1 files changed, 79 insertions, 0 deletions
diff --git a/ipc/glue/SerializedStructuredCloneBuffer.cpp b/ipc/glue/SerializedStructuredCloneBuffer.cpp
new file mode 100644
index 0000000000..9cad1ed826
--- /dev/null
+++ b/ipc/glue/SerializedStructuredCloneBuffer.cpp
@@ -0,0 +1,79 @@
+/* -*- 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/. */
+
+#include "mozilla/ipc/SerializedStructuredCloneBuffer.h"
+#include "js/StructuredClone.h"
+
+namespace IPC {
+
+void ParamTraits<JSStructuredCloneData>::Write(MessageWriter* aWriter,
+                                               const paramType& aParam) {
+  MOZ_ASSERT(!(aParam.Size() % sizeof(uint64_t)));
+
+  // We can only construct shared memory regions up to 4Gb in size, making that
+  // the maximum possible JSStructuredCloneData size.
+  mozilla::CheckedUint32 size = aParam.Size();
+  if (!size.isValid()) {
+    aWriter->FatalError("JSStructuredCloneData over 4Gb in size");
+    return;
+  }
+  WriteParam(aWriter, size.value());
+
+  MessageBufferWriter bufWriter(aWriter, size.value());
+  aParam.ForEachDataChunk([&](const char* aData, size_t aSize) {
+    return bufWriter.WriteBytes(aData, aSize);
+  });
+}
+
+bool ParamTraits<JSStructuredCloneData>::Read(MessageReader* aReader,
+                                              paramType* aResult) {
+  uint32_t length = 0;
+  if (!ReadParam(aReader, &length)) {
+    aReader->FatalError("JSStructuredCloneData length read failed");
+    return false;
+  }
+  MOZ_ASSERT(!(length % sizeof(uint64_t)));
+
+  // Borrowing is not suitable to use for IPC to hand out data because we often
+  // want to store the data somewhere for processing after IPC has released the
+  // underlying buffers.
+  //
+  // This deserializer previously used a mechanism to transfer ownership over
+  // the underlying buffers from IPC into the JSStructuredCloneData. This was
+  // removed when support for serializing over shared memory was added, as the
+  // benefit for avoiding copies was limited due to it only functioning for
+  // buffers under 64k in size (as larger buffers would be serialized using
+  // shared memory), and it added substantial complexity to the BufferList type
+  // and the IPC serialization layer due to things like buffer alignment. This
+  // can be revisited in the future if it turns out to be a noticable
+  // performance regression. (bug 1783242)
+
+  mozilla::BufferList<js::SystemAllocPolicy> buffers(0, 0, 4096);
+  MessageBufferReader bufReader(aReader, length);
+  uint32_t read = 0;
+  while (read < length) {
+    size_t bufLen;
+    char* buf = buffers.AllocateBytes(length - read, &bufLen);
+    if (!buf) {
+      // Would be nice to allow actor to control behaviour here (bug 1784307)
+      NS_ABORT_OOM(length - read);
+      return false;
+    }
+    if (!bufReader.ReadBytesInto(buf, bufLen)) {
+      aReader->FatalError("JSStructuredCloneData ReadBytesInto failed");
+      return false;
+    }
+    read += bufLen;
+  }
+
+  MOZ_ASSERT(read == length);
+  *aResult = JSStructuredCloneData(
+      std::move(buffers), JS::StructuredCloneScope::DifferentProcess,
+      OwnTransferablePolicy::IgnoreTransferablesIfAny);
+  return true;
+}
+
+}  // namespace IPC