ipc/glue/SerializedStructuredCloneBuffer.cpp

   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 file,
   5  * You can obtain one at http://mozilla.org/MPL/2.0/. */
   6
   7 #include "mozilla/ipc/SerializedStructuredCloneBuffer.h"
   8 #include "js/StructuredClone.h"
   9
  10 namespace IPC {
  11
  12 void ParamTraits<JSStructuredCloneData>::Write(MessageWriter* aWriter,
  13                                                const paramType& aParam) {
  14   MOZ_ASSERT(!(aParam.Size() % sizeof(uint64_t)));
  15
  16   // We can only construct shared memory regions up to 4Gb in size, making that
  17   // the maximum possible JSStructuredCloneData size.
  18   mozilla::CheckedUint32 size = aParam.Size();
  19   if (!size.isValid()) {
  20     aWriter->FatalError("JSStructuredCloneData over 4Gb in size");
  21     return;
  22   }
  23   WriteParam(aWriter, size.value());
  24
  25   MessageBufferWriter bufWriter(aWriter, size.value());
  26   aParam.ForEachDataChunk([&](const char* aData, size_t aSize) {
  27     return bufWriter.WriteBytes(aData, aSize);
  28   });
  29 }
  30
  31 bool ParamTraits<JSStructuredCloneData>::Read(MessageReader* aReader,
  32                                               paramType* aResult) {
  33   uint32_t length = 0;
  34   if (!ReadParam(aReader, &length)) {
  35     aReader->FatalError("JSStructuredCloneData length read failed");
  36     return false;
  37   }
  38   MOZ_ASSERT(!(length % sizeof(uint64_t)));
  39
  40   // Borrowing is not suitable to use for IPC to hand out data because we often
  41   // want to store the data somewhere for processing after IPC has released the
  42   // underlying buffers.
  43   //
  44   // This deserializer previously used a mechanism to transfer ownership over
  45   // the underlying buffers from IPC into the JSStructuredCloneData. This was
  46   // removed when support for serializing over shared memory was added, as the
  47   // benefit for avoiding copies was limited due to it only functioning for
  48   // buffers under 64k in size (as larger buffers would be serialized using
  49   // shared memory), and it added substantial complexity to the BufferList type
  50   // and the IPC serialization layer due to things like buffer alignment. This
  51   // can be revisited in the future if it turns out to be a noticable
  52   // performance regression. (bug 1783242)
  53
  54   mozilla::BufferList<js::SystemAllocPolicy> buffers(0, 0, 4096);
  55   MessageBufferReader bufReader(aReader, length);
  56   uint32_t read = 0;
  57   while (read < length) {
  58     size_t bufLen;
  59     char* buf = buffers.AllocateBytes(length - read, &bufLen);
  60     if (!buf) {
  61       // Would be nice to allow actor to control behaviour here (bug 1784307)
  62       NS_ABORT_OOM(length - read);
  63       return false;
  64     }
  65     if (!bufReader.ReadBytesInto(buf, bufLen)) {
  66       aReader->FatalError("JSStructuredCloneData ReadBytesInto failed");
  67       return false;
  68     }
  69     read += bufLen;
  70   }
  71
  72   MOZ_ASSERT(read == length);
  73   *aResult = JSStructuredCloneData(
  74       std::move(buffers), JS::StructuredCloneScope::DifferentProcess,
  75       OwnTransferablePolicy::IgnoreTransferablesIfAny);
  76   return true;
  77 }
  78
  79 }  // namespace IPC