src: add v8::Local specialization for MaybeStackBuffer

Long-term itch. Per v8 rules, we're not supposed to be
heap allocating v8::Local's; instead we're supposed to
be using v8::LocalVector. Create a specialization of
MaybeStackBuffer that uses either a stack array of
v8::Locals or v8::LocalVector with some additional
utility improvements.
Signed-off-by: James M Snell <jasnell@gmail.com>
PR-URL: #65159
Reviewed-By: Stephen Belanger <admin@stephenbelanger.com>

Author: jasnell

src/api/callback.cc

@@ -245,7 +245,7 @@ MaybeLocal<Value> InternalMakeCallback(Environment* env,
 
  Local<Context> context = env->context();
 if (use_async_hooks_trampoline) {
- MaybeStackBuffer<Local<Value>, 16> args(3 + argc);
+ MaybeStackBuffer<Value, 16> args(env->isolate(), 3 + argc);
  args[0] = Number::New(env->isolate(), asyncContext.async_id);
  args[1] = resource;
  args[2] = callback;

src/cares_wrap.cc

@@ -201,12 +201,12 @@ Local<Array> AddrTTLToArray(
  Environment* env,
 const T* addrttls,
 size_t naddrttls) {
- MaybeStackBuffer<Local<Value>, 8> ttls(naddrttls);
+ MaybeStackBuffer<Value, 8> ttls(env->isolate(), naddrttls);
 for (size_t i = 0; i < naddrttls; i++) {
  ttls[i] = Integer::NewFromUnsigned(env->isolate(), addrttls[i].ttl);
  }
 
-returnArray::New(env->isolate(), ttls.out(), naddrttls);
+return ttls.ToArray();
 }
 
 intGetAnswerCountForTTLBuffer(constunsignedchar* buf, int len) {

src/crypto/crypto_tls.cc

@@ -41,7 +41,6 @@ using ncrypto::MarkPopErrorOnReturn;
 using ncrypto::SSLPointer;
 using ncrypto::SSLSessionPointer;
 using ncrypto::X509Pointer;
-using v8::Array;
 using v8::ArrayBuffer;
 using v8::ArrayBufferView;
 using v8::BackingStore;
@@ -1956,7 +1955,7 @@ void TLSWrap::GetSharedSigalgs(const FunctionCallbackInfo<Value>& args) {
 SSL* ssl = w->ssl_.get();
 int nsig = SSL_get_shared_sigalgs(ssl, 0, nullptr, nullptr, nullptr, nullptr,
 nullptr);
- MaybeStackBuffer<Local<Value>, 16> ret_arr(nsig);
+ MaybeStackBuffer<Value, 16> ret_arr(env->isolate(), nsig);
 
 for (int i = 0; i < nsig; i++) {
 int hash_nid;
@@ -2023,8 +2022,7 @@ void TLSWrap::GetSharedSigalgs(const FunctionCallbackInfo<Value>& args) {
  ret_arr[i] = OneByteString(env->isolate(), sig_with_md);
  }
 
- args.GetReturnValue().Set(
-Array::New(env->isolate(), ret_arr.out(), ret_arr.length()));
+ args.GetReturnValue().Set(ret_arr.ToArray());
 }
 
 voidTLSWrap::ExportKeyingMaterial(const FunctionCallbackInfo<Value>& args) {

src/js_stream.cc

@@ -11,7 +11,6 @@ namespace node {
 
 using errors::TryCatchScope;
 
-using v8::Array;
 using v8::Context;
 using v8::FunctionCallbackInfo;
 using v8::FunctionTemplate;
@@ -119,17 +118,14 @@ int JSStream::DoWrite(WriteWrap* w,
 
 int value_int = UV_EPROTO;
 
- MaybeStackBuffer<Local<Value>, 16> bufs_arr(count);
+ MaybeStackBuffer<Value, 16> bufs_arr(env()->isolate(), count);
 for (size_t i = 0; i < count; i++) {
 if (!Buffer::Copy(env(), bufs[i].base, bufs[i].len).ToLocal(&bufs_arr[i])) {
 return value_int;
  }
  }
 
- Local<Value> argv[] = {
- w->object(),
-Array::New(env()->isolate(), bufs_arr.out(), count)
- };
+ Local<Value> argv[] = {w->object(), bufs_arr.ToArray()};
 
  TryCatchScope try_catch(env());
  Local<Value> value;

src/js_udp_wrap.cc

@@ -11,7 +11,6 @@
 namespacenode {
 
 using errors::TryCatchScope;
-using v8::Array;
 using v8::Context;
 using v8::FunctionCallbackInfo;
 using v8::FunctionTemplate;
@@ -98,7 +97,7 @@ ssize_t JSUDPWrap::Send(uv_buf_t* bufs,
 int64_t value_int = JS_EXCEPTION_PENDING;
 size_t total_len = 0;
 
- MaybeStackBuffer<Local<Value>, 16> buffers(nbufs);
+ MaybeStackBuffer<Value, 16> buffers(env()->isolate(), nbufs);
 for (size_t i = 0; i < nbufs; i++) {
 if (!Buffer::Copy(env(), bufs[i].base, bufs[i].len).ToLocal(&buffers[i])) {
 return value_int;
@@ -110,9 +109,9 @@ ssize_t JSUDPWrap::Send(uv_buf_t* bufs,
 if (!AddressToJS(env(), addr).ToLocal(&address)) return value_int;
 
  Local<Value> args[] = {
-listener()->CreateSendWrap(total_len)->object(),
-Array::New(env()->isolate(), buffers.out(), nbufs),
- address,
+listener()->CreateSendWrap(total_len)->object(),
+buffers.ToArray(),
+address,
  };
 
 if (!MakeCallback(env()->onwrite_string(), arraysize(args), args)

src/node_concepts.h

@@ -3,6 +3,7 @@
 
 #if defined(NODE_WANT_INTERNALS) && NODE_WANT_INTERNALS
 
+#include<v8.h>
 #include<concepts>
 #include<limits>
 #include<type_traits>
@@ -32,6 +33,12 @@ concept StandardCharType =
 template <typename T>
 concept IsCallable = std::is_function<T>::value || requires { &T::operator(); };
 
+// Types that can reside on V8's managed heap (v8::Value, v8::Object, etc.).
+// Used to select the MaybeStackBuffer specialization that holds handles in a
+// v8::LocalVector instead of malloc'd memory.
+template <typename T>
+concept V8Type = std::is_base_of_v<v8::Data, T>;
+
 } // namespace node
 
 #endif// defined(NODE_WANT_INTERNALS) && NODE_WANT_INTERNALS

src/node_dir.cc

@@ -206,7 +206,7 @@ static MaybeLocal<Array> DirentListToArray(Environment* env,
 uv_dirent_t* ents,
 int num,
 enum encoding encoding) {
- MaybeStackBuffer<Local<Value>, 64> entries(num * 2);
+ MaybeStackBuffer<Value, 64> entries(env->isolate(), num * 2);
 
 // Return an array of all read filenames.
 int j = 0;
@@ -222,7 +222,8 @@ static MaybeLocal<Array> DirentListToArray(Environment* env,
  entries[j++] = Integer::New(env->isolate(), ents[i].type);
  }
 
-returnArray::New(env->isolate(), entries.out(), j);
+CHECK_EQ(j, num * 2);
+return entries.ToArray();
 }
 
 staticvoidAfterDirRead(uv_fs_t* req) {

src/node_env_var.cc

@@ -201,7 +201,7 @@ MaybeLocal<Array> RealEnvStore::Enumerate(Isolate* isolate) const {
 auto cleanup = OnScopeLeave([&]() { uv_os_free_environ(items, count); });
 CHECK_EQ(uv_os_environ(&items, &count), 0);
 
- MaybeStackBuffer<Local<Value>, 256> env_v(count);
+ MaybeStackBuffer<Value, 256> env_v(isolate, count);
 int env_v_index = 0;
 for (int i = 0; i < count; i++) {
 #ifdef _WIN32
@@ -216,7 +216,10 @@ MaybeLocal<Array> RealEnvStore::Enumerate(Isolate* isolate) const {
  env_v[env_v_index++] = str;
  }
 
-returnArray::New(isolate, env_v.out(), env_v_index);
+// We're possibly not filling the entire buffer.
+CHECK_LE(env_v_index, count);
+ env_v.SetLength(env_v_index);
+return env_v.ToArray();
 }
 
 std::shared_ptr<KVStore> KVStore::Clone(Isolate* isolate) const {

src/node_http2.cc

@@ -1585,8 +1585,8 @@ void Http2Session::HandleHeadersFrame(const nghttp2_frame* frame) {
 // this way for performance reasons (it's faster to generate and pass an
 // array than it is to generate and pass the object).
 
- MaybeStackBuffer<Local<Value>, 64> headers_v(stream->headers_count() * 2);
- MaybeStackBuffer<Local<Value>, 32> sensitive_v(stream->headers_count());
+ MaybeStackBuffer<Value, 64> headers_v(isolate, stream->headers_count() * 2);
+ MaybeStackBuffer<Value, 32> sensitive_v(isolate, stream->headers_count());
 size_t sensitive_count = 0;
 
  stream->TransferHeaders([&](const Http2Header& header, size_t i) {
@@ -1603,13 +1603,14 @@ void Http2Session::HandleHeadersFrame(const nghttp2_frame* frame) {
  stream->retained_headers_length_ += stream->current_headers_length_;
  stream->current_headers_length_ = 0;
 
+ sensitive_v.SetLength(sensitive_count);
  Local<Value> args[] = {
- stream->object(),
-Integer::New(isolate, id),
-Integer::New(isolate, stream->headers_category()),
-Integer::New(isolate, frame->hd.flags),
-Array::New(isolate, headers_v.out(), headers_v.length()),
-Array::New(isolate, sensitive_v.out(), sensitive_count),
+stream->object(),
+Integer::New(isolate, id),
+Integer::New(isolate, stream->headers_category()),
+Integer::New(isolate, frame->hd.flags),
+ headers_v.ToArray(),
+sensitive_v.ToArray(),
  };
 MakeCallback(env()->http2session_on_headers_function(),
 arraysize(args), args);

src/node_messaging.cc

@@ -1093,7 +1093,7 @@ void MessagePort::PostMessage(const FunctionCallbackInfo<Value>& args) {
 "MessagePort.postMessage");
  }
 
- TransferList transfer_list;
+ TransferList transfer_list(env->isolate());
 if (!GetTransferList(env, context, args[1], &transfer_list)) {
 return;
  }
@@ -1607,7 +1607,7 @@ static void StructuredClone(const FunctionCallbackInfo<Value>& args) {
 
  Local<Value> value = args[0];
 
- TransferList transfer_list;
+ TransferList transfer_list(isolate);
  Local<Object> options = args[1].As<Object>();
  Local<Value> transfer_list_v;
 if (!options->Get(context, env->transfer_string())

src/api/callback.cc

@@ -245,7 +245,7 @@ MaybeLocal<Value> InternalMakeCallback(Environment* env,
 
  Local<Context> context = env->context();
 if (use_async_hooks_trampoline) {
- MaybeStackBuffer<Local<Value>, 16> args(3 + argc);
+ MaybeStackBuffer<Value, 16> args(env->isolate(), 3 + argc);
  args[0] = Number::New(env->isolate(), asyncContext.async_id);
  args[1] = resource;
  args[2] = callback;

src/cares_wrap.cc

@@ -201,12 +201,12 @@ Local<Array> AddrTTLToArray(
  Environment* env,
 const T* addrttls,
 size_t naddrttls) {
- MaybeStackBuffer<Local<Value>, 8> ttls(naddrttls);
+ MaybeStackBuffer<Value, 8> ttls(env->isolate(), naddrttls);
 for (size_t i = 0; i < naddrttls; i++) {
  ttls[i] = Integer::NewFromUnsigned(env->isolate(), addrttls[i].ttl);
  }
 
-returnArray::New(env->isolate(), ttls.out(), naddrttls);
+return ttls.ToArray();
 }
 
 intGetAnswerCountForTTLBuffer(constunsignedchar* buf, int len) {

src/crypto/crypto_tls.cc

@@ -41,7 +41,6 @@ using ncrypto::MarkPopErrorOnReturn;
 using ncrypto::SSLPointer;
 using ncrypto::SSLSessionPointer;
 using ncrypto::X509Pointer;
-using v8::Array;
 using v8::ArrayBuffer;
 using v8::ArrayBufferView;
 using v8::BackingStore;
@@ -1956,7 +1955,7 @@ void TLSWrap::GetSharedSigalgs(const FunctionCallbackInfo<Value>& args) {
 SSL* ssl = w->ssl_.get();
 int nsig = SSL_get_shared_sigalgs(ssl, 0, nullptr, nullptr, nullptr, nullptr,
 nullptr);
- MaybeStackBuffer<Local<Value>, 16> ret_arr(nsig);
+ MaybeStackBuffer<Value, 16> ret_arr(env->isolate(), nsig);
 
 for (int i = 0; i < nsig; i++) {
 int hash_nid;
@@ -2023,8 +2022,7 @@ void TLSWrap::GetSharedSigalgs(const FunctionCallbackInfo<Value>& args) {
  ret_arr[i] = OneByteString(env->isolate(), sig_with_md);
  }
 
- args.GetReturnValue().Set(
-Array::New(env->isolate(), ret_arr.out(), ret_arr.length()));
+ args.GetReturnValue().Set(ret_arr.ToArray());
 }
 
 voidTLSWrap::ExportKeyingMaterial(const FunctionCallbackInfo<Value>& args) {

src/js_stream.cc

@@ -11,7 +11,6 @@ namespace node {
 
 using errors::TryCatchScope;
 
-using v8::Array;
 using v8::Context;
 using v8::FunctionCallbackInfo;
 using v8::FunctionTemplate;
@@ -119,17 +118,14 @@ int JSStream::DoWrite(WriteWrap* w,
 
 int value_int = UV_EPROTO;
 
- MaybeStackBuffer<Local<Value>, 16> bufs_arr(count);
+ MaybeStackBuffer<Value, 16> bufs_arr(env()->isolate(), count);
 for (size_t i = 0; i < count; i++) {
 if (!Buffer::Copy(env(), bufs[i].base, bufs[i].len).ToLocal(&bufs_arr[i])) {
 return value_int;
  }
  }
 
- Local<Value> argv[] = {
- w->object(),
-Array::New(env()->isolate(), bufs_arr.out(), count)
- };
+ Local<Value> argv[] = {w->object(), bufs_arr.ToArray()};
 
  TryCatchScope try_catch(env());
  Local<Value> value;

src/js_udp_wrap.cc

@@ -11,7 +11,6 @@
 namespacenode {
 
 using errors::TryCatchScope;
-using v8::Array;
 using v8::Context;
 using v8::FunctionCallbackInfo;
 using v8::FunctionTemplate;
@@ -98,7 +97,7 @@ ssize_t JSUDPWrap::Send(uv_buf_t* bufs,
 int64_t value_int = JS_EXCEPTION_PENDING;
 size_t total_len = 0;
 
- MaybeStackBuffer<Local<Value>, 16> buffers(nbufs);
+ MaybeStackBuffer<Value, 16> buffers(env()->isolate(), nbufs);
 for (size_t i = 0; i < nbufs; i++) {
 if (!Buffer::Copy(env(), bufs[i].base, bufs[i].len).ToLocal(&buffers[i])) {
 return value_int;
@@ -110,9 +109,9 @@ ssize_t JSUDPWrap::Send(uv_buf_t* bufs,
 if (!AddressToJS(env(), addr).ToLocal(&address)) return value_int;
 
  Local<Value> args[] = {
-listener()->CreateSendWrap(total_len)->object(),
-Array::New(env()->isolate(), buffers.out(), nbufs),
- address,
+listener()->CreateSendWrap(total_len)->object(),
+buffers.ToArray(),
+address,
  };
 
 if (!MakeCallback(env()->onwrite_string(), arraysize(args), args)

src/node_concepts.h

@@ -3,6 +3,7 @@
 
 #if defined(NODE_WANT_INTERNALS) && NODE_WANT_INTERNALS
 
+#include<v8.h>
 #include<concepts>
 #include<limits>
 #include<type_traits>
@@ -32,6 +33,12 @@ concept StandardCharType =
 template <typename T>
 concept IsCallable = std::is_function<T>::value || requires { &T::operator(); };
 
+// Types that can reside on V8's managed heap (v8::Value, v8::Object, etc.).
+// Used to select the MaybeStackBuffer specialization that holds handles in a
+// v8::LocalVector instead of malloc'd memory.
+template <typename T>
+concept V8Type = std::is_base_of_v<v8::Data, T>;
+
 } // namespace node
 
 #endif// defined(NODE_WANT_INTERNALS) && NODE_WANT_INTERNALS

src/node_dir.cc

@@ -206,7 +206,7 @@ static MaybeLocal<Array> DirentListToArray(Environment* env,
 uv_dirent_t* ents,
 int num,
 enum encoding encoding) {
- MaybeStackBuffer<Local<Value>, 64> entries(num * 2);
+ MaybeStackBuffer<Value, 64> entries(env->isolate(), num * 2);
 
 // Return an array of all read filenames.
 int j = 0;
@@ -222,7 +222,8 @@ static MaybeLocal<Array> DirentListToArray(Environment* env,
  entries[j++] = Integer::New(env->isolate(), ents[i].type);
  }
 
-returnArray::New(env->isolate(), entries.out(), j);
+CHECK_EQ(j, num * 2);
+return entries.ToArray();
 }
 
 staticvoidAfterDirRead(uv_fs_t* req) {

src/node_env_var.cc

@@ -201,7 +201,7 @@ MaybeLocal<Array> RealEnvStore::Enumerate(Isolate* isolate) const {
 auto cleanup = OnScopeLeave([&]() { uv_os_free_environ(items, count); });
 CHECK_EQ(uv_os_environ(&items, &count), 0);
 
- MaybeStackBuffer<Local<Value>, 256> env_v(count);
+ MaybeStackBuffer<Value, 256> env_v(isolate, count);
 int env_v_index = 0;
 for (int i = 0; i < count; i++) {
 #ifdef _WIN32
@@ -216,7 +216,10 @@ MaybeLocal<Array> RealEnvStore::Enumerate(Isolate* isolate) const {
  env_v[env_v_index++] = str;
  }
 
-returnArray::New(isolate, env_v.out(), env_v_index);
+// We're possibly not filling the entire buffer.
+CHECK_LE(env_v_index, count);
+ env_v.SetLength(env_v_index);
+return env_v.ToArray();
 }
 
 std::shared_ptr<KVStore> KVStore::Clone(Isolate* isolate) const {

src/node_http2.cc

@@ -1585,8 +1585,8 @@ void Http2Session::HandleHeadersFrame(const nghttp2_frame* frame) {
 // this way for performance reasons (it's faster to generate and pass an
 // array than it is to generate and pass the object).
 
- MaybeStackBuffer<Local<Value>, 64> headers_v(stream->headers_count() * 2);
- MaybeStackBuffer<Local<Value>, 32> sensitive_v(stream->headers_count());
+ MaybeStackBuffer<Value, 64> headers_v(isolate, stream->headers_count() * 2);
+ MaybeStackBuffer<Value, 32> sensitive_v(isolate, stream->headers_count());
 size_t sensitive_count = 0;
 
  stream->TransferHeaders([&](const Http2Header& header, size_t i) {
@@ -1603,13 +1603,14 @@ void Http2Session::HandleHeadersFrame(const nghttp2_frame* frame) {
  stream->retained_headers_length_ += stream->current_headers_length_;
  stream->current_headers_length_ = 0;
 
+ sensitive_v.SetLength(sensitive_count);
  Local<Value> args[] = {
- stream->object(),
-Integer::New(isolate, id),
-Integer::New(isolate, stream->headers_category()),
-Integer::New(isolate, frame->hd.flags),
-Array::New(isolate, headers_v.out(), headers_v.length()),
-Array::New(isolate, sensitive_v.out(), sensitive_count),
+stream->object(),
+Integer::New(isolate, id),
+Integer::New(isolate, stream->headers_category()),
+Integer::New(isolate, frame->hd.flags),
+ headers_v.ToArray(),
+sensitive_v.ToArray(),
  };
 MakeCallback(env()->http2session_on_headers_function(),
 arraysize(args), args);

src/node_messaging.cc

@@ -1093,7 +1093,7 @@ void MessagePort::PostMessage(const FunctionCallbackInfo<Value>& args) {
 "MessagePort.postMessage");
  }
 
- TransferList transfer_list;
+ TransferList transfer_list(env->isolate());
 if (!GetTransferList(env, context, args[1], &transfer_list)) {
 return;
  }
@@ -1607,7 +1607,7 @@ static void StructuredClone(const FunctionCallbackInfo<Value>& args) {
 
  Local<Value> value = args[0];
 
- TransferList transfer_list;
+ TransferList transfer_list(isolate);
  Local<Object> options = args[1].As<Object>();
  Local<Value> transfer_list_v;
 if (!options->Get(context, env->transfer_string())

src/api/callback.cc

@@ -245,7 +245,7 @@ MaybeLocal<Value> InternalMakeCallback(Environment* env,
 
  Local<Context> context = env->context();
 if (use_async_hooks_trampoline) {
- MaybeStackBuffer<Local<Value>, 16> args(3 + argc);
+ MaybeStackBuffer<Value, 16> args(env->isolate(), 3 + argc);
  args[0] = Number::New(env->isolate(), asyncContext.async_id);
  args[1] = resource;
  args[2] = callback;

src/cares_wrap.cc

@@ -201,12 +201,12 @@ Local<Array> AddrTTLToArray(
  Environment* env,
 const T* addrttls,
 size_t naddrttls) {
- MaybeStackBuffer<Local<Value>, 8> ttls(naddrttls);
+ MaybeStackBuffer<Value, 8> ttls(env->isolate(), naddrttls);
 for (size_t i = 0; i < naddrttls; i++) {
  ttls[i] = Integer::NewFromUnsigned(env->isolate(), addrttls[i].ttl);
  }
 
-returnArray::New(env->isolate(), ttls.out(), naddrttls);
+return ttls.ToArray();
 }
 
 intGetAnswerCountForTTLBuffer(constunsignedchar* buf, int len) {

src/crypto/crypto_tls.cc

@@ -41,7 +41,6 @@ using ncrypto::MarkPopErrorOnReturn;
 using ncrypto::SSLPointer;
 using ncrypto::SSLSessionPointer;
 using ncrypto::X509Pointer;
-using v8::Array;
 using v8::ArrayBuffer;
 using v8::ArrayBufferView;
 using v8::BackingStore;
@@ -1956,7 +1955,7 @@ void TLSWrap::GetSharedSigalgs(const FunctionCallbackInfo<Value>& args) {
 SSL* ssl = w->ssl_.get();
 int nsig = SSL_get_shared_sigalgs(ssl, 0, nullptr, nullptr, nullptr, nullptr,
 nullptr);
- MaybeStackBuffer<Local<Value>, 16> ret_arr(nsig);
+ MaybeStackBuffer<Value, 16> ret_arr(env->isolate(), nsig);
 
 for (int i = 0; i < nsig; i++) {
 int hash_nid;
@@ -2023,8 +2022,7 @@ void TLSWrap::GetSharedSigalgs(const FunctionCallbackInfo<Value>& args) {
  ret_arr[i] = OneByteString(env->isolate(), sig_with_md);
  }
 
- args.GetReturnValue().Set(
-Array::New(env->isolate(), ret_arr.out(), ret_arr.length()));
+ args.GetReturnValue().Set(ret_arr.ToArray());
 }
 
 voidTLSWrap::ExportKeyingMaterial(const FunctionCallbackInfo<Value>& args) {

src/js_stream.cc

@@ -11,7 +11,6 @@ namespace node {
 
 using errors::TryCatchScope;
 
-using v8::Array;
 using v8::Context;
 using v8::FunctionCallbackInfo;
 using v8::FunctionTemplate;
@@ -119,17 +118,14 @@ int JSStream::DoWrite(WriteWrap* w,
 
 int value_int = UV_EPROTO;
 
- MaybeStackBuffer<Local<Value>, 16> bufs_arr(count);
+ MaybeStackBuffer<Value, 16> bufs_arr(env()->isolate(), count);
 for (size_t i = 0; i < count; i++) {
 if (!Buffer::Copy(env(), bufs[i].base, bufs[i].len).ToLocal(&bufs_arr[i])) {
 return value_int;
  }
  }
 
- Local<Value> argv[] = {
- w->object(),
-Array::New(env()->isolate(), bufs_arr.out(), count)
- };
+ Local<Value> argv[] = {w->object(), bufs_arr.ToArray()};
 
  TryCatchScope try_catch(env());
  Local<Value> value;

src/js_udp_wrap.cc

@@ -11,7 +11,6 @@
 namespacenode {
 
 using errors::TryCatchScope;
-using v8::Array;
 using v8::Context;
 using v8::FunctionCallbackInfo;
 using v8::FunctionTemplate;
@@ -98,7 +97,7 @@ ssize_t JSUDPWrap::Send(uv_buf_t* bufs,
 int64_t value_int = JS_EXCEPTION_PENDING;
 size_t total_len = 0;
 
- MaybeStackBuffer<Local<Value>, 16> buffers(nbufs);
+ MaybeStackBuffer<Value, 16> buffers(env()->isolate(), nbufs);
 for (size_t i = 0; i < nbufs; i++) {
 if (!Buffer::Copy(env(), bufs[i].base, bufs[i].len).ToLocal(&buffers[i])) {
 return value_int;
@@ -110,9 +109,9 @@ ssize_t JSUDPWrap::Send(uv_buf_t* bufs,
 if (!AddressToJS(env(), addr).ToLocal(&address)) return value_int;
 
  Local<Value> args[] = {
-listener()->CreateSendWrap(total_len)->object(),
-Array::New(env()->isolate(), buffers.out(), nbufs),
- address,
+listener()->CreateSendWrap(total_len)->object(),
+buffers.ToArray(),
+address,
  };
 
 if (!MakeCallback(env()->onwrite_string(), arraysize(args), args)

src/node_concepts.h

@@ -3,6 +3,7 @@
 
 #if defined(NODE_WANT_INTERNALS) && NODE_WANT_INTERNALS
 
+#include<v8.h>
 #include<concepts>
 #include<limits>
 #include<type_traits>
@@ -32,6 +33,12 @@ concept StandardCharType =
 template <typename T>
 concept IsCallable = std::is_function<T>::value || requires { &T::operator(); };
 
+// Types that can reside on V8's managed heap (v8::Value, v8::Object, etc.).
+// Used to select the MaybeStackBuffer specialization that holds handles in a
+// v8::LocalVector instead of malloc'd memory.
+template <typename T>
+concept V8Type = std::is_base_of_v<v8::Data, T>;
+
 } // namespace node
 
 #endif// defined(NODE_WANT_INTERNALS) && NODE_WANT_INTERNALS

src/node_dir.cc

@@ -206,7 +206,7 @@ static MaybeLocal<Array> DirentListToArray(Environment* env,
 uv_dirent_t* ents,
 int num,
 enum encoding encoding) {
- MaybeStackBuffer<Local<Value>, 64> entries(num * 2);
+ MaybeStackBuffer<Value, 64> entries(env->isolate(), num * 2);
 
 // Return an array of all read filenames.
 int j = 0;
@@ -222,7 +222,8 @@ static MaybeLocal<Array> DirentListToArray(Environment* env,
  entries[j++] = Integer::New(env->isolate(), ents[i].type);
  }
 
-returnArray::New(env->isolate(), entries.out(), j);
+CHECK_EQ(j, num * 2);
+return entries.ToArray();
 }
 
 staticvoidAfterDirRead(uv_fs_t* req) {

src/node_env_var.cc

@@ -201,7 +201,7 @@ MaybeLocal<Array> RealEnvStore::Enumerate(Isolate* isolate) const {
 auto cleanup = OnScopeLeave([&]() { uv_os_free_environ(items, count); });
 CHECK_EQ(uv_os_environ(&items, &count), 0);
 
- MaybeStackBuffer<Local<Value>, 256> env_v(count);
+ MaybeStackBuffer<Value, 256> env_v(isolate, count);
 int env_v_index = 0;
 for (int i = 0; i < count; i++) {
 #ifdef _WIN32
@@ -216,7 +216,10 @@ MaybeLocal<Array> RealEnvStore::Enumerate(Isolate* isolate) const {
  env_v[env_v_index++] = str;
  }
 
-returnArray::New(isolate, env_v.out(), env_v_index);
+// We're possibly not filling the entire buffer.
+CHECK_LE(env_v_index, count);
+ env_v.SetLength(env_v_index);
+return env_v.ToArray();
 }
 
 std::shared_ptr<KVStore> KVStore::Clone(Isolate* isolate) const {

src/node_http2.cc

@@ -1585,8 +1585,8 @@ void Http2Session::HandleHeadersFrame(const nghttp2_frame* frame) {
 // this way for performance reasons (it's faster to generate and pass an
 // array than it is to generate and pass the object).
 
- MaybeStackBuffer<Local<Value>, 64> headers_v(stream->headers_count() * 2);
- MaybeStackBuffer<Local<Value>, 32> sensitive_v(stream->headers_count());
+ MaybeStackBuffer<Value, 64> headers_v(isolate, stream->headers_count() * 2);
+ MaybeStackBuffer<Value, 32> sensitive_v(isolate, stream->headers_count());
 size_t sensitive_count = 0;
 
  stream->TransferHeaders([&](const Http2Header& header, size_t i) {
@@ -1603,13 +1603,14 @@ void Http2Session::HandleHeadersFrame(const nghttp2_frame* frame) {
  stream->retained_headers_length_ += stream->current_headers_length_;
  stream->current_headers_length_ = 0;
 
+ sensitive_v.SetLength(sensitive_count);
  Local<Value> args[] = {
- stream->object(),
-Integer::New(isolate, id),
-Integer::New(isolate, stream->headers_category()),
-Integer::New(isolate, frame->hd.flags),
-Array::New(isolate, headers_v.out(), headers_v.length()),
-Array::New(isolate, sensitive_v.out(), sensitive_count),
+stream->object(),
+Integer::New(isolate, id),
+Integer::New(isolate, stream->headers_category()),
+Integer::New(isolate, frame->hd.flags),
+ headers_v.ToArray(),
+sensitive_v.ToArray(),
  };
 MakeCallback(env()->http2session_on_headers_function(),
 arraysize(args), args);

src/node_messaging.cc

@@ -1093,7 +1093,7 @@ void MessagePort::PostMessage(const FunctionCallbackInfo<Value>& args) {
 "MessagePort.postMessage");
  }
 
- TransferList transfer_list;
+ TransferList transfer_list(env->isolate());
 if (!GetTransferList(env, context, args[1], &transfer_list)) {
 return;
  }
@@ -1607,7 +1607,7 @@ static void StructuredClone(const FunctionCallbackInfo<Value>& args) {
 
  Local<Value> value = args[0];
 
- TransferList transfer_list;
+ TransferList transfer_list(isolate);
  Local<Object> options = args[1].As<Object>();
  Local<Value> transfer_list_v;
 if (!options->Get(context, env->transfer_string())

src/api/callback.cc

@@ -245,7 +245,7 @@ MaybeLocal<Value> InternalMakeCallback(Environment* env,
 
  Local<Context> context = env->context();
 if (use_async_hooks_trampoline) {
- MaybeStackBuffer<Local<Value>, 16> args(3 + argc);
+ MaybeStackBuffer<Value, 16> args(env->isolate(), 3 + argc);
  args[0] = Number::New(env->isolate(), asyncContext.async_id);
  args[1] = resource;
  args[2] = callback;

src/cares_wrap.cc

@@ -201,12 +201,12 @@ Local<Array> AddrTTLToArray(
  Environment* env,
 const T* addrttls,
 size_t naddrttls) {
- MaybeStackBuffer<Local<Value>, 8> ttls(naddrttls);
+ MaybeStackBuffer<Value, 8> ttls(env->isolate(), naddrttls);
 for (size_t i = 0; i < naddrttls; i++) {
  ttls[i] = Integer::NewFromUnsigned(env->isolate(), addrttls[i].ttl);
  }
 
-returnArray::New(env->isolate(), ttls.out(), naddrttls);
+return ttls.ToArray();
 }
 
 intGetAnswerCountForTTLBuffer(constunsignedchar* buf, int len) {

src/crypto/crypto_tls.cc

@@ -41,7 +41,6 @@ using ncrypto::MarkPopErrorOnReturn;
 using ncrypto::SSLPointer;
 using ncrypto::SSLSessionPointer;
 using ncrypto::X509Pointer;
-using v8::Array;
 using v8::ArrayBuffer;
 using v8::ArrayBufferView;
 using v8::BackingStore;
@@ -1956,7 +1955,7 @@ void TLSWrap::GetSharedSigalgs(const FunctionCallbackInfo<Value>& args) {
 SSL* ssl = w->ssl_.get();
 int nsig = SSL_get_shared_sigalgs(ssl, 0, nullptr, nullptr, nullptr, nullptr,
 nullptr);
- MaybeStackBuffer<Local<Value>, 16> ret_arr(nsig);
+ MaybeStackBuffer<Value, 16> ret_arr(env->isolate(), nsig);
 
 for (int i = 0; i < nsig; i++) {
 int hash_nid;
@@ -2023,8 +2022,7 @@ void TLSWrap::GetSharedSigalgs(const FunctionCallbackInfo<Value>& args) {
  ret_arr[i] = OneByteString(env->isolate(), sig_with_md);
  }
 
- args.GetReturnValue().Set(
-Array::New(env->isolate(), ret_arr.out(), ret_arr.length()));
+ args.GetReturnValue().Set(ret_arr.ToArray());
 }
 
 voidTLSWrap::ExportKeyingMaterial(const FunctionCallbackInfo<Value>& args) {

src/js_stream.cc

@@ -11,7 +11,6 @@ namespace node {
 
 using errors::TryCatchScope;
 
-using v8::Array;
 using v8::Context;
 using v8::FunctionCallbackInfo;
 using v8::FunctionTemplate;
@@ -119,17 +118,14 @@ int JSStream::DoWrite(WriteWrap* w,
 
 int value_int = UV_EPROTO;
 
- MaybeStackBuffer<Local<Value>, 16> bufs_arr(count);
+ MaybeStackBuffer<Value, 16> bufs_arr(env()->isolate(), count);
 for (size_t i = 0; i < count; i++) {
 if (!Buffer::Copy(env(), bufs[i].base, bufs[i].len).ToLocal(&bufs_arr[i])) {
 return value_int;
  }
  }
 
- Local<Value> argv[] = {
- w->object(),
-Array::New(env()->isolate(), bufs_arr.out(), count)
- };
+ Local<Value> argv[] = {w->object(), bufs_arr.ToArray()};
 
  TryCatchScope try_catch(env());
  Local<Value> value;

src/js_udp_wrap.cc

@@ -11,7 +11,6 @@
 namespacenode {
 
 using errors::TryCatchScope;
-using v8::Array;
 using v8::Context;
 using v8::FunctionCallbackInfo;
 using v8::FunctionTemplate;
@@ -98,7 +97,7 @@ ssize_t JSUDPWrap::Send(uv_buf_t* bufs,
 int64_t value_int = JS_EXCEPTION_PENDING;
 size_t total_len = 0;
 
- MaybeStackBuffer<Local<Value>, 16> buffers(nbufs);
+ MaybeStackBuffer<Value, 16> buffers(env()->isolate(), nbufs);
 for (size_t i = 0; i < nbufs; i++) {
 if (!Buffer::Copy(env(), bufs[i].base, bufs[i].len).ToLocal(&buffers[i])) {
 return value_int;
@@ -110,9 +109,9 @@ ssize_t JSUDPWrap::Send(uv_buf_t* bufs,
 if (!AddressToJS(env(), addr).ToLocal(&address)) return value_int;
 
  Local<Value> args[] = {
-listener()->CreateSendWrap(total_len)->object(),
-Array::New(env()->isolate(), buffers.out(), nbufs),
- address,
+listener()->CreateSendWrap(total_len)->object(),
+buffers.ToArray(),
+address,
  };
 
 if (!MakeCallback(env()->onwrite_string(), arraysize(args), args)

src/node_concepts.h

@@ -3,6 +3,7 @@
 
 #if defined(NODE_WANT_INTERNALS) && NODE_WANT_INTERNALS
 
+#include<v8.h>
 #include<concepts>
 #include<limits>
 #include<type_traits>
@@ -32,6 +33,12 @@ concept StandardCharType =
 template <typename T>
 concept IsCallable = std::is_function<T>::value || requires { &T::operator(); };
 
+// Types that can reside on V8's managed heap (v8::Value, v8::Object, etc.).
+// Used to select the MaybeStackBuffer specialization that holds handles in a
+// v8::LocalVector instead of malloc'd memory.
+template <typename T>
+concept V8Type = std::is_base_of_v<v8::Data, T>;
+
 } // namespace node
 
 #endif// defined(NODE_WANT_INTERNALS) && NODE_WANT_INTERNALS

src/node_dir.cc

@@ -206,7 +206,7 @@ static MaybeLocal<Array> DirentListToArray(Environment* env,
 uv_dirent_t* ents,
 int num,
 enum encoding encoding) {
- MaybeStackBuffer<Local<Value>, 64> entries(num * 2);
+ MaybeStackBuffer<Value, 64> entries(env->isolate(), num * 2);
 
 // Return an array of all read filenames.
 int j = 0;
@@ -222,7 +222,8 @@ static MaybeLocal<Array> DirentListToArray(Environment* env,
  entries[j++] = Integer::New(env->isolate(), ents[i].type);
  }
 
-returnArray::New(env->isolate(), entries.out(), j);
+CHECK_EQ(j, num * 2);
+return entries.ToArray();
 }
 
 staticvoidAfterDirRead(uv_fs_t* req) {

src/node_env_var.cc

@@ -201,7 +201,7 @@ MaybeLocal<Array> RealEnvStore::Enumerate(Isolate* isolate) const {
 auto cleanup = OnScopeLeave([&]() { uv_os_free_environ(items, count); });
 CHECK_EQ(uv_os_environ(&items, &count), 0);
 
- MaybeStackBuffer<Local<Value>, 256> env_v(count);
+ MaybeStackBuffer<Value, 256> env_v(isolate, count);
 int env_v_index = 0;
 for (int i = 0; i < count; i++) {
 #ifdef _WIN32
@@ -216,7 +216,10 @@ MaybeLocal<Array> RealEnvStore::Enumerate(Isolate* isolate) const {
  env_v[env_v_index++] = str;
  }
 
-returnArray::New(isolate, env_v.out(), env_v_index);
+// We're possibly not filling the entire buffer.
+CHECK_LE(env_v_index, count);
+ env_v.SetLength(env_v_index);
+return env_v.ToArray();
 }
 
 std::shared_ptr<KVStore> KVStore::Clone(Isolate* isolate) const {

src/node_http2.cc

@@ -1585,8 +1585,8 @@ void Http2Session::HandleHeadersFrame(const nghttp2_frame* frame) {
 // this way for performance reasons (it's faster to generate and pass an
 // array than it is to generate and pass the object).
 
- MaybeStackBuffer<Local<Value>, 64> headers_v(stream->headers_count() * 2);
- MaybeStackBuffer<Local<Value>, 32> sensitive_v(stream->headers_count());
+ MaybeStackBuffer<Value, 64> headers_v(isolate, stream->headers_count() * 2);
+ MaybeStackBuffer<Value, 32> sensitive_v(isolate, stream->headers_count());
 size_t sensitive_count = 0;
 
  stream->TransferHeaders([&](const Http2Header& header, size_t i) {
@@ -1603,13 +1603,14 @@ void Http2Session::HandleHeadersFrame(const nghttp2_frame* frame) {
  stream->retained_headers_length_ += stream->current_headers_length_;
  stream->current_headers_length_ = 0;
 
+ sensitive_v.SetLength(sensitive_count);
  Local<Value> args[] = {
- stream->object(),
-Integer::New(isolate, id),
-Integer::New(isolate, stream->headers_category()),
-Integer::New(isolate, frame->hd.flags),
-Array::New(isolate, headers_v.out(), headers_v.length()),
-Array::New(isolate, sensitive_v.out(), sensitive_count),
+stream->object(),
+Integer::New(isolate, id),
+Integer::New(isolate, stream->headers_category()),
+Integer::New(isolate, frame->hd.flags),
+ headers_v.ToArray(),
+sensitive_v.ToArray(),
  };
 MakeCallback(env()->http2session_on_headers_function(),
 arraysize(args), args);

src/node_messaging.cc

@@ -1093,7 +1093,7 @@ void MessagePort::PostMessage(const FunctionCallbackInfo<Value>& args) {
 "MessagePort.postMessage");
  }
 
- TransferList transfer_list;
+ TransferList transfer_list(env->isolate());
 if (!GetTransferList(env, context, args[1], &transfer_list)) {
 return;
  }
@@ -1607,7 +1607,7 @@ static void StructuredClone(const FunctionCallbackInfo<Value>& args) {
 
  Local<Value> value = args[0];
 
- TransferList transfer_list;
+ TransferList transfer_list(isolate);
  Local<Object> options = args[1].As<Object>();
  Local<Value> transfer_list_v;
 if (!options->Get(context, env->transfer_string())

src/api/callback.cc

@@ -245,7 +245,7 @@ MaybeLocal<Value> InternalMakeCallback(Environment* env,
 
  Local<Context> context = env->context();
 if (use_async_hooks_trampoline) {
- MaybeStackBuffer<Local<Value>, 16> args(3 + argc);
+ MaybeStackBuffer<Value, 16> args(env->isolate(), 3 + argc);
  args[0] = Number::New(env->isolate(), asyncContext.async_id);
  args[1] = resource;
  args[2] = callback;

src/cares_wrap.cc

@@ -201,12 +201,12 @@ Local<Array> AddrTTLToArray(
  Environment* env,
 const T* addrttls,
 size_t naddrttls) {
- MaybeStackBuffer<Local<Value>, 8> ttls(naddrttls);
+ MaybeStackBuffer<Value, 8> ttls(env->isolate(), naddrttls);
 for (size_t i = 0; i < naddrttls; i++) {
  ttls[i] = Integer::NewFromUnsigned(env->isolate(), addrttls[i].ttl);
  }
 
-returnArray::New(env->isolate(), ttls.out(), naddrttls);
+return ttls.ToArray();
 }
 
 intGetAnswerCountForTTLBuffer(constunsignedchar* buf, int len) {

src/crypto/crypto_tls.cc

@@ -41,7 +41,6 @@ using ncrypto::MarkPopErrorOnReturn;
 using ncrypto::SSLPointer;
 using ncrypto::SSLSessionPointer;
 using ncrypto::X509Pointer;
-using v8::Array;
 using v8::ArrayBuffer;
 using v8::ArrayBufferView;
 using v8::BackingStore;
@@ -1956,7 +1955,7 @@ void TLSWrap::GetSharedSigalgs(const FunctionCallbackInfo<Value>& args) {
 SSL* ssl = w->ssl_.get();
 int nsig = SSL_get_shared_sigalgs(ssl, 0, nullptr, nullptr, nullptr, nullptr,
 nullptr);
- MaybeStackBuffer<Local<Value>, 16> ret_arr(nsig);
+ MaybeStackBuffer<Value, 16> ret_arr(env->isolate(), nsig);
 
 for (int i = 0; i < nsig; i++) {
 int hash_nid;
@@ -2023,8 +2022,7 @@ void TLSWrap::GetSharedSigalgs(const FunctionCallbackInfo<Value>& args) {
  ret_arr[i] = OneByteString(env->isolate(), sig_with_md);
  }
 
- args.GetReturnValue().Set(
-Array::New(env->isolate(), ret_arr.out(), ret_arr.length()));
+ args.GetReturnValue().Set(ret_arr.ToArray());
 }
 
 voidTLSWrap::ExportKeyingMaterial(const FunctionCallbackInfo<Value>& args) {

src/js_stream.cc

@@ -11,7 +11,6 @@ namespace node {
 
 using errors::TryCatchScope;
 
-using v8::Array;
 using v8::Context;
 using v8::FunctionCallbackInfo;
 using v8::FunctionTemplate;
@@ -119,17 +118,14 @@ int JSStream::DoWrite(WriteWrap* w,
 
 int value_int = UV_EPROTO;
 
- MaybeStackBuffer<Local<Value>, 16> bufs_arr(count);
+ MaybeStackBuffer<Value, 16> bufs_arr(env()->isolate(), count);
 for (size_t i = 0; i < count; i++) {
 if (!Buffer::Copy(env(), bufs[i].base, bufs[i].len).ToLocal(&bufs_arr[i])) {
 return value_int;
  }
  }
 
- Local<Value> argv[] = {
- w->object(),
-Array::New(env()->isolate(), bufs_arr.out(), count)
- };
+ Local<Value> argv[] = {w->object(), bufs_arr.ToArray()};
 
  TryCatchScope try_catch(env());
  Local<Value> value;

src/js_udp_wrap.cc

@@ -11,7 +11,6 @@
 namespacenode {
 
 using errors::TryCatchScope;
-using v8::Array;
 using v8::Context;
 using v8::FunctionCallbackInfo;
 using v8::FunctionTemplate;
@@ -98,7 +97,7 @@ ssize_t JSUDPWrap::Send(uv_buf_t* bufs,
 int64_t value_int = JS_EXCEPTION_PENDING;
 size_t total_len = 0;
 
- MaybeStackBuffer<Local<Value>, 16> buffers(nbufs);
+ MaybeStackBuffer<Value, 16> buffers(env()->isolate(), nbufs);
 for (size_t i = 0; i < nbufs; i++) {
 if (!Buffer::Copy(env(), bufs[i].base, bufs[i].len).ToLocal(&buffers[i])) {
 return value_int;
@@ -110,9 +109,9 @@ ssize_t JSUDPWrap::Send(uv_buf_t* bufs,
 if (!AddressToJS(env(), addr).ToLocal(&address)) return value_int;
 
  Local<Value> args[] = {
-listener()->CreateSendWrap(total_len)->object(),
-Array::New(env()->isolate(), buffers.out(), nbufs),
- address,
+listener()->CreateSendWrap(total_len)->object(),
+buffers.ToArray(),
+address,
  };
 
 if (!MakeCallback(env()->onwrite_string(), arraysize(args), args)

src/node_concepts.h

@@ -3,6 +3,7 @@
 
 #if defined(NODE_WANT_INTERNALS) && NODE_WANT_INTERNALS
 
+#include<v8.h>
 #include<concepts>
 #include<limits>
 #include<type_traits>
@@ -32,6 +33,12 @@ concept StandardCharType =
 template <typename T>
 concept IsCallable = std::is_function<T>::value || requires { &T::operator(); };
 
+// Types that can reside on V8's managed heap (v8::Value, v8::Object, etc.).
+// Used to select the MaybeStackBuffer specialization that holds handles in a
+// v8::LocalVector instead of malloc'd memory.
+template <typename T>
+concept V8Type = std::is_base_of_v<v8::Data, T>;
+
 } // namespace node
 
 #endif// defined(NODE_WANT_INTERNALS) && NODE_WANT_INTERNALS

src/node_dir.cc

@@ -206,7 +206,7 @@ static MaybeLocal<Array> DirentListToArray(Environment* env,
 uv_dirent_t* ents,
 int num,
 enum encoding encoding) {
- MaybeStackBuffer<Local<Value>, 64> entries(num * 2);
+ MaybeStackBuffer<Value, 64> entries(env->isolate(), num * 2);
 
 // Return an array of all read filenames.
 int j = 0;
@@ -222,7 +222,8 @@ static MaybeLocal<Array> DirentListToArray(Environment* env,
  entries[j++] = Integer::New(env->isolate(), ents[i].type);
  }
 
-returnArray::New(env->isolate(), entries.out(), j);
+CHECK_EQ(j, num * 2);
+return entries.ToArray();
 }
 
 staticvoidAfterDirRead(uv_fs_t* req) {

src/node_env_var.cc

@@ -201,7 +201,7 @@ MaybeLocal<Array> RealEnvStore::Enumerate(Isolate* isolate) const {
 auto cleanup = OnScopeLeave([&]() { uv_os_free_environ(items, count); });
 CHECK_EQ(uv_os_environ(&items, &count), 0);
 
- MaybeStackBuffer<Local<Value>, 256> env_v(count);
+ MaybeStackBuffer<Value, 256> env_v(isolate, count);
 int env_v_index = 0;
 for (int i = 0; i < count; i++) {
 #ifdef _WIN32
@@ -216,7 +216,10 @@ MaybeLocal<Array> RealEnvStore::Enumerate(Isolate* isolate) const {
  env_v[env_v_index++] = str;
  }
 
-returnArray::New(isolate, env_v.out(), env_v_index);
+// We're possibly not filling the entire buffer.
+CHECK_LE(env_v_index, count);
+ env_v.SetLength(env_v_index);
+return env_v.ToArray();
 }
 
 std::shared_ptr<KVStore> KVStore::Clone(Isolate* isolate) const {

src/node_http2.cc

@@ -1585,8 +1585,8 @@ void Http2Session::HandleHeadersFrame(const nghttp2_frame* frame) {
 // this way for performance reasons (it's faster to generate and pass an
 // array than it is to generate and pass the object).
 
- MaybeStackBuffer<Local<Value>, 64> headers_v(stream->headers_count() * 2);
- MaybeStackBuffer<Local<Value>, 32> sensitive_v(stream->headers_count());
+ MaybeStackBuffer<Value, 64> headers_v(isolate, stream->headers_count() * 2);
+ MaybeStackBuffer<Value, 32> sensitive_v(isolate, stream->headers_count());
 size_t sensitive_count = 0;
 
  stream->TransferHeaders([&](const Http2Header& header, size_t i) {
@@ -1603,13 +1603,14 @@ void Http2Session::HandleHeadersFrame(const nghttp2_frame* frame) {
  stream->retained_headers_length_ += stream->current_headers_length_;
  stream->current_headers_length_ = 0;
 
+ sensitive_v.SetLength(sensitive_count);
  Local<Value> args[] = {
- stream->object(),
-Integer::New(isolate, id),
-Integer::New(isolate, stream->headers_category()),
-Integer::New(isolate, frame->hd.flags),
-Array::New(isolate, headers_v.out(), headers_v.length()),
-Array::New(isolate, sensitive_v.out(), sensitive_count),
+stream->object(),
+Integer::New(isolate, id),
+Integer::New(isolate, stream->headers_category()),
+Integer::New(isolate, frame->hd.flags),
+ headers_v.ToArray(),
+sensitive_v.ToArray(),
  };
 MakeCallback(env()->http2session_on_headers_function(),
 arraysize(args), args);

src/node_messaging.cc

@@ -1093,7 +1093,7 @@ void MessagePort::PostMessage(const FunctionCallbackInfo<Value>& args) {
 "MessagePort.postMessage");
  }
 
- TransferList transfer_list;
+ TransferList transfer_list(env->isolate());
 if (!GetTransferList(env, context, args[1], &transfer_list)) {
 return;
  }
@@ -1607,7 +1607,7 @@ static void StructuredClone(const FunctionCallbackInfo<Value>& args) {
 
  Local<Value> value = args[0];
 
- TransferList transfer_list;
+ TransferList transfer_list(isolate);
  Local<Object> options = args[1].As<Object>();
  Local<Value> transfer_list_v;
 if (!options->Get(context, env->transfer_string())

src/api/callback.cc

@@ -245,7 +245,7 @@ MaybeLocal<Value> InternalMakeCallback(Environment* env,
 
  Local<Context> context = env->context();
 if (use_async_hooks_trampoline) {
- MaybeStackBuffer<Local<Value>, 16> args(3 + argc);
+ MaybeStackBuffer<Value, 16> args(env->isolate(), 3 + argc);
  args[0] = Number::New(env->isolate(), asyncContext.async_id);
  args[1] = resource;
  args[2] = callback;

src/cares_wrap.cc

@@ -201,12 +201,12 @@ Local<Array> AddrTTLToArray(
  Environment* env,
 const T* addrttls,
 size_t naddrttls) {
- MaybeStackBuffer<Local<Value>, 8> ttls(naddrttls);
+ MaybeStackBuffer<Value, 8> ttls(env->isolate(), naddrttls);
 for (size_t i = 0; i < naddrttls; i++) {
  ttls[i] = Integer::NewFromUnsigned(env->isolate(), addrttls[i].ttl);
  }
 
-returnArray::New(env->isolate(), ttls.out(), naddrttls);
+return ttls.ToArray();
 }
 
 intGetAnswerCountForTTLBuffer(constunsignedchar* buf, int len) {

src/crypto/crypto_tls.cc

@@ -41,7 +41,6 @@ using ncrypto::MarkPopErrorOnReturn;
 using ncrypto::SSLPointer;
 using ncrypto::SSLSessionPointer;
 using ncrypto::X509Pointer;
-using v8::Array;
 using v8::ArrayBuffer;
 using v8::ArrayBufferView;
 using v8::BackingStore;
@@ -1956,7 +1955,7 @@ void TLSWrap::GetSharedSigalgs(const FunctionCallbackInfo<Value>& args) {
 SSL* ssl = w->ssl_.get();
 int nsig = SSL_get_shared_sigalgs(ssl, 0, nullptr, nullptr, nullptr, nullptr,
 nullptr);
- MaybeStackBuffer<Local<Value>, 16> ret_arr(nsig);
+ MaybeStackBuffer<Value, 16> ret_arr(env->isolate(), nsig);
 
 for (int i = 0; i < nsig; i++) {
 int hash_nid;
@@ -2023,8 +2022,7 @@ void TLSWrap::GetSharedSigalgs(const FunctionCallbackInfo<Value>& args) {
  ret_arr[i] = OneByteString(env->isolate(), sig_with_md);
  }
 
- args.GetReturnValue().Set(
-Array::New(env->isolate(), ret_arr.out(), ret_arr.length()));
+ args.GetReturnValue().Set(ret_arr.ToArray());
 }
 
 voidTLSWrap::ExportKeyingMaterial(const FunctionCallbackInfo<Value>& args) {

src/js_stream.cc

@@ -11,7 +11,6 @@ namespace node {
 
 using errors::TryCatchScope;
 
-using v8::Array;
 using v8::Context;
 using v8::FunctionCallbackInfo;
 using v8::FunctionTemplate;
@@ -119,17 +118,14 @@ int JSStream::DoWrite(WriteWrap* w,
 
 int value_int = UV_EPROTO;
 
- MaybeStackBuffer<Local<Value>, 16> bufs_arr(count);
+ MaybeStackBuffer<Value, 16> bufs_arr(env()->isolate(), count);
 for (size_t i = 0; i < count; i++) {
 if (!Buffer::Copy(env(), bufs[i].base, bufs[i].len).ToLocal(&bufs_arr[i])) {
 return value_int;
  }
  }
 
- Local<Value> argv[] = {
- w->object(),
-Array::New(env()->isolate(), bufs_arr.out(), count)
- };
+ Local<Value> argv[] = {w->object(), bufs_arr.ToArray()};
 
  TryCatchScope try_catch(env());
  Local<Value> value;

src/js_udp_wrap.cc

@@ -11,7 +11,6 @@
 namespacenode {
 
 using errors::TryCatchScope;
-using v8::Array;
 using v8::Context;
 using v8::FunctionCallbackInfo;
 using v8::FunctionTemplate;
@@ -98,7 +97,7 @@ ssize_t JSUDPWrap::Send(uv_buf_t* bufs,
 int64_t value_int = JS_EXCEPTION_PENDING;
 size_t total_len = 0;
 
- MaybeStackBuffer<Local<Value>, 16> buffers(nbufs);
+ MaybeStackBuffer<Value, 16> buffers(env()->isolate(), nbufs);
 for (size_t i = 0; i < nbufs; i++) {
 if (!Buffer::Copy(env(), bufs[i].base, bufs[i].len).ToLocal(&buffers[i])) {
 return value_int;
@@ -110,9 +109,9 @@ ssize_t JSUDPWrap::Send(uv_buf_t* bufs,
 if (!AddressToJS(env(), addr).ToLocal(&address)) return value_int;
 
  Local<Value> args[] = {
-listener()->CreateSendWrap(total_len)->object(),
-Array::New(env()->isolate(), buffers.out(), nbufs),
- address,
+listener()->CreateSendWrap(total_len)->object(),
+buffers.ToArray(),
+address,
  };
 
 if (!MakeCallback(env()->onwrite_string(), arraysize(args), args)

src/node_concepts.h

@@ -3,6 +3,7 @@
 
 #if defined(NODE_WANT_INTERNALS) && NODE_WANT_INTERNALS
 
+#include<v8.h>
 #include<concepts>
 #include<limits>
 #include<type_traits>
@@ -32,6 +33,12 @@ concept StandardCharType =
 template <typename T>
 concept IsCallable = std::is_function<T>::value || requires { &T::operator(); };
 
+// Types that can reside on V8's managed heap (v8::Value, v8::Object, etc.).
+// Used to select the MaybeStackBuffer specialization that holds handles in a
+// v8::LocalVector instead of malloc'd memory.
+template <typename T>
+concept V8Type = std::is_base_of_v<v8::Data, T>;
+
 } // namespace node
 
 #endif// defined(NODE_WANT_INTERNALS) && NODE_WANT_INTERNALS

src/node_dir.cc

@@ -206,7 +206,7 @@ static MaybeLocal<Array> DirentListToArray(Environment* env,
 uv_dirent_t* ents,
 int num,
 enum encoding encoding) {
- MaybeStackBuffer<Local<Value>, 64> entries(num * 2);
+ MaybeStackBuffer<Value, 64> entries(env->isolate(), num * 2);
 
 // Return an array of all read filenames.
 int j = 0;
@@ -222,7 +222,8 @@ static MaybeLocal<Array> DirentListToArray(Environment* env,
  entries[j++] = Integer::New(env->isolate(), ents[i].type);
  }
 
-returnArray::New(env->isolate(), entries.out(), j);
+CHECK_EQ(j, num * 2);
+return entries.ToArray();
 }
 
 staticvoidAfterDirRead(uv_fs_t* req) {

src/node_env_var.cc

@@ -201,7 +201,7 @@ MaybeLocal<Array> RealEnvStore::Enumerate(Isolate* isolate) const {
 auto cleanup = OnScopeLeave([&]() { uv_os_free_environ(items, count); });
 CHECK_EQ(uv_os_environ(&items, &count), 0);
 
- MaybeStackBuffer<Local<Value>, 256> env_v(count);
+ MaybeStackBuffer<Value, 256> env_v(isolate, count);
 int env_v_index = 0;
 for (int i = 0; i < count; i++) {
 #ifdef _WIN32
@@ -216,7 +216,10 @@ MaybeLocal<Array> RealEnvStore::Enumerate(Isolate* isolate) const {
  env_v[env_v_index++] = str;
  }
 
-returnArray::New(isolate, env_v.out(), env_v_index);
+// We're possibly not filling the entire buffer.
+CHECK_LE(env_v_index, count);
+ env_v.SetLength(env_v_index);
+return env_v.ToArray();
 }
 
 std::shared_ptr<KVStore> KVStore::Clone(Isolate* isolate) const {

src/node_http2.cc

@@ -1585,8 +1585,8 @@ void Http2Session::HandleHeadersFrame(const nghttp2_frame* frame) {
 // this way for performance reasons (it's faster to generate and pass an
 // array than it is to generate and pass the object).
 
- MaybeStackBuffer<Local<Value>, 64> headers_v(stream->headers_count() * 2);
- MaybeStackBuffer<Local<Value>, 32> sensitive_v(stream->headers_count());
+ MaybeStackBuffer<Value, 64> headers_v(isolate, stream->headers_count() * 2);
+ MaybeStackBuffer<Value, 32> sensitive_v(isolate, stream->headers_count());
 size_t sensitive_count = 0;
 
  stream->TransferHeaders([&](const Http2Header& header, size_t i) {
@@ -1603,13 +1603,14 @@ void Http2Session::HandleHeadersFrame(const nghttp2_frame* frame) {
  stream->retained_headers_length_ += stream->current_headers_length_;
  stream->current_headers_length_ = 0;
 
+ sensitive_v.SetLength(sensitive_count);
  Local<Value> args[] = {
- stream->object(),
-Integer::New(isolate, id),
-Integer::New(isolate, stream->headers_category()),
-Integer::New(isolate, frame->hd.flags),
-Array::New(isolate, headers_v.out(), headers_v.length()),
-Array::New(isolate, sensitive_v.out(), sensitive_count),
+stream->object(),
+Integer::New(isolate, id),
+Integer::New(isolate, stream->headers_category()),
+Integer::New(isolate, frame->hd.flags),
+ headers_v.ToArray(),
+sensitive_v.ToArray(),
  };
 MakeCallback(env()->http2session_on_headers_function(),
 arraysize(args), args);

src/node_messaging.cc

@@ -1093,7 +1093,7 @@ void MessagePort::PostMessage(const FunctionCallbackInfo<Value>& args) {
 "MessagePort.postMessage");
  }
 
- TransferList transfer_list;
+ TransferList transfer_list(env->isolate());
 if (!GetTransferList(env, context, args[1], &transfer_list)) {
 return;
  }
@@ -1607,7 +1607,7 @@ static void StructuredClone(const FunctionCallbackInfo<Value>& args) {
 
  Local<Value> value = args[0];
 
- TransferList transfer_list;
+ TransferList transfer_list(isolate);
  Local<Object> options = args[1].As<Object>();
  Local<Value> transfer_list_v;
 if (!options->Get(context, env->transfer_string())

src/api/callback.cc

@@ -245,7 +245,7 @@ MaybeLocal<Value> InternalMakeCallback(Environment* env,
 
  Local<Context> context = env->context();
 if (use_async_hooks_trampoline) {
- MaybeStackBuffer<Local<Value>, 16> args(3 + argc);
+ MaybeStackBuffer<Value, 16> args(env->isolate(), 3 + argc);
  args[0] = Number::New(env->isolate(), asyncContext.async_id);
  args[1] = resource;
  args[2] = callback;

src/cares_wrap.cc

@@ -201,12 +201,12 @@ Local<Array> AddrTTLToArray(
  Environment* env,
 const T* addrttls,
 size_t naddrttls) {
- MaybeStackBuffer<Local<Value>, 8> ttls(naddrttls);
+ MaybeStackBuffer<Value, 8> ttls(env->isolate(), naddrttls);
 for (size_t i = 0; i < naddrttls; i++) {
  ttls[i] = Integer::NewFromUnsigned(env->isolate(), addrttls[i].ttl);
  }
 
-returnArray::New(env->isolate(), ttls.out(), naddrttls);
+return ttls.ToArray();
 }
 
 intGetAnswerCountForTTLBuffer(constunsignedchar* buf, int len) {

src/crypto/crypto_tls.cc

@@ -41,7 +41,6 @@ using ncrypto::MarkPopErrorOnReturn;
 using ncrypto::SSLPointer;
 using ncrypto::SSLSessionPointer;
 using ncrypto::X509Pointer;
-using v8::Array;
 using v8::ArrayBuffer;
 using v8::ArrayBufferView;
 using v8::BackingStore;
@@ -1956,7 +1955,7 @@ void TLSWrap::GetSharedSigalgs(const FunctionCallbackInfo<Value>& args) {
 SSL* ssl = w->ssl_.get();
 int nsig = SSL_get_shared_sigalgs(ssl, 0, nullptr, nullptr, nullptr, nullptr,
 nullptr);
- MaybeStackBuffer<Local<Value>, 16> ret_arr(nsig);
+ MaybeStackBuffer<Value, 16> ret_arr(env->isolate(), nsig);
 
 for (int i = 0; i < nsig; i++) {
 int hash_nid;
@@ -2023,8 +2022,7 @@ void TLSWrap::GetSharedSigalgs(const FunctionCallbackInfo<Value>& args) {
  ret_arr[i] = OneByteString(env->isolate(), sig_with_md);
  }
 
- args.GetReturnValue().Set(
-Array::New(env->isolate(), ret_arr.out(), ret_arr.length()));
+ args.GetReturnValue().Set(ret_arr.ToArray());
 }
 
 voidTLSWrap::ExportKeyingMaterial(const FunctionCallbackInfo<Value>& args) {

src/js_stream.cc

@@ -11,7 +11,6 @@ namespace node {
 
 using errors::TryCatchScope;
 
-using v8::Array;
 using v8::Context;
 using v8::FunctionCallbackInfo;
 using v8::FunctionTemplate;
@@ -119,17 +118,14 @@ int JSStream::DoWrite(WriteWrap* w,
 
 int value_int = UV_EPROTO;
 
- MaybeStackBuffer<Local<Value>, 16> bufs_arr(count);
+ MaybeStackBuffer<Value, 16> bufs_arr(env()->isolate(), count);
 for (size_t i = 0; i < count; i++) {
 if (!Buffer::Copy(env(), bufs[i].base, bufs[i].len).ToLocal(&bufs_arr[i])) {
 return value_int;
  }
  }
 
- Local<Value> argv[] = {
- w->object(),
-Array::New(env()->isolate(), bufs_arr.out(), count)
- };
+ Local<Value> argv[] = {w->object(), bufs_arr.ToArray()};
 
  TryCatchScope try_catch(env());
  Local<Value> value;

src/js_udp_wrap.cc

@@ -11,7 +11,6 @@
 namespacenode {
 
 using errors::TryCatchScope;
-using v8::Array;
 using v8::Context;
 using v8::FunctionCallbackInfo;
 using v8::FunctionTemplate;
@@ -98,7 +97,7 @@ ssize_t JSUDPWrap::Send(uv_buf_t* bufs,
 int64_t value_int = JS_EXCEPTION_PENDING;
 size_t total_len = 0;
 
- MaybeStackBuffer<Local<Value>, 16> buffers(nbufs);
+ MaybeStackBuffer<Value, 16> buffers(env()->isolate(), nbufs);
 for (size_t i = 0; i < nbufs; i++) {
 if (!Buffer::Copy(env(), bufs[i].base, bufs[i].len).ToLocal(&buffers[i])) {
 return value_int;
@@ -110,9 +109,9 @@ ssize_t JSUDPWrap::Send(uv_buf_t* bufs,
 if (!AddressToJS(env(), addr).ToLocal(&address)) return value_int;
 
  Local<Value> args[] = {
-listener()->CreateSendWrap(total_len)->object(),
-Array::New(env()->isolate(), buffers.out(), nbufs),
- address,
+listener()->CreateSendWrap(total_len)->object(),
+buffers.ToArray(),
+address,
  };
 
 if (!MakeCallback(env()->onwrite_string(), arraysize(args), args)

src/node_concepts.h

@@ -3,6 +3,7 @@
 
 #if defined(NODE_WANT_INTERNALS) && NODE_WANT_INTERNALS
 
+#include<v8.h>
 #include<concepts>
 #include<limits>
 #include<type_traits>
@@ -32,6 +33,12 @@ concept StandardCharType =
 template <typename T>
 concept IsCallable = std::is_function<T>::value || requires { &T::operator(); };
 
+// Types that can reside on V8's managed heap (v8::Value, v8::Object, etc.).
+// Used to select the MaybeStackBuffer specialization that holds handles in a
+// v8::LocalVector instead of malloc'd memory.
+template <typename T>
+concept V8Type = std::is_base_of_v<v8::Data, T>;
+
 } // namespace node
 
 #endif// defined(NODE_WANT_INTERNALS) && NODE_WANT_INTERNALS

src/node_dir.cc

@@ -206,7 +206,7 @@ static MaybeLocal<Array> DirentListToArray(Environment* env,
 uv_dirent_t* ents,
 int num,
 enum encoding encoding) {
- MaybeStackBuffer<Local<Value>, 64> entries(num * 2);
+ MaybeStackBuffer<Value, 64> entries(env->isolate(), num * 2);
 
 // Return an array of all read filenames.
 int j = 0;
@@ -222,7 +222,8 @@ static MaybeLocal<Array> DirentListToArray(Environment* env,
  entries[j++] = Integer::New(env->isolate(), ents[i].type);
  }
 
-returnArray::New(env->isolate(), entries.out(), j);
+CHECK_EQ(j, num * 2);
+return entries.ToArray();
 }
 
 staticvoidAfterDirRead(uv_fs_t* req) {

src/node_env_var.cc

@@ -201,7 +201,7 @@ MaybeLocal<Array> RealEnvStore::Enumerate(Isolate* isolate) const {
 auto cleanup = OnScopeLeave([&]() { uv_os_free_environ(items, count); });
 CHECK_EQ(uv_os_environ(&items, &count), 0);
 
- MaybeStackBuffer<Local<Value>, 256> env_v(count);
+ MaybeStackBuffer<Value, 256> env_v(isolate, count);
 int env_v_index = 0;
 for (int i = 0; i < count; i++) {
 #ifdef _WIN32
@@ -216,7 +216,10 @@ MaybeLocal<Array> RealEnvStore::Enumerate(Isolate* isolate) const {
  env_v[env_v_index++] = str;
  }
 
-returnArray::New(isolate, env_v.out(), env_v_index);
+// We're possibly not filling the entire buffer.
+CHECK_LE(env_v_index, count);
+ env_v.SetLength(env_v_index);
+return env_v.ToArray();
 }
 
 std::shared_ptr<KVStore> KVStore::Clone(Isolate* isolate) const {

src/node_http2.cc

@@ -1585,8 +1585,8 @@ void Http2Session::HandleHeadersFrame(const nghttp2_frame* frame) {
 // this way for performance reasons (it's faster to generate and pass an
 // array than it is to generate and pass the object).
 
- MaybeStackBuffer<Local<Value>, 64> headers_v(stream->headers_count() * 2);
- MaybeStackBuffer<Local<Value>, 32> sensitive_v(stream->headers_count());
+ MaybeStackBuffer<Value, 64> headers_v(isolate, stream->headers_count() * 2);
+ MaybeStackBuffer<Value, 32> sensitive_v(isolate, stream->headers_count());
 size_t sensitive_count = 0;
 
  stream->TransferHeaders([&](const Http2Header& header, size_t i) {
@@ -1603,13 +1603,14 @@ void Http2Session::HandleHeadersFrame(const nghttp2_frame* frame) {
  stream->retained_headers_length_ += stream->current_headers_length_;
  stream->current_headers_length_ = 0;
 
+ sensitive_v.SetLength(sensitive_count);
  Local<Value> args[] = {
- stream->object(),
-Integer::New(isolate, id),
-Integer::New(isolate, stream->headers_category()),
-Integer::New(isolate, frame->hd.flags),
-Array::New(isolate, headers_v.out(), headers_v.length()),
-Array::New(isolate, sensitive_v.out(), sensitive_count),
+stream->object(),
+Integer::New(isolate, id),
+Integer::New(isolate, stream->headers_category()),
+Integer::New(isolate, frame->hd.flags),
+ headers_v.ToArray(),
+sensitive_v.ToArray(),
  };
 MakeCallback(env()->http2session_on_headers_function(),
 arraysize(args), args);

src/node_messaging.cc

@@ -1093,7 +1093,7 @@ void MessagePort::PostMessage(const FunctionCallbackInfo<Value>& args) {
 "MessagePort.postMessage");
  }
 
- TransferList transfer_list;
+ TransferList transfer_list(env->isolate());
 if (!GetTransferList(env, context, args[1], &transfer_list)) {
 return;
  }
@@ -1607,7 +1607,7 @@ static void StructuredClone(const FunctionCallbackInfo<Value>& args) {
 
  Local<Value> value = args[0];
 
- TransferList transfer_list;
+ TransferList transfer_list(isolate);
  Local<Object> options = args[1].As<Object>();
  Local<Value> transfer_list_v;
 if (!options->Get(context, env->transfer_string())

src/api/callback.cc

@@ -245,7 +245,7 @@ MaybeLocal<Value> InternalMakeCallback(Environment* env,
 
  Local<Context> context = env->context();
 if (use_async_hooks_trampoline) {
- MaybeStackBuffer<Local<Value>, 16> args(3 + argc);
+ MaybeStackBuffer<Value, 16> args(env->isolate(), 3 + argc);
  args[0] = Number::New(env->isolate(), asyncContext.async_id);
  args[1] = resource;
  args[2] = callback;

src/cares_wrap.cc

@@ -201,12 +201,12 @@ Local<Array> AddrTTLToArray(
  Environment* env,
 const T* addrttls,
 size_t naddrttls) {
- MaybeStackBuffer<Local<Value>, 8> ttls(naddrttls);
+ MaybeStackBuffer<Value, 8> ttls(env->isolate(), naddrttls);
 for (size_t i = 0; i < naddrttls; i++) {
  ttls[i] = Integer::NewFromUnsigned(env->isolate(), addrttls[i].ttl);
  }
 
-returnArray::New(env->isolate(), ttls.out(), naddrttls);
+return ttls.ToArray();
 }
 
 intGetAnswerCountForTTLBuffer(constunsignedchar* buf, int len) {

src/crypto/crypto_tls.cc

@@ -41,7 +41,6 @@ using ncrypto::MarkPopErrorOnReturn;
 using ncrypto::SSLPointer;
 using ncrypto::SSLSessionPointer;
 using ncrypto::X509Pointer;
-using v8::Array;
 using v8::ArrayBuffer;
 using v8::ArrayBufferView;
 using v8::BackingStore;
@@ -1956,7 +1955,7 @@ void TLSWrap::GetSharedSigalgs(const FunctionCallbackInfo<Value>& args) {
 SSL* ssl = w->ssl_.get();
 int nsig = SSL_get_shared_sigalgs(ssl, 0, nullptr, nullptr, nullptr, nullptr,
 nullptr);
- MaybeStackBuffer<Local<Value>, 16> ret_arr(nsig);
+ MaybeStackBuffer<Value, 16> ret_arr(env->isolate(), nsig);
 
 for (int i = 0; i < nsig; i++) {
 int hash_nid;
@@ -2023,8 +2022,7 @@ void TLSWrap::GetSharedSigalgs(const FunctionCallbackInfo<Value>& args) {
  ret_arr[i] = OneByteString(env->isolate(), sig_with_md);
  }
 
- args.GetReturnValue().Set(
-Array::New(env->isolate(), ret_arr.out(), ret_arr.length()));
+ args.GetReturnValue().Set(ret_arr.ToArray());
 }
 
 voidTLSWrap::ExportKeyingMaterial(const FunctionCallbackInfo<Value>& args) {

src/js_stream.cc

@@ -11,7 +11,6 @@ namespace node {
 
 using errors::TryCatchScope;
 
-using v8::Array;
 using v8::Context;
 using v8::FunctionCallbackInfo;
 using v8::FunctionTemplate;
@@ -119,17 +118,14 @@ int JSStream::DoWrite(WriteWrap* w,
 
 int value_int = UV_EPROTO;
 
- MaybeStackBuffer<Local<Value>, 16> bufs_arr(count);
+ MaybeStackBuffer<Value, 16> bufs_arr(env()->isolate(), count);
 for (size_t i = 0; i < count; i++) {
 if (!Buffer::Copy(env(), bufs[i].base, bufs[i].len).ToLocal(&bufs_arr[i])) {
 return value_int;
  }
  }
 
- Local<Value> argv[] = {
- w->object(),
-Array::New(env()->isolate(), bufs_arr.out(), count)
- };
+ Local<Value> argv[] = {w->object(), bufs_arr.ToArray()};
 
  TryCatchScope try_catch(env());
  Local<Value> value;

src/js_udp_wrap.cc

@@ -11,7 +11,6 @@
 namespacenode {
 
 using errors::TryCatchScope;
-using v8::Array;
 using v8::Context;
 using v8::FunctionCallbackInfo;
 using v8::FunctionTemplate;
@@ -98,7 +97,7 @@ ssize_t JSUDPWrap::Send(uv_buf_t* bufs,
 int64_t value_int = JS_EXCEPTION_PENDING;
 size_t total_len = 0;
 
- MaybeStackBuffer<Local<Value>, 16> buffers(nbufs);
+ MaybeStackBuffer<Value, 16> buffers(env()->isolate(), nbufs);
 for (size_t i = 0; i < nbufs; i++) {
 if (!Buffer::Copy(env(), bufs[i].base, bufs[i].len).ToLocal(&buffers[i])) {
 return value_int;
@@ -110,9 +109,9 @@ ssize_t JSUDPWrap::Send(uv_buf_t* bufs,
 if (!AddressToJS(env(), addr).ToLocal(&address)) return value_int;
 
  Local<Value> args[] = {
-listener()->CreateSendWrap(total_len)->object(),
-Array::New(env()->isolate(), buffers.out(), nbufs),
- address,
+listener()->CreateSendWrap(total_len)->object(),
+buffers.ToArray(),
+address,
  };
 
 if (!MakeCallback(env()->onwrite_string(), arraysize(args), args)

src/node_concepts.h

@@ -3,6 +3,7 @@
 
 #if defined(NODE_WANT_INTERNALS) && NODE_WANT_INTERNALS
 
+#include<v8.h>
 #include<concepts>
 #include<limits>
 #include<type_traits>
@@ -32,6 +33,12 @@ concept StandardCharType =
 template <typename T>
 concept IsCallable = std::is_function<T>::value || requires { &T::operator(); };
 
+// Types that can reside on V8's managed heap (v8::Value, v8::Object, etc.).
+// Used to select the MaybeStackBuffer specialization that holds handles in a
+// v8::LocalVector instead of malloc'd memory.
+template <typename T>
+concept V8Type = std::is_base_of_v<v8::Data, T>;
+
 } // namespace node
 
 #endif// defined(NODE_WANT_INTERNALS) && NODE_WANT_INTERNALS

src/node_dir.cc

@@ -206,7 +206,7 @@ static MaybeLocal<Array> DirentListToArray(Environment* env,
 uv_dirent_t* ents,
 int num,
 enum encoding encoding) {
- MaybeStackBuffer<Local<Value>, 64> entries(num * 2);
+ MaybeStackBuffer<Value, 64> entries(env->isolate(), num * 2);
 
 // Return an array of all read filenames.
 int j = 0;
@@ -222,7 +222,8 @@ static MaybeLocal<Array> DirentListToArray(Environment* env,
  entries[j++] = Integer::New(env->isolate(), ents[i].type);
  }
 
-returnArray::New(env->isolate(), entries.out(), j);
+CHECK_EQ(j, num * 2);
+return entries.ToArray();
 }
 
 staticvoidAfterDirRead(uv_fs_t* req) {

src/node_env_var.cc

@@ -201,7 +201,7 @@ MaybeLocal<Array> RealEnvStore::Enumerate(Isolate* isolate) const {
 auto cleanup = OnScopeLeave([&]() { uv_os_free_environ(items, count); });
 CHECK_EQ(uv_os_environ(&items, &count), 0);
 
- MaybeStackBuffer<Local<Value>, 256> env_v(count);
+ MaybeStackBuffer<Value, 256> env_v(isolate, count);
 int env_v_index = 0;
 for (int i = 0; i < count; i++) {
 #ifdef _WIN32
@@ -216,7 +216,10 @@ MaybeLocal<Array> RealEnvStore::Enumerate(Isolate* isolate) const {
  env_v[env_v_index++] = str;
  }
 
-returnArray::New(isolate, env_v.out(), env_v_index);
+// We're possibly not filling the entire buffer.
+CHECK_LE(env_v_index, count);
+ env_v.SetLength(env_v_index);
+return env_v.ToArray();
 }
 
 std::shared_ptr<KVStore> KVStore::Clone(Isolate* isolate) const {

src/node_http2.cc

@@ -1585,8 +1585,8 @@ void Http2Session::HandleHeadersFrame(const nghttp2_frame* frame) {
 // this way for performance reasons (it's faster to generate and pass an
 // array than it is to generate and pass the object).
 
- MaybeStackBuffer<Local<Value>, 64> headers_v(stream->headers_count() * 2);
- MaybeStackBuffer<Local<Value>, 32> sensitive_v(stream->headers_count());
+ MaybeStackBuffer<Value, 64> headers_v(isolate, stream->headers_count() * 2);
+ MaybeStackBuffer<Value, 32> sensitive_v(isolate, stream->headers_count());
 size_t sensitive_count = 0;
 
  stream->TransferHeaders([&](const Http2Header& header, size_t i) {
@@ -1603,13 +1603,14 @@ void Http2Session::HandleHeadersFrame(const nghttp2_frame* frame) {
  stream->retained_headers_length_ += stream->current_headers_length_;
  stream->current_headers_length_ = 0;
 
+ sensitive_v.SetLength(sensitive_count);
  Local<Value> args[] = {
- stream->object(),
-Integer::New(isolate, id),
-Integer::New(isolate, stream->headers_category()),
-Integer::New(isolate, frame->hd.flags),
-Array::New(isolate, headers_v.out(), headers_v.length()),
-Array::New(isolate, sensitive_v.out(), sensitive_count),
+stream->object(),
+Integer::New(isolate, id),
+Integer::New(isolate, stream->headers_category()),
+Integer::New(isolate, frame->hd.flags),
+ headers_v.ToArray(),
+sensitive_v.ToArray(),
  };
 MakeCallback(env()->http2session_on_headers_function(),
 arraysize(args), args);

src/node_messaging.cc

@@ -1093,7 +1093,7 @@ void MessagePort::PostMessage(const FunctionCallbackInfo<Value>& args) {
 "MessagePort.postMessage");
  }
 
- TransferList transfer_list;
+ TransferList transfer_list(env->isolate());
 if (!GetTransferList(env, context, args[1], &transfer_list)) {
 return;
  }
@@ -1607,7 +1607,7 @@ static void StructuredClone(const FunctionCallbackInfo<Value>& args) {
 
  Local<Value> value = args[0];
 
- TransferList transfer_list;
+ TransferList transfer_list(isolate);
  Local<Object> options = args[1].As<Object>();
  Local<Value> transfer_list_v;
 if (!options->Get(context, env->transfer_string())