code: func (bundle *peerBundle) knownPeer(ip, id string) (*knownPeer, []*peerEvent) {
  	var events []*peerEvent
  	if _, ok := bundle.KnownPeers[id]; !ok {
  		now := time.Now()
  		ingress := emptyChartEntries(now, sampleLimit)
  		egress := emptyChartEntries(now, sampleLimit)
  		events = append(events, &peerEvent{
  			IP:      ip,
  			ID:      id,
  			Ingress: append([]*ChartEntry{}, ingress...),
  			Egress:  append([]*ChartEntry{}, egress...),
  		})
  		bundle.KnownPeers[id] = &knownPeer{
  			ip:      ip,
  			id:      id,
  			Ingress: ingress,
  			Egress:  egress,
  		}
  	}
  	return bundle.KnownPeers[id], events
  }
docs: // knownPeer inserts a new peer into the map, if the peer belonging
  // to the given IP address and node ID wasn't metered so far. Returns the peer
  // belonging to the given IP and ID as well as the events occurring during the
  // initialization.