Add the JS data pipe client to be used to implement serial send.

extensions/renderer/resources/data_sender.js

+// Copyright 2014 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.
+
+define('data_sender', [
+    'async_waiter',
+    'device/serial/data_stream.mojom',
+    'mojo/public/js/bindings/core',
+    'mojo/public/js/bindings/router',
+], function(asyncWaiter, dataStreamMojom, core, routerModule) {
+  /**
+   * @module data_sender
+   */
+
+  /**
+   * A pending send operation.
+   * @param {ArrayBuffer} data The data to be sent.
+   * @constructor
+   * @alias module:data_sender~PendingSend
+   * @private
+   */
+  function PendingSend(data) {
+    /**
+     * The data to be sent.

[raymes, 2014/08/20 03:34:48]

nit: Could just add a note that this is the *remaining* data to be sent whereas
sendLength is the *total* length of the data to be sent.

[Sam McNally, 2014/08/20 04:19:54]

Done.

+     * @type {ArrayBuffer}
+     * @private
+     */
+    this.data_ = data;
+    /**
+     * The length of data to be sent.
+     * @type {number}
+     * @private
+     */
+    this.sendLength_ = data.byteLength;

[raymes, 2014/08/20 03:34:48]

nit, optional: could just call it "length_"

[Sam McNally, 2014/08/20 04:19:54]

Done.

+    /**
+     * The number of bytes that have been received by the DataSink.
+     * @type {number}
+     * @private
+     */
+    this.bytesSent_ = 0;
+    /**
+     * The promise that will be resolved or rejected when this send completes
+     * or fails, respectively.
+     * @type {Promise.<number>}
+     * @private
+     */
+    this.promise_ = new Promise(function(resolve, reject) {
+      /**
+       * The callback to call on success.
+       * @type {Function}
+       * @private
+       */
+      this.successCallback_ = resolve;
+      /**
+       * The callback to call with the error on failure.
+       * @type {Function}
+       * @private
+       */
+      this.errorCallback_ = reject;
+    }.bind(this));
+  }
+
+  /**
+   * Returns the promise that will be resolved when this operation completes or
+   * rejected if an error occurs.
+   * @return {Promise.<number>} A promise to the number of bytes sent.
+   */
+  PendingSend.prototype.getPromise = function() {
+    return this.promise_;
+  };
+
+  /**
+   * @typedef module:data_sender~PendingSend.ReportBytesResult
+   * @property {number} bytesLeft The number of bytes reported that were not
+   *     sent as part of the send.
+   * @property {boolean?} done Whether this send has completed.
+   * @property {number?} bytesToFlush The number of bytes to flush in the event
+   *     of an error.
+   */
+
+  /**
+   * Invoked when the DataSink reports that bytes have been sent. Resolves the
+   * promise returned by
+   * [getPromise()]{@link module:data_sender~PendingSend#getPromise} once all
+   * bytes have been reported as sent.
+   * @param {number} numBytes The number of bytes sent.
+   * @return {module:data_sender~PendingSend.ReportBytesResult}
+   */
+  PendingSend.prototype.reportBytesSent = function(numBytes) {
+    var result = this.reportBytesSentInternal_(numBytes);
+    if (this.bytesSent_ == this.sendLength_) {
+      result.done = true;
+      this.successCallback_(this.bytesSent_);
+    }
+    return result;
+  };
+
+  /**
+   * Invoked when the DataSink reports an error. Rejects the promise returned by
+   * [getPromise()]{@link module:data_sender~PendingSend#getPromise} unless the
+   * error occurred after this send, that is, unless numBytes is greater than
+   * the nubmer of outstanding bytes.
+   * @param {number} numBytes The number of bytes sent.
+   * @param {number} error The error reported by the DataSink.
+   * @return {module:data_sender~PendingSend.ReportBytesResult}
+   */
+  PendingSend.prototype.reportBytesSentAndError = function(numBytes, error) {
+    var result = this.reportBytesSentInternal_(numBytes);
+    if (result.bytesLeft > 0)

[raymes, 2014/08/20 03:34:48]

A comment here noting that having more bytes left to send implies that no error
occurred in this PendingSend might be helpful for a reader

[Sam McNally, 2014/08/20 04:19:54]

Done.

+      return this.reportBytesSent(result.bytesLeft);

[raymes, 2014/08/20 03:34:48]

Again, I think it's confusing to call reportBytesInternal twice in this case.
Can we avoid this?

[Sam McNally, 2014/08/20 04:19:54]

Done.

+
+    var e = new Error();
+    e.error = error;
+    e.bytesSent = this.bytesSent_;
+    this.errorCallback_(e);
+    this.done = true;
+    result.bytesToFlush =
+        this.sendLength_ - this.data_.byteLength - this.bytesSent_;
+    return result;
+  };
+
+  /**
+   * Updates the internal state in response to a report from the DataSink.
+   * @param {number} numBytes The number of bytes sent.
+   * @return {module:data_sender~PendingSend.ReportBytesResult}
+   * @private
+   */
+  PendingSend.prototype.reportBytesSentInternal_ = function(numBytes) {
+    this.bytesSent_ += numBytes;
+    var result = {bytesLeft: 0, bytesToFlush: 0};
+    if (this.bytesSent_ > this.sendLength_) {
+      result.bytesLeft = this.bytesSent_ - this.sendLength_;
+      this.bytesSent_ = this.sendLength_;
+    }
+    result.done = false;
+    return result;
+  };
+
+  /**
+   * Writes pending data into the data pipe.
+   * @param {MojoHandle} handle The handle to the data pipe.
+   * @return {number} The Mojo result corresponding to the outcome:
+   *     <ul>
+   *     <li>RESULT_OK if the write completes successfully;
+   *     <li>RESULT_SHOULD_WAIT if some, but not all data was written; or
+   *     <li>the data pipe error if the write failed.
+   *     </ul>
+   */
+  PendingSend.prototype.sendData = function(handle) {
+    var result = core.writeData(
+        handle, new Int8Array(this.data_), core.WRITE_DATA_FLAG_NONE);
+    if (result.result != core.RESULT_OK)
+      return result.result;
+    this.data_ = this.data_.slice(result.numBytes);
+    return this.data_.byteLength ? core.RESULT_SHOULD_WAIT : core.RESULT_OK;
+  };
+
+  /**
+   * A DataSender that sends data to a DataSink.
+   * @param {MojoHandle} handle The handle to the DataSink.
+   * @param {number} bufferSize How large a buffer the data pipe should use.
+   * @param {number} fatalErrorValue The send error value to report in the
+   *     event of a fatal error.
+   * @constructor
+   * @alias module:data_sender.DataSender
+   */
+  function DataSender(handle, bufferSize, fatalErrorValue) {
+    /**
+     * The [Router]{@link module:mojo/public/js/bindings/router.Router} for the
+     * connection to the DataSink.
+     * @private
+     */
+    this.router_ = new routerModule.Router(handle);
+    /**
+     * The connection to the DataSink.
+     * @private
+     */
+    this.sink_ = new dataStreamMojom.DataSinkProxy(this.router_);
+    this.router_.setIncomingReceiver(this);
+    var dataPipeOptions = {
+      flags: core.CREATE_DATA_PIPE_OPTIONS_FLAG_NONE,
+      elementNumBytes: 1,
+      capacityNumBytes: bufferSize,
+    };
+    var sendPipe = core.createDataPipe(dataPipeOptions);
+    this.sink_.init(sendPipe.consumerHandle);
+    /**
+     * The handle to the data pipe to use for sending data.
+     * @private
+     */
+    this.sendPipe_ = sendPipe.producerHandle;
+    /**
+     * The error to be dispatched in the event of a fatal error.
+     * @type {number}
+     * @private
+     */
+    this.fatalErrorValue_ = fatalErrorValue;
+    /**
+     * The async waiter used to wait for
+     * {@link module:data_sender.DataSender#sendPipe_} to be writable.
+     * @type module:async_waiter.AsyncWaiter
+     * @private
+     */
+    this.waiter_ = new asyncWaiter.AsyncWaiter(
+        this.sendPipe_, core.HANDLE_SIGNAL_WRITABLE,
+        this.onHandleReady_.bind(this));
+    /**
+     * A queue of sends that have not fully written their data to the data pipe.
+     * @type module:data_sender~PendingSend[]
+     * @private
+     */
+    this.pendingSends_ = [];
+    /**
+     * A queue of sends that have written their data to the data pipe, but have
+     * not been received by the DataSink.
+     * @type module:data_sender~PendingSend[]
+     * @private
+     */
+    this.sendsAwaitingAck_ = [];
+    /**
+     * The callback that will resolve a pending cancel if one is in progress.
+     * @type Function
+     * @private
+     */
+    this.pendingCancel_ = null;
+    /**
+     * Whether this DataReceiver has shut down.
+     * @type {boolean}
+     * @private
+     */
+    this.shutDown_ = false;
+  }
+
+  DataSender.prototype =
+      $Object.create(dataStreamMojom.DataSinkClientStub.prototype);
+
+  /**
+   * Closes this DataSender.
+   */
+  DataSender.prototype.close = function() {
+    if (this.shutDown_)
+      return;
+    this.shutDown_ = true;
+    this.waiter_.stop();
+    this.router_.close();
+    core.close(this.sendPipe_);
+    while (this.pendingSends_.length) {
+      this.pendingSends_.pop().reportBytesSentAndError(
+          0, this.fatalErrorValue_);
+    }
+    while (this.sendsAwaitingAck_.length) {
+      this.sendsAwaitingAck_.pop().reportBytesSentAndError(
+          0, this.fatalErrorValue_);
+    }
+    if (this.pendingCancel_) {
+      this.pendingCancel_();
+      this.pendingCancel_ = null;
+    }
+  };
+
+  /**
+   * Sends data to the DataSink.
+   * @return {Promise.<number>} A promise to the number of bytes sent. If an
+   *     error occurs, the promise will reject with an Error object with a
+   *     property error containing the error code.
+   * @throws Will throw if this has encountered a fatal error or a cancel is in
+   *     progress.
+   */
+  DataSender.prototype.send = function(data) {
+    if (this.shutDown_)
+      throw new Error('System error');

[raymes, 2014/08/20 03:34:48]

Maybe something more descriptive? :)

[Sam McNally, 2014/08/20 04:19:54]

Done.

+    if (this.pendingCancel_)
+      throw new Error('Cancel in progress');
+    var send = new PendingSend(data);
+    this.pendingSends_.push(send);
+    if (!this.waiter_.isWaiting())
+      this.waiter_.start();
+    return send.getPromise();
+  };
+
+  /**
+   * Requests the cancellation of any in-progress sends. Calls to
+   * [send()]{@link module:data_sender.DataSender#send} will fail until the
+   * cancel has completed.
+   * @param {number} error The error to report for cancelled sends.
+   * @return {Promise} A promise that will resolve when the cancel completes.
+   * @throws Will throw if this has encountered a fatal error or another cancel
+   *     is in progress.
+   */
+  DataSender.prototype.cancel = function(error) {
+    if (this.shutDown_)
+      throw new Error('System error');
+    if (this.pendingCancel_)
+      throw new Error('Cancel already in progress');
+    if (this.pendingSends_.length + this.sendsAwaitingAck_.length == 0)
+      return Promise.resolve();
+
+    this.sink_.cancel(error);
+    return new Promise(function(resolve) {
+      this.pendingCancel_ = resolve;
+    }.bind(this));
+  };
+
+  /**
+   * Invoked when |handle_| is ready to write. Writes to the data pipe if the
+   * wait is successful.
+   * @param {number} waitResult The result of the asynchronous wait.
+   * @private
+   */
+  DataSender.prototype.onHandleReady_ = function(result) {
+    this.waiter_.stop();
+    if (this.pendingSends_.length == 0)
+      return;
+    if (result != core.RESULT_OK) {

[raymes, 2014/08/20 03:34:48]

It seems like it could be good to handle this error right at the start of this
function (more for clarity than anything).

[Sam McNally, 2014/08/20 04:19:54]

Done.

+      this.close();
+      return;
+    }
+    while (this.pendingSends_.length) {
+      var result = this.pendingSends_[0].sendData(this.sendPipe_);
+      if (result == core.RESULT_OK) {
+        this.sendsAwaitingAck_.push(this.pendingSends_.shift());
+      } else if (result == core.RESULT_SHOULD_WAIT) {
+        this.waiter_.start();
+        return;

[raymes, 2014/08/20 03:34:48]

unnecessary return

[Sam McNally, 2014/08/20 04:19:54]

One of either return or break is required.

+      } else {
+        this.close();
+        return;

[raymes, 2014/08/20 03:34:48]

unnecessary return

[Sam McNally, 2014/08/20 04:19:55]

This one is unnecessary because close() clears pendingSends_, but that feels a
bit too magic.

[raymes, 2014/08/20 04:29:41]

Ahh I missed the fact it is in a loop. 

+      }
+    }
+  };
+
+  /**
+   * Calls and clears the pending cancel callback if one is pending.
+   * @private
+   */
+  DataSender.prototype.callCancelCallback_ = function() {
+    if (this.pendingCancel_) {
+      this.pendingCancel_();
+      this.pendingCancel_ = null;
+    }
+  };
+
+  /**
+   * Invoked by the DataSink to report that data has been successfully sent.
+   * @param {number} numBytes The number of bytes sent.
+   * @private
+   */
+  DataSender.prototype.reportBytesSent = function(numBytes) {
+    while (numBytes > 0 && this.sendsAwaitingAck_.length) {
+      var result = this.sendsAwaitingAck_[0].reportBytesSent(numBytes);
+      numBytes = result.bytesLeft;
+      if (result.done)
+        this.sendsAwaitingAck_.shift();
+    }
+    if (numBytes > 0 && this.pendingSends_.length) {
+      var result = this.pendingSends_[0].reportBytesSent(numBytes);
+      numBytes = result.bytesLeft;
+    }
+    if (this.pendingSends_.length + this.sendsAwaitingAck_.length == 0)

[raymes, 2014/08/20 03:34:48]

Maybe a note on why we can call the cancel callback here.

[Sam McNally, 2014/08/20 04:19:54]

Done.

+      this.callCancelCallback_();
+  };
+
+  /**
+   * Invoked by the DataSink to report an error in sending data.
+   * @param {number} numBytes The number of bytes sent.
+   * @param {number} error The error reported by the DataSink.
+   * @private
+   */
+  DataSender.prototype.reportBytesSentAndError = function(numBytes, error) {
+    var bytesToFlush = 0;
+    while (this.sendsAwaitingAck_.length) {
+      var result = this.sendsAwaitingAck_[0].reportBytesSentAndError(
+          numBytes, error);
+      numBytes = result.bytesLeft;
+      this.sendsAwaitingAck_.shift();
+      bytesToFlush += result.bytesToFlush;
+    }
+    while (this.pendingSends_.length) {

[raymes, 2014/08/20 03:34:48]

optionally make a note here that only the first pending send has data to flush.
The code is a bit weird because it could make the reader think that that isn't
true. But I still think it's clearer the way you have it.

[Sam McNally, 2014/08/20 04:19:54]

Done.

+      var result = this.pendingSends_[0].reportBytesSentAndError(
+          numBytes, error);
+      numBytes = result.bytesLeft;
+      this.pendingSends_.shift();
+      bytesToFlush += result.bytesToFlush;
+    }
+    this.callCancelCallback_();
+    return Promise.resolve({bytes_to_flush: bytesToFlush});
+  };
+
+  return {DataSender: DataSender};
+});