abstract-xhr.js

'use strict';

var EventEmitter = require('events').EventEmitter
  , inherits = require('inherits')
  , utils = require('../../utils/event')
  , urlUtils = require('../../utils/url')
  , XHR = global.XMLHttpRequest
  ;

var debug = function() {};
if (process.env.NODE_ENV !== 'production') {
  debug = require('debug')('sockjs-client:browser:xhr');
}

function AbstractXHRObject(method, url, payload, opts) {
  debug(method, url);
  var self = this;
  EventEmitter.call(this);

  setTimeout(function () {
    self._start(method, url, payload, opts);
  }, 0);
}

inherits(AbstractXHRObject, EventEmitter);

AbstractXHRObject.prototype._start = function(method, url, payload, opts) {
  var self = this;

  try {
    this.xhr = new XHR();
  } catch (x) {
    // intentionally empty
  }

  if (!this.xhr) {
    debug('no xhr');
    this.emit('finish', 0, 'no xhr support');
    this._cleanup();
    return;
  }

  // several browsers cache POSTs
  url = urlUtils.addQuery(url, 't=' + (+new Date()));

  // Explorer tends to keep connection open, even after the
  // tab gets closed: http://bugs.jquery.com/ticket/5280
  this.unloadRef = utils.unloadAdd(function() {
    debug('unload cleanup');
    self._cleanup(true);
  });
  try {
    this.xhr.open(method, url, true);
    if (this.timeout && 'timeout' in this.xhr) {
      this.xhr.timeout = this.timeout;
      this.xhr.ontimeout = function() {
        debug('xhr timeout');
        self.emit('finish', 0, '');
        self._cleanup(false);
      };
    }
  } catch (e) {
    debug('exception', e);
    // IE raises an exception on wrong port.
    this.emit('finish', 0, '');
    this._cleanup(false);
    return;
  }

  if ((!opts || !opts.noCredentials) && AbstractXHRObject.supportsCORS) {
    debug('withCredentials');
    // Mozilla docs says https://developer.mozilla.org/en/XMLHttpRequest :
    // "This never affects same-site requests."

    this.xhr.withCredentials = 'true';
  }
  if (opts && opts.headers) {
    for (var key in opts.headers) {
      this.xhr.setRequestHeader(key, opts.headers[key]);
    }
  }

  this.xhr.onreadystatechange = function() {
    if (self.xhr) {
      var x = self.xhr;
      var text, status;
      debug('readyState', x.readyState);
      switch (x.readyState) {
      case 3:
        // IE doesn't like peeking into responseText or status
        // on Microsoft.XMLHTTP and readystate=3
        try {
          status = x.status;
          text = x.responseText;
        } catch (e) {
          // intentionally empty
        }
        debug('status', status);
        // IE returns 1223 for 204: http://bugs.jquery.com/ticket/1450
        if (status === 1223) {
          status = 204;
        }

        // IE does return readystate == 3 for 404 answers.
        if (status === 200 && text && text.length > 0) {
          debug('chunk');
          self.emit('chunk', status, text);
        }
        break;
      case 4:
        status = x.status;
        debug('status', status);
        // IE returns 1223 for 204: http://bugs.jquery.com/ticket/1450
        if (status === 1223) {
          status = 204;
        }
        // IE returns this for a bad port
        // http://msdn.microsoft.com/en-us/library/windows/desktop/aa383770(v=vs.85).aspx
        if (status === 12005 || status === 12029) {
          status = 0;
        }

        debug('finish', status, x.responseText);
        self.emit('finish', status, x.responseText);
        self._cleanup(false);
        break;
      }
    }
  };

  try {
    self.xhr.send(payload);
  } catch (e) {
    self.emit('finish', 0, '');
    self._cleanup(false);
  }
};

AbstractXHRObject.prototype._cleanup = function(abort) {
  debug('cleanup');
  if (!this.xhr) {
    return;
  }
  this.removeAllListeners();
  utils.unloadDel(this.unloadRef);

  // IE needs this field to be a function
  this.xhr.onreadystatechange = function() {};
  if (this.xhr.ontimeout) {
    this.xhr.ontimeout = null;
  }

  if (abort) {
    try {
      this.xhr.abort();
    } catch (x) {
      // intentionally empty
    }
  }
  this.unloadRef = this.xhr = null;
};

AbstractXHRObject.prototype.close = function() {
  debug('close');
  this._cleanup(true);
};

AbstractXHRObject.enabled = !!XHR;
// override XMLHttpRequest for IE6/7
// obfuscate to avoid firewalls
var axo = ['Active'].concat('Object').join('X');
if (!AbstractXHRObject.enabled && (axo in global)) {
  debug('overriding xmlhttprequest');
  XHR = function() {
    try {
      return new global[axo]('Microsoft.XMLHTTP');
    } catch (e) {
      return null;
    }
  };
  AbstractXHRObject.enabled = !!new XHR();
}

var cors = false;
try {
  cors = 'withCredentials' in new XHR();
} catch (ignored) {
  // intentionally empty
}

AbstractXHRObject.supportsCORS = cors;

module.exports = AbstractXHRObject;