java | LTC 解码器

LengthFieldBasedFrameDecoder 的用法。

构造方法

public LengthFieldBasedFrameDecoder(int maxFrameLength, int lengthFieldOffset, int lengthFieldLength, int lengthAdjustment, int initialBytesToStrip) {
    this(maxFrameLength, lengthFieldOffset, lengthFieldLength, lengthAdjustment, initialBytesToStrip, true);
}

• lengthFieldOffset
  • 长度字段偏移量
• lengthFieldLength
  • 长度字段长度
• lengthAdjustment
  • 长度字段为基准，还有几个字节是内容
• initialBytesToStrip
  • 从头剥离几个字节

* 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" |
* +------+--------+------+----------------+      +------+----------------+

• lengthFieldOffset 对应 0xCA
• lengthFieldLength = 2，表示有 2 个字节表示长度，对应 0x000C，十进制表示 12，而 HELLO, WORLD 正好是 12 字节
• lengthAdjustment 表示还有多少个字节才是正式内容，参数是 1 个字节，对应 0xFE
• initialBytesToStrip 表示去掉多少个字节，向下传递

使用

package com.chat.protocol;

import com.chat.message.LoginRequestMessage;
import io.netty.buffer.ByteBuf;
import io.netty.buffer.ByteBufAllocator;
import io.netty.channel.embedded.EmbeddedChannel;
import io.netty.handler.codec.LengthFieldBasedFrameDecoder;
import io.netty.handler.logging.LoggingHandler;

public class TestMessageCode {

    public static void main(String[] args) throws Exception {

        EmbeddedChannel embeddedChannel = new EmbeddedChannel(
                new LengthFieldBasedFrameDecoder(1024,0,4,0,0),
                new LoggingHandler()
        );

        // 4 字节长度，实际内容
        ByteBuf byteBuf = ByteBufAllocator.DEFAULT.buffer();
        byte[] bytes = "hello world".getBytes();
        int length = bytes.length;
        byteBuf.writeInt(length);
        byteBuf.writeBytes(bytes);
        embeddedChannel.writeInbound(byteBuf);


    }


}

输出

14:40:58.255 [main] DEBUG io.netty.handler.logging.LoggingHandler - [id: 0xembedded, L:embedded - R:embedded] READ: 15B
         +-------------------------------------------------+
         |  0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f |
+--------+-------------------------------------------------+----------------+
|00000000| 00 00 00 0b 68 65 6c 6c 6f 20 77 6f 72 6c 64    |....hello world |
+--------+-------------------------------------------------+----------------+
14:40:58.256 [main] DEBUG io.netty.handler.logging.LoggingHandler - [id: 0xembedded, L:embedded - R:embedded] READ COMPLETE