TCP 由于TCP协议本身的机制(面向连接的可靠地协议-三次握手机制)客户端与服务器会维持一个连接(Channel),数据在连接不断开的情况下,可以持续不断地将多个数据包发往服务器,但是如果发送的网络数据包太小,那么他本身会启用Nagle算法(可配置是否启用)对较小的数据包进行合并(基于此,TCP的网络延迟要UDP的高些)然后再发送(超时或者包大小足够)。那么这样的话,服务器在接收到消息(数据流)的时候就无法区分哪些数据包是客户端自己分开发送的,这样产生了粘包;服务器在接收到数据库后,放到缓冲区中,如果消息没有被及时从缓存区取走,下次在取数据的时候可能就会出现一次取出多个数据包的情况,造成粘包现象(确切来讲,对于基于TCP协议的应用,不应用包来描述,而应 用 流来描述),个人认为服务器接收端产生的粘包应该与linux内核处理socket的方式 select轮询机制的线性扫描频度无关。 UDP 本身作为无连接的不可靠的传输协议(适合频繁发送较小的数据包),他不会对数据包进行合并发送(也就没有Nagle算法之说了),他直接是一端发送什么数据,直接就发出去了,既然他不会对数据合并,每一个数据包都是完整的(数据+UDP头+IP头等等发一次数据封装一次)也就没有粘包一说了。
可能是IP分片传输导致的,也可能是传输过程中丢失部分包导致出现的半包,还有可能就是一个包可能被分成了两次传输,在取数据的时候,先取到了一部分(还可能与接收的缓冲区大小有关系),总之就是一个数据包被分成了多次接收。
简单的概括
(1)粘包: 1.服务端 原因收到的数据放在系统接收缓冲区,用户进程从该缓冲区取数据 2.客户端 原因TCP为提高传输效率,要收集到足够多的数据后才发送一包数据
(2).分包: 1.应用程序写入的字节大小大于套接字发送缓冲区的大小 2.进行mss(最大报文长度)大小的TCP分段,当TCP报文长度-TCP头部长度>MSS 3.以太网帧的payload(净荷)大于MTU(1500字节)进行ip分片
源码:pack目录下的error Server.java
package com.dig8.pack.error;import org.jboss.netty.bootstrap.ServerBootstrap;import org.jboss.netty.channel.ChannelPipeline;import org.jboss.netty.channel.ChannelPipelineFactory;import org.jboss.netty.channel.Channels;import org.jboss.netty.channel.socket.nio.NioServerSocketChannelFactory;import java.net.InetSocketAddress;import java.util.concurrent.ExecutorService;import java.util.concurrent.Executors;/** * netty服务端 * * @author idig8.com */public class Server { public static void main(String[] args) { // 服务类 ServerBootstrap bootstrap = new ServerBootstrap(); // boss线程,主要监听端口和获取worker线程及分配socketChannel给worker线程 ExecutorService boss = Executors.newCachedThreadPool(); // worker线程负责数据读写 ExecutorService worker = Executors.newCachedThreadPool(); // 设置niosocket工厂 bootstrap.setFactory(new NioServerSocketChannelFactory(boss, worker)); // 设置管道的工厂 bootstrap.setPipelineFactory(new ChannelPipelineFactory() { @Override public ChannelPipeline getPipeline() throws Exception { ChannelPipeline pipeline = Channels.pipeline(); // 管道过滤器 pipeline.addLast("myHandler", new ServerHandler()); return pipeline; } }); // 服务类绑定端口 bootstrap.bind(new InetSocketAddress(8888)); }}
ServerHandler.java
package com.dig8.pack.error;import org.jboss.netty.buffer.ChannelBuffer;import org.jboss.netty.channel.ChannelHandlerContext;import org.jboss.netty.channel.MessageEvent;import org.jboss.netty.channel.SimpleChannelHandler;/** * @author idig8.com */public class ServerHandler extends SimpleChannelHandler{ @Override public void messageReceived(ChannelHandlerContext ctx, MessageEvent e) throws Exception { ChannelBuffer buffer = (ChannelBuffer) e.getMessage(); byte[] bs = buffer.array(); System.out.println("server receive data: " +new String(bs)); }}
Client.java
package com.dig8.pack.error;import org.jboss.netty.bootstrap.ClientBootstrap;import org.jboss.netty.channel.ChannelPipeline;import org.jboss.netty.channel.ChannelPipelineFactory;import org.jboss.netty.channel.Channels;import org.jboss.netty.channel.socket.nio.NioClientSocketChannelFactory;import org.jboss.netty.handler.codec.string.StringEncoder;import java.net.InetSocketAddress;import java.util.concurrent.ExecutorService;import java.util.concurrent.Executors;/** * 客户端 * * @author idig8.com */public class Client { public static void main(String[] args) throws Exception { //服务类 ClientBootstrap bootstrap = new ClientBootstrap(); //线程池 ExecutorService boss = Executors.newCachedThreadPool(); ExecutorService worker = Executors.newCachedThreadPool(); //socket工厂 bootstrap.setFactory(new NioClientSocketChannelFactory(boss, worker)); //管道工厂 bootstrap.setPipelineFactory(new ChannelPipelineFactory() { @Override public ChannelPipeline getPipeline() throws Exception { ChannelPipeline pipeline = Channels.pipeline(); pipeline.addLast("1", new StringEncoder()); pipeline.addLast("2", new ClientHandler()); return pipeline; } }); //连接服务端 bootstrap.connect(new InetSocketAddress("127.0.0.1", 8888)).sync(); }}
ClientHandler.java
package com.dig8.pack.error;import org.jboss.netty.buffer.ChannelBuffer;import org.jboss.netty.buffer.ChannelBuffers;import org.jboss.netty.channel.*;/** * 客户端消息处理类 * @author idig8.com */public class ClientHandler extends SimpleChannelHandler { // 包头 private static final int HEAD_FLAG = -32323231; @Override public void channelConnected(ChannelHandlerContext ctx, ChannelStateEvent e) throws Exception { Channel channel = ctx.getChannel(); String msg = "Hello,idig8.com"; for (int i = 0; i < 1000; i++) { channel.write(msg); } } @Override public void exceptionCaught(ChannelHandlerContext ctx, ExceptionEvent e) throws Exception { }}
运行后出现粘包和分包现象
服务端和客户端约定好稳定的数据包结构
1.客户端根据约定的数据包结构发送数据 2.服务端根据约定的数据包结构来读取数据
通过MyDecoder集成FrameDecoder的方式来 源码:pack目录下的custom Server.java
package com.dig8.pack.custom;import java.net.InetSocketAddress;import java.util.concurrent.ExecutorService;import java.util.concurrent.Executors;import org.jboss.netty.bootstrap.ServerBootstrap;import org.jboss.netty.channel.ChannelPipeline;import org.jboss.netty.channel.ChannelPipelineFactory;import org.jboss.netty.channel.Channels;import org.jboss.netty.channel.socket.nio.NioServerSocketChannelFactory;/** * netty服务端 * * @author idig8.com */public class Server { public static void main(String[] args) { // 服务类 ServerBootstrap bootstrap = new ServerBootstrap(); // boss线程,主要监听端口和获取worker线程及分配socketChannel给worker线程 ExecutorService boss = Executors.newCachedThreadPool(); // worker线程负责数据读写 ExecutorService worker = Executors.newCachedThreadPool(); // 设置niosocket工厂 bootstrap.setFactory(new NioServerSocketChannelFactory(boss, worker)); // 设置管道的工厂 bootstrap.setPipelineFactory(new ChannelPipelineFactory() { @Override public ChannelPipeline getPipeline() throws Exception { ChannelPipeline pipeline = Channels.pipeline(); // 管道过滤器 pipeline.addLast("myDecoder", new MyDecoder()); pipeline.addLast("myHandler", new ServerHandler()); return pipeline; } }); // 服务类绑定端口 bootstrap.bind(new InetSocketAddress(7778)); }}
ServerHandler.java
package com.dig8.pack.custom;import org.jboss.netty.buffer.ChannelBuffer;import org.jboss.netty.channel.ChannelHandlerContext;import org.jboss.netty.channel.MessageEvent;import org.jboss.netty.channel.SimpleChannelHandler;/** * @author idig8.com */public class ServerHandler extends SimpleChannelHandler{ @Override public void messageReceived(ChannelHandlerContext ctx, MessageEvent e) throws Exception { /*ChannelBuffer buffer = (ChannelBuffer) e.getMessage(); byte[] bs = buffer.array();*/ System.out.println("server receive data: " + e.getMessage()); }}
Client.java
package com.dig8.pack.custom;import java.net.InetSocketAddress;import java.util.concurrent.ExecutorService;import java.util.concurrent.Executors;import org.jboss.netty.bootstrap.ClientBootstrap;import org.jboss.netty.channel.ChannelPipeline;import org.jboss.netty.channel.ChannelPipelineFactory;import org.jboss.netty.channel.Channels;import org.jboss.netty.channel.socket.nio.NioClientSocketChannelFactory;import org.jboss.netty.handler.codec.string.StringEncoder;/** * 客户端 * * @author idig8.com */public class Client { public static void main(String[] args) throws Exception { //服务类 ClientBootstrap bootstrap = new ClientBootstrap(); //线程池 ExecutorService boss = Executors.newCachedThreadPool(); ExecutorService worker = Executors.newCachedThreadPool(); //socket工厂 bootstrap.setFactory(new NioClientSocketChannelFactory(boss, worker)); //管道工厂 bootstrap.setPipelineFactory(new ChannelPipelineFactory() { @Override public ChannelPipeline getPipeline() throws Exception { ChannelPipeline pipeline = Channels.pipeline(); pipeline.addLast("1", new StringEncoder()); pipeline.addLast("2", new ClientHandler()); return pipeline; } }); //连接服务端 bootstrap.connect(new InetSocketAddress("127.0.0.1", 7778)).sync(); }}
ClientHandler.java
package com.dig8.pack.custom;import org.jboss.netty.buffer.ChannelBuffer;import org.jboss.netty.buffer.ChannelBuffers;import org.jboss.netty.channel.Channel;import org.jboss.netty.channel.ChannelHandlerContext;import org.jboss.netty.channel.ChannelStateEvent;import org.jboss.netty.channel.ExceptionEvent;import org.jboss.netty.channel.SimpleChannelHandler;/** * 客户端消息处理类 * @author idig8.com */public class ClientHandler extends SimpleChannelHandler { // 包头 private static final int HEAD_FLAG = -32323231; @Override public void channelConnected(ChannelHandlerContext ctx, ChannelStateEvent e) throws Exception { Channel channel = ctx.getChannel(); String msg = "Hello,idig8.com 通过定义包头+长度+数据 防止粘包和分包"; byte[] bytes = msg.getBytes(); // 定义数据包 ,结构为:包头 + 长度 + 数据 ChannelBuffer buffer = ChannelBuffers.dynamicBuffer(); // 1.写包头 buffer.writeInt(HEAD_FLAG);// 4字节 // 2.写长度 buffer.writeInt(bytes.length);// 4字节 // 3.写数据本身 buffer.writeBytes(bytes); for (int i = 0; i < 1000; i++) { channel.write(buffer); } } @Override public void exceptionCaught(ChannelHandlerContext ctx, ExceptionEvent e) throws Exception { }}
MyDecoder.java
/** * */package com.dig8.pack.custom;import org.jboss.netty.buffer.ChannelBuffer;import org.jboss.netty.channel.Channel;import org.jboss.netty.channel.ChannelHandlerContext;import org.jboss.netty.handler.codec.frame.FrameDecoder;/** * @author idig8.com */public class MyDecoder extends FrameDecoder{ // 包头 private static final int HEAD_FLAG = -32323231; // 数据包基本长度 private final static int BASE_LENGTH = 4 + 4; @Override protected Object decode(ChannelHandlerContext ctx, Channel channel, ChannelBuffer buffer) throws Exception { // 收到数据之后,先判断buffer中可读的数据长度是否大于数据包的基本长度 if(buffer.readableBytes() > BASE_LENGTH){ // 防止socket攻击: if(buffer.readableBytes() > 4096 * 2){ // 4k System.out.println("socket 攻击了"); buffer.skipBytes(buffer.readableBytes()); } // 记录包头开始的位置 int headIndex; while(true){ headIndex = buffer.readerIndex(); buffer.markReaderIndex(); // 代码很关键 if(buffer.readableBytes() < 4){// 包头的长度 buffer.readerIndex(headIndex); return null; } // 此时说明包头的长度是足够的 // 正好读取的是包头 if(buffer.readInt() == HEAD_FLAG ){ break; } // [1,2,3,4] 1 1 1 1 1 // 如果不是包头,需要略过一个字节,在略过之前,需要还原读指针位置 buffer.resetReaderIndex(); buffer.readByte();// 略过一个字节 if(buffer.readableBytes() < BASE_LENGTH){ return null; } } // 此时说明有数据包到来 // 做标记(记住当前读指针的位置) // buffer.markReaderIndex(); // 1.读长度 int dataLength = buffer.readInt(); if(buffer.readableBytes() < dataLength){ // 说明数据本身的长度还不够, 肯定要继续等待后面的数据到来 // 还原读指针的位置 buffer.readerIndex(headIndex); return null; } // 此时说明数据包已经位置 // 2.读数据本身 byte[] dst = new byte[dataLength]; buffer.readBytes(dst); // 继续传递下去 // ? // 如果此时buffer中的数据还没有读完,那么剩下的数据怎么办? return new String(dst); } // return null 表示此时的数据包不完整,需要继续等待下一个数据包的到来 ? return null; }}
消息定长
1.FixedLengthFrameDecoder
行分隔符
2.LineBasedFrameDecoder
自定义特殊符号进行分割
3.DelimiterBasedFrameDecoder
源码:pack目录下的nettysolution Server.java
package com.dig8.pack.nettysolution;import java.net.InetSocketAddress;import java.util.concurrent.ExecutorService;import java.util.concurrent.Executors;import org.jboss.netty.bootstrap.ServerBootstrap;import org.jboss.netty.buffer.ChannelBuffers;import org.jboss.netty.channel.ChannelPipeline;import org.jboss.netty.channel.ChannelPipelineFactory;import org.jboss.netty.channel.Channels;import org.jboss.netty.channel.socket.nio.NioServerSocketChannelFactory;import org.jboss.netty.handler.codec.frame.DelimiterBasedFrameDecoder;import org.jboss.netty.handler.codec.frame.FixedLengthFrameDecoder;import org.jboss.netty.handler.codec.frame.LineBasedFrameDecoder;import org.jboss.netty.handler.codec.string.StringDecoder;/** * 服务端 * @author idig8.com */public class Server { public static void main(String[] args) throws Exception { // 服务类 ServerBootstrap bootstrap = new ServerBootstrap(); // boss线程,主要监听端口和获取worker线程及分配socketChannel给worker线程 ExecutorService boss = Executors.newCachedThreadPool(); // worker线程负责数据读写 ExecutorService worker = Executors.newCachedThreadPool(); // 设置niosocket工厂 bootstrap.setFactory(new NioServerSocketChannelFactory(boss, worker)); // 设置管道的工厂 bootstrap.setPipelineFactory(new ChannelPipelineFactory() { @Override public ChannelPipeline getPipeline() throws Exception { ChannelPipeline pipeline = Channels.pipeline(); // 管道过滤器 // 方案1:消息定长 //pipeline.addLast("fixedLength", new FixedLengthFrameDecoder(18)); // 方案2:行分隔符 //pipeline.addLast("fixedLength", new LineBasedFrameDecoder(1024)); // 方案3:自定义特殊符号进行分割 pipeline.addLast("delimiter", new DelimiterBasedFrameDecoder(1024, ChannelBuffers.copiedBuffer("#@#".getBytes()))); pipeline.addLast("1",new StringDecoder()); pipeline.addLast("2",new ServerMessageHandler()); return pipeline; } }); // 服务类绑定端口 bootstrap.bind(new InetSocketAddress(7777)); System.out.println("服务端启动..."); }}
ServerMessageHandler.java
package com.dig8.pack.nettysolution;import org.jboss.netty.channel.ChannelHandlerContext;import org.jboss.netty.channel.ExceptionEvent;import org.jboss.netty.channel.MessageEvent;import org.jboss.netty.channel.SimpleChannelHandler;/** * 服务端消息处理类 * @author idig8.com */public class ServerMessageHandler extends SimpleChannelHandler { /** * 接收消息 */ @Override public void messageReceived(ChannelHandlerContext ctx, MessageEvent e) throws Exception { System.out.println("receive request: " + e.getMessage()); } /** * 异常处理 */ @Override public void exceptionCaught(ChannelHandlerContext ctx, ExceptionEvent e) throws Exception { }}
Client.java
package com.dig8.pack.nettysolution;import java.net.InetSocketAddress;import java.util.concurrent.ExecutorService;import java.util.concurrent.Executors;import org.jboss.netty.bootstrap.ClientBootstrap;import org.jboss.netty.buffer.ChannelBuffer;import org.jboss.netty.buffer.ChannelBuffers;import org.jboss.netty.channel.ChannelFuture;import org.jboss.netty.channel.ChannelPipeline;import org.jboss.netty.channel.ChannelPipelineFactory;import org.jboss.netty.channel.Channels;import org.jboss.netty.channel.socket.nio.NioClientSocketChannelFactory;import org.jboss.netty.handler.codec.frame.DelimiterBasedFrameDecoder;import org.jboss.netty.handler.codec.frame.FixedLengthFrameDecoder;import org.jboss.netty.handler.codec.frame.LineBasedFrameDecoder;import org.jboss.netty.handler.codec.string.StringEncoder;/** * 客户端 * * @author idig8.com */public class Client { public static void main(String[] args) throws Exception { //服务类 ClientBootstrap bootstrap = new ClientBootstrap(); //线程池 ExecutorService boss = Executors.newCachedThreadPool(); ExecutorService worker = Executors.newCachedThreadPool(); //socket工厂 bootstrap.setFactory(new NioClientSocketChannelFactory(boss, worker)); //管道工厂 bootstrap.setPipelineFactory(new ChannelPipelineFactory() { @Override public ChannelPipeline getPipeline() throws Exception { ChannelPipeline pipeline = Channels.pipeline(); // 方案1:消息定长 //pipeline.addLast("fixedLength", new FixedLengthFrameDecoder(18)); // 方案2:行分隔符 //pipeline.addLast("fixedLength", new LineBasedFrameDecoder(1024)); // 方案3:自定义特殊符号进行分割 pipeline.addLast("delimiter", new DelimiterBasedFrameDecoder(1024, ChannelBuffers.copiedBuffer("#@#".getBytes()))); pipeline.addLast("1",new StringEncoder()); pipeline.addLast("2", new ClientMessageHandler()); return pipeline; } }); //连接服务端 @SuppressWarnings("unused") ChannelFuture connect = bootstrap.connect(new InetSocketAddress("127.0.0.1", 7777)).sync();// Channel channel = connect.getChannel();// System.out.println("client start");// Scanner scanner = new Scanner(System.in);// while(true){// System.out.println("请输入:");// channel.write(scanner.next());// } }}
ClientMessageHandler.java
package com.dig8.pack.nettysolution;import org.jboss.netty.channel.Channel;import org.jboss.netty.channel.ChannelHandlerContext;import org.jboss.netty.channel.ChannelStateEvent;import org.jboss.netty.channel.ExceptionEvent;import org.jboss.netty.channel.MessageEvent;import org.jboss.netty.channel.SimpleChannelHandler;/** * 客户端消息接受处理类 * @author idig8.com */public class ClientMessageHandler extends SimpleChannelHandler { /** * 接收消息 */ @Override public void messageReceived(ChannelHandlerContext ctx, MessageEvent e) throws Exception { System.out.println("server response : " + e.getMessage()); } /** * 新连接 */ @Override public void channelConnected(ChannelHandlerContext ctx, ChannelStateEvent e) throws Exception { Channel channel = ctx.getChannel(); String separator = "#@#";//System.getProperty("line.separator");// 系统换行符 String msg = "idig8.com send cmd"; for (int i = 0; i < 1000; i++) { channel.write(msg + i + separator); } } /** * 异常处理 */ @Override public void exceptionCaught(ChannelHandlerContext ctx, ExceptionEvent e) throws Exception { }}
PS:基本上netty针对tcp 分包粘包已经说完了,确实有了netty真的很方便比传统的socket方便很多。下次说说http 协议实现。