DnsClient.java

/*
 * The MIT License
 * Copyright (c) 2012 Microsoft Corporation
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in
 * all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
 * THE SOFTWARE.
 */

package microsoft.exchange.webservices.data.dns;

import microsoft.exchange.webservices.data.EWSConstants;
import microsoft.exchange.webservices.data.core.exception.dns.DnsException;

import javax.naming.NamingEnumeration;
import javax.naming.NamingException;
import javax.naming.directory.Attribute;
import javax.naming.directory.Attributes;
import javax.naming.directory.DirContext;
import javax.naming.directory.InitialDirContext;

import java.util.ArrayList;
import java.util.Hashtable;
import java.util.List;

/**
 * Class that represents DNS Query client.
 */
public class DnsClient {

  /**
   * Set up the environment used to construct the DirContext.
   *
   * @param dnsServerAddress
   * @return
   */
  static Hashtable<String, String> getEnv(String dnsServerAddress) {
    // Set up environment for creating initial context
    Hashtable<String, String> env = new Hashtable<String, String>();
    env.put("java.naming.factory.initial",
            "com.sun.jndi.dns.DnsContextFactory");
    if(dnsServerAddress != null && !dnsServerAddress.isEmpty()) {
      env.put("java.naming.provider.url", "dns://" + dnsServerAddress);
    }
    return env;
  }

  /**
   * Performs Dns query.
   *
   * @param <T>              the generic type
   * @param cls              DnsRecord Type
   * @param domain           the domain
   * @param dnsServerAddress IPAddress of DNS server to use (may be null)
   * @return DnsRecord The DNS record list (never null but may be empty)
   * @throws DnsException the dns exception
   */

  public static <T extends DnsRecord> List<T> dnsQuery(Class<T> cls, String domain, String dnsServerAddress) throws
                                                                                                             DnsException {

    List<T> dnsRecordList = new ArrayList<T>();
    try {
      // Create initial context
      DirContext ictx = new InitialDirContext(getEnv(dnsServerAddress));

      // Retrieve SRV record context attribute for the specified domain
      Attributes contextAttributes = ictx.getAttributes(domain,
          new String[] {EWSConstants.SRVRECORD});
      if (contextAttributes != null) {
        NamingEnumeration<?> attributes = contextAttributes.getAll();
        if (attributes != null) {
          while (attributes.hasMore()) {
            Attribute attr = (Attribute) attributes.next();
            NamingEnumeration<?> srvValues = attr.getAll();
            if (srvValues != null) {
              while (srvValues.hasMore()) {
                T dnsRecord = cls.newInstance();

                // Loads the DNS SRV record
                dnsRecord.load((String) srvValues.next());
                dnsRecordList.add(dnsRecord);
              }
            }
          }
        }
      }
    } catch (NamingException ne) {
      throw new DnsException(ne.getMessage());
    } catch (Exception e) {
      throw new DnsException(e.getMessage());
    }
    return dnsRecordList;
  }
}