}

    // It is not any kind of IP address; must be a domain name or invalid.

    // TODO(user): different versions of this for different factories?
    InternetDomainName domain = InternetDomainName.from(host);

    if (domain.hasPublicSuffix()) {
      return new HostSpecifier(domain.toString());
    }

    throw new IllegalArgumentException(

import com.google.common.annotations.Beta;
import com.google.common.annotations.GwtCompatible;

/**
 * <b>Do not use this class directly. For access to public-suffix information, use {@link
 * com.google.common.net.InternetDomainName}.</b>
 *
 * <p>Specifies the type of a top-level domain definition.
 *
 * @since 23.3
 */
@Beta
@GwtCompatible
public enum PublicSuffixType {

import com.google.common.annotations.Beta;
import com.google.common.annotations.GwtCompatible;

/**
 * <b>Do not use this class directly. For access to public-suffix information, use {@link
 * com.google.common.net.InternetDomainName}.</b>
 *
 * <p>Specifies the type of a top-level domain definition.
 *
 * @since 23.3
 */
@Beta
@GwtCompatible
public enum PublicSuffixType {

import org.jspecify.annotations.NullUnmarked;

/**
 * {@link TestCase} for {@link HostSpecifier}. This is a relatively cursory test, as HostSpecifier
 * is a thin wrapper around {@link InetAddresses} and {@link InternetDomainName}; the unit tests for
 * those classes explore numerous corner cases. The intent here is to confirm that everything is
 * wired up properly.
 *
 * @author Craig Berry
 */
@NullUnmarked