*   private Set<Uri> visited;
 *   private Queue<Uri> toCrawl;
 *   protected void startUp() throws Exception {
 *     toCrawl = readStartingUris();
 *   }
 *
 *   protected void runOneIteration() throws Exception {
 *     Uri uri = toCrawl.remove();
 *     Collection<Uri> newUris = crawl(uri);
 *     visited.add(uri);
 *     for (Uri newUri : newUris) {

   * IP address string joined by a "/".
   *
   * @param ip {@link InetAddress} to be converted to URI string literal
   * @return {@code String} containing URI-safe string literal
   */
  public static String toUriString(InetAddress ip) {
    if (ip instanceof Inet6Address) {
      return "[" + toAddrString(ip) + "]";
    }
    return toAddrString(ip);
  }