Netty增加自定義解碼器解決粘包分包問題

netty框架自帶的粘包分包解碼器

FixedLengthFrameDecoder (固定長度解碼器)
DelimiterBasedFrameDecoder(分隔符解碼器)
LineBasedFrameDecoder("\r\n"換行符解碼器)

以上這些可以解決一般情況下的問題

一些特殊規則下，我們需要自定義解碼器

例如：aa 0a 00 00 00 02 b2 00 00 00 00 00 be
0xaa爲固定數據幀頭
0x0a爲紅色部分的數量
0xbe爲數據校驗和
這樣的數據幀解析就需要用到自定義解析器，可以參考netty框架自帶的解析器源碼來進行我們需要的規則開發
自定義解析器需要繼承ByteToMessageDecoder類

import java.util.List;

import io.netty.buffer.ByteBuf;
import io.netty.channel.ChannelHandlerContext;
import io.netty.handler.codec.ByteToMessageDecoder;

public class DlhFrameDecoder extends ByteToMessageDecoder {

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

	private Object decode(ChannelHandlerContext ctx, ByteBuf in) {
		byte aa = (byte) 0xAA;
		int index = indexOf(in,aa);
		if(index != -1){
			if (in.readableBytes() < index) {
	            return null;
	        }
			return in.readSlice(index).retain();
		}
		return null;
	}
	
	//數據和
	public static byte  getDataAdd(byte[] bs){
		byte he = 0;
		if(bs != null){
			for (int i = 0; i < bs.length; i++) {
				he += bs[i];
			}
		}
		return he;
	}
	
	/**
     * Returns the number of bytes between the readerIndex of the haystack and
     * the first needle found in the haystack.  -1 is returned if no needle is
     * found in the haystack.
     */
    private static int indexOf(ByteBuf haystack, byte b) {
        for (int i = 0; i < haystack.writerIndex(); i ++) {
            if(haystack.getByte(i) == b){
            	int index = i+haystack.getByte(i+1)+3;
            	int he = haystack.getByte(index-1);
            	byte[] hh = new byte[index-i-2];
            	haystack.getBytes(i+1, hh, 0, hh.length);
            	if(he == getDataAdd(hh)){
            		return index;
            	}
            }
        }
        return -1;
    }
    
}