LibWeb: Push a temporary execution context for setTimeout

This fixes a crash seen running stream tests.

Tests/LibWeb/Text/expected/wpt-import/streams/readable-byte-streams/tee.any.txt

@@ -0,0 +1,49 @@
+Summary
+
+Harness status: Error
+
+Rerun
+
+Found 39 tests
+
+39 Pass
+Details
+Result	Test Name	MessagePass	ReadableStream teeing with byte source: rs.tee() returns an array of two ReadableStreams	
+Pass	ReadableStream teeing with byte source: should be able to read one branch to the end without affecting the other	
+Pass	ReadableStream teeing with byte source: chunks should be cloned for each branch	
+Pass	ReadableStream teeing with byte source: chunks for BYOB requests from branch 1 should be cloned to branch 2	
+Pass	ReadableStream teeing with byte source: errors in the source should propagate to both branches	
+Pass	ReadableStream teeing with byte source: canceling branch1 should not impact branch2	
+Pass	ReadableStream teeing with byte source: canceling branch2 should not impact branch1	
+Pass	Running templatedRSTeeCancel with ReadableStream teeing with byte source	
+Pass	ReadableStream teeing with byte source: canceling both branches should aggregate the cancel reasons into an array	
+Pass	ReadableStream teeing with byte source: canceling both branches in reverse order should aggregate the cancel reasons into an array	
+Pass	ReadableStream teeing with byte source: failing to cancel the original stream should cause cancel() to reject on branches	
+Pass	ReadableStream teeing with byte source: erroring a teed stream should properly handle canceled branches	
+Pass	ReadableStream teeing with byte source: closing the original should close the branches	
+Pass	ReadableStream teeing with byte source: erroring the original should immediately error the branches	
+Pass	ReadableStream teeing with byte source: erroring the original should error pending reads from default reader	
+Pass	ReadableStream teeing with byte source: erroring the original should error pending reads from BYOB reader	
+Pass	ReadableStream teeing with byte source: canceling branch1 should finish when branch2 reads until end of stream	
+Pass	ReadableStream teeing with byte source: canceling branch1 should finish when original stream errors	
+Pass	ReadableStream teeing with byte source: should not pull any chunks if no branches are reading	
+Pass	ReadableStream teeing with byte source: should only pull enough to fill the emptiest queue	
+Pass	ReadableStream teeing with byte source: should not pull when original is already errored	
+Pass	ReadableStream teeing with byte source: stops pulling when original stream errors while branch 1 is reading	
+Pass	ReadableStream teeing with byte source: stops pulling when original stream errors while branch 2 is reading	
+Pass	ReadableStream teeing with byte source: stops pulling when original stream errors while both branches are reading	
+Pass	ReadableStream teeing with byte source: canceling both branches in sequence with delay	
+Pass	ReadableStream teeing with byte source: failing to cancel when canceling both branches in sequence with delay	
+Pass	ReadableStream teeing with byte source: read from branch1 and branch2, cancel branch1, cancel branch2	
+Pass	ReadableStream teeing with byte source: read from branch1 and branch2, cancel branch2, cancel branch1	
+Pass	ReadableStream teeing with byte source: read from branch1 and branch2, cancel branch2, enqueue to branch1	
+Pass	ReadableStream teeing with byte source: read from branch1 and branch2, cancel branch1, respond to branch2	
+Pass	ReadableStream teeing with byte source: pull with BYOB reader, then pull with default reader	
+Pass	ReadableStream teeing with byte source: pull with default reader, then pull with BYOB reader	
+Pass	ReadableStream teeing with byte source: read from branch2, then read from branch1	
+Pass	ReadableStream teeing with byte source: read from branch1 with default reader, then close while branch2 has pending BYOB read	
+Pass	ReadableStream teeing with byte source: read from branch2 with default reader, then close while branch1 has pending BYOB read	
+Pass	ReadableStream teeing with byte source: close when both branches have pending BYOB reads	
+Pass	ReadableStream teeing with byte source: enqueue() and close() while both branches are pulling	
+Pass	ReadableStream teeing with byte source: respond() and close() while both branches are pulling	
+Pass	ReadableStream teeing with byte source: reading an array with a byte offset should clone correctly	

Tests/LibWeb/Text/input/wpt-import/streams/readable-byte-streams/tee.any.html

@@ -0,0 +1,18 @@
+<!doctype html>
+<meta charset=utf-8>
+
+<script>
+self.GLOBAL = {
+  isWindow: function() { return true; },
+  isWorker: function() { return false; },
+  isShadowRealm: function() { return false; },
+};
+</script>
+<script src="../../resources/testharness.js"></script>
+<script src="../../resources/testharnessreport.js"></script>
+<script src="../resources/rs-utils.js"></script>
+<script src="../resources/test-utils.js"></script>
+<script src="../resources/recording-streams.js"></script>
+<script src="../resources/rs-test-templates.js"></script>
+<div id=log></div>
+<script src="../../streams/readable-byte-streams/tee.any.js"></script>

Tests/LibWeb/Text/input/wpt-import/streams/readable-byte-streams/tee.any.js

@@ -0,0 +1,969 @@
+// META: global=window,worker,shadowrealm
+// META: script=../resources/rs-utils.js
+// META: script=../resources/test-utils.js
+// META: script=../resources/recording-streams.js
+// META: script=../resources/rs-test-templates.js
+'use strict';
+
+test(() => {
+
+  const rs = new ReadableStream({ type: 'bytes' });
+  const result = rs.tee();
+
+  assert_true(Array.isArray(result), 'return value should be an array');
+  assert_equals(result.length, 2, 'array should have length 2');
+  assert_equals(result[0].constructor, ReadableStream, '0th element should be a ReadableStream');
+  assert_equals(result[1].constructor, ReadableStream, '1st element should be a ReadableStream');
+
+}, 'ReadableStream teeing with byte source: rs.tee() returns an array of two ReadableStreams');
+
+promise_test(async t => {
+
+  const rs = new ReadableStream({
+    type: 'bytes',
+    start(c) {
+      c.enqueue(new Uint8Array([0x01]));
+      c.enqueue(new Uint8Array([0x02]));
+      c.close();
+    }
+  });
+
+  const [branch1, branch2] = rs.tee();
+  const reader1 = branch1.getReader({ mode: 'byob' });
+  const reader2 = branch2.getReader({ mode: 'byob' });
+
+  reader2.closed.then(t.unreached_func('branch2 should not be closed'));
+
+  {
+    const result = await reader1.read(new Uint8Array(1));
+    assert_equals(result.done, false, 'done');
+    assert_typed_array_equals(result.value, new Uint8Array([0x01]), 'value');
+  }
+
+  {
+    const result = await reader1.read(new Uint8Array(1));
+    assert_equals(result.done, false, 'done');
+    assert_typed_array_equals(result.value, new Uint8Array([0x02]), 'value');
+  }
+
+  {
+    const result = await reader1.read(new Uint8Array(1));
+    assert_equals(result.done, true, 'done');
+    assert_typed_array_equals(result.value, new Uint8Array([0]).subarray(0, 0), 'value');
+  }
+
+  {
+    const result = await reader2.read(new Uint8Array(1));
+    assert_equals(result.done, false, 'done');
+    assert_typed_array_equals(result.value, new Uint8Array([0x01]), 'value');
+  }
+
+  await reader1.closed;
+
+}, 'ReadableStream teeing with byte source: should be able to read one branch to the end without affecting the other');
+
+promise_test(async () => {
+
+  let pullCount = 0;
+  const enqueuedChunk = new Uint8Array([0x01]);
+  const rs = new ReadableStream({
+    type: 'bytes',
+    pull(c) {
+      ++pullCount;
+      if (pullCount === 1) {
+        c.enqueue(enqueuedChunk);
+      }
+    }
+  });
+
+  const [branch1, branch2] = rs.tee();
+  const reader1 = branch1.getReader();
+  const reader2 = branch2.getReader();
+
+  const [result1, result2] = await Promise.all([reader1.read(), reader2.read()]);
+  assert_equals(result1.done, false, 'reader1 done');
+  assert_equals(result2.done, false, 'reader2 done');
+
+  const view1 = result1.value;
+  const view2 = result2.value;
+  assert_typed_array_equals(view1, new Uint8Array([0x01]), 'reader1 value');
+  assert_typed_array_equals(view2, new Uint8Array([0x01]), 'reader2 value');
+
+  assert_not_equals(view1.buffer, view2.buffer, 'chunks should have different buffers');
+  assert_not_equals(enqueuedChunk.buffer, view1.buffer, 'enqueued chunk and branch1\'s chunk should have different buffers');
+  assert_not_equals(enqueuedChunk.buffer, view2.buffer, 'enqueued chunk and branch2\'s chunk should have different buffers');
+
+}, 'ReadableStream teeing with byte source: chunks should be cloned for each branch');
+
+promise_test(async () => {
+
+  let pullCount = 0;
+  const rs = new ReadableStream({
+    type: 'bytes',
+    pull(c) {
+      ++pullCount;
+      if (pullCount === 1) {
+        c.byobRequest.view[0] = 0x01;
+        c.byobRequest.respond(1);
+      }
+    }
+  });
+
+  const [branch1, branch2] = rs.tee();
+  const reader1 = branch1.getReader({ mode: 'byob' });
+  const reader2 = branch2.getReader();
+  const buffer = new Uint8Array([42, 42, 42]).buffer;
+
+  {
+    const result = await reader1.read(new Uint8Array(buffer, 0, 1));
+    assert_equals(result.done, false, 'done');
+    assert_typed_array_equals(result.value, new Uint8Array([0x01, 42, 42]).subarray(0, 1), 'value');
+  }
+
+  {
+    const result = await reader2.read();
+    assert_equals(result.done, false, 'done');
+    assert_typed_array_equals(result.value, new Uint8Array([0x01]), 'value');
+  }
+
+}, 'ReadableStream teeing with byte source: chunks for BYOB requests from branch 1 should be cloned to branch 2');
+
+promise_test(async t => {
+
+  const theError = { name: 'boo!' };
+  const rs = new ReadableStream({
+    type: 'bytes',
+    start(c) {
+      c.enqueue(new Uint8Array([0x01]));
+      c.enqueue(new Uint8Array([0x02]));
+    },
+    pull() {
+      throw theError;
+    }
+  });
+
+  const [branch1, branch2] = rs.tee();
+  const reader1 = branch1.getReader({ mode: 'byob' });
+  const reader2 = branch2.getReader({ mode: 'byob' });
+
+  {
+    const result = await reader1.read(new Uint8Array(1));
+    assert_equals(result.done, false, 'first read from branch1 should not be done');
+    assert_typed_array_equals(result.value, new Uint8Array([0x01]), 'first read from branch1');
+  }
+
+  {
+    const result = await reader1.read(new Uint8Array(1));
+    assert_equals(result.done, false, 'second read from branch1 should not be done');
+    assert_typed_array_equals(result.value, new Uint8Array([0x02]), 'second read from branch1');
+  }
+
+  await promise_rejects_exactly(t, theError, reader1.read(new Uint8Array(1)));
+  await promise_rejects_exactly(t, theError, reader2.read(new Uint8Array(1)));
+
+  await Promise.all([
+    promise_rejects_exactly(t, theError, reader1.closed),
+    promise_rejects_exactly(t, theError, reader2.closed)
+  ]);
+
+}, 'ReadableStream teeing with byte source: errors in the source should propagate to both branches');
+
+promise_test(async () => {
+
+  const rs = new ReadableStream({
+    type: 'bytes',
+    start(c) {
+      c.enqueue(new Uint8Array([0x01]));
+      c.enqueue(new Uint8Array([0x02]));
+      c.close();
+    }
+  });
+
+  const [branch1, branch2] = rs.tee();
+  branch1.cancel();
+
+  const [chunks1, chunks2] = await Promise.all([readableStreamToArray(branch1), readableStreamToArray(branch2)]);
+  assert_array_equals(chunks1, [], 'branch1 should have no chunks');
+  assert_equals(chunks2.length, 2, 'branch2 should have two chunks');
+  assert_typed_array_equals(chunks2[0], new Uint8Array([0x01]), 'first chunk from branch2');
+  assert_typed_array_equals(chunks2[1], new Uint8Array([0x02]), 'second chunk from branch2');
+
+}, 'ReadableStream teeing with byte source: canceling branch1 should not impact branch2');
+
+promise_test(async () => {
+
+  const rs = new ReadableStream({
+    type: 'bytes',
+    start(c) {
+      c.enqueue(new Uint8Array([0x01]));
+      c.enqueue(new Uint8Array([0x02]));
+      c.close();
+    }
+  });
+
+  const [branch1, branch2] = rs.tee();
+  branch2.cancel();
+
+  const [chunks1, chunks2] = await Promise.all([readableStreamToArray(branch1), readableStreamToArray(branch2)]);
+  assert_equals(chunks1.length, 2, 'branch1 should have two chunks');
+  assert_typed_array_equals(chunks1[0], new Uint8Array([0x01]), 'first chunk from branch1');
+  assert_typed_array_equals(chunks1[1], new Uint8Array([0x02]), 'second chunk from branch1');
+  assert_array_equals(chunks2, [], 'branch2 should have no chunks');
+
+}, 'ReadableStream teeing with byte source: canceling branch2 should not impact branch1');
+
+templatedRSTeeCancel('ReadableStream teeing with byte source', (extras) => {
+  return new ReadableStream({ type: 'bytes', ...extras });
+});
+
+promise_test(async () => {
+
+  let controller;
+  const rs = new ReadableStream({
+    type: 'bytes',
+    start(c) {
+      controller = c;
+    }
+  });
+
+  const [branch1, branch2] = rs.tee();
+  const reader1 = branch1.getReader({ mode: 'byob' });
+  const reader2 = branch2.getReader({ mode: 'byob' });
+
+  const promise = Promise.all([reader1.closed, reader2.closed]);
+
+  controller.close();
+
+  // The branches are created with HWM 0, so we need to read from at least one of them
+  // to observe the stream becoming closed.
+  const read1 = await reader1.read(new Uint8Array(1));
+  assert_equals(read1.done, true, 'first read from branch1 should be done');
+
+  await promise;
+
+}, 'ReadableStream teeing with byte source: closing the original should close the branches');
+
+promise_test(async t => {
+
+  let controller;
+  const rs = new ReadableStream({
+    type: 'bytes',
+    start(c) {
+      controller = c;
+    }
+  });
+
+  const [branch1, branch2] = rs.tee();
+  const reader1 = branch1.getReader({ mode: 'byob' });
+  const reader2 = branch2.getReader({ mode: 'byob' });
+
+  const theError = { name: 'boo!' };
+  const promise = Promise.all([
+    promise_rejects_exactly(t, theError, reader1.closed),
+    promise_rejects_exactly(t, theError, reader2.closed)
+  ]);
+
+  controller.error(theError);
+  await promise;
+
+}, 'ReadableStream teeing with byte source: erroring the original should immediately error the branches');
+
+promise_test(async t => {
+
+  let controller;
+  const rs = new ReadableStream({
+    type: 'bytes',
+    start(c) {
+      controller = c;
+    }
+  });
+
+  const [branch1, branch2] = rs.tee();
+  const reader1 = branch1.getReader();
+  const reader2 = branch2.getReader();
+
+  const theError = { name: 'boo!' };
+  const promise = Promise.all([
+    promise_rejects_exactly(t, theError, reader1.read()),
+    promise_rejects_exactly(t, theError, reader2.read())
+  ]);
+
+  controller.error(theError);
+  await promise;
+
+}, 'ReadableStream teeing with byte source: erroring the original should error pending reads from default reader');
+
+promise_test(async t => {
+
+  let controller;
+  const rs = new ReadableStream({
+    type: 'bytes',
+    start(c) {
+      controller = c;
+    }
+  });
+
+  const [branch1, branch2] = rs.tee();
+  const reader1 = branch1.getReader({ mode: 'byob' });
+  const reader2 = branch2.getReader({ mode: 'byob' });
+
+  const theError = { name: 'boo!' };
+  const promise = Promise.all([
+    promise_rejects_exactly(t, theError, reader1.read(new Uint8Array(1))),
+    promise_rejects_exactly(t, theError, reader2.read(new Uint8Array(1)))
+  ]);
+
+  controller.error(theError);
+  await promise;
+
+}, 'ReadableStream teeing with byte source: erroring the original should error pending reads from BYOB reader');
+
+promise_test(async () => {
+
+  let controller;
+  const rs = new ReadableStream({
+    type: 'bytes',
+    start(c) {
+      controller = c;
+    }
+  });
+
+  const [branch1, branch2] = rs.tee();
+  const reader1 = branch1.getReader({ mode: 'byob' });
+  const reader2 = branch2.getReader({ mode: 'byob' });
+  const cancelPromise = reader2.cancel();
+
+  controller.enqueue(new Uint8Array([0x01]));
+
+  const read1 = await reader1.read(new Uint8Array(1));
+  assert_equals(read1.done, false, 'first read() from branch1 should not be done');
+  assert_typed_array_equals(read1.value, new Uint8Array([0x01]), 'first read() from branch1');
+
+  controller.close();
+
+  const read2 = await reader1.read(new Uint8Array(1));
+  assert_equals(read2.done, true, 'second read() from branch1 should be done');
+
+  await Promise.all([
+    reader1.closed,
+    cancelPromise
+  ]);
+
+}, 'ReadableStream teeing with byte source: canceling branch1 should finish when branch2 reads until end of stream');
+
+promise_test(async t => {
+
+  let controller;
+  const theError = { name: 'boo!' };
+  const rs = new ReadableStream({
+    type: 'bytes',
+    start(c) {
+      controller = c;
+    }
+  });
+
+  const [branch1, branch2] = rs.tee();
+  const reader1 = branch1.getReader({ mode: 'byob' });
+  const reader2 = branch2.getReader({ mode: 'byob' });
+  const cancelPromise = reader2.cancel();
+
+  controller.error(theError);
+
+  await Promise.all([
+    promise_rejects_exactly(t, theError, reader1.read(new Uint8Array(1))),
+    cancelPromise
+  ]);
+
+}, 'ReadableStream teeing with byte source: canceling branch1 should finish when original stream errors');
+
+promise_test(async () => {
+
+  const rs = recordingReadableStream({ type: 'bytes' });
+
+  // Create two branches, each with a HWM of 0. This should result in no chunks being pulled.
+  rs.tee();
+
+  await flushAsyncEvents();
+  assert_array_equals(rs.events, [], 'pull should not be called');
+
+}, 'ReadableStream teeing with byte source: should not pull any chunks if no branches are reading');
+
+promise_test(async () => {
+
+  const rs = recordingReadableStream({
+    type: 'bytes',
+    pull(controller) {
+      controller.enqueue(new Uint8Array([0x01]));
+    }
+  });
+
+  const [reader1, reader2] = rs.tee().map(branch => branch.getReader({ mode: 'byob' }));
+  await Promise.all([
+    reader1.read(new Uint8Array(1)),
+    reader2.read(new Uint8Array(1))
+  ]);
+  assert_array_equals(rs.events, ['pull'], 'pull should be called once');
+
+}, 'ReadableStream teeing with byte source: should only pull enough to fill the emptiest queue');
+
+promise_test(async t => {
+
+  const rs = recordingReadableStream({ type: 'bytes' });
+  const theError = { name: 'boo!' };
+
+  rs.controller.error(theError);
+
+  const [reader1, reader2] = rs.tee().map(branch => branch.getReader({ mode: 'byob' }));
+
+  await flushAsyncEvents();
+  assert_array_equals(rs.events, [], 'pull should not be called');
+
+  await Promise.all([
+    promise_rejects_exactly(t, theError, reader1.closed),
+    promise_rejects_exactly(t, theError, reader2.closed)
+  ]);
+
+}, 'ReadableStream teeing with byte source: should not pull when original is already errored');
+
+for (const branch of [1, 2]) {
+  promise_test(async t => {
+
+    const rs = recordingReadableStream({ type: 'bytes' });
+    const theError = { name: 'boo!' };
+
+    const [reader1, reader2] = rs.tee().map(branch => branch.getReader({ mode: 'byob' }));
+
+    await flushAsyncEvents();
+    assert_array_equals(rs.events, [], 'pull should not be called');
+
+    const reader = (branch === 1) ? reader1 : reader2;
+    const read1 = reader.read(new Uint8Array(1));
+
+    await flushAsyncEvents();
+    assert_array_equals(rs.events, ['pull'], 'pull should be called once');
+
+    rs.controller.error(theError);
+
+    await Promise.all([
+      promise_rejects_exactly(t, theError, read1),
+      promise_rejects_exactly(t, theError, reader1.closed),
+      promise_rejects_exactly(t, theError, reader2.closed)
+    ]);
+
+    await flushAsyncEvents();
+    assert_array_equals(rs.events, ['pull'], 'pull should be called once');
+
+  }, `ReadableStream teeing with byte source: stops pulling when original stream errors while branch ${branch} is reading`);
+}
+
+promise_test(async t => {
+
+  const rs = recordingReadableStream({ type: 'bytes' });
+  const theError = { name: 'boo!' };
+
+  const [reader1, reader2] = rs.tee().map(branch => branch.getReader({ mode: 'byob' }));
+
+  await flushAsyncEvents();
+  assert_array_equals(rs.events, [], 'pull should not be called');
+
+  const read1 = reader1.read(new Uint8Array(1));
+  const read2 = reader2.read(new Uint8Array(1));
+
+  await flushAsyncEvents();
+  assert_array_equals(rs.events, ['pull'], 'pull should be called once');
+
+  rs.controller.error(theError);
+
+  await Promise.all([
+    promise_rejects_exactly(t, theError, read1),
+    promise_rejects_exactly(t, theError, read2),
+    promise_rejects_exactly(t, theError, reader1.closed),
+    promise_rejects_exactly(t, theError, reader2.closed)
+  ]);
+
+  await flushAsyncEvents();
+  assert_array_equals(rs.events, ['pull'], 'pull should be called once');
+
+}, 'ReadableStream teeing with byte source: stops pulling when original stream errors while both branches are reading');
+
+promise_test(async () => {
+
+  const rs = recordingReadableStream({ type: 'bytes' });
+
+  const [reader1, reader2] = rs.tee().map(branch => branch.getReader({ mode: 'byob' }));
+
+  const read1 = reader1.read(new Uint8Array([0x11]));
+  const read2 = reader2.read(new Uint8Array([0x22]));
+
+  const cancel1 = reader1.cancel();
+  await flushAsyncEvents();
+  const cancel2 = reader2.cancel();
+
+  const result1 = await read1;
+  assert_object_equals(result1, { value: undefined, done: true });
+  const result2 = await read2;
+  assert_object_equals(result2, { value: undefined, done: true });
+
+  await Promise.all([cancel1, cancel2]);
+
+}, 'ReadableStream teeing with byte source: canceling both branches in sequence with delay');
+
+promise_test(async t => {
+
+  const theError = { name: 'boo!' };
+  const rs = new ReadableStream({
+    type: 'bytes',
+    cancel() {
+      throw theError;
+    }
+  });
+
+  const [reader1, reader2] = rs.tee().map(branch => branch.getReader({ mode: 'byob' }));
+
+  const read1 = reader1.read(new Uint8Array([0x11]));
+  const read2 = reader2.read(new Uint8Array([0x22]));
+
+  const cancel1 = reader1.cancel();
+  await flushAsyncEvents();
+  const cancel2 = reader2.cancel();
+
+  const result1 = await read1;
+  assert_object_equals(result1, { value: undefined, done: true });
+  const result2 = await read2;
+  assert_object_equals(result2, { value: undefined, done: true });
+
+  await Promise.all([
+    promise_rejects_exactly(t, theError, cancel1),
+    promise_rejects_exactly(t, theError, cancel2)
+  ]);
+
+}, 'ReadableStream teeing with byte source: failing to cancel when canceling both branches in sequence with delay');
+
+promise_test(async () => {
+
+  let cancelResolve;
+  const cancelCalled = new Promise((resolve) => {
+    cancelResolve = resolve;
+  });
+  const rs = recordingReadableStream({
+    type: 'bytes',
+    cancel() {
+      cancelResolve();
+    }
+  });
+
+  const [reader1, reader2] = rs.tee().map(branch => branch.getReader({ mode: 'byob' }));
+
+  const read1 = reader1.read(new Uint8Array([0x11]));
+  await flushAsyncEvents();
+  const read2 = reader2.read(new Uint8Array([0x22]));
+  await flushAsyncEvents();
+
+  // We are reading into branch1's buffer.
+  const byobRequest1 = rs.controller.byobRequest;
+  assert_not_equals(byobRequest1, null);
+  assert_typed_array_equals(byobRequest1.view, new Uint8Array([0x11]), 'byobRequest1.view');
+
+  // Cancelling branch1 should not affect the BYOB request.
+  const cancel1 = reader1.cancel();
+  const result1 = await read1;
+  assert_equals(result1.done, true);
+  assert_equals(result1.value, undefined);
+  await flushAsyncEvents();
+  const byobRequest2 = rs.controller.byobRequest;
+  assert_typed_array_equals(byobRequest2.view, new Uint8Array([0x11]), 'byobRequest2.view');
+
+  // Cancelling branch1 should invalidate the BYOB request.
+  const cancel2 = reader2.cancel();
+  await cancelCalled;
+  const byobRequest3 = rs.controller.byobRequest;
+  assert_equals(byobRequest3, null);
+  const result2 = await read2;
+  assert_equals(result2.done, true);
+  assert_equals(result2.value, undefined);
+
+  await Promise.all([cancel1, cancel2]);
+
+}, 'ReadableStream teeing with byte source: read from branch1 and branch2, cancel branch1, cancel branch2');
+
+promise_test(async () => {
+
+  let cancelResolve;
+  const cancelCalled = new Promise((resolve) => {
+    cancelResolve = resolve;
+  });
+  const rs = recordingReadableStream({
+    type: 'bytes',
+    cancel() {
+      cancelResolve();
+    }
+  });
+
+  const [reader1, reader2] = rs.tee().map(branch => branch.getReader({ mode: 'byob' }));
+
+  const read1 = reader1.read(new Uint8Array([0x11]));
+  await flushAsyncEvents();
+  const read2 = reader2.read(new Uint8Array([0x22]));
+  await flushAsyncEvents();
+
+  // We are reading into branch1's buffer.
+  const byobRequest1 = rs.controller.byobRequest;
+  assert_not_equals(byobRequest1, null);
+  assert_typed_array_equals(byobRequest1.view, new Uint8Array([0x11]), 'byobRequest1.view');
+
+  // Cancelling branch2 should not affect the BYOB request.
+  const cancel2 = reader2.cancel();
+  const result2 = await read2;
+  assert_equals(result2.done, true);
+  assert_equals(result2.value, undefined);
+  await flushAsyncEvents();
+  const byobRequest2 = rs.controller.byobRequest;
+  assert_typed_array_equals(byobRequest2.view, new Uint8Array([0x11]), 'byobRequest2.view');
+
+  // Cancelling branch1 should invalidate the BYOB request.
+  const cancel1 = reader1.cancel();
+  await cancelCalled;
+  const byobRequest3 = rs.controller.byobRequest;
+  assert_equals(byobRequest3, null);
+  const result1 = await read1;
+  assert_equals(result1.done, true);
+  assert_equals(result1.value, undefined);
+
+  await Promise.all([cancel1, cancel2]);
+
+}, 'ReadableStream teeing with byte source: read from branch1 and branch2, cancel branch2, cancel branch1');
+
+promise_test(async () => {
+
+  const rs = recordingReadableStream({ type: 'bytes' });
+
+  const [reader1, reader2] = rs.tee().map(branch => branch.getReader({ mode: 'byob' }));
+
+  const read1 = reader1.read(new Uint8Array([0x11]));
+  await flushAsyncEvents();
+  const read2 = reader2.read(new Uint8Array([0x22]));
+  await flushAsyncEvents();
+
+  // We are reading into branch1's buffer.
+  assert_typed_array_equals(rs.controller.byobRequest.view, new Uint8Array([0x11]), 'first byobRequest.view');
+
+  // Cancelling branch2 should not affect the BYOB request.
+  reader2.cancel();
+  const result2 = await read2;
+  assert_equals(result2.done, true);
+  assert_equals(result2.value, undefined);
+  await flushAsyncEvents();
+  assert_typed_array_equals(rs.controller.byobRequest.view, new Uint8Array([0x11]), 'second byobRequest.view');
+
+  // Respond to the BYOB request.
+  rs.controller.byobRequest.view[0] = 0x33;
+  rs.controller.byobRequest.respond(1);
+
+  // branch1 should receive the read chunk.
+  const result1 = await read1;
+  assert_equals(result1.done, false);
+  assert_typed_array_equals(result1.value, new Uint8Array([0x33]), 'first read() from branch1');
+
+}, 'ReadableStream teeing with byte source: read from branch1 and branch2, cancel branch2, enqueue to branch1');
+
+promise_test(async () => {
+
+  const rs = recordingReadableStream({ type: 'bytes' });
+
+  const [reader1, reader2] = rs.tee().map(branch => branch.getReader({ mode: 'byob' }));
+
+  const read1 = reader1.read(new Uint8Array([0x11]));
+  await flushAsyncEvents();
+  const read2 = reader2.read(new Uint8Array([0x22]));
+  await flushAsyncEvents();
+
+  // We are reading into branch1's buffer.
+  assert_typed_array_equals(rs.controller.byobRequest.view, new Uint8Array([0x11]), 'first byobRequest.view');
+
+  // Cancelling branch1 should not affect the BYOB request.
+  reader1.cancel();
+  const result1 = await read1;
+  assert_equals(result1.done, true);
+  assert_equals(result1.value, undefined);
+  await flushAsyncEvents();
+  assert_typed_array_equals(rs.controller.byobRequest.view, new Uint8Array([0x11]), 'second byobRequest.view');
+
+  // Respond to the BYOB request.
+  rs.controller.byobRequest.view[0] = 0x33;
+  rs.controller.byobRequest.respond(1);
+
+  // branch2 should receive the read chunk.
+  const result2 = await read2;
+  assert_equals(result2.done, false);
+  assert_typed_array_equals(result2.value, new Uint8Array([0x33]), 'first read() from branch2');
+
+}, 'ReadableStream teeing with byte source: read from branch1 and branch2, cancel branch1, respond to branch2');
+
+promise_test(async () => {
+
+  let pullCount = 0;
+  const byobRequestDefined = [];
+  const rs = new ReadableStream({
+    type: 'bytes',
+    pull(c) {
+      ++pullCount;
+      byobRequestDefined.push(c.byobRequest !== null);
+      c.enqueue(new Uint8Array([pullCount]));
+    }
+  });
+
+  const [branch1, _] = rs.tee();
+  const reader1 = branch1.getReader({ mode: 'byob' });
+
+  const result1 = await reader1.read(new Uint8Array([0x11]));
+  assert_equals(result1.done, false, 'first read should not be done');
+  assert_typed_array_equals(result1.value, new Uint8Array([0x1]), 'first read');
+  assert_equals(pullCount, 1, 'pull() should be called once');
+  assert_equals(byobRequestDefined[0], true, 'should have created a BYOB request for first read');
+
+  reader1.releaseLock();
+  const reader2 = branch1.getReader();
+
+  const result2 = await reader2.read();
+  assert_equals(result2.done, false, 'second read should not be done');
+  assert_typed_array_equals(result2.value, new Uint8Array([0x2]), 'second read');
+  assert_equals(pullCount, 2, 'pull() should be called twice');
+  assert_equals(byobRequestDefined[1], false, 'should not have created a BYOB request for second read');
+
+}, 'ReadableStream teeing with byte source: pull with BYOB reader, then pull with default reader');
+
+promise_test(async () => {
+
+  let pullCount = 0;
+  const byobRequestDefined = [];
+  const rs = new ReadableStream({
+    type: 'bytes',
+    pull(c) {
+      ++pullCount;
+      byobRequestDefined.push(c.byobRequest !== null);
+      c.enqueue(new Uint8Array([pullCount]));
+    }
+  });
+
+  const [branch1, _] = rs.tee();
+  const reader1 = branch1.getReader();
+
+  const result1 = await reader1.read();
+  assert_equals(result1.done, false, 'first read should not be done');
+  assert_typed_array_equals(result1.value, new Uint8Array([0x1]), 'first read');
+  assert_equals(pullCount, 1, 'pull() should be called once');
+  assert_equals(byobRequestDefined[0], false, 'should not have created a BYOB request for first read');
+
+  reader1.releaseLock();
+  const reader2 = branch1.getReader({ mode: 'byob' });
+
+  const result2 = await reader2.read(new Uint8Array([0x22]));
+  assert_equals(result2.done, false, 'second read should not be done');
+  assert_typed_array_equals(result2.value, new Uint8Array([0x2]), 'second read');
+  assert_equals(pullCount, 2, 'pull() should be called twice');
+  assert_equals(byobRequestDefined[1], true, 'should have created a BYOB request for second read');
+
+}, 'ReadableStream teeing with byte source: pull with default reader, then pull with BYOB reader');
+
+promise_test(async () => {
+
+  const rs = recordingReadableStream({
+    type: 'bytes'
+  });
+  const [reader1, reader2] = rs.tee().map(branch => branch.getReader({ mode: 'byob' }));
+
+  // Wait for each branch's start() promise to resolve.
+  await flushAsyncEvents();
+
+  const read2 = reader2.read(new Uint8Array([0x22]));
+  const read1 = reader1.read(new Uint8Array([0x11]));
+  await flushAsyncEvents();
+
+  // branch2 should provide the BYOB request.
+  const byobRequest = rs.controller.byobRequest;
+  assert_typed_array_equals(byobRequest.view, new Uint8Array([0x22]), 'first BYOB request');
+  byobRequest.view[0] = 0x01;
+  byobRequest.respond(1);
+
+  const result1 = await read1;
+  assert_equals(result1.done, false, 'first read should not be done');
+  assert_typed_array_equals(result1.value, new Uint8Array([0x1]), 'first read');
+
+  const result2 = await read2;
+  assert_equals(result2.done, false, 'second read should not be done');
+  assert_typed_array_equals(result2.value, new Uint8Array([0x1]), 'second read');
+
+}, 'ReadableStream teeing with byte source: read from branch2, then read from branch1');
+
+promise_test(async () => {
+
+  const rs = recordingReadableStream({ type: 'bytes' });
+  const [branch1, branch2] = rs.tee();
+  const reader1 = branch1.getReader();
+  const reader2 = branch2.getReader({ mode: 'byob' });
+  await flushAsyncEvents();
+
+  const read1 = reader1.read();
+  const read2 = reader2.read(new Uint8Array([0x22]));
+  await flushAsyncEvents();
+
+  // There should be no BYOB request.
+  assert_equals(rs.controller.byobRequest, null, 'first BYOB request');
+
+  // Close the stream.
+  rs.controller.close();
+
+  const result1 = await read1;
+  assert_equals(result1.done, true, 'read from branch1 should be done');
+  assert_equals(result1.value, undefined, 'read from branch1');
+
+  // branch2 should get its buffer back.
+  const result2 = await read2;
+  assert_equals(result2.done, true, 'read from branch2 should be done');
+  assert_typed_array_equals(result2.value, new Uint8Array([0x22]).subarray(0, 0), 'read from branch2');
+
+}, 'ReadableStream teeing with byte source: read from branch1 with default reader, then close while branch2 has pending BYOB read');
+
+promise_test(async () => {
+
+  const rs = recordingReadableStream({ type: 'bytes' });
+  const [branch1, branch2] = rs.tee();
+  const reader1 = branch1.getReader({ mode: 'byob' });
+  const reader2 = branch2.getReader();
+  await flushAsyncEvents();
+
+  const read2 = reader2.read();
+  const read1 = reader1.read(new Uint8Array([0x11]));
+  await flushAsyncEvents();
+
+  // There should be no BYOB request.
+  assert_equals(rs.controller.byobRequest, null, 'first BYOB request');
+
+  // Close the stream.
+  rs.controller.close();
+
+  const result2 = await read2;
+  assert_equals(result2.done, true, 'read from branch2 should be done');
+  assert_equals(result2.value, undefined, 'read from branch2');
+
+  // branch1 should get its buffer back.
+  const result1 = await read1;
+  assert_equals(result1.done, true, 'read from branch1 should be done');
+  assert_typed_array_equals(result1.value, new Uint8Array([0x11]).subarray(0, 0), 'read from branch1');
+
+}, 'ReadableStream teeing with byte source: read from branch2 with default reader, then close while branch1 has pending BYOB read');
+
+promise_test(async () => {
+
+  const rs = recordingReadableStream({ type: 'bytes' });
+  const [reader1, reader2] = rs.tee().map(branch => branch.getReader({ mode: 'byob' }));
+  await flushAsyncEvents();
+
+  const read1 = reader1.read(new Uint8Array([0x11]));
+  const read2 = reader2.read(new Uint8Array([0x22]));
+  await flushAsyncEvents();
+
+  // branch1 should provide the BYOB request.
+  const byobRequest = rs.controller.byobRequest;
+  assert_typed_array_equals(byobRequest.view, new Uint8Array([0x11]), 'first BYOB request');
+
+  // Close the stream.
+  rs.controller.close();
+  byobRequest.respond(0);
+
+  // Both branches should get their buffers back.
+  const result1 = await read1;
+  assert_equals(result1.done, true, 'first read should be done');
+  assert_typed_array_equals(result1.value, new Uint8Array([0x11]).subarray(0, 0), 'first read');
+
+  const result2 = await read2;
+  assert_equals(result2.done, true, 'second read should be done');
+  assert_typed_array_equals(result2.value, new Uint8Array([0x22]).subarray(0, 0), 'second read');
+
+}, 'ReadableStream teeing with byte source: close when both branches have pending BYOB reads');
+
+promise_test(async () => {
+
+  const rs = recordingReadableStream({ type: 'bytes' });
+
+  const [reader1, reader2] = rs.tee().map(branch => branch.getReader());
+  const branch1Reads = [reader1.read(), reader1.read()];
+  const branch2Reads = [reader2.read(), reader2.read()];
+
+  await flushAsyncEvents();
+  rs.controller.enqueue(new Uint8Array([0x11]));
+  rs.controller.close();
+
+  const result1 = await branch1Reads[0];
+  assert_equals(result1.done, false, 'first read() from branch1 should be not done');
+  assert_typed_array_equals(result1.value, new Uint8Array([0x11]), 'first chunk from branch1 should be correct');
+  const result2 = await branch2Reads[0];
+  assert_equals(result2.done, false, 'first read() from branch2 should be not done');
+  assert_typed_array_equals(result2.value, new Uint8Array([0x11]), 'first chunk from branch2 should be correct');
+
+  assert_object_equals(await branch1Reads[1], { value: undefined, done: true }, 'second read() from branch1 should be done');
+  assert_object_equals(await branch2Reads[1], { value: undefined, done: true }, 'second read() from branch2 should be done');
+
+}, 'ReadableStream teeing with byte source: enqueue() and close() while both branches are pulling');
+
+promise_test(async () => {
+
+  const rs = recordingReadableStream({ type: 'bytes' });
+
+  const [reader1, reader2] = rs.tee().map(branch => branch.getReader({ mode: 'byob' }));
+  const branch1Reads = [reader1.read(new Uint8Array(1)), reader1.read(new Uint8Array(1))];
+  const branch2Reads = [reader2.read(new Uint8Array(1)), reader2.read(new Uint8Array(1))];
+
+  await flushAsyncEvents();
+  rs.controller.byobRequest.view[0] = 0x11;
+  rs.controller.byobRequest.respond(1);
+  rs.controller.close();
+
+  const result1 = await branch1Reads[0];
+  assert_equals(result1.done, false, 'first read() from branch1 should be not done');
+  assert_typed_array_equals(result1.value, new Uint8Array([0x11]), 'first chunk from branch1 should be correct');
+  const result2 = await branch2Reads[0];
+  assert_equals(result2.done, false, 'first read() from branch2 should be not done');
+  assert_typed_array_equals(result2.value, new Uint8Array([0x11]), 'first chunk from branch2 should be correct');
+
+  const result3 = await branch1Reads[1];
+  assert_equals(result3.done, true, 'second read() from branch1 should be done');
+  assert_typed_array_equals(result3.value, new Uint8Array([0]).subarray(0, 0), 'second chunk from branch1 should be correct');
+  const result4 = await branch2Reads[1];
+  assert_equals(result4.done, true, 'second read() from branch2 should be done');
+  assert_typed_array_equals(result4.value, new Uint8Array([0]).subarray(0, 0), 'second chunk from branch2 should be correct');
+
+}, 'ReadableStream teeing with byte source: respond() and close() while both branches are pulling');
+
+promise_test(async t => {
+  let pullCount = 0;
+  const arrayBuffer = new Uint8Array([0x01, 0x02, 0x03]).buffer;
+  const enqueuedChunk = new Uint8Array(arrayBuffer, 2);
+  assert_equals(enqueuedChunk.length, 1);
+  assert_equals(enqueuedChunk.byteOffset, 2);
+  const rs = new ReadableStream({
+    type: 'bytes',
+    pull(c) {
+      ++pullCount;
+      if (pullCount === 1) {
+        c.enqueue(enqueuedChunk);
+      }
+    }
+  });
+
+  const [branch1, branch2] = rs.tee();
+  const reader1 = branch1.getReader();
+  const reader2 = branch2.getReader();
+
+  const [result1, result2] = await Promise.all([reader1.read(), reader2.read()]);
+  assert_equals(result1.done, false, 'reader1 done');
+  assert_equals(result2.done, false, 'reader2 done');
+
+  const view1 = result1.value;
+  const view2 = result2.value;
+  // The first stream has the transferred buffer, but the second stream has the
+  // cloned buffer.
+  const underlying = new Uint8Array([0x01, 0x02, 0x03]).buffer;
+  assert_typed_array_equals(view1, new Uint8Array(underlying, 2), 'reader1 value');
+  assert_typed_array_equals(view2, new Uint8Array([0x03]), 'reader2 value');
+}, 'ReadableStream teeing with byte source: reading an array with a byte offset should clone correctly');

Tests/LibWeb/Text/input/wpt-import/streams/resources/recording-streams.js

@@ -0,0 +1,131 @@
+'use strict';
+
+self.recordingReadableStream = (extras = {}, strategy) => {
+  let controllerToCopyOver;
+  const stream = new ReadableStream({
+    type: extras.type,
+    start(controller) {
+      controllerToCopyOver = controller;
+
+      if (extras.start) {
+        return extras.start(controller);
+      }
+
+      return undefined;
+    },
+    pull(controller) {
+      stream.events.push('pull');
+
+      if (extras.pull) {
+        return extras.pull(controller);
+      }
+
+      return undefined;
+    },
+    cancel(reason) {
+      stream.events.push('cancel', reason);
+      stream.eventsWithoutPulls.push('cancel', reason);
+
+      if (extras.cancel) {
+        return extras.cancel(reason);
+      }
+
+      return undefined;
+    }
+  }, strategy);
+
+  stream.controller = controllerToCopyOver;
+  stream.events = [];
+  stream.eventsWithoutPulls = [];
+
+  return stream;
+};
+
+self.recordingWritableStream = (extras = {}, strategy) => {
+  let controllerToCopyOver;
+  const stream = new WritableStream({
+    start(controller) {
+      controllerToCopyOver = controller;
+
+      if (extras.start) {
+        return extras.start(controller);
+      }
+
+      return undefined;
+    },
+    write(chunk, controller) {
+      stream.events.push('write', chunk);
+
+      if (extras.write) {
+        return extras.write(chunk, controller);
+      }
+
+      return undefined;
+    },
+    close() {
+      stream.events.push('close');
+
+      if (extras.close) {
+        return extras.close();
+      }
+
+      return undefined;
+    },
+    abort(e) {
+      stream.events.push('abort', e);
+
+      if (extras.abort) {
+        return extras.abort(e);
+      }
+
+      return undefined;
+    }
+  }, strategy);
+
+  stream.controller = controllerToCopyOver;
+  stream.events = [];
+
+  return stream;
+};
+
+self.recordingTransformStream = (extras = {}, writableStrategy, readableStrategy) => {
+  let controllerToCopyOver;
+  const stream = new TransformStream({
+    start(controller) {
+      controllerToCopyOver = controller;
+
+      if (extras.start) {
+        return extras.start(controller);
+      }
+
+      return undefined;
+    },
+
+    transform(chunk, controller) {
+      stream.events.push('transform', chunk);
+
+      if (extras.transform) {
+        return extras.transform(chunk, controller);
+      }
+
+      controller.enqueue(chunk);
+
+      return undefined;
+    },
+
+    flush(controller) {
+      stream.events.push('flush');
+
+      if (extras.flush) {
+        return extras.flush(controller);
+      }
+
+      return undefined;
+    }
+  }, writableStrategy, readableStrategy);
+
+  stream.controller = controllerToCopyOver;
+  stream.events = [];
+
+  return stream;
+};

Tests/LibWeb/Text/input/wpt-import/streams/resources/rs-test-templates.js

@@ -0,0 +1,721 @@
+'use strict';
+
+// These tests can be run against any readable stream produced by the web platform that meets the given descriptions.
+// For readable stream tests, the factory should return the stream. For reader tests, the factory should return a
+// { stream, reader } object. (You can use this to vary the time at which you acquire a reader.)
+
+self.templatedRSEmpty = (label, factory) => {
+  test(() => {}, 'Running templatedRSEmpty with ' + label);
+
+  test(() => {
+
+    const rs = factory();
+
+    assert_equals(typeof rs.locked, 'boolean', 'has a boolean locked getter');
+    assert_equals(typeof rs.cancel, 'function', 'has a cancel method');
+    assert_equals(typeof rs.getReader, 'function', 'has a getReader method');
+    assert_equals(typeof rs.pipeThrough, 'function', 'has a pipeThrough method');
+    assert_equals(typeof rs.pipeTo, 'function', 'has a pipeTo method');
+    assert_equals(typeof rs.tee, 'function', 'has a tee method');
+
+  }, label + ': instances have the correct methods and properties');
+
+  test(() => {
+    const rs = factory();
+
+    assert_throws_js(TypeError, () => rs.getReader({ mode: '' }), 'empty string mode should throw');
+    assert_throws_js(TypeError, () => rs.getReader({ mode: null }), 'null mode should throw');
+    assert_throws_js(TypeError, () => rs.getReader({ mode: 'asdf' }), 'asdf mode should throw');
+    assert_throws_js(TypeError, () => rs.getReader(5), '5 should throw');
+
+    // Should not throw
+    rs.getReader(null);
+
+  }, label + ': calling getReader with invalid arguments should throw appropriate errors');
+};
+
+self.templatedRSClosed = (label, factory) => {
+  test(() => {}, 'Running templatedRSClosed with ' + label);
+
+  promise_test(() => {
+
+    const rs = factory();
+    const cancelPromise1 = rs.cancel();
+    const cancelPromise2 = rs.cancel();
+
+    assert_not_equals(cancelPromise1, cancelPromise2, 'cancel() calls should return distinct promises');
+
+    return Promise.all([
+      cancelPromise1.then(v => assert_equals(v, undefined, 'first cancel() call should fulfill with undefined')),
+      cancelPromise2.then(v => assert_equals(v, undefined, 'second cancel() call should fulfill with undefined'))
+    ]);
+
+  }, label + ': cancel() should return a distinct fulfilled promise each time');
+
+  test(() => {
+
+    const rs = factory();
+    assert_false(rs.locked, 'locked getter should return false');
+
+  }, label + ': locked should be false');
+
+  test(() => {
+
+    const rs = factory();
+    rs.getReader(); // getReader() should not throw.
+
+  }, label + ': getReader() should be OK');
+
+  test(() => {
+
+    const rs = factory();
+
+    const reader = rs.getReader();
+    reader.releaseLock();
+
+    const reader2 = rs.getReader(); // Getting a second reader should not throw.
+    reader2.releaseLock();
+
+    rs.getReader(); // Getting a third reader should not throw.
+
+  }, label + ': should be able to acquire multiple readers if they are released in succession');
+
+  test(() => {
+
+    const rs = factory();
+
+    rs.getReader();
+
+    assert_throws_js(TypeError, () => rs.getReader(), 'getting a second reader should throw');
+    assert_throws_js(TypeError, () => rs.getReader(), 'getting a third reader should throw');
+
+  }, label + ': should not be able to acquire a second reader if we don\'t release the first one');
+};
+
+self.templatedRSErrored = (label, factory, error) => {
+  test(() => {}, 'Running templatedRSErrored with ' + label);
+
+  promise_test(t => {
+
+    const rs = factory();
+    const reader = rs.getReader();
+
+    return Promise.all([
+      promise_rejects_exactly(t, error, reader.closed),
+      promise_rejects_exactly(t, error, reader.read())
+    ]);
+
+  }, label + ': getReader() should return a reader that acts errored');
+
+  promise_test(t => {
+
+    const rs = factory();
+    const reader = rs.getReader();
+
+    return Promise.all([
+      promise_rejects_exactly(t, error, reader.read()),
+      promise_rejects_exactly(t, error, reader.read()),
+      promise_rejects_exactly(t, error, reader.closed)
+    ]);
+
+  }, label + ': read() twice should give the error each time');
+
+  test(() => {
+    const rs = factory();
+
+    assert_false(rs.locked, 'locked getter should return false');
+  }, label + ': locked should be false');
+};
+
+self.templatedRSErroredSyncOnly = (label, factory, error) => {
+  test(() => {}, 'Running templatedRSErroredSyncOnly with ' + label);
+
+  promise_test(t => {
+
+    const rs = factory();
+    rs.getReader().releaseLock();
+    const reader = rs.getReader(); // Calling getReader() twice does not throw (the stream is not locked).
+
+    return promise_rejects_exactly(t, error, reader.closed);
+
+  }, label + ': should be able to obtain a second reader, with the correct closed promise');
+
+  test(() => {
+
+    const rs = factory();
+    rs.getReader();
+
+    assert_throws_js(TypeError, () => rs.getReader(), 'getting a second reader should throw a TypeError');
+    assert_throws_js(TypeError, () => rs.getReader(), 'getting a third reader should throw a TypeError');
+
+  }, label + ': should not be able to obtain additional readers if we don\'t release the first lock');
+
+  promise_test(t => {
+
+    const rs = factory();
+    const cancelPromise1 = rs.cancel();
+    const cancelPromise2 = rs.cancel();
+
+    assert_not_equals(cancelPromise1, cancelPromise2, 'cancel() calls should return distinct promises');
+
+    return Promise.all([
+      promise_rejects_exactly(t, error, cancelPromise1),
+      promise_rejects_exactly(t, error, cancelPromise2)
+    ]);
+
+  }, label + ': cancel() should return a distinct rejected promise each time');
+
+  promise_test(t => {
+
+    const rs = factory();
+    const reader = rs.getReader();
+    const cancelPromise1 = reader.cancel();
+    const cancelPromise2 = reader.cancel();
+
+    assert_not_equals(cancelPromise1, cancelPromise2, 'cancel() calls should return distinct promises');
+
+    return Promise.all([
+      promise_rejects_exactly(t, error, cancelPromise1),
+      promise_rejects_exactly(t, error, cancelPromise2)
+    ]);
+
+  }, label + ': reader cancel() should return a distinct rejected promise each time');
+};
+
+self.templatedRSEmptyReader = (label, factory) => {
+  test(() => {}, 'Running templatedRSEmptyReader with ' + label);
+
+  test(() => {
+
+    const reader = factory().reader;
+
+    assert_true('closed' in reader, 'has a closed property');
+    assert_equals(typeof reader.closed.then, 'function', 'closed property is thenable');
+
+    assert_equals(typeof reader.cancel, 'function', 'has a cancel method');
+    assert_equals(typeof reader.read, 'function', 'has a read method');
+    assert_equals(typeof reader.releaseLock, 'function', 'has a releaseLock method');
+
+  }, label + ': instances have the correct methods and properties');
+
+  test(() => {
+
+    const stream = factory().stream;
+
+    assert_true(stream.locked, 'locked getter should return true');
+
+  }, label + ': locked should be true');
+
+  promise_test(t => {
+
+    const reader = factory().reader;
+
+    reader.read().then(
+      t.unreached_func('read() should not fulfill'),
+      t.unreached_func('read() should not reject')
+    );
+
+    return delay(500);
+
+  }, label + ': read() should never settle');
+
+  promise_test(t => {
+
+    const reader = factory().reader;
+
+    reader.read().then(
+      t.unreached_func('read() should not fulfill'),
+      t.unreached_func('read() should not reject')
+    );
+
+    reader.read().then(
+      t.unreached_func('read() should not fulfill'),
+      t.unreached_func('read() should not reject')
+    );
+
+    return delay(500);
+
+  }, label + ': two read()s should both never settle');
+
+  test(() => {
+
+    const reader = factory().reader;
+    assert_not_equals(reader.read(), reader.read(), 'the promises returned should be distinct');
+
+  }, label + ': read() should return distinct promises each time');
+
+  test(() => {
+
+    const stream = factory().stream;
+    assert_throws_js(TypeError, () => stream.getReader(), 'stream.getReader() should throw a TypeError');
+
+  }, label + ': getReader() again on the stream should fail');
+
+  promise_test(async t => {
+
+    const streamAndReader = factory();
+    const stream = streamAndReader.stream;
+    const reader = streamAndReader.reader;
+
+    const read1 = reader.read();
+    const read2 = reader.read();
+    const closed = reader.closed;
+
+    reader.releaseLock();
+
+    assert_false(stream.locked, 'the stream should be unlocked');
+
+    await Promise.all([
+      promise_rejects_js(t, TypeError, read1, 'first read should reject'),
+      promise_rejects_js(t, TypeError, read2, 'second read should reject'),
+      promise_rejects_js(t, TypeError, closed, 'closed should reject')
+    ]);
+
+  }, label + ': releasing the lock should reject all pending read requests');
+
+  promise_test(t => {
+
+    const reader = factory().reader;
+    reader.releaseLock();
+
+    return Promise.all([
+      promise_rejects_js(t, TypeError, reader.read()),
+      promise_rejects_js(t, TypeError, reader.read())
+    ]);
+
+  }, label + ': releasing the lock should cause further read() calls to reject with a TypeError');
+
+  promise_test(t => {
+
+    const reader = factory().reader;
+
+    const closedBefore = reader.closed;
+    reader.releaseLock();
+    const closedAfter = reader.closed;
+
+    assert_equals(closedBefore, closedAfter, 'the closed promise should not change identity');
+
+    return promise_rejects_js(t, TypeError, closedBefore);
+
+  }, label + ': releasing the lock should cause closed calls to reject with a TypeError');
+
+  test(() => {
+
+    const streamAndReader = factory();
+    const stream = streamAndReader.stream;
+    const reader = streamAndReader.reader;
+
+    reader.releaseLock();
+    assert_false(stream.locked, 'locked getter should return false');
+
+  }, label + ': releasing the lock should cause locked to become false');
+
+  promise_test(() => {
+
+    const reader = factory().reader;
+    reader.cancel();
+
+    return reader.read().then(r => {
+      assert_object_equals(r, { value: undefined, done: true }, 'read()ing from the reader should give a done result');
+    });
+
+  }, label + ': canceling via the reader should cause the reader to act closed');
+
+  promise_test(t => {
+
+    const stream = factory().stream;
+    return promise_rejects_js(t, TypeError, stream.cancel());
+
+  }, label + ': canceling via the stream should fail');
+};
+
+self.templatedRSClosedReader = (label, factory) => {
+  test(() => {}, 'Running templatedRSClosedReader with ' + label);
+
+  promise_test(() => {
+
+    const reader = factory().reader;
+
+    return reader.read().then(v => {
+      assert_object_equals(v, { value: undefined, done: true }, 'read() should fulfill correctly');
+    });
+
+  }, label + ': read() should fulfill with { value: undefined, done: true }');
+
+  promise_test(() => {
+
+    const reader = factory().reader;
+
+    return Promise.all([
+      reader.read().then(v => {
+        assert_object_equals(v, { value: undefined, done: true }, 'read() should fulfill correctly');
+      }),
+      reader.read().then(v => {
+        assert_object_equals(v, { value: undefined, done: true }, 'read() should fulfill correctly');
+      })
+    ]);
+
+  }, label + ': read() multiple times should fulfill with { value: undefined, done: true }');
+
+  promise_test(() => {
+
+    const reader = factory().reader;
+
+    return reader.read().then(() => reader.read()).then(v => {
+      assert_object_equals(v, { value: undefined, done: true }, 'read() should fulfill correctly');
+    });
+
+  }, label + ': read() should work when used within another read() fulfill callback');
+
+  promise_test(() => {
+
+    const reader = factory().reader;
+
+    return reader.closed.then(v => assert_equals(v, undefined, 'reader closed should fulfill with undefined'));
+
+  }, label + ': closed should fulfill with undefined');
+
+  promise_test(t => {
+
+    const reader = factory().reader;
+
+    const closedBefore = reader.closed;
+    reader.releaseLock();
+    const closedAfter = reader.closed;
+
+    assert_not_equals(closedBefore, closedAfter, 'the closed promise should change identity');
+
+    return Promise.all([
+      closedBefore.then(v => assert_equals(v, undefined, 'reader.closed acquired before release should fulfill')),
+      promise_rejects_js(t, TypeError, closedAfter)
+    ]);
+
+  }, label + ': releasing the lock should cause closed to reject and change identity');
+
+  promise_test(() => {
+
+    const reader = factory().reader;
+    const cancelPromise1 = reader.cancel();
+    const cancelPromise2 = reader.cancel();
+    const closedReaderPromise = reader.closed;
+
+    assert_not_equals(cancelPromise1, cancelPromise2, 'cancel() calls should return distinct promises');
+    assert_not_equals(cancelPromise1, closedReaderPromise, 'cancel() promise 1 should be distinct from reader.closed');
+    assert_not_equals(cancelPromise2, closedReaderPromise, 'cancel() promise 2 should be distinct from reader.closed');
+
+    return Promise.all([
+      cancelPromise1.then(v => assert_equals(v, undefined, 'first cancel() should fulfill with undefined')),
+      cancelPromise2.then(v => assert_equals(v, undefined, 'second cancel() should fulfill with undefined'))
+    ]);
+
+  }, label + ': cancel() should return a distinct fulfilled promise each time');
+};
+
+self.templatedRSErroredReader = (label, factory, error) => {
+  test(() => {}, 'Running templatedRSErroredReader with ' + label);
+
+  promise_test(t => {
+
+    const reader = factory().reader;
+    return promise_rejects_exactly(t, error, reader.closed);
+
+  }, label + ': closed should reject with the error');
+
+  promise_test(t => {
+
+    const reader = factory().reader;
+    const closedBefore = reader.closed;
+
+    return promise_rejects_exactly(t, error, closedBefore).then(() => {
+      reader.releaseLock();
+
+      const closedAfter = reader.closed;
+      assert_not_equals(closedBefore, closedAfter, 'the closed promise should change identity');
+
+      return promise_rejects_js(t, TypeError, closedAfter);
+    });
+
+  }, label + ': releasing the lock should cause closed to reject and change identity');
+
+  promise_test(t => {
+
+    const reader = factory().reader;
+    return promise_rejects_exactly(t, error, reader.read());
+
+  }, label + ': read() should reject with the error');
+};
+
+self.templatedRSTwoChunksOpenReader = (label, factory, chunks) => {
+  test(() => {}, 'Running templatedRSTwoChunksOpenReader with ' + label);
+
+  promise_test(() => {
+
+    const reader = factory().reader;
+
+    return Promise.all([
+      reader.read().then(r => {
+        assert_object_equals(r, { value: chunks[0], done: false }, 'first result should be correct');
+      }),
+      reader.read().then(r => {
+        assert_object_equals(r, { value: chunks[1], done: false }, 'second result should be correct');
+      })
+    ]);
+
+  }, label + ': calling read() twice without waiting will eventually give both chunks (sequential)');
+
+  promise_test(() => {
+
+    const reader = factory().reader;
+
+    return reader.read().then(r => {
+      assert_object_equals(r, { value: chunks[0], done: false }, 'first result should be correct');
+
+      return reader.read().then(r2 => {
+        assert_object_equals(r2, { value: chunks[1], done: false }, 'second result should be correct');
+      });
+    });
+
+  }, label + ': calling read() twice without waiting will eventually give both chunks (nested)');
+
+  test(() => {
+
+    const reader = factory().reader;
+    assert_not_equals(reader.read(), reader.read(), 'the promises returned should be distinct');
+
+  }, label + ': read() should return distinct promises each time');
+
+  promise_test(() => {
+
+    const reader = factory().reader;
+
+    const promise1 = reader.closed.then(v => {
+      assert_equals(v, undefined, 'reader closed should fulfill with undefined');
+    });
+
+    const promise2 = reader.read().then(r => {
+      assert_object_equals(r, { value: chunks[0], done: false },
+                           'promise returned before cancellation should fulfill with a chunk');
+    });
+
+    reader.cancel();
+
+    const promise3 = reader.read().then(r => {
+      assert_object_equals(r, { value: undefined, done: true },
+                           'promise returned after cancellation should fulfill with an end-of-stream signal');
+    });
+
+    return Promise.all([promise1, promise2, promise3]);
+
+  }, label + ': cancel() after a read() should still give that single read result');
+};
+
+self.templatedRSTwoChunksClosedReader = function (label, factory, chunks) {
+  test(() => {}, 'Running templatedRSTwoChunksClosedReader with ' + label);
+
+  promise_test(() => {
+
+    const reader = factory().reader;
+
+    return Promise.all([
+      reader.read().then(r => {
+        assert_object_equals(r, { value: chunks[0], done: false }, 'first result should be correct');
+      }),
+      reader.read().then(r => {
+        assert_object_equals(r, { value: chunks[1], done: false }, 'second result should be correct');
+      }),
+      reader.read().then(r => {
+        assert_object_equals(r, { value: undefined, done: true }, 'third result should be correct');
+      })
+    ]);
+
+  }, label + ': third read(), without waiting, should give { value: undefined, done: true } (sequential)');
+
+  promise_test(() => {
+
+    const reader = factory().reader;
+
+    return reader.read().then(r => {
+      assert_object_equals(r, { value: chunks[0], done: false }, 'first result should be correct');
+
+      return reader.read().then(r2 => {
+        assert_object_equals(r2, { value: chunks[1], done: false }, 'second result should be correct');
+
+        return reader.read().then(r3 => {
+          assert_object_equals(r3, { value: undefined, done: true }, 'third result should be correct');
+        });
+      });
+    });
+
+  }, label + ': third read(), without waiting, should give { value: undefined, done: true } (nested)');
+
+  promise_test(() => {
+
+    const streamAndReader = factory();
+    const stream = streamAndReader.stream;
+    const reader = streamAndReader.reader;
+
+    assert_true(stream.locked, 'stream should start locked');
+
+    const promise = reader.closed.then(v => {
+      assert_equals(v, undefined, 'reader closed should fulfill with undefined');
+      assert_true(stream.locked, 'stream should remain locked');
+    });
+
+    reader.read();
+    reader.read();
+
+    return promise;
+
+  }, label +
+     ': draining the stream via read() should cause the reader closed promise to fulfill, but locked stays true');
+
+  promise_test(() => {
+
+    const streamAndReader = factory();
+    const stream = streamAndReader.stream;
+    const reader = streamAndReader.reader;
+
+    const promise = reader.closed.then(() => {
+      assert_true(stream.locked, 'the stream should start locked');
+      reader.releaseLock(); // Releasing the lock after reader closed should not throw.
+      assert_false(stream.locked, 'the stream should end unlocked');
+    });
+
+    reader.read();
+    reader.read();
+
+    return promise;
+
+  }, label + ': releasing the lock after the stream is closed should cause locked to become false');
+
+  promise_test(t => {
+
+    const reader = factory().reader;
+
+    reader.releaseLock();
+
+    return Promise.all([
+      promise_rejects_js(t, TypeError, reader.read()),
+      promise_rejects_js(t, TypeError, reader.read()),
+      promise_rejects_js(t, TypeError, reader.read())
+    ]);
+
+  }, label + ': releasing the lock should cause further read() calls to reject with a TypeError');
+
+  promise_test(() => {
+
+    const streamAndReader = factory();
+    const stream = streamAndReader.stream;
+    const reader = streamAndReader.reader;
+
+    const readerClosed = reader.closed;
+
+    assert_equals(reader.closed, readerClosed, 'accessing reader.closed twice in succession gives the same value');
+
+    const promise = reader.read().then(() => {
+      assert_equals(reader.closed, readerClosed, 'reader.closed is the same after read() fulfills');
+
+      reader.releaseLock();
+
+      assert_equals(reader.closed, readerClosed, 'reader.closed is the same after releasing the lock');
+
+      const newReader = stream.getReader();
+      return newReader.read();
+    });
+
+    assert_equals(reader.closed, readerClosed, 'reader.closed is the same after calling read()');
+
+    return promise;
+
+  }, label + ': reader\'s closed property always returns the same promise');
+};
+
+self.templatedRSTeeCancel = (label, factory) => {
+  test(() => {}, `Running templatedRSTeeCancel with ${label}`);
+
+  promise_test(async () => {
+
+    const reason1 = new Error('We\'re wanted men.');
+    const reason2 = new Error('I have the death sentence on twelve systems.');
+
+    let resolve;
+    const promise = new Promise(r => resolve = r);
+    const rs = factory({
+      cancel(reason) {
+        assert_array_equals(reason, [reason1, reason2],
+          'the cancel reason should be an array containing those from the branches');
+        resolve();
+      }
+    });
+
+    const [branch1, branch2] = rs.tee();
+    await Promise.all([
+      branch1.cancel(reason1),
+      branch2.cancel(reason2),
+      promise
+    ]);
+
+  }, `${label}: canceling both branches should aggregate the cancel reasons into an array`);
+
+  promise_test(async () => {
+
+    const reason1 = new Error('This little one\'s not worth the effort.');
+    const reason2 = new Error('Come, let me get you something.');
+
+    let resolve;
+    const promise = new Promise(r => resolve = r);
+    const rs = factory({
+      cancel(reason) {
+        assert_array_equals(reason, [reason1, reason2],
+          'the cancel reason should be an array containing those from the branches');
+        resolve();
+      }
+    });
+
+    const [branch1, branch2] = rs.tee();
+    await Promise.all([
+      branch2.cancel(reason2),
+      branch1.cancel(reason1),
+      promise
+    ]);
+
+  }, `${label}: canceling both branches in reverse order should aggregate the cancel reasons into an array`);
+
+  promise_test(async t => {
+
+    const theError = { name: 'I\'ll be careful.' };
+    const rs = factory({
+      cancel() {
+        throw theError;
+      }
+    });
+
+    const [branch1, branch2] = rs.tee();
+    await Promise.all([
+      promise_rejects_exactly(t, theError, branch1.cancel()),
+      promise_rejects_exactly(t, theError, branch2.cancel())
+    ]);
+
+  }, `${label}: failing to cancel the original stream should cause cancel() to reject on branches`);
+
+  promise_test(async t => {
+
+    const theError = { name: 'You just watch yourself!' };
+    let controller;
+    const stream = factory({
+      start(c) {
+        controller = c;
+      }
+    });
+
+    const [branch1, branch2] = stream.tee();
+    controller.error(theError);
+
+    await Promise.all([
+      promise_rejects_exactly(t, theError, branch1.cancel()),
+      promise_rejects_exactly(t, theError, branch2.cancel())
+    ]);
+
+  }, `${label}: erroring a teed stream should properly handle canceled branches`);
+
+};

Tests/LibWeb/Text/input/wpt-import/streams/resources/rs-utils.js

@@ -0,0 +1,234 @@
+'use strict';
+(function () {
+  // Fake setInterval-like functionality in environments that don't have it
+  class IntervalHandle {
+    constructor(callback, delayMs) {
+      this.callback = callback;
+      this.delayMs = delayMs;
+      this.cancelled = false;
+      Promise.resolve().then(() => this.check());
+    }
+
+    async check() {
+      while (true) {
+        await new Promise(resolve => step_timeout(resolve, this.delayMs));
+        if (this.cancelled) {
+          return;
+        }
+        this.callback();
+      }
+    }
+
+    cancel() {
+      this.cancelled = true;
+    }
+  }
+
+  let localSetInterval, localClearInterval;
+  if (typeof globalThis.setInterval !== "undefined" &&
+      typeof globalThis.clearInterval !== "undefined") {
+    localSetInterval = globalThis.setInterval;
+    localClearInterval = globalThis.clearInterval;
+  } else {
+    localSetInterval = function setInterval(callback, delayMs) {
+      return new IntervalHandle(callback, delayMs);
+    }
+    localClearInterval = function clearInterval(handle) {
+      handle.cancel();
+    }
+  }
+
+  class RandomPushSource {
+    constructor(toPush) {
+      this.pushed = 0;
+      this.toPush = toPush;
+      this.started = false;
+      this.paused = false;
+      this.closed = false;
+
+      this._intervalHandle = null;
+    }
+
+    readStart() {
+      if (this.closed) {
+        return;
+      }
+
+      if (!this.started) {
+        this._intervalHandle = localSetInterval(writeChunk, 2);
+        this.started = true;
+      }
+
+      if (this.paused) {
+        this._intervalHandle = localSetInterval(writeChunk, 2);
+        this.paused = false;
+      }
+
+      const source = this;
+      function writeChunk() {
+        if (source.paused) {
+          return;
+        }
+
+        source.pushed++;
+
+        if (source.toPush > 0 && source.pushed > source.toPush) {
+          if (source._intervalHandle) {
+            localClearInterval(source._intervalHandle);
+            source._intervalHandle = undefined;
+          }
+          source.closed = true;
+          source.onend();
+        } else {
+          source.ondata(randomChunk(128));
+        }
+      }
+    }
+
+    readStop() {
+      if (this.paused) {
+        return;
+      }
+
+      if (this.started) {
+        this.paused = true;
+        localClearInterval(this._intervalHandle);
+        this._intervalHandle = undefined;
+      } else {
+        throw new Error('Can\'t pause reading an unstarted source.');
+      }
+    }
+  }
+
+  function randomChunk(size) {
+    let chunk = '';
+
+    for (let i = 0; i < size; ++i) {
+      // Add a random character from the basic printable ASCII set.
+      chunk += String.fromCharCode(Math.round(Math.random() * 84) + 32);
+    }
+
+    return chunk;
+  }
+
+  function readableStreamToArray(readable, reader) {
+    if (reader === undefined) {
+      reader = readable.getReader();
+    }
+
+    const chunks = [];
+
+    return pump();
+
+    function pump() {
+      return reader.read().then(result => {
+        if (result.done) {
+          return chunks;
+        }
+
+        chunks.push(result.value);
+        return pump();
+      });
+    }
+  }
+
+  class SequentialPullSource {
+    constructor(limit, options) {
+      const async = options && options.async;
+
+      this.current = 0;
+      this.limit = limit;
+      this.opened = false;
+      this.closed = false;
+
+      this._exec = f => f();
+      if (async) {
+        this._exec = f => step_timeout(f, 0);
+      }
+    }
+
+    open(cb) {
+      this._exec(() => {
+        this.opened = true;
+        cb();
+      });
+    }
+
+    read(cb) {
+      this._exec(() => {
+        if (++this.current <= this.limit) {
+          cb(null, false, this.current);
+        } else {
+          cb(null, true, null);
+        }
+      });
+    }
+
+    close(cb) {
+      this._exec(() => {
+        this.closed = true;
+        cb();
+      });
+    }
+  }
+
+  function sequentialReadableStream(limit, options) {
+    const sequentialSource = new SequentialPullSource(limit, options);
+
+    const stream = new ReadableStream({
+      start() {
+        return new Promise((resolve, reject) => {
+          sequentialSource.open(err => {
+            if (err) {
+              reject(err);
+            }
+            resolve();
+          });
+        });
+      },
+
+      pull(c) {
+        return new Promise((resolve, reject) => {
+          sequentialSource.read((err, done, chunk) => {
+            if (err) {
+              reject(err);
+            } else if (done) {
+              sequentialSource.close(err2 => {
+                if (err2) {
+                  reject(err2);
+                }
+                c.close();
+                resolve();
+              });
+            } else {
+              c.enqueue(chunk);
+              resolve();
+            }
+          });
+        });
+      }
+    });
+
+    stream.source = sequentialSource;
+
+    return stream;
+  }
+
+  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);
+  }
+
+  self.RandomPushSource = RandomPushSource;
+  self.readableStreamToArray = readableStreamToArray;
+  self.sequentialReadableStream = sequentialReadableStream;
+  self.transferArrayBufferView = transferArrayBufferView;
+
+}());

Tests/LibWeb/Text/input/wpt-import/streams/resources/test-utils.js

@@ -0,0 +1,27 @@
+'use strict';
+
+self.delay = ms => new Promise(resolve => step_timeout(resolve, ms));
+
+// For tests which verify that the implementation doesn't do something it shouldn't, it's better not to use a
+// timeout. Instead, assume that any reasonable implementation is going to finish work after 2 times around the event
+// loop, and use flushAsyncEvents().then(() => assert_array_equals(...));
+// Some tests include promise resolutions which may mean the test code takes a couple of event loop visits itself. So go
+// around an extra 2 times to avoid complicating those tests.
+self.flushAsyncEvents = () => delay(0).then(() => delay(0)).then(() => delay(0)).then(() => delay(0));
+
+self.assert_typed_array_equals = (actual, expected, message) => {
+  const prefix = message === undefined ? '' : `${message} `;
+  assert_equals(typeof actual, 'object', `${prefix}type is object`);
+  assert_equals(actual.constructor, expected.constructor, `${prefix}constructor`);
+  assert_equals(actual.byteOffset, expected.byteOffset, `${prefix}byteOffset`);
+  assert_equals(actual.byteLength, expected.byteLength, `${prefix}byteLength`);
+  assert_equals(actual.buffer.byteLength, expected.buffer.byteLength, `${prefix}buffer.byteLength`);
+  assert_array_equals([...actual], [...expected], `${prefix}contents`);
+  assert_array_equals([...new Uint8Array(actual.buffer)], [...new Uint8Array(expected.buffer)], `${prefix}buffer contents`);
+};
+
+self.makePromiseAndResolveFunc = () => {
+  let resolve;
+  const promise = new Promise(r => { resolve = r; });
+  return [promise, resolve];
+};

Userland/Libraries/LibWeb/HTML/WindowOrWorkerGlobalScope.cpp

@@ -415,7 +415,8 @@ i32 WindowOrWorkerGlobalScopeMixin::run_timer_initialization_steps(TimerHandler
 
     // 11. Let completionStep be an algorithm step which queues a global task on the timer task source given global to run task.
     Function<void()> completion_step = [this, task = move(task)]() mutable {
-        queue_global_task(Task::Source::TimerTask, this_impl(), JS::create_heap_function(this_impl().heap(), [task] {
+        queue_global_task(Task::Source::TimerTask, this_impl(), JS::create_heap_function(this_impl().heap(), [this, task] {
+            HTML::TemporaryExecutionContext execution_context { Bindings::host_defined_environment_settings_object(this_impl().realm()), HTML::TemporaryExecutionContext::CallbacksEnabled::Yes };
             task->function()();
         }));
     };
@@ -586,6 +587,7 @@ void WindowOrWorkerGlobalScopeMixin::queue_the_performance_observer_task()
     //    timeline task source.
     queue_global_task(Task::Source::PerformanceTimeline, this_impl(), JS::create_heap_function(this_impl().heap(), [this]() {
         auto& realm = this_impl().realm();
+        HTML::TemporaryExecutionContext execution_context { Bindings::host_defined_environment_settings_object(realm), HTML::TemporaryExecutionContext::CallbacksEnabled::Yes };
 
         // 1. Unset performance observer task queued flag of relevantGlobal.
         m_performance_observer_task_queued = false;