Implement author-constructible ReadableStream using V8 extras

third_party/WebKit/Source/core/streams/ReadableStream.js

+// Copyright 2015 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.
+
+(function(global, binding, v8) {
+  'use strict';
+
+  const readableStreamController = v8.createPrivateSymbol('[[controller]]');
+  const readableStreamQueue = v8.createPrivateSymbol('[[queue]]');
+  const readableStreamQueueSize =
+      v8.createPrivateSymbol('[[queue]] total size');
+  const readableStreamReader = v8.createPrivateSymbol('[[reader]]');
+  const readableStreamState = v8.createPrivateSymbol('[[state]]');
+  const readableStreamStoredError = v8.createPrivateSymbol('[[storedError]]');
+  const readableStreamStrategySize = v8.createPrivateSymbol('[[strategySize]]');
+  const readableStreamStrategyHWM = v8.createPrivateSymbol('[[strategyHWM]]');
+  const readableStreamUnderlyingSource =
+      v8.createPrivateSymbol('[[underlyingSource]]');
+
+  const readableStreamControllerControlledReadableStream =
+      v8.createPrivateSymbol('[[controlledReadableStream]]');
+
+  const readableStreamReaderClosedPromise =
+      v8.createPrivateSymbol('[[closedPromise]]');
+  const readableStreamReaderOwnerReadableStream =
+      v8.createPrivateSymbol('[[ownerReadableStream]]');
+  const readableStreamReaderReadRequests =
+      v8.createPrivateSymbol('[[readRequests]]');
+
+  const STATE_READABLE = 0;
+  const STATE_CLOSED = 1;
+  const STATE_ERRORED = 2;
+
+  const readableStreamBits = v8.createPrivateSymbol(
+      'bit field for [[started]], [[closeRequested]], [[pulling]], [[pullAgain]], [[disturbed]]');
+  const STARTED = 0b1;
+  const CLOSE_REQUESTED = 0b10;
+  const PULLING = 0b100;
+  const PULL_AGAIN = 0b1000;
+  const DISTURBED = 0b10000;
+
+  const undefined = global.undefined;
+  const Infinity = global.Infinity;
+
+  const defineProperty = global.Object.defineProperty;
+  const hasOwnProperty = v8.uncurryThis(global.Object.hasOwnProperty);
+  const callFunction = v8.uncurryThis(global.Function.prototype.call);
+
+  const TypeError = global.TypeError;
+  const RangeError = global.RangeError;
+
+  const Number = global.Number;
+  const Number_isNaN = Number.isNaN;
+  const Number_isFinite = Number.isFinite;
+
+  const Promise = global.Promise;
+  const thenPromise = v8.uncurryThis(Promise.prototype.then);
+  const Promise_resolve = v8.simpleBind(Promise.resolve, Promise);
+  const Promise_reject = v8.simpleBind(Promise.reject, Promise);
+
+  const errIllegalInvocation = 'Illegal invocation';
+  const errIllegalConstructor = 'Illegal constructor';
+  const errCancelLockedStream =
+      'Cannot cancel a readable stream that is locked to a reader';
+  const errEnqueueInCloseRequestedStream =
+      'Cannot enqueue a chunk into a readable stream that is closed or has been requested to be closed';
+  const errCancelReleasedReader =
+      'This readable stream reader has been released and cannot be used to cancel its previous owner stream';
+  const errReadReleasedReader =
+      'This readable stream reader has been released and cannot be used to read from its previous owner stream';
+  const errCloseCloseRequestedStream =
+      'Cannot close a readable stream that has already been requested to be closed';
+  const errCloseErroredStream = 'Cannot close an errored readable stream';
+  const errErrorClosedStream = 'Cannot error a close readable stream';
+  const errErrorErroredStream =
+      'Cannot error a readable stream that is already errored';
+  const errReaderConstructorBadArgument =
+      'ReadableStreamReader constructor argument is not a readable stream';
+  const errReaderConstructorStreamAlreadyLocked =
+      'ReadableStreamReader constructor can only accept readable streams that are not yet locked to a reader';
+  const errReleaseReaderWithPendingRead =
+      'Cannot release a readable stream reader when it still has outstanding read() calls that have not yet settled';
+  const errReleasedReaderClosedPromise =
+      'This readable stream reader has been released and cannot be used to monitor the stream\'s state';
+  const errInvalidSize =
+      'The return value of a queuing strategy\'s size function must be a finite, non-NaN, non-negative number';
+  const errSizeNotAFunction =
+      'A queuing strategy\'s size property must be a function';
+  const errInvalidHWM =
+      'A queueing strategy\'s highWaterMark property must be a nonnegative, non-NaN number';
+  const errTmplMustBeFunctionOrUndefined = name =>
+      `${name} must be a function or undefined`;
+
+  class ReadableStream {
+    constructor() {
+      // TODO(domenic): when V8 gets default parameters and destructuring, all
+      // this can be cleaned up.
+      const underlyingSource = arguments[0] === undefined ? {} : arguments[0];
+      const strategy = arguments[1] === undefined ? {} : arguments[1];
+      const size = strategy.size;
+      let highWaterMark = strategy.highWaterMark;
+      if (highWaterMark === undefined) {
+        highWaterMark = 1;
+      }
+
+      const normalizedStrategy =
+          ValidateAndNormalizeQueuingStrategy(size, highWaterMark);
+
+      this[readableStreamUnderlyingSource] = underlyingSource;
+
+      this[readableStreamQueue] = new v8.InternalPackedArray();
+      this[readableStreamQueueSize] = 0;
+
+      this[readableStreamState] = STATE_READABLE;
+      this[readableStreamBits] = 0b0;
+      this[readableStreamReader] = undefined;
+      this[readableStreamStoredError] = undefined;
+
+      this[readableStreamStrategySize] = normalizedStrategy.size;
+      this[readableStreamStrategyHWM] = normalizedStrategy.highWaterMark;
+
+      const controller = new ReadableStreamController(this);
+      this[readableStreamController] = controller;
+
+      const startResult = CallOrNoop(
+          underlyingSource, 'start', controller, 'underlyingSource.start');
+      thenPromise(Promise_resolve(startResult),
+          () => {
+            this[readableStreamBits] |= STARTED;
+            RequestReadableStreamPull(this);
+          },
+          r => {
+            if (this[readableStreamState] === STATE_READABLE) {
+              return ErrorReadableStream(this, r);
+            }
+          });
+    }
+
+    get locked() {
+      if (IsReadableStream(this) === false) {
+        throw new TypeError(errIllegalInvocation);
+      }
+
+      return IsReadableStreamLocked(this);
+    }
+
+    cancel(reason) {
+      if (IsReadableStream(this) === false) {
+        return Promise_reject(new TypeError(errIllegalInvocation));
+      }
+
+      if (IsReadableStreamLocked(this) === true) {
+        return Promise_reject(new TypeError(errCancelLockedStream));
+      }
+
+      return CancelReadableStream(this, reason);
+    }
+
+    getReader() {
+      if (IsReadableStream(this) === false) {
+        throw new TypeError(errIllegalInvocation);
+      }
+
+      return AcquireReadableStreamReader(this);
+    }
+
+    tee() {
+      if (IsReadableStream(this) === false) {
+        throw new TypeError(errIllegalInvocation);
+      }
+
+      return TeeReadableStream(this);
+    }
+  }
+
+  class ReadableStreamController {
+    constructor(stream) {
+      if (IsReadableStream(stream) === false) {
+        throw new TypeError(errIllegalConstructor);
+      }
+
+      if (stream[readableStreamController] !== undefined) {
+        throw new TypeError(errIllegalConstructor);
+      }
+
+      this[readableStreamControllerControlledReadableStream] = stream;
+    }
+
+    get desiredSize() {
+      if (IsReadableStreamController(this) === false) {
+        throw new TypeError(errIllegalInvocation);
+      }
+
+      return GetReadableStreamDesiredSize(
+          this[readableStreamControllerControlledReadableStream]);
+    }
+
+    close() {
+      if (IsReadableStreamController(this) === false) {
+        throw new TypeError(errIllegalInvocation);
+      }
+
+      const stream = this[readableStreamControllerControlledReadableStream];
+
+      if (stream[readableStreamBits] & CLOSE_REQUESTED) {
+        throw new TypeError(errCloseCloseRequestedStream);
+      }
+      if (stream[readableStreamState] === STATE_ERRORED) {
+        throw new TypeError(errCloseErroredStream);
+      }
+
+      return CloseReadableStream(stream);
+    }
+
+    enqueue(chunk) {
+      if (IsReadableStreamController(this) === false) {
+        throw new TypeError(errIllegalInvocation);
+      }
+
+      const stream = this[readableStreamControllerControlledReadableStream];
+
+      if (stream[readableStreamState] === STATE_ERRORED) {
+        throw stream[readableStreamStoredError];
+      }
+
+      if (stream[readableStreamBits] & CLOSE_REQUESTED) {
+        throw new TypeError(errEnqueueInCloseRequestedStream);
+      }
+
+      return EnqueueInReadableStream(stream, chunk);
+    }
+
+    error(e) {
+      if (IsReadableStreamController(this) === false) {
+        throw new TypeError(errIllegalInvocation);
+      }
+
+      const stream = this[readableStreamControllerControlledReadableStream];
+
+      const state = stream[readableStreamState];
+      if (state !== STATE_READABLE) {
+        if (state === STATE_ERRORED) {
+          throw new TypeError(errErrorErroredStream);
+        }
+        if (state === STATE_CLOSED) {
+          throw new TypeError(errErrorClosedStream);
+        }
+      }
+
+      return ErrorReadableStream(stream, e);
+    }
+  }
+
+  class ReadableStreamReader {
+    constructor(stream) {
+      if (IsReadableStream(stream) === false) {
+        throw new TypeError(errReaderConstructorBadArgument);
+      }
+      if (IsReadableStreamLocked(stream) === true) {
+        throw new TypeError(errReaderConstructorStreamAlreadyLocked);
+      }
+
+      this[readableStreamReaderOwnerReadableStream] = stream;
+      stream[readableStreamReader] = this;
+
+      this[readableStreamReaderReadRequests] = new v8.InternalPackedArray();
+
+      switch (stream[readableStreamState]) {
+        case STATE_READABLE:
+          this[readableStreamReaderClosedPromise] = v8.createPromise();
+          break;
+        case STATE_CLOSED:
+          this[readableStreamReaderClosedPromise] = Promise_resolve(undefined);
+          break;
+        case STATE_ERRORED:
+          this[readableStreamReaderClosedPromise] =
+              Promise_reject(stream[readableStreamStoredError]);
+          break;
+      }
+    }
+
+    get closed() {
+      if (IsReadableStreamReader(this) === false) {
+        return Promise_reject(new TypeError(errIllegalInvocation));
+      }
+
+      return this[readableStreamReaderClosedPromise];
+    }
+
+    cancel(reason) {
+      if (IsReadableStreamReader(this) === false) {
+        return Promise_reject(new TypeError(errIllegalInvocation));
+      }
+
+      const stream = this[readableStreamReaderOwnerReadableStream];
+      if (stream === undefined) {
+        return Promise_reject(new TypeError(errCancelReleasedReader));
+      }
+
+      return CancelReadableStream(stream, reason);
+    }
+
+    read() {
+      if (IsReadableStreamReader(this) === false) {
+        return Promise_reject(new TypeError(errIllegalInvocation));
+      }
+
+      if (this[readableStreamReaderOwnerReadableStream] === undefined) {
+        return Promise_reject(new TypeError(errReadReleasedReader));
+      }
+
+      return ReadFromReadableStreamReader(this);
+    }
+
+    releaseLock() {
+      if (IsReadableStreamReader(this) === false) {
+        throw new TypeError(errIllegalInvocation);
+      }
+
+      const stream = this[readableStreamReaderOwnerReadableStream];
+      if (stream === undefined) {
+        return undefined;
+      }
+
+      if (this[readableStreamReaderReadRequests].length > 0) {
+        throw new TypeError(errReleaseReaderWithPendingRead);
+      }
+
+      if (stream[readableStreamState] === STATE_READABLE) {
+        v8.rejectPromise(this[readableStreamReaderClosedPromise],
+            new TypeError(errReleasedReaderClosedPromise));
+      } else {
+        this[readableStreamReaderClosedPromise] = Promise_reject(new TypeError(
+            errReleasedReaderClosedPromise));
+      }
+
+      this[readableStreamReaderOwnerReadableStream][readableStreamReader] =
+          undefined;
+      this[readableStreamReaderOwnerReadableStream] = undefined;
+    }
+  }
+
+  //
+  // Readable stream abstract operations
+  //
+
+  function AcquireReadableStreamReader(stream) {
+    return new ReadableStreamReader(stream);
+  }
+
+  function CancelReadableStream(stream, reason) {
+    stream[readableStreamBits] |= DISTURBED;
+
+    const state = stream[readableStreamState];
+    if (state === STATE_CLOSED) {
+      return Promise_resolve(undefined);
+    }
+    if (state === STATE_ERRORED) {
+      return Promise_reject(stream[readableStreamStoredError]);
+    }
+
+    stream[readableStreamQueue] = new v8.InternalPackedArray();
+    FinishClosingReadableStream(stream);
+
+    const underlyingSource = stream[readableStreamUnderlyingSource];
+    const sourceCancelPromise = PromiseCallOrNoop(
+        underlyingSource, 'cancel', reason, 'underlyingSource.cancel');
+    return thenPromise(sourceCancelPromise, () => undefined);
+  }
+
+  function CloseReadableStream(stream) {
+    if (stream[readableStreamState] === STATE_CLOSED) {
+      return undefined;
+    }
+
+    stream[readableStreamBits] |= CLOSE_REQUESTED;
+
+    if (stream[readableStreamQueue].length === 0) {
+      return FinishClosingReadableStream(stream);
+    }
+  }
+
+  function EnqueueInReadableStream(stream, chunk) {
+    if (stream[readableStreamState] === STATE_CLOSED) {
+      return undefined;
+    }
+
+    if (IsReadableStreamLocked(stream) === true &&
+        stream[readableStreamReader][readableStreamReaderReadRequests].length >
+            0) {
+      const readRequest =
+          stream[readableStreamReader][readableStreamReaderReadRequests]
+              .shift();
+      v8.resolvePromise(readRequest, CreateIterResultObject(chunk, false));
+    } else {
+      let chunkSize = 1;
+
+      const strategySize = stream[readableStreamStrategySize];
+      if (strategySize !== undefined) {
+        try {
+          chunkSize = strategySize(chunk);
+        } catch (chunkSizeE) {
+          ErrorReadableStream(stream, chunkSizeE);
+          throw chunkSizeE;
+        }
+      }
+
+      try {
+        EnqueueValueWithSize(stream, chunk, chunkSize);
+      } catch (enqueueE) {
+        ErrorReadableStream(stream, enqueueE);
+        throw enqueueE;
+      }
+    }
+
+    RequestReadableStreamPull(stream);
+  }
+
+  function ErrorReadableStream(stream, e) {
+    stream[readableStreamQueue] = new v8.InternalPackedArray();
+    stream[readableStreamStoredError] = e;
+    stream[readableStreamState] = STATE_ERRORED;
+
+    const reader = stream[readableStreamReader];
+    if (reader === undefined) {
+      return undefined;
+    }
+
+    const readRequests = reader[readableStreamReaderReadRequests];
+    for (let i = 0; i < readRequests.length; ++i) {
+      v8.rejectPromise(readRequests[i], e);
+    }
+    reader[readableStreamReaderReadRequests] = new v8.InternalPackedArray();
+
+    v8.rejectPromise(reader[readableStreamReaderClosedPromise], e);
+  }
+
+  function FinishClosingReadableStream(stream) {
+    stream[readableStreamState] = STATE_CLOSED;
+
+    const reader = stream[readableStreamReader];
+    if (reader === undefined) {
+      return undefined;
+    }
+
+
+    const readRequests = reader[readableStreamReaderReadRequests];
+    for (let i = 0; i < readRequests.length; ++i) {
+      v8.resolvePromise(
+          readRequests[i], CreateIterResultObject(undefined, true));
+    }
+    reader[readableStreamReaderReadRequests] = new v8.InternalPackedArray();
+
+    v8.resolvePromise(reader[readableStreamReaderClosedPromise], undefined);
+  }
+
+  function GetReadableStreamDesiredSize(stream) {
+    const queueSize = GetTotalQueueSize(stream);
+    return stream[readableStreamStrategyHWM] - queueSize;
+  }
+
+  function IsReadableStream(x) {
+    return hasOwnProperty(x, readableStreamUnderlyingSource);
+  }
+
+  function IsReadableStreamDisturbed(stream) {
+    return stream[readableStreamBits] & DISTURBED;
+  }
+
+  function IsReadableStreamLocked(stream) {
+    return stream[readableStreamReader] !== undefined;
+  }
+
+  function IsReadableStreamController(x) {
+    return hasOwnProperty(x, readableStreamControllerControlledReadableStream);
+  }
+
+  function IsReadableStreamReader(x) {
+    return hasOwnProperty(x, readableStreamReaderOwnerReadableStream);
+  }
+
+  function ReadFromReadableStreamReader(reader) {
+    const stream = reader[readableStreamReaderOwnerReadableStream];
+    stream[readableStreamBits] |= DISTURBED;
+
+    if (stream[readableStreamState] === STATE_CLOSED) {
+      return Promise_resolve(CreateIterResultObject(undefined, true));
+    }
+
+    if (stream[readableStreamState] === STATE_ERRORED) {
+      return Promise_reject(stream[readableStreamStoredError]);
+    }
+
+    const queue = stream[readableStreamQueue];
+    if (queue.length > 0) {
+      const chunk = DequeueValue(stream);
+
+      if (stream[readableStreamBits] & CLOSE_REQUESTED && queue.length === 0) {
+        FinishClosingReadableStream(stream);
+      } else {
+        RequestReadableStreamPull(stream);
+      }
+
+      return Promise_resolve(CreateIterResultObject(chunk, false));
+    } else {
+      const readRequest = v8.createPromise();
+
+      reader[readableStreamReaderReadRequests].push(readRequest);
+      RequestReadableStreamPull(stream);
+      return readRequest;
+    }
+  }
+
+  function RequestReadableStreamPull(stream) {
+    const shouldPull = ShouldReadableStreamPull(stream);
+    if (shouldPull === false) {
+      return undefined;
+    }
+
+    if (stream[readableStreamBits] & PULLING) {
+      stream[readableStreamBits] |= PULL_AGAIN;
+      return undefined;
+    }
+
+    stream[readableStreamBits] |= PULLING;
+
+    const underlyingSource = stream[readableStreamUnderlyingSource];
+    const controller = stream[readableStreamController];
+    const pullPromise = PromiseCallOrNoop(
+        underlyingSource, 'pull', controller, 'underlyingSource.pull');
+
+    thenPromise(pullPromise,
+        () => {
+          stream[readableStreamBits] &= ~PULLING;
+
+          if (stream[readableStreamBits] & PULL_AGAIN) {
+            stream[readableStreamBits] &= ~PULL_AGAIN;
+            return RequestReadableStreamPull(stream);
+          }
+        },
+        e => {
+          if (stream[readableStreamState] === STATE_READABLE) {
+            return ErrorReadableStream(stream, e);
+          }
+        });
+  }
+
+  function ShouldReadableStreamPull(stream) {
+    const state = stream[readableStreamState];
+    if (state === STATE_CLOSED || state === STATE_ERRORED) {
+      return false;
+    }
+
+    if (stream[readableStreamBits] & CLOSE_REQUESTED) {
+      return false;
+    }
+
+    if (!(stream[readableStreamBits] & STARTED)) {
+      return false;
+    }
+
+    if (IsReadableStreamLocked(stream) === true) {
+      const reader = stream[readableStreamReader];
+      const readRequests = reader[readableStreamReaderReadRequests];
+      if (readRequests.length > 0) {
+        return true;
+      }
+    }
+
+    const desiredSize = GetReadableStreamDesiredSize(stream);
+    if (desiredSize > 0) {
+      return true;
+    }
+
+    return false;
+  }
+
+  // Potential future optimization: use class instances for the underlying
+  // sources, so that we don't re-create
+  // closures every time.
+
+  // TODO(domenic): shouldClone argument from spec not supported yet
+  function TeeReadableStream(stream) {
+    const reader = AcquireReadableStreamReader(stream);
+
+    let closedOrErrored = false;
+    let canceled1 = false;
+    let canceled2 = false;
+    let reason1;
+    let reason2;
+    let promise = v8.createPromise();
+
+    const branch1 = new ReadableStream({pull, cancel: cancel1});
+
+    const branch2 = new ReadableStream({pull, cancel: cancel2});
+
+    thenPromise(
+        reader[readableStreamReaderClosedPromise], undefined, function(r) {
+          if (closedOrErrored === true) {
+            return;
+          }
+
+          ErrorReadableStream(branch1, r);
+          ErrorReadableStream(branch2, r);
+          closedOrErrored = true;
+        });
+
+    return [branch1, branch2];
+
+
+    function pull() {
+      return thenPromise(
+          ReadFromReadableStreamReader(reader), function(result) {
+            const value = result.value;
+            const done = result.done;
+
+            if (done === true && closedOrErrored === false) {
+              CloseReadableStream(branch1);
+              CloseReadableStream(branch2);
+              closedOrErrored = true;
+            }
+
+            if (closedOrErrored === true) {
+              return;
+            }
+
+            if (canceled1 === false) {
+              EnqueueInReadableStream(branch1, value);
+            }
+
+            if (canceled2 === false) {
+              EnqueueInReadableStream(branch2, value);
+            }
+          });
+    }
+
+    function cancel1(reason) {
+      canceled1 = true;
+      reason1 = reason;
+
+      if (canceled2 === true) {
+        const compositeReason = [reason1, reason2];
+        const cancelResult = CancelReadableStream(stream, compositeReason);
+        v8.resolvePromise(promise, cancelResult);
+      }
+
+      return promise;
+    }
+
+    function cancel2(reason) {
+      canceled2 = true;
+      reason2 = reason;
+
+      if (canceled1 === true) {
+        const compositeReason = [reason1, reason2];
+        const cancelResult = CancelReadableStream(stream, compositeReason);
+        v8.resolvePromise(promise, cancelResult);
+      }
+
+      return promise;
+    }
+  }
+
+  //
+  // Queue-with-sizes
+  // Modified from taking the queue (as in the spec) to taking the stream, so we
+  // can modify the queue size alongside.
+  //
+
+  function DequeueValue(stream) {
+    const result = stream[readableStreamQueue].shift();
+    stream[readableStreamQueueSize] -= result.size;
+    return result.value;
+  }
+
+  function EnqueueValueWithSize(stream, value, size) {
+    size = Number(size);
+    if (Number_isNaN(size) || size === +Infinity || size < 0) {
+      throw new RangeError(errInvalidSize);
+    }
+
+    stream[readableStreamQueueSize] += size;
+    stream[readableStreamQueue].push({value, size});
+  }
+
+  function GetTotalQueueSize(stream) { return stream[readableStreamQueueSize]; }
+
+  //
+  // Other helpers
+  //
+
+  function ValidateAndNormalizeQueuingStrategy(size, highWaterMark) {
+    if (size !== undefined && typeof size !== 'function') {
+      throw new TypeError(errSizeNotAFunction);
+    }
+
+    highWaterMark = Number(highWaterMark);
+    if (Number_isNaN(highWaterMark)) {
+      throw new TypeError(errInvalidHWM);
+    }
+    if (highWaterMark < 0) {
+      throw new RangeError(errInvalidHWM);
+    }
+
+    return {size, highWaterMark};
+  }
+
+  // Modified from InvokeOrNoop in spec
+  function CallOrNoop(O, P, arg, nameForError) {
+    const method = O[P];
+    if (method === undefined) {
+      return undefined;
+    }
+    if (typeof method !== 'function') {
+      throw new TypeError(errTmplMustBeFunctionOrUndefined(nameForError));
+    }
+
+    return callFunction(method, O, arg);
+  }
+
+
+  // Modified from PromiseInvokeOrNoop in spec
+  function PromiseCallOrNoop(O, P, arg, nameForError) {
+    let method;
+    try {
+      method = O[P];
+    } catch (methodE) {
+      return Promise_reject(methodE);
+    }
+
+    if (method === undefined) {
+      return Promise_resolve(undefined);
+    }
+
+    if (typeof method !== 'function') {
+      return Promise_reject(errTmplMustBeFunctionOrUndefined(nameForError));
+    }
+
+    try {
+      return Promise_resolve(callFunction(method, O, arg));
+    } catch (e) {
+      return Promise_reject(e);
+    }
+  }
+
+  function CreateIterResultObject(value, done) { return {value, done}; }
+
+
+  //
+  // Additions to the global
+  //
+
+  defineProperty(global, 'ReadableStream', {
+    value: ReadableStream,
+    enumerable: false,
+    configurable: true,
+    writable: true
+  });
+
+  //
+  // Exports to Blink
+  //
+
+  binding.IsReadableStreamDisturbed = IsReadableStreamDisturbed;
+});