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/*
 * Copyright 2020 The Netty Project
 *
 * The Netty Project 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:
 *
 *   http://www.apache.org/licenses/LICENSE-2.0
 *
 * 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 io.netty.example.dns.tcp;

import io.netty.bootstrap.Bootstrap;
import io.netty.buffer.ByteBufUtil;

import io.netty.channel.Channel;
import io.netty.channel.ChannelInitializer;
import io.netty.channel.ChannelHandlerContext;
import io.netty.channel.ChannelPipeline;
import io.netty.channel.EventLoopGroup;
import io.netty.channel.nio.NioEventLoopGroup;
import io.netty.channel.socket.SocketChannel;
import io.netty.channel.socket.nio.NioSocketChannel;
import io.netty.channel.SimpleChannelInboundHandler;

import io.netty.handler.codec.dns.DefaultDnsQuestion;
import io.netty.handler.codec.dns.DefaultDnsResponse;
import io.netty.handler.codec.dns.DnsQuestion;
import io.netty.handler.codec.dns.DnsQuery;
import io.netty.handler.codec.dns.DefaultDnsQuery;
import io.netty.handler.codec.dns.DnsOpCode;
import io.netty.handler.codec.dns.DnsRecord;
import io.netty.handler.codec.dns.DnsSection;
import io.netty.handler.codec.dns.DnsRecordType;
import io.netty.handler.codec.dns.DnsRawRecord;
import io.netty.handler.codec.dns.TcpDnsQueryEncoder;
import io.netty.handler.codec.dns.TcpDnsResponseDecoder;
import io.netty.util.NetUtil;

import java.util.Random;
import java.util.concurrent.TimeUnit;

public final class TcpDnsClient {
    private static final String QUERY_DOMAIN = "www.example.com";
    private static final int DNS_SERVER_PORT = 53;
    private static final String DNS_SERVER_HOST = "8.8.8.8";

    private TcpDnsClient() {
    }

    private static void handleQueryResp(DefaultDnsResponse msg) {
        if (msg.count(DnsSection.QUESTION) > 0) {
            DnsQuestion question = msg.recordAt(DnsSection.QUESTION, 0);
            System.out.printf("name: %s%n", question.name());
        }
        for (int i = 0, count = msg.count(DnsSection.ANSWER); i < count; i++) {
            DnsRecord record = msg.recordAt(DnsSection.ANSWER, i);
            if (record.type() == DnsRecordType.A) {
                //just print the IP after query
                DnsRawRecord raw = (DnsRawRecord) record;
                System.out.println(NetUtil.bytesToIpAddress(ByteBufUtil.getBytes(raw.content())));
            }
        }
    }

    public static void main(String[] args) throws Exception {
        EventLoopGroup group = new NioEventLoopGroup();
        try {
            Bootstrap b = new Bootstrap();
            b.group(group)
                    .channel(NioSocketChannel.class)
                    .handler(new ChannelInitializer() {
                        @Override
                        protected void initChannel(SocketChannel ch) {
                            ChannelPipeline p = ch.pipeline();
                            p.addLast(new TcpDnsQueryEncoder())
                                    .addLast(new TcpDnsResponseDecoder())
                                    .addLast(new SimpleChannelInboundHandler() {
                                        @Override
                                        protected void channelRead0(ChannelHandlerContext ctx, DefaultDnsResponse msg) {
                                            try {
                                                handleQueryResp(msg);
                                            } finally {
                                                ctx.close();
                                            }
                                        }
                                    });
                        }
                    });

            final Channel ch = b.connect(DNS_SERVER_HOST, DNS_SERVER_PORT).sync().channel();

            int randomID = new Random().nextInt(60000 - 1000) + 1000;
            DnsQuery query = new DefaultDnsQuery(randomID, DnsOpCode.QUERY)
                    .setRecord(DnsSection.QUESTION, new DefaultDnsQuestion(QUERY_DOMAIN, DnsRecordType.A));
            ch.writeAndFlush(query).sync();
            boolean success = ch.closeFuture().await(10, TimeUnit.SECONDS);
            if (!success) {
                System.err.println("dns query timeout!");
                ch.close().sync();
            }
        } finally {
            group.shutdownGracefully();
        }
    }
}