ipc/glue/ByteBuf.h
author Mike Conley <mconley@mozilla.com>
Fri, 01 Mar 2019 22:36:33 +0000
changeset 519920 b7a51e2d1d66f6cc8a9792741dd911014a9e0db3
parent 505383 6f3709b3878117466168c40affa7bca0b60cf75b
child 520122 87858af7a3cc594ed1eb1cc86c86ee08f9c76d21
permissions -rw-r--r--
Bug 1521964 - Allow VideoSink to have a secondary VideoFrameContainer assigned to it. r=jya Differential Revision: https://phabricator.services.mozilla.com/D20022

/* -*- 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/. */

/* A type that can be sent without needing to make a copy during
 * serialization. In addition the receiver can take ownership of the
 * data to avoid having to make an additional copy. */

#ifndef mozilla_ipc_ByteBuf_h
#define mozilla_ipc_ByteBuf_h

#include "ipc/IPCMessageUtils.h"

namespace mozilla {

namespace ipc {

class ByteBuf final {
  friend struct IPC::ParamTraits<mozilla::ipc::ByteBuf>;

 public:
  bool Allocate(size_t aLength) {
    MOZ_ASSERT(mData == nullptr);
    mData = (uint8_t*)malloc(aLength);
    if (!mData) {
      return false;
    }
    mLen = aLength;
    mCapacity = aLength;
    return true;
  }

  ByteBuf() : mData(nullptr), mLen(0), mCapacity(0) {}

  ByteBuf(uint8_t* aData, size_t aLen, size_t aCapacity)
      : mData(aData), mLen(aLen), mCapacity(aCapacity) {}

  ByteBuf(const ByteBuf& aFrom) = delete;

  ByteBuf(ByteBuf&& aFrom)
      : mData(aFrom.mData), mLen(aFrom.mLen), mCapacity(aFrom.mCapacity) {
    aFrom.mData = nullptr;
    aFrom.mLen = 0;
    aFrom.mCapacity = 0;
  }

  ByteBuf& operator=(ByteBuf&& aFrom) {
    std::swap(mData, aFrom.mData);
    std::swap(mLen, aFrom.mLen);
    std::swap(mCapacity, aFrom.mCapacity);
    return *this;
  }

  ~ByteBuf() { free(mData); }

  uint8_t* mData;
  size_t mLen;
  size_t mCapacity;
};

}  // namespace ipc
}  // namespace mozilla

namespace IPC {

template <>
struct ParamTraits<mozilla::ipc::ByteBuf> {
  typedef mozilla::ipc::ByteBuf paramType;

  // this is where we transfer the memory from the ByteBuf to IPDL, avoiding a
  // copy
  static void Write(Message* aMsg, paramType& aParam) {
    WriteParam(aMsg, aParam.mLen);
    // hand over ownership of the buffer to the Message
    aMsg->WriteBytesZeroCopy(aParam.mData, aParam.mLen, aParam.mCapacity);
    aParam.mData = nullptr;
    aParam.mCapacity = 0;
    aParam.mLen = 0;
  }

  static bool Read(const Message* aMsg, PickleIterator* aIter,
                   paramType* aResult) {
    // We make a copy from the BufferList so that we get a contigous result.
    // For users the can handle a non-contiguous result using ExtractBuffers
    // is an option, alternatively if the users don't need to take ownership of
    // the data they can use the removed FlattenBytes (bug 1297981)
    size_t length;
    return ReadParam(aMsg, aIter, &length) && aResult->Allocate(length) &&
           aMsg->ReadBytesInto(aIter, aResult->mData, length);
  }

  static void Log(const paramType& aParam, std::wstring* aLog) {
    aLog->append(L"(byte buf)");
  }
};

}  // namespace IPC

#endif  // ifndef mozilla_ipc_Shmem_h