if rl, wl := l.ReadLimit, l.WriteLimit; rl > 0 || wl > 0 {
	// Notice that the ReadLimit stands for the read limit *from* a proxy, and the WriteLimit
	// stands for the write limit *to* a proxy, thus the ReadLimit is in fact
	// a txBandwidth and the WriteLimit is a rxBandwidth.
	ll = ratelimit.NewListener(ll, wl, rl)
}