kvlog/writer.go
func (w *Writer) Handle(h Handler) {
	w.mutex.Lock()
	defer w.mutex.Unlock()

	if h != nil {
		w.handlers = append(w.handlers, h)
	}
}
func (w *Writer) Handle(h Handler) {
	w.mutex.Lock()
	defer w.mutex.Unlock()

	if h != nil {
		w.handlers = append(w.handlers, h)
	}
}
// Handle registers a handler that will be called for every logging
// event. The function receives a message, which is a structured
// representation of the log message text.
//
// This function is useful for registering handlers that send log
// information to external sources.