[编织消息框架][设计协议]解决粘包半包(中)

上节介绍问题出现跟处理方式，写数据部份已经实现

这节介绍如何读处理

处理流程分三部分

1.校验包是否合法

2.读取包内容

3.切割包

由于切割包用的是netty处理，所以只需集中精力解决前两个问题即可

ByteToMessageHandler.class

 @Override
 public QPacket decode(ChannelHandlerContext ctx, ByteBuf in) throws Exception {
    ByteBuf byteBuf = decoder.decode(ctx, in);//解释包 netty框架处理
    if (byteBuf == null || !byteBuf.isReadable()) { //netty解释失败或未成功会返回null 
        return null;
    }
    if (byteBuf.readableBytes() < QPacket.PACK_FIXED_LENG) { //缓冲内容bytes长度少于包最小固定长度
        return null;
    }
    final short headFlag = byteBuf.readShort(); //读取头部开始信息 2byte
    final int packetLen = byteBuf.readInt(); //读取内容长度
    final int endLen = 1; //尾部结束标志 1byte
　　//比较头部信息是否合法
    if (headFlag != QMConfig.getInstance().getPacketHeadFlag(packetLen)) {
        throw new QSocketException(QCode.SOCKET_ERROR_PCKET_FLAG, "解码包头标识不对");
    }

    // 缓冲可读长度是否少于包长度 netty 处理过了
    // if (byteBuf.readableBytes() - endLen < packetLen) {
    // return null;
    // }
  
    final int mark = byteBuf.readerIndex(); //标记已读坐标，目的先读最后结束信息做比较
    byteBuf.skipBytes(packetLen); //跳到最后结束标记
    final byte endFlag = byteBuf.readByte(); //读取结束标记1byte
    if (endFlag != QMConfig.getInstance().getPacketEndFlag(packetLen)) {
        throw new QSocketException(QCode.SOCKET_ERROR_PCKET_FLAG, "解码包尾标识不对");
    }
    byteBuf.readerIndex(mark);//还原坐标，开始处理QPacket
    QPacket ret = QPacket.of(byteBuf, packetLen); //构造QPacket
    byteBuf.skipBytes(endLen); //跳结束标记
    return ret;
 }

QPacket

  public static QPacket of(ByteBuf byteBuf, int packetLen) { //按写入顺序读取
    long sn = byteBuf.readLong(); //读包序列
    short c = byteBuf.readShort();//读opcode
    byte[] b = new byte[packetLen - QPacket.PACK_FIXED_LENG]; //算出内容实际大小
    byteBuf.readBytes(b); //读取内容
    long sid = byteBuf.readLong(); //读取sessionId
    return of(c, sn, sid, null, b);
  }

  public static QPacket of(byte[] bytes) {
    int offset = 0;
    long sn = PacketUtil.readLong(offset, bytes);
    short c = PacketUtil.readShort(offset += Long.BYTES, bytes);
    byte[] b = PacketUtil.readBytes(offset += Short.BYTES, bytes.length - QPacket.PACK_FIXED_LENG, bytes);
    long sid = PacketUtil.readLong(offset += b.length, bytes);
    return of(c, sn, sid, null, b);
  }

为什么没有直接用第二种方式去构造QPacket?

如果多一个临时对象array byte 会有损耗，无必要占创建时间，多一份内存开销

之前写入消息也采取相同处理方式，直接把数据传给netty ByteBuf 底层

  public void writeToByteBuf(ByteBuf byteBuf) {
    final int packetLen = toSize();
    byteBuf.writeShort(QMConfig.getInstance().getPacketHeadFlag(packetLen));
    byteBuf.writeInt(packetLen);
    writeBytes(byteBuf);
    byteBuf.writeByte(QMConfig.getInstance().getPacketEndFlag(packetLen));
  }    

　　@Override
  public byte[] toBytes() {
    final int len = toSize();
    byte[] ret = new byte[len];
    int offset = 0;
    PacketUtil.writeLong(offset, sn, ret);
    PacketUtil.writeShort(offset += Long.BYTES, c, ret);
    PacketUtil.writeBytes(offset += Short.BYTES, b, ret);
    PacketUtil.writeLong(offset += b.length, sid, ret);
    return ret;
  }