Read string and reply with bytes in Netty

Question

I'm new to Netty and have succeeded in creating a server that works over TLS. I'm now designing a second server but I'm having some issues with the pipeline. What I need is a dynamic pipeline like the port unification example from Netty: http://netty.io/4.0/xref/io/netty/example/portunification/PortUnificationServerHandler.html

Each connection starts with the client sending a UTF-8 encoded string. I can read this fine, but my reply isn't coming through. My reply is just a byte array of 3 bytes.

Here's my server:

// Configure the server
EventLoopGroup bossGroup = new NioEventLoopGroup(1);
EventLoopGroup workerGroup = new NioEventLoopGroup();
try {
    ServerBootstrap b = new ServerBootstrap();
    b.group(bossGroup, workerGroup)
            .channel(NioServerSocketChannel.class)
            .option(ChannelOption.SO_BACKLOG, 100)
            .handler(new LoggingHandler(LogLevel.INFO))
            .childHandler(new ChannelInitializer<SocketChannel>() {
                @Override
                public void initChannel(SocketChannel ch) throws Exception {
                    ChannelPipeline pipeline = ch.pipeline();
                    pipeline.addLast(new LineBasedFrameDecoder(192));
                    pipeline.addLast(new StringDecoder(CharsetUtil.UTF_8));
                    pipeline.addLast(new ByteArrayEncoder());
                    pipeline.addLast(new TokenHandler());
                }
            });

    // Start the server
    ChannelFuture f = b.bind(port).sync();

    // Wait until the server socket is closed
    f.channel().closeFuture().sync();
}
finally {
    // Shut down all event loops to terminate all threads
    bossGroup.shutdownGracefully();
    workerGroup.shutdownGracefully();
}

And my TokenHandler, which is a SimpleChannelInboundHandler:

public class TokenHandler extends SimpleChannelInboundHandler<String> {
    @Override
    protected void channelRead0(ChannelHandlerContext channelHandlerContext, String token) throws Exception {
        System.out.println("Token received: " + token);
        channelHandlerContext.writeAndFlush(new byte[] {2, 1, 0});
    }
}

I've also tried replacing that last line with

channelHandlerContext.writeAndFlush(Unpooled.copiedBuffer(new byte[] {2, 1, 0}));

and removing the ByteArrayEncoder from my pipeline, but this doesn't make any difference: no bytes are being sent. I can send strings just fine if I add a StringEncoder, and the Echo example from Netty also works (available from the user guide: http://netty.io/wiki/user-guide-for-4.x.html). I'm guessing it's a basic mistake being new to Netty, but I can't find other people with cases with a similar issue.

EDIT: I'm using Netty 4.0.34.Final

delucasvb · Accepted Answer · 2016-03-16 16:54:12Z

1

I should've read the docs more carefully. The solution was to add super(true) to the constructor of my TokenHandler because by default a SimpleChannelInboundHandler releases its messages after processing which stops the response from propagating further through the pipeline.

answered Mar 16, 2016 at 16:54

delucasvb

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