Java Communication netty server - Socket client

Question

For a chat server project I use netty as server, with the following code in my handler :

public class PacketHandler extends ChannelInboundHandlerAdapter{

        @Override
        public void channelRead(ChannelHandlerContext ctx, Object msg) {
            ByteBuf in = (ByteBuf) msg;
            try {
                AbstractClientPacket packet = ClientPacketHandler.handle(in);
                if(packet != null && packet.read()){
                    packet.run();
                    ctx.write(msg+"\r\n");
                }
            } finally {
                ReferenceCountUtil.release(msg);
            }
        }

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

So, my packet is correctly handled and it works fine, but then, i do ctx.write(msg+"\r\n"); to send back the message to my client, acting like an echo server.

Here is the Client's code :

public class ChatClient {

    static Socket socket;
    static DataOutputStream out;
    static BufferedReader in;

    public static void main(String[] args){

        try {
            initSocket();

            String test = "Salut 1";

            TestPacket packet = new TestPacket(0x18,test.getBytes());

            sendPacket(packet);

            while(true){
                try {

                    String message = in.readLine();
                    System.out.println(message);

                } catch (IOException e) {

                    e.printStackTrace();
                }
            }

            //TEST
        } catch (IOException  e) {
            e.printStackTrace();
        }finally{
            try {
                socket.close();
            } catch (IOException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
        }
    }

    private static void initSocket(){
        try {
            socket = new Socket("localhost",58008);
            out = new DataOutputStream(socket.getOutputStream());
            in = new BufferedReader(new InputStreamReader((socket.getInputStream())));
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    private static void sendPacket(TestPacket p) throws IOException{
        out.write(p.getRawData());
        out.flush();
    }
}

The packet is correctly sent, but i get nothing as reply, and when i stop my server, the client is spamming null because of my while(true), but i don't get my message back, nothing is displayed and i really don't know why.

I can't use netty for the client because this one is just for test purpose, the final client will be written in C# (Unity Engine), so i can't use netty in this one, I have to do it with native socket handling.

EDIT:

According to wireshark, The packet from client is sent but the server answer is not, i don't see the packet From server containing "Salut 1".

I tried to flush after doing ctx.write() but still same problem. — Supamiu
readLine() returns null at end of stream, which happens when the peer disconnects. You need to test for that, and break, and close the connection, when you get it. — user207421

trustin trustin · Accepted Answer · 2015-03-18T07:27:40

You did:

ctx.write(msg+"\r\n");

msg is not a String but a ByteBuf. If you want to append \r\n to the received message, you should do the following:

in.writeByte('\r');
in.writeByte('\n');
ctx.write(in);

Also, because you reused the received message (in) as a response, you should not release it:

// Do NOT call this.
ReferenceCountUtil.release(in);

If you really intended to call ctx.write(msg + "\r\n"), please make sure that your pipeline has StringEncoder.

Java Communication netty server - Socket client

1 Answers