code: func (b *Filter) Greylist(err error) {
  	s, ok := status.FromError(err)
  	if !ok {
  		return
  	}
  	if ok, peerURL := required(s); ok && peerURL != "" {
  		logger.Infof("Greylisting peer %s", peerURL)
  		b.greylistURLs.Store(peerURL, time.Now())
  	}
  }
docs: // Greylist the given peer URL