var request_v2 = function(url, opt){
  var req = new XMLHttpRequest(), ret = new Deferred();

  opt = update({
    method: 'GET',
    sendContent: {}
  }, opt || {});

  if(opt.queryString){
    var qs = queryString(opt.queryString, true);
    url += qs;
  }

  if('username' in opt){
    req.open(opt.method ? opt.method : (opt.sendContent)? 'POST' : 'GET', url, true, opt.username, opt.password);
  } else {
    req.open(opt.method ? opt.method : (opt.sendContent)? 'POST' : 'GET', url, true);
  }

  if(opt.charset) req.overrideMimeType(opt.charset);

  if(opt.sendContent){
    var content = queryString(opt.sendContent, false);
    req.setRequestHeader('Content-Type', 'application/x-www-form-urlencoded');
  } else {
    req.setRequestHeader('Content-Type', 'application/octet-stream');
  }

  req.setRequestHeader("X-Requested-With", "XMLHttpRequest");
  if(opt.headers){
    Object.keys(opt.headers).forEach(function(key){
      req.setRequestHeader(key, opt.headers[key]);
    });
  }

  var position = -1;
  var error = false;

  req.onprogress = function(e){
    position = e.position;
  }
  req.onreadystatechange = function(e){
    if(req.readyState === 4){
      var length = 0;
      try {
        length = parseInt(req.getResponseHeader('Content-Length'), 10);
      } catch(e) {
        console.log('ERROR', e);
      }
      // 最終時のlengthと比較
      if(position !== length){
        if(opt.denyRedirection){
          ret.errback(req);
          error = true;
        }
      }
      if(!error){
        if (req.status >= 200 && req.status < 300)
          ret.callback(req);
        else
          ret.errback(req);
      }
    }
  }
  req.send(opt.sendContent);
  return ret;
}