src: allow not materializing ArrayBuffers from C++

Where appropriate, use a helper that wraps around
`ArrayBufferView::Buffer()` or `ArrayBufferView::CopyContents()`
rather than `Buffer::Data()`, as that may help to avoid materializing
the underlying `ArrayBuffer` when reading small typed arrays from C++.
This allows keeping the performance benefits of the faster creation of
heap-allocated small typed arrays in many cases.

PR-URL: https://github.com/nodejs/node/pull/26301
Reviewed-By: Matteo Collina <matteo.collina@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>

1 files changed, 21 insertions, 0 deletions

diff --git a/src/util.h b/src/util.h
index 4cd04dc6af9..4c930e637c5 100644
--- a/src/util.h
+++ b/src/util.h
@@ -417,6 +417,27 @@ class MaybeStackBuffer {
   T buf_st_[kStackStorageSize];
 };
 
+// Provides access to an ArrayBufferView's storage, either the original,
+// or for small data, a copy of it. This object's lifetime is bound to the
+// original ArrayBufferView's lifetime.
+template <typename T, size_t kStackStorageSize = 64>
+class ArrayBufferViewContents {
+ public:
+  ArrayBufferViewContents() {}
+
+  explicit inline ArrayBufferViewContents(v8::Local<v8::Value> value);
+  explicit inline ArrayBufferViewContents(v8::Local<v8::ArrayBufferView> abv);
+  inline void Read(v8::Local<v8::ArrayBufferView> abv);
+
+  inline const T* data() const { return data_; }
+  inline size_t length() const { return length_; }
+
+ private:
+  T stack_storage_[kStackStorageSize];
+  T* data_ = nullptr;
+  size_t length_ = 0;
+};
+
 class Utf8Value : public MaybeStackBuffer<char> {
  public:
   explicit Utf8Value(v8::Isolate* isolate, v8::Local<v8::Value> value);