Allow client app to automatically connect to server app on same network

Question

I've created two apps (A client and a server) which can communicate with each other as long as I input the local IP address of the machine the server app is running on into the client app (in code).

I would like the client app to automatically discover the local IP address of the machine running the server app and connect to it, so they can be run on any network without the need to enter the IP in code.

Both of these apps with be running on the same network (ie. Over WiFi, not the Internet)

Here is what I have so far in my client app:

// COMMUNICATE WITH SERVER

    private TcpClient client = new TcpClient();
    private IPEndPoint serverEndPoint = new IPEndPoint(IPAddress.Parse("192.168.2.35"), 8888);

    public Console()
    {
        InitializeComponent();
        client.Connect(serverEndPoint);
    }

    private void SendMessage(string msg)
    {
        NetworkStream clientStream = client.GetStream();

        ASCIIEncoding encoder = new ASCIIEncoding();
        byte[] buffer = encoder.GetBytes(msg);

        clientStream.Write(buffer, 0, buffer.Length);
        clientStream.Flush();
    }

In this example I can only connect to a server running on "192.168.2.35", I would like it to be able to find the server running on port 8888 on any machine on the network.

Alternatively, if this isn't possible I would like the server to broadcast its IP as a message (of some sort) and have the client receive this message and verify it is the server and connect to it.

I think my second example is the proper way to do this, but I can't seem to wrap my head around how to get it working (I'm fairly new to C#), and any other examples I've found I can't seem to get to work with my applications.

Here is my server code if it helps answer my question:

private void Server()
    {
        this.tcpListener = new TcpListener(IPAddress.Any, 8888);
        this.listenThread = new Thread(new ThreadStart(ListenForClients));
        this.listenThread.Start();
    }

    private void ListenForClients()
    {
        this.tcpListener.Start();

        while (true)
        {
            TcpClient client = this.tcpListener.AcceptTcpClient();


            connectedClients++;
            lblNumberOfConnections.Text = connectedClients.ToString();

            Thread clientThread = new Thread(new ParameterizedThreadStart(HandleClientComm));
            clientThread.Start(client);

        }

Thanks

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EDIT: I've tried adding THIS to my project, but being so new I'm unsure how to implement it properly, and it didn't get me anywhere.

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2nd EDIT: I've tried implementing a UDP broadcast a few times now, with no luck on any attempt yet. My latest attempt was at implementing THIS (minus the chat parts). I just can't seem to get a UDP broadcast working at all with my project, as it seems to be way over my head at my current skill level. Unfortunately, having my client automatically connect to the server is 100% necessary for my project to function...

My other problem, which is maybe best to start a separate question for, but somewhat correlates to this issue is: My client GUI consists of a panel that switches between multiple custom classes, each containing different buttons, etc. (works similar to tab pages) that communicate to the server I'm trying to connect to. Once I get the UDP broadcast figured out, will I need to code that into every class separately? or is there a way of having all classes running in my panel connect to the same server?

Answer 1

A simple, but possibly costly(in terms of network traffic) solution would be for your server application to broadcast over UDP it's application and connection info. Your client could listen for all broadcast packets that have your servers custom header. Assuming a connection is made you could stop the broadcast. The downside is you would have to be broadcasting constantly if a client is not connected and this can clog your network if there aren't limits placed on the broadcast speed.

EDIT: Here is a boiled down explanation generated from the MSDN article https://msdn.microsoft.com/en-us/library/tst0kwb1(v=vs.110).aspx?cs-save-lang=1&cs-lang=csharp#code-snippet-1

EDIT #2: I've expanded on this answer on my blog, as well as provided downloadable example projects. the article can be found at http://martialdeveloper.com/wordpress/?p=21

1. Find your network's broadcast IP

A special “Broadcast Address” must be used when using UDP for the purpose of sending a datagram to all machines connected to a given network. For example, the typical home network host/gateway of 192.168.0.1 has a broadcast address of 192.168.0.255. If your network differs from this you can use an IPv4 broadcast address calculator like the one found here http://jodies.de/ipcalc Or read the introductory section on MSDN describing the broadcast address. https://msdn.microsoft.com/en-us/library/tst0kwb1(v=vs.110).aspx?cs-save-lang=1&cs-lang=csharp#code-snippet-1

2. Select a listening/broadcast port

Any port that is free on your client & server is fine. The MSDN example uses 11000. This port number is used in your broadcaster, and listener.

3. Code for the Listener

Note to the reader. All error handling has been omitted for clarity of the example.

int listenPort = 11000;
bool done = false;

UdpClient listener = new UdpClient(listenPort);
IPEndPoint groupEP = new IPEndPoint(IPAddress.Any,listenPort);


while (!done) // This loop listens for your broadcast packets
{
    Console.WriteLine("Waiting for broadcast");
    byte[] bytes = listener.Receive( ref groupEP);

    Console.WriteLine("Received broadcast from {0} :\n {1}\n",
            groupEP.ToString(),
            Encoding.ASCII.GetString(bytes,0,bytes.Length));
}
listener.Close();

Note: The third parameter to Console.WriteLine, "Encoding.ASCII..." represents the string value sent over UDP in the datagram packet. This contains the desired negotiation information for a discovery situation, such as the IP address of the client or server you wish to connect to.

4. Code for the Broadcaster

Socket s = new Socket(AddressFamily.InterNetwork, SocketType.Dgram,
            ProtocolType.Udp);

IPAddress broadcast = IPAddress.Parse("This string should be the broadcast IP address");  //NOTE: Broadcast IP goes here!!

byte[] sendbuf = Encoding.ASCII.GetBytes("This is the message string to be broadcast"); //Your message to the client/server goes here, I.E. an
         // app/client name or ID and an IP to connect with over TCP

IPEndPoint ep = new IPEndPoint(broadcast, 11000);

s.SendTo(sendbuf, ep);

Console.WriteLine("Message sent to the broadcast address");

NOTE: This is a very simple example. The broadcaster may need to rebroadcast for a period of time to make sure the Listener receives it. Even after the UDP datagram is sent/received there will need to be some negotiation to ensure the TCP connection is made properly.