func relevantCaller() runtime.Frame {
	pc := make([]uintptr, 16)
	n := runtime.Callers(1, pc)
	frames := runtime.CallersFrames(pc[:n])
	var frame runtime.Frame
	for {
		frame, more := frames.Next()
		if !strings.HasPrefix(frame.Function, "net/http.") {
			return frame
		}
		if !more {
			break
		}
	}
	return frame
}

func (w *response) WriteHeader(code int) {