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diff --git a/ipc/glue/RawShmem.h b/ipc/glue/RawShmem.h
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+/* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* 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_IPC_RAWSHMEM_H_
+#define MOZILLA_IPC_RAWSHMEM_H_
+
+#include "mozilla/ipc/SharedMemoryBasic.h"
+#include "mozilla/Span.h"
+#include <utility>
+
+namespace mozilla::ipc {
+
+class WritableSharedMemoryMapping;
+
+/// A handle to shared memory.
+///
+/// See the doc comment for `WritableSharedMemoryMapping` below.
+class UnsafeSharedMemoryHandle {
+  friend class WritableSharedMemoryMapping;
+  friend struct IPC::ParamTraits<UnsafeSharedMemoryHandle>;
+
+ public:
+  UnsafeSharedMemoryHandle();
+  UnsafeSharedMemoryHandle(UnsafeSharedMemoryHandle&& aOther) noexcept;
+  UnsafeSharedMemoryHandle& operator=(
+      UnsafeSharedMemoryHandle&& aOther) noexcept;
+
+  /// Attempts to allocate a shmem.
+  ///
+  /// Returns `Nothing()` if allocation fails.
+  /// If `aSize` is zero, a valid empty WritableSharedMemoryMapping is returned.
+  static Maybe<std::pair<UnsafeSharedMemoryHandle, WritableSharedMemoryMapping>>
+  CreateAndMap(size_t aSize);
+
+ private:
+  UnsafeSharedMemoryHandle(SharedMemoryBasic::Handle&& aHandle, uint64_t aSize)
+      : mHandle(std::move(aHandle)), mSize(aSize) {}
+
+  SharedMemoryBasic::Handle mHandle;
+  uint64_t mSize;
+};
+
+/// A Shared memory buffer mapping.
+///
+/// Unlike `ipc::Shmem`, the underlying shared memory buffer on each side of
+/// the process boundary is only deallocated with there respective
+/// `WritableSharedMemoryMapping`.
+///
+/// ## Usage
+///
+/// Typical usage goes as follows:
+/// - Allocate the memory using `UnsafeSharedMemoryHandle::Create`, returning a
+///   handle and a mapping.
+/// - Send the handle to the other process using an IPDL message.
+/// - On the other process, map the shared memory by creating
+///   WritableSharedMemoryMapping via `WritableSharedMemoryMapping::Open` and
+///   the received handle.
+///
+/// Do not send the shared memory handle again, it is only intended to establish
+/// the mapping on each side during initialization. The user of this class is
+/// responsible for managing the lifetime of the buffers on each side, as well
+/// as their identity, by for example storing them in hash map and referring to
+/// them via IDs in IPDL message if need be.
+///
+/// ## Empty shmems
+///
+/// An empty WritableSharedMemoryMapping is one that was created with size zero.
+/// It is analogous to a null RefPtr. It can be used like a non-empty shmem,
+/// including sending the handle and openning it on another process (resulting
+/// in an empty mapping on the other side).
+class WritableSharedMemoryMapping {
+  friend class UnsafeSharedMemoryHandle;
+
+ public:
+  WritableSharedMemoryMapping() = default;
+
+  WritableSharedMemoryMapping(WritableSharedMemoryMapping&& aMoved) = default;
+
+  WritableSharedMemoryMapping& operator=(WritableSharedMemoryMapping&& aMoved) =
+      default;
+
+  /// Open the shmem and immediately close the handle.
+  static Maybe<WritableSharedMemoryMapping> Open(
+      UnsafeSharedMemoryHandle aHandle);
+
+  // Returns the size in bytes.
+  size_t Size() const;
+
+  // Returns the shared memory as byte range.
+  Span<uint8_t> Bytes();
+
+ private:
+  explicit WritableSharedMemoryMapping(
+      RefPtr<mozilla::ipc::SharedMemoryBasic>&& aRef);
+
+  RefPtr<mozilla::ipc::SharedMemoryBasic> mRef;
+};
+
+}  // namespace mozilla::ipc
+
+namespace IPC {
+template <>
+struct ParamTraits<mozilla::ipc::UnsafeSharedMemoryHandle> {
+  typedef mozilla::ipc::UnsafeSharedMemoryHandle paramType;
+  static void Write(IPC::MessageWriter* aWriter, paramType&& aVar);
+  static bool Read(IPC::MessageReader* aReader, paramType* aVar);
+};
+
+}  // namespace IPC
+
+#endif