NetMQ - messages only work on reply to incoming message, not to other port

Question

On initialize of my router application I call the following code. It binds fine, receives messages fine but refuses to work for the On_ReceiveXXX methods unless it's a direct response. I want to know why

    public void Initialize(string frontEndAddress, string backEndAddress)
    {
        _poller = new Poller();
        _timeAllowedBetweenPings = TimeSpan.FromMinutes(1);
        _lastPingResponse = DateTime.Now;

        using (var ctx = NetMQContext.Create())
        {
            _frontEnd = ctx.CreateRouterSocket();
            _backEnd = ctx.CreateRouterSocket();

            _frontEnd.Bind(frontEndAddress);
            Console.WriteLine(string.Format("[Router]: Connected to {0}", frontEndAddress));
            _backEnd.Bind(backEndAddress);
            Console.WriteLine(string.Format("[Router]: Connected to {0}", backEndAddress));

            _frontEnd.ReceiveReady += On_ReceiveFrontEnd;
            _backEnd.ReceiveReady += On_ReceiveBackEnd;

            _poller.AddSocket(_frontEnd);
            _poller.AddSocket(_backEnd);


            var timer = new NetMQTimer(TimeSpan.FromSeconds(1));
            timer.Elapsed += On_Ping;
            _poller.AddTimer(timer);
            _poller.PollTillCancelled();
        }
    }

This fails to call the dealer ReceiveReady event:

private void On_ReceiveFrontEnd(object sender, NetMQSocketEventArgs e) { _lastPingResponse = DateTime.Now; var frontEndMsg = e.Socket.ReceiveMultipartBytes(); var streamData = frontEndMsg.Last(); ApplicationMessage msg = PackageHelper.DeserializeOutgoing(streamData); Console.WriteLine(string.Format("Command received: {0}", msg.CO));

        _backEnd.SendMultipartBytes(frontEndMsg);
    }

BUT if I change the line

 _backEnd.SendMultipartBytes(frontEndMsg);

to

_frontEnd.SendMultipartBytes(frontEndMsg);

It suddenly works... so messages coming from my front end application can only be responded to, not passed on to the back end application. The same is true the other way round, for the back end messages.

Answer 1

When working with router the first frame is the routing id and it specific to the socket. So you can't pass the entire message from router to router. Change the backend to dealer and it will work, or prefix the message with routing id of the backend socket.