Question

We’ve got a server which is already implemented in TCP/IP but we now have a requirement for the protocol to support UDP as well.

Each UDP datagram sent contains everything I need to decode so it is a very simple reply and response system with data in the datagram separated by line breaks.

The code for the bootstrap when the server is started is shown below:

    //SETUP UDP SERVER
    DatagramChannelFactory udpFactory = new NioDatagramChannelFactory(Executors.newCachedThreadPool());

    ConnectionlessBootstrap udpBootstrap = new ConnectionlessBootstrap(udpFactory);

    udpBootstrap.setOption("sendBufferSize", 65536);
    udpBootstrap.setOption("receiveBufferSize", 65536);
    udpBootstrap.setOption("receiveBufferSizePredictorFactory", new AdaptiveReceiveBufferSizePredictorFactory());

    udpBootstrap.setOption("broadcast", "true");
    udpBootstrap.setPipelineFactory(new ServerPipeLineFactoryUDP());
    udpBootstrap.bind(new InetSocketAddress(hostIp, 4000)); 

The Pipeline code is:

class ServerPipeLineFactoryUDP implements ChannelPipelineFactory
{

    private final static ExecutionHandler EXECUTION_HANDLER = new ExecutionHandler(new OrderedMemoryAwareThreadPoolExecutor(ScorpionFMS.THREAD_POOL_COUNT, 0, 0));

    public ServerPipeLineFactoryUDP()
    {

    }

    @Override
    public ChannelPipeline getPipeline() throws Exception
    {

    ChannelPipeline pipeline = pipeline();
    pipeline.addLast("debugup", new DebugUpstreamHandler("UDP"));
    pipeline.addLast("debugdown", new DebugDownstreamHandler("UDP"));

    pipeline.addLast("framer", new DelimiterBasedFrameDecoder(256, Delimiters.lineDelimiter()));

    pipeline.addLast("decoder", new UDPRequestDecoder(true));
    pipeline.addLast("encoder", new StringEncoder());
    pipeline.addLast("executor", EXECUTION_HANDLER);
    pipeline.addLast("handler", new UDPRequestHandler(

    return pipeline;
    }
}

The problem im having is each datagram is using the same instance of this pipeline (i hoped each datagram would use a new instance of the pipeline), so all the state i store while processing the contents of a datagram is saved and the next datagram uses it as well,( whereas for TCP each connection would have its own channel and therefore its own instance of the pipeline and its own state)

I know this is the expected behaviour from reading the documentation but is there anyway to force netty to recreate the pipeline for each datagram? Or am i going about this the completely wrong way?

To put it succinctly, i want each datagram to have a new instance of the pipeline (the same as tcp)

Answer 1

Like I said in IRC, I think that could do what you want or at least give you some idea.

public class Example {

    public static void main(String[] args) {
        final ChannelPipelineHandlerImpl perDatagramFactory = new ChannelPipelineHandlerImpl();

        DatagramChannelFactory udpFactory = new NioDatagramChannelFactory(Executors.newCachedThreadPool());

        ConnectionlessBootstrap udpBootstrap = new ConnectionlessBootstrap(udpFactory);

        udpBootstrap.setPipelineFactory(new ChannelPipelineFactory() {

            public ChannelPipeline getPipeline() throws Exception {
                return Channels.pipeline(new DistinctChannelPipelineHandler(perDatagramFactory));
            }
        });

    }

    private static final class DistinctChannelPipelineHandler implements ChannelDownstreamHandler, ChannelUpstreamHandler {
        private ChannelPipelineFactory factory;

        public DistinctChannelPipelineHandler(ChannelPipelineFactory factory) {
            this.factory = factory;
        }

        public void handleUpstream(ChannelHandlerContext ctx, ChannelEvent e) throws Exception {
            ChannelPipeline pipeline = factory.getPipeline();
            pipeline.attach(ctx.getChannel(), ctx.getPipeline().getSink());
            pipeline.sendUpstream(e);

            ctx.sendUpstream(e);

        }

        public void handleDownstream(ChannelHandlerContext ctx, ChannelEvent e) throws Exception {
            ChannelPipeline pipeline = factory.getPipeline();
            pipeline.attach(ctx.getChannel(), ctx.getPipeline().getSink());
            pipeline.sendDownstream(e);

            ctx.sendDownstream(e);
        }

    }

    private static final class ChannelPipelineHandlerImpl implements ChannelPipelineFactory {

        public ChannelPipeline getPipeline() throws Exception {
            // Add your handlers here
            return Channels.pipeline();
        }

    }
}