前言
DNS协议作为着互联网客户端-服务器通信模式得第一关，在当下每天都有成千上亿上网记录产生得当今社会，其重要性自然不可言喻。在国内比较有名得DNS服务器有电信得114.114.114.114、阿里云得223.5.5.5，DNSPod得119.29.29.29，配置一个好的DNS服务器可以缩短请求响应时间、降低DNS劫持概率，提升上网体验。
上面这些都是互联网公用DNS服务器，本文博主教大家使用 Java Netty 自建DNS代理服务器，目前网上对于使用Netty自建DNS服务器得教程良莠不齐，大多没有代理步骤，达不到博主想要得代理效果，因而创建此文。觉得本文有帮助得可以关注博主
一、自建DNS代理服务器有哪些优势
- 域名控制：对于特定域名可以自由控制访问权限（屏蔽对特定网站访问）
- 域名记录：记录局域网内各个主机得域名访问（记录员工上网记录）
- 配置内网域名：通过自建DNS服务器可以配置内网域名，节约成本
- DNS负载均衡：通过自建DNS服务器可以轻松实现对于访问域名得负载均衡配置
- CDN网络：返回距离客户端最近的可用IP
- ...
二、自建DNS代理服务器代码
1. 添加域名黑名单文件，Maven项目在 resources 文件夹下添加 black_list.txt 文件，注意域名最后的 .，在 Netty 自带的DNS查询Handler中，报文返回的域名最后都是带 . 的。实际上每个域名后都有一个 .，它表示根域名，通常它都是被隐藏的。
// 添加域名黑名单 google.com. facebook.com.
接着解析 black_list.txt 文件，初始化内容放入 BLACK_LIST_DOMAIN
private static final List<String> BLACK_LIST_DOMAIN = new ArrayList<>(); static { String s; try (InputStream is = DnsServer.class.getClassLoader().getResourceAsStream("black_list.txt"); BufferedReader br = new BufferedReader(new InputStreamReader(is))) { while (StrUtil.isNotBlank(s = br.readLine())) { BLACK_LIST_DOMAIN.add(s); } } catch (Exception e) { log.error(e.getMessage(), e); } }
2. 使用UDP协议绑定本机53端口（DNS协议默认使用UDP 53端口），并初始化 ProxyUdp DNS请求代理对象
@Slf4j public final class DnsServer { private static final List<String> BLACK_LIST_DOMAIN = new ArrayList<>(); static { ... } public static void main(String[] args) throws Exception { ProxyUdp proxyUdp = new ProxyUdp(); proxyUdp.init(); final int[] num = {0}; final NioEventLoopGroup group = new NioEventLoopGroup(); Bootstrap bootstrap = new Bootstrap(); bootstrap.group(group).channel(NioDatagramChannel.class) .handler(new ChannelInitializer<NioDatagramChannel>() { @Override protected void initChannel(NioDatagramChannel nioDatagramChannel) { nioDatagramChannel.pipeline().addLast(...); } }).option(ChannelOption.SO_BROADCAST, true); int port = 53; ChannelFuture future = bootstrap.bind(port).addListener(future1 -> { log.info("server listening port:{}", port); }); future.channel().closeFuture().addListener(future1 -> { if (future.isSuccess()) { log.info(future.channel().toString()); } }); } }
3. 给 nioDatagramChannel.pipeline() 添加多个 ChannelHandler 对象，接受DNS查询报文以及发送DNS响应报文。划重点来了 在 new SimpleChannelInboundHandler<DatagramDnsQuery>() 中解析客户端发送DNS查询报文, 获取访问域名信息，如果访问域名在黑名单中，则通过 getDatagramDnsResponse() 方法直接返回 192.168.1.1 的DNS响应报文，反之则通过 proxyUdp 对象转发DNS查询。
nioDatagramChannel.pipeline().addLast(new DatagramDnsQueryDecoder()); nioDatagramChannel.pipeline().addLast(new SimpleChannelInboundHandler<DatagramDnsQuery>() { @Override protected void channelRead0(ChannelHandlerContext ctx, DatagramDnsQuery msg) { try { DefaultDnsQuestion dnsQuestion = msg.recordAt(DnsSection.QUESTION); String name = dnsQuestion.name(); log.info(name + ++num[0]); Channel channel = ctx.channel(); int id = msg.id(); channel.attr(AttributeKey.<DatagramDnsQuery>valueOf(String.valueOf(id))).set(msg); if (BLACK_LIST_DOMAIN.contains(name)) { DnsQuestion question = msg.recordAt(DnsSection.QUESTION); DatagramDnsResponse dnsResponse = getDatagramDnsResponse(msg, id, question); channel.writeAndFlush(dnsResponse); return; } proxyUdp.send(name, msg.id(), channel); } catch (Exception e) { log.error(e.getMessage(), e); } } private DatagramDnsResponse getDatagramDnsResponse(DatagramDnsQuery msg, int id, DnsQuestion question) { DatagramDnsResponse dnsResponse = new DatagramDnsResponse(msg.recipient(), msg.sender(), id); dnsResponse.addRecord(DnsSection.QUESTION, question); DefaultDnsRawRecord queryAnswer = new DefaultDnsRawRecord( question.name(), DnsRecordType.A, 600, Unpooled.wrappedBuffer(new byte[]{(byte) 192, (byte) 168, 1, 1})); dnsResponse.addRecord(DnsSection.ANSWER, queryAnswer); return dnsResponse; } @Override public void exceptionCaught(ChannelHandlerContext ctx, Throwable e) { log.error(e.getMessage(), e); } }); nioDatagramChannel.pipeline().addLast(new DatagramDnsResponseEncoder());
4.ProxyUdp 作为DNS查询代理类会通过 send(String domain, int id, Channel serverChannel) 方法传入DnsServer类收到的访问域名、DNS事务ID、serverChannel。随后包装访问域名请求DNS服务器114.114.114.114，最后通过 new SimpleChannelInboundHandler<DatagramDnsResponse>() 将收到的DNS响应报文通过上一步传入得 serverChannel 输出到客户端。
@Slf4j class ProxyUdp { private Channel serverChannel; private Channel proxyChannel; public void init() throws InterruptedException { EventLoopGroup proxyGroup = new NioEventLoopGroup(); Bootstrap b = new Bootstrap(); b.group(proxyGroup) .channel(NioDatagramChannel.class) .handler(new ChannelInitializer<DatagramChannel>() { @Override protected void initChannel(DatagramChannel ch) { ChannelPipeline p = ch.pipeline(); p.addLast(new DatagramDnsQueryEncoder()) .addLast(new DatagramDnsResponseDecoder()) .addLast(new SimpleChannelInboundHandler<DatagramDnsResponse>() { @Override public void channelActive(ChannelHandlerContext ctx) { log.info(ctx.channel().toString()); } @Override protected void channelRead0(ChannelHandlerContext ctx, DatagramDnsResponse msg) { DatagramDnsQuery dnsQuery = localChannel.attr(AttributeKey.<DatagramDnsQuery>valueOf(String.valueOf(msg.id()))).get(); DnsQuestion question = msg.recordAt(DnsSection.QUESTION); DatagramDnsResponse dnsResponse = new DatagramDnsResponse(dnsQuery.recipient(), dnsQuery.sender(), msg.id()); dnsResponse.addRecord(DnsSection.QUESTION, question); 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; DefaultDnsRawRecord queryAnswer = new DefaultDnsRawRecord( question.name(), DnsRecordType.A, 600, Unpooled.wrappedBuffer(ByteBufUtil.getBytes(raw.content()))); dnsResponse.addRecord(DnsSection.ANSWER, queryAnswer); } } serverChannel.writeAndFlush(dnsResponse); } @Override public void exceptionCaught(ChannelHandlerContext ctx, Throwable e) { log.error(e.getMessage(), e); } }); } }); proxyChannel = b.bind(0).sync().addListener(future1 -> { log.info("绑定成功"); }).channel(); } public void send(String domain, int id, Channel serverChannel) { this.serverChannel = serverChannel; DnsQuery query = new DatagramDnsQuery(null, new InetSocketAddress("114.114.114.114", 53), id).setRecord( DnsSection.QUESTION, new DefaultDnsQuestion(domain, DnsRecordType.A)); this.proxyChannel.writeAndFlush(query); } }
5. 客户端请求DNS代理服务器流程图如下
6. 自建DNS服务器全部代码
@Slf4j public final class DnsServer { private static final List<String> BLACK_LIST_DOMAIN = new ArrayList<>(); static { String s; try (InputStream is = DnsServer.class.getClassLoader().getResourceAsStream("black_list.txt"); BufferedReader br = new BufferedReader(new InputStreamReader(is))) { while (StrUtil.isNotBlank(s = br.readLine())) { BLACK_LIST_DOMAIN.add(s); } } catch (Exception e) { log.error(e.getMessage(), e); } } public static void main(String[] args) throws Exception { ProxyUdp proxyUdp = new ProxyUdp(); proxyUdp.init(); final int[] num = {0}; final NioEventLoopGroup group = new NioEventLoopGroup(); Bootstrap bootstrap = new Bootstrap(); bootstrap.group(group).channel(NioDatagramChannel.class) .handler(new ChannelInitializer<NioDatagramChannel>() { @Override protected void initChannel(NioDatagramChannel nioDatagramChannel) { nioDatagramChannel.pipeline().addLast(new DatagramDnsQueryDecoder()); nioDatagramChannel.pipeline().addLast(new SimpleChannelInboundHandler<DatagramDnsQuery>() { @Override protected void channelRead0(ChannelHandlerContext ctx, DatagramDnsQuery msg) { try { DefaultDnsQuestion dnsQuestion = msg.recordAt(DnsSection.QUESTION); String name = dnsQuestion.name(); log.info(name + ++num[0]); Channel channel = ctx.channel(); int id = msg.id(); channel.attr(AttributeKey.<DatagramDnsQuery>valueOf(String.valueOf(id))).set(msg); if (BLACK_LIST_DOMAIN.contains(name)) { DnsQuestion question = msg.recordAt(DnsSection.QUESTION); DatagramDnsResponse dnsResponse = getDatagramDnsResponse(msg, id, question); channel.writeAndFlush(dnsResponse); return; } proxyUdp.send(name, msg.id(), channel); } catch (Exception e) { log.error(e.getMessage(), e); } } private DatagramDnsResponse getDatagramDnsResponse(DatagramDnsQuery msg, int id, DnsQuestion question) { DatagramDnsResponse dnsResponse = new DatagramDnsResponse(msg.recipient(), msg.sender(), id); dnsResponse.addRecord(DnsSection.QUESTION, question); // just print the IP after query DefaultDnsRawRecord queryAnswer = new DefaultDnsRawRecord( question.name(), DnsRecordType.A, 600, Unpooled.wrappedBuffer(new byte[]{(byte) 192, (byte) 168, 1, 1})); dnsResponse.addRecord(DnsSection.ANSWER, queryAnswer); return dnsResponse; } @Override public void exceptionCaught(ChannelHandlerContext ctx, Throwable e) { log.error(e.getMessage(), e); } }); nioDatagramChannel.pipeline().addLast(new DatagramDnsResponseEncoder()); } }).option(ChannelOption.SO_BROADCAST, true); int port = 53; ChannelFuture future = bootstrap.bind(port).addListener(future1 -> { log.info("server listening port:{}", port); }); future.channel().closeFuture().addListener(future1 -> { if (future.isSuccess()) { log.info(future.channel().toString()); } }); } } @Slf4j class ProxyUdp { private Channel localChannel; private Channel proxyChannel; public void init() throws InterruptedException { EventLoopGroup proxyGroup = new NioEventLoopGroup(); Bootstrap b = new Bootstrap(); b.group(proxyGroup) .channel(NioDatagramChannel.class) .handler(new ChannelInitializer<DatagramChannel>() { @Override protected void initChannel(DatagramChannel ch) { ChannelPipeline p = ch.pipeline(); p.addLast(new DatagramDnsQueryEncoder()) .addLast(new DatagramDnsResponseDecoder()) .addLast(new SimpleChannelInboundHandler<DatagramDnsResponse>() { @Override public void channelActive(ChannelHandlerContext ctx) { log.info(ctx.channel().toString()); } @Override protected void channelRead0(ChannelHandlerContext ctx, DatagramDnsResponse msg) { DatagramDnsQuery dnsQuery = localChannel.attr(AttributeKey.<DatagramDnsQuery>valueOf(String.valueOf(msg.id()))).get(); DnsQuestion question = msg.recordAt(DnsSection.QUESTION); DatagramDnsResponse dnsResponse = new DatagramDnsResponse(dnsQuery.recipient(), dnsQuery.sender(), msg.id()); dnsResponse.addRecord(DnsSection.QUESTION, question); 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; DefaultDnsRawRecord queryAnswer = new DefaultDnsRawRecord( question.name(), DnsRecordType.A, 600, Unpooled.wrappedBuffer(ByteBufUtil.getBytes(raw.content()))); dnsResponse.addRecord(DnsSection.ANSWER, queryAnswer); } } localChannel.writeAndFlush(dnsResponse); } @Override public void exceptionCaught(ChannelHandlerContext ctx, Throwable e) { log.error(e.getMessage(), e); } }); } }); proxyChannel = b.bind(0).sync().addListener(future1 -> { log.info("绑定成功"); }).channel(); } public void send(String domain, int id, Channel localChannel) { this.localChannel = localChannel; DnsQuery query = new DatagramDnsQuery(null, new InetSocketAddress("114.114.114.114", 53), id).setRecord( DnsSection.QUESTION, new DefaultDnsQuestion(domain, DnsRecordType.A)); this.proxyChannel.writeAndFlush(query); } }
三、本地测试
- 修改本机DNS设置(win11)，修改首选、备选DNS地址为127.0.0.1
- 打开命令行工具，执行DNS缓存清除命令
ipconfig/flushdns 
打开浏览器访问常用网站，控制台输出如下
自此，自建的DNS代理服务器就可以正常使用了参考资料用 Node.js 手写一个 DNS 服务器DNS中有哪些值得学习的优秀设计netty dns example
