基于之前的例子（参见netty5自定义私有协议实例），我们修改下客户端handler，让发送的数据超过1024字节：
NettyClientHandler：
/** * 构造PCM请求消息体 * * @return */ private byte[] buildPcmData() throws Exception { byte[] resultByte = longToBytes(System.currentTimeMillis()); // 读取一个本地文件 String AUDIO_PATH = "D:\input\test_1.pcm"; try (RandomAccessFile raf = new RandomAccessFile(AUDIO_PATH, "r")) { byte[] content = new byte[1024]; raf.read(content); resultByte = addAll(resultByte, content); } return resultByte; } /** * 将两个数组合并起来 * @param array1 * @param array2 * @return */ private byte[] addAll(byte[] array1, byte... array2) { byte[] joinedArray = new byte[array1.length + array2.length]; System.arraycopy(array1, 0, joinedArray, 0, array1.length); System.arraycopy(array2, 0, joinedArray, array1.length, array2.length); return joinedArray; }
原来发送一个8字节的long型当前时间，现在我们加上一个音频文件（你也可以用文本文件）读取到的1024字节二进制流，现在data数据包的总大小是8+1024=1032字节，再加上消息头的10字节，整个客户端二进制流是1042字节。再跑下，只能看到客户端打印了日志，不见服务端日志有啥输出了：
10:41:28.150 [nioEventLoopGroup-1-0] INFO com.wlf.netty.nettyclient.handler.NettyClientHandler - [client] client send data : NettyMessage{header=Header{delimiter=-1410399999, length=1032, type=1, reserved=0}, data=[B@7e29c808}
为啥呢？让我们来debug下NettyMessageDecoder的decode方法，打上端点，用debug模式重起服务端，客户端也需重启：
从上图可以看到，服务端每次请求能接收的最大字节流是1024，而我们实际上是整个包是1044字节，所以拆包了。继续debug下去，你会发现第二次请求过来的是剩下的18个字节：
而且你会发现死循环了，程序一直在while里转圈圈，因为第二次发送过来的只是data数据包里剩下的18个字节，没有消息头，满足不了break或者return的条件。既然这里无法解决拆包的问题，那么我们只能另寻他路了。最简单的办法是拿来主义，netty自带的粘包拆包解决方案有4种：固定包大小、指定包大小、固定以换行符结束、指定标志结束。结合我们的这里的场景，我们的消息头里已经有包大小，那么采用第二种方案是最理所当然的选择了。
怎么使用方案二？既然数据包长度我们已经包含在消息头中发送出去，那么就没必要再通过LengthFieldPrepender来计算整个大包（包括消息头）大小并追加一个长度字段来在外面包一层，我们只需通过LengthFieldBasedFrameDecoder来解码即可。那么LengthFieldBasedFrameDecoder怎么解码的？可参考它的源码介绍：
/** * A decoder that splits the received {@link ByteBuf}s dynamically by the * value of the length field in the message. It is particularly useful when you * decode a binary message which has an integer header field that represents the * length of the message body or the whole message. * <p> * {@link LengthFieldBasedFrameDecoder} has many configuration parameters so * that it can decode any message with a length field, which is often seen in * proprietary client-server protocols. Here are some example that will give * you the basic idea on which option does what. * * <h3>2 bytes length field at offset 0, do not strip header</h3> * * The value of the length field in this example is <tt>12 (0x0C)</tt> which * represents the length of "HELLO, WORLD". By default, the decoder assumes * that the length field represents the number of the bytes that follows the * length field. Therefore, it can be decoded with the simplistic parameter * combination. * <pre> * <b>lengthFieldOffset</b> = <b>0</b> * <b>lengthFieldLength</b> = <b>2</b> * lengthAdjustment = 0 * initialBytesToStrip = 0 (= do not strip header) * * BEFORE DECODE (14 bytes) AFTER DECODE (14 bytes) * +--------+----------------+ +--------+----------------+ * | Length | Actual Content |----->| Length | Actual Content | * | 0x000C | "HELLO, WORLD" | | 0x000C | "HELLO, WORLD" | * +--------+----------------+ +--------+----------------+ * </pre> * * <h3>2 bytes length field at offset 0, strip header</h3> * * Because we can get the length of the content by calling * {@link ByteBuf#readableBytes()}, you might want to strip the length * field by specifying <tt>initialBytesToStrip</tt>. In this example, we * specified <tt>2</tt>, that is same with the length of the length field, to * strip the first two bytes. * <pre> * lengthFieldOffset = 0 * lengthFieldLength = 2 * lengthAdjustment = 0 * <b>initialBytesToStrip</b> = <b>2</b> (= the length of the Length field) * * BEFORE DECODE (14 bytes) AFTER DECODE (12 bytes) * +--------+----------------+ +----------------+ * | Length | Actual Content |----->| Actual Content | * | 0x000C | "HELLO, WORLD" | | "HELLO, WORLD" | * +--------+----------------+ +----------------+ * </pre> * * <h3>2 bytes length field at offset 0, do not strip header, the length field * represents the length of the whole message</h3> * * In most cases, the length field represents the length of the message body * only, as shown in the previous examples. However, in some protocols, the * length field represents the length of the whole message, including the * message header. In such a case, we specify a non-zero * <tt>lengthAdjustment</tt>. Because the length value in this example message * is always greater than the body length by <tt>2</tt>, we specify <tt>-2</tt> * as <tt>lengthAdjustment</tt> for compensation. * <pre> * lengthFieldOffset = 0 * lengthFieldLength = 2 * <b>lengthAdjustment</b> = <b>-2</b> (= the length of the Length field) * initialBytesToStrip = 0 * * BEFORE DECODE (14 bytes) AFTER DECODE (14 bytes) * +--------+----------------+ +--------+----------------+ * | Length | Actual Content |----->| Length | Actual Content | * | 0x000E | "HELLO, WORLD" | | 0x000E | "HELLO, WORLD" | * +--------+----------------+ +--------+----------------+ * </pre> * * <h3>3 bytes length field at the end of 5 bytes header, do not strip header</h3> * * The following message is a simple variation of the first example. An extra * header value is prepended to the message. <tt>lengthAdjustment</tt> is zero * again because the decoder always takes the length of the prepended data into * account during frame length calculation. * <pre> * <b>lengthFieldOffset</b> = <b>2</b> (= the length of Header 1) * <b>lengthFieldLength</b> = <b>3</b> * lengthAdjustment = 0 * initialBytesToStrip = 0 * * BEFORE DECODE (17 bytes) AFTER DECODE (17 bytes) * +----------+----------+----------------+ +----------+----------+----------------+ * | Header 1 | Length | Actual Content |----->| Header 1 | Length | Actual Content | * | 0xCAFE | 0x00000C | "HELLO, WORLD" | | 0xCAFE | 0x00000C | "HELLO, WORLD" | * +----------+----------+----------------+ +----------+----------+----------------+ * </pre> * * <h3>3 bytes length field at the beginning of 5 bytes header, do not strip header</h3> * * This is an advanced example that shows the case where there is an extra * header between the length field and the message body. You have to specify a * positive <tt>lengthAdjustment</tt> so that the decoder counts the extra * header into the frame length calculation. * <pre> * lengthFieldOffset = 0 * lengthFieldLength = 3 * <b>lengthAdjustment</b> = <b>2</b> (= the length of Header 1) * initialBytesToStrip = 0 * * BEFORE DECODE (17 bytes) AFTER DECODE (17 bytes) * +----------+----------+----------------+ +----------+----------+----------------+ * | Length | Header 1 | Actual Content |----->| Length | Header 1 | Actual Content | * | 0x00000C | 0xCAFE | "HELLO, WORLD" | | 0x00000C | 0xCAFE | "HELLO, WORLD" | * +----------+----------+----------------+ +----------+----------+----------------+ * </pre> * * <h3>2 bytes length field at offset 1 in the middle of 4 bytes header, * strip the first header field and the length field</h3> * * This is a combination of all the examples above. There are the prepended * header before the length field and the extra header after the length field. * The prepended header affects the <tt>lengthFieldOffset</tt> and the extra * header affects the <tt>lengthAdjustment</tt>. We also specified a non-zero * <tt>initialBytesToStrip</tt> to strip the length field and the prepended * header from the frame. If you don't want to strip the prepended header, you * could specify <tt>0</tt> for <tt>initialBytesToSkip</tt>. * <pre> * lengthFieldOffset = 1 (= the length of HDR1) * lengthFieldLength = 2 * <b>lengthAdjustment</b> = <b>1</b> (= the length of HDR2) * <b>initialBytesToStrip</b> = <b>3</b> (= the length of HDR1 + LEN) * * BEFORE DECODE (16 bytes) AFTER DECODE (13 bytes) * +------+--------+------+----------------+ +------+----------------+ * | HDR1 | Length | HDR2 | Actual Content |----->| HDR2 | Actual Content | * | 0xCA | 0x000C | 0xFE | "HELLO, WORLD" | | 0xFE | "HELLO, WORLD" | * +------+--------+------+----------------+ +------+----------------+ * </pre> * * <h3>2 bytes length field at offset 1 in the middle of 4 bytes header, * strip the first header field and the length field, the length field * represents the length of the whole message</h3> * * Let's give another twist to the previous example. The only difference from * the previous example is that the length field represents the length of the * whole message instead of the message body, just like the third example. * We have to count the length of HDR1 and Length into <tt>lengthAdjustment</tt>. * Please note that we don't need to take the length of HDR2 into account * because the length field already includes the whole header length. * <pre> * lengthFieldOffset = 1 * lengthFieldLength = 2 * <b>lengthAdjustment</b> = <b>-3</b> (= the length of HDR1 + LEN, negative) * <b>initialBytesToStrip</b> = <b> 3</b> * * BEFORE DECODE (16 bytes) AFTER DECODE (13 bytes) * +------+--------+------+----------------+ +------+----------------+ * | HDR1 | Length | HDR2 | Actual Content |----->| HDR2 | Actual Content | * | 0xCA | 0x0010 | 0xFE | "HELLO, WORLD" | | 0xFE | "HELLO, WORLD" | * +------+--------+------+----------------+ +------+----------------+ * </pre> * @see LengthFieldPrepender */
巴拉巴拉举了7个例子，对我们这个场景来说，具有参考价值的是最后一个例子，但它解码后的东西不是我们想要的，我们要的是整个大包里的东西。我们要的参数值如下：
lengthFieldOffset = 4 (长度字段的偏差，因为Delimiter长度为4字节，所以偏移量为0+4=4)
lengthFieldLength = 4 (长度字段占的字节数，Length大小为4个字节)
lengthAdjustment = 2 (长度字段后面到消息体之间的字节数，Type+Reserved=2）
initialBytesToStrip = 0 (从解码帧中第一次去除的字节数，所有字段我们全要，所以不去除，0）
BEFORE DECODE AFTER DECODE
+-----------+-----------+--------+--------------+-------------------------+ +-----------+-----------+--------+-------------+-------------------------+
| Delimiter | Length | Type | Reserved | Actual Content | ----> | Delimiter | Length | Type | Reserved | Actual Content |
| 0xCA | 0x0010 | 0xFE | 0x000 | "HELLO, WORLD" | | 0xCA | 0x0010 | 0xFE | 0x000 | "HELLO, WORLD" |
+-----------+-----------+--------+--------------+-------------------------+ +-----------+-----------+--------+-------------+--------------------------+
现在我们分别在客户端和服务端的启动类里加这个解码器，对了，第一个参数是允许传输的二进制流的最大值，我们设大一点，给它一个G：
客户端：
public void connect(int port, String host) throws Exception { NioEventLoopGroup workGroup = new NioEventLoopGroup(); try { Bootstrap bootstrap = new Bootstrap(); bootstrap.group(workGroup).channel(NioSocketChannel.class).option(ChannelOption.TCP_NODELAY, true) .handler(new ChannelInitializer<SocketChannel>() { @Override public void initChannel(SocketChannel channel) throws Exception { channel.pipeline().addLast(new LengthFieldBasedFrameDecoder(1024*1024*1024,4,4,2,0)); channel.pipeline().addLast(new NettyMessageDecoder()); channel.pipeline().addLast(new NettyMessageEncoder()); channel.pipeline().addLast(new NettyClientHandler()); } }); ChannelFuture future = bootstrap.connect(host, port).sync(); future.channel().closeFuture().sync(); } finally { workGroup.shutdownGracefully(); } }
服务端：
public void bind(int port) throws Exception{ try{ ServerBootstrap serverBootstrap = new ServerBootstrap(); serverBootstrap.group(bossGroup, workGroup).channel(NioServerSocketChannel.class) .option(ChannelOption.SO_BACKLOG, 100) .handler(new LoggingHandler(LogLevel.INFO)) .childHandler(new ChannelInitializer<SocketChannel>() { @Override public void initChannel(SocketChannel channel) throws Exception { channel.pipeline().addLast(new LengthFieldBasedFrameDecoder(1024*1024*1024,4,4,2,0)); channel.pipeline().addLast(new NettyMessageDecoder()); channel.pipeline().addLast(new NettyMessageEncoder()); channel.pipeline().addLast(new NettyServerHandler()); } }); // 绑定端口 ChannelFuture channelFuture = serverBootstrap.bind(port).sync(); channelFuture.channel().closeFuture().sync(); }finally { bossGroup.shutdownGracefully(); workGroup.shutdownGracefully(); } }
分别重启服务端和客户端：
客户端输出：
12:35:37.033 [nioEventLoopGroup-1-0] INFO com.wlf.netty.nettyclient.handler.NettyClientHandler - [client] client send data : NettyMessage{header=Header{delimiter=-1410399999, length=1032, type=1, reserved=0}, data=[B@7048748c}
服务端输出：
12:35:37.111 [nioEventLoopGroup-1-0] INFO com.wlf.netty.nettyserver.handler.NettyServerHandler - [server] server receive client message : NettyMessage{header=Header{delimiter=-1410399999, length=1032, type=1, reserved=0}, data=[B@517111}
12:35:37.127 [nioEventLoopGroup-1-0] INFO com.wlf.netty.nettyserver.handler.NettyServerHandler - data length: 1032
12:35:37.127 [nioEventLoopGroup-1-0] INFO com.wlf.netty.nettyserver.handler.NettyServerHandler - startTime: 1570854937033