path: root/chromium/third_party/blink/renderer/core/streams/WritableStream.js

// Copyright 2016 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

// Implementation of WritableStream for Blink.  See
// https://streams.spec.whatwg.org/#ws. The implementation closely follows the
// standard, except where required for performance or integration with Blink.
// In particular, classes, methods and abstract operations are implemented in
// the same order as in the standard, to simplify side-by-side reading.

(function(global, binding, v8) {
  'use strict';

  // Private symbols. These correspond to the internal slots in the standard.
  // "[[X]]" in the standard is spelt _X in this implementation.

  // TODO(ricea): Optimise [[closeRequest]] and [[inFlightCloseRequest]] into a
  // single slot + a flag to say which one is set at the moment.
  const _abortAlgorithm = v8.createPrivateSymbol('[[abortAlgorithm]]');
  const _closeAlgorithm = v8.createPrivateSymbol('[[closeAlgorithm]]');
  const _closeRequest = v8.createPrivateSymbol('[[closeRequest]]');
  const _inFlightWriteRequest =
        v8.createPrivateSymbol('[[inFlightWriteRequest]]');
  const _inFlightCloseRequest =
        v8.createPrivateSymbol('[[inFlightCloseRequest]]');
  const _pendingAbortRequest =
        v8.createPrivateSymbol('[[pendingAbortRequest]]');
  // Flags and state are combined into a single integer field for efficiency.
  const _stateAndFlags = v8.createPrivateSymbol('[[state]] and flags');
  const _storedError = v8.createPrivateSymbol('[[storedError]]');
  const _writableStreamController =
        v8.createPrivateSymbol('[[writableStreamController]]');
  const _writer = v8.createPrivateSymbol('[[writer]]');
  const _writeRequests = v8.createPrivateSymbol('[[writeRequests]]');
  const _closedPromise = v8.createPrivateSymbol('[[closedPromise]]');
  const _ownerWritableStream =
        v8.createPrivateSymbol('[[ownerWritableStream]]');
  const _readyPromise = v8.createPrivateSymbol('[[readyPromise]]');
  const _controlledWritableStream =
        v8.createPrivateSymbol('[[controlledWritableStream]]');
  const _started = v8.createPrivateSymbol('[[started]]');
  const _strategyHWM = v8.createPrivateSymbol('[[strategyHWM]]');
  const _strategySizeAlgorithm =
        v8.createPrivateSymbol('[[strategySizeAlgorithm]]');
  const _writeAlgorithm = v8.createPrivateSymbol('[[writeAlgorithm]]');

  // Numeric encodings of stream states. Stored in the _stateAndFlags slot.
  const WRITABLE = 0;
  const CLOSED = 1;
  const ERRORING = 2;
  const ERRORED = 3;

  // Mask to extract or assign states to _stateAndFlags.
  const STATE_MASK = 0xF;

  // Also stored in _stateAndFlags.
  const BACKPRESSURE_FLAG = 0x10;

  // Javascript functions. It is important to use these copies, as the ones on
  // the global object may have been overwritten. See "V8 Extras Design Doc",
  // section "Security Considerations".
  // https://docs.google.com/document/d/1AT5-T0aHGp7Lt29vPWFr2-qG8r3l9CByyvKwEuA8Ec0/edit#heading=h.9yixony1a18r
  const defineProperty = global.Object.defineProperty;
  const ObjectCreate = global.Object.create;

  const Function_call = v8.uncurryThis(global.Function.prototype.call);

  const TypeError = global.TypeError;
  const RangeError = global.RangeError;

  const Boolean = global.Boolean;

  const Promise = global.Promise;
  const thenPromise = v8.uncurryThis(Promise.prototype.then);
  const Promise_resolve = Promise.resolve.bind(Promise);
  const Promise_reject = Promise.reject.bind(Promise);

  // From CommonOperations.js
  const {
    _queue,
    _queueTotalSize,
    hasOwnPropertyNoThrow,
    rejectPromise,
    resolvePromise,
    markPromiseAsHandled,
    promiseState,
    CreateAlgorithmFromUnderlyingMethod,
    CreateAlgorithmFromUnderlyingMethodPassingController,
    DequeueValue,
    EnqueueValueWithSize,
    MakeSizeAlgorithmFromSizeFunction,
    PeekQueueValue,
    ResetQueue,
    ValidateAndNormalizeHighWaterMark,
    CallOrNoop1,
  } = binding.streamOperations;

  // User-visible strings.
  const streamErrors = binding.streamErrors;
  const errAbortLockedStream =
        'Cannot abort a writable stream that is locked to a writer';
  const errWriterLockReleasedPrefix =
        'This writable stream writer has been released and cannot be ';
  const errCloseCloseRequestedStream = 'Cannot close a writable stream that ' +
        'has already been requested to be closed';
  const templateErrorCannotActionOnStateStream = (action, state) =>
        `Cannot ${action} a ${state} writable stream`;
  const errReleasedWriterClosedPromise = 'This writable stream writer has ' +
        'been released and cannot be used to monitor the stream\'s state';

  // These verbs are used after errWriterLockReleasedPrefix
  const verbUsedToGetTheDesiredSize = 'used to get the desiredSize';
  const verbAborted = 'aborted';
  const verbClosed = 'closed';
  const verbWrittenTo = 'written to';

  let useCounted = false;

  // Utility functions (not from the standard).
  function createWriterLockReleasedError(verb) {
    return new TypeError(errWriterLockReleasedPrefix + verb);
  }

  const stateNames = {
    [CLOSED]: 'closed',
    [ERRORED]: 'errored'
  };
  function createCannotActionOnStateStreamError(action, state) {
    // assert(stateNames[state] !== undefined,
    //        `name for state ${state} exists in stateNames`);
    return new TypeError(
        templateErrorCannotActionOnStateStream(action, stateNames[state]));
  }

  function rejectPromises(queue, e) {
    queue.forEach(promise => rejectPromise(promise, e));
  }

  class WritableStream {
    constructor(underlyingSink = {}, strategy = {}) {
      if (!useCounted) {
        binding.countUse('WritableStreamConstructor');
        useCounted = true;
      }

      InitializeWritableStream(this);
      const type = underlyingSink.type;
      const size = strategy.size;
      let highWaterMark = strategy.highWaterMark;
      if (type !== undefined) {
        throw new RangeError(streamErrors.invalidType);
      }
      const sizeAlgorithm = MakeSizeAlgorithmFromSizeFunction(size);
      if (highWaterMark === undefined) {
        highWaterMark = 1;
      }
      highWaterMark = ValidateAndNormalizeHighWaterMark(highWaterMark);
      SetUpWritableStreamDefaultControllerFromUnderlyingSink(
          this, underlyingSink, highWaterMark, sizeAlgorithm);
    }

    get locked() {
      if (!IsWritableStream(this)) {
        throw new TypeError(streamErrors.illegalInvocation);
      }
      return IsWritableStreamLocked(this);
    }

    abort(reason) {
      if (!IsWritableStream(this)) {
        return Promise_reject(new TypeError(streamErrors.illegalInvocation));
      }
      if (IsWritableStreamLocked(this)) {
        return Promise_reject(new TypeError(errAbortLockedStream));
      }
      return WritableStreamAbort(this, reason);
    }

    getWriter() {
      if (!IsWritableStream(this)) {
        throw new TypeError(streamErrors.illegalInvocation);
      }
      return AcquireWritableStreamDefaultWriter(this);
    }
  }

  const WritableStream_prototype = WritableStream.prototype;

  // General Writable Stream Abstract Operations

  function AcquireWritableStreamDefaultWriter(stream) {
    return new WritableStreamDefaultWriter(stream);
  }

  function CreateWritableStream(
      startAlgorithm, writeAlgorithm, closeAlgorithm, abortAlgorithm,
      highWaterMark, sizeAlgorithm) {
    if (highWaterMark === undefined) {
      highWaterMark = 1;
    }
    if (sizeAlgorithm === undefined) {
      sizeAlgorithm = () => 1;
    }
    // assert(IsNonNegativeNumber(highWaterMark),
    // '! IsNonNegativeNumber(_highWaterMark_) is *true*.')
    const stream = ObjectCreate(WritableStream_prototype);
    InitializeWritableStream(stream);
    const controller = ObjectCreate(WritableStreamDefaultController_prototype);
    SetUpWritableStreamDefaultController(
        stream, controller, startAlgorithm, writeAlgorithm, closeAlgorithm,
        abortAlgorithm, highWaterMark, sizeAlgorithm);
    return stream;
  }

  function InitializeWritableStream(stream) {
    stream[_stateAndFlags] = WRITABLE;
    stream[_storedError] = undefined;
    stream[_writer] = undefined;
    stream[_writableStreamController] = undefined;
    stream[_inFlightWriteRequest] = undefined;
    stream[_closeRequest] = undefined;
    stream[_inFlightCloseRequest] = undefined;
    stream[_pendingAbortRequest] = undefined;
    stream[_writeRequests] = new binding.SimpleQueue();
  }

  function IsWritableStream(x) {
    return hasOwnPropertyNoThrow(x, _writableStreamController);
  }

  function IsWritableStreamLocked(stream) {
    // assert(IsWritableStream(stream),
    //        '! IsWritableStream(stream) is true.');
    return stream[_writer] !== undefined;
  }

  function WritableStreamAbort(stream, reason) {
    const state = stream[_stateAndFlags] & STATE_MASK;
    if (state === CLOSED || state === ERRORED) {
      return Promise_resolve(undefined);
    }
    if (stream[_pendingAbortRequest] !== undefined) {
      return stream[_pendingAbortRequest].promise;
    }

    // assert(state === WRITABLE || state === ERRORING,
    //        '_state_ is `"writable"` or `"erroring"`');

    const wasAlreadyErroring = state === ERRORING;
    if (wasAlreadyErroring) {
      reason = undefined;
    }

    const promise = v8.createPromise();
    stream[_pendingAbortRequest] = {promise, reason, wasAlreadyErroring};

    if (!wasAlreadyErroring) {
      WritableStreamStartErroring(stream, reason);
    }
    return promise;
  }

  // Writable Stream Abstract Operations Used by Controllers

  function WritableStreamAddWriteRequest(stream) {
    // assert(IsWritableStreamLocked(stream),
    //        '! IsWritableStreamLocked(writer) is true.');
    // assert((stream[_stateAndFlags] & STATE_MASK) === WRITABLE,
    //        'stream.[[state]] is "writable".');
    const promise = v8.createPromise();
    stream[_writeRequests].push(promise);
    return promise;
  }

  function WritableStreamDealWithRejection(stream, error) {
    const state = stream[_stateAndFlags] & STATE_MASK;
    if (state === WRITABLE) {
      WritableStreamStartErroring(stream, error);
      return;
    }

    // assert(state === ERRORING, '_state_ is `"erroring"`');
    WritableStreamFinishErroring(stream);
  }

  function WritableStreamStartErroring(stream, reason) {
    // assert(stream[_storedError] === undefined,
    //        '_stream_.[[storedError]] is *undefined*');
    // assert((stream[_stateAndFlags] & STATE_MASK) === WRITABLE,
    //        '_stream_.[[state]] is `"writable"`');

    const controller = stream[_writableStreamController];
    // assert(controller !== undefined, '_controller_ is not *undefined*');

    stream[_stateAndFlags] = (stream[_stateAndFlags] & ~STATE_MASK) | ERRORING;
    stream[_storedError] = reason;

    const writer = stream[_writer];
    if (writer !== undefined) {
      WritableStreamDefaultWriterEnsureReadyPromiseRejected(writer, reason);
    }

    if (!WritableStreamHasOperationMarkedInFlight(stream) &&
        controller[_started]) {
      WritableStreamFinishErroring(stream);
    }
  }

  function WritableStreamFinishErroring(stream) {
    // assert((stream[_stateAndFlags] & STATE_MASK) === ERRORING,
    //        '_stream_.[[state]] is `"erroring"`');
    // assert(!WritableStreamHasOperationMarkedInFlight(stream),
    //        '! WritableStreamHasOperationMarkedInFlight(_stream_) is ' +
    //        '*false*');

    stream[_stateAndFlags] = (stream[_stateAndFlags] & ~STATE_MASK) | ERRORED;

    WritableStreamDefaultControllerErrorSteps(
        stream[_writableStreamController]);

    const storedError = stream[_storedError];
    rejectPromises(stream[_writeRequests], storedError);
    stream[_writeRequests] = new binding.SimpleQueue();

    if (stream[_pendingAbortRequest] === undefined) {
      WritableStreamRejectCloseAndClosedPromiseIfNeeded(stream);
      return;
    }

    const abortRequest = stream[_pendingAbortRequest];
    stream[_pendingAbortRequest] = undefined;

    if (abortRequest.wasAlreadyErroring === true) {
      rejectPromise(abortRequest.promise, storedError);
      WritableStreamRejectCloseAndClosedPromiseIfNeeded(stream);
      return;
    }

    const promise = WritableStreamDefaultControllerAbortSteps(
        stream[_writableStreamController], abortRequest.reason);

    thenPromise(
        promise,
        () => {
          resolvePromise(abortRequest.promise, undefined);
          WritableStreamRejectCloseAndClosedPromiseIfNeeded(stream);
        },
        reason => {
          rejectPromise(abortRequest.promise, reason);
          WritableStreamRejectCloseAndClosedPromiseIfNeeded(stream);
        });
  }

  function WritableStreamFinishInFlightWrite(stream) {
    // assert(stream[_inFlightWriteRequest] !== undefined,
    //        '_stream_.[[inFlightWriteRequest]] is not *undefined*.');
    resolvePromise(stream[_inFlightWriteRequest], undefined);
    stream[_inFlightWriteRequest] = undefined;
  }

  function WritableStreamFinishInFlightWriteWithError(stream, error) {
    // assert(stream[_inFlightWriteRequest] !== undefined,
    //        '_stream_.[[inFlightWriteRequest]] is not *undefined*.');
    rejectPromise(stream[_inFlightWriteRequest], error);
    stream[_inFlightWriteRequest] = undefined;

    // const state = stream[_stateAndFlags] & STATE_MASK;
    // assert(state === WRITABLE || state === ERRORING,
    //        '_stream_.[[state]] is `"writable"` or `"erroring"`');

    WritableStreamDealWithRejection(stream, error);
  }

  function WritableStreamFinishInFlightClose(stream) {
    // assert(stream[_inFlightCloseRequest] !== undefined,
    //        '_stream_.[[inFlightCloseRequest]] is not *undefined*.');
    resolvePromise(stream[_inFlightCloseRequest], undefined);
    stream[_inFlightCloseRequest] = undefined;

    const state = stream[_stateAndFlags] & STATE_MASK;
    // assert(state === WRITABLE || state === ERRORING,
    //        '_stream_.[[state]] is `"writable"` or `"erroring"`');

    if (state === ERRORING) {
      stream[_storedError] = undefined;
      if (stream[_pendingAbortRequest] !== undefined) {
        resolvePromise(stream[_pendingAbortRequest].promise, undefined);
        stream[_pendingAbortRequest] = undefined;
      }
    }

    stream[_stateAndFlags] = (stream[_stateAndFlags] & ~STATE_MASK) | CLOSED;
    const writer = stream[_writer];
    if (writer !== undefined) {
      resolvePromise(writer[_closedPromise], undefined);
    }

    // assert(stream[_pendingAbortRequest] === undefined,
    //        '_stream_.[[pendingAbortRequest]] is *undefined*');
    // assert(stream[_storedError] === undefined,
    //        '_stream_.[[storedError]] is *undefined*');
  }

  function WritableStreamFinishInFlightCloseWithError(stream, error) {
    // assert(stream[_inFlightCloseRequest] !== undefined,
    //        '_stream_.[[inFlightCloseRequest]] is not *undefined*.');
    rejectPromise(stream[_inFlightCloseRequest], error);
    stream[_inFlightCloseRequest] = undefined;

    // const state = stream[_stateAndFlags] & STATE_MASK;
    // assert(state === WRITABLE || state === ERRORING,
    //        '_stream_.[[state]] is `"writable"` or `"erroring"`');

    if (stream[_pendingAbortRequest] !== undefined) {
      rejectPromise(stream[_pendingAbortRequest].promise, error);
      stream[_pendingAbortRequest] = undefined;
    }

    WritableStreamDealWithRejection(stream, error);
  }

  function WritableStreamCloseQueuedOrInFlight(stream) {
    return stream[_closeRequest] !== undefined ||
        stream[_inFlightCloseRequest] !== undefined;
  }

  function WritableStreamHasOperationMarkedInFlight(stream) {
    return stream[_inFlightWriteRequest] !== undefined ||
        stream[_inFlightCloseRequest] !== undefined;
  }

  function WritableStreamMarkCloseRequestInFlight(stream) {
    // assert(stream[_inFlightCloseRequest] === undefined,
    //        '_stream_.[[inFlightCloseRequest]] is *undefined*.');
    // assert(stream[_closeRequest] !== undefined,
    //        '_stream_.[[closeRequest]] is not *undefined*.');
    stream[_inFlightCloseRequest] = stream[_closeRequest];
    stream[_closeRequest] = undefined;
  }

  function WritableStreamMarkFirstWriteRequestInFlight(stream) {
    // assert(stream[_inFlightWriteRequest] === undefined,
    //        '_stream_.[[inFlightWriteRequest]] is *undefined*.');
    // assert(stream[_writeRequests].length !== 0,
    //        '_stream_.[[writeRequests]] is not empty.');
    const writeRequest = stream[_writeRequests].shift();
    stream[_inFlightWriteRequest] = writeRequest;
  }

  function WritableStreamRejectCloseAndClosedPromiseIfNeeded(stream) {
    // assert((stream[_stateAndFlags] & STATE_MASK) === ERRORED,
    //        '_stream_.[[state]] is `"errored"`');

    if (stream[_closeRequest] !== undefined) {
      // assert(stream[_inFlightCloseRequest] === undefined,
      //        '_stream_.[[inFlightCloseRequest]] is *undefined*');
      rejectPromise(stream[_closeRequest], stream[_storedError]);
      stream[_closeRequest] = undefined;
    }

    const writer = stream[_writer];
    if (writer !== undefined) {
      rejectPromise(writer[_closedPromise], stream[_storedError]);
      markPromiseAsHandled(writer[_closedPromise]);
    }
  }

  function WritableStreamUpdateBackpressure(stream, backpressure) {
    // assert((stream[_stateAndFlags] & STATE_MASK) === WRITABLE,
    //        'stream.[[state]] is "writable".');
    // assert(!WritableStreamCloseQueuedOrInFlight(stream),
    //        'WritableStreamCloseQueuedOrInFlight(_stream_) is *false*.');
    const writer = stream[_writer];
    if (writer !== undefined &&
        backpressure !== Boolean(stream[_stateAndFlags] & BACKPRESSURE_FLAG)) {
      if (backpressure) {
        writer[_readyPromise] = v8.createPromise();
      } else {
        // assert(!backpressure, '_backpressure_ is *false*.');
        resolvePromise(writer[_readyPromise], undefined);
      }
    }
    if (backpressure) {
      stream[_stateAndFlags] |= BACKPRESSURE_FLAG;
    } else {
      stream[_stateAndFlags] &= ~BACKPRESSURE_FLAG;
    }
  }

  // Functions to expose internals for ReadableStream.pipeTo. These are not
  // part of the standard.
  function isWritableStreamErrored(stream) {
    // assert(
    //     IsWritableStream(stream), '! IsWritableStream(stream) is true.');
    return (stream[_stateAndFlags] & STATE_MASK) === ERRORED;
  }

  function isWritableStreamClosingOrClosed(stream) {
    // assert(
    //     IsWritableStream(stream), '! IsWritableStream(stream) is true.');
    return WritableStreamCloseQueuedOrInFlight(stream) ||
        (stream[_stateAndFlags] & STATE_MASK) === CLOSED;
  }

  function getWritableStreamStoredError(stream) {
    // assert(
    //     IsWritableStream(stream), '! IsWritableStream(stream) is true.');
    return stream[_storedError];
  }

  // Expose internals for TransformStream
  function isWritableStreamWritable(stream) {
    // assert(
    //     IsWritableStream(stream), '! IsWritableStream(stream) is true.');
    return  (stream[_stateAndFlags] & STATE_MASK) === WRITABLE;
  }

  function isWritableStreamErroring(stream) {
    // assert(
    //     IsWritableStream(stream), '! IsWritableStream(stream) is true.');
    return  (stream[_stateAndFlags] & STATE_MASK) === ERRORING;
  }

  function getWritableStreamController(stream) {
    // assert(
    //     IsWritableStream(stream), '! IsWritableStream(stream) is true.');
    return stream[_writableStreamController];
  }

  class WritableStreamDefaultWriter {
    constructor(stream) {
      if (!IsWritableStream(stream)) {
        throw new TypeError(streamErrors.illegalConstructor);
      }
      if (IsWritableStreamLocked(stream)) {
        throw new TypeError(streamErrors.illegalConstructor);
      }
      this[_ownerWritableStream] = stream;
      stream[_writer] = this;
      const state = stream[_stateAndFlags] & STATE_MASK;
      switch (state) {
        case WRITABLE: {
          if (!WritableStreamCloseQueuedOrInFlight(stream) &&
              stream[_stateAndFlags] & BACKPRESSURE_FLAG) {
            this[_readyPromise] = v8.createPromise();
          } else {
            this[_readyPromise] = Promise_resolve(undefined);
          }
          this[_closedPromise] = v8.createPromise();
          break;
        }

        case ERRORING: {
          this[_readyPromise] = Promise_reject(stream[_storedError]);
          markPromiseAsHandled(this[_readyPromise]);
          this[_closedPromise] = v8.createPromise();
          break;
        }

        case CLOSED: {
          this[_readyPromise] = Promise_resolve(undefined);
          this[_closedPromise] = Promise_resolve(undefined);
          break;
        }

        default: {
          // assert(state === ERRORED, '_state_ is `"errored"`.');
          const storedError = stream[_storedError];
          this[_readyPromise] = Promise_reject(storedError);
          markPromiseAsHandled(this[_readyPromise]);
          this[_closedPromise] = Promise_reject(storedError);
          markPromiseAsHandled(this[_closedPromise]);
          break;
        }
      }
    }

    get closed() {
      if (!IsWritableStreamDefaultWriter(this)) {
        return Promise_reject(new TypeError(streamErrors.illegalInvocation));
      }
      return this[_closedPromise];
    }

    get desiredSize() {
      if (!IsWritableStreamDefaultWriter(this)) {
        throw new TypeError(streamErrors.illegalInvocation);
      }
      if (this[_ownerWritableStream] === undefined) {
        throw createWriterLockReleasedError(verbUsedToGetTheDesiredSize);
      }
      return WritableStreamDefaultWriterGetDesiredSize(this);
    }

    get ready() {
      if (!IsWritableStreamDefaultWriter(this)) {
        return Promise_reject(new TypeError(streamErrors.illegalInvocation));
      }
      return this[_readyPromise];
    }

    abort(reason) {
      if (!IsWritableStreamDefaultWriter(this)) {
        return Promise_reject(new TypeError(streamErrors.illegalInvocation));
      }
      if (this[_ownerWritableStream] === undefined) {
        return Promise_reject(createWriterLockReleasedError(verbAborted));
      }
      return WritableStreamDefaultWriterAbort(this, reason);
    }

    close() {
      if (!IsWritableStreamDefaultWriter(this)) {
        return Promise_reject(new TypeError(streamErrors.illegalInvocation));
      }
      const stream = this[_ownerWritableStream];
      if (stream === undefined) {
        return Promise_reject(createWriterLockReleasedError(verbClosed));
      }
      if (WritableStreamCloseQueuedOrInFlight(stream)) {
        return Promise_reject(new TypeError(errCloseCloseRequestedStream));
      }
      return WritableStreamDefaultWriterClose(this);
    }

    releaseLock() {
      if (!IsWritableStreamDefaultWriter(this)) {
        throw new TypeError(streamErrors.illegalInvocation);
      }
      const stream = this[_ownerWritableStream];
      if (stream === undefined) {
        return;
      }
      // assert(stream[_writer] !== undefined,
      //        'stream.[[writer]] is not undefined.');
      WritableStreamDefaultWriterRelease(this);
    }

    write(chunk) {
      if (!IsWritableStreamDefaultWriter(this)) {
        return Promise_reject(new TypeError(streamErrors.illegalInvocation));
      }
      if (this[_ownerWritableStream] === undefined) {
        return Promise_reject(createWriterLockReleasedError(verbWrittenTo));
      }
      return WritableStreamDefaultWriterWrite(this, chunk);
    }
  }

  // Writable Stream Writer Abstract Operations

  function IsWritableStreamDefaultWriter(x) {
    return hasOwnPropertyNoThrow(x, _ownerWritableStream);
  }

  function WritableStreamDefaultWriterAbort(writer, reason) {
    const stream = writer[_ownerWritableStream];
    // assert(stream !== undefined,
    //        'stream is not undefined.');
    return WritableStreamAbort(stream, reason);
  }

  function WritableStreamDefaultWriterClose(writer) {
    const stream = writer[_ownerWritableStream];
    // assert(stream !== undefined, 'stream is not undefined.');
    const state = stream[_stateAndFlags] & STATE_MASK;
    if (state === CLOSED || state === ERRORED) {
      return Promise_reject(
          createCannotActionOnStateStreamError('close', state));
    }

    // assert(state === WRITABLE || state === ERRORING,
    //        '_state_ is `"writable"` or `"erroring"`.');
    // assert(!WritableStreamCloseQueuedOrInFlight(stream),
    //        '! WritableStreamCloseQueuedOrInFlight(_stream_) is *false*.');
    const promise = v8.createPromise();
    stream[_closeRequest] = promise;

    if ((stream[_stateAndFlags] & BACKPRESSURE_FLAG) && state === WRITABLE) {
      resolvePromise(writer[_readyPromise], undefined);
    }
    WritableStreamDefaultControllerClose(stream[_writableStreamController]);
    return promise;
  }

  function WritableStreamDefaultWriterCloseWithErrorPropagation(writer) {
    const stream = writer[_ownerWritableStream];
    // assert(stream !== undefined, 'stream is not undefined.');
    const state = stream[_stateAndFlags] & STATE_MASK;
    if (WritableStreamCloseQueuedOrInFlight(stream) || state === CLOSED) {
      return Promise_resolve(undefined);
    }
    if (state === ERRORED) {
      return Promise_reject(stream[_storedError]);
    }

    // assert(state === WRITABLE || state === ERRORING,
    //        '_state_ is `"writable"` or `"erroring"`.');

    return WritableStreamDefaultWriterClose(writer);
  }

  function WritableStreamDefaultWriterEnsureClosedPromiseRejected(
      writer, error) {
    if (promiseState(writer[_closedPromise]) === v8.kPROMISE_PENDING) {
      rejectPromise(writer[_closedPromise], error);
    } else {
      writer[_closedPromise] = Promise_reject(error);
    }
    markPromiseAsHandled(writer[_closedPromise]);
  }


  function WritableStreamDefaultWriterEnsureReadyPromiseRejected(
      writer, error) {
    if (promiseState(writer[_readyPromise]) === v8.kPROMISE_PENDING) {
      rejectPromise(writer[_readyPromise], error);
    } else {
      writer[_readyPromise] = Promise_reject(error);
    }
    markPromiseAsHandled(writer[_readyPromise]);
  }

  function WritableStreamDefaultWriterGetDesiredSize(writer) {
    const stream = writer[_ownerWritableStream];
    const state = stream[_stateAndFlags] & STATE_MASK;
    if (state === ERRORED || state === ERRORING) {
      return null;
    }
    if (state === CLOSED) {
      return 0;
    }
    return WritableStreamDefaultControllerGetDesiredSize(
        stream[_writableStreamController]);
  }

  function WritableStreamDefaultWriterRelease(writer) {
    const stream = writer[_ownerWritableStream];
    // assert(stream !== undefined,
    //        'stream is not undefined.');
    // assert(stream[_writer] === writer,
    //        'stream.[[writer]] is writer.');
    const releasedError = new TypeError(errReleasedWriterClosedPromise);
    WritableStreamDefaultWriterEnsureReadyPromiseRejected(
        writer, releasedError);
    WritableStreamDefaultWriterEnsureClosedPromiseRejected(
        writer, releasedError);
    stream[_writer] = undefined;
    writer[_ownerWritableStream] = undefined;
  }

  function WritableStreamDefaultWriterWrite(writer, chunk) {
    const stream = writer[_ownerWritableStream];
    // assert(stream !== undefined, 'stream is not undefined.');
    const controller = stream[_writableStreamController];
    const chunkSize =
          WritableStreamDefaultControllerGetChunkSize(controller, chunk);
    if (stream !== writer[_ownerWritableStream]) {
      return Promise_reject(createWriterLockReleasedError(verbWrittenTo));
    }
    const state = stream[_stateAndFlags] & STATE_MASK;
    if (state === ERRORED) {
      return Promise_reject(stream[_storedError]);
    }
    if (WritableStreamCloseQueuedOrInFlight(stream)) {
      return Promise_reject(new TypeError(
          templateErrorCannotActionOnStateStream('write to', 'closing')));
    }
    if (state === CLOSED) {
      return Promise_reject(
          createCannotActionOnStateStreamError('write to', CLOSED));
    }
    if (state === ERRORING) {
      return Promise_reject(stream[_storedError]);
    }
    // assert(state === WRITABLE, '_state_ is `"writable"`');
    const promise = WritableStreamAddWriteRequest(stream);
    WritableStreamDefaultControllerWrite(controller, chunk, chunkSize);
    return promise;
  }

  // Functions to expose internals for ReadableStream.pipeTo. These do not
  // appear in the standard.
  function getWritableStreamDefaultWriterClosedPromise(writer) {
    // assert(
    //     IsWritableStreamDefaultWriter(writer),
    //     'writer is a WritableStreamDefaultWriter.');
    return writer[_closedPromise];
  }

  function getWritableStreamDefaultWriterReadyPromise(writer) {
    // assert(
    //     IsWritableStreamDefaultWriter(writer),
    //     'writer is a WritableStreamDefaultWriter.');
    return writer[_readyPromise];
  }

  class WritableStreamDefaultController {
    constructor() {
      throw new TypeError(streamErrors.illegalConstructor);
    }

    error(e) {
      if (!IsWritableStreamDefaultController(this)) {
        throw new TypeError(streamErrors.illegalInvocation);
      }
      const state =
            this[_controlledWritableStream][_stateAndFlags] & STATE_MASK;
      if (state !== WRITABLE) {
        return;
      }
      WritableStreamDefaultControllerError(this, e);
    }
  }

  const WritableStreamDefaultController_prototype =
        WritableStreamDefaultController.prototype;

  // Writable Stream Default Controller Internal Methods

  // TODO(ricea): Virtual dispatch via V8 Private Symbols seems to be difficult
  // or impossible, so use static dispatch for now. This will have to be fixed
  // when adding a byte controller.
  function WritableStreamDefaultControllerAbortSteps(controller, reason) {
    return controller[_abortAlgorithm](reason);
  }

  function WritableStreamDefaultControllerErrorSteps(controller) {
    ResetQueue(controller);
  }

  // Writable Stream Default Controller Abstract Operations

  function IsWritableStreamDefaultController(x) {
    return hasOwnPropertyNoThrow(x, _controlledWritableStream);
  }

  function SetUpWritableStreamDefaultController(
      stream, controller, startAlgorithm, writeAlgorithm, closeAlgorithm,
      abortAlgorithm, highWaterMark, sizeAlgorithm) {
    // assert(IsWritableStream(stream), '! IsWritableStream(_stream_) is
    // *true*.');
    // assert(stream[_writableStreamController] === undefined,
    //        '_stream_.[[writableStreamController]] is *undefined*.');
    controller[_controlledWritableStream] = stream;
    stream[_writableStreamController] = controller;
    // These are just initialised to avoid triggering the assert() in
    // ResetQueue. They are overwritten by ResetQueue().
    controller[_queue] = undefined;
    controller[_queueTotalSize] = undefined;
    ResetQueue(controller);
    controller[_started] = false;
    controller[_strategySizeAlgorithm] = sizeAlgorithm;
    controller[_strategyHWM] = highWaterMark;
    controller[_writeAlgorithm] = writeAlgorithm;
    controller[_closeAlgorithm] = closeAlgorithm;
    controller[_abortAlgorithm] = abortAlgorithm;
    const backpressure =
          WritableStreamDefaultControllerGetBackpressure(controller);
    WritableStreamUpdateBackpressure(stream, backpressure);
    const startResult = startAlgorithm();
    const startPromise = Promise_resolve(startResult);
    thenPromise(
        startPromise,
        () => {
          // const state = stream[_stateAndFlags] & STATE_MASK;
          // assert(state === WRITABLE || state === ERRORING,
          //        '_stream_.[[state]] is `"writable"` or `"erroring"`');
          controller[_started] = true;
          WritableStreamDefaultControllerAdvanceQueueIfNeeded(controller);
        },
        r => {
          // const state = stream[_stateAndFlags] & STATE_MASK;
          // assert(state === WRITABLE || state === ERRORING,
          //        '_stream_.[[state]] is `"writable"` or `"erroring"`');
          controller[_started] = true;
          WritableStreamDealWithRejection(stream, r);
        });
  }

  function SetUpWritableStreamDefaultControllerFromUnderlyingSink(
      stream, underlyingSink, highWaterMark, sizeAlgorithm) {
    // assert(underlyingSink !== undefined, '_underlyingSink_ is not ' +
    // '*undefined*.');
    const controller = ObjectCreate(WritableStreamDefaultController_prototype);
    const startAlgorithm =
          () => CallOrNoop1(underlyingSink, 'start', controller,
                            'underlyingSink.start');
    const writeAlgorithm = CreateAlgorithmFromUnderlyingMethodPassingController(
        underlyingSink, 'write', 1, controller, 'underlyingSink.write');
    const closeAlgorithm = CreateAlgorithmFromUnderlyingMethod(
        underlyingSink, 'close', 0, 'underlyingSink.close');
    const abortAlgorithm = CreateAlgorithmFromUnderlyingMethod(
        underlyingSink, 'abort', 1, 'underlyingSink.abort');
    SetUpWritableStreamDefaultController(stream, controller, startAlgorithm,
        writeAlgorithm, closeAlgorithm, abortAlgorithm, highWaterMark,
        sizeAlgorithm);
  }

  function WritableStreamDefaultControllerClose(controller) {
    EnqueueValueWithSize(controller, 'close', 0);
    WritableStreamDefaultControllerAdvanceQueueIfNeeded(controller);
  }

  function WritableStreamDefaultControllerGetChunkSize(controller, chunk) {
    try {
      // Unlike other algorithms, strategySizeAlgorithm isn't indirected, so we
      // need to be careful with the |this| value.
      return Function_call(controller[_strategySizeAlgorithm], undefined,
                           chunk);
    } catch (e) {
      WritableStreamDefaultControllerErrorIfNeeded(controller, e);
      return 1;
    }
  }

  function WritableStreamDefaultControllerGetDesiredSize(controller) {
    return controller[_strategyHWM] - controller[_queueTotalSize];
  }

  function WritableStreamDefaultControllerWrite(controller, chunk, chunkSize) {
    const writeRecord = {chunk};
    try {
      EnqueueValueWithSize(controller, writeRecord, chunkSize);
    } catch (e) {
      WritableStreamDefaultControllerErrorIfNeeded(controller, e);
      return;
    }
    const stream = controller[_controlledWritableStream];
    if (!WritableStreamCloseQueuedOrInFlight(stream) &&
        (stream[_stateAndFlags] & STATE_MASK) === WRITABLE) {
      const backpressure =
            WritableStreamDefaultControllerGetBackpressure(controller);
      WritableStreamUpdateBackpressure(stream, backpressure);
    }
    WritableStreamDefaultControllerAdvanceQueueIfNeeded(controller);
  }

  function WritableStreamDefaultControllerAdvanceQueueIfNeeded(controller) {
    const stream = controller[_controlledWritableStream];
    if (!controller[_started]) {
      return;
    }
    if (stream[_inFlightWriteRequest] !== undefined) {
      return;
    }
    const state = stream[_stateAndFlags] & STATE_MASK;
    if (state === CLOSED || state === ERRORED) {
      return;
    }
    if (state === ERRORING) {
      WritableStreamFinishErroring(stream);
      return;
    }
    if (controller[_queue].length === 0) {
      return;
    }
    const writeRecord = PeekQueueValue(controller);
    if (writeRecord === 'close') {
      WritableStreamDefaultControllerProcessClose(controller);
    } else {
      WritableStreamDefaultControllerProcessWrite(
          controller, writeRecord.chunk);
    }
  }

  function WritableStreamDefaultControllerErrorIfNeeded(controller, error) {
    const state =
          controller[_controlledWritableStream][_stateAndFlags] & STATE_MASK;
    if (state === WRITABLE) {
      WritableStreamDefaultControllerError(controller, error);
    }
  }

  function WritableStreamDefaultControllerProcessClose(controller) {
    const stream = controller[_controlledWritableStream];
    WritableStreamMarkCloseRequestInFlight(stream);
    DequeueValue(controller);
    // assert(controller[_queue].length === 0,
    //        'controller.[[queue]] is empty.');
    const sinkClosePromise = controller[_closeAlgorithm]();
    thenPromise(
        sinkClosePromise, () => WritableStreamFinishInFlightClose(stream),
        reason => WritableStreamFinishInFlightCloseWithError(stream, reason));
  }

  function WritableStreamDefaultControllerProcessWrite(controller, chunk) {
    const stream = controller[_controlledWritableStream];
    WritableStreamMarkFirstWriteRequestInFlight(stream);
    const sinkWritePromise = controller[_writeAlgorithm](chunk);
    thenPromise(
        sinkWritePromise,
        () => {
          WritableStreamFinishInFlightWrite(stream);
          const state = stream[_stateAndFlags] & STATE_MASK;
          // assert(state === WRITABLE || state === ERRORING,
          //        '_state_ is `"writable"` or `"erroring"`');
          DequeueValue(controller);
          if (!WritableStreamCloseQueuedOrInFlight(stream) &&
              state === WRITABLE) {
            const backpressure =
                  WritableStreamDefaultControllerGetBackpressure(controller);
            WritableStreamUpdateBackpressure(stream, backpressure);
          }
          WritableStreamDefaultControllerAdvanceQueueIfNeeded(controller);
        },
        reason => {
          WritableStreamFinishInFlightWriteWithError(stream, reason);
        });
  }

  function WritableStreamDefaultControllerGetBackpressure(controller) {
    const desiredSize =
          WritableStreamDefaultControllerGetDesiredSize(controller);
    return desiredSize <= 0;
  }

  function WritableStreamDefaultControllerError(controller, error) {
    const stream = controller[_controlledWritableStream];
    // assert((stream[_stateAndFlags] & STATE_MASK) === WRITABLE,
    //        '_stream_.[[state]] is `"writable"`.');
    WritableStreamStartErroring(stream, error);
  }

  //
  // Additions to the global object
  //

  defineProperty(global, 'WritableStream', {
    value: WritableStream,
    enumerable: false,
    configurable: true,
    writable: true
  });

  // TODO(ricea): Exports to Blink

  // Exports for ReadableStream
  binding.AcquireWritableStreamDefaultWriter =
      AcquireWritableStreamDefaultWriter;
  binding.IsWritableStream = IsWritableStream;
  binding.isWritableStreamClosingOrClosed = isWritableStreamClosingOrClosed;
  binding.isWritableStreamErrored = isWritableStreamErrored;
  binding.IsWritableStreamLocked = IsWritableStreamLocked;
  binding.WritableStreamAbort = WritableStreamAbort;
  binding.WritableStreamDefaultWriterCloseWithErrorPropagation =
      WritableStreamDefaultWriterCloseWithErrorPropagation;
  binding.getWritableStreamDefaultWriterClosedPromise =
      getWritableStreamDefaultWriterClosedPromise;
  binding.WritableStreamDefaultWriterGetDesiredSize =
      WritableStreamDefaultWriterGetDesiredSize;
  binding.getWritableStreamDefaultWriterReadyPromise =
      getWritableStreamDefaultWriterReadyPromise;
  binding.WritableStreamDefaultWriterRelease =
      WritableStreamDefaultWriterRelease;
  binding.WritableStreamDefaultWriterWrite = WritableStreamDefaultWriterWrite;
  binding.getWritableStreamStoredError = getWritableStreamStoredError;

  // Exports for TransformStream
  binding.CreateWritableStream = CreateWritableStream;
  binding.WritableStream = WritableStream;
  binding.WritableStreamDefaultControllerErrorIfNeeded =
      WritableStreamDefaultControllerErrorIfNeeded;
  binding.isWritableStreamWritable = isWritableStreamWritable;
  binding.isWritableStreamErroring = isWritableStreamErroring;
  binding.getWritableStreamController = getWritableStreamController;
});