Meta: implement TransferArrayBuffer correctly in reference implementation

Author: MattiasBuelens

reference-implementation/lib/abstract-ops/ecmascript.js

@@ -1,7 +1,8 @@
 'use strict';
 const assert = require('assert');
 
-const isFakeDetached = Symbol('is "detached" for our purposes');
+const ArrayBufferPrototypeTransferToFixedLength = ArrayBuffer.prototype.transferToFixedLength;
+const ArrayBufferPrototypeDetachedGetter = Object.getOwnPropertyDescriptor(ArrayBuffer.prototype, 'detached').get;
 
 exports.typeIsObject = x => (typeof x === 'object' && x !== null) || typeof x === 'function';
 
@@ -15,31 +16,17 @@ exports.CopyDataBlockBytes = (dest, destOffset, src, srcOffset, n) => {
   new Uint8Array(dest).set(new Uint8Array(src, srcOffset, n), destOffset);
 };
 
-// Not implemented correctly
 exports.TransferArrayBuffer = O => {
   assert(!exports.IsDetachedBuffer(O));
-  const transferredIshVersion = O.slice();
-
-  // This is specifically to fool tests that test "is transferred" by taking a non-zero-length
-  // ArrayBuffer and checking if its byteLength starts returning 0.
-  Object.defineProperty(O, 'byteLength', {
-    get() {
-      return 0;
-    }
-  });
-  O[isFakeDetached] = true;
-
-  return transferredIshVersion;
+  return ArrayBufferPrototypeTransferToFixedLength.call(O);
 };
 
-// Not implemented correctly
 exports.CanTransferArrayBuffer = O => {
   return !exports.IsDetachedBuffer(O);
 };
 
-// Not implemented correctly
 exports.IsDetachedBuffer = O => {
-  return isFakeDetached in O;
+  return ArrayBufferPrototypeDetachedGetter.call(O) === true;
 };
 
 exports.Call = (F, V, args = []) => {

reference-implementation/lib/abstract-ops/readable-streams.js

@@ -1584,6 +1584,8 @@ function ReadableByteStreamControllerPullInto(controller, view, min, readIntoReq
   assert(minimumFill >= elementSize && minimumFill <= view.byteLength);
   assert(minimumFill % elementSize === 0);
 
+  const byteOffset = view.byteOffset;
+  const byteLength = view.byteLength;
   const ctor = view.constructor;
 
   let buffer;
@@ -1597,8 +1599,8 @@ function ReadableByteStreamControllerPullInto(controller, view, min, readIntoReq
   const pullIntoDescriptor = {
     buffer,
     bufferByteLength: buffer.byteLength,
-    byteOffset: view.byteOffset,
-    byteLength: view.byteLength,
+    byteOffset,
+    byteLength,
     bytesFilled: 0,
     minimumFill,
     elementSize,