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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 */
#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 {
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<1>() ?<1>().get() : nullptr;
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) {
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