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src: use native CopyArrayBufferBytes for webstream buffer copy #66400

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src: use native CopyArrayBufferBytes for webstream buffer copy #66400

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80 changes: 37 additions & 43 deletions src/node_buffer.cc
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Original file line number Diff line number Diff line change
Expand Up @@ -1655,65 +1655,54 @@ static void SetDetachKey(const FunctionCallbackInfo<Value>& args) {
ab->SetDetachKey(key);
}

namespace {

std::pair<void*, size_t> DecomposeBufferToParts(Local<Value> buffer) {
void* pointer;
size_t byte_length;
if (buffer->IsArrayBuffer()) {
Local<ArrayBuffer> ab = buffer.As<ArrayBuffer>();
pointer = ab->Data();
byte_length = ab->ByteLength();
} else if (buffer->IsSharedArrayBuffer()) {
Local<SharedArrayBuffer> ab = buffer.As<SharedArrayBuffer>();
pointer = ab->Data();
byte_length = ab->ByteLength();
} else {
UNREACHABLE(); // Caller must validate.
}
return {pointer, byte_length};
void CopyArrayBufferImpl(Local<ArrayBuffer> target,
uint32_t target_start,
Local<ArrayBuffer> source,
uint32_t source_start,
uint32_t bytes_to_copy) {
uint32_t bytes_copied = source->CopyArrayBufferBytes(
source_start, bytes_to_copy, target, target_start);
CHECK_EQ(bytes_copied, bytes_to_copy);
}

} // namespace

void CopyArrayBuffer(const FunctionCallbackInfo<Value>& args) {
// args[0] == Destination ArrayBuffer
// args[1] == Destination ArrayBuffer Offset
// args[2] == Source ArrayBuffer
// args[3] == Source ArrayBuffer Offset
// args[4] == bytesToCopy

CHECK(args[0]->IsArrayBuffer() || args[0]->IsSharedArrayBuffer());
CHECK(args[0]->IsArrayBuffer());
CHECK(args[1]->IsUint32());
CHECK(args[2]->IsArrayBuffer() || args[2]->IsSharedArrayBuffer());
CHECK(args[2]->IsArrayBuffer());
Comment on lines +1675 to +1677

@Renegade334 Renegade334 Sep 29, 2026

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SharedArrayBuffers could never make it down this path, as canCopyArrayBuffer() uses ArrayBuffer primordials which throw on SharedArrayBuffers.

CHECK(args[3]->IsUint32());
CHECK(args[4]->IsUint32());

void* destination;
size_t destination_byte_length;
std::tie(destination, destination_byte_length) =
DecomposeBufferToParts(args[0]);

void* source;
size_t source_byte_length;
std::tie(source, source_byte_length) = DecomposeBufferToParts(args[2]);

uint32_t destination_offset = args[1].As<Uint32>()->Value();
uint32_t source_offset = args[3].As<Uint32>()->Value();
size_t bytes_to_copy = args[4].As<Uint32>()->Value();
CopyArrayBufferImpl(args[0].As<ArrayBuffer>(),
args[1].As<Uint32>()->Value(),
args[2].As<ArrayBuffer>(),
args[3].As<Uint32>()->Value(),
args[4].As<Uint32>()->Value());
}

// Assert the offsets are within bounds before the subtractions below, which
// would otherwise underflow and defeat the bytes_to_copy bounds checks.
CHECK_LE(destination_offset, destination_byte_length);
CHECK_LE(source_offset, source_byte_length);
CHECK_GE(destination_byte_length - destination_offset, bytes_to_copy);
CHECK_GE(source_byte_length - source_offset, bytes_to_copy);
void FastCopyArrayBuffer(Local<Value> receiver,
Local<Value> target,
uint32_t target_start,
Local<Value> source,
uint32_t source_start,
uint32_t bytes_to_copy) {
CHECK(target->IsArrayBuffer());
CHECK(source->IsArrayBuffer());

uint8_t* dest = static_cast<uint8_t*>(destination) + destination_offset;
uint8_t* src = static_cast<uint8_t*>(source) + source_offset;
memcpy(dest, src, bytes_to_copy);
CopyArrayBufferImpl(target.As<ArrayBuffer>(),
target_start,
source.As<ArrayBuffer>(),
source_start,
bytes_to_copy);
}

static CFunction fast_copy_array_buffer(CFunction::Make(FastCopyArrayBuffer));

// Converts a number parameter to size_t suitable for ArrayBuffer sizes
// Could be larger than uint32_t
// See v8::internal::TryNumberToSize and v8::internal::NumberToSize
Expand Down Expand Up @@ -1937,7 +1926,11 @@ void Initialize(Local<Object> target,
&fast_index_of_number);
SetMethodNoSideEffect(context, target, "indexOfString", IndexOfString);

SetMethod(context, target, "copyArrayBuffer", CopyArrayBuffer);
SetFastMethod(context,
target,
"copyArrayBuffer",
CopyArrayBuffer,
&fast_copy_array_buffer);
SetMethodNoSideEffect(
context, target, "createUnsafeArrayBuffer", CreateUnsafeArrayBuffer);
SetMethodNoSideEffect(
Expand Down Expand Up @@ -2060,6 +2053,7 @@ void RegisterExternalReferences(ExternalReferenceRegistry* registry) {
registry->Register(StringWrite<UTF8>);

registry->Register(CopyArrayBuffer);
registry->Register(fast_copy_array_buffer);
registry->Register(CreateUnsafeArrayBuffer);
registry->Register(ArrayBufferAlignedOffset);

Expand Down
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