code: function isMultipart(req) {
  
    if (!req || !req.headers) {
      return false;
    }
  
    var contentType = req.headers["content-type"];
    if (!contentType) {
      return false;
    }
  
    return /^multipart\/(?:form-data|related)(?:;|$)/i.exec(contentType);
  }
docs: 判断是否是Multipart上传
  @param req
  @returns {boolean}