, then populate it with
* data (at which point the scope *is* known.)
* This scope is used when the deserialization context is unknown. When
* writing, DifferentProcess or SameProcess scope is chosen based on the
* nature of the object.
enum TransferableOwnership {
/** Transferable data has not been filled in yet */
/** Structured clone buffer does not yet own the data */
/** All values at least this large are owned by the clone buffer */
/** Data is a pointer that can be freed */
/** Data is a memory mapped pointer */
* Data is embedding-specific. The engine can free it by calling the
* freeTransfer op. The embedding can also use SCTAG_TMO_USER_MIN and
* greater, up to 32 bits, to distinguish specific ownership variants.
class CloneDataPolicy {
bool allowIntraClusterClonableSharedObjects_;
bool allowSharedMemoryObjects_;
// The default is to deny all policy-controlled aspects.
: allowIntraClusterClonableSharedObjects_(false),
allowSharedMemoryObjects_(false) {}
// SharedArrayBuffers and WASM modules can only be cloned intra-process
// because the shared memory areas are allocated in process-private memory or
// because there are security issues of sharing them cross agent clusters.
// y default, we don't allow shared-memory and intra-cluster objects. Clients
// should therefore enable these 2 clone features when needed.
void allowIntraClusterClonableSharedObjects() {
allowIntraClusterClonableSharedObjects_ = true;
bool areIntraClusterClonableSharedObjectsAllowed() const {
return allowIntraClusterClonableSharedObjects_;
void allowSharedMemoryObjects() { allowSharedMemoryObjects_ = true; }
bool areSharedMemoryObjectsAllowed() const {
return allowSharedMemoryObjects_;
} /* namespace JS */
* Read structured data from the reader r. This hook is used to read a value
* previously serialized by a call to the WriteStructuredCloneOp hook.
* tag and data are the pair of uint32_t values from the header. The callback
* may use the JS_Read* APIs to read any other relevant parts of the object
* from the reader r. closure is any value passed to the JS_ReadStructuredClone
* function. Return the new object on success, nullptr on error/exception.
typedef JSObject* (*ReadStructuredCloneOp)(
JSContext* cx, JSStructuredCloneReader* r,
const JS::CloneDataPolicy& cloneDataPolicy, uint32_t tag, uint32_t data,
void* closure);
* Structured data serialization hook. The engine can write primitive values,
* Objects, Arrays, Dates, RegExps, TypedArrays, ArrayBuffers, Sets, Maps,
* and SharedTypedArrays. Any other type of object requires application support.
* This callback must first use the JS_WriteUint32Pair API to write an object
* header, passing a value greater than JS_SCTAG_USER to the tag parameter.
* Then it can use the JS_Write* APIs to write any other relevant parts of
* the value v to the writer w. closure is any value passed to the
* JS_WriteStructuredClone function.
* Return true on success, false on error/exception.
typedef bool (*WriteStructuredCloneOp)(JSContext* cx,
JSStructuredCloneWriter* w,
JS::HandleObject obj,
bool* sameProcessScopeRequired,
void* closure);
* This is called when JS_WriteStructuredClone is given an invalid transferable.
* To follow HTML5, the application must throw a DATA_CLONE_ERR DOMException
* with error set to one of the JS_SCERR_* values.
typedef void (*StructuredCloneErrorOp)(JSContext* cx, uint32_t errorid,
void* closure, const char* errorMessage);
* This is called when JS_ReadStructuredClone receives a transferable object
* not known to the engine. If this hook does not exist or returns false, the
* JS engine calls the reportError op if set, otherwise it throws a
* DATA_CLONE_ERR DOM Exception. This method is called before any other
* callback and must return a non-null object in returnObject on success.
typedef bool (*ReadTransferStructuredCloneOp)(
JSContext* cx, JSStructuredCloneReader* r, uint32_t tag, void* content,
uint64_t extraData, void* closure, JS::MutableHandleObject returnObject);
* Called when JS_WriteStructuredClone receives a transferable object not
* handled by the engine. If this hook does not exist or returns false, the JS
* engine will call the reportError hook or fall back to throwing a
* DATA_CLONE_ERR DOM Exception. This method is called before any other
* callback.
* tag: indicates what type of transferable this is. Must be greater than
* 0xFFFF0201 (value of the internal SCTAG_TRANSFER_MAP_PENDING_ENTRY)
* ownership: see TransferableOwnership, above. Used to communicate any needed
* ownership info to the FreeTransferStructuredCloneOp.
* content, extraData: what the ReadTransferStructuredCloneOp will receive
typedef bool (*TransferStructuredCloneOp)(JSContext* cx,
JS::Handle<JSObject*> obj,
void* closure,
// Output:
uint32_t* tag,
JS::TransferableOwnership* ownership,
void** content, uint64_t* extraData);
* Called when freeing an unknown transferable object. Note that it
* should never trigger a garbage collection (and will assert in a
* debug build if it does.)
typedef void (*FreeTransferStructuredCloneOp)(
uint32_t tag, JS::TransferableOwnership ownership, void* content,
uint64_t extraData, void* closure);
* Called when the transferring objects are checked. If this function returns
* false, the serialization ends throwing a DataCloneError exception.
typedef bool (*CanTransferStructuredCloneOp)(JSContext* cx,
JS::Handle<JSObject*> obj,
bool* sameProcessScopeRequired,
void* closure);
* Called when a SharedArrayBuffer (including one owned by a Wasm memory object)
* has been processed in context `cx` by structured cloning. If `receiving` is
* true then the SAB has been received from a channel and a new SAB object has
* been created; if false then an existing SAB has been serialized onto a
* channel.
* If the callback returns false then the clone operation (read or write) will
* signal a failure.
typedef bool (*SharedArrayBufferClonedOp)(JSContext* cx, bool receiving,
void* closure);
struct JSStructuredCloneCallbacks {
ReadStructuredCloneOp read;
WriteStructuredCloneOp write;
StructuredCloneErrorOp reportError;
ReadTransferStructuredCloneOp readTransfer;
TransferStructuredCloneOp writeTransfer;
FreeTransferStructuredCloneOp freeTransfer;
CanTransferStructuredCloneOp canTransfer;
SharedArrayBufferClonedOp sabCloned;
enum OwnTransferablePolicy {
* The buffer owns any Transferables that it might contain, and should
* properly release them upon destruction.
* Do not free any Transferables within this buffer when deleting it. This
* is used to mark as clone buffer as containing data from another process,
* and so it can't legitimately contain pointers. If the buffer claims to
* have transferables, it's a bug or an attack. This is also used for
* abandon(), where a buffer still contains raw data but the ownership has
* been given over to some other entity.
* A buffer that cannot contain Transferables at all. This usually means
* the buffer is empty (not yet filled in, or having been cleared).
namespace js {
class SharedArrayRawBuffer;
class SharedArrayRawBufferRefs {
SharedArrayRawBufferRefs() = default;
SharedArrayRawBufferRefs(SharedArrayRawBufferRefs&& other) = default;
SharedArrayRawBufferRefs& operator=(SharedArrayRawBufferRefs&& other);
[[nodiscard]] bool acquire(JSContext* cx, SharedArrayRawBuffer* rawbuf);
[[nodiscard]] bool acquireAll(JSContext* cx,
const SharedArrayRawBufferRefs& that);
void takeOwnership(SharedArrayRawBufferRefs&&);
void releaseAll();
js::Vector<js::SharedArrayRawBuffer*, 0, js::SystemAllocPolicy> refs_;
template <typename T, typename AllocPolicy>
struct BufferIterator;
} // namespace js
* JSStructuredCloneData represents structured clone data together with the
* information needed to read/write/transfer/free the records within it, in the
* form of a set of callbacks.
using BufferList = mozilla::BufferList<js::SystemAllocPolicy>;
using Iterator = BufferList::IterImpl;
static const size_t kStandardCapacity = 4096;
BufferList bufList_;
// The (address space, thread) scope within which this clone is valid. Note
// that this must be either set during construction, or start out as
// Unassigned and transition once to something else.
JS::StructuredCloneScope scope_;
const JSStructuredCloneCallbacks* callbacks_ = nullptr;
void* closure_ = nullptr;
OwnTransferablePolicy ownTransferables_ =
js::SharedArrayRawBufferRefs refsHeld_;
friend struct JSStructuredCloneWriter;
friend class JS_PUBLIC_API JSAutoStructuredCloneBuffer;
template <typename T, typename AllocPolicy>
friend struct js::BufferIterator;
// The constructor must be infallible but SystemAllocPolicy is not, so both
// the initial size and initial capacity of the BufferList must be zero.
explicit JSStructuredCloneData(JS::StructuredCloneScope scope)
: bufList_(0, 0, kStandardCapacity, js::SystemAllocPolicy()),
ownTransferables_(OwnTransferablePolicy::NoTransferables) {}
// Steal the raw data from a BufferList. In this case, we don't know the
// scope and none of the callback info is assigned yet.
JSStructuredCloneData(BufferList&& buffers, JS::StructuredCloneScope scope)
: bufList_(std::move(buffers)),
ownTransferables_(OwnTransferablePolicy::NoTransferables) {}
MOZ_IMPLICIT JSStructuredCloneData(BufferList&& buffers)
: JSStructuredCloneData(std::move(buffers),
JS::StructuredCloneScope::Unassigned) {}
JSStructuredCloneData(JSStructuredCloneData&& other) = default;
JSStructuredCloneData& operator=(JSStructuredCloneData&& other) = default;
void setCallbacks(const JSStructuredCloneCallbacks* callbacks, void* closure,
OwnTransferablePolicy policy) {
callbacks_ = callbacks;
closure_ = closure;
ownTransferables_ = policy;
[[nodiscard]] bool Init(size_t initialCapacity = 0) {
return bufList_.Init(0, initialCapacity);
JS::StructuredCloneScope scope() const {
if (scope_ == JS::StructuredCloneScope::UnknownDestination) {
return JS::StructuredCloneScope::DifferentProcess;
return scope_;
void sameProcessScopeRequired() {
if (scope_ == JS::StructuredCloneScope::UnknownDestination) {
scope_ = JS::StructuredCloneScope::SameProcess;
void initScope(JS::StructuredCloneScope newScope) {
MOZ_ASSERT(Size() == 0, "initScope() of nonempty JSStructuredCloneData");
if (scope() != JS::StructuredCloneScope::Unassigned) {
MOZ_ASSERT(scope() == newScope,
"Cannot change scope after it has been initialized");
scope_ = newScope;
size_t Size() const { return bufList_.Size(); }
const Iterator Start() const { return bufList_.Iter(); }
[[nodiscard]] bool Advance(Iterator& iter, size_t distance) const {
return iter.AdvanceAcrossSegments(bufList_, distance);
[[nodiscard]] bool ReadBytes(Iterator& iter, char* buffer,
size_t size) const {
return bufList_.ReadBytes(iter, buffer, size);
// Append new data to the end of the buffer.
[[nodiscard]] bool AppendBytes(const char* data, size_t size) {
MOZ_ASSERT(scope() != JS::StructuredCloneScope::Unassigned);
return bufList_.WriteBytes(data, size);
// Update data stored within the existing buffer. There must be at least
// 'size' bytes between the position of 'iter' and the end of the buffer.
[[nodiscard]] bool UpdateBytes(Iterator& iter, const char* data,
size_t size) const {
MOZ_ASSERT(scope() != JS::StructuredCloneScope::Unassigned);
while (size > 0) {
size_t remaining = iter.RemainingInSegment();
size_t nbytes = std::min(remaining, size);
memcpy(iter.Data(), data, nbytes);
data += nbytes;
size -= nbytes;
iter.Advance(bufList_, nbytes);
return true;
char* AllocateBytes(size_t maxSize, size_t* size) {
return bufList_.AllocateBytes(maxSize, size);
void Clear() {
// Return a new read-only JSStructuredCloneData that "borrows" the contents
// of |this|. Its lifetime should not exceed the donor's. This is only
// allowed for DifferentProcess clones, so finalization of the borrowing
// clone will do nothing.
JSStructuredCloneData Borrow(Iterator& iter, size_t size,
bool* success) const {
MOZ_ASSERT(scope() == JS::StructuredCloneScope::DifferentProcess);
return JSStructuredCloneData(
bufList_.Borrow<js::SystemAllocPolicy>(iter, size, success), scope());
// Iterate over all contained data, one BufferList segment's worth at a
// time, and invoke the given FunctionToApply with the data pointer and
// size. The function should return a bool value, and this loop will exit
// with false if the function ever returns false.
template <typename FunctionToApply>
bool ForEachDataChunk(FunctionToApply&& function) const {
Iterator iter = bufList_.Iter();
while (!iter.Done()) {
if (!function(iter.Data(), iter.RemainingInSegment())) {
return false;
iter.Advance(bufList_, iter.RemainingInSegment());
return true;
// Append the entire contents of other's bufList_ to our own.
[[nodiscard]] bool Append(const JSStructuredCloneData& other) {
MOZ_ASSERT(scope() == other.scope());
return other.ForEachDataChunk(
[&](const char* data, size_t size) { return AppendBytes(data, size); });
size_t SizeOfExcludingThis(mozilla::MallocSizeOf mallocSizeOf) {
return bufList_.SizeOfExcludingThis(mallocSizeOf);
void discardTransferables();
// This internal method exposes the real value of scope_. It's meant to be
// used only when starting the writing.
JS::StructuredCloneScope scopeForInternalWriting() const { return scope_; }
* Implements StructuredDeserialize and StructuredDeserializeWithTransfer.
* Note: If `data` contains transferable objects, it can be read only once.
JS_PUBLIC_API bool JS_ReadStructuredClone(
JSContext* cx, const JSStructuredCloneData& data, uint32_t version,
JS::StructuredCloneScope scope, JS::MutableHandleValue vp,
const JS::CloneDataPolicy& cloneDataPolicy,
const JSStructuredCloneCallbacks* optionalCallbacks, void* closure);
* Implements StructuredSerialize, StructuredSerializeForStorage, and
* StructuredSerializeWithTransfer.
* Note: If the scope is DifferentProcess then the cloneDataPolicy must deny
* shared-memory objects, or an error will be signaled if a shared memory object
* is seen.
JS_PUBLIC_API bool JS_WriteStructuredClone(
JSContext* cx, JS::HandleValue v, JSStructuredCloneData* data,
JS::StructuredCloneScope scope, const JS::CloneDataPolicy& cloneDataPolicy,
const JSStructuredCloneCallbacks* optionalCallbacks, void* closure,
JS::HandleValue transferable);
JS_PUBLIC_API bool JS_StructuredCloneHasTransferables(
JSStructuredCloneData& data, bool* hasTransferable);
JS_PUBLIC_API bool JS_StructuredClone(
JSContext* cx, JS::HandleValue v, JS::MutableHandleValue vp,
const JSStructuredCloneCallbacks* optionalCallbacks, void* closure);
* The C-style API calls to read and write structured clones are fragile --
* they rely on the caller to properly handle ownership of the clone data, and
* the handling of the input data as well as the interpretation of the contents
* of the clone buffer are dependent on the callbacks passed in. If you
* serialize and deserialize with different callbacks, the results are
* questionable.
* JSAutoStructuredCloneBuffer wraps things up in an RAII class for data
* management, and uses the same callbacks for both writing and reading
* (serializing and deserializing).
class JS_PUBLIC_API JSAutoStructuredCloneBuffer {
JSStructuredCloneData data_;
uint32_t version_;
JSAutoStructuredCloneBuffer(JS::StructuredCloneScope scope,
const JSStructuredCloneCallbacks* callbacks,
void* closure)
: data_(scope), version_(JS_STRUCTURED_CLONE_VERSION) {
data_.setCallbacks(callbacks, closure,
JSAutoStructuredCloneBuffer(JSAutoStructuredCloneBuffer&& other);
JSAutoStructuredCloneBuffer& operator=(JSAutoStructuredCloneBuffer&& other);
~JSAutoStructuredCloneBuffer() { clear(); }
JSStructuredCloneData& data() { return data_; }
bool empty() const { return !data_.Size(); }
void clear();
JS::StructuredCloneScope scope() const { return data_.scope(); }
* Adopt some memory. It will be automatically freed by the destructor.
* data must have been allocated by the JS engine (e.g., extracted via
* JSAutoStructuredCloneBuffer::steal).
void adopt(JSStructuredCloneData&& data,
const JSStructuredCloneCallbacks* callbacks = nullptr,
void* closure = nullptr);
* Release the buffer and transfer ownership to the caller.
void steal(JSStructuredCloneData* data, uint32_t* versionp = nullptr,
const JSStructuredCloneCallbacks** callbacks = nullptr,
void** closure = nullptr);
* Abandon ownership of any transferable objects stored in the buffer,
* without freeing the buffer itself. Useful when copying the data out into
* an external container, though note that you will need to use adopt() to
* properly release that data eventually.
void abandon() {
data_.ownTransferables_ = OwnTransferablePolicy::IgnoreTransferablesIfAny;
bool read(JSContext* cx, JS::MutableHandleValue vp,
const JS::CloneDataPolicy& cloneDataPolicy = JS::CloneDataPolicy(),
const JSStructuredCloneCallbacks* optionalCallbacks = nullptr,
void* closure = nullptr);
bool write(JSContext* cx, JS::HandleValue v,
const JSStructuredCloneCallbacks* optionalCallbacks = nullptr,
void* closure = nullptr);
bool write(JSContext* cx, JS::HandleValue v, JS::HandleValue transferable,
const JS::CloneDataPolicy& cloneDataPolicy,
const JSStructuredCloneCallbacks* optionalCallbacks = nullptr,
void* closure = nullptr);
size_t sizeOfExcludingThis(mozilla::MallocSizeOf mallocSizeOf) {
return data_.SizeOfExcludingThis(mallocSizeOf);
size_t sizeOfIncludingThis(mozilla::MallocSizeOf mallocSizeOf) {
return mallocSizeOf(this) + sizeOfExcludingThis(mallocSizeOf);
// Copy and assignment are not supported.
JSAutoStructuredCloneBuffer(const JSAutoStructuredCloneBuffer& other) =
JSAutoStructuredCloneBuffer& operator=(
const JSAutoStructuredCloneBuffer& other) = delete;
// The range of tag values the application may use for its own custom object
// types.
#define JS_SCTAG_USER_MIN ((uint32_t)0xFFFF8000)
#define JS_SCTAG_USER_MAX ((uint32_t)0xFFFFFFFF)
JS_PUBLIC_API bool JS_ReadUint32Pair(JSStructuredCloneReader* r, uint32_t* p1,
uint32_t* p2);
JS_PUBLIC_API bool JS_ReadBytes(JSStructuredCloneReader* r, void* p,
size_t len);
JS_PUBLIC_API bool JS_ReadTypedArray(JSStructuredCloneReader* r,
JS::MutableHandleValue vp);
JS_PUBLIC_API bool JS_WriteUint32Pair(JSStructuredCloneWriter* w, uint32_t tag,
uint32_t data);
JS_PUBLIC_API bool JS_WriteBytes(JSStructuredCloneWriter* w, const void* p,
size_t len);
JS_PUBLIC_API bool JS_WriteString(JSStructuredCloneWriter* w,
JS::HandleString str);
JS_PUBLIC_API bool JS_WriteTypedArray(JSStructuredCloneWriter* w,
JS::HandleValue v);
JS_PUBLIC_API bool JS_ObjectNotWritten(JSStructuredCloneWriter* w,
JS::HandleObject obj);
JS_PUBLIC_API JS::StructuredCloneScope JS_GetStructuredCloneScope(
JSStructuredCloneWriter* w);
#endif /* js_StructuredClone_h */