Ok, I solved this one on my own last week so I'll add the answer for completness.
I was wrong in 3. because I thought I'll have to change both the client and the server side for a heartbeat. As described in this question you can use the IdleStateAwareHandler
for this purpose. I implemented it like this:
The IdleStateAwareHandler:
public class IdleStateAwareHandler extends IdleStateAwareChannelHandler {
@Override
public void channelIdle(ChannelHandlerContext ctx, IdleStateEvent e) {
if (e.getState() == IdleState.READER_IDLE) {
e.getChannel().write("heartbeat-reader_idle");
}
else if (e.getState() == IdleState.WRITER_IDLE) {
Logger.getLogger(IdleStateAwareHandler.class.getName()).log(
Level.WARNING, "WriteIdle detected, closing channel");
e.getChannel().close();
e.getChannel().write("heartbeat-writer_idle");
}
else if (e.getState() == IdleState.ALL_IDLE) {
e.getChannel().write("heartbeat-all_idle");
}
}
}
The PipeLine:
public class ICAPClientChannelPipeline implements ICAPClientPipeline {
ICAPClientHandler icapClientHandler;
ChannelPipeline pipeline;
public ICAPClientChannelPipeline(){
icapClientHandler = new ICAPClientHandler();
pipeline = pipeline();
pipeline.addLast("idleStateHandler", new IdleStateHandler(new HashedWheelTimer(10, TimeUnit.MILLISECONDS), 5, 5, 5));
pipeline.addLast("idleStateAwareHandler", new IdleStateAwareHandler());
pipeline.addLast("encoder",new IcapRequestEncoder());
pipeline.addLast("chunkSeparator",new IcapChunkSeparator(1024*4));
pipeline.addLast("decoder",new IcapResponseDecoder());
pipeline.addLast("chunkAggregator",new IcapChunkAggregator(1024*4));
pipeline.addLast("handler", icapClientHandler);
}
@Override
public ChannelPipeline getPipeline() throws Exception {
return pipeline;
}
}
This detects any read or write idle state on the channel after 5 seconds. As you can see it is a little bit ICAP-specific but this doesn't matter for the question.
To react to an idle event I need the following listener:
channel.getCloseFuture().addListener(new ChannelFutureListener() {
@Override
public void operationComplete(ChannelFuture future) throws Exception {
doSomething();
}
});