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1   /*
2    * Copyright 2020 The Netty Project
3    *
4    * The Netty Project licenses this file to you under the Apache License,
5    * version 2.0 (the "License"); you may not use this file except in compliance
6    * with the License. You may obtain a copy of the License at:
7    *
8    *   https://www.apache.org/licenses/LICENSE-2.0
9    *
10   * Unless required by applicable law or agreed to in writing, software
11   * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
12   * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
13   * License for the specific language governing permissions and limitations
14   * under the License.
15   */
16  package io.netty.example.dns.udp;
17  
18  import java.net.InetSocketAddress;
19  import java.util.concurrent.TimeUnit;
20  
21  import io.netty.bootstrap.Bootstrap;
22  import io.netty.buffer.ByteBufUtil;
23  import io.netty.channel.Channel;
24  import io.netty.channel.ChannelHandlerContext;
25  import io.netty.channel.ChannelInitializer;
26  import io.netty.channel.ChannelPipeline;
27  import io.netty.channel.EventLoopGroup;
28  import io.netty.channel.MultiThreadIoEventLoopGroup;
29  import io.netty.channel.SimpleChannelInboundHandler;
30  import io.netty.channel.nio.NioIoHandler;
31  import io.netty.channel.socket.DatagramChannel;
32  import io.netty.channel.socket.nio.NioDatagramChannel;
33  import io.netty.handler.codec.dns.DatagramDnsQuery;
34  import io.netty.handler.codec.dns.DatagramDnsQueryEncoder;
35  import io.netty.handler.codec.dns.DatagramDnsResponse;
36  import io.netty.handler.codec.dns.DatagramDnsResponseDecoder;
37  import io.netty.handler.codec.dns.DefaultDnsQuestion;
38  import io.netty.handler.codec.dns.DnsQuery;
39  import io.netty.handler.codec.dns.DnsQuestion;
40  import io.netty.handler.codec.dns.DnsRawRecord;
41  import io.netty.handler.codec.dns.DnsRecord;
42  import io.netty.handler.codec.dns.DnsRecordType;
43  import io.netty.handler.codec.dns.DnsSection;
44  import io.netty.util.NetUtil;
45  
46  public final class DnsClient {
47  
48      private static final String QUERY_DOMAIN = "www.example.com";
49      private static final int DNS_SERVER_PORT = 53;
50      private static final String DNS_SERVER_HOST = "8.8.8.8";
51  
52      private DnsClient() { }
53  
54      private static void handleQueryResp(DatagramDnsResponse msg) {
55          if (msg.count(DnsSection.QUESTION) > 0) {
56              DnsQuestion question = msg.recordAt(DnsSection.QUESTION, 0);
57              System.out.printf("name: %s%n", question.name());
58          }
59          for (int i = 0, count = msg.count(DnsSection.ANSWER); i < count; i++) {
60              DnsRecord record = msg.recordAt(DnsSection.ANSWER, i);
61              if (record.type() == DnsRecordType.A) {
62                  //just print the IP after query
63                  DnsRawRecord raw = (DnsRawRecord) record;
64                  System.out.println(NetUtil.bytesToIpAddress(ByteBufUtil.getBytes(raw.content())));
65              }
66          }
67      }
68  
69      public static void main(String[] args) throws Exception {
70          InetSocketAddress addr = new InetSocketAddress(DNS_SERVER_HOST, DNS_SERVER_PORT);
71          EventLoopGroup group = new MultiThreadIoEventLoopGroup(NioIoHandler.newFactory());
72          try {
73              Bootstrap b = new Bootstrap();
74              b.group(group)
75               .channel(NioDatagramChannel.class)
76               .handler(new ChannelInitializer<DatagramChannel>() {
77                   @Override
78                   protected void initChannel(DatagramChannel ch) throws Exception {
79                       ChannelPipeline p = ch.pipeline();
80                       p.addLast(new DatagramDnsQueryEncoder())
81                       .addLast(new DatagramDnsResponseDecoder())
82                       .addLast(new SimpleChannelInboundHandler<DatagramDnsResponse>() {
83                          @Override
84                          protected void channelRead0(ChannelHandlerContext ctx, DatagramDnsResponse msg) {
85                              try {
86                                  handleQueryResp(msg);
87                              } finally {
88                                  ctx.close();
89                              }
90                          }
91                      });
92                   }
93               });
94              final Channel ch = b.bind(0).sync().channel();
95              DnsQuery query = new DatagramDnsQuery(null, addr, 1).setRecord(
96                      DnsSection.QUESTION,
97                      new DefaultDnsQuestion(QUERY_DOMAIN, DnsRecordType.A));
98              ch.writeAndFlush(query).sync();
99              boolean succ = ch.closeFuture().await(10, TimeUnit.SECONDS);
100             if (!succ) {
101                 System.err.println("dns query timeout!");
102                 ch.close().sync();
103             }
104         } finally {
105             group.shutdownGracefully();
106         }
107     }
108 }