Netty Decoder generate different output in Windows and Linux

Question

  public class TCPNetty {
        static class Handler extends SimpleChannelUpstreamHandler {
            private static final char[] hexCode = "0123456789ABCDEF".toCharArray();
            public String printHexBinary(byte[] data) {
                StringBuilder r = new StringBuilder(data.length * 2);
                for (byte b: data) {
                    r.append(hexCode[(b >> 4) & 0xF]);
                    r.append(hexCode[(b & 0xF)]);
                }
                return r.toString();
            }@
            Override
            public void messageReceived(ChannelHandlerContext ctx, MessageEvent e) {
                String msg = (String) e.getMessage();
                String mainstr = "";

                mainstr = printHexBinary(msg.getBytes()).toUpperCase();
                System.out.println("========================" + mainstr);
                System.out.println("@@@@@@@@@@@@@@@@@@@@" + mainstr);
                ctx.sendUpstream(e);
            }@
            Override@ SuppressWarnings({
                "ThrowableResultOfMethodCallIgnored"
            })
            public void exceptionCaught(ChannelHandlerContext ctx, ExceptionEvent e) {
                e.getChannel().close();
            }
        }
        public static void main(String[] args) {
            ServerBootstrap bootstrap = new ServerBootstrap(
                new NioServerSocketChannelFactory(
                    Executors.newCachedThreadPool(),
                    Executors.newCachedThreadPool()));
            bootstrap.setPipelineFactory(new ChannelPipelineFactory() {
                public ChannelPipeline getPipeline() throws Exception {
                    final ChannelPipeline pipeline = Channels.pipeline();
                    pipeline.addLast("decoder", new StringDecoder());
                    pipeline.addLast("encoder", new StringEncoder());
                    pipeline.addLast("handler", new Handler());
                    //    pipeline.addLast("executor", executionHandler);
                    //  pipeline.addLast("handler", new EchoCloseServerHandler());
                    return pipeline;
                }
            });
            bootstrap.bind(new InetSocketAddress(5002));
        }
    }

problem is that when i received hex string its showing different output in linux and windows

for example : in Windows getting : 2929B10007003F972D30BD0D in Linux getting : 2929EFBFBD000700EFBFBDEFBFBD2D30EFBFBD0D

i think issue with netty string decoder but not sure .

Answer 1

StringEncoder and StringDecoder use the default Charset unless otherwise specified. The default charset on Linux is (probably) UTF-8, whereas on windows it's typically cp-1251. This means the encoded forms will differ, as you are seeing.

To fix this, change your pipeline code to:

pipeline.addLast("decoder", new StringDecoder(StandardCharsets.UTF_8));
pipeline.addLast("encoder", new StringEncoder(StandardCharsets.UTF_8));

and

mainstr = printHexBinary(msg.getBytes()).toUpperCase();

to

mainstr = printHexBinary(msg.getBytes(StandardCharsets.UTF_8)).toUpperCase();

StandardCharsets requires Java 1.7.

Any other Charset that can represent all of your input would also suffice, but UTF-8 is typical, so you should probably stick with that.