Netty writeAndFlush () incomplete

My tcp client netty server and netty server use writeAndFlush () return 393718 bytes. But the client only gets 262142 bytes. I am using "tcpdump -A" for apturing packages less than 393718. So I believe the isty not write function in writeAndFlush () function?

Here is the code

Tcp server:

public static void main (String args[]) {

        int processorsNumber = Runtime.getRuntime().availableProcessors() * 3;
        ThreadFactory threadFactory = new DefaultThreadFactory("work thread pool");
        EventLoopGroup bossLoopGroup = new NioEventLoopGroup(1);
        EventLoopGroup workLoopGroup = new NioEventLoopGroup(processorsNumber, threadFactory, SelectorProvider.provider());

        try {
            ServerBootstrap sb = new ServerBootstrap();
            sb.group(bossLoopGroup , workLoopGroup)
                    .channel(NioServerSocketChannel.class)
                    .option(ChannelOption.SO_BACKLOG, 128)
                    .childOption(ChannelOption.SO_KEEPALIVE, true)
                    .childHandler(new ChannelInitializer<NioSocketChannel>() {
                        @Override
                        protected void initChannel(NioSocketChannel ch) throws Exception {
                            //ch.pipeline().addLast(new LineBasedFrameDecoder(1000));
                            ch.pipeline().addLast(new TcpServerHandler());
                        }
                    });

            sb.bind(new InetSocketAddress("0.0.0.0", 18881)).sync().channel().closeFuture().sync();
        } catch (InterruptedException e) {
            logger.error("netty error", e);
            e.printStackTrace();
        } finally {
            bossLoopGroup.shutdownGracefully();
            workLoopGroup.shutdownGracefully();
        }
    }

      

        
        
        
      

    

server handler:

public void channelRead(ChannelHandlerContext ctx, Object msg) {

        ByteBuf in = (ByteBuf) msg;
        String cmd = in.toString(CharsetUtil.UTF_8);
        logger.info(cmd);

        String retCode = "";
        String file = "E:\\sz\\app.log";
        try {
            FileReader fr = new FileReader(file);
            BufferedReader br = new BufferedReader(fr);
            String buffer = null;
            while ((buffer = br.readLine()) != null) {
                retCode += buffer;
            }
        } catch (FileNotFoundException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }

        logger.info("return：" + retCode);
        byte[] result = retCode.getBytes();
        logger.info("======================="+result.length);
        ByteBuf resultBuf = Unpooled.buffer(result.length);
        resultBuf.writeBytes(result);
        ctx.writeAndFlush(resultBuf);

        ctx.close();
    }

      

        
        
        
      

    

tcp client:

public static void main(String[] args) {
        StringBuilder response = new StringBuilder();
        try {
            Socket socket = new Socket();
            InetSocketAddress address = new InetSocketAddress("127.0.0.1", 18881);
            socket.connect(address, 3000);
            socket.setSoTimeout(10 * 1000);

            OutputStream clientRequest = socket.getOutputStream();
            String cmd = "cmd";
            clientRequest.write(cmd.getBytes());
            clientRequest.flush();

            InputStream clientResponse = socket.getInputStream();
            int maxLen = 1024;
            byte[] contextBytes = new byte[maxLen];
            int readLen;
            while ((readLen = clientResponse.read(contextBytes, 0, maxLen)) != -1) {
                response.append(new String(contextBytes, 0, readLen));
            }

            clientRequest.close();
            clientResponse.close();
        } catch (IOException e) {
            logger.error("tcp error", e);
            e.printStackTrace();
        }
        String result = response.toString();
        System.out.println(result);
        System.out.println(result.getBytes().length);
    }