code: func (it *IPTracker) AddContact(host string) {
  	now := it.clock.Now()
  	it.contact[host] = now
  	if time.Duration(now-it.lastContactGC) >= it.contactWindow {
  		it.gcContact(now)
  	}
  }
docs: // AddContact records that a packet containing our endpoint information has been sent to a
  // certain host.