TracingHandler.java

 public static class TracingHandler extends SimpleChannelUpstreamHandler {
        private Tagging tagging;

        public TracingHandler(Tagging tagging) {
             this.tagging = tagging;
        }

        @Override
        public void messageReceived(ChannelHandlerContext ctx, MessageEvent e) throws Exception {
            HttpRequest httpRequest = (HttpRequest)e.getMessage();
            String tagString = httpRequest.getHeader(DT_HEADER);
            if(tagString !=null && tagging.isTagValid(tagString)) {
                tagging.setTagFromString(tagString);
                tagging.startServerPurePath();
            }    
        
            //code you want to trace goes here
            
            tagging.endServerPurePath(); //this could probably go in the writeComplete or channelClosed
        }
 }