1 files changed, 137 insertions, 0 deletions
diff --git a/dom/ipc/RefMessageBodyService.h b/dom/ipc/RefMessageBodyService.h
new file mode 100644
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+++ b/dom/ipc/RefMessageBodyService.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_RefMessageBodyService_h
+#define mozilla_dom_RefMessageBodyService_h
+
+#include <cstdint>
+#include "js/TypeDecls.h"
+#include "mozilla/Maybe.h"
+#include "mozilla/Mutex.h"
+#include "mozilla/StaticMutex.h"
+#include "mozilla/UniquePtr.h"
+#include "nsHashKeys.h"
+#include "nsID.h"
+#include "nsISupports.h"
+#include "nsRefPtrHashtable.h"
+
+namespace JS {
+class CloneDataPolicy;
+}  // namespace JS
+
+namespace mozilla {
+
+class ErrorResult;
+template <class T>
+class OwningNonNull;
+
+namespace dom {
+
+class MessagePort;
+template <typename T>
+class Sequence;
+
+namespace ipc {
+class StructuredCloneData;
+}
+
+/**
+ * At the time a BroadcastChannel or MessagePort sends messages, we don't know
+ * which process is going to receive it. Because of this, we need to check if
+ * the message is able to cross the process boundary.
+ * If the message contains objects such as SharedArrayBuffers, WASM modules or
+ * ImageBitmaps, it can be delivered on the current process only.
+ * Instead of sending the whole message via IPC, we send a unique ID, while the
+ * message is kept alive by RefMessageBodyService, on the current process using
+ * a ref-counted RefMessageBody object.
+ * When the receiver obtains the message ID, it checks if the local
+ * RefMessageBodyService knows that ID. If yes, the sender and the receiver are
+ * on the same process and the delivery can be completed; if not, a
+ * messageerror event has to be dispatched instead.
+ *
+ * For MessagePort communication is 1-to-1 and because of this, the
+ * receiver takes ownership of the message (RefMessageBodyService::Steal()).
+ * If the receiver port is on a different process, RefMessageBodyService will
+ * return a nullptr and a messageerror event will be dispatched.
+
+ * For BroadcastChannel, the life-time of a message is a bit different than for
+ * MessagePort. It has a 1-to-many communication and we could have multiple
+ * receivers. Each one needs to deliver the message without taking full
+ * ownership of it.
+ * In order to support this feature, BroadcastChannel needs to call
+ * RefMessageBodyService::SetMaxCount() to inform how many ports are allowed to
+ * retrieve the current message, on the current process. Receivers on other
+ * processes are not kept in consideration because they will not be able to
+ * retrieve the message from RefMessageBodyService. When the last allowed
+ * port has called RefMessageBodyService::GetAndCount(), the message is
+ * released.
+ */
+class RefMessageBody final {
+  friend class RefMessageBodyService;
+
+ public:
+  NS_INLINE_DECL_THREADSAFE_REFCOUNTING(RefMessageBody)
+
+  RefMessageBody(const nsID& aPortID,
+                 UniquePtr<ipc::StructuredCloneData>&& aCloneData);
+
+  const nsID& PortID() const { return mPortID; }
+
+  void Read(JSContext* aCx, JS::MutableHandle<JS::Value> aValue,
+            const JS::CloneDataPolicy& aCloneDataPolicy, ErrorResult& aRv);
+
+  // This method can be called only if the RefMessageBody is not supposed to be
+  // ref-counted (see mMaxCount).
+  bool TakeTransferredPortsAsSequence(
+      Sequence<OwningNonNull<mozilla::dom::MessagePort>>& aPorts);
+
+ private:
+  ~RefMessageBody();
+
+  const nsID mPortID;
+
+  // In case the RefMessageBody is shared and refcounted (see mCount/mMaxCount),
+  // we must enforce that the reading does not happen simultaneously on
+  // different threads.
+  Mutex mMutex MOZ_UNANNOTATED;
+
+  UniquePtr<ipc::StructuredCloneData> mCloneData;
+
+  // When mCount reaches mMaxCount, this object is released by the service.
+  Maybe<uint32_t> mMaxCount;
+  uint32_t mCount;
+};
+
+class RefMessageBodyService final {
+ public:
+  NS_INLINE_DECL_THREADSAFE_REFCOUNTING(RefMessageBodyService)
+
+  static already_AddRefed<RefMessageBodyService> GetOrCreate();
+
+  void ForgetPort(const nsID& aPortID);
+
+  const nsID Register(already_AddRefed<RefMessageBody> aBody, ErrorResult& aRv);
+
+  already_AddRefed<RefMessageBody> Steal(const nsID& aID);
+
+  already_AddRefed<RefMessageBody> GetAndCount(const nsID& aID);
+
+  void SetMaxCount(const nsID& aID, uint32_t aMaxCount);
+
+ private:
+  explicit RefMessageBodyService(const StaticMutexAutoLock& aProofOfLock);
+  ~RefMessageBodyService();
+
+  static RefMessageBodyService* GetOrCreateInternal(
+      const StaticMutexAutoLock& aProofOfLock);
+
+  nsRefPtrHashtable<nsIDHashKey, RefMessageBody> mMessages;
+};
+
+}  // namespace dom
+}  // namespace mozilla
+
+#endif  // mozilla_dom_RefMessageBodyService_h