ipc/glue/ByteBufUtils.h

   1 /* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
   2 /* vim: set ts=8 sts=2 et sw=2 tw=80: */
   3 /* This Source Code Form is subject to the terms of the Mozilla Public
   4  * License, v. 2.0. If a copy of the MPL was not distributed with this
   5  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
   6
   7 /* A type that can be sent without needing to make a copy during
   8  * serialization. In addition the receiver can take ownership of the
   9  * data to avoid having to make an additional copy. */
  10
  11 #ifndef mozilla_ipc_ByteBufUtils_h
  12 #define mozilla_ipc_ByteBufUtils_h
  13
  14 #include "mozilla/ipc/ByteBuf.h"
  15 #include "mozilla/CheckedInt.h"
  16 #include "mozilla/mozalloc_oom.h"
  17 #include "ipc/IPCMessageUtils.h"
  18
  19 namespace IPC {
  20
  21 template <>
  22 struct ParamTraits<mozilla::ipc::ByteBuf> {
  23   typedef mozilla::ipc::ByteBuf paramType;
  24
  25   // this is where we transfer the memory from the ByteBuf to IPDL, avoiding a
  26   // copy
  27   static void Write(MessageWriter* aWriter, paramType&& aParam) {
  28     // We need to send the length as a 32-bit value, not a size_t, because on
  29     // ARM64 Windows we end up with a 32-bit GMP process sending a ByteBuf to
  30     // a 64-bit parent process. WriteBytesZeroCopy takes a uint32_t as an
  31     // argument, so it would end up getting truncated anyways. See bug 1757534.
  32     mozilla::CheckedInt<uint32_t> length = aParam.mLen;
  33     MOZ_RELEASE_ASSERT(length.isValid());
  34     WriteParam(aWriter, length.value());
  35     // hand over ownership of the buffer to the Message
  36     aWriter->WriteBytesZeroCopy(aParam.mData, length.value(), aParam.mCapacity);
  37     aParam.mData = nullptr;
  38     aParam.mCapacity = 0;
  39     aParam.mLen = 0;
  40   }
  41
  42   static bool Read(MessageReader* aReader, paramType* aResult) {
  43     // We make a copy from the BufferList so that we get a contigous result.
  44     uint32_t length;
  45     if (!ReadParam(aReader, &length)) return false;
  46     if (!aResult->Allocate(length)) {
  47       mozalloc_handle_oom(length);
  48       return false;
  49     }
  50     return aReader->ReadBytesInto(aResult->mData, length);
  51   }
  52 };
  53
  54 }  // namespace IPC
  55
  56 #endif  // ifndef mozilla_ipc_ByteBufUtils_h