*/
  public static HostSpecifier fromValid(String specifier) {
    // Verify that no port was specified, and strip optional brackets from
    // IPv6 literals.
    HostAndPort parsedHost = HostAndPort.fromString(specifier);
    Preconditions.checkArgument(!parsedHost.hasPort());
    String host = parsedHost.getHost();

    // Try to interpret the specifier as an IP address. Note we build