code: func (c *localClient) Lookup(device protocol.DeviceID) (addresses []string, err error) {
  	if cache, ok := c.Get(device); ok {
  		if time.Since(cache.when) < CacheLifeTime {
  			addresses = cache.Addresses
  		}
  	}
  
  	return
  }
docs: // Lookup returns a list of addresses the device is available at.