jinzaifoodadmin/src/main/java/com/qlm/netty/codec/CustomDecoder.java

package com.qlm.netty.codec;

import com.qlm.netty.protocol.CustomProtocol;
import io.netty.buffer.ByteBuf;
import io.netty.channel.ChannelHandlerContext;
import io.netty.handler.codec.LengthFieldBasedFrameDecoder;

public class CustomDecoder extends LengthFieldBasedFrameDecoder {

    // 长度字段的偏移量
    private static final int LENGTH_FIELD_OFFSET = 21;  // deviceId(20字节) + type(1字节)
    // 长度字段的长度
    private static final int LENGTH_FIELD_LENGTH = 4;

    public CustomDecoder() {
        // maxFrameLength: 最大帧长度
        // lengthFieldOffset: 长度字段的偏移量
        // lengthFieldLength: 长度字段的长度
        // lengthAdjustment: 长度调整值
        // initialBytesToStrip: 跳过的初始字节数
        super(Integer.MAX_VALUE, LENGTH_FIELD_OFFSET, LENGTH_FIELD_LENGTH, 0, LENGTH_FIELD_OFFSET + LENGTH_FIELD_LENGTH);
    }

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

        try {
            // 读取设备ID (20字节)
            byte[] deviceIdBytes = new byte[20];
            frame.readBytes(deviceIdBytes);
            String deviceId = new String(deviceIdBytes).trim();

            // 读取消息类型
            byte type = frame.readByte();

            // 读取消息长度
            int length = frame.readInt();

            // 读取消息内容
            byte[] content = new byte[length];
            frame.readBytes(content);

            return new CustomProtocol(deviceId, type, content);
        } finally {
            frame.release();
        }
    }
}