1 files changed, 131 insertions, 0 deletions
diff --git a/ipc/glue/BigBuffer.h b/ipc/glue/BigBuffer.h
new file mode 100644
index 0000000000..7136b6c03c
--- /dev/null
+++ b/ipc/glue/BigBuffer.h
@@ -0,0 +1,131 @@
+/* -*- 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_ipc_BigBuffer_h
+#define mozilla_ipc_BigBuffer_h
+
+#include <stdlib.h>
+#include <inttypes.h>
+#include "mozilla/Span.h"
+#include "mozilla/Variant.h"
+#include "mozilla/ipc/SharedMemory.h"
+
+namespace mozilla::ipc {
+
+class BigBuffer {
+ public:
+  static constexpr size_t kShmemThreshold = 64 * 1024;
+
+  static BigBuffer TryAlloc(const size_t aSize) {
+    auto ret = BigBuffer{};
+    auto data = TryAllocBuffer(aSize);
+    if (data) {
+      ret.mSize = aSize;
+      ret.mData = std::move(data.ref());
+    }
+    return ret;
+  }
+
+  // Return a new BigBuffer which wraps no data.
+  BigBuffer() : mSize(0), mData(NoData()) {}
+
+  BigBuffer(const BigBuffer&) = delete;
+  BigBuffer& operator=(const BigBuffer&) = delete;
+
+  BigBuffer(BigBuffer&& aOther) noexcept
+      : mSize(std::exchange(aOther.mSize, 0)),
+        mData(std::exchange(aOther.mData, NoData())) {}
+
+  BigBuffer& operator=(BigBuffer&& aOther) noexcept {
+    mSize = std::exchange(aOther.mSize, 0);
+    mData = std::exchange(aOther.mData, NoData());
+    return *this;
+  }
+
+  // Create a new BigBuffer with the given size.
+  // The buffer will be created uninitialized and must be fully initialized
+  // before sending over IPC to avoid leaking uninitialized memory to another
+  // process.
+  explicit BigBuffer(size_t aSize) : mSize(aSize), mData(AllocBuffer(aSize)) {}
+
+  // Create a new BigBuffer containing the data from the provided byte slice.
+  explicit BigBuffer(Span<const uint8_t> aData) : BigBuffer(aData.Length()) {
+    memcpy(Data(), aData.Elements(), aData.Length());
+  }
+
+  // Marker to indicate that a particular constructor of BigBuffer adopts
+  // ownership of the provided data.
+  struct Adopt {};
+
+  // Create a new BigBuffer from an existing shared memory region, taking
+  // ownership of that shared memory region. The shared memory region must be
+  // non-null, mapped, and large enough to fit aSize bytes.
+  BigBuffer(Adopt, SharedMemory* aSharedMemory, size_t aSize);
+
+  // Create a new BigBuffer from an existing memory buffer, taking ownership of
+  // that memory region. The region will be freed using `free()` when it is no
+  // longer needed.
+  BigBuffer(Adopt, uint8_t* aData, size_t aSize);
+
+  ~BigBuffer() = default;
+
+  // Returns a pointer to the data stored by this BigBuffer, regardless of
+  // backing storage type.
+  uint8_t* Data();
+  const uint8_t* Data() const;
+
+  // Returns the size of the data stored by this BigBuffer, regardless of
+  // backing storage type.
+  size_t Size() const { return mSize; }
+
+  // Get a view of the BigBuffer's data as a span.
+  Span<uint8_t> AsSpan() { return Span{Data(), Size()}; }
+  Span<const uint8_t> AsSpan() const { return Span{Data(), Size()}; }
+
+  // If the BigBuffer is backed by shared memory, returns a pointer to the
+  // backing SharedMemory region.
+  SharedMemory* GetSharedMemory() const {
+    return mData.is<1>() ? mData.as<1>().get() : nullptr;
+  }
+
+ private:
+  friend struct IPC::ParamTraits<mozilla::ipc::BigBuffer>;
+
+  using Storage = Variant<UniqueFreePtr<uint8_t[]>, RefPtr<SharedMemory>>;
+
+  // Empty storage which holds no data.
+  static Storage NoData() { return AsVariant(UniqueFreePtr<uint8_t[]>{}); }
+
+  // Fallibly allocate a new storage of the given size.
+  static Maybe<Storage> TryAllocBuffer(size_t aSize);
+
+  // Infallibly allocate a new storage of the given size.
+  static Storage AllocBuffer(size_t aSize) {
+    auto ret = TryAllocBuffer(aSize);
+    if (!ret) {
+      NS_ABORT_OOM(aSize);
+    }
+    return std::move(ret.ref());
+  }
+
+  size_t mSize;
+  Storage mData;
+};
+
+}  // namespace mozilla::ipc
+
+namespace IPC {
+
+template <>
+struct ParamTraits<mozilla::ipc::BigBuffer> {
+  using paramType = mozilla::ipc::BigBuffer;
+  static void Write(MessageWriter* aWriter, paramType&& aParam);
+  static bool Read(MessageReader* aReader, paramType* aResult);
+};
+
+}  // namespace IPC
+
+#endif  // mozilla_BigBuffer_h