code: func (db *DB) LastPongReceived(id ID, ip net.IP) time.Time {
  	// Launch expirer
  	db.ensureExpirer()
  	return time.Unix(db.fetchInt64(nodeItemKey(id, ip, dbNodePong)), 0)
  }
docs: // LastPongReceived retrieves the time of the last successful pong from remote node.