worker: add public method for marking objects as untransferable

We currently mark a number of `ArrayBuffer`s as not transferable,
including the `Buffer` pool and ones with finalizers provided
by C++ addons.

There is no good reason to assume that userland code might not
encounter similar problems, for example when doing `ArrayBuffer`
pooling similar to ours. Therefore, provide an API that lets
userland code also mark objects as not transferable.

PR-URL: https://github.com/nodejs/node/pull/33979
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Gus Caplan <me@gus.host>

1 files changed, 14 insertions, 1 deletions

diff --git a/lib/internal/buffer.js b/lib/internal/buffer.js
index c344a994181..be509088ada 100644
--- a/lib/internal/buffer.js
+++ b/lib/internal/buffer.js
@@ -27,6 +27,10 @@ const {
   ucs2Write,
   utf8Write
 } = internalBinding('buffer');
+const {
+  untransferable_object_private_symbol,
+  setHiddenValue,
+} = internalBinding('util');
 
 // Temporary buffers to convert numbers.
 const float32Array = new Float32Array(1);
@@ -1007,7 +1011,16 @@ function addBufferPrototypeMethods(proto) {
   proto.utf8Write = utf8Write;
 }
 
+// This would better be placed in internal/worker/io.js, but that doesn't work
+// because Buffer needs this and that would introduce a cyclic dependency.
+function markAsUntransferable(obj) {
+  if ((typeof obj !== 'object' && typeof obj !== 'function') || obj === null)
+    return;  // This object is a primitive and therefore already untransferable.
+  setHiddenValue(obj, untransferable_object_private_symbol, true);
+}
+
 module.exports = {
   FastBuffer,
-  addBufferPrototypeMethods
+  addBufferPrototypeMethods,
+  markAsUntransferable,
 };