Streams: test whether patched then() sees correct byobRequest

See whatwg/streams#1326 for context.

This also updates the `transferArrayBufferView` test utility to be synchronous, which slightly changes the timings of some tests in `streams/readable-byte-streams/general.any.js`.

streams/readable-byte-streams/general.any.js

@@ -870,11 +870,11 @@ promise_test(() => {
     start(c) {
       controller = c;
     },
-    async pull() {
+    pull() {
       byobRequestDefined.push(controller.byobRequest !== null);
       const initialByobRequest = controller.byobRequest;
 
-      const transferredView = await transferArrayBufferView(controller.byobRequest.view);
+      const transferredView = transferArrayBufferView(controller.byobRequest.view);
       transferredView[0] = 0x01;
       controller.byobRequest.respondWithNewView(transferredView);
 
@@ -2288,7 +2288,7 @@ promise_test(async t => {
   await pullCalledPromise;
 
   // Transfer the original BYOB request's buffer, and respond with a new view on that buffer
-  const transferredView = await transferArrayBufferView(controller.byobRequest.view);
+  const transferredView = transferArrayBufferView(controller.byobRequest.view);
   const newView = transferredView.subarray(0, 1);
   newView[0] = 42;
 
@@ -2328,7 +2328,7 @@ promise_test(async t => {
   await pullCalledPromise;
 
   // Transfer the original BYOB request's buffer, and respond with an empty view on that buffer
-  const transferredView = await transferArrayBufferView(controller.byobRequest.view);
+  const transferredView = transferArrayBufferView(controller.byobRequest.view);
   const newView = transferredView.subarray(0, 0);
 
   controller.close();

streams/readable-byte-streams/patched-global.any.js

@@ -0,0 +1,54 @@
+// META: global=window,worker,shadowrealm
+// META: script=../resources/test-utils.js
+'use strict';
+
+// Tests which patch the global environment are kept separate to avoid
+// interfering with other tests.
+
+promise_test(async (t) => {
+  let controller;
+  const rs = new ReadableStream({
+    type: 'bytes',
+    start(c) {
+      controller = c;
+    }
+  });
+  const reader = rs.getReader({mode: 'byob'});
+
+  const length = 0x4000;
+  const buffer = new ArrayBuffer(length);
+  const bigArray = new BigUint64Array(buffer, length - 8, 1);
+
+  const read1 = reader.read(new Uint8Array(new ArrayBuffer(0x100)));
+  const read2 = reader.read(bigArray);
+
+  let flag = false;
+  Object.defineProperty(Object.prototype, 'then', {
+    get: t.step_func(() => {
+      if (!flag) {
+        flag = true;
+        assert_equals(controller.byobRequest, null, 'byobRequest should be null after filling both views');
+      }
+    }),
+    configurable: true
+  });
+  t.add_cleanup(() => {
+    delete Object.prototype.then;
+  });
+
+  controller.enqueue(new Uint8Array(0x110).fill(0x42));
+  assert_true(flag, 'patched then() should be called');
+
+  // The first read() is filled entirely with 0x100 bytes
+  const result1 = await read1;
+  assert_false(result1.done, 'result1.done');
+  assert_typed_array_equals(result1.value, new Uint8Array(0x100).fill(0x42), 'result1.value');
+
+  // The second read() is filled with the remaining 0x10 bytes
+  const result2 = await read2;
+  assert_false(result2.done, 'result2.done');
+  assert_equals(result2.value.constructor, BigUint64Array, 'result2.value constructor');
+  assert_equals(result2.value.byteOffset, length - 8, 'result2.value byteOffset');
+  assert_equals(result2.value.length, 1, 'result2.value length');
+  assert_array_equals([...result2.value], [0x42424242_42424242n], 'result2.value contents');
+}, 'Patched then() sees byobRequest after filling all pending pull-into descriptors');

streams/resources/rs-utils.js

@@ -215,15 +215,7 @@
   }
 
   function transferArrayBufferView(view) {
-    const noopByteStream = new ReadableStream({
-      type: 'bytes',
-      pull(c) {
-        c.byobRequest.respond(c.byobRequest.view.byteLength);
-        c.close();
-      }
-    });
-    const reader = noopByteStream.getReader({ mode: 'byob' });
-    return reader.read(view).then((result) => result.value);
+    return structuredClone(view, { transfer: [view.buffer] });
   }
 
   self.RandomPushSource = RandomPushSource;