netty client端无法拆包

Question

client：

public class Client {
    public static void main(String[] args) throws InterruptedException {

        EventLoopGroup workgroup = new NioEventLoopGroup();
        final Bootstrap b = new Bootstrap();
        b.group(workgroup)
                .channel(NioSocketChannel.class) 
                .handler(new ChannelInitializer<SocketChannel>() {
                    protected void initChannel(SocketChannel socketChannel) throws Exception {
                    //这里如果用解码，就两边都收不到消息了
//                        ByteBuf buf = Unpooled.copiedBuffer("$".getBytes());
//                        socketChannel.pipeline().addLast(new DelimiterBasedFrameDecoder(1024,buf));
//                        socketChannel.pipeline().addLast(new StringDecoder());
                        socketChannel.pipeline().addLast(new ClientHandler());
                    }
                });

        ChannelFuture cf = b.connect("127.0.0.1",8888); //**问题出在这里，最后少了.syn()**
       cf.channel().writeAndFlush(Unpooled.copiedBuffer("aa$".getBytes()));
        cf.channel().writeAndFlush(Unpooled.copiedBuffer("bbbb$".getBytes()));

        cf.channel().closeFuture().sync();//异步
        workgroup.shutdownGracefully();
    }

}

clientHandler：

    public class ClientHandler extends ChannelInboundHandlerAdapter {
        @Override
        public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception {
            try {
    //            读取Server的信息，只能用ButeBuf读取
                ByteBuf buf = (ByteBuf) msg;
                byte[] data = new byte[buf.readableBytes()];
                buf.readBytes(data);
                String request = new String(data, "utf-8");
                System.out.println("服务端反馈的消息: " + request);
    //            String request = (String)msg;
    //            System.out.println("服务端反馈的消息: "+ request);
            }finally {
                ReferenceCountUtil.release(msg);
            }
        }
    
        @Override
        public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) throws Exception {
            cause.printStackTrace();
            ctx.close();
        }
    }

Server：

public class Server {
    public static void main(String[] args) throws InterruptedException {

        EventLoopGroup bossGroup = new NioEventLoopGroup();
        EventLoopGroup workerGroup = new NioEventLoopGroup();

        final ServerBootstrap  b = new ServerBootstrap();

        b.group(bossGroup,workerGroup)
                .channel(NioServerSocketChannel.class)
                .childHandler(new ChannelInitializer<SocketChannel>() {
                    protected void initChannel(SocketChannel socketChannel) throws Exception {
                        ByteBuf buf = Unpooled.copiedBuffer("$".getBytes());
                        socketChannel.pipeline().addLast(new DelimiterBasedFrameDecoder(1024,buf));
                        socketChannel.pipeline().addLast(new StringDecoder());
                        socketChannel.pipeline().addLast(new ServerHandler());
                    }
                });

        ChannelFuture future = b.bind(8888).sync();

        future.channel().closeFuture().sync();

        bossGroup.shutdownGracefully();
        workerGroup.shutdownGracefully();

    }
}

serverHandler:

public class ServerHandler extends ChannelInboundHandlerAdapter{
    @Override
    public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception {
        String str = (String)msg;
        System.out.println("Server: "+str);
        ctx.writeAndFlush(Unpooled.copiedBuffer("这是服务器响应$".getBytes()));
    }

    @Override
    public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) throws Exception {
        cause.printStackTrace();
        ctx.close();
    }
}

现在的问题是我从client发送的信息在server端直接使用String，并且能按指定的字符串拆包
但是从服务端返回的信息在客户端上为什么不能直接解码成字符串？

netty是现在最新的版本，好像是4.1.15

server收到的消息：
Server: aa
Server: bbbb

client收到server反馈的消息：
服务端反馈的消息: 这是服务器响应$这是服务器响应$

我在Client端直接拆包也不行（就是两边都没响应）

ByteBuf buf = Unpooled.copiedBuffer("$".getBytes());
socketChannel.pipeline().addLast(new DelimiterBasedFrameDecoder(1024,buf));

然后单独解码没问题，看起来就是拆包的问题