// Copyright (c) 2006-2008 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#ifndef CHROME_COMMON_IPC_MESSAGE_UTILS_H_
#define CHROME_COMMON_IPC_MESSAGE_UTILS_H_

#include <array>
#include <bitset>
#include <cstdint>
#include <iterator>
#include <map>
#include <optional>
#include <set>
#include <span>
#include <string>
#include <tuple>
#include <type_traits>
#include <unordered_map>
#include <unordered_set>
#include <utility>
#include <variant>
#include <vector>
#include "ErrorList.h"
#include "base/logging.h"
#include "base/pickle.h"
#include "chrome/common/ipc_message.h"
#include "mozilla/CheckedInt.h"
#include "mozilla/ipc/SharedMemoryMapping.h"

#if defined(XP_WIN)
#  include <windows.h>
#endif

template <typename T>
class RefPtr;
template <typename T>
class nsCOMPtr;

namespace mozilla::ipc {
class IProtocol;
namespace shared_memory {
class Cursor;
}

// Implemented in ProtocolUtils.cpp
MOZ_NEVER_INLINE void PickleFatalError(const char* aMsg, IProtocol* aActor);
}  // namespace mozilla::ipc

namespace IPC {

/**
 * This constant determines the threshold size (in bytes) for deciding whether
 * shared memory should be used during serialization/deserialization handled
 * by the MessageBufferWriter class.
 *
 * NOTE: Even above this threshold, if MessageBufferWriter fails to allocate a
 * shared memory region, it may still fall-back to sending the message inline.
 */
constexpr uint32_t kMessageBufferShmemThreshold = 64 * 1024;  // 64 KB

/**
 * Context used to serialize into an IPC::Message. Provides relevant context
 * used when serializing.
 */
class MOZ_STACK_CLASS MessageWriter final {
 public:
  explicit MessageWriter(Message& message,
                         mozilla::ipc::IProtocol* actor = nullptr)
      : message_(message), actor_(actor) {}

  MessageWriter(const MessageWriter&) = delete;
  MessageWriter& operator=(const MessageWriter&) = delete;

  mozilla::ipc::IProtocol* GetActor() const { return actor_; }

#define FORWARD_WRITE(name, type) \
  bool Write##name(const type& result) { return message_.Write##name(result); }

  FORWARD_WRITE(Bool, bool)
  FORWARD_WRITE(Int16, int16_t)
  FORWARD_WRITE(UInt16, uint16_t)
  FORWARD_WRITE(Int, int)
  FORWARD_WRITE(Long, long)
  FORWARD_WRITE(ULong, unsigned long)
  FORWARD_WRITE(Int32, int32_t)
  FORWARD_WRITE(UInt32, uint32_t)
  FORWARD_WRITE(Int64, int64_t)
  FORWARD_WRITE(UInt64, uint64_t)
  FORWARD_WRITE(Double, double)
  FORWARD_WRITE(IntPtr, intptr_t)
  FORWARD_WRITE(UnsignedChar, unsigned char)
  FORWARD_WRITE(String, std::string)
  FORWARD_WRITE(WString, std::wstring)

#undef FORWARD_WRITE

  template <class T>
  bool WriteScalar(const T& result) {
    return message_.WriteScalar(result);
  }

  bool WriteData(const char* data, uint32_t length) {
    return message_.WriteData(data, length);
  }

  bool WriteBytes(const void* data, uint32_t data_len) {
    return message_.WriteBytes(data, data_len);
  }

  bool WriteBytesZeroCopy(void* data, uint32_t data_len, uint32_t capacity) {
    return message_.WriteBytesZeroCopy(data, data_len, capacity);
  }

  bool WriteSentinel(uint32_t sentinel) {
    return message_.WriteSentinel(sentinel);
  }

  bool WriteFileHandle(mozilla::UniqueFileHandle handle) {
    return message_.WriteFileHandle(std::move(handle));
  }

  void WritePort(mozilla::ipc::ScopedPort port) {
    message_.WritePort(std::move(port));
  }

#if defined(XP_DARWIN)
  bool WriteMachSendRight(mozilla::UniqueMachSendRight port) {
    return message_.WriteMachSendRight(std::move(port));
  }

  bool WriteMachReceiveRight(mozilla::UniqueMachReceiveRight port) {
    return message_.WriteMachReceiveRight(std::move(port));
  }
#endif

  void FatalError(const char* aErrorMsg) const {
    mozilla::ipc::PickleFatalError(aErrorMsg, actor_);
  }

  void NoteLargeBufferShmemFailure(uint32_t aLargeBufferSize) {
    message_.NoteLargeBufferShmemFailure(aLargeBufferSize);
  }

 private:
  Message& message_;
  mozilla::ipc::IProtocol* actor_;
};

/**
 * Context used to read data from an IPC::Message. Provides relevant context
 * used when deserializing and tracks iteration.
 */
class MOZ_STACK_CLASS MessageReader final {
 public:
  explicit MessageReader(const Message& message,
                         mozilla::ipc::IProtocol* actor = nullptr)
      : message_(message), iter_(message), actor_(actor) {}

  MessageReader(const MessageReader&) = delete;
  MessageReader& operator=(const MessageReader&) = delete;

  mozilla::ipc::IProtocol* GetActor() const { return actor_; }

#define FORWARD_READ(name, type)                \
  [[nodiscard]] bool Read##name(type* result) { \
    return message_.Read##name(&iter_, result); \
  }

  FORWARD_READ(Bool, bool)
  FORWARD_READ(Int16, int16_t)
  FORWARD_READ(UInt16, uint16_t)
  FORWARD_READ(Short, short)
  FORWARD_READ(Int, int)
  FORWARD_READ(Long, long)
  FORWARD_READ(ULong, unsigned long)
  FORWARD_READ(Int32, int32_t)
  FORWARD_READ(UInt32, uint32_t)
  FORWARD_READ(Int64, int64_t)
  FORWARD_READ(UInt64, uint64_t)
  FORWARD_READ(Double, double)
  FORWARD_READ(IntPtr, intptr_t)
  FORWARD_READ(UnsignedChar, unsigned char)
  FORWARD_READ(String, std::string)
  FORWARD_READ(WString, std::wstring)

  // Special version of ReadInt() which rejects negative values
  FORWARD_READ(Length, int);

#undef FORWARD_READ

  template <class T>
  [[nodiscard]] bool ReadScalar(T* const result) {
    return message_.ReadScalar(&iter_, result);
  }

  [[nodiscard]] bool ReadBytesInto(void* data, uint32_t length) {
    return message_.ReadBytesInto(&iter_, data, length);
  }

  [[nodiscard]] bool IgnoreBytes(uint32_t length) {
    return message_.IgnoreBytes(&iter_, length);
  }

  [[nodiscard]] bool ReadSentinel(uint32_t sentinel) {
    return message_.ReadSentinel(&iter_, sentinel);
  }

  bool IgnoreSentinel() { return message_.IgnoreSentinel(&iter_); }

  bool HasBytesAvailable(uint32_t len) {
    return message_.HasBytesAvailable(&iter_, len);
  }

  void EndRead() { message_.EndRead(iter_, message_.type()); }

  [[nodiscard]] bool ConsumeFileHandle(mozilla::UniqueFileHandle* handle) {
    return message_.ConsumeFileHandle(&iter_, handle);
  }

  [[nodiscard]] bool ConsumePort(mozilla::ipc::ScopedPort* port) {
    return message_.ConsumePort(&iter_, port);
  }

#if defined(XP_DARWIN)
  [[nodiscard]] bool ConsumeMachSendRight(mozilla::UniqueMachSendRight* port) {
    return message_.ConsumeMachSendRight(&iter_, port);
  }

  [[nodiscard]] bool ConsumeMachReceiveRight(
      mozilla::UniqueMachReceiveRight* port) {
    return message_.ConsumeMachReceiveRight(&iter_, port);
  }
#endif

  void FatalError(const char* aErrorMsg) const {
    mozilla::ipc::PickleFatalError(aErrorMsg, actor_);
  }

 private:
  const Message& message_;
  PickleIterator iter_;
  mozilla::ipc::IProtocol* actor_;
};

namespace detail {

// Helper for checking `T::kHasDeprecatedReadParamPrivateConstructor` using a
// fallback when the member isn't defined.
template <typename T>
inline constexpr auto HasDeprecatedReadParamPrivateConstructor(int)
    -> decltype(T::kHasDeprecatedReadParamPrivateConstructor) {
  return T::kHasDeprecatedReadParamPrivateConstructor;
}

template <typename T>
inline constexpr bool HasDeprecatedReadParamPrivateConstructor(...) {
  return false;
}

}  // namespace detail

/**
 * Result type returned from some `ParamTraits<T>::Read` implementations, and
 * from `IPC::ReadParam<T>(MessageReader*)`. Either contains the value or
 * indicates a failure to deserialize.
 *
 * This type can be thought of as a variant on `Maybe<T>`, except that it
 * unconditionally constructs the underlying value if it is default
 * constructible. This helps keep code size down, especially when calling
 * outparameter-based ReadParam implementations (bug 1815177).
 */
template <typename T,
          bool = std::is_default_constructible_v<T> ||
                 detail::HasDeprecatedReadParamPrivateConstructor<T>(0)>
class ReadResult {
 public:
  ReadResult() = default;

  template <typename U, std::enable_if_t<std::is_convertible_v<U, T>, int> = 0>
  MOZ_IMPLICIT ReadResult(U&& aData)
      : mIsOk(true), mData(std::forward<U>(aData)) {}

  template <typename... Args>
  explicit ReadResult(std::in_place_t, Args&&... aArgs)
      : mIsOk(true), mData(std::forward<Args>(aArgs)...) {}

  ReadResult(const ReadResult&) = default;
  ReadResult(ReadResult&&) = default;

  template <typename U, std::enable_if_t<std::is_convertible_v<U, T>, int> = 0>
  MOZ_IMPLICIT ReadResult& operator=(U&& aData) {
    mIsOk = true;
    mData = std::forward<U>(aData);
    return *this;
  }

  ReadResult& operator=(const ReadResult&) = default;
  ReadResult& operator=(ReadResult&&) noexcept = default;

  // Check if the ReadResult contains a valid value.
  explicit operator bool() const { return isOk(); }
  bool isOk() const { return mIsOk; }

  // Get the data from this ReadResult.
  T& get() {
    MOZ_ASSERT(mIsOk);
    return mData;
  }
  const T& get() const {
    MOZ_ASSERT(mIsOk);
    return mData;
  }

  T& operator*() { return get(); }
  const T& operator*() const { return get(); }

  T* operator->() { return &get(); }
  const T* operator->() const { return &get(); }

  // Try to extract a `Maybe<T>` from this ReadResult.
  mozilla::Maybe<T> TakeMaybe() {
    if (mIsOk) {
      mIsOk = false;
      return mozilla::Some(std::move(mData));
    }
    return mozilla::Nothing();
  }

  // Get the underlying data from this ReadResult, even if not OK.
  //
  // This is only available for types which are default constructible, and is
  // used to optimize old-style `ReadParam` calls.
  T& GetStorage() { return mData; }

  // Compliment to `GetStorage` used to set the ReadResult into an OK state
  // without constructing the underlying value.
  void SetOk(bool aIsOk) { mIsOk = aIsOk; }

 private:
  bool mIsOk = false;
  T mData{};
};

template <typename T>
class ReadResult<T, false> {
 public:
  ReadResult() = default;

  template <typename U, std::enable_if_t<std::is_convertible_v<U, T>, int> = 0>
  MOZ_IMPLICIT ReadResult(U&& aData)
      : mData(std::in_place, std::forward<U>(aData)) {}

  template <typename... Args>
  explicit ReadResult(std::in_place_t, Args&&... aArgs)
      : mData(std::in_place, std::forward<Args>(aArgs)...) {}

  ReadResult(const ReadResult&) = default;
  ReadResult(ReadResult&&) = default;

  template <typename U, std::enable_if_t<std::is_convertible_v<U, T>, int> = 0>
  MOZ_IMPLICIT ReadResult& operator=(U&& aData) {
    mData.reset();
    mData.emplace(std::forward<U>(aData));
    return *this;
  }

  ReadResult& operator=(const ReadResult&) = default;
  ReadResult& operator=(ReadResult&&) noexcept = default;

  // Check if the ReadResult contains a valid value.
  explicit operator bool() const { return isOk(); }
  bool isOk() const { return mData.isSome(); }

  // Get the data from this ReadResult.
  T& get() { return mData.ref(); }
  const T& get() const { return mData.ref(); }

  T& operator*() { return get(); }
  const T& operator*() const { return get(); }

  T* operator->() { return &get(); }
  const T* operator->() const { return &get(); }

  // Try to extract a `Maybe<T>` from this ReadResult.
  mozilla::Maybe<T> TakeMaybe() { return std::move(mData); }

  // These methods are only available if the type is default constructible.
  T& GetStorage() = delete;
  void SetOk(bool aIsOk) = delete;

 private:
  mozilla::Maybe<T> mData;
};

//-----------------------------------------------------------------------------
// An iterator class for reading the fields contained within a Message.

class MessageIterator {
 public:
  explicit MessageIterator(const Message& m) : msg_(m), iter_(m) {}
  int NextInt() const {
    int val;
    if (!msg_.ReadInt(&iter_, &val)) NOTREACHED();
    return val;
  }
  intptr_t NextIntPtr() const {
    intptr_t val;
    if (!msg_.ReadIntPtr(&iter_, &val)) NOTREACHED();
    return val;
  }
  const std::string NextString() const {
    std::string val;
    if (!msg_.ReadString(&iter_, &val)) NOTREACHED();
    return val;
  }
  const std::wstring NextWString() const {
    std::wstring val;
    if (!msg_.ReadWString(&iter_, &val)) NOTREACHED();
    return val;
  }

 private:
  const Message& msg_;
  mutable PickleIterator iter_;
};

//-----------------------------------------------------------------------------
// ParamTraits specializations, etc.
//
// The full set of types ParamTraits is specialized upon contains *possibly*
// repeated types: unsigned long may be uint32_t or size_t, unsigned long long
// may be uint64_t or size_t, nsresult may be uint32_t, and so on.  You can't
// have ParamTraits<unsigned int> *and* ParamTraits<uint32_t> if unsigned int
// is uint32_t -- that's multiple definitions, and you can only have one.
//
// You could use #ifs and macro conditions to avoid duplicates, but they'd be
// hairy: heavily dependent upon OS and compiler author choices, forced to
// address all conflicts by hand.  Happily there's a better way.  The basic
// idea looks like this, where T -> U represents T inheriting from U:
//
// class ParamTraits<P>
// |
// --> class ParamTraits1<P>
//     |
//     --> class ParamTraits2<P>
//         |
//         --> class ParamTraitsN<P> // or however many levels
//
// The default specialization of ParamTraits{M}<P> is an empty class that
// inherits from ParamTraits{M + 1}<P> (or nothing in the base case).
//
// Now partition the set of parameter types into sets without duplicates.
// Assign each set of types to a level M.  Then specialize ParamTraitsM for
// each of those types.  A reference to ParamTraits<P> will consist of some
// number of empty classes inheriting in sequence, ending in a non-empty
// ParamTraits{N}<P>.  It's okay for the parameter types to be duplicative:
// either name of a type will resolve to the same ParamTraits{N}<P>.
//
// The nice thing is that because templates are instantiated lazily, if we
// indeed have uint32_t == unsigned int, say, with the former in level N and
// the latter in M > N, ParamTraitsM<unsigned int> won't be created (as long as
// nobody uses ParamTraitsM<unsigned int>, but why would you), and no duplicate
// code will be compiled or extra symbols generated.  It's as efficient at
// runtime as manually figuring out and avoiding conflicts by #ifs.
//
// The scheme we follow below names the various classes according to the types
// in them, and the number of ParamTraits levels is larger, but otherwise it's
// exactly the above idea.
//

template <class P>
struct ParamTraits;

template <typename P>
inline void WriteParam(MessageWriter* writer, P&& p) {
  ParamTraits<std::remove_cvref_t<P>>::Write(writer, std::forward<P>(p));
}

namespace detail {

template <typename P>
inline constexpr auto ParamTraitsReadUsesOutParam()
    -> decltype(ParamTraits<P>::Read(std::declval<MessageReader*>(),
                                     std::declval<P*>())) {
  return true;
}

template <typename P>
inline constexpr auto ParamTraitsReadUsesOutParam()
    -> decltype(ParamTraits<P>::Read(std::declval<MessageReader*>()), bool{}) {
  return false;
}

}  // namespace detail

template <typename P>
[[nodiscard]] inline bool ReadParam(MessageReader* reader, P* p) {
  static_assert(!std::is_const_v<P>,
                "ReadParam may only be used with const types when returning a "
                "ReadResult (call as ReadParam<T>(reader)).");
  if constexpr (!detail::ParamTraitsReadUsesOutParam<P>()) {
    auto maybe = ParamTraits<P>::Read(reader);
    if (maybe) {
      *p = std::move(*maybe);
      return true;
    }
    return false;
  } else {
    return ParamTraits<P>::Read(reader, p);
  }
}

template <typename P>
[[nodiscard]] inline ReadResult<std::remove_cv_t<P>> ReadParam(
    MessageReader* reader) {
  using ReadType = std::remove_cv_t<P>;
  if constexpr (!detail::ParamTraitsReadUsesOutParam<ReadType>()) {
    return ParamTraits<ReadType>::Read(reader);
  } else {
    ReadResult<ReadType> p;
    p.SetOk(ParamTraits<ReadType>::Read(reader, &p.GetStorage()));
    return p;
  }
}

class MOZ_STACK_CLASS MessageBufferWriter {
 public:
  // Create a MessageBufferWriter to write `full_len` bytes into `writer`.
  // If the length exceeds a threshold, a shared memory region may be used
  // instead of including the data inline.
  //
  // NOTE: This does _NOT_ write out the length of the buffer.
  // NOTE: Data written this way _MUST_ be read using `MessageBufferReader`.
  MessageBufferWriter(MessageWriter* writer, uint32_t full_len);
  ~MessageBufferWriter();

  MessageBufferWriter(const MessageBufferWriter&) = delete;
  MessageBufferWriter& operator=(const MessageBufferWriter&) = delete;

  // Write `len` bytes from `data` into the message.
  //
  // Exactly `full_len` bytes should be written across multiple calls before the
  // `MessageBufferWriter` is destroyed.
  //
  // WARNING: all writes (other than the last write) must be multiples of 4
  // bytes in length. Not doing this will lead to padding being introduced into
  // the payload and break things. This can probably be improved in the future
  // with deeper integration between `MessageBufferWriter` and `Pickle`.
  bool WriteBytes(const void* data, uint32_t len);

 private:
  MessageWriter* writer_;
  mozilla::UniquePtr<mozilla::ipc::shared_memory::Cursor> shmem_cursor_;
  uint32_t remaining_ = 0;
};

class MOZ_STACK_CLASS MessageBufferReader {
 public:
  // Create a MessageBufferReader to read `full_len` bytes from `reader` which
  // were written using `MessageBufferWriter`.
  //
  // NOTE: This may consume a shared memory region from the message, meaning
  // that the same data cannot be read multiple times.
  // NOTE: Data read this way _MUST_ be written using `MessageBufferWriter`.
  MessageBufferReader(MessageReader* reader, uint32_t full_len);
  ~MessageBufferReader();

  MessageBufferReader(const MessageBufferReader&) = delete;
  MessageBufferReader& operator=(const MessageBufferReader&) = delete;

  // Read `count` bytes from the message into `data`.
  //
  // Exactly `full_len` bytes should be read across multiple calls before the
  // `MessageBufferReader` is destroyed.
  //
  // WARNING: all reads (other than the last read) must be multiples of 4 bytes
  // in length. Not doing this will lead to bytes being skipped in the payload
  // and break things. This can probably be improved in the future with deeper
  // integration between `MessageBufferReader` and `Pickle`.
  [[nodiscard]] bool ReadBytesInto(void* data, uint32_t len);

 private:
  MessageReader* reader_;
  mozilla::UniquePtr<mozilla::ipc::shared_memory::Cursor> shmem_cursor_;
  uint32_t remaining_ = 0;
};

// Whether or not it is safe to serialize the given type using
// `WriteBytesOrShmem`.
template <typename P>
constexpr bool kUseWriteBytes =
    !std::is_same_v<std::remove_const_t<std::remove_reference_t<P>>, bool> &&
    (std::is_integral_v<std::remove_const_t<std::remove_reference_t<P>>> ||
     std::is_floating_point_v<std::remove_const_t<std::remove_reference_t<P>>>);

/**
 * Helper for writing a contiguous sequence (such as for a string or array) into
 * a message, with optimizations for basic integral and floating point types.
 *
 * Integral types will be copied into shared memory if the sequence exceeds 64k
 * bytes in size.
 *
 * Values written with this method must be read with `ReadSequenceParam`.
 *
 * The type parameter specifies the semantics to use, and should generally
 * either be `P&&` or `const P&`. The constness of the `data` argument should
 * match this parameter.
 */
template <typename P>
void WriteSequenceParam(MessageWriter* writer, std::remove_reference_t<P>* data,
                        size_t length) {
  mozilla::CheckedUint32 ipc_length(length);
  if (!ipc_length.isValid()) {
    writer->FatalError("invalid length passed to WriteSequenceParam");
    return;
  }
  writer->WriteUInt32(ipc_length.value());

  if constexpr (kUseWriteBytes<P>) {
    mozilla::CheckedUint32 byte_length =
        ipc_length * sizeof(std::remove_reference_t<P>);
    if (!byte_length.isValid()) {
      writer->FatalError("invalid byte length in WriteSequenceParam");
      return;
    }
    MessageBufferWriter buf_writer(writer, byte_length.value());
    buf_writer.WriteBytes(data, byte_length.value());
  } else {
    auto* end = data + length;
    for (auto* it = data; it != end; ++it) {
      WriteParam(writer, std::forward<P>(*it));
    }
  }
}

template <typename P>
bool ReadSequenceParamImpl(MessageReader* reader, P* data, uint32_t length) {
  if (length == 0) {
    return true;
  }
  if (!data) {
    reader->FatalError("allocation failed in ReadSequenceParam");
    return false;
  }

  if constexpr (kUseWriteBytes<P>) {
    mozilla::CheckedUint32 byte_length(length);
    byte_length *= sizeof(P);
    if (!byte_length.isValid()) {
      reader->FatalError("invalid byte length in ReadSequenceParam");
      return false;
    }
    MessageBufferReader buf_reader(reader, byte_length.value());
    return buf_reader.ReadBytesInto(data, byte_length.value());
  } else {
    P* end = data + length;
    for (auto* it = data; it != end; ++it) {
      if (!ReadParam(reader, it)) {
        return false;
      }
    }
    return true;
  }
}

template <typename P, typename I>
bool ReadSequenceParamImpl(MessageReader* reader, mozilla::Maybe<I>&& data,
                           uint32_t length) {
  static_assert(!kUseWriteBytes<P>,
                "Cannot return an output iterator if !kUseWriteBytes<P>");
  static_assert(
      std::is_base_of_v<std::output_iterator_tag,
                        typename std::iterator_traits<I>::iterator_category>,
      "must be Maybe<output iterator>");
  if (length == 0) {
    return true;
  }
  if (!data) {
    reader->FatalError("allocation failed in ReadSequenceParam");
    return false;
  }

  for (uint32_t i = 0; i < length; ++i) {
    auto elt = ReadParam<P>(reader);
    if (!elt) {
      return false;
    }
    *data.ref() = std::move(*elt);
    ++data.ref();
  }
  return true;
}

/**
 * Helper for reading a contiguous sequence (such as a string or array) into a
 * message which was previously written using `WriteSequenceParam`.
 *
 * The function argument `allocator` will be called with the length of the
 * sequence, and must return either a pointer to the memory region which the
 * sequence should be read into, or a Maybe of a C++ output iterator which will
 * infallibly accept length elements, and append them to the output sequence.
 *
 * If the type satisfies kUseWriteBytes, output iterators are not supported.
 */
template <typename P, typename F>
[[nodiscard]] bool ReadSequenceParam(MessageReader* reader, F&& allocator) {
  uint32_t length = 0;
  if (!reader->ReadUInt32(&length)) {
    reader->FatalError("failed to read byte length in ReadSequenceParam");
    return false;
  }

  return ReadSequenceParamImpl<P>(reader, allocator(length), length);
}

// Fundamental types.

template <class P>
struct ParamTraitsFundamental;

template <>
struct ParamTraitsFundamental<bool> {
  typedef bool param_type;
  static void Write(MessageWriter* writer, const param_type& p) {
    writer->WriteBool(p);
  }
  static bool Read(MessageReader* reader, param_type* r) {
    return reader->ReadBool(r);
  }
};

template <>
struct ParamTraitsFundamental<char> {
  typedef char param_type;
  static void Write(MessageWriter* writer, const param_type& p) {
    writer->WriteScalar(p);
  }
  static bool Read(MessageReader* reader, param_type* r) {
    return reader->ReadScalar(r);
  }
};

template <>
struct ParamTraitsFundamental<int> {
  typedef int param_type;
  static void Write(MessageWriter* writer, const param_type& p) {
    writer->WriteInt(p);
  }
  static bool Read(MessageReader* reader, param_type* r) {
    return reader->ReadInt(r);
  }
};

template <>
struct ParamTraitsFundamental<long> {
  typedef long param_type;
  static void Write(MessageWriter* writer, const param_type& p) {
    writer->WriteLong(p);
  }
  static bool Read(MessageReader* reader, param_type* r) {
    return reader->ReadLong(r);
  }
};

template <>
struct ParamTraitsFundamental<unsigned long> {
  typedef unsigned long param_type;
  static void Write(MessageWriter* writer, const param_type& p) {
    writer->WriteULong(p);
  }
  static bool Read(MessageReader* reader, param_type* r) {
    return reader->ReadULong(r);
  }
};

template <>
struct ParamTraitsFundamental<long long> {
  typedef long long param_type;
  static void Write(MessageWriter* writer, const param_type& p) {
    writer->WriteBytes(&p, sizeof(param_type));
  }
  static bool Read(MessageReader* reader, param_type* r) {
    return reader->ReadBytesInto(r, sizeof(*r));
  }
};

template <>
struct ParamTraitsFundamental<unsigned long long> {
  typedef unsigned long long param_type;
  static void Write(MessageWriter* writer, const param_type& p) {
    writer->WriteBytes(&p, sizeof(param_type));
  }
  static bool Read(MessageReader* reader, param_type* r) {
    return reader->ReadBytesInto(r, sizeof(*r));
  }
};

template <>
struct ParamTraitsFundamental<double> {
  typedef double param_type;
  static void Write(MessageWriter* writer, const param_type& p) {
    writer->WriteDouble(p);
  }
  static bool Read(MessageReader* reader, param_type* r) {
    return reader->ReadDouble(r);
  }
};

// Fixed-size <stdint.h> types.

template <class P>
struct ParamTraitsFixed : ParamTraitsFundamental<P> {};

template <>
struct ParamTraitsFixed<int8_t> {
  typedef int8_t param_type;
  static void Write(MessageWriter* writer, const param_type& p) {
    writer->WriteScalar(p);
  }
  static bool Read(MessageReader* reader, param_type* r) {
    return reader->ReadScalar(r);
  }
};

template <>
struct ParamTraitsFixed<uint8_t> {
  typedef uint8_t param_type;
  static void Write(MessageWriter* writer, const param_type& p) {
    writer->WriteScalar(p);
  }
  static bool Read(MessageReader* reader, param_type* r) {
    return reader->ReadScalar(r);
  }
};

template <>
struct ParamTraitsFixed<int16_t> {
  typedef int16_t param_type;
  static void Write(MessageWriter* writer, const param_type& p) {
    writer->WriteInt16(p);
  }
  static bool Read(MessageReader* reader, param_type* r) {
    return reader->ReadInt16(r);
  }
};

template <>
struct ParamTraitsFixed<uint16_t> {
  typedef uint16_t param_type;
  static void Write(MessageWriter* writer, const param_type& p) {
    writer->WriteUInt16(p);
  }
  static bool Read(MessageReader* reader, param_type* r) {
    return reader->ReadUInt16(r);
  }
};

template <>
struct ParamTraitsFixed<uint32_t> {
  typedef uint32_t param_type;
  static void Write(MessageWriter* writer, const param_type& p) {
    writer->WriteUInt32(p);
  }
  static bool Read(MessageReader* reader, param_type* r) {
    return reader->ReadUInt32(r);
  }
};

template <>
struct ParamTraitsFixed<int64_t> {
  typedef int64_t param_type;
  static void Write(MessageWriter* writer, const param_type& p) {
    writer->WriteInt64(p);
  }
  static bool Read(MessageReader* reader, param_type* r) {
    return reader->ReadInt64(r);
  }
};

template <>
struct ParamTraitsFixed<uint64_t> {
  typedef uint64_t param_type;
  static void Write(MessageWriter* writer, const param_type& p) {
    writer->WriteInt64(static_cast<int64_t>(p));
  }
  static bool Read(MessageReader* reader, param_type* r) {
    return reader->ReadInt64(reinterpret_cast<int64_t*>(r));
  }
};

// std::* types.

template <class P>
struct ParamTraitsStd : ParamTraitsFixed<P> {};

template <class T>
struct ParamTraitsStd<std::unique_ptr<T>> {
  using param_type = std::unique_ptr<T>;

  static void Write(MessageWriter* writer, const param_type& p) {
    bool isNull = p == nullptr;
    WriteParam(writer, isNull);

    if (!isNull) {
      WriteParam(writer, *p.get());
    }
  }

  static bool Read(IPC::MessageReader* reader, param_type* r) {
    bool isNull = true;
    if (!ReadParam(reader, &isNull)) {
      return false;
    }

    if (isNull) {
      r->reset();
    } else {
      // NOTE: We need to use outparam-style deserialization here, as unique_ptr
      // is used to deserialize data structures without move constructors.
      *r = std::make_unique<T>();
      if (!ReadParam(reader, r->get())) {
        return false;
      }
    }
    return true;
  }
};

template <class T>
struct ParamTraitsStd<std::basic_string<T>> {
  typedef std::basic_string<T> param_type;
  static void Write(MessageWriter* writer, const param_type& p) {
    WriteSequenceParam<const T&>(writer, p.data(), p.size());
  }
  static bool Read(MessageReader* reader, param_type* r) {
    return ReadSequenceParam<T>(reader, [&](uint32_t length) -> T* {
      r->resize(length);
      return r->data();
    });
  }
};

// Sending-only specialization for std::basic_string_view<T>. Uses an identical
// serialization format as std::basic_string<T>.
template <class T>
struct ParamTraitsStd<std::basic_string_view<T>> {
  using param_type = std::basic_string_view<T>;
  static void Write(MessageWriter* writer, const param_type& p) {
    WriteSequenceParam<const T&>(writer, p.data(), p.size());
  }
};

template <class T>
  requires(!std::same_as<T, bool>)
struct ParamTraitsStd<std::vector<T>> {
  using param_type = std::vector<T>;
  static void Write(MessageWriter* writer, const param_type& p) {
    WriteSequenceParam<const T&>(writer, p.data(), p.size());
  }
  static void Write(MessageWriter* writer, param_type&& p) {
    WriteSequenceParam<T&&>(writer, p.data(), p.size());
  }
  static bool Read(MessageReader* reader, param_type* r) {
    return ReadSequenceParam<T>(reader, [&](uint32_t length) -> T* {
      r->resize(length);
      return r->data();
    });
  }
};

// Sending-only specialization for std::span<T const>. Uses an identical
// serialization format as const std::vector<T>&.
template <class T>
struct ParamTraitsStd<std::span<const T>> {
  using param_type = std::span<const T>;
  static void Write(MessageWriter* writer, const param_type& p) {
    WriteSequenceParam<const T&>(writer, p.data(), p.size());
  }
};

template <class T>
decltype(auto) ForwardSubscript(T&& t, size_t index) {
  if constexpr (std::is_lvalue_reference_v<T&&>) {
    return t[index];
  } else {
    return std::move(t[index]);
  }
}

template <class C, class E, size_t N>
struct ParamTraitsFixedSizeCollectionHelper {
  using param_type = C;
  template <class P>
    requires std::same_as<std::remove_cvref_t<P>, param_type>
  static void Write(MessageWriter* writer, P&& p) {
    if constexpr (kUseWriteBytes<E>) {
      constexpr uint32_t byte_length = N * sizeof(E);
      MessageBufferWriter buf_writer(writer, byte_length);
      buf_writer.WriteBytes(std::data(p), byte_length);
    } else {
      WriteImpl(writer, std::forward<P>(p), std::make_index_sequence<N>{});
    }
  }

  static bool Read(MessageReader* reader, param_type* r) {
    if constexpr (kUseWriteBytes<E>) {
      constexpr uint32_t byte_length = N * sizeof(E);
      MessageBufferReader buf_reader(reader, byte_length);
      if (!buf_reader.ReadBytesInto(std::data(*r), byte_length)) {
        return false;
      }
      return true;
    } else {
      return ReadImpl(reader, r, std::make_index_sequence<N>{});
    }
  }

 private:
  template <class P, size_t... Is>
  static void WriteImpl(MessageWriter* writer, P&& p,
                        std::index_sequence<Is...>) {
    (WriteParam(writer, ForwardSubscript<P>(p, Is)), ...);
  }

  template <size_t... Is>
  static bool ReadImpl(MessageReader* reader, param_type* r,
                       std::index_sequence<Is...>) {
    if ((!ReadParam(reader, &(*r)[Is]) || ...)) {
      return false;
    }
    return true;
  }
};

template <class T, size_t N>
struct ParamTraitsStd<std::array<T, N>>
    : ParamTraitsFixedSizeCollectionHelper<std::array<T, N>, T, N> {};

template <class T, size_t N>
struct ParamTraitsStd<T[N]> : ParamTraitsFixedSizeCollectionHelper<T[N], T, N> {
};

template <class T>
struct ParamTraitsStd<std::optional<T>> {
  using param_type = std::optional<T>;
  template <class P>
    requires std::same_as<std::remove_cvref_t<P>, param_type>
  static void Write(MessageWriter* writer, P&& p) {
    WriteParam(writer, p.has_value());
    if (p.has_value()) {
      WriteParam(writer, *std::forward<P>(p));
    }
  }
  static bool Read(MessageReader* reader, param_type* r) {
    bool has_value;
    if (!ReadParam(reader, &has_value)) {
      return false;
    }
    *r = std::nullopt;
    if (has_value) {
      auto result = ReadParam<T>(reader);
      if (!result.isOk()) {
        return false;
      }
      r->emplace(std::move(*result));
    }
    return true;
  }
};

template <class T, class U>
struct ParamTraitsStd<std::pair<T, U>> {
  using param_type = std::pair<T, U>;
  template <class P>
    requires std::same_as<std::remove_cvref_t<P>, param_type>
  static void Write(MessageWriter* writer, P&& p) {
    WriteParam(writer, std::get<0>(std::forward<P>(p)));
    WriteParam(writer, std::get<1>(std::forward<P>(p)));
  }
  static ReadResult<param_type> Read(MessageReader* reader) {
    auto first = ReadParam<T>(reader);
    if (!first) {
      return {};
    }
    auto second = ReadParam<U>(reader);
    if (!second) {
      return {};
    }
    return ReadResult<param_type>{std::in_place, std::move(*first),
                                  std::move(*second)};
  }
};

template <class... Ts>
struct ParamTraitsStd<std::tuple<Ts...>> {
  using param_type = std::tuple<Ts...>;
  template <class P>
    requires std::same_as<std::remove_cvref_t<P>, param_type>
  static void Write(MessageWriter* writer, P&& p) {
    WriteImpl(writer, std::forward<P>(p), std::index_sequence_for<Ts...>{});
  }
  static ReadResult<param_type> Read(MessageReader* reader) {
    return ReadImpl<Ts...>(reader);
  }

 private:
  template <class P, size_t... Is>
  static void WriteImpl(MessageWriter* writer, P&& p,
                        std::index_sequence<Is...>) {
    (WriteParam(writer, std::get<Is>(std::forward<P>(p))), ...);
  }

  template <class T, class... Rest>
  static ReadResult<std::tuple<T, Rest...>> ReadImpl(MessageReader* reader) {
    auto element = ReadParam<T>(reader);
    if (!element) {
      return {};
    }
    if constexpr (sizeof...(Rest) == 0) {
      return ReadResult<std::tuple<T>>{std::in_place, std::move(*element)};
    } else {
      auto rest = ReadImpl<Rest...>(reader);
      if (!rest) {
        return {};
      }
      return ReadResult<std::tuple<T, Rest...>>{
          std::in_place,
          std::tuple_cat(std::tuple(std::move(*element)), std::move(*rest))};
    }
  }
};

template <class C>
struct ParamTraitsStlCollectionHelper {
  using param_type = C;
  using value_type = typename C::value_type;

  static void Write(MessageWriter* writer, const param_type& p) {
    WriteParam(writer, static_cast<uint64_t>(p.size()));
    for (const value_type& elt : p) {
      WriteParam(writer, elt);
    }
  }

  static bool Read(MessageReader* reader, param_type* r) {
    uint64_t size;
    if (!ReadParam(reader, &size)) {
      return false;
    }
    for (uint64_t i = 0; i < size; ++i) {
      auto elt = ReadParam<value_type>(reader);
      if (!elt) {
        return false;
      }
      r->emplace(std::move(*elt));
    }
    return true;
  }
};

template <class K, class V, class C>
struct ParamTraitsStd<std::map<K, V, C>>
    : public ParamTraitsStlCollectionHelper<std::map<K, V, C>> {};

template <class K, class V, class H, class P>
struct ParamTraitsStd<std::unordered_map<K, V, H, P>>
    : public ParamTraitsStlCollectionHelper<std::unordered_map<K, V, H, P>> {};

template <class K, class C>
struct ParamTraitsStd<std::set<K, C>>
    : public ParamTraitsStlCollectionHelper<std::set<K, C>> {};

template <class K, class H, class P>
struct ParamTraitsStd<std::unordered_set<K, H, P>>
    : public ParamTraitsStlCollectionHelper<std::unordered_set<K, H, P>> {};

template <>
struct ParamTraitsStd<std::monostate> {
  using param_type = std::monostate;
  static void Write(MessageWriter*, const param_type&) {}
  static bool Read(MessageReader*, param_type*) { return true; }
};

template <class... Ts>
struct ParamTraitsStd<std::variant<Ts...>> {
  using param_type = std::variant<Ts...>;

  template <class U>
  static void Write(MessageWriter* writer, U&& p) {
    WriteParam(writer, static_cast<uint64_t>(p.index()));
    std::visit(
        [&](auto&& param) {
          WriteParam(writer, std::forward<decltype(param)>(param));
        },
        std::forward<U>(p));
  }

  static ReadResult<param_type> Read(MessageReader* reader) {
    uint64_t index;
    if (!ReadParam(reader, &index)) {
      return {};
    }
    return ReadI<0>(reader, static_cast<size_t>(index));
  }

 private:
  template <size_t I>
  static ReadResult<param_type> ReadI(MessageReader* reader, size_t index) {
    if constexpr (I >= std::variant_size_v<param_type>) {
      return {};  // No matching variant index
    } else {
      if (index == I) {
        using alt_type = std::variant_alternative_t<I, param_type>;
        ReadResult<alt_type> alt = ReadParam<alt_type>(reader);
        if (!alt) {
          return {};
        }
        return ReadResult<param_type>{std::in_place, std::in_place_index<I>,
                                      std::move(alt.get())};
      }
      return ReadI<I + 1>(reader, index);
    }
  }
};

template <size_t N>
struct ParamTraitsStd<std::bitset<N>> {
  using paramType = std::bitset<N>;
  static void Write(MessageWriter* aWriter, const paramType& aParam) {
    paramType mask(UINT64_MAX);
    for (size_t i = 0; i < N; i += 64) {
      uint64_t value = ((aParam >> i) & mask).to_ullong();
      WriteParam(aWriter, value);
    }
  }

  static bool Read(MessageReader* aReader, paramType* aResult) {
    for (size_t i = 0; i < N; i += 64) {
      uint64_t value = 0;
      if (!ReadParam(aReader, &value)) {
        return false;
      }
      *aResult |= std::bitset<N>(value) << i;
    }
    return true;
  }
};

// Windows-specific types.

template <class P>
struct ParamTraitsWindows : ParamTraitsStd<P> {};

#if defined(XP_WIN)
template <>
struct ParamTraitsWindows<HANDLE> {
  static_assert(sizeof(HANDLE) == sizeof(intptr_t), "Wrong size for HANDLE?");

  static void Write(MessageWriter* writer, HANDLE p) {
    writer->WriteIntPtr(reinterpret_cast<intptr_t>(p));
  }
  static bool Read(MessageReader* reader, HANDLE* r) {
    return reader->ReadIntPtr(reinterpret_cast<intptr_t*>(r));
  }
};

template <>
struct ParamTraitsWindows<HWND> {
  static_assert(sizeof(HWND) == sizeof(intptr_t), "Wrong size for HWND?");

  static void Write(MessageWriter* writer, HWND p) {
    writer->WriteIntPtr(reinterpret_cast<intptr_t>(p));
  }
  static bool Read(MessageReader* reader, HWND* r) {
    return reader->ReadIntPtr(reinterpret_cast<intptr_t*>(r));
  }
};
#endif  // defined(XP_WIN)

// Various ipc/chromium types.

template <class P>
struct ParamTraitsIPC : ParamTraitsWindows<P> {};

// `UniqueFileHandle` may be serialized over IPC channels. On the receiving
// side, the UniqueFileHandle is a valid duplicate of the handle which was
// transmitted.
//
// When sending a UniqueFileHandle, the handle must be valid at the time of
// transmission. As transmission is asynchronous, this requires passing
// ownership of the handle to IPC.
//
// A UniqueFileHandle may only be read once. After it has been read once, it
// will be consumed, and future reads will return an invalid handle.
template <>
struct ParamTraitsIPC<mozilla::UniqueFileHandle> {
  typedef mozilla::UniqueFileHandle param_type;
  static void Write(MessageWriter* writer, param_type&& p) {
    const bool valid = p != nullptr;
    WriteParam(writer, valid);
    if (valid) {
      if (!writer->WriteFileHandle(std::move(p))) {
        writer->FatalError("Too many file handles for one message!");
        NOTREACHED() << "Too many file handles for one message!";
      }
    }
  }
  static bool Read(MessageReader* reader, param_type* r) {
    bool valid;
    if (!ReadParam(reader, &valid)) {
      reader->FatalError("Error reading file handle validity");
      return false;
    }

    if (!valid) {
      *r = nullptr;
      return true;
    }

    if (!reader->ConsumeFileHandle(r)) {
      reader->FatalError("File handle not found in message!");
      return false;
    }
    return true;
  }
};

#if defined(XP_DARWIN)
// `UniqueMachSendRight` may be serialized over IPC channels. On the receiving
// side, the UniqueMachSendRight is the local name of the right which was
// transmitted.
//
// When sending a UniqueMachSendRight, the right must be valid at the time of
// transmission. As transmission is asynchronous, this requires passing
// ownership of the handle to IPC.
//
// A UniqueMachSendRight may only be read once. After it has been read once, it
// will be consumed, and future reads will return an invalid right.
template <>
struct ParamTraitsIPC<mozilla::UniqueMachSendRight> {
  typedef mozilla::UniqueMachSendRight param_type;
  static void Write(MessageWriter* writer, param_type&& p) {
    const bool valid = p != nullptr;
    WriteParam(writer, valid);
    if (valid) {
      if (!writer->WriteMachSendRight(std::move(p))) {
        writer->FatalError("Too many mach send rights for one message!");
        NOTREACHED() << "Too many mach send rights for one message!";
      }
    }
  }
  static bool Read(MessageReader* reader, param_type* r) {
    bool valid;
    if (!ReadParam(reader, &valid)) {
      reader->FatalError("Error reading mach send right validity");
      return false;
    }

    if (!valid) {
      *r = nullptr;
      return true;
    }

    if (!reader->ConsumeMachSendRight(r)) {
      reader->FatalError("Mach send right not found in message!");
      return false;
    }
    return true;
  }
};

// `UniqueMachReceiveRight` may be serialized over IPC channels. On the
// receiving side, the UniqueMachReceiveRight is the local name of the right
// which was transmitted.
//
// When sending a UniqueMachReceiveRight, the right must be valid at the time of
// transmission. As transmission is asynchronous, this requires passing
// ownership of the handle to IPC.
//
// A UniqueMachReceiveRight may only be read once. After it has been read once,
// it will be consumed, and future reads will return an invalid right.
template <>
struct ParamTraitsIPC<mozilla::UniqueMachReceiveRight> {
  typedef mozilla::UniqueMachReceiveRight param_type;
  static void Write(MessageWriter* writer, param_type&& p) {
    const bool valid = p != nullptr;
    WriteParam(writer, valid);
    if (valid) {
      if (!writer->WriteMachReceiveRight(std::move(p))) {
        writer->FatalError("Too many mach receive rights for one message!");
        NOTREACHED() << "Too many mach receive rights for one message!";
      }
    }
  }
  static bool Read(MessageReader* reader, param_type* r) {
    bool valid;
    if (!ReadParam(reader, &valid)) {
      reader->FatalError("Error reading mach receive right validity");
      return false;
    }

    if (!valid) {
      *r = nullptr;
      return true;
    }

    if (!reader->ConsumeMachReceiveRight(r)) {
      reader->FatalError("Mach receive right not found in message!");
      return false;
    }
    return true;
  }
};
#endif

// Mozilla-specific types.

template <class P>
struct ParamTraitsMozilla : ParamTraitsIPC<P> {};

// Sending-only specialization for mozilla::Span<T const>. Uses an identical
// serialization format as `const nsTArray<T>&`.
template <class T>
struct ParamTraitsMozilla<mozilla::Span<const T>> {
  static void Write(MessageWriter* writer, mozilla::Span<const T> p) {
    WriteSequenceParam<const T>(writer, p.Elements(), p.Length());
  }
};

template <>
struct ParamTraitsMozilla<nsresult> {
  typedef nsresult param_type;
  static void Write(MessageWriter* writer, const param_type& p) {
    writer->WriteUInt32(static_cast<uint32_t>(p));
  }
  static bool Read(MessageReader* reader, param_type* r) {
    return reader->ReadUInt32(reinterpret_cast<uint32_t*>(r));
  }
};

// When being passed `RefPtr<T>` or `nsCOMPtr<T>`, forward to a specialization
// for the underlying target type. The parameter type will be passed as `T*`,
// and result as `RefPtr<T>*`.
//
// This is done explicitly to ensure that the deleted `&&` overload for
// `operator T*` is not selected in generic contexts, and to support
// deserializing into `nsCOMPtr<T>`.
template <class T>
struct ParamTraitsMozilla<RefPtr<T>> {
  static void Write(MessageWriter* writer, const RefPtr<T>& p) {
    ParamTraits<T*>::Write(writer, p.get());
  }

  static bool Read(MessageReader* reader, RefPtr<T>* r) {
    return ParamTraits<T*>::Read(reader, r);
  }
};

template <class T>
struct ParamTraitsMozilla<nsCOMPtr<T>> {
  static void Write(MessageWriter* writer, const nsCOMPtr<T>& p) {
    ParamTraits<T*>::Write(writer, p.get());
  }

  static bool Read(MessageReader* reader, nsCOMPtr<T>* r) {
    RefPtr<T> refptr;
    if (!ParamTraits<T*>::Read(reader, &refptr)) {
      return false;
    }
    *r = std::move(refptr);
    return true;
  }
};

template <class T>
struct ParamTraitsMozilla<mozilla::NotNull<T>> {
  static void Write(MessageWriter* writer, const mozilla::NotNull<T>& p) {
    ParamTraits<T>::Write(writer, p.get());
  }

  static ReadResult<mozilla::NotNull<T>> Read(MessageReader* reader) {
    auto ptr = ReadParam<T>(reader);
    if (!ptr) {
      return {};
    }
    if (!*ptr) {
      reader->FatalError("unexpected null value");
      return {};
    }
    return mozilla::WrapNotNull(std::move(*ptr));
  }
};

template <class T, size_t N>
struct ParamTraitsMozilla<mozilla::Array<T, N>>
    : ParamTraitsFixedSizeCollectionHelper<mozilla::Array<T, N>, T, N> {};

template <class T>
struct ParamTraitsMozilla<mozilla::Maybe<T>> {
  typedef mozilla::Maybe<T> paramType;
  static void Write(MessageWriter* writer, const mozilla::Maybe<T>& m) {
    bool isSome = m.isSome();
    WriteParam(writer, isSome);
    if (isSome) {
      WriteParam(writer, m.ref());
    }
  }

  static bool Read(MessageReader* reader, mozilla::Maybe<T>* r) {
    bool isSome;
    if (!ReadParam(reader, &isSome)) {
      return false;
    }
    if (isSome) {
      r->emplace();
      if (!ReadParam(reader, r->ptr())) {
        return false;
      }
    }
    return true;
  }
};

template <>
struct ParamTraits<mozilla::Nothing> {
  // Serialize as if it is a mozilla::Maybe (though in practice this is used for
  // a monostate Variant alternative type).

  typedef mozilla::Nothing paramType;
  static void Write(MessageWriter* writer, const paramType& aParam) {
    bool isSome = false;
    WriteParam(writer, isSome);
  }

  static bool Read(MessageReader* aReader, paramType* aResult) {
    bool isSome;
    if (!ReadParam(aReader, &isSome)) {
      return false;
    }
    MOZ_ASSERT(!isSome, "attempt to read Nothing from a Some value");
    *aResult = mozilla::Nothing();
    return true;
  }
};

// Finally, ParamTraits itself.

template <class P>
struct ParamTraits : ParamTraitsMozilla<P> {};

}  // namespace IPC

#endif  // CHROME_COMMON_IPC_MESSAGE_UTILS_H_