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(一) netty 拆包，粘包处理（自定义协议）

2021-03-05 03:26

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一、netty 为啥要进行拆包粘包处理

　　简单点描述，netty底层通讯是走的TCP协议，接收到的都是字节流，然后以字节字节队列的形式存在缓存堆里面。而TCP协议每一次最大接收的字节长度是1024个字节，一旦超过这个长度，那么就会出现一下各种形式：

 

技术图片

 

 技术图片

 

 

 

 所以在字节长度超过1024的时候，一个完整的包可能会被TCP拆分成多个包进行发送，也有可能把多个小的包封装成一个大的数据包发送，这就是所谓的TCP粘包和拆包问题。

二、解决方案
　　netty基于以上问题也提供了一些组件，比如：

  1. 固定长度的拆包器 FixedLengthFrameDecoder，每个应用层数据包的都拆分成都是固定长度的大小
  2. 行拆包器 LineBasedFrameDecoder，每个应用层数据包，都以换行符作为分隔符，进行分割拆分
  3. 分隔符拆包器 DelimiterBasedFrameDecoder，每个应用层数据包，都通过自定义的分隔符，进行分割拆分
  4. 基于数据包长度的拆包器 LengthFieldBasedFrameDecoder，将应用层数据包的长度，作为接收端应用层数据包的拆分依据。按照应用层数据包的大小，拆包。这个拆包器，有一个要求，就是应用层协议中包含数据包的长度

    因为是自定义协议，在上面的方式不适用。所以在这里我基于LengthFieldBasedFrameDecoder实现的原理下，重新编写了一个实现方式。
    我们先看一下LengthFieldBasedFrameDecoder的代码： 
    /*
 * Copyright 2012 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.handler.codec;

import java.nio.ByteOrder;
import java.util.List;

import io.netty.buffer.ByteBuf;
import io.netty.channel.ChannelHandlerContext;
import io.netty.handler.codec.serialization.ObjectDecoder;

/**
 * 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.
 * 
    
 * {
    @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.
 *
 * 
    2 bytes length field at offset 0, do not strip header
    
 *
 * The value of the length field in this example is 12 (0x0C) 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.
 * 
     * lengthFieldOffset   = 0
 * lengthFieldLength   = 2
 * 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" |
 * +--------+----------------+      +--------+----------------+
 * 
    
 *
 * 
    2 bytes length field at offset 0, strip header
    
 *
 * Because we can get the length of the content by calling
 * {    @link ByteBuf#readableBytes()}, you might want to strip the length
 * field by specifying initialBytesToStrip.  In this example, we
 * specified 2, that is same with the length of the length field, to
 * strip the first two bytes.
 * 
     * lengthFieldOffset   = 0
 * lengthFieldLength   = 2
 * lengthAdjustment    = 0
 * initialBytesToStrip = 2 (= the length of the Length field)
 *
 * BEFORE DECODE (14 bytes)         AFTER DECODE (12 bytes)
 * +--------+----------------+      +----------------+
 * | Length | Actual Content |----->| Actual Content |
 * | 0x000C | "HELLO, WORLD" |      | "HELLO, WORLD" |
 * +--------+----------------+      +----------------+
 * 
    
 *
 * 
    2 bytes length field at offset 0, do not strip header, the length field
 *     represents the length of the whole message
    
 *
 * 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
 * lengthAdjustment.  Because the length value in this example message
 * is always greater than the body length by 2, we specify -2
 * as lengthAdjustment for compensation.
 * 
     * lengthFieldOffset   =  0
 * lengthFieldLength   =  2
 * lengthAdjustment    = -2 (= 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" |
 * +--------+----------------+      +--------+----------------+
 * 
    
 *
 * 
    3 bytes length field at the end of 5 bytes header, do not strip header
    
 *
 * The following message is a simple variation of the first example.  An extra
 * header value is prepended to the message.  lengthAdjustment is zero
 * again because the decoder always takes the length of the prepended data into
 * account during frame length calculation.
 * 
     * lengthFieldOffset   = 2 (= the length of Header 1)
 * lengthFieldLength   = 3
 * 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" |
 * +----------+----------+----------------+      +----------+----------+----------------+
 * 
    
 *
 * 
    3 bytes length field at the beginning of 5 bytes header, do not strip header
    
 *
 * 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 lengthAdjustment so that the decoder counts the extra
 * header into the frame length calculation.
 * 
     * lengthFieldOffset   = 0
 * lengthFieldLength   = 3
 * lengthAdjustment    = 2 (= 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" |
 * +----------+----------+----------------+      +----------+----------+----------------+
 * 
    
 *
 * 
    2 bytes length field at offset 1 in the middle of 4 bytes header,
 *     strip the first header field and the length field
    
 *
 * 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 lengthFieldOffset and the extra
 * header affects the lengthAdjustment.  We also specified a non-zero
 * initialBytesToStrip 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 0 for initialBytesToSkip.
 * 
     * lengthFieldOffset   = 1 (= the length of HDR1)
 * lengthFieldLength   = 2
 * lengthAdjustment    = 1 (= the length of HDR2)
 * initialBytesToStrip = 3 (= 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" |
 * +------+--------+------+----------------+      +------+----------------+
 * 
    
 *
 * 
    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
    
 *
 * 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 lengthAdjustment.
 * 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.
 * 
     * lengthFieldOffset   =  1
 * lengthFieldLength   =  2
 * lengthAdjustment    = -3 (= the length of HDR1 + LEN, negative)
 * initialBytesToStrip =  3
 *
 * BEFORE DECODE (16 bytes)                       AFTER DECODE (13 bytes)
 * +------+--------+------+----------------+      +------+----------------+
 * | HDR1 | Length | HDR2 | Actual Content |----->| HDR2 | Actual Content |
 * | 0xCA | 0x0010 | 0xFE | "HELLO, WORLD" |      | 0xFE | "HELLO, WORLD" |
 * +------+--------+------+----------------+      +------+----------------+
 * 
    
 *     @see LengthFieldPrepender
 */
public class LengthFieldBasedFrameDecoder extends ByteToMessageDecoder {

    private final ByteOrder byteOrder;
    private final int maxFrameLength;
    private final int lengthFieldOffset;
    private final int lengthFieldLength;
    private final int lengthFieldEndOffset;
    private final int lengthAdjustment;
    private final int initialBytesToStrip;
    private final boolean failFast;
    private boolean discardingTooLongFrame;
    private long tooLongFrameLength;
    private long bytesToDiscard;

    /**
     * Creates a new instance.
     *
     * @param maxFrameLength
     *        the maximum length of the frame.  If the length of the frame is
     *        greater than this value, {@link TooLongFrameException} will be
     *        thrown.
     * @param lengthFieldOffset
     *        the offset of the length field
     * @param lengthFieldLength
     *        the length of the length field
     */
    public LengthFieldBasedFrameDecoder(
            int maxFrameLength,
            int lengthFieldOffset, int lengthFieldLength) {
        this(maxFrameLength, lengthFieldOffset, lengthFieldLength, 0, 0);
    }

    /**
     * Creates a new instance.
     *
     * @param maxFrameLength
     *        the maximum length of the frame.  If the length of the frame is
     *        greater than this value, {@link TooLongFrameException} will be
     *        thrown.
     * @param lengthFieldOffset
     *        the offset of the length field
     * @param lengthFieldLength
     *        the length of the length field
     * @param lengthAdjustment
     *        the compensation value to add to the value of the length field
     * @param initialBytesToStrip
     *        the number of first bytes to strip out from the decoded frame
     */
    public LengthFieldBasedFrameDecoder(
            int maxFrameLength,
            int lengthFieldOffset, int lengthFieldLength,
            int lengthAdjustment, int initialBytesToStrip) {
        this(
                maxFrameLength,
                lengthFieldOffset, lengthFieldLength, lengthAdjustment,
                initialBytesToStrip, true);
    }

    /**
     * Creates a new instance.
     *
     * @param maxFrameLength
     *        the maximum length of the frame.  If the length of the frame is
     *        greater than this value, {@link TooLongFrameException} will be
     *        thrown.
     * @param lengthFieldOffset
     *        the offset of the length field
     * @param lengthFieldLength
     *        the length of the length field
     * @param lengthAdjustment
     *        the compensation value to add to the value of the length field
     * @param initialBytesToStrip
     *        the number of first bytes to strip out from the decoded frame
     * @param failFast
     *        If true, a {@link TooLongFrameException} is thrown as
     *        soon as the decoder notices the length of the frame will exceed
     *        maxFrameLength regardless of whether the entire frame
     *        has been read.  If false, a {@link TooLongFrameException}
     *        is thrown after the entire frame that exceeds maxFrameLength
     *        has been read.
     */
    public LengthFieldBasedFrameDecoder(
            int maxFrameLength, int lengthFieldOffset, int lengthFieldLength,
            int lengthAdjustment, int initialBytesToStrip, boolean failFast) {
        this(
                ByteOrder.BIG_ENDIAN, maxFrameLength, lengthFieldOffset, lengthFieldLength,
                lengthAdjustment, initialBytesToStrip, failFast);
    }

    /**
     * Creates a new instance.
     *
     * @param byteOrder
     *        the {@link ByteOrder} of the length field
     * @param maxFrameLength
     *        the maximum length of the frame.  If the length of the frame is
     *        greater than this value, {@link TooLongFrameException} will be
     *        thrown.
     * @param lengthFieldOffset
     *        the offset of the length field
     * @param lengthFieldLength
     *        the length of the length field
     * @param lengthAdjustment
     *        the compensation value to add to the value of the length field
     * @param initialBytesToStrip
     *        the number of first bytes to strip out from the decoded frame
     * @param failFast
     *        If true, a {@link TooLongFrameException} is thrown as
     *        soon as the decoder notices the length of the frame will exceed
     *        maxFrameLength regardless of whether the entire frame
     *        has been read.  If false, a {@link TooLongFrameException}
     *        is thrown after the entire frame that exceeds maxFrameLength
     *        has been read.
     */
    public LengthFieldBasedFrameDecoder(
            ByteOrder byteOrder, int maxFrameLength, int lengthFieldOffset, int lengthFieldLength,
            int lengthAdjustment, int initialBytesToStrip, boolean failFast) {
        if (byteOrder == null) {
            throw new NullPointerException("byteOrder");
        }

        if (maxFrameLength ) {
            throw new IllegalArgumentException(
                    "maxFrameLength must be a positive integer: " +
                    maxFrameLength);
        }

        if (lengthFieldOffset ) {
            throw new IllegalArgumentException(
                    "lengthFieldOffset must be a non-negative integer: " +
                    lengthFieldOffset);
        }

        if (initialBytesToStrip ) {
            throw new IllegalArgumentException(
                    "initialBytesToStrip must be a non-negative integer: " +
                    initialBytesToStrip);
        }

        if (lengthFieldOffset > maxFrameLength - lengthFieldLength) {
            throw new IllegalArgumentException(
                    "maxFrameLength (" + maxFrameLength + ") " +
                    "must be equal to or greater than " +
                    "lengthFieldOffset (" + lengthFieldOffset + ") + " +
                    "lengthFieldLength (" + lengthFieldLength + ").");
        }

        this.byteOrder = byteOrder;
        this.maxFrameLength = maxFrameLength;
        this.lengthFieldOffset = lengthFieldOffset;
        this.lengthFieldLength = lengthFieldLength;
        this.lengthAdjustment = lengthAdjustment;
        lengthFieldEndOffset = lengthFieldOffset + lengthFieldLength;
        this.initialBytesToStrip = initialBytesToStrip;
        this.failFast = failFast;
    }

    @Override
    protected final void decode(ChannelHandlerContext ctx, ByteBuf in, List out) throws Exception {
        Object decoded = decode(ctx, in);
        if (decoded != null) {
            out.add(decoded);
        }
    }

    private void discardingTooLongFrame(ByteBuf in) {
        long bytesToDiscard = this.bytesToDiscard;
        int localBytesToDiscard = (int) Math.min(bytesToDiscard, in.readableBytes());
        in.skipBytes(localBytesToDiscard);
        bytesToDiscard -= localBytesToDiscard;
        this.bytesToDiscard = bytesToDiscard;

        failIfNecessary(false);
    }

    private static void failOnNegativeLengthField(ByteBuf in, long frameLength, int lengthFieldEndOffset) {
        in.skipBytes(lengthFieldEndOffset);
        throw new CorruptedFrameException(
           "negative pre-adjustment length field: " + frameLength);
    }

    private static void failOnFrameLengthLessThanLengthFieldEndOffset(ByteBuf in,
                                                                      long frameLength,
                                                                      int lengthFieldEndOffset) {
        in.skipBytes(lengthFieldEndOffset);
        throw new CorruptedFrameException(
           "Adjusted frame length (" + frameLength + ") is less " +
              "than lengthFieldEndOffset: " + lengthFieldEndOffset);
    }

    private void exceededFrameLength(ByteBuf in, long frameLength) {
        long discard = frameLength - in.readableBytes();
        tooLongFrameLength = frameLength;

        if (discard ) {
            // buffer contains more bytes then the frameLength so we can discard all now
            in.skipBytes((int) frameLength);
        } else {
            // Enter the discard mode and discard everything received so far.
            discardingTooLongFrame = true;
            bytesToDiscard = discard;
            in.skipBytes(in.readableBytes());
        }
        failIfNecessary(true);
    }

    private static void failOnFrameLengthLessThanInitialBytesToStrip(ByteBuf in,
                                                                     long frameLength,
                                                                     int initialBytesToStrip) {
        in.skipBytes((int) frameLength);
        throw new CorruptedFrameException(
           "Adjusted frame length (" + frameLength + ") is less " +
              "than initialBytesToStrip: " + initialBytesToStrip);
    }

    /**
     * Create a frame out of the {@link ByteBuf} and return it.
     *
     * @param   ctx             the {@link ChannelHandlerContext} which this {@link ByteToMessageDecoder} belongs to
     * @param   in              the {@link ByteBuf} from which to read data
     * @return  frame           the {@link ByteBuf} which represent the frame or {@code null} if no frame could
     *                          be created.
     */
    protected Object decode(ChannelHandlerContext ctx, ByteBuf in) throws Exception {
        if (discardingTooLongFrame) {
            discardingTooLongFrame(in);
        }

        if (in.readableBytes()  lengthFieldEndOffset) {
            return null;
        }

        int actualLengthFieldOffset = in.readerIndex() + lengthFieldOffset;
        long frameLength = getUnadjustedFrameLength(in, actualLengthFieldOffset, lengthFieldLength, byteOrder);

        if (frameLength ) {
            failOnNegativeLengthField(in, frameLength, lengthFieldEndOffset);
        }

        frameLength += lengthAdjustment + lengthFieldEndOffset;

        if (frameLength  lengthFieldEndOffset) {
            failOnFrameLengthLessThanLengthFieldEndOffset(in, frameLength, lengthFieldEndOffset);
        }

        if (frameLength > maxFrameLength) {
            exceededFrameLength(in, frameLength);
            return null;
        }

        // never overflows because it‘s less than maxFrameLength
        int frameLengthInt = (int) frameLength;
        if (in.readableBytes()  frameLengthInt) {
            return null;
        }

        if (initialBytesToStrip > frameLengthInt) {
            failOnFrameLengthLessThanInitialBytesToStrip(in, frameLength, initialBytesToStrip);
        }
        in.skipBytes(initialBytesToStrip);

        // extract frame
        int readerIndex = in.readerIndex();
        int actualFrameLength = frameLengthInt - initialBytesToStrip;
        ByteBuf frame = extractFrame(ctx, in, readerIndex, actualFrameLength);
        in.readerIndex(readerIndex + actualFrameLength);
        return frame;
    }

    /**
     * Decodes the specified region of the buffer into an unadjusted frame length.  The default implementation is
     * capable of decoding the specified region into an unsigned 8/16/24/32/64 bit integer.  Override this method to
     * decode the length field encoded differently.  Note that this method must not modify the state of the specified
     * buffer (e.g. {@code readerIndex}, {@code writerIndex}, and the content of the buffer.)
     *
     * @throws DecoderException if failed to decode the specified region
     */
    protected long getUnadjustedFrameLength(ByteBuf buf, int offset, int length, ByteOrder order) {
        buf = buf.order(order);
        long frameLength;
        switch (length) {
        case 1:
            frameLength = buf.getUnsignedByte(offset);
            break;
        case 2:
            frameLength = buf.getUnsignedShort(offset);
            break;
        case 3:
            frameLength = buf.getUnsignedMedium(offset);
            break;
        case 4:
            frameLength = buf.getUnsignedInt(offset);
            break;
        case 8:
            frameLength = buf.getLong(offset);
            break;
        default:
            throw new DecoderException(
                    "unsupported lengthFieldLength: " + lengthFieldLength + " (expected: 1, 2, 3, 4, or 8)");
        }
        return frameLength;
    }

    private void failIfNecessary(boolean firstDetectionOfTooLongFrame) {
        if (bytesToDiscard == 0) {
            // Reset to the initial state and tell the handlers that
            // the frame was too large.
            long tooLongFrameLength = this.tooLongFrameLength;
            this.tooLongFrameLength = 0;
            discardingTooLongFrame = false;
            if (!failFast || firstDetectionOfTooLongFrame) {
                fail(tooLongFrameLength);
            }
        } else {
            // Keep discarding and notify handlers if necessary.
            if (failFast && firstDetectionOfTooLongFrame) {
                fail(tooLongFrameLength);
            }
        }
    }

    /**
     * Extract the sub-region of the specified buffer.
     * 
    
     * If you are sure that the frame and its content are not accessed after
     * the current {
    @link #decode(ChannelHandlerContext, ByteBuf)}
     * call returns, you can even avoid memory copy by returning the sliced
     * sub-region (i.e. return buffer.slice(index, length)).
     * It‘s often useful when you convert the extracted frame into an object.
     * Refer to the source code of {@link ObjectDecoder} to see how this method
     * is overridden to avoid memory copy.
     */
    protected ByteBuf extractFrame(ChannelHandlerContext ctx, ByteBuf buffer, int index, int length) {
        return buffer.retainedSlice(index, length);
    }

    private void fail(long frameLength) {
        if (frameLength > 0) {
            throw new TooLongFrameException(
                            "Adjusted frame length exceeds " + maxFrameLength +
                            ": " + frameLength + " - discarded");
        } else {
            throw new TooLongFrameException(
                            "Adjusted frame length exceeds " + maxFrameLength +
                            " - discarding");
        }
    }
}

    通过源码我们可以知道核心方法是：

     protected Object decode(ChannelHandlerContext ctx, ByteBuf in) throws Exception {
        if (discardingTooLongFrame) {
            discardingTooLongFrame(in);
        }

        if (in.readableBytes()  lengthFieldEndOffset) {
            return null;
        }

        int actualLengthFieldOffset = in.readerIndex() + lengthFieldOffset;
        long frameLength = getUnadjustedFrameLength(in, actualLengthFieldOffset, lengthFieldLength, byteOrder);

        if (frameLength ) {
            failOnNegativeLengthField(in, frameLength, lengthFieldEndOffset);
        }

        frameLength += lengthAdjustment + lengthFieldEndOffset;

        if (frameLength  lengthFieldEndOffset) {
            failOnFrameLengthLessThanLengthFieldEndOffset(in, frameLength, lengthFieldEndOffset);
        }

        if (frameLength > maxFrameLength) {
            exceededFrameLength(in, frameLength);
            return null;
        }

        // never overflows because it‘s less than maxFrameLength
        int frameLengthInt = (int) frameLength;
        if (in.readableBytes()  frameLengthInt) {
            return null;
        }

        if (initialBytesToStrip > frameLengthInt) {
            failOnFrameLengthLessThanInitialBytesToStrip(in, frameLength, initialBytesToStrip);
        }
        in.skipBytes(initialBytesToStrip);

        // extract frame
        int readerIndex = in.readerIndex();
        int actualFrameLength = frameLengthInt - initialBytesToStrip;
        ByteBuf frame = extractFrame(ctx, in, readerIndex, actualFrameLength);
        in.readerIndex(readerIndex + actualFrameLength);
        return frame;
    }

    所以根据自己得协议，写了一个实现方式：

    public class MessageEncoder extends ByteToMessageDecoder {
    
     @Override
        protected final void decode(ChannelHandlerContext ctx, ByteBuf buffer, List out) throws Exception {
            // 可读长度必须大于基本长度  
            if (buffer.readableBytes() >= 12) {  
                      
                // 记录包头开始的index  
                int beginReader = buffer.readerIndex();  
                // 标记包头开始的index  
                buffer.markReaderIndex();  
                // 读到了协议的开始标志，结束while循环  
                String startDataStr = buffer.getByte(0)+""+buffer.getByte(1)+"";                    
                if (startDataStr.equals("7188")) {  

                } else {
                    buffer.skipBytes(buffer.readableBytes());  
                    return;
                }  
      
                // 消息的长度  
                // String dataLen = buffer.getByte(10)+""+buffer.getByte(11)+"";
                String commond = ByteBufUtil.hexDump(buffer);
                String str = commond.substring(20,24);
                Integer length = Integer.parseInt(str.substring(2,4)+str.substring(0,2),16); 
                System.out.println("内容区数据包长度："+length);
                // 判断请求数据包数据是否到齐  
                if (buffer.readableBytes() ) {  
                    // 还原读指针  
                    buffer.readerIndex(beginReader);  
                    return;  
                }  
                // 读取data数据  
                //buffer.readBytes(length+14);  
                out.add(buffer.readSlice(length+14).retain());  
            }  
        
        }

}
    public void start() throws Exception {
        new Thread(new Runnable() {

            @Override
            public void run() {

                EventLoopGroup group = new NioEventLoopGroup();
                EventLoopGroup workerGroup = new NioEventLoopGroup();
                try {
                    ServerBootstrap sb = new ServerBootstrap();
                    sb.group(group, workerGroup) // 绑定线程池
                            .channel(NioServerSocketChannel.class) // 指定使用的channel
                            .localAddress(port)// 绑定监听端口
                            .childHandler(new ChannelInitializer() { // 绑定客户端连接时候触发操作

                                @Override
                                protected void initChannel(SocketChannel ch) throws Exception {
                                    System.out.println("connected...; Client:" + ch.remoteAddress());
                                    ch.pipeline()/*
                                                     * .addLast("logging",new
                                                     * LoggingHandler(LogLevel.
                                                     * ERROR ))
                                                     */
                                            .addLast(new MessageEncoder())
                                            .addLast(new EchoServerHandler()); // 客户端触发操作
                                }
                            });
                    ChannelFuture cf;

                    cf = sb.bind().sync();
                    cf.channel().closeFuture().sync(); // 关闭服务器通道
                    System.out.println(EchoServer.class + " started and listen on " + cf.channel().localAddress());
                } catch (InterruptedException e) {
                    logger.error("listen Exception,the msg is >>"+e);
                    e.printStackTrace();
                } // 服务器异步创建绑定
                finally {
                    group.shutdownGracefully();
                    workerGroup.shutdownGracefully();
                }

            }
        }).start();
    }

    这个写法是基于自定义协议，然后又是非规范协议的操作来实现的。比如类似下面16进制组合ascii码的协议：
    475831393530303810d901000069da

(一) netty 拆包，粘包处理（自定义协议）

标签：copyright   操作   its   有一个   efault   trap   监听端口   解决方案   expected   

原文地址：https://www.cnblogs.com/zcsheng/p/12910665.html

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文章标题：(一) netty 拆包，粘包处理（自定义协议）
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