code: func (srv *Server) Serve() error {
  	if !srv.Validate() {
  		return fmt.Errorf("请求校验失败")
  	}
  
  	echostr, exists := srv.GetQuery("echostr")
  	if exists {
  		srv.String(echostr)
  		return nil
  	}
  
  	response, err := srv.handleRequest()
  	if err != nil {
  		return err
  	}
  
  	//debug
  	//fmt.Println("request msg = ", string(srv.requestRawXMLMsg))
  
  	return srv.buildResponse(response)
  }
docs: //Serve 处理微信的请求消息