code: func (oas *ObservedAddrSet) AddrsFor(addr ma.Multiaddr) (addrs []ma.Multiaddr) {
  	oas.RLock()
  	defer oas.RUnlock()
  
  	if len(oas.addrs) == 0 {
  		return nil
  	}
  
  	key := string(addr.Bytes())
  	observedAddrs, ok := oas.addrs[key]
  	if !ok {
  		return
  	}
  
  	now := time.Now()
  	for _, a := range observedAddrs {
  		if now.Sub(a.LastSeen) <= oas.ttl && a.activated(oas.ttl) {
  			addrs = append(addrs, a.Addr)
  		}
  	}
  
  	return addrs
  }
docs: // AddrsFor return all activated observed addresses associated with the given
  // (resolved) listen address.