if code < 100 || code > 999 {
		panic(fmt.Sprintf("invalid WriteHeader code %v", code))
	}
}

// relevantCaller searches the call stack for the first function outside of net/http.
// The purpose of this function is to provide more helpful error messages.
func relevantCaller() runtime.Frame {
	pc := make([]uintptr, 16)
	n := runtime.Callers(1, pc)
	frames := runtime.CallersFrames(pc[:n])