polling-xhr.js

/**
 * Module requirements.
 */

var XMLHttpRequest = require('xmlhttprequest');
var Polling = require('./polling');
var Emitter = require('component-emitter');
var inherit = require('component-inherit');
var debug = require('debug')('engine.io-client:polling-xhr');

/**
 * Module exports.
 */

module.exports = XHR;
module.exports.Request = Request;

/**
 * Empty function
 */

function empty(){}

/**
 * XHR Polling constructor.
 *
 * @param {Object} opts
 * @api public
 */

function XHR(opts){
  Polling.call(this, opts);

  if (global.location) {
    var isSSL = 'https:' == location.protocol;
    var port = location.port;

    // some user agents have empty `location.port`
    if (!port) {
      port = isSSL ? 443 : 80;
    }

    this.xd = opts.hostname != global.location.hostname ||
      port != opts.port;
  }
}

/**
 * Inherits from Polling.
 */

inherit(XHR, Polling);

/**
 * XHR supports binary
 */

XHR.prototype.supportsBinary = true;

/**
 * Creates a request.
 *
 * @param {String} method
 * @api private
 */

XHR.prototype.request = function(opts){
  opts = opts || {};
  opts.uri = this.uri();
  opts.xd = this.xd;
  opts.agent = this.agent || false;
  opts.supportsBinary = this.supportsBinary;
  return new Request(opts);
};

/**
 * Sends data.
 *
 * @param {String} data to send.
 * @param {Function} called upon flush.
 * @api private
 */

XHR.prototype.doWrite = function(data, fn){
  var isBinary = typeof data !== 'string' && data !== undefined;
  var req = this.request({ method: 'POST', data: data, isBinary: isBinary });
  var self = this;
  req.on('success', fn);
  req.on('error', function(err){
    self.onError('xhr post error', err);
  });
  this.sendXhr = req;
};

/**
 * Starts a poll cycle.
 *
 * @api private
 */

XHR.prototype.doPoll = function(){
  debug('xhr poll');
  var req = this.request();
  var self = this;
  req.on('data', function(data){
    self.onData(data);
  });
  req.on('error', function(err){
    self.onError('xhr poll error', err);
  });
  this.pollXhr = req;
};

/**
 * Request constructor
 *
 * @param {Object} options
 * @api public
 */

function Request(opts){
  this.method = opts.method || 'GET';
  this.uri = opts.uri;
  this.xd = !!opts.xd;
  this.async = false !== opts.async;
  this.data = undefined != opts.data ? opts.data : null;
  this.agent = opts.agent;
  this.create(opts.isBinary, opts.supportsBinary);
}

/**
 * Mix in `Emitter`.
 */

Emitter(Request.prototype);

/**
 * Creates the XHR object and sends the request.
 *
 * @api private
 */

Request.prototype.create = function(isBinary, supportsBinary){
  var xhr = this.xhr = new XMLHttpRequest({ agent: this.agent, xdomain: this.xd });
  var self = this;

  try {
    debug('xhr open %s: %s', this.method, this.uri);
    xhr.open(this.method, this.uri, this.async);
    if (supportsBinary) {
      // This has to be done after open because Firefox is stupid
      // http://stackoverflow.com/questions/13216903/get-binary-data-with-xmlhttprequest-in-a-firefox-extension
      xhr.responseType = 'arraybuffer';
    }

    if ('POST' == this.method) {
      try {
        if (isBinary) {
          xhr.setRequestHeader('Content-type', 'application/octet-stream');
        } else {
          xhr.setRequestHeader('Content-type', 'text/plain;charset=UTF-8');
        }
      } catch (e) {}
    }

    // ie6 check
    if ('withCredentials' in xhr) {
      xhr.withCredentials = true;
    }

    xhr.onreadystatechange = function(){
      var data;

      try {
        if (4 != xhr.readyState) return;
        if (200 == xhr.status || 1223 == xhr.status) {
          var contentType = xhr.getResponseHeader('Content-Type');
          if (contentType === 'application/octet-stream') {
            data = xhr.response;
          } else {
            if (!supportsBinary) {
              data = xhr.responseText;
            } else {
              data = 'ok';
            }
          }
        } else {
          // make sure the `error` event handler that's user-set
          // does not throw in the same tick and gets caught here
          setTimeout(function(){
            self.onError(xhr.status);
          }, 0);
        }
      } catch (e) {
        self.onError(e);
      }

      if (null != data) {
        self.onData(data);
      }
    };

    debug('xhr data %s', this.data);
    xhr.send(this.data);
  } catch (e) {
    // Need to defer since .create() is called directly fhrom the constructor
    // and thus the 'error' event can only be only bound *after* this exception
    // occurs.  Therefore, also, we cannot throw here at all.
    setTimeout(function() {
      self.onError(e);
    }, 0);
    return;
  }

  if (global.document) {
    this.index = Request.requestsCount++;
    Request.requests[this.index] = this;
  }
};

/**
 * Called upon successful response.
 *
 * @api private
 */

Request.prototype.onSuccess = function(){
  this.emit('success');
  this.cleanup();
};

/**
 * Called if we have data.
 *
 * @api private
 */

Request.prototype.onData = function(data){
  this.emit('data', data);
  this.onSuccess();
};

/**
 * Called upon error.
 *
 * @api private
 */

Request.prototype.onError = function(err){
  this.emit('error', err);
  this.cleanup(true);
};

/**
 * Cleans up house.
 *
 * @api private
 */

Request.prototype.cleanup = function(fromError){
  if ('undefined' == typeof this.xhr || null === this.xhr) {
    return;
  }
  // xmlhttprequest
  this.xhr.onreadystatechange = empty;

  if (fromError) {
    try {
      this.xhr.abort();
    } catch(e) {}
  }

  if (global.document) {
    delete Request.requests[this.index];
  }

  this.xhr = null;
};

/**
 * Aborts the request.
 *
 * @api public
 */

Request.prototype.abort = function(){
  this.cleanup();
};

/**
 * Aborts pending requests when unloading the window. This is needed to prevent
 * memory leaks (e.g. when using IE) and to ensure that no spurious error is
 * emitted.
 */

if (global.document) {
  Request.requestsCount = 0;
  Request.requests = {};
  if (global.attachEvent) {
    global.attachEvent('onunload', unloadHandler);
  } else if (global.addEventListener) {
    global.addEventListener('beforeunload', unloadHandler);
  }
}

function unloadHandler() {
  for (var i in Request.requests) {
    if (Request.requests.hasOwnProperty(i)) {
      Request.requests[i].abort();
    }
  }
}