buffer: handle detached instances

Author: araujogui

src/node_buffer.cc

@@ -1404,14 +1404,8 @@ std::pair<void*, size_t> DecomposeBufferToParts(Local<Value> buffer) {
     Local<ArrayBufferView> view = buffer.As<ArrayBufferView>();
     Local<ArrayBuffer> buffer = view->Buffer();
 
-    // Handle potential detached buffer case
-    if (buffer.IsEmpty() || buffer->Data() == nullptr) {
-      pointer = nullptr;
-      byte_length = 0;
-    } else {
-      pointer = static_cast<uint8_t*>(buffer->Data()) + view->ByteOffset();
-      byte_length = view->ByteLength();
-    }
+    pointer = static_cast<uint8_t*>(buffer->Data()) + view->ByteOffset();
+    byte_length = view->ByteLength();
   } else if (buffer->IsArrayBuffer()) {
     Local<ArrayBuffer> ab = buffer.As<ArrayBuffer>();
     pointer = ab->Data();

test/parallel/test-buffer-copy-within.js

@@ -61,6 +61,16 @@ describe('Buffer.copy', () => {
       Buffer.copy(src, dst, 0);
       assert.deepStrictEqual(new Uint8Array(ab), new Uint8Array([1, 2, 1, 2, 3, 4, 5]));
     });
+
+    test("should handle detached instances", () => {
+      const src = new Uint8Array([5, 6]).buffer;
+      src.transfer()
+      const dst = Buffer.from([0, 0, 0, 0]);
+
+      Buffer.copy(src, dst, 1);
+
+      assert.deepStrictEqual(dst, Buffer.from([0, 0, 0, 0]));
+    })
   });
 
   describe('DataView to Buffer', () => {