Simple Netty Echo Server/Client not receiving messages

Question

I'm trying to write a simple echo server with Netty. I'm reading Netty in Action MEAP v8 to get down some theory and learn the core basics of Netty. The client connects successfully, but no messages get through from the client. I am able to telnet a message to the server and receive the response, so I guess the issue is on the client, I just have no idea what is wrong, due to me being new to Netty.

Here is the client:

public class Client {

    private final String host;
    private final int port;

    public Client(String host, int port) {
        this.host = host;
        this.port = port;
    }

    public void start() throws Exception {
        EventLoopGroup group = new NioEventLoopGroup();
        try {
            Bootstrap b = new Bootstrap();
            b.group(group).channel(NioSocketChannel.class)
                          .remoteAddress(new InetSocketAddress(host, port))
                          .handler(new ChannelInitializer<SocketChannel>() {

                              @Override
                              public void initChannel(SocketChannel ch) throws Exception {
                                  ch.pipeline().addLast(new EchoClientHandler());
                              }
                          });

            ChannelFuture f = b.connect().sync();

            f.channel().closeFuture().sync();
        } finally {
            group.shutdownGracefully().sync();
        }
    }


    public static void main (String [] args) throws Exception {
        new Client("127.0.0.1", 11235).start();
    }
}

And the Client handler: (I did try appending '\r\n' to the sent message, but that did not make a difference, which I found here: Netty Client to Server message)

@Sharable 
public class EchoClientHandler extends SimpleChannelInboundHandler<ByteBuf> {

    public void channelActive(ChannelHandlerContext ctx) {
        System.out.println("Connected");
        ctx.write(Unpooled.copiedBuffer("Netty MAY rock!", CharsetUtil.UTF_8));
    }

    protected void channelRead0(ChannelHandlerContext ctx, ByteBuf in) throws Exception {
        System.out.println(
                "Client received: " + in.toString(CharsetUtil.UTF_8));

    }

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

The server:

public class EchoServer {

    private final int port;

    public EchoServer(int port) {
        this.port = port;
    }

    public void start() throws Exception {
        EventLoopGroup group = new NioEventLoopGroup();
        try {
            ServerBootstrap b = new ServerBootstrap();
            b.group(group)
                    .channel(NioServerSocketChannel.class)
                    .localAddress(new InetSocketAddress(port))
                    .childHandler(new ChannelInitializer<SocketChannel>() {
                                    @Override
                                    public void initChannel(SocketChannel ch) throws Exception {
                                        System.out.println("New client connected: " + ch.localAddress());

                                        ch.pipeline().addLast(new EchoServerHandler());
                                    }
                                });
            ChannelFuture f = b.bind().sync();
            f.channel().closeFuture().sync();
        } finally {
            group.shutdownGracefully().sync();
        }
    }

    public static void main (String [] args) throws Exception {
        new EchoServer(11235).start();
    }
}

The server handler:

@Sharable
public class EchoServerHandler extends ChannelInboundHandlerAdapter {

    public void channelRead(ChannelHandlerContext ctx, Object msg) {
        ByteBuf in = (ByteBuf) msg;
        System.out.println(
            "Server received: " + in.toString(CharsetUtil.UTF_8));
        ctx.write(in);
    }

    public void channelReadComplete(ChannelHandlerContext ctx) {
        ctx.writeAndFlush(Unpooled.EMPTY_BUFFER)
            .addListener(ChannelFutureListener.CLOSE);
    }

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

It must be something small I'm missing, so any help will preserve my fleeting sanity and will be much appreciated!

Answer 1

Instead of write use writeAndFlush in your ClientHandler:

public void channelActive(ChannelHandlerContext ctx) {
    System.out.println("Connected");
    ctx.writeAndFlush(Unpooled.copiedBuffer("Netty MAY rock!", CharsetUtil.UTF_8));
}