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Licensed to the Apache Software Foundation (ASF) under one or more contributor license agreements. See the NOTICE file distributed with this work for additional information regarding copyright ownership. The ASF licenses this file to you under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with the License. You may obtain a copy of the License at Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the specific language governing permissions and limitations under the License.
package org.apache.whirr.util;
import  org.xbill.DNS.DClass;
import  org.xbill.DNS.ExtendedResolver;
import  org.xbill.DNS.Message;
import  org.xbill.DNS.Name;
import  org.xbill.DNS.Record;
import  org.xbill.DNS.Resolver;
import  org.xbill.DNS.ReverseMap;
import  org.xbill.DNS.Section;
import  org.xbill.DNS.Type;

Utility functions for DNS.
public class DnsUtil {

resolve the reverse dns name for the given IP address

The resolved DNS name.
  public static String resolveAddress(String hostIpthrows IOException {
    Resolver res = new ExtendedResolver();
    res.setTimeout(5); // seconds
    Name name = ReverseMap.fromAddress(hostIp);
    int type = Type.PTR;
    int dclass = DClass.IN;
    Record rec = Record.newRecord(nametypedclass);
    Message query = Message.newQuery(rec);
    Message response = res.send(query);
    Record[] answers = response.getSectionArray(Section.ANSWER);
    if (answers.length == 0) {
      // Fall back to standard Java: in contrast to dnsjava, this also reads /etc/hosts
      return new InetSocketAddress(hostIp, 0).getAddress().getCanonicalHostName();
    } else {
      String revaddr = answers[0].rdataToString();
      return revaddr.endsWith(".") ? revaddr.substring(0, revaddr.length() - 1) : revaddr;
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