nsqlookup/topology.go
func WithClientIP(ctx context.Context, ip net.IP) context.Context {
	if ip == nil {
		return ctx
	}
	return context.WithValue(ctx, clientIPKey{}, ip)
}
func WithClientIP(ctx context.Context, ip net.IP) context.Context {
	if ip == nil {
		return ctx
	}
	return context.WithValue(ctx, clientIPKey{}, ip)
}
// WithClientIP returns a context which carries the given client IP.