logger.go
func (opt *Options) Debugf(format string, v ...interface{}) {
	if opt.Logger == nil {
		return
	}
	opt.Logger.Debugf(format, v...)
}
func (opt *Options) Debugf(format string, v ...interface{}) {
	if opt.Logger == nil {
		return
	}
	opt.Logger.Debugf(format, v...)
}
// Warningf logs a WARNING message to the logger specified in opts.