util/log/file_logger.go
func NewWriterLogger(conf *WriterConfig, out io.Writer) (Logger, error) {
	l := &writerLogger{}

	base, err := NewLoggerBase(conf.BaseConfig, l.log)
	if err != nil {
		return nil, err
	}

	flags := log.LstdFlags
	if conf.UTC {
		flags |= log.LUTC
	}

	l.logger = log.New(out, conf.Prefix, flags)
	l.LoggerBase = base

	return l, nil
}
func NewWriterLogger(conf *WriterConfig, out io.Writer) (Logger, error) {
	l := &writerLogger{}

	base, err := NewLoggerBase(conf.BaseConfig, l.log)
	if err != nil {
		return nil, err
	}

	flags := log.LstdFlags
	if conf.UTC {
		flags |= log.LUTC
	}

	l.logger = log.New(out, conf.Prefix, flags)
	l.LoggerBase = base

	return l, nil
}
// NewWriterLogger creates a new io.Writer based logger.