/*
 * Microsoft JDBC Driver for SQL Server Copyright(c) Microsoft Corporation All rights reserved. This program is made
 * available under the terms of the MIT License. See the LICENSE file in the project root for more information.
 */
package com.microsoft.sqlserver.jdbc.dns;

import java.util.Set;

import javax.naming.NameNotFoundException;
import javax.naming.NamingException;

Represents a DNS Kerberos Locator
/**
 * Represents a DNS Kerberos Locator
 */
public final class DNSKerberosLocator {

    private DNSKerberosLocator() {}

    
Returns whether a realm is valid by retrieving the KDC list in DNS SRV records.
This will only work if DNS lookup is setup properly or the realms are properly defined in krb5 config file.
Otherwise this will fail since the realm cannot be found.
Params:
realmName – 
       the realm to test
Throws:
NamingException – 
        if DNS failed, so realm existence cannot be determined
Returns:
true if realm is valid, false otherwise/**
     * Returns whether a realm is valid by retrieving the KDC list in DNS SRV records.
     * This will only work if DNS lookup is setup properly or the realms are properly defined in krb5 config file.
     * Otherwise this will fail since the realm cannot be found.
     *
     * @param realmName
     *        the realm to test
     * @return true if realm is valid, false otherwise
     * @throws NamingException
     *         if DNS failed, so realm existence cannot be determined
     */
    public static boolean isRealmValid(String realmName) throws NamingException {
        if (realmName == null || realmName.length() < 2) {
            return false;
        }
        if (realmName.charAt(0) == ('.')) {
            realmName = realmName.substring(1);
        }
        try {
            Set<DNSRecordSRV> records = DNSUtilities.findSrvRecords("_kerberos._udp." + realmName);
            return !records.isEmpty();
        } catch (NameNotFoundException wrongDomainException) {
            // config error - domain controller cannot be located via DNS 
            return false;
        }
    }
}