Add m-esr52 at 52.6.0

1 files changed, 1368 insertions, 0 deletions

diff --git a/dom/base/StructuredCloneHolder.cpp b/dom/base/StructuredCloneHolder.cpp
new file mode 100644
index 0000000000..1c27c632e0
--- /dev/null
+++ b/dom/base/StructuredCloneHolder.cpp
@@ -0,0 +1,1368 @@
+/* -*- 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 http://mozilla.org/MPL/2.0/. */
+
+#include "StructuredCloneHolder.h"
+
+#include "ImageContainer.h"
+#include "mozilla/AutoRestore.h"
+#include "mozilla/dom/BlobBinding.h"
+#include "mozilla/dom/CryptoKey.h"
+#include "mozilla/dom/Directory.h"
+#include "mozilla/dom/DirectoryBinding.h"
+#include "mozilla/dom/File.h"
+#include "mozilla/dom/FileList.h"
+#include "mozilla/dom/FileListBinding.h"
+#include "mozilla/dom/FormData.h"
+#include "mozilla/dom/ImageBitmap.h"
+#include "mozilla/dom/ImageBitmapBinding.h"
+#include "mozilla/dom/ImageData.h"
+#include "mozilla/dom/ImageDataBinding.h"
+#include "mozilla/dom/ipc/BlobChild.h"
+#include "mozilla/dom/StructuredClone.h"
+#include "mozilla/dom/MessagePort.h"
+#include "mozilla/dom/MessagePortBinding.h"
+#include "mozilla/dom/OffscreenCanvas.h"
+#include "mozilla/dom/OffscreenCanvasBinding.h"
+#include "mozilla/dom/PMessagePort.h"
+#include "mozilla/dom/StructuredCloneTags.h"
+#include "mozilla/dom/SubtleCryptoBinding.h"
+#include "mozilla/dom/ToJSValue.h"
+#include "mozilla/dom/URLSearchParams.h"
+#include "mozilla/dom/URLSearchParamsBinding.h"
+#include "mozilla/dom/WebCryptoCommon.h"
+#include "mozilla/gfx/2D.h"
+#include "mozilla/ipc/BackgroundChild.h"
+#include "mozilla/ipc/BackgroundUtils.h"
+#include "mozilla/ipc/PBackgroundSharedTypes.h"
+#include "MultipartBlobImpl.h"
+#include "nsIRemoteBlob.h"
+#include "nsQueryObject.h"
+
+#ifdef MOZ_WEBRTC
+#include "mozilla/dom/RTCCertificate.h"
+#include "mozilla/dom/RTCCertificateBinding.h"
+#endif
+
+using namespace mozilla::ipc;
+
+namespace mozilla {
+namespace dom {
+
+namespace {
+
+JSObject*
+StructuredCloneCallbacksRead(JSContext* aCx,
+                             JSStructuredCloneReader* aReader,
+                             uint32_t aTag, uint32_t aIndex,
+                             void* aClosure)
+{
+  StructuredCloneHolderBase* holder =
+    static_cast<StructuredCloneHolderBase*>(aClosure);
+  MOZ_ASSERT(holder);
+  return holder->CustomReadHandler(aCx, aReader, aTag, aIndex);
+}
+
+bool
+StructuredCloneCallbacksWrite(JSContext* aCx,
+                              JSStructuredCloneWriter* aWriter,
+                              JS::Handle<JSObject*> aObj,
+                              void* aClosure)
+{
+  StructuredCloneHolderBase* holder =
+    static_cast<StructuredCloneHolderBase*>(aClosure);
+  MOZ_ASSERT(holder);
+  return holder->CustomWriteHandler(aCx, aWriter, aObj);
+}
+
+bool
+StructuredCloneCallbacksReadTransfer(JSContext* aCx,
+                                     JSStructuredCloneReader* aReader,
+                                     uint32_t aTag,
+                                     void* aContent,
+                                     uint64_t aExtraData,
+                                     void* aClosure,
+                                     JS::MutableHandleObject aReturnObject)
+{
+  StructuredCloneHolderBase* holder =
+    static_cast<StructuredCloneHolderBase*>(aClosure);
+  MOZ_ASSERT(holder);
+  return holder->CustomReadTransferHandler(aCx, aReader, aTag, aContent,
+                                           aExtraData, aReturnObject);
+}
+
+bool
+StructuredCloneCallbacksWriteTransfer(JSContext* aCx,
+                                      JS::Handle<JSObject*> aObj,
+                                      void* aClosure,
+                                      // Output:
+                                      uint32_t* aTag,
+                                      JS::TransferableOwnership* aOwnership,
+                                      void** aContent,
+                                      uint64_t* aExtraData)
+{
+  StructuredCloneHolderBase* holder =
+    static_cast<StructuredCloneHolderBase*>(aClosure);
+  MOZ_ASSERT(holder);
+  return holder->CustomWriteTransferHandler(aCx, aObj, aTag, aOwnership,
+                                            aContent, aExtraData);
+}
+
+void
+StructuredCloneCallbacksFreeTransfer(uint32_t aTag,
+                                     JS::TransferableOwnership aOwnership,
+                                     void* aContent,
+                                     uint64_t aExtraData,
+                                     void* aClosure)
+{
+  StructuredCloneHolderBase* holder =
+    static_cast<StructuredCloneHolderBase*>(aClosure);
+  MOZ_ASSERT(holder);
+  return holder->CustomFreeTransferHandler(aTag, aOwnership, aContent,
+                                           aExtraData);
+}
+
+void
+StructuredCloneCallbacksError(JSContext* aCx,
+                              uint32_t aErrorId)
+{
+  NS_WARNING("Failed to clone data.");
+}
+
+} // anonymous namespace
+
+const JSStructuredCloneCallbacks StructuredCloneHolder::sCallbacks = {
+  StructuredCloneCallbacksRead,
+  StructuredCloneCallbacksWrite,
+  StructuredCloneCallbacksError,
+  StructuredCloneCallbacksReadTransfer,
+  StructuredCloneCallbacksWriteTransfer,
+  StructuredCloneCallbacksFreeTransfer
+};
+
+// StructuredCloneHolderBase class
+
+StructuredCloneHolderBase::StructuredCloneHolderBase(StructuredCloneScope aScope)
+  : mStructuredCloneScope(aScope)
+#ifdef DEBUG
+  , mClearCalled(false)
+#endif
+{}
+
+StructuredCloneHolderBase::~StructuredCloneHolderBase()
+{
+#ifdef DEBUG
+  MOZ_ASSERT(mClearCalled);
+#endif
+}
+
+void
+StructuredCloneHolderBase::Clear()
+{
+#ifdef DEBUG
+  mClearCalled = true;
+#endif
+
+  mBuffer = nullptr;
+}
+
+bool
+StructuredCloneHolderBase::Write(JSContext* aCx,
+                                 JS::Handle<JS::Value> aValue)
+{
+  return Write(aCx, aValue, JS::UndefinedHandleValue,
+               JS::CloneDataPolicy().denySharedArrayBuffer());
+}
+
+bool
+StructuredCloneHolderBase::Write(JSContext* aCx,
+                                 JS::Handle<JS::Value> aValue,
+                                 JS::Handle<JS::Value> aTransfer,
+                                 JS::CloneDataPolicy cloneDataPolicy)
+{
+  MOZ_ASSERT(!mBuffer, "Double Write is not allowed");
+  MOZ_ASSERT(!mClearCalled, "This method cannot be called after Clear.");
+
+  mBuffer = MakeUnique<JSAutoStructuredCloneBuffer>(mStructuredCloneScope, &StructuredCloneHolder::sCallbacks, this);
+
+  if (!mBuffer->write(aCx, aValue, aTransfer, cloneDataPolicy,
+                      &StructuredCloneHolder::sCallbacks, this))
+  {
+    mBuffer = nullptr;
+    return false;
+  }
+
+  return true;
+}
+
+bool
+StructuredCloneHolderBase::Read(JSContext* aCx,
+                                JS::MutableHandle<JS::Value> aValue)
+{
+  MOZ_ASSERT(mBuffer, "Read() without Write() is not allowed.");
+  MOZ_ASSERT(!mClearCalled, "This method cannot be called after Clear.");
+
+  bool ok = mBuffer->read(aCx, aValue, &StructuredCloneHolder::sCallbacks, this);
+  return ok;
+}
+
+bool
+StructuredCloneHolderBase::CustomReadTransferHandler(JSContext* aCx,
+                                                     JSStructuredCloneReader* aReader,
+                                                     uint32_t aTag,
+                                                     void* aContent,
+                                                     uint64_t aExtraData,
+                                                     JS::MutableHandleObject aReturnObject)
+{
+  MOZ_CRASH("Nothing to read.");
+  return false;
+}
+
+bool
+StructuredCloneHolderBase::CustomWriteTransferHandler(JSContext* aCx,
+                                                      JS::Handle<JSObject*> aObj,
+                                                      uint32_t* aTag,
+                                                      JS::TransferableOwnership* aOwnership,
+                                                      void** aContent,
+                                                      uint64_t* aExtraData)
+{
+  // No transfers are supported by default.
+  return false;
+}
+
+void
+StructuredCloneHolderBase::CustomFreeTransferHandler(uint32_t aTag,
+                                                     JS::TransferableOwnership aOwnership,
+                                                     void* aContent,
+                                                     uint64_t aExtraData)
+{
+  MOZ_CRASH("Nothing to free.");
+}
+
+// StructuredCloneHolder class
+
+StructuredCloneHolder::StructuredCloneHolder(CloningSupport aSupportsCloning,
+                                             TransferringSupport aSupportsTransferring,
+                                             StructuredCloneScope aScope)
+  : StructuredCloneHolderBase(aScope)
+  , mSupportsCloning(aSupportsCloning == CloningSupported)
+  , mSupportsTransferring(aSupportsTransferring == TransferringSupported)
+  , mParent(nullptr)
+#ifdef DEBUG
+  , mCreationThread(NS_GetCurrentThread())
+#endif
+{}
+
+StructuredCloneHolder::~StructuredCloneHolder()
+{
+  Clear();
+  MOZ_ASSERT(mTransferredPorts.IsEmpty());
+}
+
+void
+StructuredCloneHolder::Write(JSContext* aCx,
+                             JS::Handle<JS::Value> aValue,
+                             ErrorResult& aRv)
+{
+  Write(aCx, aValue, JS::UndefinedHandleValue,
+        JS::CloneDataPolicy().denySharedArrayBuffer(), aRv);
+}
+
+void
+StructuredCloneHolder::Write(JSContext* aCx,
+                             JS::Handle<JS::Value> aValue,
+                             JS::Handle<JS::Value> aTransfer,
+                             JS::CloneDataPolicy cloneDataPolicy,
+                             ErrorResult& aRv)
+{
+  MOZ_ASSERT_IF(mStructuredCloneScope == StructuredCloneScope::SameProcessSameThread,
+                mCreationThread == NS_GetCurrentThread());
+
+  if (!StructuredCloneHolderBase::Write(aCx, aValue, aTransfer, cloneDataPolicy)) {
+    aRv.Throw(NS_ERROR_DOM_DATA_CLONE_ERR);
+    return;
+  }
+}
+
+void
+StructuredCloneHolder::Read(nsISupports* aParent,
+                            JSContext* aCx,
+                            JS::MutableHandle<JS::Value> aValue,
+                            ErrorResult& aRv)
+{
+  MOZ_ASSERT_IF(mStructuredCloneScope == StructuredCloneScope::SameProcessSameThread,
+                mCreationThread == NS_GetCurrentThread());
+  MOZ_ASSERT(aParent);
+
+  mozilla::AutoRestore<nsISupports*> guard(mParent);
+  mParent = aParent;
+
+  if (!StructuredCloneHolderBase::Read(aCx, aValue)) {
+    JS_ClearPendingException(aCx);
+    aRv.Throw(NS_ERROR_DOM_DATA_CLONE_ERR);
+  }
+
+  // If we are tranferring something, we cannot call 'Read()' more than once.
+  if (mSupportsTransferring) {
+    mBlobImplArray.Clear();
+    mClonedSurfaces.Clear();
+    Clear();
+  }
+}
+
+void
+StructuredCloneHolder::ReadFromBuffer(nsISupports* aParent,
+                                      JSContext* aCx,
+                                      JSStructuredCloneData& aBuffer,
+                                      JS::MutableHandle<JS::Value> aValue,
+                                      ErrorResult& aRv)
+{
+  ReadFromBuffer(aParent, aCx, aBuffer,
+                 JS_STRUCTURED_CLONE_VERSION, aValue, aRv);
+}
+
+void
+StructuredCloneHolder::ReadFromBuffer(nsISupports* aParent,
+                                      JSContext* aCx,
+                                      JSStructuredCloneData& aBuffer,
+                                      uint32_t aAlgorithmVersion,
+                                      JS::MutableHandle<JS::Value> aValue,
+                                      ErrorResult& aRv)
+{
+  MOZ_ASSERT_IF(mStructuredCloneScope == StructuredCloneScope::SameProcessSameThread,
+                mCreationThread == NS_GetCurrentThread());
+
+  MOZ_ASSERT(!mBuffer, "ReadFromBuffer() must be called without a Write().");
+
+  mozilla::AutoRestore<nsISupports*> guard(mParent);
+  mParent = aParent;
+
+  if (!JS_ReadStructuredClone(aCx, aBuffer, aAlgorithmVersion,
+                              mStructuredCloneScope, aValue, &sCallbacks,
+                              this)) {
+    JS_ClearPendingException(aCx);
+    aRv.Throw(NS_ERROR_DOM_DATA_CLONE_ERR);
+  }
+}
+
+/* static */ JSObject*
+StructuredCloneHolder::ReadFullySerializableObjects(JSContext* aCx,
+                                                    JSStructuredCloneReader* aReader,
+                                                    uint32_t aTag)
+{
+  if (aTag == SCTAG_DOM_IMAGEDATA) {
+    return ReadStructuredCloneImageData(aCx, aReader);
+  }
+
+  if (aTag == SCTAG_DOM_WEBCRYPTO_KEY || aTag == SCTAG_DOM_URLSEARCHPARAMS) {
+    nsIGlobalObject *global = xpc::NativeGlobal(JS::CurrentGlobalOrNull(aCx));
+    if (!global) {
+      return nullptr;
+    }
+
+    // Prevent the return value from being trashed by a GC during ~nsRefPtr.
+    JS::Rooted<JSObject*> result(aCx);
+    {
+      if (aTag == SCTAG_DOM_WEBCRYPTO_KEY) {
+        RefPtr<CryptoKey> key = new CryptoKey(global);
+        if (!key->ReadStructuredClone(aReader)) {
+         result = nullptr;
+        } else {
+          result = key->WrapObject(aCx, nullptr);
+        }
+      } else if (aTag == SCTAG_DOM_URLSEARCHPARAMS) {
+        RefPtr<URLSearchParams> usp = new URLSearchParams(global);
+       if (!usp->ReadStructuredClone(aReader)) {
+          result = nullptr;
+        } else {
+          result = usp->WrapObject(aCx, nullptr);
+        }
+      }
+    }
+    return result;
+  }
+
+  if (aTag == SCTAG_DOM_NULL_PRINCIPAL ||
+      aTag == SCTAG_DOM_SYSTEM_PRINCIPAL ||
+      aTag == SCTAG_DOM_CONTENT_PRINCIPAL ||
+      aTag == SCTAG_DOM_EXPANDED_PRINCIPAL) {
+    JSPrincipals* prin;
+    if (!nsJSPrincipals::ReadKnownPrincipalType(aCx, aReader, aTag, &prin)) {
+      return nullptr;
+    }
+    // nsJSPrincipals::ReadKnownPrincipalType addrefs for us, but because of the
+    // casting between JSPrincipals* and nsIPrincipal* we can't use
+    // getter_AddRefs above and have to already_AddRefed here.
+    nsCOMPtr<nsIPrincipal> principal = already_AddRefed<nsIPrincipal>(nsJSPrincipals::get(prin));
+
+    JS::RootedValue result(aCx);
+    nsresult rv = nsContentUtils::WrapNative(aCx, principal,
+                                             &NS_GET_IID(nsIPrincipal),
+                                             &result);
+    if (NS_FAILED(rv)) {
+      xpc::Throw(aCx, NS_ERROR_DOM_DATA_CLONE_ERR);
+      return nullptr;
+    }
+
+    return result.toObjectOrNull();
+  }
+
+#ifdef MOZ_WEBRTC
+  if (aTag == SCTAG_DOM_RTC_CERTIFICATE) {
+    if (!NS_IsMainThread()) {
+      return nullptr;
+    }
+
+    nsIGlobalObject *global = xpc::NativeGlobal(JS::CurrentGlobalOrNull(aCx));
+    if (!global) {
+      return nullptr;
+    }
+
+    // Prevent the return value from being trashed by a GC during ~nsRefPtr.
+    JS::Rooted<JSObject*> result(aCx);
+    {
+      RefPtr<RTCCertificate> cert = new RTCCertificate(global);
+      if (!cert->ReadStructuredClone(aReader)) {
+        result = nullptr;
+      } else {
+        result = cert->WrapObject(aCx, nullptr);
+      }
+    }
+    return result;
+  }
+#endif
+
+  // Don't know what this is. Bail.
+  xpc::Throw(aCx, NS_ERROR_DOM_DATA_CLONE_ERR);
+  return nullptr;
+}
+
+/* static */ bool
+StructuredCloneHolder::WriteFullySerializableObjects(JSContext* aCx,
+                                                     JSStructuredCloneWriter* aWriter,
+                                                     JS::Handle<JSObject*> aObj)
+{
+  JS::Rooted<JSObject*> obj(aCx, aObj);
+
+  // See if this is a ImageData object.
+  {
+    ImageData* imageData = nullptr;
+    if (NS_SUCCEEDED(UNWRAP_OBJECT(ImageData, &obj, imageData))) {
+      return WriteStructuredCloneImageData(aCx, aWriter, imageData);
+    }
+  }
+
+  // Handle URLSearchParams cloning
+  {
+    URLSearchParams* usp = nullptr;
+    if (NS_SUCCEEDED(UNWRAP_OBJECT(URLSearchParams, &obj, usp))) {
+      return JS_WriteUint32Pair(aWriter, SCTAG_DOM_URLSEARCHPARAMS, 0) &&
+             usp->WriteStructuredClone(aWriter);
+    }
+  }
+
+  // Handle Key cloning
+  {
+    CryptoKey* key = nullptr;
+    if (NS_SUCCEEDED(UNWRAP_OBJECT(CryptoKey, &obj, key))) {
+      return JS_WriteUint32Pair(aWriter, SCTAG_DOM_WEBCRYPTO_KEY, 0) &&
+             key->WriteStructuredClone(aWriter);
+    }
+  }
+
+#ifdef MOZ_WEBRTC
+  {
+    // Handle WebRTC Certificate cloning
+    RTCCertificate* cert = nullptr;
+    if (NS_SUCCEEDED(UNWRAP_OBJECT(RTCCertificate, &obj, cert))) {
+      MOZ_ASSERT(NS_IsMainThread());
+      return JS_WriteUint32Pair(aWriter, SCTAG_DOM_RTC_CERTIFICATE, 0) &&
+             cert->WriteStructuredClone(aWriter);
+    }
+  }
+#endif
+
+  if (NS_IsMainThread() && xpc::IsReflector(obj)) {
+    nsCOMPtr<nsISupports> base = xpc::UnwrapReflectorToISupports(obj);
+    nsCOMPtr<nsIPrincipal> principal = do_QueryInterface(base);
+    if (principal) {
+      auto nsjsprincipals = nsJSPrincipals::get(principal);
+      return nsjsprincipals->write(aCx, aWriter);
+    }
+  }
+
+  // Don't know what this is
+  xpc::Throw(aCx, NS_ERROR_DOM_DATA_CLONE_ERR);
+  return false;
+}
+
+namespace {
+
+// Recursive!
+already_AddRefed<BlobImpl>
+EnsureBlobForBackgroundManager(BlobImpl* aBlobImpl,
+                               PBackgroundChild* aManager,
+                               ErrorResult& aRv)
+{
+  MOZ_ASSERT(aBlobImpl);
+  RefPtr<BlobImpl> blobImpl = aBlobImpl;
+
+  if (!aManager) {
+    aManager = BackgroundChild::GetForCurrentThread();
+    if (!aManager) {
+      return blobImpl.forget();
+    }
+  }
+
+  const nsTArray<RefPtr<BlobImpl>>* subBlobImpls =
+    aBlobImpl->GetSubBlobImpls();
+
+  if (!subBlobImpls || !subBlobImpls->Length()) {
+    if (nsCOMPtr<nsIRemoteBlob> remoteBlob = do_QueryObject(blobImpl)) {
+      // Always make sure we have a blob from an actor we can use on this
+      // thread.
+      BlobChild* blobChild = BlobChild::GetOrCreate(aManager, blobImpl);
+      MOZ_ASSERT(blobChild);
+
+      blobImpl = blobChild->GetBlobImpl();
+      MOZ_ASSERT(blobImpl);
+
+      DebugOnly<bool> isMutable;
+      MOZ_ASSERT(NS_SUCCEEDED(blobImpl->GetMutable(&isMutable)));
+      MOZ_ASSERT(!isMutable);
+    } else {
+      MOZ_ALWAYS_SUCCEEDS(blobImpl->SetMutable(false));
+    }
+
+    return blobImpl.forget();
+  }
+
+  const uint32_t subBlobCount = subBlobImpls->Length();
+  MOZ_ASSERT(subBlobCount);
+
+  nsTArray<RefPtr<BlobImpl>> newSubBlobImpls;
+  newSubBlobImpls.SetLength(subBlobCount);
+
+  bool newBlobImplNeeded = false;
+
+  for (uint32_t index = 0; index < subBlobCount; index++) {
+    const RefPtr<BlobImpl>& subBlobImpl = subBlobImpls->ElementAt(index);
+    MOZ_ASSERT(subBlobImpl);
+
+    RefPtr<BlobImpl>& newSubBlobImpl = newSubBlobImpls[index];
+
+    newSubBlobImpl = EnsureBlobForBackgroundManager(subBlobImpl, aManager, aRv);
+    if (NS_WARN_IF(aRv.Failed())) {
+      return nullptr;
+    }
+
+    MOZ_ASSERT(newSubBlobImpl);
+
+    if (subBlobImpl != newSubBlobImpl) {
+      newBlobImplNeeded = true;
+    }
+  }
+
+  if (newBlobImplNeeded) {
+    nsString contentType;
+    blobImpl->GetType(contentType);
+
+    if (blobImpl->IsFile()) {
+      nsString name;
+      blobImpl->GetName(name);
+
+      blobImpl = MultipartBlobImpl::Create(Move(newSubBlobImpls), name,
+                                           contentType, aRv);
+    } else {
+      blobImpl = MultipartBlobImpl::Create(Move(newSubBlobImpls), contentType, aRv);
+    }
+
+    if (NS_WARN_IF(aRv.Failed())) {
+      return nullptr;
+    }
+
+    MOZ_ALWAYS_SUCCEEDS(blobImpl->SetMutable(false));
+  }
+
+  return blobImpl.forget();
+}
+
+JSObject*
+ReadBlob(JSContext* aCx,
+         uint32_t aIndex,
+         StructuredCloneHolder* aHolder)
+{
+  MOZ_ASSERT(aHolder);
+  MOZ_ASSERT(aIndex < aHolder->BlobImpls().Length());
+  RefPtr<BlobImpl> blobImpl = aHolder->BlobImpls()[aIndex];
+
+  ErrorResult rv;
+  blobImpl = EnsureBlobForBackgroundManager(blobImpl, nullptr, rv);
+  if (NS_WARN_IF(rv.Failed())) {
+    rv.SuppressException();
+    return nullptr;
+  }
+
+  MOZ_ASSERT(blobImpl);
+
+  // RefPtr<File> needs to go out of scope before toObject() is
+  // called because the static analysis thinks dereferencing XPCOM objects
+  // can GC (because in some cases it can!), and a return statement with a
+  // JSObject* type means that JSObject* is on the stack as a raw pointer
+  // while destructors are running.
+  JS::Rooted<JS::Value> val(aCx);
+  {
+    RefPtr<Blob> blob = Blob::Create(aHolder->ParentDuringRead(), blobImpl);
+    if (!ToJSValue(aCx, blob, &val)) {
+      return nullptr;
+    }
+  }
+
+  return &val.toObject();
+}
+
+bool
+WriteBlob(JSStructuredCloneWriter* aWriter,
+          Blob* aBlob,
+          StructuredCloneHolder* aHolder)
+{
+  MOZ_ASSERT(aWriter);
+  MOZ_ASSERT(aBlob);
+  MOZ_ASSERT(aHolder);
+
+  if (JS_GetStructuredCloneScope(aWriter) != JS::StructuredCloneScope::SameProcessSameThread &&
+      !aBlob->Impl()->MayBeClonedToOtherThreads()) {
+    return false;
+  }
+
+  ErrorResult rv;
+  RefPtr<BlobImpl> blobImpl =
+    EnsureBlobForBackgroundManager(aBlob->Impl(), nullptr, rv);
+  if (NS_WARN_IF(rv.Failed())) {
+    rv.SuppressException();
+    return false;
+  }
+
+  MOZ_ASSERT(blobImpl);
+
+  MOZ_ALWAYS_SUCCEEDS(blobImpl->SetMutable(false));
+
+  // We store the position of the blobImpl in the array as index.
+  if (JS_WriteUint32Pair(aWriter, SCTAG_DOM_BLOB,
+                         aHolder->BlobImpls().Length())) {
+    aHolder->BlobImpls().AppendElement(blobImpl);
+    return true;
+  }
+
+  return false;
+}
+
+// A directory is serialized as:
+// - pair of ints: SCTAG_DOM_DIRECTORY, path length
+// - path as string
+bool
+WriteDirectory(JSStructuredCloneWriter* aWriter,
+               Directory* aDirectory)
+{
+  MOZ_ASSERT(aWriter);
+  MOZ_ASSERT(aDirectory);
+
+  nsAutoString path;
+  aDirectory->GetFullRealPath(path);
+
+  size_t charSize = sizeof(nsString::char_type);
+  return JS_WriteUint32Pair(aWriter, SCTAG_DOM_DIRECTORY, path.Length()) &&
+         JS_WriteBytes(aWriter, path.get(), path.Length() * charSize);
+}
+
+already_AddRefed<Directory>
+ReadDirectoryInternal(JSStructuredCloneReader* aReader,
+                      uint32_t aPathLength,
+                      StructuredCloneHolder* aHolder)
+{
+  MOZ_ASSERT(aReader);
+  MOZ_ASSERT(aHolder);
+
+  nsAutoString path;
+  path.SetLength(aPathLength);
+  size_t charSize = sizeof(nsString::char_type);
+  if (!JS_ReadBytes(aReader, (void*) path.BeginWriting(),
+                    aPathLength * charSize)) {
+    return nullptr;
+  }
+
+  nsCOMPtr<nsIFile> file;
+  nsresult rv = NS_NewLocalFile(path, true, getter_AddRefs(file));
+  if (NS_WARN_IF(NS_FAILED(rv))) {
+    return nullptr;
+  }
+
+  RefPtr<Directory> directory =
+    Directory::Create(aHolder->ParentDuringRead(), file);
+  return directory.forget();
+}
+
+JSObject*
+ReadDirectory(JSContext* aCx,
+              JSStructuredCloneReader* aReader,
+              uint32_t aPathLength,
+              StructuredCloneHolder* aHolder)
+{
+  MOZ_ASSERT(aCx);
+  MOZ_ASSERT(aReader);
+  MOZ_ASSERT(aHolder);
+
+  // RefPtr<Directory> needs to go out of scope before toObject() is
+  // called because the static analysis thinks dereferencing XPCOM objects
+  // can GC (because in some cases it can!), and a return statement with a
+  // JSObject* type means that JSObject* is on the stack as a raw pointer
+  // while destructors are running.
+  JS::Rooted<JS::Value> val(aCx);
+  {
+    RefPtr<Directory> directory =
+      ReadDirectoryInternal(aReader, aPathLength, aHolder);
+    if (!directory) {
+      return nullptr;
+    }
+
+    if (!ToJSValue(aCx, directory, &val)) {
+      return nullptr;
+    }
+  }
+
+  return &val.toObject();
+}
+
+// Read the WriteFileList for the format.
+JSObject*
+ReadFileList(JSContext* aCx,
+             JSStructuredCloneReader* aReader,
+             uint32_t aCount,
+             StructuredCloneHolder* aHolder)
+{
+  MOZ_ASSERT(aCx);
+  MOZ_ASSERT(aReader);
+
+  JS::Rooted<JS::Value> val(aCx);
+  {
+    RefPtr<FileList> fileList = new FileList(aHolder->ParentDuringRead());
+
+    uint32_t zero, index;
+    // |index| is the index of the first blobImpl.
+    if (!JS_ReadUint32Pair(aReader, &zero, &index)) {
+      return nullptr;
+    }
+
+    MOZ_ASSERT(zero == 0);
+
+    // |aCount| is the number of BlobImpls to use from the |index|.
+    for (uint32_t i = 0; i < aCount; ++i) {
+      uint32_t pos = index + i;
+      MOZ_ASSERT(pos < aHolder->BlobImpls().Length());
+
+      RefPtr<BlobImpl> blobImpl = aHolder->BlobImpls()[pos];
+      MOZ_ASSERT(blobImpl->IsFile());
+
+      ErrorResult rv;
+      blobImpl = EnsureBlobForBackgroundManager(blobImpl, nullptr, rv);
+      if (NS_WARN_IF(rv.Failed())) {
+        rv.SuppressException();
+        return nullptr;
+      }
+
+      MOZ_ASSERT(blobImpl);
+
+      RefPtr<File> file = File::Create(aHolder->ParentDuringRead(), blobImpl);
+      if (!fileList->Append(file)) {
+        return nullptr;
+      }
+    }
+
+    if (!ToJSValue(aCx, fileList, &val)) {
+      return nullptr;
+    }
+  }
+
+  return &val.toObject();
+}
+
+// The format of the FileList serialization is:
+// - pair of ints: SCTAG_DOM_FILELIST, Length of the FileList
+// - pair of ints: 0, The offset of the BlobImpl array
+bool
+WriteFileList(JSStructuredCloneWriter* aWriter,
+              FileList* aFileList,
+              StructuredCloneHolder* aHolder)
+{
+  MOZ_ASSERT(aWriter);
+  MOZ_ASSERT(aFileList);
+  MOZ_ASSERT(aHolder);
+
+  // A FileList is serialized writing the X number of elements and the offset
+  // from mBlobImplArray. The Read will take X elements from mBlobImplArray
+  // starting from the offset.
+  if (!JS_WriteUint32Pair(aWriter, SCTAG_DOM_FILELIST,
+                          aFileList->Length()) ||
+      !JS_WriteUint32Pair(aWriter, 0,
+                          aHolder->BlobImpls().Length())) {
+    return false;
+  }
+
+  ErrorResult rv;
+  nsTArray<RefPtr<BlobImpl>> blobImpls;
+
+  for (uint32_t i = 0; i < aFileList->Length(); ++i) {
+    RefPtr<BlobImpl> blobImpl =
+      EnsureBlobForBackgroundManager(aFileList->Item(i)->Impl(), nullptr, rv);
+    if (NS_WARN_IF(rv.Failed())) {
+      rv.SuppressException();
+      return false;
+    }
+
+    MOZ_ASSERT(blobImpl);
+    blobImpls.AppendElement(blobImpl);
+  }
+
+  aHolder->BlobImpls().AppendElements(blobImpls);
+  return true;
+}
+
+// Read the WriteFormData for the format.
+JSObject*
+ReadFormData(JSContext* aCx,
+             JSStructuredCloneReader* aReader,
+             uint32_t aCount,
+             StructuredCloneHolder* aHolder)
+{
+  MOZ_ASSERT(aCx);
+  MOZ_ASSERT(aReader);
+  MOZ_ASSERT(aHolder);
+
+  // See the serialization of the FormData for the format.
+  JS::Rooted<JS::Value> val(aCx);
+  {
+    RefPtr<FormData> formData =
+      new FormData(aHolder->ParentDuringRead());
+
+    Optional<nsAString> thirdArg;
+    for (uint32_t i = 0; i < aCount; ++i) {
+      nsAutoString name;
+      if (!ReadString(aReader, name)) {
+        return nullptr;
+      }
+
+      uint32_t tag, indexOrLengthOfString;
+      if (!JS_ReadUint32Pair(aReader, &tag, &indexOrLengthOfString)) {
+        return nullptr;
+      }
+
+      if (tag == SCTAG_DOM_BLOB) {
+        MOZ_ASSERT(indexOrLengthOfString < aHolder->BlobImpls().Length());
+
+        RefPtr<BlobImpl> blobImpl =
+          aHolder->BlobImpls()[indexOrLengthOfString];
+
+        ErrorResult rv;
+        blobImpl = EnsureBlobForBackgroundManager(blobImpl, nullptr, rv);
+        if (NS_WARN_IF(rv.Failed())) {
+          rv.SuppressException();
+          return nullptr;
+        }
+
+        MOZ_ASSERT(blobImpl);
+
+        RefPtr<Blob> blob =
+          Blob::Create(aHolder->ParentDuringRead(), blobImpl);
+        MOZ_ASSERT(blob);
+
+        formData->Append(name, *blob, thirdArg, rv);
+        if (NS_WARN_IF(rv.Failed())) {
+          rv.SuppressException();
+          return nullptr;
+        }
+
+      } else if (tag == SCTAG_DOM_DIRECTORY) {
+        RefPtr<Directory> directory =
+          ReadDirectoryInternal(aReader, indexOrLengthOfString, aHolder);
+        if (!directory) {
+          return nullptr;
+        }
+
+        formData->Append(name, directory);
+
+      } else {
+        MOZ_ASSERT(tag == 0);
+
+        nsAutoString value;
+        value.SetLength(indexOrLengthOfString);
+        size_t charSize = sizeof(nsString::char_type);
+        if (!JS_ReadBytes(aReader, (void*) value.BeginWriting(),
+                          indexOrLengthOfString * charSize)) {
+          return nullptr;
+        }
+
+        ErrorResult rv;
+        formData->Append(name, value, rv);
+        if (NS_WARN_IF(rv.Failed())) {
+          rv.SuppressException();
+          return nullptr;
+        }
+      }
+    }
+
+    if (!ToJSValue(aCx, formData, &val)) {
+      return nullptr;
+    }
+  }
+
+  return &val.toObject();
+}
+
+// The format of the FormData serialization is:
+// - pair of ints: SCTAG_DOM_FORMDATA, Length of the FormData elements
+// - for each Element element:
+//   - name string
+//   - if it's a blob:
+//     - pair of ints: SCTAG_DOM_BLOB, index of the BlobImpl in the array
+//       mBlobImplArray.
+//   - if it's a directory (See WriteDirectory):
+//     - pair of ints: SCTAG_DOM_DIRECTORY, path length
+//     - path as string
+//   - else:
+//     - pair of ints: 0, string length
+//     - value string
+bool
+WriteFormData(JSStructuredCloneWriter* aWriter,
+              FormData* aFormData,
+              StructuredCloneHolder* aHolder)
+{
+  MOZ_ASSERT(aWriter);
+  MOZ_ASSERT(aFormData);
+  MOZ_ASSERT(aHolder);
+
+  if (!JS_WriteUint32Pair(aWriter, SCTAG_DOM_FORMDATA,
+                          aFormData->Length())) {
+    return false;
+  }
+
+  class MOZ_STACK_CLASS Closure final
+  {
+    JSStructuredCloneWriter* mWriter;
+    StructuredCloneHolder* mHolder;
+
+  public:
+    Closure(JSStructuredCloneWriter* aWriter,
+            StructuredCloneHolder* aHolder)
+      : mWriter(aWriter),
+        mHolder(aHolder)
+    { }
+
+    static bool
+    Write(const nsString& aName, const OwningBlobOrDirectoryOrUSVString& aValue,
+          void* aClosure)
+    {
+      Closure* closure = static_cast<Closure*>(aClosure);
+      if (!WriteString(closure->mWriter, aName)) {
+        return false;
+      }
+
+      if (aValue.IsBlob()) {
+        ErrorResult rv;
+        RefPtr<BlobImpl> blobImpl =
+          EnsureBlobForBackgroundManager(aValue.GetAsBlob()->Impl(), nullptr,
+                                         rv);
+        if (NS_WARN_IF(rv.Failed())) {
+          rv.SuppressException();
+          return false;
+        }
+
+        if (!JS_WriteUint32Pair(closure->mWriter, SCTAG_DOM_BLOB,
+                                closure->mHolder->BlobImpls().Length())) {
+          return false;
+        }
+
+        closure->mHolder->BlobImpls().AppendElement(blobImpl);
+        return true;
+      }
+
+      if (aValue.IsDirectory()) {
+        Directory* directory = aValue.GetAsDirectory();
+
+        if (closure->mHolder->CloneScope() !=
+              StructuredCloneHolder::StructuredCloneScope::SameProcessSameThread &&
+            !directory->ClonableToDifferentThreadOrProcess()) {
+          return false;
+        }
+
+        return WriteDirectory(closure->mWriter, directory);
+      }
+
+      size_t charSize = sizeof(nsString::char_type);
+      if (!JS_WriteUint32Pair(closure->mWriter, 0,
+                              aValue.GetAsUSVString().Length()) ||
+          !JS_WriteBytes(closure->mWriter, aValue.GetAsUSVString().get(),
+                         aValue.GetAsUSVString().Length() * charSize)) {
+        return false;
+      }
+
+      return true;
+    }
+  };
+  Closure closure(aWriter, aHolder);
+  return aFormData->ForEach(Closure::Write, &closure);
+}
+
+JSObject*
+ReadWasmModule(JSContext* aCx,
+               uint32_t aIndex,
+               StructuredCloneHolder* aHolder)
+{
+  MOZ_ASSERT(aHolder);
+  MOZ_ASSERT(aIndex < aHolder->WasmModules().Length());
+  MOZ_ASSERT(aHolder->CloneScope() == StructuredCloneHolder::StructuredCloneScope::SameProcessSameThread ||
+             aHolder->CloneScope() == StructuredCloneHolder::StructuredCloneScope::SameProcessDifferentThread);
+
+  RefPtr<JS::WasmModule> wasmModule = aHolder->WasmModules()[aIndex];
+  return wasmModule->createObject(aCx);
+}
+
+bool
+WriteWasmModule(JSStructuredCloneWriter* aWriter,
+                JS::WasmModule* aWasmModule,
+                StructuredCloneHolder* aHolder)
+{
+  MOZ_ASSERT(aWriter);
+  MOZ_ASSERT(aWasmModule);
+  MOZ_ASSERT(aHolder);
+  MOZ_ASSERT(aHolder->CloneScope() == StructuredCloneHolder::StructuredCloneScope::SameProcessSameThread ||
+             aHolder->CloneScope() == StructuredCloneHolder::StructuredCloneScope::SameProcessDifferentThread);
+
+  // We store the position of the wasmModule in the array as index.
+  if (JS_WriteUint32Pair(aWriter, SCTAG_DOM_WASM,
+                         aHolder->WasmModules().Length())) {
+    aHolder->WasmModules().AppendElement(aWasmModule);
+    return true;
+  }
+
+  return false;
+}
+
+} // anonymous namespace
+
+JSObject*
+StructuredCloneHolder::CustomReadHandler(JSContext* aCx,
+                                         JSStructuredCloneReader* aReader,
+                                         uint32_t aTag,
+                                         uint32_t aIndex)
+{
+  MOZ_ASSERT(mSupportsCloning);
+
+  if (aTag == SCTAG_DOM_BLOB) {
+    return ReadBlob(aCx, aIndex, this);
+  }
+
+  if (aTag == SCTAG_DOM_DIRECTORY) {
+    return ReadDirectory(aCx, aReader, aIndex, this);
+  }
+
+  if (aTag == SCTAG_DOM_FILELIST) {
+    return ReadFileList(aCx, aReader, aIndex, this);
+  }
+
+  if (aTag == SCTAG_DOM_FORMDATA) {
+    return ReadFormData(aCx, aReader, aIndex, this);
+  }
+
+  if (aTag == SCTAG_DOM_IMAGEBITMAP) {
+    MOZ_ASSERT(mStructuredCloneScope == StructuredCloneScope::SameProcessSameThread ||
+               mStructuredCloneScope == StructuredCloneScope::SameProcessDifferentThread);
+
+    // Get the current global object.
+    // This can be null.
+    nsCOMPtr<nsIGlobalObject> parent = do_QueryInterface(mParent);
+    // aIndex is the index of the cloned image.
+    return ImageBitmap::ReadStructuredClone(aCx, aReader,
+                                            parent, GetSurfaces(), aIndex);
+  }
+
+  if (aTag == SCTAG_DOM_WASM) {
+    return ReadWasmModule(aCx, aIndex, this);
+  }
+
+  return ReadFullySerializableObjects(aCx, aReader, aTag);
+}
+
+bool
+StructuredCloneHolder::CustomWriteHandler(JSContext* aCx,
+                                          JSStructuredCloneWriter* aWriter,
+                                          JS::Handle<JSObject*> aObj)
+{
+  if (!mSupportsCloning) {
+    return false;
+  }
+
+  JS::Rooted<JSObject*> obj(aCx, aObj);
+
+  // See if this is a File/Blob object.
+  {
+    Blob* blob = nullptr;
+    if (NS_SUCCEEDED(UNWRAP_OBJECT(Blob, &obj, blob))) {
+      return WriteBlob(aWriter, blob, this);
+    }
+  }
+
+  // See if this is a Directory object.
+  {
+    Directory* directory = nullptr;
+    if (NS_SUCCEEDED(UNWRAP_OBJECT(Directory, &obj, directory))) {
+      if (mStructuredCloneScope != StructuredCloneScope::SameProcessSameThread &&
+          !directory->ClonableToDifferentThreadOrProcess()) {
+        return false;
+      }
+
+      return WriteDirectory(aWriter, directory);
+    }
+  }
+
+  // See if this is a FileList object.
+  {
+    FileList* fileList = nullptr;
+    if (NS_SUCCEEDED(UNWRAP_OBJECT(FileList, &obj, fileList))) {
+      return WriteFileList(aWriter, fileList, this);
+    }
+  }
+
+  // See if this is a FormData object.
+  {
+    FormData* formData = nullptr;
+    if (NS_SUCCEEDED(UNWRAP_OBJECT(FormData, &obj, formData))) {
+      return WriteFormData(aWriter, formData, this);
+    }
+  }
+
+  // See if this is an ImageBitmap object.
+  if (mStructuredCloneScope == StructuredCloneScope::SameProcessSameThread ||
+      mStructuredCloneScope == StructuredCloneScope::SameProcessDifferentThread) {
+    ImageBitmap* imageBitmap = nullptr;
+    if (NS_SUCCEEDED(UNWRAP_OBJECT(ImageBitmap, &obj, imageBitmap))) {
+      return ImageBitmap::WriteStructuredClone(aWriter,
+                                               GetSurfaces(),
+                                               imageBitmap);
+    }
+  }
+
+  // See if this is a WasmModule.
+  if ((mStructuredCloneScope == StructuredCloneScope::SameProcessSameThread ||
+       mStructuredCloneScope == StructuredCloneScope::SameProcessDifferentThread) &&
+      JS::IsWasmModuleObject(obj)) {
+    RefPtr<JS::WasmModule> module = JS::GetWasmModule(obj);
+    MOZ_ASSERT(module);
+
+    return WriteWasmModule(aWriter, module, this);
+  }
+
+  return WriteFullySerializableObjects(aCx, aWriter, aObj);
+}
+
+bool
+StructuredCloneHolder::CustomReadTransferHandler(JSContext* aCx,
+                                                 JSStructuredCloneReader* aReader,
+                                                 uint32_t aTag,
+                                                 void* aContent,
+                                                 uint64_t aExtraData,
+                                                 JS::MutableHandleObject aReturnObject)
+{
+  MOZ_ASSERT(mSupportsTransferring);
+
+  if (aTag == SCTAG_DOM_MAP_MESSAGEPORT) {
+    MOZ_ASSERT(aExtraData < mPortIdentifiers.Length());
+    const MessagePortIdentifier& portIdentifier = mPortIdentifiers[aExtraData];
+
+    nsCOMPtr<nsIGlobalObject> global = do_QueryInterface(mParent);
+
+    ErrorResult rv;
+    RefPtr<MessagePort> port =
+      MessagePort::Create(global, portIdentifier, rv);
+    if (NS_WARN_IF(rv.Failed())) {
+      rv.SuppressException();
+      return false;
+    }
+
+    mTransferredPorts.AppendElement(port);
+
+    JS::Rooted<JS::Value> value(aCx);
+    if (!GetOrCreateDOMReflector(aCx, port, &value)) {
+      JS_ClearPendingException(aCx);
+      return false;
+    }
+
+    aReturnObject.set(&value.toObject());
+    return true;
+  }
+
+  if (aTag == SCTAG_DOM_CANVAS) {
+    MOZ_ASSERT(mStructuredCloneScope == StructuredCloneScope::SameProcessSameThread ||
+               mStructuredCloneScope == StructuredCloneScope::SameProcessDifferentThread);
+    MOZ_ASSERT(aContent);
+    OffscreenCanvasCloneData* data =
+      static_cast<OffscreenCanvasCloneData*>(aContent);
+    nsCOMPtr<nsIGlobalObject> parent = do_QueryInterface(mParent);
+    RefPtr<OffscreenCanvas> canvas = OffscreenCanvas::CreateFromCloneData(parent, data);
+    delete data;
+
+    JS::Rooted<JS::Value> value(aCx);
+    if (!GetOrCreateDOMReflector(aCx, canvas, &value)) {
+      JS_ClearPendingException(aCx);
+      return false;
+    }
+
+    aReturnObject.set(&value.toObject());
+    return true;
+  }
+
+  if (aTag == SCTAG_DOM_IMAGEBITMAP) {
+    MOZ_ASSERT(mStructuredCloneScope == StructuredCloneScope::SameProcessSameThread ||
+               mStructuredCloneScope == StructuredCloneScope::SameProcessDifferentThread);
+    MOZ_ASSERT(aContent);
+    ImageBitmapCloneData* data =
+      static_cast<ImageBitmapCloneData*>(aContent);
+    nsCOMPtr<nsIGlobalObject> parent = do_QueryInterface(mParent);
+    RefPtr<ImageBitmap> bitmap = ImageBitmap::CreateFromCloneData(parent, data);
+    delete data;
+
+    JS::Rooted<JS::Value> value(aCx);
+    if (!GetOrCreateDOMReflector(aCx, bitmap, &value)) {
+      JS_ClearPendingException(aCx);
+      return false;
+    }
+
+    aReturnObject.set(&value.toObject());
+    return true;
+  }
+
+  return false;
+}
+
+bool
+StructuredCloneHolder::CustomWriteTransferHandler(JSContext* aCx,
+                                                  JS::Handle<JSObject*> aObj,
+                                                  uint32_t* aTag,
+                                                  JS::TransferableOwnership* aOwnership,
+                                                  void** aContent,
+                                                  uint64_t* aExtraData)
+{
+  if (!mSupportsTransferring) {
+    return false;
+  }
+
+  JS::Rooted<JSObject*> obj(aCx, aObj);
+
+  {
+    MessagePort* port = nullptr;
+    nsresult rv = UNWRAP_OBJECT(MessagePort, &obj, port);
+    if (NS_SUCCEEDED(rv)) {
+      // We use aExtraData to store the index of this new port identifier.
+      *aExtraData = mPortIdentifiers.Length();
+      MessagePortIdentifier* identifier = mPortIdentifiers.AppendElement();
+
+      port->CloneAndDisentangle(*identifier);
+
+      *aTag = SCTAG_DOM_MAP_MESSAGEPORT;
+      *aOwnership = JS::SCTAG_TMO_CUSTOM;
+      *aContent = nullptr;
+
+      return true;
+    }
+
+    if (mStructuredCloneScope == StructuredCloneScope::SameProcessSameThread ||
+        mStructuredCloneScope == StructuredCloneScope::SameProcessDifferentThread) {
+      OffscreenCanvas* canvas = nullptr;
+      rv = UNWRAP_OBJECT(OffscreenCanvas, &obj, canvas);
+      if (NS_SUCCEEDED(rv)) {
+        MOZ_ASSERT(canvas);
+
+        *aExtraData = 0;
+        *aTag = SCTAG_DOM_CANVAS;
+        *aOwnership = JS::SCTAG_TMO_CUSTOM;
+        *aContent = canvas->ToCloneData();
+        MOZ_ASSERT(*aContent);
+        canvas->SetNeutered();
+
+        return true;
+      }
+
+      ImageBitmap* bitmap = nullptr;
+      rv = UNWRAP_OBJECT(ImageBitmap, &obj, bitmap);
+      if (NS_SUCCEEDED(rv)) {
+        MOZ_ASSERT(bitmap);
+
+        *aExtraData = 0;
+        *aTag = SCTAG_DOM_IMAGEBITMAP;
+        *aOwnership = JS::SCTAG_TMO_CUSTOM;
+        *aContent = bitmap->ToCloneData().release();
+        MOZ_ASSERT(*aContent);
+        bitmap->Close();
+
+        return true;
+      }
+    }
+  }
+
+  return false;
+}
+
+void
+StructuredCloneHolder::CustomFreeTransferHandler(uint32_t aTag,
+                                                 JS::TransferableOwnership aOwnership,
+                                                 void* aContent,
+                                                 uint64_t aExtraData)
+{
+  MOZ_ASSERT(mSupportsTransferring);
+
+  if (aTag == SCTAG_DOM_MAP_MESSAGEPORT) {
+    MOZ_ASSERT(!aContent);
+    MOZ_ASSERT(aExtraData < mPortIdentifiers.Length());
+    MessagePort::ForceClose(mPortIdentifiers[aExtraData]);
+    return;
+  }
+
+  if (aTag == SCTAG_DOM_CANVAS) {
+    MOZ_ASSERT(mStructuredCloneScope == StructuredCloneScope::SameProcessSameThread ||
+               mStructuredCloneScope == StructuredCloneScope::SameProcessDifferentThread);
+    MOZ_ASSERT(aContent);
+    OffscreenCanvasCloneData* data =
+      static_cast<OffscreenCanvasCloneData*>(aContent);
+    delete data;
+    return;
+  }
+
+  if (aTag == SCTAG_DOM_IMAGEBITMAP) {
+    MOZ_ASSERT(mStructuredCloneScope == StructuredCloneScope::SameProcessSameThread ||
+               mStructuredCloneScope == StructuredCloneScope::SameProcessDifferentThread);
+    MOZ_ASSERT(aContent);
+    ImageBitmapCloneData* data =
+      static_cast<ImageBitmapCloneData*>(aContent);
+    delete data;
+    return;
+  }
+}
+
+bool
+StructuredCloneHolder::TakeTransferredPortsAsSequence(Sequence<OwningNonNull<mozilla::dom::MessagePort>>& aPorts)
+{
+  nsTArray<RefPtr<MessagePort>> ports = TakeTransferredPorts();
+
+  aPorts.Clear();
+  for (uint32_t i = 0, len = ports.Length(); i < len; ++i) {
+    if (!aPorts.AppendElement(ports[i].forget(), fallible)) {
+      return false;
+    }
+  }
+
+  return true;
+}
+
+} // dom namespace
+} // mozilla namespace