JAVA基于Netty实现内网穿透功能【设计实践】

目录

背景

实践

项目结构

原理分析

代码实现

cc-common项目

 cc-server项目

 cc-client项目

使用

启动服务端

启动客户端 

备注

---

背景

本文实现了一个简单的内网穿透服务，可以满足代理基于TCP协议的项目，如Tomcat、Redis、MySQL、windows远程桌面等。

实践

项目结构

拆分了三个项目：

1、cc-common项目:存放了消息格式和消息编解码器

2、cc-server项目:内网穿透服务端项目

3、cc-client项目:内网穿透客户端项目

原理分析

内网穿透的实现过程主要分三步

1、启动服务端，这时服务端监听了两个端口（16001，16002，可根据启动参数修改），

一个用来接收客户端请求（16001端口），

一个用来接收访客代理（16002端口）

2、启动客户端，客户端访问服务端提供的（16001端口）建立连接（server-client通道）

3、访客访问代理接口（16002端口），服务端监听到之后创建访客ID，然后通过（server-client通道）向客户端发送指令，客户端接收指令后连接到真实服务端口（8080，可根据启动参数修改），连接真实服务成功后，客户端会重新向服务端建立一条连接（访客-server通道），服务端把访客和该通道进行绑定

这三步最终形成了（访客-代理-客户端-真实服务）完整的通道。

代码实现

cc-common项目

maven配置

	4.0.0
	com.luck.cc
	cc-common
	1.0-SNAPSHOT
	cc-common
	http://maven.apache.org

	
		${env.JAVA_HOME}
		UTF-8
		1.8
	

	
		
			io.netty
			netty-all
			4.1.74.Final
		
	
	
		
			
				maven-compiler-plugin
				
					1.8
					1.8
				
			
		
	

 java代码

 消息类

package com.luck.msg;

import java.util.Arrays;

public class MyMsg {

	/** 心跳 */
	public static final byte TYPE_HEARTBEAT = 0X00;

	/** 连接成功 */
	public static final byte TYPE_CONNECT = 0X01;

	/** 数据传输 */
	public static final byte TYPE_TRANSFER = 0X02;

	/** 连接断开 */
	public static final byte TYPE_DISCONNECT = 0X09;

	/** 数据类型 */
	private byte type;

	/** 消息传输数据 */
	private byte[] data;

	public byte getType() {
		return type;
	}

	public void setType(byte type) {
		this.type = type;
	}

	public byte[] getData() {
		return data;
	}

	public void setData(byte[] data) {
		this.data = data;
	}

	@Override
	public String toString() {
		return "MyMsg [type=" + type + ", data=" + Arrays.toString(data) + "]";
	}

}

消息编码类

package com.luck.msg;

import io.netty.buffer.ByteBuf;
import io.netty.channel.ChannelHandlerContext;
import io.netty.handler.codec.MessageToByteEncoder;

public class MyMsgEncoder extends MessageToByteEncoder {

	public MyMsgEncoder() {

	}

	@Override
	protected void encode(ChannelHandlerContext ctx, MyMsg msg, ByteBuf out) throws Exception {
		int bodyLength = 5;
		if (msg.getData() != null) {
			bodyLength += msg.getData().length;
		}

		out.writeInt(bodyLength);

		out.writeByte(msg.getType());

		if (msg.getData() != null) {
			out.writeBytes(msg.getData());
		}
	}
}

 消息解码类

package com.luck.msg;

import io.netty.buffer.ByteBuf;
import io.netty.channel.ChannelHandlerContext;
import io.netty.handler.codec.LengthFieldBasedFrameDecoder;

public class MyMsgDecoder extends LengthFieldBasedFrameDecoder {

	public MyMsgDecoder(int maxFrameLength, int lengthFieldOffset, int lengthFieldLength, int lengthAdjustment,
			int initialBytesToStrip) {
		super(maxFrameLength, lengthFieldOffset, lengthFieldLength, lengthAdjustment, initialBytesToStrip);
	}

	public MyMsgDecoder(int maxFrameLength, int lengthFieldOffset, int lengthFieldLength, int lengthAdjustment,
			int initialBytesToStrip, boolean failFast) {
		super(maxFrameLength, lengthFieldOffset, lengthFieldLength, lengthAdjustment, initialBytesToStrip, failFast);
	}

	@Override
	protected MyMsg decode(ChannelHandlerContext ctx, ByteBuf in2) throws Exception {
		ByteBuf in = (ByteBuf) super.decode(ctx, in2);
		if (in == null) {
			return null;
		}

		if (in.readableBytes() < 4) {
			return null;
		}

		MyMsg myMsg = new MyMsg();
		int dataLength = in.readInt();
		byte type = in.readByte();
		myMsg.setType(type);
		byte[] data = new byte[dataLength - 5];
		in.readBytes(data);
		myMsg.setData(data);
		in.release();

		return myMsg;
	}
}

 cc-server项目

maven配置

	4.0.0
	com.luck.cc
	cc-server
	1.0-SNAPSHOT
	cc-server
	http://maven.apache.org

	
		${env.JAVA_HOME}
		UTF-8
		1.8
	

	
		
			com.luck.cc
			cc-common
			1.0-SNAPSHOT
		
	
	
		
			
				maven-compiler-plugin
				
					1.8
					1.8
				
			
	        
	            maven-assembly-plugin
	            3.0.0
	            
	                
	                    
	                        com.luck.server.ServerStart
	                    
	                
	                
	                    jar-with-dependencies
	                
	            
	            
	                
	                    make-assembly
	                    package
	                    
	                        single
	                    
	                
	            
	        
		
	

Java代码 

 常量类

package com.luck.server;

import java.util.Map;
import java.util.concurrent.ConcurrentHashMap;

import io.netty.channel.Channel;
import io.netty.util.AttributeKey;
import io.netty.util.internal.StringUtil;

public class Constant {
	/** 客户端服务channel */
	public static Channel clientChannel = null;

	/** 绑定channel_id */
	public static final AttributeKey VID = AttributeKey.newInstance("vid");

	/** 访客，客户服务channel */
	public static Map vcc = new ConcurrentHashMap<>();

	/** 访客，访客服务channel */
	public static Map vvc = new ConcurrentHashMap<>();

	/** 服务代理端口 */
	public static int visitorPort = 16002;

	/** 服务端口 */
	public static int serverPort = 16001;

	/**
	 * 清除连接
	 * 
	 * @param vid 访客ID
	 */
	public static void clearVccVvc(String vid) {
		if (StringUtil.isNullOrEmpty(vid)) {
			return;
		}
		Channel clientChannel = vcc.get(vid);
		if (null != clientChannel) {
			clientChannel.attr(VID).set(null);
			vcc.remove(vid);
		}
		Channel visitorChannel = vvc.get(vid);
		if (null != visitorChannel) {
			visitorChannel.attr(VID).set(null);
			vvc.remove(vid);
		}
	}

	/**
	 * 清除关闭连接
	 * 
	 * @param vid 访客ID
	 */
	public static void clearVccVvcAndClose(String vid) {
		if (StringUtil.isNullOrEmpty(vid)) {
			return;
		}
		Channel clientChannel = vcc.get(vid);
		if (null != clientChannel) {
			clientChannel.attr(VID).set(null);
			vcc.remove(vid);
			clientChannel.close();
		}
		Channel visitorChannel = vvc.get(vid);
		if (null != visitorChannel) {
			visitorChannel.attr(VID).set(null);
			vvc.remove(vid);
			visitorChannel.close();
		}
	}
}

 服务代理handler

package com.luck.server;

import com.luck.msg.MyMsg;

import io.netty.buffer.ByteBuf;
import io.netty.buffer.Unpooled;
import io.netty.channel.Channel;
import io.netty.channel.ChannelFutureListener;
import io.netty.channel.ChannelHandlerContext;
import io.netty.channel.ChannelOption;
import io.netty.channel.SimpleChannelInboundHandler;
import io.netty.handler.timeout.IdleStateEvent;
import io.netty.util.internal.StringUtil;

public class ClientHandler extends SimpleChannelInboundHandler {

	@Override
	public void channelRead0(ChannelHandlerContext ctx, MyMsg myMsg) {
		// 代理服务器读到客户端数据了
		byte type = myMsg.getType();
		switch (type) {
		case MyMsg.TYPE_HEARTBEAT:
			MyMsg hb = new MyMsg();
			hb.setType(MyMsg.TYPE_HEARTBEAT);
			ctx.channel().writeAndFlush(hb);
			break;
		case MyMsg.TYPE_CONNECT:
			String vid = new String(myMsg.getData());
			if (StringUtil.isNullOrEmpty(vid) || "client".equals(vid)) {
				Constant.clientChannel = ctx.channel();
			} else {
				// 绑定访客和客户端的连接
				Channel visitorChannel = Constant.vvc.get(vid);
				if (null != visitorChannel) {
					ctx.channel().attr(Constant.VID).set(vid);
					Constant.vcc.put(vid, ctx.channel());

					// 通道绑定完成可以读取访客数据
					visitorChannel.config().setOption(ChannelOption.AUTO_READ, true);
				}
			}
			break;
		case MyMsg.TYPE_DISCONNECT:
			String disVid = new String(myMsg.getData());
			Constant.clearVccVvcAndClose(disVid);
			break;
		case MyMsg.TYPE_TRANSFER:
			// 把数据转到用户服务
			ByteBuf buf = ctx.alloc().buffer(myMsg.getData().length);
			buf.writeBytes(myMsg.getData());

			String visitorId = ctx.channel().attr(Constant.VID).get();
			Channel vchannel = Constant.vvc.get(visitorId);
			if (null != vchannel) {
				vchannel.writeAndFlush(buf);
			}
			break;
		default:
			// 操作有误
		}
		// 代理服务器发送数据到用户了
	}

	@Override
	public void channelWritabilityChanged(ChannelHandlerContext ctx) throws Exception {
		String vid = ctx.channel().attr(Constant.VID).get();
		if(StringUtil.isNullOrEmpty(vid)) {
			super.channelWritabilityChanged(ctx);
			return;
		}
		Channel visitorChannel = Constant.vvc.get(vid);
		if (visitorChannel != null) {
			visitorChannel.config().setOption(ChannelOption.AUTO_READ, ctx.channel().isWritable());
		}

		super.channelWritabilityChanged(ctx);
	}

	@Override
	public void channelInactive(ChannelHandlerContext ctx) throws Exception {
		String vid = ctx.channel().attr(Constant.VID).get();
		if (StringUtil.isNullOrEmpty(vid)) {
			super.channelInactive(ctx);
			return;
		}
		Channel visitorChannel = Constant.vvc.get(vid);
		if (visitorChannel != null && visitorChannel.isActive()) {
			// 数据发送完成后再关闭连接，解决http1.0数据传输问题
			visitorChannel.writeAndFlush(Unpooled.EMPTY_BUFFER).addListener(ChannelFutureListener.CLOSE);
			visitorChannel.close();
		} else {
			ctx.channel().close();
		}
		Constant.clearVccVvc(vid);
		super.channelInactive(ctx);
	}

	@Override
	public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) throws Exception {
		super.exceptionCaught(ctx, cause);
	}

	@Override
	public void userEventTriggered(ChannelHandlerContext ctx, Object evt) throws Exception {
		if (evt instanceof IdleStateEvent) {
			IdleStateEvent event = (IdleStateEvent) evt;
			switch (event.state()) {
			case READER_IDLE:
				ctx.channel().close();
				break;
			case WRITER_IDLE:
				break;
			case ALL_IDLE:
				break;
			}
		}
	}
}

 访客handler

package com.luck.server;

import java.util.UUID;

import com.luck.msg.MyMsg;

import io.netty.buffer.ByteBuf;
import io.netty.channel.Channel;
import io.netty.channel.ChannelHandlerContext;
import io.netty.channel.ChannelOption;
import io.netty.channel.SimpleChannelInboundHandler;
import io.netty.util.internal.StringUtil;

public class VisitorHandler extends SimpleChannelInboundHandler {

	@Override
	public void channelActive(ChannelHandlerContext ctx) throws Exception {
		// 访客连接上代理服务器了
		Channel visitorChannel = ctx.channel();
		// 先不读取访客数据
		visitorChannel.config().setOption(ChannelOption.AUTO_READ, false);

		// 生成访客ID
		String vid = UUID.randomUUID().toString();

		// 绑定访客通道
		visitorChannel.attr(Constant.VID).set(vid);
		Constant.vvc.put(vid, visitorChannel);

		MyMsg myMsg = new MyMsg();
		myMsg.setType(MyMsg.TYPE_CONNECT);
		myMsg.setData(vid.getBytes());
		Constant.clientChannel.writeAndFlush(myMsg);

		super.channelActive(ctx);
	}

	@Override
	public void channelRead0(ChannelHandlerContext ctx, ByteBuf buf) {
		String vid = ctx.channel().attr(Constant.VID).get();
		if (StringUtil.isNullOrEmpty(vid)) {
			return;
		}
		byte[] bytes = new byte[buf.readableBytes()];
		buf.readBytes(bytes);
		MyMsg myMsg = new MyMsg();
		myMsg.setType(MyMsg.TYPE_TRANSFER);
		myMsg.setData(bytes);

		// 代理服务器发送数据到客户端了
		Channel clientChannel = Constant.vcc.get(vid);
		clientChannel.writeAndFlush(myMsg);
	}

	@Override
	public void channelInactive(ChannelHandlerContext ctx) throws Exception {
		String vid = ctx.channel().attr(Constant.VID).get();
		if (StringUtil.isNullOrEmpty(vid)) {
			super.channelInactive(ctx);
			return;
		}
		Channel clientChannel = Constant.vcc.get(vid);
		if (clientChannel != null && clientChannel.isActive()) {

			clientChannel.config().setOption(ChannelOption.AUTO_READ, true);

			// 通知客户端，访客连接已经断开
			MyMsg myMsg = new MyMsg();
			myMsg.setType(MyMsg.TYPE_DISCONNECT);
			myMsg.setData(vid.getBytes());
			clientChannel.writeAndFlush(myMsg);
		}
		Constant.clearVccVvc(vid);
		super.channelInactive(ctx);
	}

	@Override
	public void channelWritabilityChanged(ChannelHandlerContext ctx) throws Exception {

		Channel visitorChannel = ctx.channel();
		String vid = visitorChannel.attr(Constant.VID).get();
		if (StringUtil.isNullOrEmpty(vid)) {
			super.channelWritabilityChanged(ctx);
			return;
		}
		Channel clientChannel = Constant.vcc.get(vid);
		if (clientChannel != null) {
			clientChannel.config().setOption(ChannelOption.AUTO_READ, visitorChannel.isWritable());
		}

		super.channelWritabilityChanged(ctx);
	}

	@Override
	public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) throws Exception {
		ctx.close();
	}
}

 服务代理socket

package com.luck.server;

import com.luck.msg.MyMsgDecoder;
import com.luck.msg.MyMsgEncoder;

import io.netty.bootstrap.ServerBootstrap;
import io.netty.channel.ChannelFuture;
import io.netty.channel.ChannelFutureListener;
import io.netty.channel.ChannelInitializer;
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.NioServerSocketChannel;
import io.netty.handler.timeout.IdleStateHandler;

public class ServerSocket {
	private static EventLoopGroup bossGroup = new NioEventLoopGroup();
	private static EventLoopGroup workerGroup = new NioEventLoopGroup();
	private static ChannelFuture channelFuture;

	/**
	 * 启动服务端
	 * @throws Exception
	 */
	public static void startServer() throws Exception {
		try {

			ServerBootstrap b = new ServerBootstrap();
			b.group(bossGroup, workerGroup).channel(NioServerSocketChannel.class)
					.childHandler(new ChannelInitializer() {
						@Override
						public void initChannel(SocketChannel ch) throws Exception {
							ChannelPipeline pipeline = ch.pipeline();
							pipeline.addLast(new MyMsgDecoder(Integer.MAX_VALUE, 0, 4, -4, 0));
							pipeline.addLast(new MyMsgEncoder());
							pipeline.addLast(new IdleStateHandler(40, 10, 0));
							pipeline.addLast(new ClientHandler());
						}

					});
			channelFuture = b.bind(Constant.serverPort).sync();

			channelFuture.addListener((ChannelFutureListener) channelFuture -> {
				// 服务器已启动
			});
			channelFuture.channel().closeFuture().sync();
		} finally {
			shutdown();
			// 服务器已关闭
		}
	}

	public static void shutdown() {
		if (channelFuture != null) {
			channelFuture.channel().close().syncUninterruptibly();
		}
		if ((bossGroup != null) && (!bossGroup.isShutdown())) {
			bossGroup.shutdownGracefully();
		}
		if ((workerGroup != null) && (!workerGroup.isShutdown())) {
			workerGroup.shutdownGracefully();
		}
	}
}

访客代理socket

package com.luck.server;

import io.netty.bootstrap.ServerBootstrap;
import io.netty.channel.ChannelDuplexHandler;
import io.netty.channel.ChannelInitializer;
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.NioServerSocketChannel;

public class VisitorSocket {
	private static EventLoopGroup bossGroup = new NioEventLoopGroup();
	private static EventLoopGroup workerGroup = new NioEventLoopGroup();

	/**
	 * 启动服务代理
	 * 
	 * @throws Exception
	 */
	public static void startServer() throws Exception {

		ServerBootstrap b = new ServerBootstrap();
		b.group(bossGroup, workerGroup).channel(NioServerSocketChannel.class)
				.childHandler(new ChannelInitializer() {
					@Override
					public void initChannel(SocketChannel ch) throws Exception {
						ChannelPipeline pipeline = ch.pipeline();
						pipeline.addLast(new ChannelDuplexHandler());
						pipeline.addLast(new VisitorHandler());
					}
				});
		b.bind(Constant.visitorPort).get();

	}

}

 启动类

package com.luck.server;

public class ServerStart {
	public static void main(String[] args) throws Exception {
		if (null != args && args.length == 2) {
			int visitorPort = Integer.parseInt(args[1]);
			int serverPort = Integer.parseInt(args[0]);
			Constant.visitorPort = visitorPort;
			Constant.serverPort = serverPort;
			// 启动访客服务端，用于接收访客请求
			VisitorSocket.startServer();
			// 启动代理服务端，用于接收客户端请求
			ServerSocket.startServer();
		}
	}
}

 cc-client项目

maven配置

	4.0.0
	com.luck.cc
	cc-client
	1.0-SNAPSHOT
	cc-client
	http://maven.apache.org

	
		${env.JAVA_HOME}
		UTF-8
		1.8
	

	
		
			com.luck.cc
			cc-common
			1.0-SNAPSHOT
		
	
	
		
			
				maven-compiler-plugin
				
					1.8
					1.8
				
			
	        
	            maven-assembly-plugin
	            3.0.0
	            
	                
	                    
	                        com.luck.client.ClientStart
	                    
	                
	                
	                    jar-with-dependencies
	                
	            
	            
	                
	                    make-assembly
	                    package
	                    
	                        single
	                    
	                
	            
	        
		
	

JAVA代码

常量类

package com.luck.client;

import java.util.Map;
import java.util.concurrent.ConcurrentHashMap;

import io.netty.channel.Channel;
import io.netty.util.AttributeKey;
import io.netty.util.internal.StringUtil;

public class Constant {
	/** 代理服务channel */
	public static Channel proxyChannel = null;

	/** 绑定访客id */
	public static final AttributeKey VID = AttributeKey.newInstance("vid");

	/** 访客，代理服务channel */
	public static Map vpc = new ConcurrentHashMap<>();

	/** 访客，真实服务channel */
	public static Map vrc = new ConcurrentHashMap<>();

	/** 真实服务端口 */
	public static int realPort = 8080;

	/** 服务端口 */
	public static int serverPort = 16001;

	/** 服务IP */
	public static String serverIp = "127.0.0.1";

	/**
	 * 清除连接
	 * 
	 * @param vid 访客ID
	 */
	public static void clearvpcvrc(String vid) {
		if (StringUtil.isNullOrEmpty(vid)) {
			return;
		}
		Channel clientChannel = vpc.get(vid);
		if (null != clientChannel) {
			clientChannel.attr(VID).set(null);
			vpc.remove(vid);
		}
		Channel visitorChannel = vrc.get(vid);
		if (null != visitorChannel) {
			visitorChannel.attr(VID).set(null);
			vrc.remove(vid);
		}
	}

	/**
	 * 清除关闭连接
	 * 
	 * @param vid 访客ID
	 */
	public static void clearvpcvrcAndClose(String vid) {
		if (StringUtil.isNullOrEmpty(vid)) {
			return;
		}
		Channel clientChannel = vpc.get(vid);
		if (null != clientChannel) {
			clientChannel.attr(VID).set(null);
			vpc.remove(vid);
			clientChannel.close();
		}
		Channel visitorChannel = vrc.get(vid);
		if (null != visitorChannel) {
			visitorChannel.attr(VID).set(null);
			vrc.remove(vid);
			visitorChannel.close();
		}
	}
}

  客户端代理handler

package com.luck.client;

import com.luck.msg.MyMsg;

import io.netty.buffer.ByteBuf;
import io.netty.channel.Channel;
import io.netty.channel.ChannelHandlerContext;
import io.netty.channel.ChannelOption;
import io.netty.channel.SimpleChannelInboundHandler;
import io.netty.handler.timeout.IdleStateEvent;
import io.netty.util.internal.StringUtil;

public class ProxyHandler extends SimpleChannelInboundHandler {

	@Override
	public void channelRead0(ChannelHandlerContext ctx, MyMsg myMsg) {
		// 客户端读取到代理过来的数据了
		byte type = myMsg.getType();
		String vid = new String(myMsg.getData());
		switch (type) {
		case MyMsg.TYPE_HEARTBEAT:
			break;
		case MyMsg.TYPE_CONNECT:
			RealSocket.connectRealServer(vid);
			break;
		case MyMsg.TYPE_DISCONNECT:
			Constant.clearvpcvrcAndClose(vid);
			break;
		case MyMsg.TYPE_TRANSFER:
			// 把数据转到真实服务
			ByteBuf buf = ctx.alloc().buffer(myMsg.getData().length);
			buf.writeBytes(myMsg.getData());

			String visitorId = ctx.channel().attr(Constant.VID).get();
			Channel rchannel = Constant.vrc.get(visitorId);
			if (null != rchannel) {
				rchannel.writeAndFlush(buf);
			}
			break;
		default:
			// 操作有误
		}
		// 客户端发数据到真实服务了
	}

	@Override
	public void channelWritabilityChanged(ChannelHandlerContext ctx) throws Exception {
		String vid = ctx.channel().attr(Constant.VID).get();
		if (StringUtil.isNullOrEmpty(vid)) {
			super.channelWritabilityChanged(ctx);
			return;
		}
		Channel realChannel = Constant.vrc.get(vid);
		if (realChannel != null) {
			realChannel.config().setOption(ChannelOption.AUTO_READ, ctx.channel().isWritable());
		}

		super.channelWritabilityChanged(ctx);
	}

	@Override
	public void channelInactive(ChannelHandlerContext ctx) throws Exception {
		String vid = ctx.channel().attr(Constant.VID).get();
		if (StringUtil.isNullOrEmpty(vid)) {
			super.channelInactive(ctx);
			return;
		}
		Channel realChannel = Constant.vrc.get(vid);
		if (realChannel != null && realChannel.isActive()) {
			realChannel.close();
		}
		super.channelInactive(ctx);
	}

	@Override
	public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) throws Exception {
		super.exceptionCaught(ctx, cause);
		cause.printStackTrace();
	}

	@Override
	public void userEventTriggered(ChannelHandlerContext ctx, Object evt) throws Exception {
		if (evt instanceof IdleStateEvent) {
			IdleStateEvent event = (IdleStateEvent) evt;
			switch (event.state()) {
			case READER_IDLE:
				ctx.channel().close();
				break;
			case WRITER_IDLE:
				MyMsg myMsg = new MyMsg();
				myMsg.setType(MyMsg.TYPE_HEARTBEAT);
				ctx.channel().writeAndFlush(myMsg);
				break;
			case ALL_IDLE:
				break;
			}
		}
	}
}

 真实服务handler

package com.luck.client;

import com.luck.msg.MyMsg;

import io.netty.buffer.ByteBuf;
import io.netty.channel.Channel;
import io.netty.channel.ChannelHandlerContext;
import io.netty.channel.ChannelOption;
import io.netty.channel.SimpleChannelInboundHandler;
import io.netty.util.internal.StringUtil;

public class RealHandler extends SimpleChannelInboundHandler {

	@Override
	public void channelRead0(ChannelHandlerContext ctx, ByteBuf buf) {
		// 客户读取到真实服务数据了
		byte[] bytes = new byte[buf.readableBytes()];
		buf.readBytes(bytes);
		MyMsg myMsg = new MyMsg();
		myMsg.setType(MyMsg.TYPE_TRANSFER);
		myMsg.setData(bytes);
		String vid = ctx.channel().attr(Constant.VID).get();
		if (StringUtil.isNullOrEmpty(vid)) {
			return;
		}
		Channel proxyChannel = Constant.vpc.get(vid);
		if (null != proxyChannel) {
			proxyChannel.writeAndFlush(myMsg);
		}
		// 客户端发送真实数据到代理了
	}

	@Override
	public void channelActive(ChannelHandlerContext ctx) throws Exception {
		super.channelActive(ctx);
	}

	@Override
	public void channelInactive(ChannelHandlerContext ctx) throws Exception {
		String vid = ctx.channel().attr(Constant.VID).get();
		if (StringUtil.isNullOrEmpty(vid)) {
			super.channelInactive(ctx);
			return;
		}
		Channel proxyChannel = Constant.vpc.get(vid);
		if (proxyChannel != null) {
			MyMsg myMsg = new MyMsg();
			myMsg.setType(MyMsg.TYPE_DISCONNECT);
			myMsg.setData(vid.getBytes());
			proxyChannel.writeAndFlush(myMsg);
		}

		super.channelInactive(ctx);
	}

	@Override
	public void channelWritabilityChanged(ChannelHandlerContext ctx) throws Exception {
		String vid = ctx.channel().attr(Constant.VID).get();
		if (StringUtil.isNullOrEmpty(vid)) {
			super.channelWritabilityChanged(ctx);
			return;
		}
		Channel proxyChannel = Constant.vpc.get(vid);
		if (proxyChannel != null) {
			proxyChannel.config().setOption(ChannelOption.AUTO_READ, ctx.channel().isWritable());
		}

		super.channelWritabilityChanged(ctx);
	}

	@Override
	public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) throws Exception {
		super.exceptionCaught(ctx, cause);
	}
}

 客户端代理socket

package com.luck.client;

import java.util.concurrent.Executors;
import java.util.concurrent.ScheduledExecutorService;
import java.util.concurrent.TimeUnit;

import com.luck.msg.MyMsg;
import com.luck.msg.MyMsgDecoder;
import com.luck.msg.MyMsgEncoder;

import io.netty.bootstrap.Bootstrap;
import io.netty.channel.Channel;
import io.netty.channel.ChannelFuture;
import io.netty.channel.ChannelFutureListener;
import io.netty.channel.ChannelInitializer;
import io.netty.channel.ChannelOption;
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.handler.timeout.IdleStateHandler;
import io.netty.util.internal.StringUtil;

public class ProxySocket {
	private static EventLoopGroup eventLoopGroup = new NioEventLoopGroup();

	/** 重连代理服务 */
	private static final ScheduledExecutorService reconnectExecutor = Executors.newSingleThreadScheduledExecutor();

	public static Channel connectProxyServer() throws Exception {
		reconnectExecutor.scheduleAtFixedRate(new Runnable() {
			public void run() {
				try {
					connectProxyServer(null);
				} catch (Exception e) {
					e.printStackTrace();
				}
			}
		}, 3, 3, TimeUnit.SECONDS);
		return connectProxyServer(null);
	}

	public static Channel connectProxyServer(String vid) throws Exception {
		if (StringUtil.isNullOrEmpty(vid)) {
			if (Constant.proxyChannel == null || !Constant.proxyChannel.isActive()) {
				newConnect(null);
			}
			return null;
		} else {
			Channel channel = Constant.vpc.get(vid);
			if (null == channel) {
				newConnect(vid);
				channel = Constant.vpc.get(vid);
			}
			return channel;
		}
	}

	private static void newConnect(String vid) throws InterruptedException {
		Bootstrap bootstrap = new Bootstrap();
		bootstrap.group(eventLoopGroup).channel(NioSocketChannel.class)
				.handler(new ChannelInitializer() {
					@Override
					public void initChannel(SocketChannel ch) throws Exception {
						ChannelPipeline pipeline = ch.pipeline();
						pipeline.addLast(new MyMsgDecoder(Integer.MAX_VALUE, 0, 4, -4, 0));
						pipeline.addLast(new MyMsgEncoder());
						pipeline.addLast(new IdleStateHandler(40, 8, 0));
						pipeline.addLast(new ProxyHandler());
					}
				});

		bootstrap.connect(Constant.serverIp, Constant.serverPort).addListener(new ChannelFutureListener() {
			@Override
			public void operationComplete(ChannelFuture future) throws Exception {
				if (future.isSuccess()) {
					// 客户端链接代理服务器成功
					Channel channel = future.channel();
					if (StringUtil.isNullOrEmpty(vid)) {
						// 告诉服务端这条连接是client的连接
						MyMsg myMsg = new MyMsg();
						myMsg.setType(MyMsg.TYPE_CONNECT);
						myMsg.setData("client".getBytes());
						channel.writeAndFlush(myMsg);

						Constant.proxyChannel = channel;
					} else {

						// 告诉服务端这条连接是vid的连接
						MyMsg myMsg = new MyMsg();
						myMsg.setType(MyMsg.TYPE_CONNECT);
						myMsg.setData(vid.getBytes());
						channel.writeAndFlush(myMsg);

						// 客户端绑定通道关系
						Constant.vpc.put(vid, channel);
						channel.attr(Constant.VID).set(vid);

						Channel realChannel = Constant.vrc.get(vid);
						if (null != realChannel) {
							realChannel.config().setOption(ChannelOption.AUTO_READ, true);
						}
					}
				}
			}
		});
	}
}

真实服务socket 

package com.luck.client;

import io.netty.bootstrap.Bootstrap;
import io.netty.channel.Channel;
import io.netty.channel.ChannelFuture;
import io.netty.channel.ChannelFutureListener;
import io.netty.channel.ChannelInitializer;
import io.netty.channel.ChannelOption;
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.util.internal.StringUtil;

public class RealSocket {
	static EventLoopGroup eventLoopGroup = new NioEventLoopGroup();

	/**
	 * 连接真实服务
	 * 
	 * @param vid 访客ID
	 * @return
	 */
	public static Channel connectRealServer(String vid) {
		if (StringUtil.isNullOrEmpty(vid)) {
			return null;
		}
		Channel channel = Constant.vrc.get(vid);
		if (null == channel) {
			newConnect(vid);
			channel = Constant.vrc.get(vid);
		}
		return channel;
	}

	private static void newConnect(String vid) {
		try {
			Bootstrap bootstrap = new Bootstrap();
			bootstrap.group(eventLoopGroup).channel(NioSocketChannel.class)
					.handler(new ChannelInitializer() {
						@Override
						public void initChannel(SocketChannel ch) throws Exception {
							ChannelPipeline pipeline = ch.pipeline();
							pipeline.addLast(new RealHandler());
						}

					});
			bootstrap.connect("127.0.0.1", Constant.realPort).addListener(new ChannelFutureListener() {
				@Override
				public void operationComplete(ChannelFuture future) throws Exception {
					if (future.isSuccess()) {
						// 客户端链接真实服务成功
						future.channel().config().setOption(ChannelOption.AUTO_READ, false);
						future.channel().attr(Constant.VID).set(vid);
						Constant.vrc.put(vid, future.channel());
						ProxySocket.connectProxyServer(vid);
					}
				}
			});
		} catch (Exception e) {
			e.printStackTrace();
		}
	}
}

 启动类

package com.luck.client;

public class ClientStart {

	public static void main(String[] args) throws Exception {
		if (null != args && args.length == 3) {
			int realPort = Integer.parseInt(args[2]);
			int serverPort = Integer.parseInt(args[1]);
			String serverIp = args[0];
			Constant.serverIp = serverIp;
			Constant.serverPort = serverPort;
			Constant.realPort = realPort;
			// 连接代理服务
			ProxySocket.connectProxyServer();
		}
	}
}

使用

启动服务端

java -jar cc-server.jar 16001 16002

启动客户端 

java -jar cc-client.jar 127.0.0.1 16001 8080

备注

参考：中微子代理: 一款基于netty的内网穿透神器 (gitee.com)

中微子代理（neutrino-proxy）是一个基于netty的、开源的java内网穿透项目。遵循MIT许可，因此您可以对它进行复制、修改、传播并用于任何个人或商业行为。

中微子代理项目还在完善中，目前有比较完整的管理功能，支持多租户，代码也比较易读，需要的同学可以去看下。