c# - make public an object created inside a function

Question

How can I use the object "communicator" created in main(), in the callback function? The PacketCommunicator class doesn't have a constructor.

class Program
{
    //public static PacketCommunicator communicator = new PacketCommunicator(); - can't do this; PacketCommunicator constructor doesn't exist
    //public static PacketCommunicator communicator = null; - this gives "Object reference not set to an instance of an object"
    public static void Main(string[] args)
    {
        PacketCommunicator communicator = selectedDevice.Open(...)
        communicator.ReceivePackets(0, PacketHandler);
    }

    // Callback function invoked by ReceivePackets for every incoming packet
    private static void PacketHandler(Packet packet)
    {
        communicator.SendPacket(packet);
    }
}

The library I'm using is Pcap.Net. Basically, what I'm trying to do is to capture packets on one interface, perform NAT on them, and send them on another interface.

Answer 1

As @SLaks mentioned in the comments, you could use a lambda. Then communicator would not lose scope.

communicator.ReceivePackets(
    0, (packet) => 
        {
           //processing code goes here...
           communicator.SendPacket(packet);
        });

The way that PCAP works with receive packets is to just put it in a continual loop, breaking when you hit a time when you want to close.

There is a nice example of that here, though they are just reporting on the packets, not sending them on as you appear to be.

In this example you would instantiate communicator thusly

PacketCommunicator communicator = selectedDevice.Open(...)