log/filehandler.go
func (h *RotatingFileHandler) Write(p []byte) (n int, err error) {
	h.doRollover()
	n, err = h.fd.Write(p)
	h.curBytes += n
	return
}
func (h *RotatingFileHandler) Write(p []byte) (n int, err error) {
	h.doRollover()
	n, err = h.fd.Write(p)
	h.curBytes += n
	return
}
// Write implements Handler interface