text: // Copyright 2006 The Closure Library Authors. All Rights Reserved.
  //
  // Licensed under the Apache License, Version 2.0 (the "License");
  // you may not use this file except in compliance with the License.
  // You may obtain a copy of the License at
  //
  //      http://www.apache.org/licenses/LICENSE-2.0
  //
  // Unless required by applicable law or agreed to in writing, software
  // distributed under the License is distributed on an "AS-IS" BASIS,
  // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  // See the License for the specific language governing permissions and
  // limitations under the License.
  
  /**
   * @fileoverview Definition of the BrowserChannel class.  A BrowserChannel
   * simulates a bidirectional socket over HTTP. It is the basis of the
   * Gmail Chat IM connections to the server.
   *
   * See http://wiki/Main/BrowserChannel
   * This doesn't yet completely comform to the design document as we've done
   * some renaming and cleanup in the design document that hasn't yet been
   * implemented in the protocol.
   *
   * Typical usage will look like
   *  var handler = [handler object];
   *  var channel = new BrowserChannel(clientVersion);
   *  channel.setHandler(handler);
   *  channel.connect('channel/test', 'channel/bind');
   *
   * See goog.net.BrowserChannel.Handler for the handler interface.
   *
  *
   */
  
  
  goog.provide('goog.net.BrowserChannel');
  goog.provide('goog.net.BrowserChannel.Handler');
  goog.provide('goog.net.BrowserChannel.LogSaver');
  goog.provide('goog.net.BrowserChannel.QueuedMap');
  goog.provide('goog.net.BrowserChannel.StatEvent');
  goog.provide('goog.net.BrowserChannel.TimingEvent');
  
  goog.require('goog.Uri');
  goog.require('goog.array');
  goog.require('goog.debug.TextFormatter');
  goog.require('goog.events.Event');
  goog.require('goog.events.EventTarget');
  goog.require('goog.json');
  goog.require('goog.net.BrowserTestChannel');
  goog.require('goog.net.ChannelDebug');
  goog.require('goog.net.ChannelRequest');
  goog.require('goog.net.XhrIo');
  goog.require('goog.string');
  goog.require('goog.structs.CircularBuffer');
  goog.require('goog.userAgent');
  
  
  /**
   * Encapsulates the logic for a single BrowserChannel.
   *
   * @param {string} clientVersion An application-specific version number that
   *        is sent to the server when connected.
   * @constructor
   */
  goog.net.BrowserChannel = function(clientVersion) {
    /**
     * The application specific version that is passed to the server.
     * @type {string}
     * @private
     */
    this.clientVersion_ = clientVersion;
  
    /**
     * The current state of the BrowserChannel. It should be one of the
     * goog.net.BrowserChannel.State constants.
     * @type {goog.net.BrowserChannel.State}
     * @private
     */
    this.state_ = goog.net.BrowserChannel.State.INIT;
  
    /**
     * An array of queued maps that need to be sent to the server.
     * @type {Array.<goog.net.BrowserChannel.QueuedMap>}
     * @private
     */
    this.outgoingMaps_ = [];
  
    /**
     * An array of dequeued maps that we have either received a non-successful
     * response for, or no response at all, and which therefore may or may not
     * have been received by the server.
     * @type {Array.<goog.net.BrowserChannel.QueuedMap>}
     * @private
     */
    this.pendingMaps_ = [];
  
    /**
     * The channel debug used for browserchannel logging
     * @type {goog.net.ChannelDebug}
     * @private
     */
    this.channelDebug_ = new goog.net.ChannelDebug();
  };
  
  /**
   * Simple container class for a (mapId, map) pair.
   * @param {number} mapId The id for this map.
   * @param {Object|goog.structs.Map} map The map itself.
   * @constructor
   */
  goog.net.BrowserChannel.QueuedMap = function(mapId, map) {
    /**
     * The id for this map.
     * @type {number}
     */
    this.mapId = mapId;
  
    /**
     * The map itself.
     * @type {Object|goog.structs.Map}
     */
    this.map = map;
  };
  
  /**
   * Extra HTTP headers to add to all the requests sent to the server.
   * @type {Object}
   * @private
   */
  goog.net.BrowserChannel.prototype.extraHeaders_ = null;
  
  /**
   * Extra parameters to add to all the requests sent to the server.
   * @type {Object}
   * @private
   */
  goog.net.BrowserChannel.prototype.extraParams_ = null;
  
  /**
   * The current ChannelRequest object for the forwardchannel.
   * @type {goog.net.ChannelRequest?}
   * @private
   */
  goog.net.BrowserChannel.prototype.forwardChannelRequest_ = null;
  
  /**
   * The ChannelRequest object for the backchannel.
   * @type {goog.net.ChannelRequest?}
   * @private
   */
  goog.net.BrowserChannel.prototype.backChannelRequest_ = null;
  
  /**
   * The relative path (in the context of the the page hosting the browser
   * channel) for making requests to the server.
   * @type {?string}
   * @private
   */
  goog.net.BrowserChannel.prototype.path_ = null;
  
  /**
   * The absolute URI for the forwardchannel request.
   * @type {goog.Uri}
   * @private
   */
  goog.net.BrowserChannel.prototype.forwardChannelUri_ = null;
  
  /**
   * The absolute URI for the backchannel request.
   * @type {goog.Uri}
   * @private
   */
  goog.net.BrowserChannel.prototype.backChannelUri_ = null;
  
  /**
   * A subdomain prefix for using a subdomain in IE for the backchannel
   * requests.
   * @type {?string}
   * @private
   */
  goog.net.BrowserChannel.prototype.hostPrefix_ = null;
  
  /**
   * Whether we allow the use of a subdomain in IE for the backchannel requests.
   * @private
   */
  goog.net.BrowserChannel.prototype.allowHostPrefix_ = true;
  
  /**
   * The next id to use for the RID (request identifier) parameter. This
   * identifier uniquely identifies the forward channel request.
   * @type {number}
   * @private
   */
  goog.net.BrowserChannel.prototype.nextRid_ = 0;
  
  /**
   * The id to use for the next outgoing map. This identifier uniquely
   * identifies a sent map.
   * @type {number}
   * @private
   */
  goog.net.BrowserChannel.prototype.nextMapId_ = 0;
  
  /**
   * Whether to fail forward-channel requests after one try, or after a few tries.
   * @type {boolean}
   * @private
   */
  goog.net.BrowserChannel.prototype.failFast_ = false;
  
  /**
   * The handler that receive callbacks for state changes and data.
   * @type {goog.net.BrowserChannel.Handler}
   * @private
   */
  goog.net.BrowserChannel.prototype.handler_ = null;
  
  /**
   * Timer identifier for asynchronously making a forward channel request.
   * @type {?number}
   * @private
   */
  goog.net.BrowserChannel.prototype.forwardChannelTimerId_ = null;
  
  /**
   * Timer identifier for asynchronously making a back channel request.
   * @type {?number}
   * @private
   */
  goog.net.BrowserChannel.prototype.backChannelTimerId_ = null;
  
  /**
   * Timer identifier for the timer that waits for us to retry the backchannel in
   * the case where it is dead and no longer receiving data.
   * @type {?number}
   * @private
   */
  goog.net.BrowserChannel.prototype.deadBackChannelTimerId_ = null;
  
  /**
   * The BrowserTestChannel object which encapsulates the logic for determining
   * interesting network conditions about the client.
   * @type {goog.net.BrowserTestChannel?}
   * @private
   */
  goog.net.BrowserChannel.prototype.connectionTest_ = null;
  
  /**
   * Whether the client's network conditions can support chunked responses.
   * @type {?boolean}
   * @private
   */
  goog.net.BrowserChannel.prototype.useChunked_ = null;
  
  /**
   * Whether chunked mode is allowed. In certain debugging situations, it's
   * useful to disable this.
   * @private
   */
  goog.net.BrowserChannel.prototype.allowChunkedMode_ = true;
  
  /**
   * The array identifier of the last array received from the server for the
   * backchannel request.
   * @type {number}
   * @private
   */
  goog.net.BrowserChannel.prototype.lastArrayId_ = -1;
  
  /**
   * The array identifier of the last array sent by the server that we know about.
   * @type {number}
   * @private
   */
  goog.net.BrowserChannel.prototype.lastPostResponseArrayId_ = -1;
  
  /**
   * The last status code received.
   * @type {number}
   * @private
   */
  goog.net.BrowserChannel.prototype.lastStatusCode_ = -1;
  
  /**
   * Number of times we have retried the current forward channel request.
   * @type {number}
   * @private
   */
  goog.net.BrowserChannel.prototype.forwardChannelRetryCount_ = 0;
  
  /**
   * Number of times it a row that we have retried the current back channel
   * request and received no data.
   * @type {number}
   * @private
   */
  goog.net.BrowserChannel.prototype.backChannelRetryCount_ = 0;
  
  /**
   * The attempt id for the current back channel request. Starts at 1 and
   * increments for each reconnect. The server uses this to log if our connection
   * is flaky or not.
   * @type {number}
   * @private
   */
  goog.net.BrowserChannel.prototype.backChannelAttemptId_;
  
  /**
   * The latest protocol version that this class supports. We request this version
   * from the server when opening the connection. Should match
   * com.google.net.browserchannel.BrowserChannel.LATEST_CHANNEL_VERSION.
   * @type {number}
   */
  goog.net.BrowserChannel.LATEST_CHANNEL_VERSION = 8;
  
  /**
   * The channel version that we negotiated with the server for this session.
   * Starts out as the version we request, and then is changed to the negotiated
   * version after the initial open.
   * @type {number}
   * @private
   */
  goog.net.BrowserChannel.prototype.channelVersion_ =
      goog.net.BrowserChannel.LATEST_CHANNEL_VERSION;
  
  /**
   * Enum type for the browser channel state machine.
   * @enum {number}
   */
  goog.net.BrowserChannel.State = {
    /** The channel is closed. */
    CLOSED: 0,
  
    /** The channel has been initialized but hasn't yet initiated a connection. */
    INIT: 1,
  
    /** The channel is in the process of opening a connection to the server. */
    OPENING: 2,
  
    /** The channel is open. */
    OPENED: 3
  };
  
  
  /**
   * Maximum number of attempts to connect to the server for forward channel
   * requests.
   * @type {number}
   */
  goog.net.BrowserChannel.FORWARD_CHANNEL_MAX_RETRIES = 2;
  
  /**
   * The timeout in milliseconds for a forward channel request.
   * @type {number}
   */
  goog.net.BrowserChannel.FORWARD_CHANNEL_RETRY_TIMEOUT = 20 * 1000;
  
  /**
   * Maximum number of attempts to connect to the server for back channel
   * requests.
   * @type {number}
   */
  goog.net.BrowserChannel.BACK_CHANNEL_MAX_RETRIES = 3;
  
  /**
   * Default timeout in MS before the initial retry. Subsequent retries will be
   * slower.
   * @type {number}
   */
  goog.net.BrowserChannel.RETRY_DELAY_MS = 5 * 1000;
  
  /**
   * We will add a random time between 0 and this number of MS to retries to
   * the retry time for this request.
   * @type {number}
   */
  goog.net.BrowserChannel.RETRY_DELAY_SEED = 10 * 1000;
  
  /**
   * A number in MS of how long we guess the maxmium amount of time a round trip
   * to the server should take. In the future this could be substituted with a
   * real measurement of the RTT.
   * @type {number}
   */
  goog.net.BrowserChannel.RTT_ESTIMATE = 3 * 1000;
  
  /**
   * When retrying for an inactive channel, we will multiply the total delay by
   * this number.
   * @type {number}
   */
  goog.net.BrowserChannel.INACTIVE_CHANNEL_RETRY_FACTOR = 2;
  
  
  /**
   * Enum type for identifying a BrowserChannel error.
   * @enum {number}
   */
  goog.net.BrowserChannel.Error = {
    /** Value that indicates no error has occurred. */
    OK: 0,
  
    /** An error due to a request failing. */
    REQUEST_FAILED: 2,
  
    /** An error due to the user being logged out. */
    LOGGED_OUT: 4,
  
    /** An error due to server response which contains no data. */
    NO_DATA: 5,
  
    /** An error due to a server response indicating an unknown session id */
    UNKNOWN_SESSION_ID: 6,
  
    /** An error due to a server response requesting to stop the channel. */
    STOP: 7,
  
    /** A general network error. */
    NETWORK: 8,
  
    /** An error due to the channel being blocked by a network administrator. */
    BLOCKED: 9,
  
    /** An error due to bad data being returned from the server. */
    BAD_DATA: 10,
  
    /** An error due to a response that doesn't start with the magic cookie. */
    BAD_RESPONSE: 11
  };
  
  
  /**
   * Internal enum type for the two browser channel channel types.
   * @enum {number}
   * @private
   */
  goog.net.BrowserChannel.ChannelType_ = {
    FORWARD_CHANNEL: 1,
  
    BACK_CHANNEL: 2
  };
  
  /**
   * The maximum number of maps that can be sent in one POST. Should match
   * com.google.net.browserchannel.BrowserChannel.MAX_MAPS_PER_REQUEST.
   * @type {number}
   * @private
   */
  goog.net.BrowserChannel.MAX_MAPS_PER_REQUEST_ = 1000;
  
  
  /**
   * Singleton event target for firing stat events
   * @type {goog.events.EventTarget}
   * @private
   */
  goog.net.BrowserChannel.statEventTarget_ = new goog.events.EventTarget();
  
  /**
   * Events fired by BrowserChannel and associated objects
   * @type {Object}
   */
  goog.net.BrowserChannel.Event = {};
  
  
  /**
   * Stat Event that fires when things of interest happen that may be useful for
   * applications to know about for stats or debugging purposes. This event fires
   * on the EventTarget returned by getStatEventTarget.
   */
  goog.net.BrowserChannel.Event.STAT_EVENT = 'statevent';
  
  
  /**
   * Event class for goog.net.BrowserChannel.Event.STAT_EVENT
   *
   * @param {goog.events.EventTarget} eventTarget The stat event target for
         the browser channel.
   * @param {goog.net.BrowserChannel.Stat} stat The stat.
   * @constructor
   * @extends {goog.events.Event}
   */
  goog.net.BrowserChannel.StatEvent = function(eventTarget, stat) {
    goog.events.Event.call(this, goog.net.BrowserChannel.Event.STAT_EVENT,
        eventTarget);
  
    /**
     * The stat
     * @type {goog.net.BrowserChannel.Stat}
     */
    this.stat = stat;
  
  };
  goog.inherits(goog.net.BrowserChannel.StatEvent, goog.events.Event);
  
  
  /**
   * An event that fires when POST requests complete successfully, indicating
   * the size of the POST and the round trip time.
   * This event fires on the EventTarget returned by getStatEventTarget.
   */
  goog.net.BrowserChannel.Event.TIMING_EVENT = 'timingevent';
  
  
  /**
   * Event class for goog.net.BrowserChannel.Event.TIMING_EVENT
   *
   * @param {goog.events.EventTarget} target The stat event target for
         the browser channel.
   * @param {number} size The number of characters in the POST data.
   * @param {number} rtt The total round trip time from POST to response in MS.
   * @param {number} retries The number of times the POST had to be retried.
   * @constructor
   * @extends {goog.events.Event}
   */
  goog.net.BrowserChannel.TimingEvent = function(target, size, rtt, retries) {
    goog.events.Event.call(this, goog.net.BrowserChannel.Event.TIMING_EVENT,
        target);
  
    /**
     * @type {number}
     */
    this.size = size;
  
    /**
     * @type {number}
     */
    this.rtt = rtt
  
    /**
     * @type {number}
     */
    this.retries = retries;
  
  };
  goog.inherits(goog.net.BrowserChannel.TimingEvent, goog.events.Event);
  
  
  /**
   * Enum that identifies events for statistics that are interesting to track.
   * TODO(user) - Change name not to use Event or use EventTarget
   * @enum {number}
   */
  goog.net.BrowserChannel.Stat = {
    /** Event indicating a new connection attempt. */
    CONNECT_ATTEMPT: 0,
  
    /** Event indicating a connection error due to a general network problem. */
    ERROR_NETWORK: 1,
  
    /**
     * Event indicating a connection error that isn't due to a general network
     * problem.
     */
    ERROR_OTHER: 2,
  
    /** Event indicating the start of test stage one. */
    TEST_STAGE_ONE_START: 3,
  
  
    /** Event indicating the channel is blocked by a network administrator. */
    CHANNEL_BLOCKED: 4,
  
    /** Event indicating the start of test stage two. */
    TEST_STAGE_TWO_START: 5,
  
    /** Event indicating the first piece of test data was received. */
    TEST_STAGE_TWO_DATA_ONE: 6,
  
    /**
     * Event indicating that the second piece of test data was received and it was
     * recieved separately from the first.
     */
    TEST_STAGE_TWO_DATA_TWO: 7,
  
    /** Event indicating both pieces of test data were received simultaneously. */
    TEST_STAGE_TWO_DATA_BOTH: 8,
  
    /** Event indicating stage one of the test request failed. */
    TEST_STAGE_ONE_FAILED: 9,
  
    /** Event indicating stage two of the test request failed. */
    TEST_STAGE_TWO_FAILED: 10,
  
    /**
     * Event indicating that a buffering proxy is likely between the client and
     * the server.
     */
    PROXY: 11,
  
    /**
     * Event indicating that no buffering proxy is likely between the client and
     * the server.
     */
    NOPROXY: 12,
  
    /** Event indicating an unknown SID error. */
    REQUEST_UNKNOWN_SESSION_ID: 13,
  
    /** Event indicating a bad status code was received. */
    REQUEST_BAD_STATUS: 14,
  
    /** Event indicating incomplete data was received */
    REQUEST_INCOMPLETE_DATA: 15,
  
    /** Event indicating bad data was received */
    REQUEST_BAD_DATA: 16,
  
    /** Event indicating no data was received when data was expected. */
    REQUEST_NO_DATA: 17,
  
    /** Event indicating a request timeout. */
    REQUEST_TIMEOUT: 18,
  
    /**
     * Event indicating that the server never received our hanging GET and so it
     * is being retried.
     */
    BACKCHANNEL_MISSING: 19,
  
    /**
     * Event indicating that we have determined that our hanging GET is not
     * receiving data when it should be. Thus it is dead dead and will be retried.
     */
    BACKCHANNEL_DEAD: 20
  };
  
  
  /**
   * The normal response for forward channel requests.
   * Used only before version 8 of the protocol.
   * @type {string}
   */
  goog.net.BrowserChannel.MAGIC_RESPONSE_COOKIE = 'y2f%';
  
  /**
   * A guess at a cutoff at which to no longer assume the backchannel is dead
   * when we are slow to receive data. Number in bytes.
   *
   * Assumption: The worst bandwidth we work on is 50 kilobits/sec
   * 50kbits/sec * (1 byte / 8 bits) * 6 sec dead backchannel timeout
   * @type {number}
   */
  goog.net.BrowserChannel.OUTSTANDING_DATA_BACKCHANNEL_RETRY_CUTOFF = 37500;
  
  /**
   * Returns the browserchannel logger.
   *
   * @return {goog.net.ChannelDebug} The channel debug object.
   */
  goog.net.BrowserChannel.prototype.getChannelDebug = function() {
    return this.channelDebug_;
  };
  
  
  /**
   * Set the browserchannel logger.
   * TODO(user): Add interface for channel loggers or remove this function.
   *
   * @param {goog.net.ChannelDebug} channelDebug The channel debug object.
   */
  goog.net.BrowserChannel.prototype.setChannelDebug = function(
      channelDebug) {
    this.channelDebug_ = channelDebug;
  };
  
  
  /**
   * Allows the application to set an execution hooks for when BrowserChannel
   * starts processing requests. This is useful to track timing or logging
   * special information. The function takes no parameters and return void.
   * @param {Function} startHook  The function for the start hook.
   */
  goog.net.BrowserChannel.setStartThreadExecutionHook = function(startHook) {
    goog.net.BrowserChannel.startExecutionHook_ = startHook;
  };
  
  
  /**
   * Allows the application to set an execution hooks for when BrowserChannel
   * stops processing requests. This is useful to track timing or logging
   * special information. The function takes no parameters and return void.
   * @param {Function} endHook  The function for the end hook.
   */
  goog.net.BrowserChannel.setEndThreadExecutionHook = function(endHook) {
    goog.net.BrowserChannel.endExecutionHook_ = endHook;
  };
  
  
  /**
   * Application provided execution hook for the start hook.
   *
   * @type {Function}
   * @private
   */
  goog.net.BrowserChannel.startExecutionHook_ = function() { };
  
  
  /**
   * Application provided execution hook for the end hook.
   *
   * @type {Function}
   * @private
   */
  goog.net.BrowserChannel.endExecutionHook_ = function() { };
  
  
  /**
   * Instantiates a ChannelRequest with the given parameters. Overidden in tests.
   *
   * @param {goog.net.BrowserChannel|goog.net.BrowserTestChannel} channel
   *     The BrowserChannel that owns this request.
   * @param {goog.net.ChannelDebug} channelDebug A ChannelDebug to use for
   *     logging.
   * @param {string=} opt_sessionId  The session id for the channel.
   * @param {string|number=} opt_requestId  The request id for this request.
   * @param {number=} opt_retryId  The retry id for this request.
   * @return {goog.net.ChannelRequest} The created channel request.
   */
  goog.net.BrowserChannel.createChannelRequest = function(
      channel, channelDebug, opt_sessionId, opt_requestId, opt_retryId) {
    return new goog.net.ChannelRequest(
        channel,
        channelDebug,
        opt_sessionId,
        opt_requestId,
        opt_retryId);
  };
  
  
  /**
   * Starts the channel. This initiates connections to the server.
   *
   * @param {string} testPath  The path for the test connection.
   * @param {string} channelPath  The path for the channel connection.
   * @param {Object} extraParams  Extra parameter keys and values to add to the
   *     requests.
   * @param {string=} opt_oldSessionId  Session ID from a previous session.
   * @param {number=} opt_oldArrayId  The last array ID from a previous session.
   */
  goog.net.BrowserChannel.prototype.connect = function(testPath, channelPath,
      extraParams, opt_oldSessionId, opt_oldArrayId) {
    this.channelDebug_.debug('connect()');
  
    goog.net.BrowserChannel.notifyStatEvent(
        goog.net.BrowserChannel.Stat.CONNECT_ATTEMPT);
  
    this.path_ = channelPath;
    this.extraParams_ = extraParams || {};
  
    // Attach parameters about the previous session if reconnecting.
    if (opt_oldSessionId && goog.isDef(opt_oldArrayId)) {
      this.extraParams_['OSID'] = opt_oldSessionId;
      this.extraParams_['OAID'] = opt_oldArrayId;
    }
  
    this.connectTest_(testPath);
  };
  
  /**
   * Disconnects and closes the channel.
   */
  goog.net.BrowserChannel.prototype.disconnect = function() {
    this.channelDebug_.debug('disconnect()');
  
    this.cancelRequests_();
  
    if (this.state_ == goog.net.BrowserChannel.State.OPENED) {
      var rid = this.nextRid_++;
      var uri = this.forwardChannelUri_.clone();
      uri.setParameterValue('SID', this.sid_);
      uri.setParameterValue('RID', rid);
      uri.setParameterValue('TYPE', 'terminate');
  
      // Add the reconnect parameters.
      this.addAdditionalParams_(uri);
  
      var request = goog.net.BrowserChannel.createChannelRequest(
          this, this.channelDebug_, this.sid_, rid);
      request.sendUsingImgTag(uri);
      this.onClose_();
    }
  };
  
  
  /**
   * Returns the session id of the channel. Only available after the
   * channel has been opened.
   * @return {string} Session ID.
   */
  goog.net.BrowserChannel.prototype.getSessionId = function() {
    return this.sid_;
  };
  
  
  /**
   * Starts the test channel to determine network conditions.
   *
   * @param {string} testPath  The relative PATH for the test connection.
   * @private
   */
  goog.net.BrowserChannel.prototype.connectTest_ = function(testPath) {
    this.channelDebug_.debug('connectTest_()');
    this.connectionTest_ = new goog.net.BrowserTestChannel(
        this, this.channelDebug_);
    this.connectionTest_.setExtraHeaders(this.extraHeaders_);
    this.connectionTest_.connect(testPath);
  };
  
  
  /**
   * Starts the regular channel which is run after the test channel is complete.
   * @private
   */
  goog.net.BrowserChannel.prototype.connectChannel_ = function() {
    this.channelDebug_.debug('connectChannel_()');
    this.ensureInState_(goog.net.BrowserChannel.State.INIT,
        goog.net.BrowserChannel.State.CLOSED);
    this.forwardChannelUri_ =
        this.getForwardChannelUri(/** @type {string} */ (this.path_));
    this.ensureForwardChannel_();
  };
  
  
  /**
   * Cancels all outstanding requests.
   * @private
   */
  goog.net.BrowserChannel.prototype.cancelRequests_ = function() {
    if (this.connectionTest_) {
      this.connectionTest_.abort();
      this.connectionTest_ = null;
    }
  
    if (this.backChannelRequest_) {
      this.backChannelRequest_.cancel();
      this.backChannelRequest_ = null;
    }
  
    if (this.backChannelTimerId_) {
      goog.global.clearTimeout(this.backChannelTimerId_);
      this.backChannelTimerId_ = null;
    }
  
    this.clearDeadBackchannelTimer_();
  
    if (this.forwardChannelRequest_) {
      this.forwardChannelRequest_.cancel();
      this.forwardChannelRequest_ = null;
    }
  
    if (this.forwardChannelTimerId_) {
      goog.global.clearTimeout(this.forwardChannelTimerId_);
      this.forwardChannelTimerId_ = null;
    }
  };
  
  
  /**
   * Returns the extra HTTP headers to add to all the requests sent to the server.
   *
   * @return {Object} The HTTP headers, or null.
   */
  goog.net.BrowserChannel.prototype.getExtraHeaders = function() {
    return this.extraHeaders_;
  };
  
  
  /**
   * Sets extra HTTP headers to add to all the requests sent to the server.
   *
   * @param {Object} extraHeaders The HTTP headers, or null.
   */
  goog.net.BrowserChannel.prototype.setExtraHeaders = function(extraHeaders) {
    this.extraHeaders_ = extraHeaders;
  };
  
  
  /**
   * Returns the handler used for channel callback events.
   *
   * @return {goog.net.BrowserChannel.Handler} The handler.
   */
  goog.net.BrowserChannel.prototype.getHandler = function() {
    return this.handler_;
  };
  
  
  /**
   * Sets the handler used for channel callback events.
   * @param {goog.net.BrowserChannel.Handler} handler The handler to set.
   */
  goog.net.BrowserChannel.prototype.setHandler = function(handler) {
    this.handler_ = handler;
  };
  
  
  /**
   * Returns whether the channel allows the use of a subdomain. There may be
   * cases where this isn't allowed.
   * @return {boolean} Whether a host prefix is allowed.
   */
  goog.net.BrowserChannel.prototype.getAllowHostPrefix = function() {
    return this.allowHostPrefix_;
  };
  
  
  /**
   * Sets whether the channel allows the use of a subdomain. There may be cases
   * where this isn't allowed, for example, logging in with troutboard where
   * using a subdomain causes Apache to force the user to authenticate twice.
   * @param {boolean} allowHostPrefix Whether a host prefix is allowed.
   */
  goog.net.BrowserChannel.prototype.setAllowHostPrefix =
      function(allowHostPrefix) {
    this.allowHostPrefix_ = allowHostPrefix;
  };
  
  
  /**
   * Returns whether the channel is buffered or not. This state is valid for
   * querying only after the test connection has completed. This may be
   * queried in the goog.net.BrowserChannel.okToMakeRequest() callback.
   * A channel may be buffered if the test connection determines that
   * a chunked response could not be sent down within a suitable time.
   * @return {boolean} Whether the channel is buffered.
   */
  goog.net.BrowserChannel.prototype.isBuffered = function() {
    return !this.useChunked_;
  };
  
  
  /**
   * Returns whether chunked mode is allowed. In certain debugging situations,
   * it's useful for the application to have a way to disable chunked mode for a
   * user.
  
   * @return {boolean} Whether chunked mode is allowed.
   */
  goog.net.BrowserChannel.prototype.getAllowChunkedMode =
      function() {
    return this.allowChunkedMode_;
  };
  
  
  /**
   * Sets whether chunked mode is allowed. In certain debugging situations, it's
   * useful for the application to have a way to disable chunked mode for a user.
   * @param {boolean} allowChunkedMode  Whether chunked mode is allowed.
   */
  goog.net.BrowserChannel.prototype.setAllowChunkedMode =
      function(allowChunkedMode) {
    this.allowChunkedMode_ = allowChunkedMode;
  };
  
  
  /**
   * Sends a request to the server. The format of the request is a Map data
   * structure of key/value pairs. These maps are then encoded in a format
   * suitable for the wire and then reconstituted as a Map data structure that
   * the server can process.
   * @param {Object|goog.structs.Map} map  The map to send.
   */
  goog.net.BrowserChannel.prototype.sendMap = function(map) {
    if (this.state_ == goog.net.BrowserChannel.State.CLOSED) {
      throw Error('Invalid operation: sending map when state is closed');
    }
  
    // We can only send 1000 maps per POST, but typically we should never have
    // that much to send, so warn if we exceed that (we still send all the maps).
    if (this.outgoingMaps_.length ==
        goog.net.BrowserChannel.MAX_MAPS_PER_REQUEST_) {
      // severe() is temporary so that we get these uploaded and can figure out
      // what's causing them. Afterwards can change to warning().
      this.channelDebug_.severe(
          'Already have ' + goog.net.BrowserChannel.MAX_MAPS_PER_REQUEST_ +
          ' queued maps upon queueing ' + goog.json.serialize(map));
    }
  
    this.outgoingMaps_.push(
        new goog.net.BrowserChannel.QueuedMap(this.nextMapId_++, map));
    if (this.state_ == goog.net.BrowserChannel.State.OPENING ||
        this.state_ == goog.net.BrowserChannel.State.OPENED) {
      this.ensureForwardChannel_();
    }
  };
  
  
  /**
   * When set to true, this changes the behavior of the forward channel so it
   * will not retry requests; it will fail after one network failure, and if
   * there was already one network failure, the request will fail immediately.
   * @param {boolean} failFast  Whether or not to fail fast.
   */
  goog.net.BrowserChannel.prototype.setFailFast = function(failFast) {
    this.failFast_ = failFast;
    this.channelDebug_.info('setFailFast: ' + failFast);
    if ((this.forwardChannelRequest_ || this.forwardChannelTimerId_) &&
        this.forwardChannelRetryCount_ > this.getForwardChannelMaxRetries()) {
      this.channelDebug_.info(
          'Retry count ' + this.forwardChannelRetryCount_ +
          ' > new maxRetries ' + this.getForwardChannelMaxRetries() +
          '. Fail immediately!');
      if (this.forwardChannelRequest_) {
        this.forwardChannelRequest_.cancel();
        // Go through the standard onRequestComplete logic to expose the max-retry
        // failure in the standard way.
        this.onRequestComplete(this.forwardChannelRequest_);
      } else {  // i.e., this.forwardChannelTimerId_
        goog.global.clearTimeout(this.forwardChannelTimerId_);
        this.forwardChannelTimerId_ = null;
        // The error code from the last failed request is gone, so just use a
        // generic one.
        this.signalError_(goog.net.BrowserChannel.Error.REQUEST_FAILED);
      }
    }
  };
  
  
  /**
   * @return {number} The max number of forward-channel retries, which will be 0
   * in fail-fast mode.
   */
  goog.net.BrowserChannel.prototype.getForwardChannelMaxRetries = function() {
    return this.failFast_ ?
           0 : goog.net.BrowserChannel.FORWARD_CHANNEL_MAX_RETRIES;
  };
  
  
  /**
   * @return {number} The max number of back-channel retries, which is a constant.
   */
  goog.net.BrowserChannel.prototype.getBackChannelMaxRetries = function() {
    // Back-channel retries is a constant.
    return goog.net.BrowserChannel.BACK_CHANNEL_MAX_RETRIES;
  };
  
  
  /**
   * Returns whether the channel is closed
   * @return {boolean} true if the channel is closed.
   */
  goog.net.BrowserChannel.prototype.isClosed = function() {
    return this.state_ == goog.net.BrowserChannel.State.CLOSED;
  };
  
  
  /**
   * Returns the browser channel state.
   * @return {goog.net.BrowserChannel.State} The current state of the browser
   * channel.
   */
  goog.net.BrowserChannel.prototype.getState = function() {
    return this.state_;
  };
  
  
  /**
   * Return the last status code received for a request.
   * @return {number} The last status code received for a request.
   */
  goog.net.BrowserChannel.prototype.getLastStatusCode = function() {
    return this.lastStatusCode_;
  };
  
  
  /**
   * @return {number} The last array id received.
   */
  goog.net.BrowserChannel.prototype.getLastArrayId = function() {
    return this.lastArrayId_;
  };
  
  
  /**
   * Returns whether there are outstanding requests servicing the channel.
   * @return {boolean} true if there are outstanding requests.
   */
  goog.net.BrowserChannel.prototype.hasOutstandingRequests = function() {
    return this.outstandingRequests_() != 0;
  };
  
  
  /**
   * Returns the number of outstanding requests.
   * @return {number} The number of outstanding requests to the server.
   * @private
   */
  goog.net.BrowserChannel.prototype.outstandingRequests_ = function() {
    var count = 0;
    if (this.backChannelRequest_) {
      count++;
    }
    if (this.forwardChannelRequest_) {
      count++;
    }
    return count;
  };
  
  
  /**
   * Ensures that a forward channel request is scheduled.
   * @private
   */
  goog.net.BrowserChannel.prototype.ensureForwardChannel_ = function() {
    if (this.forwardChannelRequest_) {
      // connection in process - no need to start a new request
      return;
    }
  
    if (this.forwardChannelTimerId_) {
      // no need to start a new request - one is already scheduled
      return;
    }
  
    this.forwardChannelTimerId_ = goog.net.BrowserChannel.setTimeout(
        goog.bind(this.onStartForwardChannelTimer_, this), 0);
    this.forwardChannelRetryCount_ = 0;
  };
  
  
  /**
   * Schedules a forward-channel retry for the specified request, unless the max
   * retries has been reached.
   * @param {goog.net.ChannelRequest} request The failed request to retry.
   * @return {boolean} true iff a retry was scheduled.
   * @private
   */
  goog.net.BrowserChannel.prototype.maybeRetryForwardChannel_ =
      function(request) {
    if (this.forwardChannelRequest_ || this.forwardChannelTimerId_) {
      // Should be impossible to be called in this state.
      this.channelDebug_.severe('Request already in progress');
      return false;
    }
  
    if (this.state_ == goog.net.BrowserChannel.State.INIT ||  // no retry open_()
        (this.forwardChannelRetryCount_ >= this.getForwardChannelMaxRetries())) {
      return false;
    }
  
    this.channelDebug_.debug('Going to retry POST');
  
    this.forwardChannelTimerId_ = goog.net.BrowserChannel.setTimeout(
        goog.bind(this.onStartForwardChannelTimer_, this, request),
        this.getRetryTime_(this.forwardChannelRetryCount_));
    this.forwardChannelRetryCount_++;
    return true;
  };
  
  
  /**
   * Timer callback for ensureForwardChannel
   * @param {goog.net.ChannelRequest=} opt_retryRequest A failed request to retry.
   * @private
   */
  goog.net.BrowserChannel.prototype.onStartForwardChannelTimer_ = function(
      opt_retryRequest) {
    this.forwardChannelTimerId_ = null;
    this.startForwardChannel_(opt_retryRequest);
  };
  
  
  /**
   * Begins a new forward channel operation to the server.
   * @param {goog.net.ChannelRequest=} opt_retryRequest A failed request to retry.
   * @private
   */
  goog.net.BrowserChannel.prototype.startForwardChannel_ = function(
      opt_retryRequest) {
    this.channelDebug_.debug('startForwardChannel_');
  
    if (this.state_ == goog.net.BrowserChannel.State.INIT) {
      if (opt_retryRequest) {
        this.channelDebug_.severe('Not supposed to retry the open');
        return;
      }
      this.open_();
      this.state_ = goog.net.BrowserChannel.State.OPENING;
    } else if (this.state_ == goog.net.BrowserChannel.State.OPENED) {
      if (!this.okToMakeRequest_()) {
        // channel is cancelled
        return;
      }
  
      if (opt_retryRequest) {
        this.makeForwardChannelRequest_(opt_retryRequest);
        return;
      }
  
      if (this.outgoingMaps_.length == 0) {
        this.channelDebug_.debug('startForwardChannel_ returned: ' +
                                    'nothing to send');
        // no need to start a new forward channel request
        return;
      }
  
      if (this.forwardChannelRequest_) {
        // Should be impossible to be called in this state.
        this.channelDebug_.severe('startForwardChannel_ returned: ' +
                                      'connection already in progress');
        return;
      }
  
      this.makeForwardChannelRequest_();
      this.channelDebug_.debug('startForwardChannel_ finished, sent request');
    }
  };
  
  
  /**
   * Establishes a new channel session with the the server.
   * @private
   */
  goog.net.BrowserChannel.prototype.open_ = function() {
    this.channelDebug_.debug('open_()');
    this.nextRid_ = Math.floor(Math.random() * 100000);
  
    var rid = this.nextRid_++;
    var request = goog.net.BrowserChannel.createChannelRequest(
        this, this.channelDebug_, '', rid);
    request.setExtraHeaders(this.extraHeaders_);
    var requestText = this.dequeueOutgoingMaps_();
    var uri = this.forwardChannelUri_.clone();
    uri.setParameterValue('RID', rid);
    if (this.clientVersion_) {
     uri.setParameterValue('CVER', this.clientVersion_);
    }
  
    // Add the reconnect parameters.
    this.addAdditionalParams_(uri);
  
    request.xmlHttpPost(uri, requestText, true);
    this.forwardChannelRequest_ = request;
  };
  
  
  /**
   * Makes a forward channel request using XMLHTTP.
   * @param {goog.net.ChannelRequest=} opt_retryRequest A failed request to retry.
   * @private
   */
  goog.net.BrowserChannel.prototype.makeForwardChannelRequest_ =
      function(opt_retryRequest) {
    var rid;
    var requestText;
    if (opt_retryRequest) {
      if (this.channelVersion_ > 6) {
        // In version 7 and up we can tack on new arrays to a retry.
        this.requeuePendingMaps_();
        rid = this.nextRid_ - 1;  // Must use last RID
        requestText = this.dequeueOutgoingMaps_();
      } else {
        // TODO(user): Remove this code and the opt_retryRequest passing
        // once server-side support for ver 7 is ubiquitous.
        rid = opt_retryRequest.getRequestId();
        requestText = /** @type {string} */ (opt_retryRequest.getPostData());
      }
    } else {
      rid = this.nextRid_++;
      requestText = this.dequeueOutgoingMaps_();
    }
  
    var uri = this.forwardChannelUri_.clone();
    uri.setParameterValue('SID', this.sid_);
    uri.setParameterValue('RID', rid);
    uri.setParameterValue('AID', this.lastArrayId_);
    // Add the additional reconnect parameters.
    this.addAdditionalParams_(uri);
  
    var request = goog.net.BrowserChannel.createChannelRequest(
        this,
        this.channelDebug_,
        this.sid_,
        rid,
        this.forwardChannelRetryCount_ + 1);
    request.setExtraHeaders(this.extraHeaders_);
  
    // randomize from 50%-100% of the forward channel timeout to avoid
    // a big hit if servers happen to die at once.
    request.setTimeout(
        Math.round(goog.net.BrowserChannel.FORWARD_CHANNEL_RETRY_TIMEOUT * 0.50) +
        Math.round(goog.net.BrowserChannel.FORWARD_CHANNEL_RETRY_TIMEOUT * 0.50 *
                   Math.random()));
    this.forwardChannelRequest_ = request;
    request.xmlHttpPost(uri, requestText, true);
  };
  
  
  /**
   * Adds the additional parameters from the handler to the given URI.
   * @param {goog.Uri} uri The URI to add the parameters to.
   * @private
   */
  goog.net.BrowserChannel.prototype.addAdditionalParams_ = function(uri) {
    // Add the additional reconnect parameters as needed.
    if (this.handler_) {
      var params = this.handler_.getAdditionalParams(this);
      if (params) {
        goog.structs.forEach(params, function(value, key, coll) {
          uri.setParameterValue(key, value);
        });
      }
    }
  };
  
  
  /**
   * Returns the request text from the outgoing maps and resets it.
   * @return {string} The encoded request text created from all the currently
   *                  queued outgoing maps.
   * @private
   */
  goog.net.BrowserChannel.prototype.dequeueOutgoingMaps_ = function() {
    var count = Math.min(this.outgoingMaps_.length,
                         goog.net.BrowserChannel.MAX_MAPS_PER_REQUEST_);
    var sb = ['count=' + count];
    var offset;
    if (this.channelVersion_ > 6 && count > 0) {
      // To save a bit of bandwidth, specify the base mapId and the rest as
      // offsets from it.
      offset = this.outgoingMaps_[0].mapId;
      sb.push('ofs=' + offset);
    } else {
      offset = 0;
    }
    for (var i = 0; i < count; i++) {
      var mapId = this.outgoingMaps_[i].mapId;
      var map = this.outgoingMaps_[i].map;
      if (this.channelVersion_ <= 6) {
        // Map IDs were not used in ver 6 and before, just indexes in the request.
        mapId = i;
      } else {
        mapId -= offset;
      }
      try {
        goog.structs.forEach(map, function(value, key, coll) {
          sb.push('req' + mapId + '_' + key + '=' + encodeURIComponent(value));
        });
      } catch (ex) {
        // We send a map here because lots of the retry logic relies on map IDs,
        // so we have to send something.
        sb.push('req' + mapId + '_' + 'type' + '=' +
                encodeURIComponent('_badmap'));
        if (this.handler_) {
          this.handler_.badMapError(this, map);
        }
      }
    }
    this.pendingMaps_ = this.pendingMaps_.concat(
        this.outgoingMaps_.splice(0, count));
    return sb.join('&');
  };
  
  
  /**
   * Requeues unacknowledged sent arrays for retransmission in the next forward
   * channel request.
   * @private
   */
  goog.net.BrowserChannel.prototype.requeuePendingMaps_ = function() {
    this.outgoingMaps_ = this.pendingMaps_.concat(this.outgoingMaps_);
    this.pendingMaps_.length = 0;
  };
  
  
  /**
   * Ensures there is a backchannel request for receiving data from the server.
   * @private
   */
  goog.net.BrowserChannel.prototype.ensureBackChannel_ = function() {
    if (this.backChannelRequest_) {
      // already have one
      return;
    }
  
    if (this.backChannelTimerId_) {
      // no need to start a new request - one is already scheduled
      return;
    }
  
    this.backChannelAttemptId_ = 1;
    this.backChannelTimerId_ = goog.net.BrowserChannel.setTimeout(
        goog.bind(this.onStartBackChannelTimer_, this), 0);
    this.backChannelRetryCount_ = 0;
  };
  
  
  /**
   * Schedules a back-channel retry, unless the max retries has been reached.
   * @return {boolean} true iff a retry was scheduled.
   * @private
   */
  goog.net.BrowserChannel.prototype.maybeRetryBackChannel_ = function() {
    if (this.backChannelRequest_ || this.backChannelTimerId_) {
      // Should be impossible to be called in this state.
      this.channelDebug_.severe('Request already in progress');
      return false;
    }
  
    if (this.backChannelRetryCount_ >= this.getBackChannelMaxRetries()) {
      return false;
    }
  
    this.channelDebug_.debug('Going to retry GET');
  
    this.backChannelAttemptId_++;
    this.backChannelTimerId_ = goog.net.BrowserChannel.setTimeout(
        goog.bind(this.onStartBackChannelTimer_, this),
        this.getRetryTime_(this.backChannelRetryCount_));
    this.backChannelRetryCount_++;
    return true;
  };
  
  
  /**
   * Timer callback for ensureBackChannel_.
   * @private
   */
  goog.net.BrowserChannel.prototype.onStartBackChannelTimer_ = function() {
    this.backChannelTimerId_ = null;
    this.startBackChannel_();
  };
  
  
  /**
   * Begins a new back channel operation to the server.
   * @private
   */
  goog.net.BrowserChannel.prototype.startBackChannel_ = function() {
    if (!this.okToMakeRequest_()) {
      // channel is cancelled
      return;
    }
  
    this.channelDebug_.debug('Creating new HttpRequest');
    this.backChannelRequest_ = goog.net.BrowserChannel.createChannelRequest(
        this,
        this.channelDebug_,
        this.sid_,
        'rpc',
        this.backChannelAttemptId_);
    this.backChannelRequest_.setExtraHeaders(this.extraHeaders_);
    var uri = this.backChannelUri_.clone();
    uri.setParameterValue('RID', 'rpc');
    uri.setParameterValue('SID', this.sid_);
    uri.setParameterValue('CI', this.useChunked_ ? '0' : '1');
    uri.setParameterValue('AID', this.lastArrayId_);
  
    // Add the reconnect parameters.
    this.addAdditionalParams_(uri);
  
    if (goog.userAgent.IE) {
      uri.setParameterValue('TYPE', 'html');
      this.backChannelRequest_.tridentGet(uri, Boolean(this.hostPrefix_));
    } else {
      uri.setParameterValue('TYPE', 'xmlhttp');
      this.backChannelRequest_.xmlHttpGet(uri, true /* decodeChunks */,
          this.hostPrefix_, false /* opt_noClose */);
    }
    this.channelDebug_.debug('New Request created');
  };
  
  
  /**
   * Gives the handler a chance to return an error code and stop channel
   * execution. A handler might want to do this to check that the user is still
   * logged in, for example.
   * @private
   * @return {boolean} If it's OK to make a request.
   */
  goog.net.BrowserChannel.prototype.okToMakeRequest_ = function() {
    if (this.handler_) {
      var result = this.handler_.okToMakeRequest(this);
      if (result != goog.net.BrowserChannel.Error.OK) {
        this.channelDebug_.debug('Handler returned error code from ' +
                                    'okToMakeRequest');
        this.signalError_(result);
        return false;
      }
    }
    return true;
  };
  
  
  /**
   * Callback from BrowserTestChannel for when the channel is finished.
   * @param {goog.net.BrowserTestChannel} testChannel The BrowserTestChannel.
   * @param {boolean} useChunked  Whether we can chunk responses.
   */
  goog.net.BrowserChannel.prototype.testConnectionFinished =
      function(testChannel, useChunked) {
    this.channelDebug_.debug('Test Connection Finished');
  
    this.useChunked_ = this.allowChunkedMode_ && useChunked;
    this.lastStatusCode_ = testChannel.getLastStatusCode();
    this.connectChannel_();
  };
  
  
  /**
   * Callback from BrowserTestChannel for when the channel has an error.
   * @param {goog.net.BrowserTestChannel} testChannel The BrowserTestChannel.
   * @param {goog.net.ChannelRequest.Error} errorCode  The error code of the
         failure.
   */
  goog.net.BrowserChannel.prototype.testConnectionFailure =
      function(testChannel, errorCode) {
    this.channelDebug_.debug('Test Connection Failed');
    this.lastStatusCode_ = testChannel.getLastStatusCode();
    this.signalError_(goog.net.BrowserChannel.Error.REQUEST_FAILED);
  };
  
  
  /**
   * Callback from BrowserTestChannel for when the channel is blocked.
   * @param {goog.net.BrowserTestChannel} testChannel The BrowserTestChannel.
   */
  goog.net.BrowserChannel.prototype.testConnectionBlocked =
      function(testChannel) {
    this.channelDebug_.debug('Test Connection Blocked');
    this.lastStatusCode_ = this.connectionTest_.getLastStatusCode();
    this.signalError_(goog.net.BrowserChannel.Error.BLOCKED);
  };
  
  
  /**
   * Callback from ChannelRequest for when new data is received
   * @param {goog.net.ChannelRequest} request  The request object.
   * @param {string} responseText The text of the response.
   */
  goog.net.BrowserChannel.prototype.onRequestData =
      function(request, responseText) {
    if (this.state_ == goog.net.BrowserChannel.State.CLOSED ||
        (this.backChannelRequest_ != request &&
         this.forwardChannelRequest_ != request)) {
      // either CLOSED or a request we don't know about (perhaps an old request)
      return;
    }
    this.lastStatusCode_ = request.getLastStatusCode();
  
    if (this.forwardChannelRequest_ == request &&
        this.state_ == goog.net.BrowserChannel.State.OPENED) {
      if (this.channelVersion_ > 7) {
        var response;
        try {
          response = (/** @type {Array} */ goog.json.unsafeParse(responseText));
        } catch (ex) {
          response = null;
        }
        if (goog.isArray(response) && response.length == 3) {
          this.handlePostResponse_(response);
        } else {
          this.channelDebug_.debug('Bad POST response data returned');
          this.signalError_(goog.net.BrowserChannel.Error.BAD_RESPONSE);
        }
      } else if (responseText != goog.net.BrowserChannel.MAGIC_RESPONSE_COOKIE) {
        this.channelDebug_.debug('Bad data returned - missing/invald ' +
                                    'magic cookie');
        this.signalError_(goog.net.BrowserChannel.Error.BAD_RESPONSE);
      }
    } else {
      if (this.backChannelRequest_ == request) {
        this.clearDeadBackchannelTimer_();
      }
      if (!goog.string.isEmpty(responseText)) {
        this.onInput_(/** @type {Array} */ (goog.json.unsafeParse(responseText)));
      }
    }
  };
  
  
  /**
   * Handles a POST response from the server.
   * @param {Array} responseValues The key value pairs in the POST response.
   * @private
   */
  goog.net.BrowserChannel.prototype.handlePostResponse_ = function(
      responseValues) {
    // The first response value is set to 0 if server is missing backchannel.
    if (responseValues[0] == 0) {
      this.handleBackchannelMissing_();
      return;
    }
    this.lastPostResponseArrayId_ = responseValues[1];
    var outstandingArrays = this.lastPostResponseArrayId_ - this.lastArrayId_;
    if (0 < outstandingArrays) {
      var numOutstandingBackchannelBytes = responseValues[2];
      this.channelDebug_.debug(numOutstandingBackchannelBytes + ' bytes (in ' +
           outstandingArrays + ' arrays) are outstanding on the BackChannel');
      if (!this.shouldRetryBackChannel_(numOutstandingBackchannelBytes)) {
        return;
      }
      if (!this.deadBackChannelTimerId_) {
        // We expect to receive data within 2 RTTs or we retry the backchannel.
        this.deadBackChannelTimerId_ = goog.net.BrowserChannel.setTimeout(
          goog.bind(this.onBackChannelDead_, this),
          2 * goog.net.BrowserChannel.RTT_ESTIMATE);
      }
    }
  };
  
  
  /**
   * Handles a POST response from the server telling us that it has detected that
   * we have no hanging GET connection.
   * @private
   */
  goog.net.BrowserChannel.prototype.handleBackchannelMissing_ = function() {
    // As long as the back channel was started before the POST was sent,
    // we should retry the backchannel. We give a slight buffer of RTT_ESTIMATE
    // so as not to excessively retry the backchannel
    this.channelDebug_.debug('Server claims our backchannel is missing.')
    if (this.backChannelTimerId_) {
      this.channelDebug_.debug('But we are currently starting the request.');
      return;
    } else if (!this.backChannelRequest_) {
      this.channelDebug_.warning(
          'We do not have a BackChannel established');
    } else if (this.backChannelRequest_.getRequestStartTime() +
        goog.net.BrowserChannel.RTT_ESTIMATE <
        this.forwardChannelRequest_.getRequestStartTime()) {
      this.clearDeadBackchannelTimer_();
      this.backChannelRequest_.cancel();
      this.backChannelRequest_ = null;
    } else {
      return;
    }
    this.maybeRetryBackChannel_();
    goog.net.BrowserChannel.notifyStatEvent(
          goog.net.BrowserChannel.Stat.BACKCHANNEL_MISSING);
  };
  
  
  /**
   * Determines whether we should start the process of retrying a possibly
   * dead backchannel.
   * @param {number} outstandingBytes The number of bytes for which the server has
   *     not yet received acknowledgement.
   * @return {boolean} Whether to start the backchannel retry timer.
   * @private
   */
  goog.net.BrowserChannel.prototype.shouldRetryBackChannel_ = function(
      outstandingBytes) {
    // Not too many outstanding bytes, not buffered and not after a retry.
    return outstandingBytes <
        goog.net.BrowserChannel.OUTSTANDING_DATA_BACKCHANNEL_RETRY_CUTOFF &&
        !this.isBuffered() &&
        this.backChannelRetryCount_ == 0;
  };
  
  
  /**
   * Handles the timer that indicates that our backchannel is no longer able to
   * successfully receive data from the server.
   * @private
   */
  goog.net.BrowserChannel.prototype.onBackChannelDead_ = function() {
    if (goog.isDefAndNotNull(this.deadBackChannelTimerId_)) {
      this.deadBackChannelTimerId_ = null;
      this.backChannelRequest_.cancel();
      this.backChannelRequest_ = null;
      this.maybeRetryBackChannel_();
      goog.net.BrowserChannel.notifyStatEvent(
          goog.net.BrowserChannel.Stat.BACKCHANNEL_DEAD);
    }
  };
  
  
  /**
   * Clears the timer that indicates that our backchannel is no longer able to
   * successfully receive data from the server.
   * @private
   */
  goog.net.BrowserChannel.prototype.clearDeadBackchannelTimer_ = function() {
    if (goog.isDefAndNotNull(this.deadBackChannelTimerId_)) {
      goog.global.clearTimeout(this.deadBackChannelTimerId_)
      this.deadBackChannelTimerId_ = null;
    }
  };
  
  
  /**
   * Returns whether or not the given error/status combination is fatal or not.
   * On fatal errors we immediately close the session rather than retrying the
   * failed request.
   * @param {goog.net.ChannelRequest.Error?} error The error code for the failed
   * request.
   * @param {number} statusCode The last HTTP status code.
   * @return {boolean} Whether or not the error is fatal.
   * @private
   */
  goog.net.BrowserChannel.isFatalError_ =
      function(error, statusCode) {
    return error == goog.net.ChannelRequest.Error.UNKNOWN_SESSION_ID ||
        (error == goog.net.ChannelRequest.Error.STATUS &&
         statusCode > 0);
  };
  
  
  /**
   * Callback from ChannelRequest that indicates a request has completed.
   * @param {goog.net.ChannelRequest} request  The request object.
   */
  goog.net.BrowserChannel.prototype.onRequestComplete =
      function(request) {
    this.channelDebug_.debug('Request complete');
    var type;
    if (this.backChannelRequest_ == request) {
      this.clearDeadBackchannelTimer_();
      this.backChannelRequest_ = null;
      type = goog.net.BrowserChannel.ChannelType_.BACK_CHANNEL;
    } else if (this.forwardChannelRequest_ == request) {
      this.forwardChannelRequest_ = null;
      type = goog.net.BrowserChannel.ChannelType_.FORWARD_CHANNEL;
    } else {
      // return if it was an old request from a previous session
      return;
    }
  
    this.lastStatusCode_ = request.getLastStatusCode();
  
    if (this.state_ == goog.net.BrowserChannel.State.CLOSED) {
      return;
    }
  
    if (request.getSuccess()) {
      // Yay!
      if (type == goog.net.BrowserChannel.ChannelType_.FORWARD_CHANNEL) {
        var size = request.getPostData() ? request.getPostData().length : 0;
        goog.net.BrowserChannel.notifyTimingEvent(size,
            goog.now() - request.getRequestStartTime(),
            this.forwardChannelRetryCount_);
        this.ensureForwardChannel_();
        this.pendingMaps_.length = 0;
      } else {  // i.e., back-channel
        this.ensureBackChannel_();
      }
      return;
    }
    // Else unsuccessful. Fall through.
  
    var lastError = request.getLastError();
    if (!goog.net.BrowserChannel.isFatalError_(lastError,
                                               this.lastStatusCode_)) {
      // Maybe retry.
      this.channelDebug_.debug('Maybe retrying, last error: ' +
          goog.net.ChannelRequest.errorStringFromCode(
              /** @type {goog.net.ChannelRequest.Error} */ (lastError),
              this.lastStatusCode_));
      if (type == goog.net.BrowserChannel.ChannelType_.FORWARD_CHANNEL) {
        if (this.maybeRetryForwardChannel_(request)) {
          return;
        }
      }
      if (type == goog.net.BrowserChannel.ChannelType_.BACK_CHANNEL) {
        if (this.maybeRetryBackChannel_()) {
          return;
        }
      }
      // Else exceeded max retries. Fall through.
      this.channelDebug_.debug('Exceeded max number of retries');
    } else {
      // Else fatal error. Fall through and mark the pending maps as failed.
      this.channelDebug_.debug('Not retrying due to error type');
    }
  
  
    // Can't save this session. :(
    this.channelDebug_.debug('Error: HTTP request failed');
    switch (lastError) {
      case goog.net.ChannelRequest.Error.NO_DATA:
        this.signalError_(goog.net.BrowserChannel.Error.NO_DATA);
        break;
      case goog.net.ChannelRequest.Error.BAD_DATA:
        this.signalError_(goog.net.BrowserChannel.Error.BAD_DATA);
        break;
      case goog.net.ChannelRequest.Error.UNKNOWN_SESSION_ID:
        this.signalError_(goog.net.BrowserChannel.Error.UNKNOWN_SESSION_ID);
        break;
      default:
        this.signalError_(goog.net.BrowserChannel.Error.REQUEST_FAILED);
        break;
    }
  };
  
  
  /**
   * @param {number} retryCount Number of retries so far.
   * @return {number} Time in ms before firing next retry request.
   * @private
   */
  goog.net.BrowserChannel.prototype.getRetryTime_ = function(retryCount) {
    var retryTime = goog.net.BrowserChannel.RETRY_DELAY_MS +
        Math.floor(Math.random() * goog.net.BrowserChannel.RETRY_DELAY_SEED);
    if (!this.isActive()) {
      this.channelDebug_.debug('Inactive channel');
      retryTime =
          retryTime * goog.net.BrowserChannel.INACTIVE_CHANNEL_RETRY_FACTOR;
    }
    // Backoff for subsequent retries
    retryTime = retryTime * retryCount;
    return retryTime;
  };
  
  
  /**
   * Processes the data returned by the server.
   * @param {Array} respArray The response array returned by the server.
   * @private
   */
  goog.net.BrowserChannel.prototype.onInput_ = function(respArray) {
    // respArray is an array of arrays
    var batch = this.handler_ && this.handler_.channelHandleMultipleArrays ?
        [] : null;
    for (var i = 0; i < respArray.length; i++) {
      var nextArray = respArray[i];
      this.lastArrayId_ = nextArray[0];
      nextArray = nextArray[1];
      if (this.state_ == goog.net.BrowserChannel.State.OPENING) {
        if (nextArray[0] == 'c') {
          this.sid_ = nextArray[1];
          if (this.allowHostPrefix_) {
            this.hostPrefix_ = nextArray[2];
          } else {
            this.hostPrefix_ = null;
          }
          var negotiatedVersion = nextArray[3];
          if (goog.isDefAndNotNull(negotiatedVersion)) {
            this.channelVersion_ = negotiatedVersion;
          } else {
            // Servers prior to version 7 did not send this, so assume version 6.
            this.channelVersion_ = 6;
          }
          this.state_ = goog.net.BrowserChannel.State.OPENED;
          if (this.handler_) {
            this.handler_.channelOpened(this);
          }
          this.backChannelUri_ = this.getBackChannelUri(
              this.hostPrefix_, /** @type {string} */ (this.path_));
          // Open connection to receive data
          this.ensureBackChannel_();
        } else if (nextArray[0] == 'stop') {
          this.signalError_(goog.net.BrowserChannel.Error.STOP);
        }
      } else if (this.state_ == goog.net.BrowserChannel.State.OPENED) {
        if (nextArray[0] == 'stop') {
          if (batch && batch.length) {
            this.handler_.channelHandleMultipleArrays(this, batch);
            batch.length = 0;
          }
          this.signalError_(goog.net.BrowserChannel.Error.STOP);
        } else if (nextArray[0] == 'noop') {
          // ignore - noop to keep connection happy
        } else {
          if (batch) {
            batch.push(nextArray);
          } else if (this.handler_) {
            this.handler_.channelHandleArray(this, nextArray);
          }
        }
        // We have received useful data on the back-channel, so clear its retry
        // count. We do this because back-channels by design do not complete
        // quickly, so on a flaky connection we could have many fail to complete
        // fully but still deliver a lot of data before they fail. We don't want
        // to count such failures towards the retry limit, because we don't want
        // to give up on a session if we can still receive data.
        this.backChannelRetryCount_ = 0;
      }
    }
    if (batch && batch.length) {
      this.handler_.channelHandleMultipleArrays(this, batch);
    }
  };
  
  
  /**
   * Helper to ensure the BrowserChannel is in the expected state.
   * @param {...number} var_args The channel must be in one of the indicated
   *     states.
   * @private
   */
  goog.net.BrowserChannel.prototype.ensureInState_ = function(var_args) {
    if (!goog.array.contains(arguments, this.state_)) {
      throw Error('Unexpected channel state: ' + this.state_);
    }
  };
  
  
  /**
   * Signals an error has occurred.
   * @param {goog.net.BrowserChannel.Error} error  The error code for the failure.
   * @private
   */
  goog.net.BrowserChannel.prototype.signalError_ = function(error) {
    this.channelDebug_.info('Error code ' + error);
    if (error == goog.net.BrowserChannel.Error.REQUEST_FAILED ||
        error == goog.net.BrowserChannel.Error.BLOCKED) {
      // Ping google to check if it's a server error or user's network error.
      var imageUri = null;
      if (this.handler_) {
        imageUri = this.handler_.getNetworkTestImageUri(this);
      }
      goog.net.testGoogleCom(
          goog.bind(this.testGoogleComCallback_, this), imageUri);
    } else {
      goog.net.BrowserChannel.notifyStatEvent(
          goog.net.BrowserChannel.Stat.ERROR_OTHER);
    }
    this.onError_(error);
  };
  
  
  /**
   * Callback for testGoogleCom during error handling.
   * @param {boolean} networkUp Whether the network is up.
   * @private
   */
  goog.net.BrowserChannel.prototype.testGoogleComCallback_ = function(networkUp) {
    if (networkUp) {
      this.channelDebug_.info('Successfully pinged google.com');
      goog.net.BrowserChannel.notifyStatEvent(
          goog.net.BrowserChannel.Stat.ERROR_OTHER);
    } else {
      this.channelDebug_.info('Failed to ping google.com');
      goog.net.BrowserChannel.notifyStatEvent(
          goog.net.BrowserChannel.Stat.ERROR_NETWORK);
      // We cann onError_ here instead of signalError_ because the latter just
      // calls notifyStatEvent, and we don't want to have another stat event.
      this.onError_(goog.net.BrowserChannel.Error.NETWORK);
    }
  };
  
  
  /**
   * Called when we've determined the final error for a channel. It closes the
   * notifiers the handler of the error and closes the channel.
   * @param {goog.net.BrowserChannel.Error} error  The error code for the failure.
   * @private
   */
  goog.net.BrowserChannel.prototype.onError_ = function(error) {
    this.channelDebug_.debug('HttpChannel: error - ' + error);
    this.state_ = goog.net.BrowserChannel.State.CLOSED;
    if (this.handler_) {
      this.handler_.channelError(this, error);
    }
    this.onClose_();
    this.cancelRequests_();
  };
  
  
  /**
   * Called when the channel has been closed. It notifiers the handler of the
   * event, and reports any pending or undelivered maps.
   * @private
   */
  goog.net.BrowserChannel.prototype.onClose_ = function() {
    this.state_ = goog.net.BrowserChannel.State.CLOSED;
    this.lastStatusCode_ = -1;
    if (this.handler_) {
      if (this.pendingMaps_.length == 0 && this.outgoingMaps_.length == 0) {
        this.handler_.channelClosed(this);
      } else {
        this.channelDebug_.debug('Number of undelivered maps' +
            ', pending: ' + this.pendingMaps_.length +
            ', outgoing: ' + this.outgoingMaps_.length);
  
        var copyOfPendingMaps = goog.array.clone(this.pendingMaps_);
        var copyOfUndeliveredMaps = goog.array.clone(this.outgoingMaps_);
        this.pendingMaps_.length = 0;
        this.outgoingMaps_.length = 0;
  
        this.handler_.channelClosed(this,
            copyOfPendingMaps,
            copyOfUndeliveredMaps);
      }
    }
  };
  
  
  /**
   * Gets the Uri used for the connection that sends data to the server.
   * @param {string} path The path on the host.
   * @return {goog.Uri} The forward channel URI.
   */
  goog.net.BrowserChannel.prototype.getForwardChannelUri =
      function(path) {
    var uri = this.createDataUri(null, path);
    this.channelDebug_.debug('GetForwardChannelUri: ' + uri);
    return uri;
  };
  
  
  /**
   * Gets the Uri used for the connection that receives data from the server.
   * @param {?string} hostPrefix The host prefix.
   * @param {string} path The path on the host.
   * @return {goog.Uri} The back channel URI.
   */
  goog.net.BrowserChannel.prototype.getBackChannelUri =
      function(hostPrefix, path) {
    var uri = this.createDataUri(this.shouldUseSecondaryDomains() ?
        hostPrefix : null, path);
    this.channelDebug_.debug('GetBackChannelUri: ' + uri);
    return uri;
  };
  
  
  /**
   * Creates a data Uri applying logic for secondary hostprefix, port
   * overrides, and versioning.
   * @param {?string} hostPrefix The host prefix.
   * @param {string} path The path on the host.
   * @param {number=} opt_overridePort Optional override port.
   * @return {goog.Uri} The data URI.
   */
  goog.net.BrowserChannel.prototype.createDataUri =
      function(hostPrefix, path, opt_overridePort) {
    var locationPage = window.location;
    var hostName;
    if (hostPrefix) {
      hostName = hostPrefix + '.' + locationPage.hostname;
    } else {
      hostName = locationPage.hostname;
    }
  
    var port = opt_overridePort || locationPage.port;
  
    var uri = goog.Uri.create(locationPage.protocol, null, hostName, port, path);
    if (this.extraParams_) {
      goog.structs.forEach(this.extraParams_, function(value, key, coll) {
        uri.setParameterValue(key, value);
      });
    }
  
    // Add the protocol version to the URI.
    uri.setParameterValue('VER', this.channelVersion_);
  
    // Add the reconnect parameters.
    this.addAdditionalParams_(uri);
  
    return uri;
  };
  
  
  /**
   * Called when BC needs to create an XhrIo object.  Override in a subclass if
   * you need to customize the behavior, for example to enable the creation of
   * XHR's capable of calling a secondary domain.
   * @param {?string} hostPrefix The host prefix, if we need an XhrIo object
   *     capable of calling a secondary domain.
   * @return {!goog.net.XhrIo} A new XhrIo object.
   */
  goog.net.BrowserChannel.prototype.createXhrIo = function(hostPrefix) {
    if (hostPrefix) {
      throw new Error('Can\'t create secondary domain capable XhrIo object.');
    } else {
      return new goog.net.XhrIo();
    }
  };
  
  
  /**
   * Gets whether this channel is currently active. This is used to determine the
   * length of time to wait before retrying. This call delegates to the handler.
   * @return {boolean} Whether the channel is currently active.
   */
  goog.net.BrowserChannel.prototype.isActive = function() {
    return this.handler_.isActive(this);
  };
  
  
  /**
   * Wrapper around SafeTimeout which calls the start and end execution hooks
   * with a try...finally block.
   * @param {Function} fn The callback function.
   * @param {number} ms The time in MS for the timer.
   * @return {number} The ID of the timer.
   */
  goog.net.BrowserChannel.setTimeout = function(fn, ms) {
    if (!goog.isFunction(fn)) {
      throw Error('Fn must not be null and must be a function');
    }
    return goog.global.setTimeout(function() {
      goog.net.BrowserChannel.onStartExecution();
      try {
        fn();
      } finally {
        goog.net.BrowserChannel.onEndExecution();
      }
    }, ms);
  };
  
  
  /**
   * Helper function to call the start hook
   */
  goog.net.BrowserChannel.onStartExecution = function() {
    goog.net.BrowserChannel.startExecutionHook_();
  };
  
  
  /**
   * Helper function to call the end hook
   */
  goog.net.BrowserChannel.onEndExecution = function() {
    goog.net.BrowserChannel.endExecutionHook_();
  };
  
  
  /**
   * Returns the singleton event target for stat events.
   * @return {goog.events.EventTarget} The event target for stat events.
   */
  goog.net.BrowserChannel.getStatEventTarget = function() {
    return goog.net.BrowserChannel.statEventTarget_;
  };
  
  
  /**
   * Helper function to call the stat event callback.
   * @param {goog.net.BrowserChannel.Stat} stat The stat.
   */
  goog.net.BrowserChannel.notifyStatEvent = function(stat) {
    var target = goog.net.BrowserChannel.statEventTarget_;
    target.dispatchEvent(
        new goog.net.BrowserChannel.StatEvent(target, stat));
  };
  
  
  /**
   * Helper function to notify listeners about POST request performance.
   *
   * @param {number} size Number of characters in the POST data.
   * @param {number} rtt The amount of time from POST start to response.
   * @param {number} retries The number of times the POST had to be retried.
   */
  goog.net.BrowserChannel.notifyTimingEvent = function(size, rtt, retries) {
    var target = goog.net.BrowserChannel.statEventTarget_;
    target.dispatchEvent(
        new goog.net.BrowserChannel.TimingEvent(target, size, rtt, retries));
  };
  
  
  /**
   * Override this in a subclass to enable secondary domains for non-IE browsers.
   * @return {boolean} Whether to use a secondary domain when the server
   *     recommends it.
   */
  goog.net.BrowserChannel.prototype.shouldUseSecondaryDomains = function() {
    return goog.userAgent.IE;
  };
  
  
  /**
   * A LogSaver that can be used to accumulate all the debug logs for
   * BrowserChannels so they can be sent to the server when a problem is
   * detected.
   */
  goog.net.BrowserChannel.LogSaver = {};
  
  /**
   * Buffer for accumulating the debug log
   * @type {goog.structs.CircularBuffer}
   * @private
   */
  goog.net.BrowserChannel.LogSaver.buffer_ =
      new goog.structs.CircularBuffer(1000);
  
  /**
   * Whether we're currently accumulating the debug log.
   * @type {boolean}
   * @private
   */
  goog.net.BrowserChannel.LogSaver.enabled_ = false;
  
  
  /**
   * Formatter for saving logs.
   * @type {goog.debug.Formatter}
   * @private
   */
  goog.net.BrowserChannel.LogSaver.formatter_ = new goog.debug.TextFormatter();
  
  /**
   * Returns whether the LogSaver is enabled.
   * @return {boolean} Whether saving is enabled or disabled.
   */
  goog.net.BrowserChannel.LogSaver.isEnabled = function() {
    return goog.net.BrowserChannel.LogSaver.enabled_
  };
  
  
  /**
   * Enables of disables the LogSaver.
   * @param {boolean} enable Whether to enable or disable saving.
   */
  goog.net.BrowserChannel.LogSaver.setEnabled = function(enable) {
    if (enable == goog.net.BrowserChannel.LogSaver.enabled_) {
      return;
    }
  
    var fn = goog.net.BrowserChannel.LogSaver.addLogRecord;
    var logger = goog.debug.Logger.getLogger('goog.net');
    if (enable) {
      logger.addHandler(fn);
    } else {
      logger.removeHandler(fn);
    }
  };
  
  
  /**
   * Adds a log record.
   * @param {goog.debug.LogRecord} logRecord the LogRecord.
   */
  goog.net.BrowserChannel.LogSaver.addLogRecord = function(logRecord) {
    goog.net.BrowserChannel.LogSaver.buffer_.add(
        goog.net.BrowserChannel.LogSaver.formatter_.formatRecord(logRecord));
  };
  
  /**
   * Returns the log as a single string.
   * @return {string} The log as a single string.
   */
  goog.net.BrowserChannel.LogSaver.getBuffer = function() {
    return goog.net.BrowserChannel.LogSaver.buffer_.getValues().join('');
  };
  
  
  /**
   * Clears the buffer
   */
  goog.net.BrowserChannel.LogSaver.clearBuffer = function() {
    goog.net.BrowserChannel.LogSaver.buffer_.clear();
  };
  
  
  
  /**
   * Interface for the browser channel handler
   * @constructor
   */
  goog.net.BrowserChannel.Handler = function() {
  };
  
  
  /**
   * Callback handler for when a batch of response arrays is received from the
   * server.
   * @type {Function}
   */
  goog.net.BrowserChannel.Handler.prototype.channelHandleMultipleArrays = null;
  
  
  /**
   * Whether it's okay to make a request to the server. A handler can return
   * false if the channel should fail. For example, if the user has logged out,
   * the handler may want all requests to fail immediately.
   * @param {goog.net.BrowserChannel} browserChannel The browser channel.
   * @return {goog.net.BrowserChannel.Error} An error code. The code should
   * return goog.net.BrowserChannel.Error.OK to indicate it's okay. Any other
   * error code will cause a failure.
   */
  goog.net.BrowserChannel.Handler.prototype.okToMakeRequest =
      function(browserChannel) {
    return goog.net.BrowserChannel.Error.OK;
  };
  
  
  /**
   * Indicates the BrowserChannel has successfully negotiated with the server
   * and can now send and receive data.
   * @param {goog.net.BrowserChannel} browserChannel The browser channel.
   */
  goog.net.BrowserChannel.Handler.prototype.channelOpened =
      function(browserChannel) {
  };
  
  
  /**
   * New input is available for the application to process.
   *
   * @param {goog.net.BrowserChannel} browserChannel The browser channel.
   * @param {Array} array The data array.
   */
  goog.net.BrowserChannel.Handler.prototype.channelHandleArray =
      function(browserChannel, array) {
  };
  
  
  /**
   * Indicates an error occurred on the BrowserChannel.
   *
   * @param {goog.net.BrowserChannel} browserChannel The browser channel.
   * @param {goog.net.BrowserChannel.Error} error The error code.
   */
  goog.net.BrowserChannel.Handler.prototype.channelError =
      function(browserChannel, error) {
  };
  
  
  /**
   * Indicates the BrowserChannel is closed. Also notifies about which maps,
   * if any, that may not have been delivered to the server.
   * @param {goog.net.BrowserChannel} browserChannel The browser channel.
   * @param {Array.<goog.net.BrowserChannel.QueuedMap>=} opt_pendingMaps The
   *     array of pending maps, which may or may not have been delivered to the
   *     server.
   * @param {Array.<goog.net.BrowserChannel.QueuedMap>=} opt_undeliveredMaps
   *     The array of undelivered maps, which have definitely not been delivered
   *     to the server.
   */
  goog.net.BrowserChannel.Handler.prototype.channelClosed =
      function(browserChannel, opt_pendingMaps, opt_undeliveredMaps) {
  };
  
  
  /**
   * Gets any parameters that should be added at the time another connection is
   * made to the server.
   * @param {goog.net.BrowserChannel} browserChannel The browser channel.
   * @return {Object} Extra parameter keys and values to add to the
   *                  requests.
   */
  goog.net.BrowserChannel.Handler.prototype.getAdditionalParams =
      function(browserChannel) {
    return {};
  };
  
  
  /**
   * Gets the URI of an image that can be used to test network connectivity.
   * @param {goog.net.BrowserChannel} browserChannel The browser channel.
   * @return {goog.Uri?} A custom URI to load for the network test.
   */
  goog.net.BrowserChannel.Handler.prototype.getNetworkTestImageUri =
      function(browserChannel) {
    return null;
  };
  
  
  /**
   * Gets whether this channel is currently active. This is used to determine the
   * length of time to wait before retrying.
   * @param {goog.net.BrowserChannel} browserChannel The browser channel.
   * @return {boolean} Whether the channel is currently active.
   */
  goog.net.BrowserChannel.Handler.prototype.isActive = function(browserChannel) {
    return true;
  };
  
  
  /**
   * Called by the channel if enumeration of the map throws an exception.
   * @param {goog.net.BrowserChannel} browserChannel The browser channel.
   * @param {Object} map The map that can't be enumerated.
   */
  goog.net.BrowserChannel.Handler.prototype.badMapError =
      function(browserChannel, map) {
    return;
  };
  