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test/fixtures/wpt/streams/piping/abort.any.js

@@ -0,0 +1,448 @@
+// META: global=window,worker,shadowrealm
+// META: script=../resources/recording-streams.js
+// META: script=../resources/test-utils.js
+'use strict';
+
+// Tests for the use of pipeTo with AbortSignal.
+// There is some extra complexity to avoid timeouts in environments where abort is not implemented.
+
+const error1 = new Error('error1');
+error1.name = 'error1';
+const error2 = new Error('error2');
+error2.name = 'error2';
+
+const errorOnPull = {
+  pull(controller) {
+    // This will cause the test to error if pipeTo abort is not implemented.
+    controller.error('failed to abort');
+  }
+};
+
+// To stop pull() being called immediately when the stream is created, we need to set highWaterMark to 0.
+const hwm0 = { highWaterMark: 0 };
+
+for (const invalidSignal of [null, 'AbortSignal', true, -1, Object.create(AbortSignal.prototype)]) {
+  promise_test(t => {
+    const rs = recordingReadableStream(errorOnPull, hwm0);
+    const ws = recordingWritableStream();
+    return promise_rejects_js(t, TypeError, rs.pipeTo(ws, { signal: invalidSignal }), 'pipeTo should reject')
+        .then(() => {
+          assert_equals(rs.events.length, 0, 'no ReadableStream methods should have been called');
+          assert_equals(ws.events.length, 0, 'no WritableStream methods should have been called');
+        });
+  }, `a signal argument '${invalidSignal}' should cause pipeTo() to reject`);
+}
+
+promise_test(t => {
+  const rs = recordingReadableStream(errorOnPull, hwm0);
+  const ws = new WritableStream();
+  const abortController = new AbortController();
+  const signal = abortController.signal;
+  abortController.abort();
+  return promise_rejects_dom(t, 'AbortError', rs.pipeTo(ws, { signal }), 'pipeTo should reject')
+      .then(() => Promise.all([
+        rs.getReader().closed,
+        promise_rejects_dom(t, 'AbortError', ws.getWriter().closed, 'writer.closed should reject')
+      ]))
+      .then(() => {
+        assert_equals(rs.events.length, 2, 'cancel should have been called');
+        assert_equals(rs.events[0], 'cancel', 'first event should be cancel');
+        assert_equals(rs.events[1].name, 'AbortError', 'the argument to cancel should be an AbortError');
+        assert_equals(rs.events[1].constructor.name, 'DOMException',
+                      'the argument to cancel should be a DOMException');
+      });
+}, 'an aborted signal should cause the writable stream to reject with an AbortError');
+
+for (const reason of [null, undefined, error1]) {
+  promise_test(async t => {
+    const rs = recordingReadableStream(errorOnPull, hwm0);
+    const ws = new WritableStream();
+    const abortController = new AbortController();
+    const signal = abortController.signal;
+    abortController.abort(reason);
+    const pipeToPromise = rs.pipeTo(ws, { signal });
+    if (reason !== undefined) {
+      await promise_rejects_exactly(t, reason, pipeToPromise, 'pipeTo rejects with abort reason');
+    } else {
+      await promise_rejects_dom(t, 'AbortError', pipeToPromise, 'pipeTo rejects with AbortError');
+    }
+    const error = await pipeToPromise.catch(e => e);
+    await rs.getReader().closed;
+    await promise_rejects_exactly(t, error, ws.getWriter().closed, 'the writable should be errored with the same object');
+    assert_equals(signal.reason, error, 'signal.reason should be error'),
+    assert_equals(rs.events.length, 2, 'cancel should have been called');
+    assert_equals(rs.events[0], 'cancel', 'first event should be cancel');
+    assert_equals(rs.events[1], error, 'the readable should be canceled with the same object');
+  }, `(reason: '${reason}') all the error objects should be the same object`);
+}
+
+promise_test(t => {
+  const rs = recordingReadableStream(errorOnPull, hwm0);
+  const ws = new WritableStream();
+  const abortController = new AbortController();
+  const signal = abortController.signal;
+  abortController.abort();
+  return promise_rejects_dom(t, 'AbortError', rs.pipeTo(ws, { signal, preventCancel: true }), 'pipeTo should reject')
+      .then(() => assert_equals(rs.events.length, 0, 'cancel should not be called'));
+}, 'preventCancel should prevent canceling the readable');
+
+promise_test(t => {
+  const rs = new ReadableStream(errorOnPull, hwm0);
+  const ws = recordingWritableStream();
+  const abortController = new AbortController();
+  const signal = abortController.signal;
+  abortController.abort();
+  return promise_rejects_dom(t, 'AbortError', rs.pipeTo(ws, { signal, preventAbort: true }), 'pipeTo should reject')
+      .then(() => {
+        assert_equals(ws.events.length, 0, 'writable should not have been aborted');
+        return ws.getWriter().ready;
+      });
+}, 'preventAbort should prevent aborting the readable');
+
+promise_test(t => {
+  const rs = recordingReadableStream(errorOnPull, hwm0);
+  const ws = recordingWritableStream();
+  const abortController = new AbortController();
+  const signal = abortController.signal;
+  abortController.abort();
+  return promise_rejects_dom(t, 'AbortError', rs.pipeTo(ws, { signal, preventCancel: true, preventAbort: true }),
+                         'pipeTo should reject')
+    .then(() => {
+      assert_equals(rs.events.length, 0, 'cancel should not be called');
+      assert_equals(ws.events.length, 0, 'writable should not have been aborted');
+      return ws.getWriter().ready;
+    });
+}, 'preventCancel and preventAbort should prevent canceling the readable and aborting the readable');
+
+for (const reason of [null, undefined, error1]) {
+  promise_test(async t => {
+    const rs = new ReadableStream({
+      start(controller) {
+        controller.enqueue('a');
+        controller.enqueue('b');
+        controller.close();
+      }
+    });
+    const abortController = new AbortController();
+    const signal = abortController.signal;
+    const ws = recordingWritableStream({
+      write() {
+        abortController.abort(reason);
+      }
+    });
+    const pipeToPromise = rs.pipeTo(ws, { signal });
+    if (reason !== undefined) {
+      await promise_rejects_exactly(t, reason, pipeToPromise, 'pipeTo rejects with abort reason');
+    } else {
+      await promise_rejects_dom(t, 'AbortError', pipeToPromise, 'pipeTo rejects with AbortError');
+    }
+    const error = await pipeToPromise.catch(e => e);
+    assert_equals(signal.reason, error, 'signal.reason should be error');
+    assert_equals(ws.events.length, 4, 'only chunk "a" should have been written');
+    assert_array_equals(ws.events.slice(0, 3), ['write', 'a', 'abort'], 'events should match');
+    assert_equals(ws.events[3], error, 'abort reason should be error');
+  }, `(reason: '${reason}') abort should prevent further reads`);
+}
+
+for (const reason of [null, undefined, error1]) {
+  promise_test(async t => {
+    let readController;
+    const rs = new ReadableStream({
+      start(c) {
+        readController = c;
+        c.enqueue('a');
+        c.enqueue('b');
+      }
+    });
+    const abortController = new AbortController();
+    const signal = abortController.signal;
+    let resolveWrite;
+    const writePromise = new Promise(resolve => {
+      resolveWrite = resolve;
+    });
+    const ws = recordingWritableStream({
+      write() {
+        return writePromise;
+      }
+    }, new CountQueuingStrategy({ highWaterMark: Infinity }));
+    const pipeToPromise = rs.pipeTo(ws, { signal });
+    await delay(0);
+    await abortController.abort(reason);
+    await readController.close(); // Make sure the test terminates when signal is not implemented.
+    await resolveWrite();
+    if (reason !== undefined) {
+      await promise_rejects_exactly(t, reason, pipeToPromise, 'pipeTo rejects with abort reason');
+    } else {
+      await promise_rejects_dom(t, 'AbortError', pipeToPromise, 'pipeTo rejects with AbortError');
+    }
+    const error = await pipeToPromise.catch(e => e);
+    assert_equals(signal.reason, error, 'signal.reason should be error');
+    assert_equals(ws.events.length, 6, 'chunks "a" and "b" should have been written');
+    assert_array_equals(ws.events.slice(0, 5), ['write', 'a', 'write', 'b', 'abort'], 'events should match');
+    assert_equals(ws.events[5], error, 'abort reason should be error');
+  }, `(reason: '${reason}') all pending writes should complete on abort`);
+}
+
+for (const reason of [null, undefined, error1]) {
+  promise_test(async t => {
+    let rejectPull;
+    const pullPromise = new Promise((_, reject) => {
+      rejectPull = reject;
+    });
+    let rejectCancel;
+    const cancelPromise = new Promise((_, reject) => {
+      rejectCancel = reject;
+    });
+    const rs = recordingReadableStream({
+      async pull() {
+        await Promise.race([
+          pullPromise,
+          cancelPromise,
+        ]);
+      },
+      cancel(reason) {
+        rejectCancel(reason);
+      },
+    });
+    const ws = new WritableStream();
+    const abortController = new AbortController();
+    const signal = abortController.signal;
+    const pipeToPromise = rs.pipeTo(ws, { signal });
+    pipeToPromise.catch(() => {}); // Prevent unhandled rejection.
+    await delay(0);
+    abortController.abort(reason);
+    rejectPull('should not catch pull rejection');
+    await delay(0);
+    assert_equals(rs.eventsWithoutPulls.length, 2, 'cancel should have been called');
+    assert_equals(rs.eventsWithoutPulls[0], 'cancel', 'first event should be cancel');
+    if (reason !== undefined) {
+      await promise_rejects_exactly(t, reason, pipeToPromise, 'pipeTo rejects with abort reason');
+    } else {
+      await promise_rejects_dom(t, 'AbortError', pipeToPromise, 'pipeTo rejects with AbortError');
+    }
+  }, `(reason: '${reason}') underlyingSource.cancel() should called when abort, even with pending pull`);
+}
+
+promise_test(t => {
+  const rs = new ReadableStream({
+    pull(controller) {
+      controller.error('failed to abort');
+    },
+    cancel() {
+      return Promise.reject(error1);
+    }
+  }, hwm0);
+  const ws = new WritableStream();
+  const abortController = new AbortController();
+  const signal = abortController.signal;
+  abortController.abort();
+  return promise_rejects_exactly(t, error1, rs.pipeTo(ws, { signal }), 'pipeTo should reject');
+}, 'a rejection from underlyingSource.cancel() should be returned by pipeTo()');
+
+promise_test(t => {
+  const rs = new ReadableStream(errorOnPull, hwm0);
+  const ws = new WritableStream({
+    abort() {
+      return Promise.reject(error1);
+    }
+  });
+  const abortController = new AbortController();
+  const signal = abortController.signal;
+  abortController.abort();
+  return promise_rejects_exactly(t, error1, rs.pipeTo(ws, { signal }), 'pipeTo should reject');
+}, 'a rejection from underlyingSink.abort() should be returned by pipeTo()');
+
+promise_test(t => {
+  const events = [];
+  const rs = new ReadableStream({
+    pull(controller) {
+      controller.error('failed to abort');
+    },
+    cancel() {
+      events.push('cancel');
+      return Promise.reject(error1);
+    }
+  }, hwm0);
+  const ws = new WritableStream({
+    abort() {
+      events.push('abort');
+      return Promise.reject(error2);
+    }
+  });
+  const abortController = new AbortController();
+  const signal = abortController.signal;
+  abortController.abort();
+  return promise_rejects_exactly(t, error2, rs.pipeTo(ws, { signal }), 'pipeTo should reject')
+      .then(() => assert_array_equals(events, ['abort', 'cancel'], 'abort() should be called before cancel()'));
+}, 'a rejection from underlyingSink.abort() should be preferred to one from underlyingSource.cancel()');
+
+promise_test(t => {
+  const rs = new ReadableStream({
+    start(controller) {
+      controller.close();
+    }
+  });
+  const ws = new WritableStream();
+  const abortController = new AbortController();
+  const signal = abortController.signal;
+  abortController.abort();
+  return promise_rejects_dom(t, 'AbortError', rs.pipeTo(ws, { signal }), 'pipeTo should reject');
+}, 'abort signal takes priority over closed readable');
+
+promise_test(t => {
+  const rs = new ReadableStream({
+    start(controller) {
+      controller.error(error1);
+    }
+  });
+  const ws = new WritableStream();
+  const abortController = new AbortController();
+  const signal = abortController.signal;
+  abortController.abort();
+  return promise_rejects_dom(t, 'AbortError', rs.pipeTo(ws, { signal }), 'pipeTo should reject');
+}, 'abort signal takes priority over errored readable');
+
+promise_test(t => {
+  const rs = new ReadableStream({
+    pull(controller) {
+      controller.error('failed to abort');
+    }
+  }, hwm0);
+  const ws = new WritableStream();
+  const abortController = new AbortController();
+  const signal = abortController.signal;
+  abortController.abort();
+  const writer = ws.getWriter();
+  return writer.close().then(() => {
+    writer.releaseLock();
+    return promise_rejects_dom(t, 'AbortError', rs.pipeTo(ws, { signal }), 'pipeTo should reject');
+  });
+}, 'abort signal takes priority over closed writable');
+
+promise_test(t => {
+  const rs = new ReadableStream({
+    pull(controller) {
+      controller.error('failed to abort');
+    }
+  }, hwm0);
+  const ws = new WritableStream({
+    start(controller) {
+      controller.error(error1);
+    }
+  });
+  const abortController = new AbortController();
+  const signal = abortController.signal;
+  abortController.abort();
+  return promise_rejects_dom(t, 'AbortError', rs.pipeTo(ws, { signal }), 'pipeTo should reject');
+}, 'abort signal takes priority over errored writable');
+
+promise_test(() => {
+  let readController;
+  const rs = new ReadableStream({
+    start(c) {
+      readController = c;
+    }
+  });
+  const ws = new WritableStream();
+  const abortController = new AbortController();
+  const signal = abortController.signal;
+  const pipeToPromise = rs.pipeTo(ws, { signal, preventClose: true });
+  readController.close();
+  return Promise.resolve().then(() => {
+    abortController.abort();
+    return pipeToPromise;
+  }).then(() => ws.getWriter().write('this should succeed'));
+}, 'abort should do nothing after the readable is closed');
+
+promise_test(t => {
+  let readController;
+  const rs = new ReadableStream({
+    start(c) {
+      readController = c;
+    }
+  });
+  const ws = new WritableStream();
+  const abortController = new AbortController();
+  const signal = abortController.signal;
+  const pipeToPromise = rs.pipeTo(ws, { signal, preventAbort: true });
+  readController.error(error1);
+  return Promise.resolve().then(() => {
+    abortController.abort();
+    return promise_rejects_exactly(t, error1, pipeToPromise, 'pipeTo should reject');
+  }).then(() => ws.getWriter().write('this should succeed'));
+}, 'abort should do nothing after the readable is errored');
+
+promise_test(t => {
+  let readController;
+  const rs = new ReadableStream({
+    start(c) {
+      readController = c;
+    }
+  });
+  let resolveWrite;
+  const writePromise = new Promise(resolve => {
+    resolveWrite = resolve;
+  });
+  const ws = new WritableStream({
+    write() {
+      readController.error(error1);
+      return writePromise;
+    }
+  });
+  const abortController = new AbortController();
+  const signal = abortController.signal;
+  const pipeToPromise = rs.pipeTo(ws, { signal, preventAbort: true });
+  readController.enqueue('a');
+  return delay(0).then(() => {
+    abortController.abort();
+    resolveWrite();
+    return promise_rejects_exactly(t, error1, pipeToPromise, 'pipeTo should reject');
+  }).then(() => ws.getWriter().write('this should succeed'));
+}, 'abort should do nothing after the readable is errored, even with pending writes');
+
+promise_test(t => {
+  const rs = recordingReadableStream({
+    pull(controller) {
+      return delay(0).then(() => controller.close());
+    }
+  });
+  let writeController;
+  const ws = new WritableStream({
+    start(c) {
+      writeController = c;
+    }
+  });
+  const abortController = new AbortController();
+  const signal = abortController.signal;
+  const pipeToPromise = rs.pipeTo(ws, { signal, preventCancel: true });
+  return Promise.resolve().then(() => {
+    writeController.error(error1);
+    return Promise.resolve();
+  }).then(() => {
+    abortController.abort();
+    return promise_rejects_exactly(t, error1, pipeToPromise, 'pipeTo should reject');
+  }).then(() => {
+    assert_array_equals(rs.events, ['pull'], 'cancel should not have been called');
+  });
+}, 'abort should do nothing after the writable is errored');
+
+promise_test(async t => {
+  const rs = new ReadableStream({
+    pull(c) {
+      c.enqueue(new Uint8Array([]));
+    },
+    type: "bytes",
+  });
+  const ws = new WritableStream();
+  const [first, second] = rs.tee();
+
+  let aborted = false;
+  first.pipeTo(ws, { signal: AbortSignal.abort() }).catch(() => {
+    aborted = true;
+  });
+  await delay(0);
+  assert_true(!aborted, "pipeTo should not resolve yet");
+  await second.cancel();
+  await delay(0);
+  assert_true(aborted, "pipeTo should be aborted now");
+}, "pipeTo on a teed readable byte stream should only be aborted when both branches are aborted");

test/fixtures/wpt/streams/piping/close-propagation-backward.any.js

@@ -0,0 +1,153 @@
+// META: global=window,worker,shadowrealm
+// META: script=../resources/recording-streams.js
+'use strict';
+
+const error1 = new Error('error1!');
+error1.name = 'error1';
+
+promise_test(() => {
+
+  const rs = recordingReadableStream();
+
+  const ws = recordingWritableStream();
+  const writer = ws.getWriter();
+  writer.close();
+  writer.releaseLock();
+
+  return rs.pipeTo(ws).then(
+    () => assert_unreached('the promise must not fulfill'),
+    err => {
+      assert_equals(err.name, 'TypeError', 'the promise must reject with a TypeError');
+
+      assert_array_equals(rs.eventsWithoutPulls, ['cancel', err]);
+      assert_array_equals(ws.events, ['close']);
+
+      return Promise.all([
+        rs.getReader().closed,
+        ws.getWriter().closed
+      ]);
+    }
+  );
+
+}, 'Closing must be propagated backward: starts closed; preventCancel omitted; fulfilled cancel promise');
+
+promise_test(t => {
+
+  // Our recording streams do not deal well with errors generated by the system, so give them some help
+  let recordedError;
+  const rs = recordingReadableStream({
+    cancel(cancelErr) {
+      recordedError = cancelErr;
+      throw error1;
+    }
+  });
+
+  const ws = recordingWritableStream();
+  const writer = ws.getWriter();
+  writer.close();
+  writer.releaseLock();
+
+  return promise_rejects_exactly(t, error1, rs.pipeTo(ws), 'pipeTo must reject with the same error').then(() => {
+    assert_equals(recordedError.name, 'TypeError', 'the cancel reason must be a TypeError');
+
+    assert_array_equals(rs.eventsWithoutPulls, ['cancel', recordedError]);
+    assert_array_equals(ws.events, ['close']);
+
+    return Promise.all([
+      rs.getReader().closed,
+      ws.getWriter().closed
+    ]);
+  });
+
+}, 'Closing must be propagated backward: starts closed; preventCancel omitted; rejected cancel promise');
+
+for (const falsy of [undefined, null, false, +0, -0, NaN, '']) {
+  const stringVersion = Object.is(falsy, -0) ? '-0' : String(falsy);
+
+  promise_test(() => {
+
+    const rs = recordingReadableStream();
+
+    const ws = recordingWritableStream();
+    const writer = ws.getWriter();
+    writer.close();
+    writer.releaseLock();
+
+    return rs.pipeTo(ws, { preventCancel: falsy }).then(
+      () => assert_unreached('the promise must not fulfill'),
+      err => {
+        assert_equals(err.name, 'TypeError', 'the promise must reject with a TypeError');
+
+        assert_array_equals(rs.eventsWithoutPulls, ['cancel', err]);
+        assert_array_equals(ws.events, ['close']);
+
+        return Promise.all([
+          rs.getReader().closed,
+          ws.getWriter().closed
+        ]);
+      }
+    );
+
+  }, `Closing must be propagated backward: starts closed; preventCancel = ${stringVersion} (falsy); fulfilled cancel ` +
+     `promise`);
+}
+
+for (const truthy of [true, 'a', 1, Symbol(), { }]) {
+  promise_test(t => {
+
+    const rs = recordingReadableStream();
+
+    const ws = recordingWritableStream();
+    const writer = ws.getWriter();
+    writer.close();
+    writer.releaseLock();
+
+    return promise_rejects_js(t, TypeError, rs.pipeTo(ws, { preventCancel: truthy })).then(() => {
+      assert_array_equals(rs.eventsWithoutPulls, []);
+      assert_array_equals(ws.events, ['close']);
+
+      return ws.getWriter().closed;
+    });
+
+  }, `Closing must be propagated backward: starts closed; preventCancel = ${String(truthy)} (truthy)`);
+}
+
+promise_test(t => {
+
+  const rs = recordingReadableStream();
+
+  const ws = recordingWritableStream();
+  const writer = ws.getWriter();
+  writer.close();
+  writer.releaseLock();
+
+  return promise_rejects_js(t, TypeError, rs.pipeTo(ws, { preventCancel: true, preventAbort: true }))
+    .then(() => {
+      assert_array_equals(rs.eventsWithoutPulls, []);
+      assert_array_equals(ws.events, ['close']);
+
+      return ws.getWriter().closed;
+    });
+
+}, 'Closing must be propagated backward: starts closed; preventCancel = true, preventAbort = true');
+
+promise_test(t => {
+
+  const rs = recordingReadableStream();
+
+  const ws = recordingWritableStream();
+  const writer = ws.getWriter();
+  writer.close();
+  writer.releaseLock();
+
+  return promise_rejects_js(t, TypeError,
+                         rs.pipeTo(ws, { preventCancel: true, preventAbort: true, preventClose: true }))
+  .then(() => {
+    assert_array_equals(rs.eventsWithoutPulls, []);
+    assert_array_equals(ws.events, ['close']);
+
+    return ws.getWriter().closed;
+  });
+
+}, 'Closing must be propagated backward: starts closed; preventCancel = true, preventAbort = true, preventClose ' +
+   '= true');

test/fixtures/wpt/streams/piping/close-propagation-forward.any.js

@@ -0,0 +1,589 @@
+// META: global=window,worker,shadowrealm
+// META: script=../resources/test-utils.js
+// META: script=../resources/recording-streams.js
+'use strict';
+
+const error1 = new Error('error1!');
+error1.name = 'error1';
+
+promise_test(() => {
+
+  const rs = recordingReadableStream({
+    start(controller) {
+      controller.close();
+    }
+  });
+
+  const ws = recordingWritableStream();
+
+  return rs.pipeTo(ws).then(value => {
+    assert_equals(value, undefined, 'the promise must fulfill with undefined');
+  })
+  .then(() => {
+    assert_array_equals(rs.events, []);
+    assert_array_equals(ws.events, ['close']);
+
+    return Promise.all([
+      rs.getReader().closed,
+      ws.getWriter().closed
+    ]);
+  });
+
+}, 'Closing must be propagated forward: starts closed; preventClose omitted; fulfilled close promise');
+
+promise_test(t => {
+
+  const rs = recordingReadableStream({
+    start(controller) {
+      controller.close();
+    }
+  });
+
+  const ws = recordingWritableStream({
+    close() {
+      throw error1;
+    }
+  });
+
+  return promise_rejects_exactly(t, error1, rs.pipeTo(ws), 'pipeTo must reject with the same error').then(() => {
+    assert_array_equals(rs.events, []);
+    assert_array_equals(ws.events, ['close']);
+
+    return Promise.all([
+      rs.getReader().closed,
+      promise_rejects_exactly(t, error1, ws.getWriter().closed)
+    ]);
+  });
+
+}, 'Closing must be propagated forward: starts closed; preventClose omitted; rejected close promise');
+
+for (const falsy of [undefined, null, false, +0, -0, NaN, '']) {
+  const stringVersion = Object.is(falsy, -0) ? '-0' : String(falsy);
+
+  promise_test(() => {
+
+    const rs = recordingReadableStream({
+      start(controller) {
+        controller.close();
+      }
+    });
+
+    const ws = recordingWritableStream();
+
+    return rs.pipeTo(ws, { preventClose: falsy }).then(value => {
+      assert_equals(value, undefined, 'the promise must fulfill with undefined');
+    })
+    .then(() => {
+      assert_array_equals(rs.events, []);
+      assert_array_equals(ws.events, ['close']);
+
+      return Promise.all([
+        rs.getReader().closed,
+        ws.getWriter().closed
+      ]);
+    });
+
+  }, `Closing must be propagated forward: starts closed; preventClose = ${stringVersion} (falsy); fulfilled close ` +
+     `promise`);
+}
+
+for (const truthy of [true, 'a', 1, Symbol(), { }]) {
+  promise_test(() => {
+
+    const rs = recordingReadableStream({
+      start(controller) {
+        controller.close();
+      }
+    });
+
+    const ws = recordingWritableStream();
+
+    return rs.pipeTo(ws, { preventClose: truthy }).then(value => {
+      assert_equals(value, undefined, 'the promise must fulfill with undefined');
+    })
+    .then(() => {
+      assert_array_equals(rs.events, []);
+      assert_array_equals(ws.events, []);
+
+      return rs.getReader().closed;
+    });
+
+  }, `Closing must be propagated forward: starts closed; preventClose = ${String(truthy)} (truthy)`);
+}
+
+promise_test(() => {
+
+  const rs = recordingReadableStream({
+    start(controller) {
+      controller.close();
+    }
+  });
+
+  const ws = recordingWritableStream();
+
+  return rs.pipeTo(ws, { preventClose: true, preventAbort: true }).then(value => {
+    assert_equals(value, undefined, 'the promise must fulfill with undefined');
+  })
+  .then(() => {
+    assert_array_equals(rs.events, []);
+    assert_array_equals(ws.events, []);
+
+    return rs.getReader().closed;
+  });
+
+}, 'Closing must be propagated forward: starts closed; preventClose = true, preventAbort = true');
+
+promise_test(() => {
+
+  const rs = recordingReadableStream({
+    start(controller) {
+      controller.close();
+    }
+  });
+
+  const ws = recordingWritableStream();
+
+  return rs.pipeTo(ws, { preventClose: true, preventAbort: true, preventCancel: true }).then(value => {
+    assert_equals(value, undefined, 'the promise must fulfill with undefined');
+  })
+  .then(() => {
+    assert_array_equals(rs.events, []);
+    assert_array_equals(ws.events, []);
+
+    return rs.getReader().closed;
+  });
+
+}, 'Closing must be propagated forward: starts closed; preventClose = true, preventAbort = true, preventCancel = true');
+
+promise_test(t => {
+
+  const rs = recordingReadableStream();
+
+  const ws = recordingWritableStream();
+
+  const pipePromise = rs.pipeTo(ws);
+
+  t.step_timeout(() => rs.controller.close());
+
+  return pipePromise.then(value => {
+    assert_equals(value, undefined, 'the promise must fulfill with undefined');
+  })
+  .then(() => {
+    assert_array_equals(rs.eventsWithoutPulls, []);
+    assert_array_equals(ws.events, ['close']);
+
+    return Promise.all([
+      rs.getReader().closed,
+      ws.getWriter().closed
+    ]);
+  });
+
+}, 'Closing must be propagated forward: becomes closed asynchronously; preventClose omitted; fulfilled close promise');
+
+promise_test(t => {
+
+  const rs = recordingReadableStream();
+
+  const ws = recordingWritableStream({
+    close() {
+      throw error1;
+    }
+  });
+
+  const pipePromise = promise_rejects_exactly(t, error1, rs.pipeTo(ws), 'pipeTo must reject with the same error');
+
+  t.step_timeout(() => rs.controller.close());
+
+  return pipePromise.then(() => {
+    assert_array_equals(rs.eventsWithoutPulls, []);
+    assert_array_equals(ws.events, ['close']);
+
+    return Promise.all([
+      rs.getReader().closed,
+      promise_rejects_exactly(t, error1, ws.getWriter().closed)
+    ]);
+  });
+
+}, 'Closing must be propagated forward: becomes closed asynchronously; preventClose omitted; rejected close promise');
+
+promise_test(t => {
+
+  const rs = recordingReadableStream();
+
+  const ws = recordingWritableStream();
+
+  const pipePromise = rs.pipeTo(ws, { preventClose: true });
+
+  t.step_timeout(() => rs.controller.close());
+
+  return pipePromise.then(value => {
+    assert_equals(value, undefined, 'the promise must fulfill with undefined');
+  })
+  .then(() => {
+    assert_array_equals(rs.eventsWithoutPulls, []);
+    assert_array_equals(ws.events, []);
+
+    return rs.getReader().closed;
+  });
+
+}, 'Closing must be propagated forward: becomes closed asynchronously; preventClose = true');
+
+promise_test(t => {
+
+  const rs = recordingReadableStream();
+
+  const ws = recordingWritableStream(undefined, new CountQueuingStrategy({ highWaterMark: 0 }));
+
+  const pipePromise = rs.pipeTo(ws);
+
+  t.step_timeout(() => rs.controller.close());
+
+  return pipePromise.then(value => {
+    assert_equals(value, undefined, 'the promise must fulfill with undefined');
+  })
+  .then(() => {
+    assert_array_equals(rs.eventsWithoutPulls, []);
+    assert_array_equals(ws.events, ['close']);
+
+    return Promise.all([
+      rs.getReader().closed,
+      ws.getWriter().closed
+    ]);
+  });
+
+}, 'Closing must be propagated forward: becomes closed asynchronously; dest never desires chunks; ' +
+   'preventClose omitted; fulfilled close promise');
+
+promise_test(t => {
+
+  const rs = recordingReadableStream();
+
+  const ws = recordingWritableStream({
+    close() {
+      throw error1;
+    }
+  }, new CountQueuingStrategy({ highWaterMark: 0 }));
+
+  const pipePromise = promise_rejects_exactly(t, error1, rs.pipeTo(ws), 'pipeTo must reject with the same error');
+
+  t.step_timeout(() => rs.controller.close());
+
+  return pipePromise.then(() => {
+    assert_array_equals(rs.eventsWithoutPulls, []);
+    assert_array_equals(ws.events, ['close']);
+
+    return Promise.all([
+      rs.getReader().closed,
+      promise_rejects_exactly(t, error1, ws.getWriter().closed)
+    ]);
+  });
+
+}, 'Closing must be propagated forward: becomes closed asynchronously; dest never desires chunks; ' +
+   'preventClose omitted; rejected close promise');
+
+promise_test(t => {
+
+  const rs = recordingReadableStream();
+
+  const ws = recordingWritableStream(undefined, new CountQueuingStrategy({ highWaterMark: 0 }));
+
+  const pipePromise = rs.pipeTo(ws, { preventClose: true });
+
+  t.step_timeout(() => rs.controller.close());
+
+  return pipePromise.then(value => {
+    assert_equals(value, undefined, 'the promise must fulfill with undefined');
+  })
+  .then(() => {
+    assert_array_equals(rs.eventsWithoutPulls, []);
+    assert_array_equals(ws.events, []);
+
+    return rs.getReader().closed;
+  });
+
+}, 'Closing must be propagated forward: becomes closed asynchronously; dest never desires chunks; ' +
+   'preventClose = true');
+
+promise_test(t => {
+
+  const rs = recordingReadableStream();
+
+  const ws = recordingWritableStream();
+
+  const pipePromise = rs.pipeTo(ws);
+
+  t.step_timeout(() => {
+    rs.controller.enqueue('Hello');
+    t.step_timeout(() => rs.controller.close());
+  }, 10);
+
+  return pipePromise.then(value => {
+    assert_equals(value, undefined, 'the promise must fulfill with undefined');
+  })
+  .then(() => {
+    assert_array_equals(rs.eventsWithoutPulls, []);
+    assert_array_equals(ws.events, ['write', 'Hello', 'close']);
+
+    return Promise.all([
+      rs.getReader().closed,
+      ws.getWriter().closed
+    ]);
+  });
+
+}, 'Closing must be propagated forward: becomes closed after one chunk; preventClose omitted; fulfilled close promise');
+
+promise_test(t => {
+
+  const rs = recordingReadableStream();
+
+  const ws = recordingWritableStream({
+    close() {
+      throw error1;
+    }
+  });
+
+  const pipePromise = promise_rejects_exactly(t, error1, rs.pipeTo(ws), 'pipeTo must reject with the same error');
+
+  t.step_timeout(() => {
+    rs.controller.enqueue('Hello');
+    t.step_timeout(() => rs.controller.close());
+  }, 10);
+
+  return pipePromise.then(() => {
+    assert_array_equals(rs.eventsWithoutPulls, []);
+    assert_array_equals(ws.events, ['write', 'Hello', 'close']);
+
+    return Promise.all([
+      rs.getReader().closed,
+      promise_rejects_exactly(t, error1, ws.getWriter().closed)
+    ]);
+  });
+
+}, 'Closing must be propagated forward: becomes closed after one chunk; preventClose omitted; rejected close promise');
+
+promise_test(t => {
+
+  const rs = recordingReadableStream();
+
+  const ws = recordingWritableStream();
+
+  const pipePromise = rs.pipeTo(ws, { preventClose: true });
+
+  t.step_timeout(() => {
+    rs.controller.enqueue('Hello');
+    t.step_timeout(() => rs.controller.close());
+  }, 10);
+
+  return pipePromise.then(value => {
+    assert_equals(value, undefined, 'the promise must fulfill with undefined');
+  })
+  .then(() => {
+    assert_array_equals(rs.eventsWithoutPulls, []);
+    assert_array_equals(ws.events, ['write', 'Hello']);
+
+    return rs.getReader().closed;
+  });
+
+}, 'Closing must be propagated forward: becomes closed after one chunk; preventClose = true');
+
+promise_test(() => {
+
+  const rs = recordingReadableStream();
+
+  let resolveWritePromise;
+  const ws = recordingWritableStream({
+    write() {
+      return new Promise(resolve => {
+        resolveWritePromise = resolve;
+      });
+    }
+  });
+
+  let pipeComplete = false;
+  const pipePromise = rs.pipeTo(ws).then(() => {
+    pipeComplete = true;
+  });
+
+  rs.controller.enqueue('a');
+  rs.controller.close();
+
+  // Flush async events and verify that no shutdown occurs.
+  return flushAsyncEvents().then(() => {
+    assert_array_equals(ws.events, ['write', 'a']); // no 'close'
+    assert_equals(pipeComplete, false, 'the pipe must not be complete');
+
+    resolveWritePromise();
+
+    return pipePromise.then(() => {
+      assert_array_equals(ws.events, ['write', 'a', 'close']);
+    });
+  });
+
+}, 'Closing must be propagated forward: shutdown must not occur until the final write completes');
+
+promise_test(() => {
+
+  const rs = recordingReadableStream();
+
+  let resolveWritePromise;
+  const ws = recordingWritableStream({
+    write() {
+      return new Promise(resolve => {
+        resolveWritePromise = resolve;
+      });
+    }
+  });
+
+  let pipeComplete = false;
+  const pipePromise = rs.pipeTo(ws, { preventClose: true }).then(() => {
+    pipeComplete = true;
+  });
+
+  rs.controller.enqueue('a');
+  rs.controller.close();
+
+  // Flush async events and verify that no shutdown occurs.
+  return flushAsyncEvents().then(() => {
+    assert_array_equals(ws.events, ['write', 'a'],
+      'the chunk must have been written, but close must not have happened');
+    assert_equals(pipeComplete, false, 'the pipe must not be complete');
+
+    resolveWritePromise();
+
+    return pipePromise;
+  }).then(() => flushAsyncEvents()).then(() => {
+    assert_array_equals(ws.events, ['write', 'a'],
+      'the chunk must have been written, but close must not have happened');
+  });
+
+}, 'Closing must be propagated forward: shutdown must not occur until the final write completes; preventClose = true');
+
+promise_test(() => {
+
+  const rs = recordingReadableStream();
+
+  let resolveWriteCalled;
+  const writeCalledPromise = new Promise(resolve => {
+    resolveWriteCalled = resolve;
+  });
+
+  let resolveWritePromise;
+  const ws = recordingWritableStream({
+    write() {
+      resolveWriteCalled();
+
+      return new Promise(resolve => {
+        resolveWritePromise = resolve;
+      });
+    }
+  }, new CountQueuingStrategy({ highWaterMark: 2 }));
+
+  let pipeComplete = false;
+  const pipePromise = rs.pipeTo(ws).then(() => {
+    pipeComplete = true;
+  });
+
+  rs.controller.enqueue('a');
+  rs.controller.enqueue('b');
+
+  return writeCalledPromise.then(() => flushAsyncEvents()).then(() => {
+    assert_array_equals(ws.events, ['write', 'a'],
+      'the first chunk must have been written, but close must not have happened yet');
+    assert_false(pipeComplete, 'the pipe should not complete while the first write is pending');
+
+    rs.controller.close();
+    resolveWritePromise();
+  }).then(() => flushAsyncEvents()).then(() => {
+    assert_array_equals(ws.events, ['write', 'a', 'write', 'b'],
+      'the second chunk must have been written, but close must not have happened yet');
+    assert_false(pipeComplete, 'the pipe should not complete while the second write is pending');
+
+    resolveWritePromise();
+    return pipePromise;
+  }).then(() => {
+    assert_array_equals(ws.events, ['write', 'a', 'write', 'b', 'close'],
+      'all chunks must have been written and close must have happened');
+  });
+
+}, 'Closing must be propagated forward: shutdown must not occur until the final write completes; becomes closed after first write');
+
+promise_test(() => {
+
+  const rs = recordingReadableStream();
+
+  let resolveWriteCalled;
+  const writeCalledPromise = new Promise(resolve => {
+    resolveWriteCalled = resolve;
+  });
+
+  let resolveWritePromise;
+  const ws = recordingWritableStream({
+    write() {
+      resolveWriteCalled();
+
+      return new Promise(resolve => {
+        resolveWritePromise = resolve;
+      });
+    }
+  }, new CountQueuingStrategy({ highWaterMark: 2 }));
+
+  let pipeComplete = false;
+  const pipePromise = rs.pipeTo(ws, { preventClose: true }).then(() => {
+    pipeComplete = true;
+  });
+
+  rs.controller.enqueue('a');
+  rs.controller.enqueue('b');
+
+  return writeCalledPromise.then(() => flushAsyncEvents()).then(() => {
+    assert_array_equals(ws.events, ['write', 'a'],
+      'the first chunk must have been written, but close must not have happened');
+    assert_false(pipeComplete, 'the pipe should not complete while the first write is pending');
+
+    rs.controller.close();
+    resolveWritePromise();
+  }).then(() => flushAsyncEvents()).then(() => {
+    assert_array_equals(ws.events, ['write', 'a', 'write', 'b'],
+      'the second chunk must have been written, but close must not have happened');
+    assert_false(pipeComplete, 'the pipe should not complete while the second write is pending');
+
+    resolveWritePromise();
+    return pipePromise;
+  }).then(() => flushAsyncEvents()).then(() => {
+    assert_array_equals(ws.events, ['write', 'a', 'write', 'b'],
+      'all chunks must have been written, but close must not have happened');
+  });
+
+}, 'Closing must be propagated forward: shutdown must not occur until the final write completes; becomes closed after first write; preventClose = true');
+
+
+promise_test(t => {
+  const rs = recordingReadableStream({
+    start(c) {
+      c.enqueue('a');
+      c.enqueue('b');
+      c.close();
+    }
+  });
+  let rejectWritePromise;
+  const ws = recordingWritableStream({
+    write() {
+      return new Promise((resolve, reject) => {
+        rejectWritePromise = reject;
+      });
+    }
+  }, { highWaterMark: 3 });
+  const pipeToPromise = rs.pipeTo(ws);
+  return delay(0).then(() => {
+    rejectWritePromise(error1);
+    return promise_rejects_exactly(t, error1, pipeToPromise, 'pipeTo should reject');
+  }).then(() => {
+    assert_array_equals(rs.events, []);
+    assert_array_equals(ws.events, ['write', 'a']);
+
+    return Promise.all([
+      rs.getReader().closed,
+      promise_rejects_exactly(t, error1, ws.getWriter().closed, 'ws should be errored')
+    ]);
+  });
+}, 'Closing must be propagated forward: erroring the writable while flushing pending writes should error pipeTo');

test/fixtures/wpt/streams/piping/crashtests/cross-piping.html

@@ -0,0 +1,12 @@
+<!DOCTYPE html>
+<script type="module">
+  let a = new ReadableStream();
+  let b = self.open()
+  let f = new b.WritableStream();
+  a.pipeThrough(
+    { "readable": a, "writable": f },
+    { "signal": AbortSignal.abort() }
+  )
+  await new Promise(setTimeout);
+  structuredClone(undefined, { "transfer": [f] })
+</script>

test/fixtures/wpt/streams/piping/crashtests/cross-piping2.https.html

@@ -0,0 +1,14 @@
+<!DOCTYPE html>
+<script type="module">
+  let a = self.open()
+  let d = await a.navigator.storage.getDirectory()
+  let h = await d.getFileHandle("c5c9960b-a637-4232-be3d-3ccc5704852f", {"create": true})
+  let r = new ReadableStream({
+    start(c) {
+      c.enqueue(h)
+      c.close();
+    }
+  });
+  let w = await h.createWritable({ })
+  r.pipeThrough({"readable": r, "writable": w}, {})
+</script>

test/fixtures/wpt/streams/piping/error-propagation-backward.any.js

@@ -0,0 +1,630 @@
+// META: global=window,worker,shadowrealm
+// META: script=../resources/test-utils.js
+// META: script=../resources/recording-streams.js
+'use strict';
+
+const error1 = new Error('error1!');
+error1.name = 'error1';
+
+const error2 = new Error('error2!');
+error2.name = 'error2';
+
+promise_test(t => {
+
+  const rs = recordingReadableStream();
+
+  const ws = recordingWritableStream({
+    start() {
+      return Promise.reject(error1);
+    }
+  });
+
+  return promise_rejects_exactly(t, error1, rs.pipeTo(ws), 'pipeTo must reject with the same error')
+    .then(() => {
+      assert_array_equals(rs.eventsWithoutPulls, ['cancel', error1]);
+      assert_array_equals(ws.events, []);
+    });
+
+}, 'Errors must be propagated backward: starts errored; preventCancel omitted; fulfilled cancel promise');
+
+promise_test(t => {
+
+  const rs = recordingReadableStream();
+
+  const ws = recordingWritableStream({
+    write() {
+      return Promise.reject(error1);
+    }
+  });
+
+  const writer = ws.getWriter();
+
+  return promise_rejects_exactly(t, error1, writer.write('Hello'), 'writer.write() must reject with the write error')
+    .then(() => promise_rejects_exactly(t, error1, writer.closed, 'writer.closed must reject with the write error'))
+    .then(() => {
+      writer.releaseLock();
+
+      return promise_rejects_exactly(t, error1, rs.pipeTo(ws), 'pipeTo must reject with the write error')
+        .then(() => {
+          assert_array_equals(rs.eventsWithoutPulls, ['cancel', error1]);
+          assert_array_equals(ws.events, ['write', 'Hello']);
+        });
+    });
+
+}, 'Errors must be propagated backward: becomes errored before piping due to write; preventCancel omitted; ' +
+   'fulfilled cancel promise');
+
+promise_test(t => {
+
+  const rs = recordingReadableStream({
+    cancel() {
+      throw error2;
+    }
+  });
+
+  const ws = recordingWritableStream({
+    write() {
+      return Promise.reject(error1);
+    }
+  });
+
+  const writer = ws.getWriter();
+
+  return promise_rejects_exactly(t, error1, writer.write('Hello'), 'writer.write() must reject with the write error')
+    .then(() => promise_rejects_exactly(t, error1, writer.closed, 'writer.closed must reject with the write error'))
+    .then(() => {
+      writer.releaseLock();
+
+      return promise_rejects_exactly(t, error2, rs.pipeTo(ws), 'pipeTo must reject with the cancel error')
+        .then(() => {
+          assert_array_equals(rs.eventsWithoutPulls, ['cancel', error1]);
+          assert_array_equals(ws.events, ['write', 'Hello']);
+        });
+    });
+
+}, 'Errors must be propagated backward: becomes errored before piping due to write; preventCancel omitted; rejected ' +
+   'cancel promise');
+
+for (const falsy of [undefined, null, false, +0, -0, NaN, '']) {
+  const stringVersion = Object.is(falsy, -0) ? '-0' : String(falsy);
+
+  promise_test(t => {
+
+    const rs = recordingReadableStream();
+
+    const ws = recordingWritableStream({
+      write() {
+        return Promise.reject(error1);
+      }
+    });
+
+    const writer = ws.getWriter();
+
+    return promise_rejects_exactly(t, error1, writer.write('Hello'), 'writer.write() must reject with the write error')
+      .then(() => promise_rejects_exactly(t, error1, writer.closed, 'writer.closed must reject with the write error'))
+      .then(() => {
+        writer.releaseLock();
+
+        return promise_rejects_exactly(t, error1, rs.pipeTo(ws, { preventCancel: falsy }),
+                               'pipeTo must reject with the write error')
+          .then(() => {
+            assert_array_equals(rs.eventsWithoutPulls, ['cancel', error1]);
+            assert_array_equals(ws.events, ['write', 'Hello']);
+          });
+      });
+
+  }, `Errors must be propagated backward: becomes errored before piping due to write; preventCancel = ` +
+     `${stringVersion} (falsy); fulfilled cancel promise`);
+}
+
+for (const truthy of [true, 'a', 1, Symbol(), { }]) {
+  promise_test(t => {
+
+    const rs = recordingReadableStream();
+
+    const ws = recordingWritableStream({
+      write() {
+        return Promise.reject(error1);
+      }
+    });
+
+    const writer = ws.getWriter();
+
+    return promise_rejects_exactly(t, error1, writer.write('Hello'), 'writer.write() must reject with the write error')
+      .then(() => promise_rejects_exactly(t, error1, writer.closed, 'writer.closed must reject with the write error'))
+      .then(() => {
+        writer.releaseLock();
+
+        return promise_rejects_exactly(t, error1, rs.pipeTo(ws, { preventCancel: truthy }),
+                               'pipeTo must reject with the write error')
+          .then(() => {
+            assert_array_equals(rs.eventsWithoutPulls, []);
+            assert_array_equals(ws.events, ['write', 'Hello']);
+          });
+      });
+
+  }, `Errors must be propagated backward: becomes errored before piping due to write; preventCancel = ` +
+     `${String(truthy)} (truthy)`);
+}
+
+promise_test(t => {
+
+  const rs = recordingReadableStream();
+
+  const ws = recordingWritableStream({
+    write() {
+      return Promise.reject(error1);
+    }
+  });
+
+  const writer = ws.getWriter();
+
+  return promise_rejects_exactly(t, error1, writer.write('Hello'), 'writer.write() must reject with the write error')
+    .then(() => promise_rejects_exactly(t, error1, writer.closed, 'writer.closed must reject with the write error'))
+    .then(() => {
+      writer.releaseLock();
+
+      return promise_rejects_exactly(t, error1, rs.pipeTo(ws, { preventCancel: true, preventAbort: true }),
+                             'pipeTo must reject with the write error')
+        .then(() => {
+          assert_array_equals(rs.eventsWithoutPulls, []);
+          assert_array_equals(ws.events, ['write', 'Hello']);
+        });
+    });
+
+}, 'Errors must be propagated backward: becomes errored before piping due to write, preventCancel = true; ' +
+   'preventAbort = true');
+
+promise_test(t => {
+
+  const rs = recordingReadableStream();
+
+  const ws = recordingWritableStream({
+    write() {
+      return Promise.reject(error1);
+    }
+  });
+
+  const writer = ws.getWriter();
+
+  return promise_rejects_exactly(t, error1, writer.write('Hello'), 'writer.write() must reject with the write error')
+    .then(() => promise_rejects_exactly(t, error1, writer.closed, 'writer.closed must reject with the write error'))
+    .then(() => {
+      writer.releaseLock();
+
+      return promise_rejects_exactly(t, error1, rs.pipeTo(ws, { preventCancel: true, preventAbort: true, preventClose: true }),
+                             'pipeTo must reject with the write error')
+        .then(() => {
+          assert_array_equals(rs.eventsWithoutPulls, []);
+          assert_array_equals(ws.events, ['write', 'Hello']);
+        });
+    });
+
+}, 'Errors must be propagated backward: becomes errored before piping due to write; preventCancel = true, ' +
+   'preventAbort = true, preventClose = true');
+
+promise_test(t => {
+
+  const rs = recordingReadableStream({
+    start(controller) {
+      controller.enqueue('Hello');
+    }
+  });
+
+  const ws = recordingWritableStream({
+    write() {
+      throw error1;
+    }
+  });
+
+  return promise_rejects_exactly(t, error1, rs.pipeTo(ws), 'pipeTo must reject with the same error').then(() => {
+    assert_array_equals(rs.eventsWithoutPulls, ['cancel', error1]);
+    assert_array_equals(ws.events, ['write', 'Hello']);
+  });
+
+}, 'Errors must be propagated backward: becomes errored during piping due to write; preventCancel omitted; fulfilled ' +
+   'cancel promise');
+
+promise_test(t => {
+
+  const rs = recordingReadableStream({
+    start(controller) {
+      controller.enqueue('Hello');
+    },
+    cancel() {
+      throw error2;
+    }
+  });
+
+  const ws = recordingWritableStream({
+    write() {
+      throw error1;
+    }
+  });
+
+  return promise_rejects_exactly(t, error2, rs.pipeTo(ws), 'pipeTo must reject with the cancel error').then(() => {
+    assert_array_equals(rs.eventsWithoutPulls, ['cancel', error1]);
+    assert_array_equals(ws.events, ['write', 'Hello']);
+  });
+
+}, 'Errors must be propagated backward: becomes errored during piping due to write; preventCancel omitted; rejected ' +
+   'cancel promise');
+
+promise_test(t => {
+
+  const rs = recordingReadableStream({
+    start(controller) {
+      controller.enqueue('Hello');
+    }
+  });
+
+  const ws = recordingWritableStream({
+    write() {
+      throw error1;
+    }
+  });
+
+  return promise_rejects_exactly(t, error1, rs.pipeTo(ws, { preventCancel: true }), 'pipeTo must reject with the same error')
+  .then(() => {
+    assert_array_equals(rs.eventsWithoutPulls, []);
+    assert_array_equals(ws.events, ['write', 'Hello']);
+  });
+
+}, 'Errors must be propagated backward: becomes errored during piping due to write; preventCancel = true');
+
+promise_test(t => {
+
+  const rs = recordingReadableStream({
+    start(controller) {
+      controller.enqueue('a');
+      controller.enqueue('b');
+      controller.enqueue('c');
+    }
+  });
+
+  const ws = recordingWritableStream({
+    write() {
+      if (ws.events.length > 2) {
+        return delay(0).then(() => {
+          throw error1;
+        });
+      }
+      return undefined;
+    }
+  });
+
+  return promise_rejects_exactly(t, error1, rs.pipeTo(ws), 'pipeTo must reject with the same error').then(() => {
+    assert_array_equals(rs.eventsWithoutPulls, ['cancel', error1]);
+    assert_array_equals(ws.events, ['write', 'a', 'write', 'b']);
+  });
+
+}, 'Errors must be propagated backward: becomes errored during piping due to write, but async; preventCancel = ' +
+   'false; fulfilled cancel promise');
+
+promise_test(t => {
+
+  const rs = recordingReadableStream({
+    start(controller) {
+      controller.enqueue('a');
+      controller.enqueue('b');
+      controller.enqueue('c');
+    },
+    cancel() {
+      throw error2;
+    }
+  });
+
+  const ws = recordingWritableStream({
+    write() {
+      if (ws.events.length > 2) {
+        return delay(0).then(() => {
+          throw error1;
+        });
+      }
+      return undefined;
+    }
+  });
+
+  return promise_rejects_exactly(t, error2, rs.pipeTo(ws), 'pipeTo must reject with the cancel error').then(() => {
+    assert_array_equals(rs.eventsWithoutPulls, ['cancel', error1]);
+    assert_array_equals(ws.events, ['write', 'a', 'write', 'b']);
+  });
+
+}, 'Errors must be propagated backward: becomes errored during piping due to write, but async; preventCancel = ' +
+   'false; rejected cancel promise');
+
+promise_test(t => {
+
+  const rs = recordingReadableStream({
+    start(controller) {
+      controller.enqueue('a');
+      controller.enqueue('b');
+      controller.enqueue('c');
+    }
+  });
+
+  const ws = recordingWritableStream({
+    write() {
+      if (ws.events.length > 2) {
+        return delay(0).then(() => {
+          throw error1;
+        });
+      }
+      return undefined;
+    }
+  });
+
+  return promise_rejects_exactly(t, error1, rs.pipeTo(ws, { preventCancel: true }), 'pipeTo must reject with the same error')
+  .then(() => {
+    assert_array_equals(rs.eventsWithoutPulls, []);
+    assert_array_equals(ws.events, ['write', 'a', 'write', 'b']);
+  });
+
+}, 'Errors must be propagated backward: becomes errored during piping due to write, but async; preventCancel = true');
+
+promise_test(t => {
+
+  const rs = recordingReadableStream();
+
+  const ws = recordingWritableStream();
+
+  const pipePromise = promise_rejects_exactly(t, error1, rs.pipeTo(ws), 'pipeTo must reject with the same error');
+
+  t.step_timeout(() => ws.controller.error(error1), 10);
+
+  return pipePromise.then(() => {
+    assert_array_equals(rs.eventsWithoutPulls, ['cancel', error1]);
+    assert_array_equals(ws.events, []);
+  });
+
+}, 'Errors must be propagated backward: becomes errored after piping; preventCancel omitted; fulfilled cancel promise');
+
+promise_test(t => {
+
+  const rs = recordingReadableStream({
+    cancel() {
+      throw error2;
+    }
+  });
+
+  const ws = recordingWritableStream();
+
+  const pipePromise = promise_rejects_exactly(t, error2, rs.pipeTo(ws), 'pipeTo must reject with the cancel error');
+
+  t.step_timeout(() => ws.controller.error(error1), 10);
+
+  return pipePromise.then(() => {
+    assert_array_equals(rs.eventsWithoutPulls, ['cancel', error1]);
+    assert_array_equals(ws.events, []);
+  });
+
+}, 'Errors must be propagated backward: becomes errored after piping; preventCancel omitted; rejected cancel promise');
+
+promise_test(t => {
+
+  const rs = recordingReadableStream();
+
+  const ws = recordingWritableStream();
+
+  const pipePromise = promise_rejects_exactly(t, error1, rs.pipeTo(ws, { preventCancel: true }),
+                                              'pipeTo must reject with the same error');
+
+  t.step_timeout(() => ws.controller.error(error1), 10);
+
+  return pipePromise.then(() => {
+    assert_array_equals(rs.eventsWithoutPulls, []);
+    assert_array_equals(ws.events, []);
+  });
+
+}, 'Errors must be propagated backward: becomes errored after piping; preventCancel = true');
+
+promise_test(t => {
+
+  const rs = recordingReadableStream({
+    start(controller) {
+      controller.enqueue('a');
+      controller.enqueue('b');
+      controller.enqueue('c');
+      controller.close();
+    }
+  });
+
+  const ws = recordingWritableStream({
+    write(chunk) {
+      if (chunk === 'c') {
+        return Promise.reject(error1);
+      }
+      return undefined;
+    }
+  });
+
+  return promise_rejects_exactly(t, error1, rs.pipeTo(ws), 'pipeTo must reject with the same error').then(() => {
+    assert_array_equals(rs.eventsWithoutPulls, []);
+    assert_array_equals(ws.events, ['write', 'a', 'write', 'b', 'write', 'c']);
+  });
+
+}, 'Errors must be propagated backward: becomes errored after piping due to last write; source is closed; ' +
+   'preventCancel omitted (but cancel is never called)');
+
+promise_test(t => {
+
+  const rs = recordingReadableStream({
+    start(controller) {
+      controller.enqueue('a');
+      controller.enqueue('b');
+      controller.enqueue('c');
+      controller.close();
+    }
+  });
+
+  const ws = recordingWritableStream({
+    write(chunk) {
+      if (chunk === 'c') {
+        return Promise.reject(error1);
+      }
+      return undefined;
+    }
+  });
+
+  return promise_rejects_exactly(t, error1, rs.pipeTo(ws, { preventCancel: true }), 'pipeTo must reject with the same error')
+    .then(() => {
+      assert_array_equals(rs.eventsWithoutPulls, []);
+      assert_array_equals(ws.events, ['write', 'a', 'write', 'b', 'write', 'c']);
+    });
+
+}, 'Errors must be propagated backward: becomes errored after piping due to last write; source is closed; ' +
+   'preventCancel = true');
+
+promise_test(t => {
+
+  const rs = recordingReadableStream();
+
+  const ws = recordingWritableStream(undefined, new CountQueuingStrategy({ highWaterMark: 0 }));
+
+  const pipePromise = promise_rejects_exactly(t, error1, rs.pipeTo(ws), 'pipeTo must reject with the same error');
+
+  t.step_timeout(() => ws.controller.error(error1), 10);
+
+  return pipePromise.then(() => {
+    assert_array_equals(rs.eventsWithoutPulls, ['cancel', error1]);
+    assert_array_equals(ws.events, []);
+  });
+
+}, 'Errors must be propagated backward: becomes errored after piping; dest never desires chunks; preventCancel = ' +
+   'false; fulfilled cancel promise');
+
+promise_test(t => {
+
+  const rs = recordingReadableStream({
+    cancel() {
+      throw error2;
+    }
+  });
+
+  const ws = recordingWritableStream(undefined, new CountQueuingStrategy({ highWaterMark: 0 }));
+
+  const pipePromise = promise_rejects_exactly(t, error2, rs.pipeTo(ws), 'pipeTo must reject with the cancel error');
+
+  t.step_timeout(() => ws.controller.error(error1), 10);
+
+  return pipePromise.then(() => {
+    assert_array_equals(rs.eventsWithoutPulls, ['cancel', error1]);
+    assert_array_equals(ws.events, []);
+  });
+
+}, 'Errors must be propagated backward: becomes errored after piping; dest never desires chunks; preventCancel = ' +
+   'false; rejected cancel promise');
+
+promise_test(t => {
+
+  const rs = recordingReadableStream();
+
+  const ws = recordingWritableStream(undefined, new CountQueuingStrategy({ highWaterMark: 0 }));
+
+  const pipePromise = promise_rejects_exactly(t, error1, rs.pipeTo(ws, { preventCancel: true }),
+                                              'pipeTo must reject with the same error');
+
+  t.step_timeout(() => ws.controller.error(error1), 10);
+
+  return pipePromise.then(() => {
+    assert_array_equals(rs.eventsWithoutPulls, []);
+    assert_array_equals(ws.events, []);
+  });
+
+}, 'Errors must be propagated backward: becomes errored after piping; dest never desires chunks; preventCancel = ' +
+   'true');
+
+promise_test(() => {
+
+  const rs = recordingReadableStream();
+
+  const ws = recordingWritableStream();
+
+  ws.abort(error1);
+
+  return rs.pipeTo(ws).then(
+    () => assert_unreached('the promise must not fulfill'),
+    err => {
+      assert_equals(err, error1, 'the promise must reject with error1');
+
+      assert_array_equals(rs.eventsWithoutPulls, ['cancel', err]);
+      assert_array_equals(ws.events, ['abort', error1]);
+    }
+  );
+
+}, 'Errors must be propagated backward: becomes errored before piping via abort; preventCancel omitted; fulfilled ' +
+   'cancel promise');
+
+promise_test(t => {
+
+  const rs = recordingReadableStream({
+    cancel() {
+      throw error2;
+    }
+  });
+
+  const ws = recordingWritableStream();
+
+  ws.abort(error1);
+
+  return promise_rejects_exactly(t, error2, rs.pipeTo(ws), 'pipeTo must reject with the cancel error')
+    .then(() => {
+      return ws.getWriter().closed.then(
+        () => assert_unreached('the promise must not fulfill'),
+        err => {
+          assert_equals(err, error1, 'the promise must reject with error1');
+
+          assert_array_equals(rs.eventsWithoutPulls, ['cancel', err]);
+          assert_array_equals(ws.events, ['abort', error1]);
+        }
+      );
+    });
+
+}, 'Errors must be propagated backward: becomes errored before piping via abort; preventCancel omitted; rejected ' +
+   'cancel promise');
+
+promise_test(t => {
+
+  const rs = recordingReadableStream();
+
+  const ws = recordingWritableStream();
+
+  ws.abort(error1);
+
+  return promise_rejects_exactly(t, error1, rs.pipeTo(ws, { preventCancel: true })).then(() => {
+    assert_array_equals(rs.eventsWithoutPulls, []);
+    assert_array_equals(ws.events, ['abort', error1]);
+  });
+
+}, 'Errors must be propagated backward: becomes errored before piping via abort; preventCancel = true');
+
+promise_test(t => {
+
+  const rs = recordingReadableStream();
+
+  let resolveWriteCalled;
+  const writeCalledPromise = new Promise(resolve => {
+    resolveWriteCalled = resolve;
+  });
+
+  const ws = recordingWritableStream({
+    write() {
+      resolveWriteCalled();
+      return flushAsyncEvents();
+    }
+  });
+
+  const pipePromise = rs.pipeTo(ws);
+
+  rs.controller.enqueue('a');
+
+  return writeCalledPromise.then(() => {
+    ws.controller.error(error1);
+
+    return promise_rejects_exactly(t, error1, pipePromise);
+  }).then(() => {
+    assert_array_equals(rs.eventsWithoutPulls, ['cancel', error1]);
+    assert_array_equals(ws.events, ['write', 'a']);
+  });
+
+}, 'Errors must be propagated backward: erroring via the controller errors once pending write completes');

test/fixtures/wpt/streams/piping/error-propagation-forward.any.js

@@ -0,0 +1,569 @@
+// META: global=window,worker,shadowrealm
+// META: script=../resources/test-utils.js
+// META: script=../resources/recording-streams.js
+'use strict';
+
+const error1 = new Error('error1!');
+error1.name = 'error1';
+
+const error2 = new Error('error2!');
+error2.name = 'error2';
+
+promise_test(t => {
+
+  const rs = recordingReadableStream({
+    start() {
+      return Promise.reject(error1);
+    }
+  });
+
+  const ws = recordingWritableStream();
+
+  return promise_rejects_exactly(t, error1, rs.pipeTo(ws), 'pipeTo must reject with the same error')
+    .then(() => {
+      assert_array_equals(rs.events, []);
+      assert_array_equals(ws.events, ['abort', error1]);
+    });
+
+}, 'Errors must be propagated forward: starts errored; preventAbort = false; fulfilled abort promise');
+
+promise_test(t => {
+
+  const rs = recordingReadableStream({
+    start() {
+      return Promise.reject(error1);
+    }
+  });
+
+  const ws = recordingWritableStream({
+    abort() {
+      throw error2;
+    }
+  });
+
+  return promise_rejects_exactly(t, error2, rs.pipeTo(ws), 'pipeTo must reject with the abort error')
+    .then(() => {
+      assert_array_equals(rs.events, []);
+      assert_array_equals(ws.events, ['abort', error1]);
+    });
+
+}, 'Errors must be propagated forward: starts errored; preventAbort = false; rejected abort promise');
+
+for (const falsy of [undefined, null, false, +0, -0, NaN, '']) {
+  const stringVersion = Object.is(falsy, -0) ? '-0' : String(falsy);
+
+  promise_test(t => {
+
+    const rs = recordingReadableStream({
+      start() {
+        return Promise.reject(error1);
+      }
+    });
+
+    const ws = recordingWritableStream();
+
+    return promise_rejects_exactly(t, error1, rs.pipeTo(ws, { preventAbort: falsy }), 'pipeTo must reject with the same error')
+      .then(() => {
+        assert_array_equals(rs.events, []);
+        assert_array_equals(ws.events, ['abort', error1]);
+      });
+
+  }, `Errors must be propagated forward: starts errored; preventAbort = ${stringVersion} (falsy); fulfilled abort ` +
+     `promise`);
+}
+
+for (const truthy of [true, 'a', 1, Symbol(), { }]) {
+  promise_test(t => {
+
+    const rs = recordingReadableStream({
+      start() {
+        return Promise.reject(error1);
+      }
+    });
+
+    const ws = recordingWritableStream();
+
+    return promise_rejects_exactly(t, error1, rs.pipeTo(ws, { preventAbort: truthy }),
+      'pipeTo must reject with the same error')
+      .then(() => {
+        assert_array_equals(rs.events, []);
+        assert_array_equals(ws.events, []);
+      });
+
+  }, `Errors must be propagated forward: starts errored; preventAbort = ${String(truthy)} (truthy)`);
+}
+
+
+promise_test(t => {
+
+  const rs = recordingReadableStream({
+    start() {
+      return Promise.reject(error1);
+    }
+  });
+
+  const ws = recordingWritableStream();
+
+  return promise_rejects_exactly(t, error1, rs.pipeTo(ws, { preventAbort: true, preventCancel: true }),
+    'pipeTo must reject with the same error')
+    .then(() => {
+      assert_array_equals(rs.events, []);
+      assert_array_equals(ws.events, []);
+    });
+
+}, 'Errors must be propagated forward: starts errored; preventAbort = true, preventCancel = true');
+
+promise_test(t => {
+
+  const rs = recordingReadableStream({
+    start() {
+      return Promise.reject(error1);
+    }
+  });
+
+  const ws = recordingWritableStream();
+
+  return promise_rejects_exactly(t, error1, rs.pipeTo(ws, { preventAbort: true, preventCancel: true, preventClose: true }),
+    'pipeTo must reject with the same error')
+    .then(() => {
+      assert_array_equals(rs.events, []);
+      assert_array_equals(ws.events, []);
+    });
+
+}, 'Errors must be propagated forward: starts errored; preventAbort = true, preventCancel = true, preventClose = true');
+
+promise_test(t => {
+
+  const rs = recordingReadableStream();
+
+  const ws = recordingWritableStream();
+
+  const pipePromise = promise_rejects_exactly(t, error1, rs.pipeTo(ws), 'pipeTo must reject with the same error');
+
+  t.step_timeout(() => rs.controller.error(error1), 10);
+
+  return pipePromise.then(() => {
+    assert_array_equals(rs.eventsWithoutPulls, []);
+    assert_array_equals(ws.events, ['abort', error1]);
+  });
+
+}, 'Errors must be propagated forward: becomes errored while empty; preventAbort = false; fulfilled abort promise');
+
+promise_test(t => {
+
+  const rs = recordingReadableStream();
+
+  const ws = recordingWritableStream({
+    abort() {
+      throw error2;
+    }
+  });
+
+  const pipePromise = promise_rejects_exactly(t, error2, rs.pipeTo(ws), 'pipeTo must reject with the abort error');
+
+  t.step_timeout(() => rs.controller.error(error1), 10);
+
+  return pipePromise.then(() => {
+    assert_array_equals(rs.eventsWithoutPulls, []);
+    assert_array_equals(ws.events, ['abort', error1]);
+  });
+
+}, 'Errors must be propagated forward: becomes errored while empty; preventAbort = false; rejected abort promise');
+
+promise_test(t => {
+
+  const rs = recordingReadableStream();
+
+  const ws = recordingWritableStream();
+
+  const pipePromise = promise_rejects_exactly(t, error1, rs.pipeTo(ws, { preventAbort: true }),
+                                              'pipeTo must reject with the same error');
+
+  t.step_timeout(() => rs.controller.error(error1), 10);
+
+  return pipePromise.then(() => {
+    assert_array_equals(rs.eventsWithoutPulls, []);
+    assert_array_equals(ws.events, []);
+  });
+
+}, 'Errors must be propagated forward: becomes errored while empty; preventAbort = true');
+
+promise_test(t => {
+
+  const rs = recordingReadableStream();
+
+  const ws = recordingWritableStream(undefined, new CountQueuingStrategy({ highWaterMark: 0 }));
+
+  const pipePromise = promise_rejects_exactly(t, error1, rs.pipeTo(ws), 'pipeTo must reject with the same error');
+
+  t.step_timeout(() => rs.controller.error(error1), 10);
+
+  return pipePromise.then(() => {
+    assert_array_equals(rs.eventsWithoutPulls, []);
+    assert_array_equals(ws.events, ['abort', error1]);
+  });
+
+}, 'Errors must be propagated forward: becomes errored while empty; dest never desires chunks; ' +
+   'preventAbort = false; fulfilled abort promise');
+
+promise_test(t => {
+
+  const rs = recordingReadableStream();
+
+  const ws = recordingWritableStream({
+    abort() {
+      throw error2;
+    }
+  }, new CountQueuingStrategy({ highWaterMark: 0 }));
+
+  const pipePromise = promise_rejects_exactly(t, error2, rs.pipeTo(ws), 'pipeTo must reject with the abort error');
+
+  t.step_timeout(() => rs.controller.error(error1), 10);
+
+  return pipePromise.then(() => {
+    assert_array_equals(rs.eventsWithoutPulls, []);
+    assert_array_equals(ws.events, ['abort', error1]);
+  });
+
+}, 'Errors must be propagated forward: becomes errored while empty; dest never desires chunks; ' +
+   'preventAbort = false; rejected abort promise');
+
+promise_test(t => {
+
+  const rs = recordingReadableStream();
+
+  const ws = recordingWritableStream(undefined, new CountQueuingStrategy({ highWaterMark: 0 }));
+
+  const pipePromise = promise_rejects_exactly(t, error1, rs.pipeTo(ws, { preventAbort: true }),
+                                              'pipeTo must reject with the same error');
+
+  t.step_timeout(() => rs.controller.error(error1), 10);
+
+  return pipePromise.then(() => {
+    assert_array_equals(rs.eventsWithoutPulls, []);
+    assert_array_equals(ws.events, []);
+  });
+
+}, 'Errors must be propagated forward: becomes errored while empty; dest never desires chunks; ' +
+   'preventAbort = true');
+
+promise_test(t => {
+
+  const rs = recordingReadableStream();
+
+  const ws = recordingWritableStream();
+
+  const pipePromise = promise_rejects_exactly(t, error1, rs.pipeTo(ws), 'pipeTo must reject with the same error');
+
+  t.step_timeout(() => {
+    rs.controller.enqueue('Hello');
+    t.step_timeout(() => rs.controller.error(error1), 10);
+  }, 10);
+
+  return pipePromise.then(() => {
+    assert_array_equals(rs.eventsWithoutPulls, []);
+    assert_array_equals(ws.events, ['write', 'Hello', 'abort', error1]);
+  });
+
+}, 'Errors must be propagated forward: becomes errored after one chunk; preventAbort = false; fulfilled abort promise');
+
+promise_test(t => {
+
+  const rs = recordingReadableStream();
+
+  const ws = recordingWritableStream({
+    abort() {
+      throw error2;
+    }
+  });
+
+  const pipePromise = promise_rejects_exactly(t, error2, rs.pipeTo(ws), 'pipeTo must reject with the abort error');
+
+  t.step_timeout(() => {
+    rs.controller.enqueue('Hello');
+    t.step_timeout(() => rs.controller.error(error1), 10);
+  }, 10);
+
+  return pipePromise.then(() => {
+    assert_array_equals(rs.eventsWithoutPulls, []);
+    assert_array_equals(ws.events, ['write', 'Hello', 'abort', error1]);
+  });
+
+}, 'Errors must be propagated forward: becomes errored after one chunk; preventAbort = false; rejected abort promise');
+
+promise_test(t => {
+
+  const rs = recordingReadableStream();
+
+  const ws = recordingWritableStream();
+
+  const pipePromise = promise_rejects_exactly(t, error1, rs.pipeTo(ws, { preventAbort: true }),
+                                              'pipeTo must reject with the same error');
+
+  t.step_timeout(() => {
+    rs.controller.enqueue('Hello');
+    t.step_timeout(() => rs.controller.error(error1), 10);
+  }, 10);
+
+  return pipePromise.then(() => {
+    assert_array_equals(rs.eventsWithoutPulls, []);
+    assert_array_equals(ws.events, ['write', 'Hello']);
+  });
+
+}, 'Errors must be propagated forward: becomes errored after one chunk; preventAbort = true');
+
+promise_test(t => {
+
+  const rs = recordingReadableStream();
+
+  const ws = recordingWritableStream(undefined, new CountQueuingStrategy({ highWaterMark: 0 }));
+
+  const pipePromise = promise_rejects_exactly(t, error1, rs.pipeTo(ws), 'pipeTo must reject with the same error');
+
+  t.step_timeout(() => {
+    rs.controller.enqueue('Hello');
+    t.step_timeout(() => rs.controller.error(error1), 10);
+  }, 10);
+
+  return pipePromise.then(() => {
+    assert_array_equals(rs.eventsWithoutPulls, []);
+    assert_array_equals(ws.events, ['abort', error1]);
+  });
+
+}, 'Errors must be propagated forward: becomes errored after one chunk; dest never desires chunks; ' +
+   'preventAbort = false; fulfilled abort promise');
+
+promise_test(t => {
+
+  const rs = recordingReadableStream();
+
+  const ws = recordingWritableStream({
+    abort() {
+      throw error2;
+    }
+  }, new CountQueuingStrategy({ highWaterMark: 0 }));
+
+  const pipePromise = promise_rejects_exactly(t, error2, rs.pipeTo(ws), 'pipeTo must reject with the abort error');
+
+  t.step_timeout(() => {
+    rs.controller.enqueue('Hello');
+    t.step_timeout(() => rs.controller.error(error1), 10);
+  }, 10);
+
+  return pipePromise.then(() => {
+    assert_array_equals(rs.eventsWithoutPulls, []);
+    assert_array_equals(ws.events, ['abort', error1]);
+  });
+
+}, 'Errors must be propagated forward: becomes errored after one chunk; dest never desires chunks; ' +
+   'preventAbort = false; rejected abort promise');
+
+promise_test(t => {
+
+  const rs = recordingReadableStream();
+
+  const ws = recordingWritableStream(undefined, new CountQueuingStrategy({ highWaterMark: 0 }));
+
+  const pipePromise = promise_rejects_exactly(t, error1, rs.pipeTo(ws, { preventAbort: true }),
+                                              'pipeTo must reject with the same error');
+
+  t.step_timeout(() => {
+    rs.controller.enqueue('Hello');
+    t.step_timeout(() => rs.controller.error(error1), 10);
+  }, 10);
+
+  return pipePromise.then(() => {
+    assert_array_equals(rs.eventsWithoutPulls, []);
+    assert_array_equals(ws.events, []);
+  });
+
+}, 'Errors must be propagated forward: becomes errored after one chunk; dest never desires chunks; ' +
+   'preventAbort = true');
+
+promise_test(t => {
+
+  const rs = recordingReadableStream();
+
+  let resolveWriteCalled;
+  const writeCalledPromise = new Promise(resolve => {
+    resolveWriteCalled = resolve;
+  });
+
+  let resolveWritePromise;
+  const ws = recordingWritableStream({
+    write() {
+      resolveWriteCalled();
+
+      return new Promise(resolve => {
+        resolveWritePromise = resolve;
+      });
+    }
+  });
+
+  let pipeComplete = false;
+  const pipePromise = promise_rejects_exactly(t, error1, rs.pipeTo(ws)).then(() => {
+    pipeComplete = true;
+  });
+
+  rs.controller.enqueue('a');
+
+  return writeCalledPromise.then(() => {
+    rs.controller.error(error1);
+
+    // Flush async events and verify that no shutdown occurs.
+    return flushAsyncEvents();
+  }).then(() => {
+    assert_array_equals(ws.events, ['write', 'a']); // no 'abort'
+    assert_equals(pipeComplete, false, 'the pipe must not be complete');
+
+    resolveWritePromise();
+
+    return pipePromise.then(() => {
+      assert_array_equals(ws.events, ['write', 'a', 'abort', error1]);
+    });
+  });
+
+}, 'Errors must be propagated forward: shutdown must not occur until the final write completes');
+
+promise_test(t => {
+
+  const rs = recordingReadableStream();
+
+  let resolveWriteCalled;
+  const writeCalledPromise = new Promise(resolve => {
+    resolveWriteCalled = resolve;
+  });
+
+  let resolveWritePromise;
+  const ws = recordingWritableStream({
+    write() {
+      resolveWriteCalled();
+
+      return new Promise(resolve => {
+        resolveWritePromise = resolve;
+      });
+    }
+  });
+
+  let pipeComplete = false;
+  const pipePromise = promise_rejects_exactly(t, error1, rs.pipeTo(ws, { preventAbort: true })).then(() => {
+    pipeComplete = true;
+  });
+
+  rs.controller.enqueue('a');
+
+  return writeCalledPromise.then(() => {
+    rs.controller.error(error1);
+
+    // Flush async events and verify that no shutdown occurs.
+    return flushAsyncEvents();
+  }).then(() => {
+    assert_array_equals(ws.events, ['write', 'a']); // no 'abort'
+    assert_equals(pipeComplete, false, 'the pipe must not be complete');
+
+    resolveWritePromise();
+    return pipePromise;
+  }).then(() => flushAsyncEvents()).then(() => {
+    assert_array_equals(ws.events, ['write', 'a']); // no 'abort'
+  });
+
+}, 'Errors must be propagated forward: shutdown must not occur until the final write completes; preventAbort = true');
+
+promise_test(t => {
+
+  const rs = recordingReadableStream();
+
+  let resolveWriteCalled;
+  const writeCalledPromise = new Promise(resolve => {
+    resolveWriteCalled = resolve;
+  });
+
+  let resolveWritePromise;
+  const ws = recordingWritableStream({
+    write() {
+      resolveWriteCalled();
+
+      return new Promise(resolve => {
+        resolveWritePromise = resolve;
+      });
+    }
+  }, new CountQueuingStrategy({ highWaterMark: 2 }));
+
+  let pipeComplete = false;
+  const pipePromise = promise_rejects_exactly(t, error1, rs.pipeTo(ws)).then(() => {
+    pipeComplete = true;
+  });
+
+  rs.controller.enqueue('a');
+  rs.controller.enqueue('b');
+
+  return writeCalledPromise.then(() => flushAsyncEvents()).then(() => {
+    assert_array_equals(ws.events, ['write', 'a'],
+      'the first chunk must have been written, but abort must not have happened yet');
+    assert_false(pipeComplete, 'the pipe should not complete while the first write is pending');
+
+    rs.controller.error(error1);
+    resolveWritePromise();
+    return flushAsyncEvents();
+  }).then(() => {
+    assert_array_equals(ws.events, ['write', 'a', 'write', 'b'],
+      'the second chunk must have been written, but abort must not have happened yet');
+    assert_false(pipeComplete, 'the pipe should not complete while the second write is pending');
+
+    resolveWritePromise();
+    return pipePromise;
+  }).then(() => {
+    assert_array_equals(ws.events, ['write', 'a', 'write', 'b', 'abort', error1],
+      'all chunks must have been written and abort must have happened');
+  });
+
+}, 'Errors must be propagated forward: shutdown must not occur until the final write completes; becomes errored after first write');
+
+promise_test(t => {
+
+  const rs = recordingReadableStream();
+
+  let resolveWriteCalled;
+  const writeCalledPromise = new Promise(resolve => {
+    resolveWriteCalled = resolve;
+  });
+
+  let resolveWritePromise;
+  const ws = recordingWritableStream({
+    write() {
+      resolveWriteCalled();
+
+      return new Promise(resolve => {
+        resolveWritePromise = resolve;
+      });
+    }
+  }, new CountQueuingStrategy({ highWaterMark: 2 }));
+
+  let pipeComplete = false;
+  const pipePromise = promise_rejects_exactly(t, error1, rs.pipeTo(ws, { preventAbort: true })).then(() => {
+    pipeComplete = true;
+  });
+
+  rs.controller.enqueue('a');
+  rs.controller.enqueue('b');
+
+  return writeCalledPromise.then(() => flushAsyncEvents()).then(() => {
+    assert_array_equals(ws.events, ['write', 'a'],
+      'the first chunk must have been written, but abort must not have happened');
+    assert_false(pipeComplete, 'the pipe should not complete while the first write is pending');
+
+    rs.controller.error(error1);
+    resolveWritePromise();
+  }).then(() => flushAsyncEvents()).then(() => {
+    assert_array_equals(ws.events, ['write', 'a', 'write', 'b'],
+      'the second chunk must have been written, but abort must not have happened');
+    assert_false(pipeComplete, 'the pipe should not complete while the second write is pending');
+
+    resolveWritePromise();
+    return pipePromise;
+  }).then(() => flushAsyncEvents()).then(() => {
+    assert_array_equals(ws.events, ['write', 'a', 'write', 'b'],
+      'all chunks must have been written, but abort must not have happened');
+  });
+
+}, 'Errors must be propagated forward: shutdown must not occur until the final write completes; becomes errored after first write; preventAbort = true');

test/fixtures/wpt/streams/piping/flow-control.any.js

@@ -0,0 +1,297 @@
+// META: global=window,worker,shadowrealm
+// META: script=../resources/test-utils.js
+// META: script=../resources/rs-utils.js
+// META: script=../resources/recording-streams.js
+'use strict';
+
+const error1 = new Error('error1!');
+error1.name = 'error1';
+
+promise_test(t => {
+
+  const rs = recordingReadableStream({
+    start(controller) {
+      controller.enqueue('a');
+      controller.enqueue('b');
+      controller.close();
+    }
+  });
+
+  const ws = recordingWritableStream(undefined, new CountQueuingStrategy({ highWaterMark: 0 }));
+
+  const pipePromise = rs.pipeTo(ws, { preventCancel: true });
+
+  // Wait and make sure it doesn't do any reading.
+  return flushAsyncEvents().then(() => {
+    ws.controller.error(error1);
+  })
+  .then(() => promise_rejects_exactly(t, error1, pipePromise, 'pipeTo must reject with the same error'))
+  .then(() => {
+    assert_array_equals(rs.eventsWithoutPulls, []);
+    assert_array_equals(ws.events, []);
+  })
+  .then(() => readableStreamToArray(rs))
+  .then(chunksNotPreviouslyRead => {
+    assert_array_equals(chunksNotPreviouslyRead, ['a', 'b']);
+  });
+
+}, 'Piping from a non-empty ReadableStream into a WritableStream that does not desire chunks');
+
+promise_test(() => {
+
+  const rs = recordingReadableStream({
+    start(controller) {
+      controller.enqueue('b');
+      controller.close();
+    }
+  });
+
+  let resolveWritePromise;
+  const ws = recordingWritableStream({
+    write() {
+      if (!resolveWritePromise) {
+        // first write
+        return new Promise(resolve => {
+          resolveWritePromise = resolve;
+        });
+      }
+      return undefined;
+    }
+  });
+
+  const writer = ws.getWriter();
+  const firstWritePromise = writer.write('a');
+  assert_equals(writer.desiredSize, 0, 'after writing the writer\'s desiredSize must be 0');
+  writer.releaseLock();
+
+  // firstWritePromise won't settle until we call resolveWritePromise.
+
+  const pipePromise = rs.pipeTo(ws);
+
+  return flushAsyncEvents().then(() => resolveWritePromise())
+    .then(() => Promise.all([firstWritePromise, pipePromise]))
+    .then(() => {
+      assert_array_equals(rs.eventsWithoutPulls, []);
+      assert_array_equals(ws.events, ['write', 'a', 'write', 'b', 'close']);
+    });
+
+}, 'Piping from a non-empty ReadableStream into a WritableStream that does not desire chunks, but then does');
+
+promise_test(() => {
+
+  const rs = recordingReadableStream();
+
+  let resolveWritePromise;
+  const ws = recordingWritableStream({
+    write() {
+      if (!resolveWritePromise) {
+        // first write
+        return new Promise(resolve => {
+          resolveWritePromise = resolve;
+        });
+      }
+      return undefined;
+    }
+  });
+
+  const writer = ws.getWriter();
+  writer.write('a');
+
+  return flushAsyncEvents().then(() => {
+    assert_array_equals(ws.events, ['write', 'a']);
+    assert_equals(writer.desiredSize, 0, 'after writing the writer\'s desiredSize must be 0');
+    writer.releaseLock();
+
+    const pipePromise = rs.pipeTo(ws);
+
+    rs.controller.enqueue('b');
+    resolveWritePromise();
+    rs.controller.close();
+
+    return pipePromise.then(() => {
+      assert_array_equals(rs.eventsWithoutPulls, []);
+      assert_array_equals(ws.events, ['write', 'a', 'write', 'b', 'close']);
+    });
+  });
+
+}, 'Piping from an empty ReadableStream into a WritableStream that does not desire chunks, but then the readable ' +
+   'stream becomes non-empty and the writable stream starts desiring chunks');
+
+promise_test(() => {
+  const unreadChunks = ['b', 'c', 'd'];
+
+  const rs = recordingReadableStream({
+    pull(controller) {
+      controller.enqueue(unreadChunks.shift());
+      if (unreadChunks.length === 0) {
+        controller.close();
+      }
+    }
+  }, new CountQueuingStrategy({ highWaterMark: 0 }));
+
+  let resolveWritePromise;
+  const ws = recordingWritableStream({
+    write() {
+      if (!resolveWritePromise) {
+        // first write
+        return new Promise(resolve => {
+          resolveWritePromise = resolve;
+        });
+      }
+      return undefined;
+    }
+  }, new CountQueuingStrategy({ highWaterMark: 3 }));
+
+  const writer = ws.getWriter();
+  const firstWritePromise = writer.write('a');
+  assert_equals(writer.desiredSize, 2, 'after writing the writer\'s desiredSize must be 2');
+  writer.releaseLock();
+
+  // firstWritePromise won't settle until we call resolveWritePromise.
+
+  const pipePromise = rs.pipeTo(ws);
+
+  return flushAsyncEvents().then(() => {
+    assert_array_equals(ws.events, ['write', 'a']);
+    assert_equals(unreadChunks.length, 1, 'chunks should continue to be enqueued until the HWM is reached');
+  }).then(() => resolveWritePromise())
+    .then(() => Promise.all([firstWritePromise, pipePromise]))
+    .then(() => {
+      assert_array_equals(rs.events, ['pull', 'pull', 'pull']);
+      assert_array_equals(ws.events, ['write', 'a', 'write', 'b','write', 'c','write', 'd', 'close']);
+    });
+
+}, 'Piping from a ReadableStream to a WritableStream that desires more chunks before finishing with previous ones');
+
+class StepTracker {
+  constructor() {
+    this.waiters = [];
+    this.wakers = [];
+  }
+
+  // Returns promise which resolves when step `n` is reached. Also schedules step n + 1 to happen shortly after the
+  // promise is resolved.
+  waitThenAdvance(n) {
+    if (this.waiters[n] === undefined) {
+      this.waiters[n] = new Promise(resolve => {
+        this.wakers[n] = resolve;
+      });
+      this.waiters[n]
+          .then(() => flushAsyncEvents())
+          .then(() => {
+            if (this.wakers[n + 1] !== undefined) {
+              this.wakers[n + 1]();
+            }
+          });
+    }
+    if (n == 0) {
+      this.wakers[0]();
+    }
+    return this.waiters[n];
+  }
+}
+
+promise_test(() => {
+  const steps = new StepTracker();
+  const desiredSizes = [];
+  const rs = recordingReadableStream({
+    start(controller) {
+      steps.waitThenAdvance(1).then(() => enqueue('a'));
+      steps.waitThenAdvance(3).then(() => enqueue('b'));
+      steps.waitThenAdvance(5).then(() => enqueue('c'));
+      steps.waitThenAdvance(7).then(() => enqueue('d'));
+      steps.waitThenAdvance(11).then(() => controller.close());
+
+      function enqueue(chunk) {
+        controller.enqueue(chunk);
+        desiredSizes.push(controller.desiredSize);
+      }
+    }
+  });
+
+  const chunksFinishedWriting = [];
+  const writableStartPromise = Promise.resolve();
+  let writeCalled = false;
+  const ws = recordingWritableStream({
+    start() {
+      return writableStartPromise;
+    },
+    write(chunk) {
+      const waitForStep = writeCalled ? 12 : 9;
+      writeCalled = true;
+      return steps.waitThenAdvance(waitForStep).then(() => {
+        chunksFinishedWriting.push(chunk);
+      });
+    }
+  });
+
+  return writableStartPromise.then(() => {
+    const pipePromise = rs.pipeTo(ws);
+    steps.waitThenAdvance(0);
+
+    return Promise.all([
+      steps.waitThenAdvance(2).then(() => {
+        assert_array_equals(chunksFinishedWriting, [], 'at step 2, zero chunks must have finished writing');
+        assert_array_equals(ws.events, ['write', 'a'], 'at step 2, one chunk must have been written');
+
+        // When 'a' (the very first chunk) was enqueued, it was immediately used to fulfill the outstanding read request
+        // promise, leaving the queue empty.
+        assert_array_equals(desiredSizes, [1],
+                            'at step 2, the desiredSize at the last enqueue (step 1) must have been 1');
+        assert_equals(rs.controller.desiredSize, 1, 'at step 2, the current desiredSize must be 1');
+      }),
+
+      steps.waitThenAdvance(4).then(() => {
+        assert_array_equals(chunksFinishedWriting, [], 'at step 4, zero chunks must have finished writing');
+        assert_array_equals(ws.events, ['write', 'a'], 'at step 4, one chunk must have been written');
+
+        // When 'b' was enqueued at step 3, the queue was also empty, since immediately after enqueuing 'a' at
+        // step 1, it was dequeued in order to fulfill the read() call that was made at step 0. Thus the queue
+        // had size 1 (thus desiredSize of 0).
+        assert_array_equals(desiredSizes, [1, 0],
+                            'at step 4, the desiredSize at the last enqueue (step 3) must have been 0');
+        assert_equals(rs.controller.desiredSize, 0, 'at step 4, the current desiredSize must be 0');
+      }),
+
+      steps.waitThenAdvance(6).then(() => {
+        assert_array_equals(chunksFinishedWriting, [], 'at step 6, zero chunks must have finished writing');
+        assert_array_equals(ws.events, ['write', 'a'], 'at step 6, one chunk must have been written');
+
+        // When 'c' was enqueued at step 5, the queue was not empty; it had 'b' in it, since 'b' will not be read until
+        // the first write completes at step 9. Thus, the queue size is 2 after enqueuing 'c', giving a desiredSize of
+        // -1.
+        assert_array_equals(desiredSizes, [1, 0, -1],
+                            'at step 6, the desiredSize at the last enqueue (step 5) must have been -1');
+        assert_equals(rs.controller.desiredSize, -1, 'at step 6, the current desiredSize must be -1');
+      }),
+
+      steps.waitThenAdvance(8).then(() => {
+        assert_array_equals(chunksFinishedWriting, [], 'at step 8, zero chunks must have finished writing');
+        assert_array_equals(ws.events, ['write', 'a'], 'at step 8, one chunk must have been written');
+
+        // When 'd' was enqueued at step 7, the situation is the same as before, leading to a queue containing 'b', 'c',
+        // and 'd'.
+        assert_array_equals(desiredSizes, [1, 0, -1, -2],
+                            'at step 8, the desiredSize at the last enqueue (step 7) must have been -2');
+        assert_equals(rs.controller.desiredSize, -2, 'at step 8, the current desiredSize must be -2');
+      }),
+
+      steps.waitThenAdvance(10).then(() => {
+        assert_array_equals(chunksFinishedWriting, ['a'], 'at step 10, one chunk must have finished writing');
+        assert_array_equals(ws.events, ['write', 'a', 'write', 'b'],
+                            'at step 10, two chunks must have been written');
+
+        assert_equals(rs.controller.desiredSize, -1, 'at step 10, the current desiredSize must be -1');
+      }),
+
+      pipePromise.then(() => {
+        assert_array_equals(desiredSizes, [1, 0, -1, -2], 'backpressure must have been exerted at the source');
+        assert_array_equals(chunksFinishedWriting, ['a', 'b', 'c', 'd'], 'all chunks finished writing');
+
+        assert_array_equals(rs.eventsWithoutPulls, [], 'nothing unexpected should happen to the ReadableStream');
+        assert_array_equals(ws.events, ['write', 'a', 'write', 'b', 'write', 'c', 'write', 'd', 'close'],
+                            'all chunks were written (and the WritableStream closed)');
+      })
+    ]);
+  });
+}, 'Piping to a WritableStream that does not consume the writes fast enough exerts backpressure on the ReadableStream');

test/fixtures/wpt/streams/piping/general-addition.any.js

@@ -0,0 +1,15 @@
+// META: global=window,worker,shadowrealm
+'use strict';
+
+promise_test(async t => {
+  /** @type {ReadableStreamDefaultController} */
+  var con;
+  let synchronous = false;
+  new ReadableStream({ start(c) { con = c }}, { highWaterMark: 0 }).pipeTo(
+    new WritableStream({ write() { synchronous = true; } })
+  )
+  // wait until start algorithm finishes
+  await Promise.resolve();
+  con.enqueue();
+  assert_false(synchronous, 'write algorithm must not run synchronously');
+}, "enqueue() must not synchronously call write algorithm");

test/fixtures/wpt/streams/piping/general.any.js

@@ -0,0 +1,212 @@
+// META: global=window,worker,shadowrealm
+// META: script=../resources/recording-streams.js
+'use strict';
+
+test(() => {
+
+  const rs = new ReadableStream();
+  const ws = new WritableStream();
+
+  assert_false(rs.locked, 'sanity check: the ReadableStream must not start locked');
+  assert_false(ws.locked, 'sanity check: the WritableStream must not start locked');
+
+  rs.pipeTo(ws);
+
+  assert_true(rs.locked, 'the ReadableStream must become locked');
+  assert_true(ws.locked, 'the WritableStream must become locked');
+
+}, 'Piping must lock both the ReadableStream and WritableStream');
+
+promise_test(() => {
+
+  const rs = new ReadableStream({
+    start(controller) {
+      controller.close();
+    }
+  });
+  const ws = new WritableStream();
+
+  return rs.pipeTo(ws).then(() => {
+    assert_false(rs.locked, 'the ReadableStream must become unlocked');
+    assert_false(ws.locked, 'the WritableStream must become unlocked');
+  });
+
+}, 'Piping finishing must unlock both the ReadableStream and WritableStream');
+
+promise_test(t => {
+
+  const fakeRS = Object.create(ReadableStream.prototype);
+  const ws = new WritableStream();
+
+  return promise_rejects_js(t, TypeError, ReadableStream.prototype.pipeTo.apply(fakeRS, [ws]),
+    'pipeTo should reject with a TypeError');
+
+}, 'pipeTo must check the brand of its ReadableStream this value');
+
+promise_test(t => {
+
+  const rs = new ReadableStream();
+  const fakeWS = Object.create(WritableStream.prototype);
+
+  return promise_rejects_js(t, TypeError, ReadableStream.prototype.pipeTo.apply(rs, [fakeWS]),
+    'pipeTo should reject with a TypeError');
+
+}, 'pipeTo must check the brand of its WritableStream argument');
+
+promise_test(t => {
+
+  const rs = new ReadableStream();
+  const ws = new WritableStream();
+
+  rs.getReader();
+
+  assert_true(rs.locked, 'sanity check: the ReadableStream starts locked');
+  assert_false(ws.locked, 'sanity check: the WritableStream does not start locked');
+
+  return promise_rejects_js(t, TypeError, rs.pipeTo(ws)).then(() => {
+    assert_false(ws.locked, 'the WritableStream must still be unlocked');
+  });
+
+}, 'pipeTo must fail if the ReadableStream is locked, and not lock the WritableStream');
+
+promise_test(t => {
+
+  const rs = new ReadableStream();
+  const ws = new WritableStream();
+
+  ws.getWriter();
+
+  assert_false(rs.locked, 'sanity check: the ReadableStream does not start locked');
+  assert_true(ws.locked, 'sanity check: the WritableStream starts locked');
+
+  return promise_rejects_js(t, TypeError, rs.pipeTo(ws)).then(() => {
+    assert_false(rs.locked, 'the ReadableStream must still be unlocked');
+  });
+
+}, 'pipeTo must fail if the WritableStream is locked, and not lock the ReadableStream');
+
+promise_test(() => {
+
+  const CHUNKS = 10;
+
+  const rs = new ReadableStream({
+    start(c) {
+      for (let i = 0; i < CHUNKS; ++i) {
+        c.enqueue(i);
+      }
+      c.close();
+    }
+  });
+
+  const written = [];
+  const ws = new WritableStream({
+    write(chunk) {
+      written.push(chunk);
+    },
+    close() {
+      written.push('closed');
+    }
+  }, new CountQueuingStrategy({ highWaterMark: CHUNKS }));
+
+  return rs.pipeTo(ws).then(() => {
+    const targetValues = [];
+    for (let i = 0; i < CHUNKS; ++i) {
+      targetValues.push(i);
+    }
+    targetValues.push('closed');
+
+    assert_array_equals(written, targetValues, 'the correct values must be written');
+
+    // Ensure both readable and writable are closed by the time the pipe finishes.
+    return Promise.all([
+      rs.getReader().closed,
+      ws.getWriter().closed
+    ]);
+  });
+
+  // NOTE: no requirement on *when* the pipe finishes; that is left to implementations.
+
+}, 'Piping from a ReadableStream from which lots of chunks are synchronously readable');
+
+promise_test(t => {
+
+  let controller;
+  const rs = recordingReadableStream({
+    start(c) {
+      controller = c;
+    }
+  });
+
+  const ws = recordingWritableStream();
+
+  const pipePromise = rs.pipeTo(ws).then(() => {
+    assert_array_equals(ws.events, ['write', 'Hello', 'close']);
+  });
+
+  t.step_timeout(() => {
+    controller.enqueue('Hello');
+    t.step_timeout(() => controller.close(), 10);
+  }, 10);
+
+  return pipePromise;
+
+}, 'Piping from a ReadableStream for which a chunk becomes asynchronously readable after the pipeTo');
+
+for (const preventAbort of [true, false]) {
+  promise_test(() => {
+
+    const rs = new ReadableStream({
+      pull() {
+        return Promise.reject(undefined);
+      }
+    });
+
+    return rs.pipeTo(new WritableStream(), { preventAbort }).then(
+        () => assert_unreached('pipeTo promise should be rejected'),
+        value => assert_equals(value, undefined, 'rejection value should be undefined'));
+
+  }, `an undefined rejection from pull should cause pipeTo() to reject when preventAbort is ${preventAbort}`);
+}
+
+for (const preventCancel of [true, false]) {
+  promise_test(() => {
+
+    const rs = new ReadableStream({
+      pull(controller) {
+        controller.enqueue(0);
+      }
+    });
+
+    const ws = new WritableStream({
+      write() {
+        return Promise.reject(undefined);
+      }
+    });
+
+    return rs.pipeTo(ws, { preventCancel }).then(
+         () => assert_unreached('pipeTo promise should be rejected'),
+        value => assert_equals(value, undefined, 'rejection value should be undefined'));
+
+  }, `an undefined rejection from write should cause pipeTo() to reject when preventCancel is ${preventCancel}`);
+}
+
+promise_test(t => {
+  const rs = new ReadableStream();
+  const ws = new WritableStream();
+  return promise_rejects_js(t, TypeError, rs.pipeTo(ws, {
+    get preventAbort() {
+      ws.getWriter();
+    }
+  }), 'pipeTo should reject');
+}, 'pipeTo() should reject if an option getter grabs a writer');
+
+promise_test(t => {
+  const rs = new ReadableStream({
+    start(controller) {
+      controller.close();
+    }
+  });
+  const ws = new WritableStream();
+
+  return rs.pipeTo(ws, null);
+}, 'pipeTo() promise should resolve if null is passed');

test/fixtures/wpt/streams/piping/multiple-propagation.any.js

@@ -0,0 +1,227 @@
+// META: global=window,worker,shadowrealm
+// META: script=../resources/test-utils.js
+// META: script=../resources/recording-streams.js
+'use strict';
+
+const error1 = new Error('error1!');
+error1.name = 'error1';
+
+const error2 = new Error('error2!');
+error2.name = 'error2';
+
+function createErroredWritableStream(t) {
+  return Promise.resolve().then(() => {
+    const ws = recordingWritableStream({
+      start(c) {
+        c.error(error2);
+      }
+    });
+
+    const writer = ws.getWriter();
+    return promise_rejects_exactly(t, error2, writer.closed, 'the writable stream must be errored with error2')
+        .then(() => {
+          writer.releaseLock();
+          assert_array_equals(ws.events, []);
+          return ws;
+        });
+  });
+}
+
+promise_test(t => {
+  const rs = recordingReadableStream({
+    start(c) {
+      c.error(error1);
+    }
+  });
+  const ws = recordingWritableStream({
+    start(c) {
+      c.error(error2);
+    }
+  });
+
+  // Trying to abort a stream that is erroring will give the writable's error
+  return promise_rejects_exactly(t, error2, rs.pipeTo(ws), 'pipeTo must reject with the writable stream\'s error').then(() => {
+    assert_array_equals(rs.events, []);
+    assert_array_equals(ws.events, []);
+
+    return Promise.all([
+      promise_rejects_exactly(t, error1, rs.getReader().closed, 'the readable stream must be errored with error1'),
+      promise_rejects_exactly(t, error2, ws.getWriter().closed, 'the writable stream must be errored with error2')
+    ]);
+  });
+
+}, 'Piping from an errored readable stream to an erroring writable stream');
+
+promise_test(t => {
+  const rs = recordingReadableStream({
+    start(c) {
+      c.error(error1);
+    }
+  });
+
+  return createErroredWritableStream(t)
+      .then(ws => promise_rejects_exactly(t, error1, rs.pipeTo(ws), 'pipeTo must reject with the readable stream\'s error'))
+      .then(() => {
+        assert_array_equals(rs.events, []);
+
+        return promise_rejects_exactly(t, error1, rs.getReader().closed, 'the readable stream must be errored with error1');
+      });
+}, 'Piping from an errored readable stream to an errored writable stream');
+
+promise_test(t => {
+  const rs = recordingReadableStream({
+    start(c) {
+      c.error(error1);
+    }
+  });
+  const ws = recordingWritableStream({
+    start(c) {
+      c.error(error2);
+    }
+  });
+
+  return promise_rejects_exactly(t, error1, rs.pipeTo(ws, { preventAbort: true }),
+    'pipeTo must reject with the readable stream\'s error')
+  .then(() => {
+    assert_array_equals(rs.events, []);
+    assert_array_equals(ws.events, []);
+
+    return Promise.all([
+      promise_rejects_exactly(t, error1, rs.getReader().closed, 'the readable stream must be errored with error1'),
+      promise_rejects_exactly(t, error2, ws.getWriter().closed, 'the writable stream must be errored with error2')
+    ]);
+  });
+
+}, 'Piping from an errored readable stream to an erroring writable stream; preventAbort = true');
+
+promise_test(t => {
+  const rs = recordingReadableStream({
+    start(c) {
+      c.error(error1);
+    }
+  });
+  return createErroredWritableStream(t)
+  .then(ws => promise_rejects_exactly(t, error1, rs.pipeTo(ws, { preventAbort: true }),
+                                      'pipeTo must reject with the readable stream\'s error'))
+  .then(() => {
+    assert_array_equals(rs.events, []);
+
+    return promise_rejects_exactly(t, error1, rs.getReader().closed, 'the readable stream must be errored with error1');
+  });
+
+}, 'Piping from an errored readable stream to an errored writable stream; preventAbort = true');
+
+promise_test(t => {
+  const rs = recordingReadableStream({
+    start(c) {
+      c.error(error1);
+    }
+  });
+  const ws = recordingWritableStream();
+  const writer = ws.getWriter();
+  const closePromise = writer.close();
+  writer.releaseLock();
+
+  return promise_rejects_exactly(t, error1, rs.pipeTo(ws), 'pipeTo must reject with the readable stream\'s error').then(() => {
+    assert_array_equals(rs.events, []);
+    assert_array_equals(ws.events, ['abort', error1]);
+
+    return Promise.all([
+      promise_rejects_exactly(t, error1, rs.getReader().closed, 'the readable stream must be errored with error1'),
+      promise_rejects_exactly(t, error1, ws.getWriter().closed,
+        'closed must reject with error1'),
+      promise_rejects_exactly(t, error1, closePromise,
+        'close() must reject with error1')
+    ]);
+  });
+
+}, 'Piping from an errored readable stream to a closing writable stream');
+
+promise_test(t => {
+  const rs = recordingReadableStream({
+    start(c) {
+      c.error(error1);
+    }
+  });
+  const ws = recordingWritableStream();
+  const writer = ws.getWriter();
+  const closePromise = writer.close();
+  writer.releaseLock();
+
+  return flushAsyncEvents().then(() => {
+    return promise_rejects_exactly(t, error1, rs.pipeTo(ws), 'pipeTo must reject with the readable stream\'s error').then(() => {
+      assert_array_equals(rs.events, []);
+      assert_array_equals(ws.events, ['close']);
+
+      return Promise.all([
+        promise_rejects_exactly(t, error1, rs.getReader().closed, 'the readable stream must be errored with error1'),
+        ws.getWriter().closed,
+        closePromise
+      ]);
+    });
+  });
+
+}, 'Piping from an errored readable stream to a closed writable stream');
+
+promise_test(t => {
+  const rs = recordingReadableStream({
+    start(c) {
+      c.close();
+    }
+  });
+  const ws = recordingWritableStream({
+    start(c) {
+      c.error(error1);
+    }
+  });
+
+  return promise_rejects_exactly(t, error1, rs.pipeTo(ws), 'pipeTo must reject with the writable stream\'s error').then(() => {
+    assert_array_equals(rs.events, []);
+    assert_array_equals(ws.events, []);
+
+    return Promise.all([
+      rs.getReader().closed,
+      promise_rejects_exactly(t, error1, ws.getWriter().closed, 'the writable stream must be errored with error1')
+    ]);
+  });
+
+}, 'Piping from a closed readable stream to an erroring writable stream');
+
+promise_test(t => {
+  const rs = recordingReadableStream({
+    start(c) {
+      c.close();
+    }
+  });
+  return createErroredWritableStream(t)
+  .then(ws => promise_rejects_exactly(t, error2, rs.pipeTo(ws), 'pipeTo must reject with the writable stream\'s error'))
+  .then(() => {
+    assert_array_equals(rs.events, []);
+
+    return rs.getReader().closed;
+  });
+
+}, 'Piping from a closed readable stream to an errored writable stream');
+
+promise_test(() => {
+  const rs = recordingReadableStream({
+    start(c) {
+      c.close();
+    }
+  });
+  const ws = recordingWritableStream();
+  const writer = ws.getWriter();
+  writer.close();
+  writer.releaseLock();
+
+  return rs.pipeTo(ws).then(() => {
+    assert_array_equals(rs.events, []);
+    assert_array_equals(ws.events, ['close']);
+
+    return Promise.all([
+      rs.getReader().closed,
+      ws.getWriter().closed
+    ]);
+  });
+
+}, 'Piping from a closed readable stream to a closed writable stream');

test/fixtures/wpt/streams/piping/pipe-through.any.js

@@ -0,0 +1,331 @@
+// META: global=window,worker,shadowrealm
+// META: script=../resources/rs-utils.js
+// META: script=../resources/test-utils.js
+// META: script=../resources/recording-streams.js
+'use strict';
+
+function duckTypedPassThroughTransform() {
+  let enqueueInReadable;
+  let closeReadable;
+
+  return {
+    writable: new WritableStream({
+      write(chunk) {
+        enqueueInReadable(chunk);
+      },
+
+      close() {
+        closeReadable();
+      }
+    }),
+
+    readable: new ReadableStream({
+      start(c) {
+        enqueueInReadable = c.enqueue.bind(c);
+        closeReadable = c.close.bind(c);
+      }
+    })
+  };
+}
+
+function uninterestingReadableWritablePair() {
+  return { writable: new WritableStream(), readable: new ReadableStream() };
+}
+
+promise_test(() => {
+  const readableEnd = sequentialReadableStream(5).pipeThrough(duckTypedPassThroughTransform());
+
+  return readableStreamToArray(readableEnd).then(chunks =>
+    assert_array_equals(chunks, [1, 2, 3, 4, 5]), 'chunks should match');
+}, 'Piping through a duck-typed pass-through transform stream should work');
+
+promise_test(() => {
+  const transform = {
+    writable: new WritableStream({
+      start(c) {
+        c.error(new Error('this rejection should not be reported as unhandled'));
+      }
+    }),
+    readable: new ReadableStream()
+  };
+
+  sequentialReadableStream(5).pipeThrough(transform);
+
+  // The test harness should complain about unhandled rejections by then.
+  return flushAsyncEvents();
+
+}, 'Piping through a transform errored on the writable end does not cause an unhandled promise rejection');
+
+test(() => {
+  let calledPipeTo = false;
+  class BadReadableStream extends ReadableStream {
+    pipeTo() {
+      calledPipeTo = true;
+    }
+  }
+
+  const brs = new BadReadableStream({
+    start(controller) {
+      controller.close();
+    }
+  });
+  const readable = new ReadableStream();
+  const writable = new WritableStream();
+  const result = brs.pipeThrough({ readable, writable });
+
+  assert_false(calledPipeTo, 'the overridden pipeTo should not have been called');
+  assert_equals(result, readable, 'return value should be the passed readable property');
+}, 'pipeThrough should not call pipeTo on this');
+
+test(t => {
+  let calledFakePipeTo = false;
+  const realPipeTo = ReadableStream.prototype.pipeTo;
+  t.add_cleanup(() => {
+    ReadableStream.prototype.pipeTo = realPipeTo;
+  });
+  ReadableStream.prototype.pipeTo = () => {
+    calledFakePipeTo = true;
+  };
+  const rs = new ReadableStream();
+  const readable = new ReadableStream();
+  const writable = new WritableStream();
+  const result = rs.pipeThrough({ readable, writable });
+
+  assert_false(calledFakePipeTo, 'the monkey-patched pipeTo should not have been called');
+  assert_equals(result, readable, 'return value should be the passed readable property');
+
+}, 'pipeThrough should not call pipeTo on the ReadableStream prototype');
+
+const badReadables = [null, undefined, 0, NaN, true, 'ReadableStream', Object.create(ReadableStream.prototype)];
+for (const readable of badReadables) {
+  test(() => {
+    assert_throws_js(TypeError,
+                     ReadableStream.prototype.pipeThrough.bind(readable, uninterestingReadableWritablePair()),
+                     'pipeThrough should throw');
+  }, `pipeThrough should brand-check this and not allow '${readable}'`);
+
+  test(() => {
+    const rs = new ReadableStream();
+    let writableGetterCalled = false;
+    assert_throws_js(
+      TypeError,
+      () => rs.pipeThrough({
+        get writable() {
+          writableGetterCalled = true;
+          return new WritableStream();
+        },
+        readable
+      }),
+      'pipeThrough should brand-check readable'
+    );
+    assert_false(writableGetterCalled, 'writable should not have been accessed');
+  }, `pipeThrough should brand-check readable and not allow '${readable}'`);
+}
+
+const badWritables = [null, undefined, 0, NaN, true, 'WritableStream', Object.create(WritableStream.prototype)];
+for (const writable of badWritables) {
+  test(() => {
+    const rs = new ReadableStream({
+      start(c) {
+        c.close();
+      }
+    });
+    let readableGetterCalled = false;
+    assert_throws_js(TypeError, () => rs.pipeThrough({
+      get readable() {
+        readableGetterCalled = true;
+        return new ReadableStream();
+      },
+      writable
+    }),
+                  'pipeThrough should brand-check writable');
+    assert_true(readableGetterCalled, 'readable should have been accessed');
+  }, `pipeThrough should brand-check writable and not allow '${writable}'`);
+}
+
+test(t => {
+  const error = new Error();
+  error.name = 'custom';
+
+  const rs = new ReadableStream({
+    pull: t.unreached_func('pull should not be called')
+  }, { highWaterMark: 0 });
+
+  const throwingWritable = {
+    readable: rs,
+    get writable() {
+      throw error;
+    }
+  };
+  assert_throws_exactly(error,
+                        () => ReadableStream.prototype.pipeThrough.call(rs, throwingWritable, {}),
+                        'pipeThrough should rethrow the error thrown by the writable getter');
+
+  const throwingReadable = {
+    get readable() {
+      throw error;
+    },
+    writable: {}
+  };
+  assert_throws_exactly(error,
+                        () => ReadableStream.prototype.pipeThrough.call(rs, throwingReadable, {}),
+                        'pipeThrough should rethrow the error thrown by the readable getter');
+
+}, 'pipeThrough should rethrow errors from accessing readable or writable');
+
+const badSignals = [null, 0, NaN, true, 'AbortSignal', Object.create(AbortSignal.prototype)];
+for (const signal of badSignals) {
+  test(() => {
+    const rs = new ReadableStream();
+    assert_throws_js(TypeError, () => rs.pipeThrough(uninterestingReadableWritablePair(), { signal }),
+                     'pipeThrough should throw');
+  }, `invalid values of signal should throw; specifically '${signal}'`);
+}
+
+test(() => {
+  const rs = new ReadableStream();
+  const controller = new AbortController();
+  const signal = controller.signal;
+  rs.pipeThrough(uninterestingReadableWritablePair(), { signal });
+}, 'pipeThrough should accept a real AbortSignal');
+
+test(() => {
+  const rs = new ReadableStream();
+  rs.getReader();
+  assert_throws_js(TypeError, () => rs.pipeThrough(uninterestingReadableWritablePair()),
+                   'pipeThrough should throw');
+}, 'pipeThrough should throw if this is locked');
+
+test(() => {
+  const rs = new ReadableStream();
+  const writable = new WritableStream();
+  const readable = new ReadableStream();
+  writable.getWriter();
+  assert_throws_js(TypeError, () => rs.pipeThrough({writable, readable}),
+                   'pipeThrough should throw');
+}, 'pipeThrough should throw if writable is locked');
+
+test(() => {
+  const rs = new ReadableStream();
+  const writable = new WritableStream();
+  const readable = new ReadableStream();
+  readable.getReader();
+  assert_equals(rs.pipeThrough({ writable, readable }), readable,
+                'pipeThrough should not throw');
+}, 'pipeThrough should not care if readable is locked');
+
+promise_test(() => {
+  const rs = recordingReadableStream();
+  const writable = new WritableStream({
+    start(controller) {
+      controller.error();
+    }
+  });
+  const readable = new ReadableStream();
+  rs.pipeThrough({ writable, readable }, { preventCancel: true });
+  return flushAsyncEvents(0).then(() => {
+    assert_array_equals(rs.events, ['pull'], 'cancel should not have been called');
+  });
+}, 'preventCancel should work');
+
+promise_test(() => {
+  const rs = new ReadableStream({
+    start(controller) {
+      controller.close();
+    }
+  });
+  const writable = recordingWritableStream();
+  const readable = new ReadableStream();
+  rs.pipeThrough({ writable, readable }, { preventClose: true });
+  return flushAsyncEvents(0).then(() => {
+    assert_array_equals(writable.events, [], 'writable should not be closed');
+  });
+}, 'preventClose should work');
+
+promise_test(() => {
+  const rs = new ReadableStream({
+    start(controller) {
+      controller.error();
+    }
+  });
+  const writable = recordingWritableStream();
+  const readable = new ReadableStream();
+  rs.pipeThrough({ writable, readable }, { preventAbort: true });
+  return flushAsyncEvents(0).then(() => {
+    assert_array_equals(writable.events, [], 'writable should not be aborted');
+  });
+}, 'preventAbort should work');
+
+test(() => {
+  const rs = new ReadableStream();
+  const readable = new ReadableStream();
+  const writable = new WritableStream();
+  assert_throws_js(TypeError, () => rs.pipeThrough({readable, writable}, {
+    get preventAbort() {
+      writable.getWriter();
+    }
+  }), 'pipeThrough should throw');
+}, 'pipeThrough() should throw if an option getter grabs a writer');
+
+test(() => {
+  const rs = new ReadableStream();
+  const readable = new ReadableStream();
+  const writable = new WritableStream();
+  rs.pipeThrough({readable, writable}, null);
+}, 'pipeThrough() should not throw if option is null');
+
+test(() => {
+  const rs = new ReadableStream();
+  const readable = new ReadableStream();
+  const writable = new WritableStream();
+  rs.pipeThrough({readable, writable}, {signal:undefined});
+}, 'pipeThrough() should not throw if signal is undefined');
+
+function tryPipeThrough(pair, options)
+{
+  const rs = new ReadableStream();
+  if (!pair)
+    pair = {readable:new ReadableStream(), writable:new WritableStream()};
+  try {
+    rs.pipeThrough(pair, options)
+  } catch (e) {
+    return e;
+  }
+}
+
+test(() => {
+  let result = tryPipeThrough({
+    get readable() {
+      return new ReadableStream();
+    },
+    get writable() {
+      throw "writable threw";
+    }
+  }, { });
+  assert_equals(result, "writable threw");
+
+  result = tryPipeThrough({
+    get readable() {
+      throw "readable threw";
+    },
+    get writable() {
+      throw "writable threw";
+    }
+  }, { });
+  assert_equals(result, "readable threw");
+
+  result = tryPipeThrough({
+    get readable() {
+      throw "readable threw";
+    },
+    get writable() {
+      throw "writable threw";
+    }
+  }, {
+    get preventAbort() {
+      throw "preventAbort threw";
+    }
+  });
+  assert_equals(result, "readable threw");
+
+}, 'pipeThrough() should throw if readable/writable getters throw');

test/fixtures/wpt/streams/piping/then-interception.any.js

@@ -0,0 +1,68 @@
+// META: global=window,worker,shadowrealm
+// META: script=../resources/test-utils.js
+// META: script=../resources/recording-streams.js
+'use strict';
+
+function interceptThen() {
+  const intercepted = [];
+  let callCount = 0;
+  Object.prototype.then = function(resolver) {
+    if (!this.done) {
+      intercepted.push(this.value);
+    }
+    const retval = Object.create(null);
+    retval.done = ++callCount === 3;
+    retval.value = callCount;
+    resolver(retval);
+    if (retval.done) {
+      delete Object.prototype.then;
+    }
+  }
+  return intercepted;
+}
+
+promise_test(async t => {
+  const rs = new ReadableStream({
+    start(controller) {
+      controller.enqueue('a');
+      controller.close();
+    }
+  });
+  const ws = recordingWritableStream();
+
+  const intercepted = interceptThen();
+  t.add_cleanup(() => {
+    delete Object.prototype.then;
+  });
+
+  await rs.pipeTo(ws);
+  delete Object.prototype.then;
+
+
+  assert_array_equals(intercepted, [], 'nothing should have been intercepted');
+  assert_array_equals(ws.events, ['write', 'a', 'close'], 'written chunk should be "a"');
+}, 'piping should not be observable');
+
+promise_test(async t => {
+  const rs = new ReadableStream({
+    start(controller) {
+      controller.enqueue('a');
+      controller.close();
+    }
+  });
+  const ws = recordingWritableStream();
+
+  const [ branch1, branch2 ] = rs.tee();
+
+  const intercepted = interceptThen();
+  t.add_cleanup(() => {
+    delete Object.prototype.then;
+  });
+
+  await branch1.pipeTo(ws);
+  delete Object.prototype.then;
+  branch2.cancel();
+
+  assert_array_equals(intercepted, [], 'nothing should have been intercepted');
+  assert_array_equals(ws.events, ['write', 'a', 'close'], 'written chunk should be "a"');
+}, 'tee should not be observable');

test/fixtures/wpt/streams/piping/throwing-options.any.js

@@ -0,0 +1,65 @@
+// META: global=window,worker,shadowrealm
+'use strict';
+
+class ThrowingOptions {
+  constructor(whatShouldThrow) {
+    this.whatShouldThrow = whatShouldThrow;
+    this.touched = [];
+  }
+
+  get preventClose() {
+    this.maybeThrow('preventClose');
+    return false;
+  }
+
+  get preventAbort() {
+    this.maybeThrow('preventAbort');
+    return false;
+  }
+
+  get preventCancel() {
+    this.maybeThrow('preventCancel');
+    return false;
+  }
+
+  get signal() {
+    this.maybeThrow('signal');
+    return undefined;
+  }
+
+  maybeThrow(forWhat) {
+    this.touched.push(forWhat);
+    if (this.whatShouldThrow === forWhat) {
+      throw new Error(this.whatShouldThrow);
+    }
+  }
+}
+
+const checkOrder = ['preventAbort', 'preventCancel', 'preventClose', 'signal'];
+
+for (let i = 0; i < checkOrder.length; ++i) {
+  const whatShouldThrow = checkOrder[i];
+  const whatShouldBeTouched = checkOrder.slice(0, i + 1);
+
+  promise_test(t => {
+    const options = new ThrowingOptions(whatShouldThrow);
+    return promise_rejects_js(
+               t, Error,
+               new ReadableStream().pipeTo(new WritableStream(), options),
+               'pipeTo should reject')
+        .then(() => assert_array_equals(
+            options.touched, whatShouldBeTouched,
+            'options should be touched in the right order'));
+  }, `pipeTo should stop after getting ${whatShouldThrow} throws`);
+
+  test(() => {
+    const options = new ThrowingOptions(whatShouldThrow);
+    assert_throws_js(
+        Error,
+        () => new ReadableStream().pipeThrough(new TransformStream(), options),
+        'pipeThrough should throw');
+    assert_array_equals(
+        options.touched, whatShouldBeTouched,
+        'options should be touched in the right order');
+  }, `pipeThrough should stop after getting ${whatShouldThrow} throws`);
+}

test/fixtures/wpt/streams/piping/transform-streams.any.js

@@ -0,0 +1,22 @@
+// META: global=window,worker,shadowrealm
+'use strict';
+
+promise_test(() => {
+  const rs = new ReadableStream({
+    start(c) {
+      c.enqueue('a');
+      c.enqueue('b');
+      c.enqueue('c');
+      c.close();
+    }
+  });
+
+  const ts = new TransformStream();
+
+  const ws = new WritableStream();
+
+  return rs.pipeThrough(ts).pipeTo(ws).then(() => {
+    const writer = ws.getWriter();
+    return writer.closed;
+  });
+}, 'Piping through an identity transform stream should close the destination when the source closes');