Trouble with Netty IdleStateHandler - am I testing it the wrong way?

Question

I have a toy Netty server and am trying to send heartbeat messages to clients when nothing has happened on their channels. I am testing this by telnetting to the server, writing a message and then not sending anything, but I get no hearbeat!

Console:

>>telnet localhost 6969
Trying 127.0.0.1...
Connected to localhost.
Escape character is '^]'.
>>foo
Did you say 'foo'?

MyPipelineFactory.java

public class MyPipelineFactory implements ChannelPipelineFactory {
    private final Timer timer;
    private static final ChannelHandler stringDecoder = new StringDecoder();
    private static final ChannelHandler stringEncoder = new StringEncoder();
    private final ChannelHandler idleStateHandler;

    public MyPipelineFactory(Timer t) {
        this.timer = t;
        this.idleStateHandler = new IdleStateHandler(timer, 5, 5, 5);
    }

    public ChannelPipeline getPipeline() {
        // create default pipeline from static method
        ChannelPipeline pipeline = Channels.pipeline();
        pipeline.addLast("idleStateHandler", this.idleStateHandler); // heartbeat
        pipeline.addLast("framer", new DelimiterBasedFrameDecoder(1024, Delimiters.lineDelimiter()));
        //pipeline.addLast("frameDecoder", new LengthFieldBasedFrameDecoder(1024,0,1)); // get header from message
        pipeline.addLast("stringDecoder", stringDecoder);
        pipeline.addLast("stringEncoder", stringEncoder);
        pipeline.addLast("ServerHandler", new ServerHandler()); // goes at the end

        return pipeline;
    }
}

HeartbeatHandler.java

public class HeartbeatHandler extends IdleStateAwareChannelHandler {

    @Override
    public void channelIdle(ChannelHandlerContext ctx, IdleStateEvent e) {
        if (e.getState() == IdleState.READER_IDLE) {
            System.out.println("Reader idle, closing channel");
            //e.getChannel().close();
            e.getChannel().write("heartbeat-reader_idle");
        }
        else if (e.getState() == IdleState.WRITER_IDLE) {
            System.out.println("Writer idle, sending heartbeat");
            e.getChannel().write("heartbeat-writer_idle");
        }
        else if (e.getState() == IdleState.ALL_IDLE) {
            System.out.println("All idle, sending heartbeat");
            e.getChannel().write("heartbeat-all_idle");
        }
    }
}

---

Fixed:

I forgot to have the HeartbeatHandler, which requires the IdleStateHandler (this part wasn't obvious to me). That works.

public class MyPipelineFactory implements ChannelPipelineFactory {
    private final Timer timer;
    private static final ChannelHandler stringDecoder = new StringDecoder();
    private static final ChannelHandler stringEncoder = new StringEncoder();
    private final ChannelHandler idleStateHandler;
    private final ChannelHandler heartbeatHandler;

    public MyPipelineFactory(Timer t) {
        this.timer = t;
        this.idleStateHandler = new IdleStateHandler(timer, 5, 5, 5);
        this.heartbeatHandler = new HeartbeatHandler();
    }

    public ChannelPipeline getPipeline() {
        // create default pipeline from static method
        ChannelPipeline pipeline = Channels.pipeline();
        pipeline.addLast("idleStateHandler", this.idleStateHandler);
        pipeline.addLast("heartbeatHandler", this.heartbeatHandler); // heartbeat
        pipeline.addLast("framer", new DelimiterBasedFrameDecoder(1024, Delimiters.lineDelimiter()));
        //pipeline.addLast("frameDecoder", new LengthFieldBasedFrameDecoder(1024,0,1)); // get header from message
        pipeline.addLast("stringDecoder", stringDecoder);
        pipeline.addLast("stringEncoder", stringEncoder);
        pipeline.addLast("ServerHandler", new ServerHandler()); // goes at the end

        return pipeline;
    }
}

Answer 1

You missed to add the HeartbeatHandler in the ChannelPipeline. You need to add IdleStateHandler AND HeartbeatHandler to the ChannelPipeline to have it work.

Answer 2

Norman’s answer is a really helpful,but what I'd like to point out another thing: the idleStateHandler and the heartbeatHandler should be channel specific, so in the PipeLineFactory , you shouldn't construct these two handlers as private members, but need to create new ones in the getPipeline() method. You's also have a channel map to save the constructed channels, if you need to release them, you'd better also stop the timer to release the resources.