// 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
    // the address rather than using the .is* methods because we want to
    // use InetAddresses.toUriString to convert the result to a string in
    // canonical form.