fix: ensure transferred ArrayBuffer are Transferable

packages/cli/src/cmds/validator/keymanager/decryptKeystores/worker.ts

@@ -1,9 +1,29 @@
 import fs from "node:fs";
+import worker from "node:worker_threads";
 import {expose} from "@chainsafe/threads/worker";
 import {Transfer, TransferDescriptor} from "@chainsafe/threads";
 import {Keystore} from "@chainsafe/bls-keystore";
 import {DecryptKeystoreArgs, DecryptKeystoreWorkerAPI, isLocalKeystoreDefinition} from "./types.js";
 
+/**
+ * @param buffer The ArrayBuffer to be returned as transferable
+ * @returns a buffer that can be transferred. If the provided buffer is marked as untransferable, a copy is returned
+ */
+function transferableArrayBuffer(buffer: ArrayBuffer): ArrayBuffer {
+  // eslint-disable-next-line @typescript-eslint/no-explicit-any, @typescript-eslint/no-unsafe-assignment
+  const unknownWorker = worker as any;
+  // eslint-disable-next-line @typescript-eslint/no-unsafe-member-access, @typescript-eslint/no-unsafe-assignment
+  const isMarkedAsUntransferable = unknownWorker["isMarkedAsUntransferable"];
+  // Can be updated to direct access once minimal version of node is 21
+  // eslint-disable-next-line @typescript-eslint/no-unsafe-call
+  if (isMarkedAsUntransferable && isMarkedAsUntransferable(buffer)) {
+    // Return a copy of the buffer so that it can be transferred
+    return buffer.slice(0);
+  } else {
+    return buffer;
+  }
+}
+
 /**
  * Decrypt a single keystore, returning the secret key as a Uint8Array
  *
@@ -18,7 +38,7 @@ export async function decryptKeystore(args: DecryptKeystoreArgs): Promise<Transf
   const secret = await keystore.decrypt(args.password);
   // Transfer the underlying ArrayBuffer back to the main thread: https://threads.js.org/usage-advanced#transferable-objects
   // This small performance gain may help in cases where this is run for many keystores
-  return Transfer(secret, [secret.buffer]);
+  return Transfer(secret, [transferableArrayBuffer(secret.buffer)]);
 }
 
 expose({decryptKeystore} as unknown as DecryptKeystoreWorkerAPI);