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diff --git a/dom/base/StructuredCloneHolder.h b/dom/base/StructuredCloneHolder.h
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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 http://mozilla.org/MPL/2.0/. */
+
+#ifndef mozilla_dom_StructuredCloneHolder_h
+#define mozilla_dom_StructuredCloneHolder_h
+
+#include <cstddef>
+#include <cstdint>
+#include <utility>
+#include "js/StructuredClone.h"
+#include "js/TypeDecls.h"
+#include "mozilla/Assertions.h"
+#include "mozilla/Attributes.h"
+#include "mozilla/MemoryReporting.h"
+#include "mozilla/RefPtr.h"
+#include "mozilla/UniquePtr.h"
+#include "nsCOMPtr.h"
+#include "nsString.h"
+#include "nsTArray.h"
+
+class nsIEventTarget;
+class nsIGlobalObject;
+class nsIInputStream;
+struct JSStructuredCloneReader;
+struct JSStructuredCloneWriter;
+
+namespace JS {
+class Value;
+struct WasmModule;
+}  // namespace JS
+
+namespace mozilla {
+class ErrorResult;
+template <class T>
+class OwningNonNull;
+
+namespace layers {
+class Image;
+}
+
+namespace gfx {
+class DataSourceSurface;
+}
+
+namespace dom {
+
+class BlobImpl;
+class MessagePort;
+class MessagePortIdentifier;
+template <typename T>
+class Sequence;
+
+class StructuredCloneHolderBase {
+ public:
+  typedef JS::StructuredCloneScope StructuredCloneScope;
+
+  StructuredCloneHolderBase(
+      StructuredCloneScope aScope = StructuredCloneScope::SameProcess);
+  virtual ~StructuredCloneHolderBase();
+
+  // Note, it is unsafe to std::move() a StructuredCloneHolderBase since a raw
+  // this pointer is passed to mBuffer as a callback closure.  That must
+  // be fixed if you want to implement a move constructor here.
+  StructuredCloneHolderBase(StructuredCloneHolderBase&& aOther) = delete;
+
+  // These methods should be implemented in order to clone data.
+  // Read more documentation in js/public/StructuredClone.h.
+
+  virtual JSObject* CustomReadHandler(
+      JSContext* aCx, JSStructuredCloneReader* aReader,
+      const JS::CloneDataPolicy& aCloneDataPolicy, uint32_t aTag,
+      uint32_t aIndex) = 0;
+
+  virtual bool CustomWriteHandler(JSContext* aCx,
+                                  JSStructuredCloneWriter* aWriter,
+                                  JS::Handle<JSObject*> aObj,
+                                  bool* aSameProcessScopeRequired) = 0;
+
+  // This method has to be called when this object is not needed anymore.
+  // It will free memory and the buffer. This has to be called because
+  // otherwise the buffer will be freed in the DTOR of this class and at that
+  // point we cannot use the overridden methods.
+  void Clear();
+
+  // If these 3 methods are not implement, transfering objects will not be
+  // allowed. Otherwise only arrayBuffers will be transferred.
+
+  virtual bool CustomReadTransferHandler(
+      JSContext* aCx, JSStructuredCloneReader* aReader, uint32_t aTag,
+      void* aContent, uint64_t aExtraData,
+      JS::MutableHandle<JSObject*> aReturnObject);
+
+  virtual bool CustomWriteTransferHandler(JSContext* aCx,
+                                          JS::Handle<JSObject*> aObj,
+                                          // Output:
+                                          uint32_t* aTag,
+                                          JS::TransferableOwnership* aOwnership,
+                                          void** aContent,
+                                          uint64_t* aExtraData);
+
+  virtual void CustomFreeTransferHandler(uint32_t aTag,
+                                         JS::TransferableOwnership aOwnership,
+                                         void* aContent, uint64_t aExtraData);
+
+  virtual bool CustomCanTransferHandler(JSContext* aCx,
+                                        JS::Handle<JSObject*> aObj,
+                                        bool* aSameProcessScopeRequired);
+
+  // These methods are what you should use to read/write data.
+
+  // Execute the serialization of aValue using the Structured Clone Algorithm.
+  // The data can read back using Read().
+  bool Write(JSContext* aCx, JS::Handle<JS::Value> aValue);
+
+  // Like Write() but it supports the transferring of objects and handling
+  // of cloning policy.
+  bool Write(JSContext* aCx, JS::Handle<JS::Value> aValue,
+             JS::Handle<JS::Value> aTransfer,
+             const JS::CloneDataPolicy& aCloneDataPolicy);
+
+  // If Write() has been called, this method retrieves data and stores it into
+  // aValue.
+  bool Read(JSContext* aCx, JS::MutableHandle<JS::Value> aValue);
+
+  // Like Read() but it supports handling of clone policy.
+  bool Read(JSContext* aCx, JS::MutableHandle<JS::Value> aValue,
+            const JS::CloneDataPolicy& aCloneDataPolicy);
+
+  bool HasData() const { return !!mBuffer; }
+
+  JSStructuredCloneData& BufferData() const {
+    MOZ_ASSERT(mBuffer, "Write() has never been called.");
+    return mBuffer->data();
+  }
+
+  size_t SizeOfExcludingThis(mozilla::MallocSizeOf aMallocSizeOf) {
+    size_t size = 0;
+    if (HasData()) {
+      size += mBuffer->sizeOfIncludingThis(aMallocSizeOf);
+    }
+    return size;
+  }
+
+  void SetErrorMessage(const char* aErrorMessage) {
+    mErrorMessage.Assign(aErrorMessage);
+  }
+
+ protected:
+  UniquePtr<JSAutoStructuredCloneBuffer> mBuffer;
+
+  StructuredCloneScope mStructuredCloneScope;
+
+  // Error message when a data clone error is about to throw. It's held while
+  // the error callback is fired and it will be throw with a data clone error
+  // later.
+  nsCString mErrorMessage;
+
+#ifdef DEBUG
+  bool mClearCalled;
+#endif
+};
+
+class BlobImpl;
+class MessagePort;
+class MessagePortIdentifier;
+struct VideoFrameSerializedData;
+
+class StructuredCloneHolder : public StructuredCloneHolderBase {
+ public:
+  enum CloningSupport { CloningSupported, CloningNotSupported };
+
+  enum TransferringSupport { TransferringSupported, TransferringNotSupported };
+
+  // If cloning is supported, this object will clone objects such as Blobs,
+  // FileList, ImageData, etc.
+  // If transferring is supported, we will transfer MessagePorts and in the
+  // future other transferrable objects.
+  // The StructuredCloneScope is useful to know where the cloned/transferred
+  // data can be read and written. Additional checks about the nature of the
+  // objects will be done based on this scope value because not all the
+  // objects can be sent between threads or processes.
+  explicit StructuredCloneHolder(CloningSupport aSupportsCloning,
+                                 TransferringSupport aSupportsTransferring,
+                                 StructuredCloneScope aStructuredCloneScope);
+  virtual ~StructuredCloneHolder();
+
+  StructuredCloneHolder(StructuredCloneHolder&& aOther) = delete;
+
+  // Normally you should just use Write() and Read().
+
+  virtual void Write(JSContext* aCx, JS::Handle<JS::Value> aValue,
+                     ErrorResult& aRv);
+
+  virtual void Write(JSContext* aCx, JS::Handle<JS::Value> aValue,
+                     JS::Handle<JS::Value> aTransfer,
+                     const JS::CloneDataPolicy& aCloneDataPolicy,
+                     ErrorResult& aRv);
+
+  void Read(nsIGlobalObject* aGlobal, JSContext* aCx,
+            JS::MutableHandle<JS::Value> aValue, ErrorResult& aRv);
+
+  void Read(nsIGlobalObject* aGlobal, JSContext* aCx,
+            JS::MutableHandle<JS::Value> aValue,
+            const JS::CloneDataPolicy& aCloneDataPolicy, ErrorResult& aRv);
+
+  // Call this method to know if this object is keeping some DOM object alive.
+  bool HasClonedDOMObjects() const {
+    return !mBlobImplArray.IsEmpty() || !mWasmModuleArray.IsEmpty() ||
+           !mClonedSurfaces.IsEmpty() || !mInputStreamArray.IsEmpty() ||
+           !mVideoFrames.IsEmpty();
+  }
+
+  nsTArray<RefPtr<BlobImpl>>& BlobImpls() {
+    MOZ_ASSERT(mSupportsCloning,
+               "Blobs cannot be taken/set if cloning is not supported.");
+    return mBlobImplArray;
+  }
+
+  nsTArray<RefPtr<JS::WasmModule>>& WasmModules() {
+    MOZ_ASSERT(mSupportsCloning,
+               "WasmModules cannot be taken/set if cloning is not supported.");
+    return mWasmModuleArray;
+  }
+
+  nsTArray<nsCOMPtr<nsIInputStream>>& InputStreams() {
+    MOZ_ASSERT(mSupportsCloning,
+               "InputStreams cannot be taken/set if cloning is not supported.");
+    return mInputStreamArray;
+  }
+
+  // This method returns the final scope. If the final scope is unknown,
+  // DifferentProcess is returned because it's the most restrictive one.
+  StructuredCloneScope CloneScope() const {
+    if (mStructuredCloneScope == StructuredCloneScope::UnknownDestination) {
+      return StructuredCloneScope::DifferentProcess;
+    }
+    return mStructuredCloneScope;
+  }
+
+  // The global object is set internally just during the Read(). This method
+  // can be used by read functions to retrieve it.
+  nsIGlobalObject* GlobalDuringRead() const { return mGlobal; }
+
+  // This must be called if the transferring has ports generated by Read().
+  // MessagePorts are not thread-safe and they must be retrieved in the thread
+  // where they are created.
+  nsTArray<RefPtr<MessagePort>>&& TakeTransferredPorts() {
+    MOZ_ASSERT(mSupportsTransferring);
+    return std::move(mTransferredPorts);
+  }
+
+  // This method uses TakeTransferredPorts() to populate a sequence of
+  // MessagePorts for WebIDL binding classes.
+  bool TakeTransferredPortsAsSequence(
+      Sequence<OwningNonNull<mozilla::dom::MessagePort>>& aPorts);
+
+  nsTArray<MessagePortIdentifier>& PortIdentifiers() const {
+    MOZ_ASSERT(mSupportsTransferring);
+    return mPortIdentifiers;
+  }
+
+  nsTArray<RefPtr<gfx::DataSourceSurface>>& GetSurfaces() {
+    return mClonedSurfaces;
+  }
+
+  nsTArray<VideoFrameSerializedData>& VideoFrames() { return mVideoFrames; }
+
+  // Implementations of the virtual methods to allow cloning of objects which
+  // JS engine itself doesn't clone.
+
+  virtual JSObject* CustomReadHandler(
+      JSContext* aCx, JSStructuredCloneReader* aReader,
+      const JS::CloneDataPolicy& aCloneDataPolicy, uint32_t aTag,
+      uint32_t aIndex) override;
+
+  virtual bool CustomWriteHandler(JSContext* aCx,
+                                  JSStructuredCloneWriter* aWriter,
+                                  JS::Handle<JSObject*> aObj,
+                                  bool* aSameProcessScopeRequired) override;
+
+  virtual bool CustomReadTransferHandler(
+      JSContext* aCx, JSStructuredCloneReader* aReader, uint32_t aTag,
+      void* aContent, uint64_t aExtraData,
+      JS::MutableHandle<JSObject*> aReturnObject) override;
+
+  virtual bool CustomWriteTransferHandler(JSContext* aCx,
+                                          JS::Handle<JSObject*> aObj,
+                                          uint32_t* aTag,
+                                          JS::TransferableOwnership* aOwnership,
+                                          void** aContent,
+                                          uint64_t* aExtraData) override;
+
+  virtual void CustomFreeTransferHandler(uint32_t aTag,
+                                         JS::TransferableOwnership aOwnership,
+                                         void* aContent,
+                                         uint64_t aExtraData) override;
+
+  virtual bool CustomCanTransferHandler(
+      JSContext* aCx, JS::Handle<JSObject*> aObj,
+      bool* aSameProcessScopeRequired) override;
+
+  // These 2 static methods are useful to read/write fully serializable objects.
+  // They can be used by custom StructuredCloneHolderBase classes to
+  // serialize objects such as ImageData, CryptoKey, RTCCertificate, etc.
+
+  static JSObject* ReadFullySerializableObjects(
+      JSContext* aCx, JSStructuredCloneReader* aReader, uint32_t aTag);
+
+  static bool WriteFullySerializableObjects(JSContext* aCx,
+                                            JSStructuredCloneWriter* aWriter,
+                                            JS::Handle<JSObject*> aObj);
+
+  // Helper functions for reading and writing strings.
+  static bool ReadString(JSStructuredCloneReader* aReader, nsString& aString);
+  static bool WriteString(JSStructuredCloneWriter* aWriter,
+                          const nsAString& aString);
+  static bool ReadCString(JSStructuredCloneReader* aReader, nsCString& aString);
+  static bool WriteCString(JSStructuredCloneWriter* aWriter,
+                           const nsACString& aString);
+
+  static const JSStructuredCloneCallbacks sCallbacks;
+
+ protected:
+  // If you receive a buffer from IPC, you can use this method to retrieve a
+  // JS::Value. It can happen that you want to pre-populate the array of Blobs
+  // and/or the PortIdentifiers.
+  void ReadFromBuffer(nsIGlobalObject* aGlobal, JSContext* aCx,
+                      JSStructuredCloneData& aBuffer,
+                      JS::MutableHandle<JS::Value> aValue,
+                      const JS::CloneDataPolicy& aCloneDataPolicy,
+                      ErrorResult& aRv);
+
+  void ReadFromBuffer(nsIGlobalObject* aGlobal, JSContext* aCx,
+                      JSStructuredCloneData& aBuffer,
+                      uint32_t aAlgorithmVersion,
+                      JS::MutableHandle<JS::Value> aValue,
+                      const JS::CloneDataPolicy& aCloneDataPolicy,
+                      ErrorResult& aRv);
+
+  void SameProcessScopeRequired(bool* aSameProcessScopeRequired);
+
+  already_AddRefed<MessagePort> ReceiveMessagePort(uint64_t aIndex);
+
+  bool mSupportsCloning;
+  bool mSupportsTransferring;
+
+  // SizeOfExcludingThis is inherited from StructuredCloneHolderBase. It doesn't
+  // account for objects in the following arrays because a) they're not expected
+  // to be stored in long-lived StructuredCloneHolder objects, and b) in the
+  // case of BlobImpl objects, MemoryBlobImpls have their own memory reporters,
+  // and the other types do not hold significant amounts of memory alive.
+
+  // Used for cloning blobs in the structured cloning algorithm.
+  nsTArray<RefPtr<BlobImpl>> mBlobImplArray;
+
+  // Used for cloning JS::WasmModules in the structured cloning algorithm.
+  nsTArray<RefPtr<JS::WasmModule>> mWasmModuleArray;
+
+  // Used for cloning InputStream in the structured cloning algorithm.
+  nsTArray<nsCOMPtr<nsIInputStream>> mInputStreamArray;
+
+  // This is used for sharing the backend of ImageBitmaps.
+  // The DataSourceSurface object must be thread-safely reference-counted.
+  // The DataSourceSurface object will not be written ever via any ImageBitmap
+  // instance, so no race condition will occur.
+  nsTArray<RefPtr<gfx::DataSourceSurface>> mClonedSurfaces;
+
+  // Used for cloning VideoFrame in the structured cloning algorithm.
+  nsTArray<VideoFrameSerializedData> mVideoFrames;
+
+  // This raw pointer is only set within ::Read() and is unset by the end.
+  nsIGlobalObject* MOZ_NON_OWNING_REF mGlobal;
+
+  // This array contains the ports once we've finished the reading. It's
+  // generated from the mPortIdentifiers array.
+  nsTArray<RefPtr<MessagePort>> mTransferredPorts;
+
+  // This array contains the identifiers of the MessagePorts. Based on these we
+  // are able to reconnect the new transferred ports with the other
+  // MessageChannel ports.
+  mutable nsTArray<MessagePortIdentifier> mPortIdentifiers;
+
+#ifdef DEBUG
+  nsCOMPtr<nsIEventTarget> mCreationEventTarget;
+#endif
+};
+
+}  // namespace dom
+}  // namespace mozilla
+
+#endif  // mozilla_dom_StructuredCloneHolder_h