Robovoice/DhcpTunnelTest/Program.cs

using System.Net;
using System.Net.NetworkInformation;
using System.Net.Sockets;
using System.Text;

// Args: [interface_ip] [interval_ms]
// Defaults: auto-detect LAN IP, 50ms

string localIp = args.Length > 0 ? args[0] : GetLanInterfaceIp() ?? "0.0.0.0";
int intervalMs = args.Length > 1 && int.TryParse(args[1], out int iv) ? iv : 50;

using var sock = new Socket(AddressFamily.InterNetwork, SocketType.Dgram, ProtocolType.Udp);
sock.SetSocketOption(SocketOptionLevel.Socket, SocketOptionName.ReuseAddress, true);
sock.EnableBroadcast = true;

var localEp = new IPEndPoint(IPAddress.Parse(localIp), 68);
sock.Bind(localEp);

Console.WriteLine($"Bound to {localEp} (SO_REUSEADDR)");
Console.WriteLine("Sending NOPs + listening. Press Ctrl+C to stop.");
Console.WriteLine();

var cts = new CancellationTokenSource();
var recvTask = Task.Run(() => ReceiveLoop(sock, cts.Token));

var destEp = new IPEndPoint(IPAddress.Broadcast, 67);
uint nonce = 0;

while (!cts.Token.IsCancellationRequested)
{
    nonce++;
    string msg = $"HKMSTR {nonce}\n";
    byte[] payload = Encoding.UTF8.GetBytes(msg);

    try
    {
        int sent = sock.SendTo(payload, destEp);
        Console.WriteLine($"[{DateTime.Now:HH:mm:ss.fff}] SENT n={nonce} {sent} bytes");
    }
    catch (Exception ex)
    {
        Console.WriteLine($"[{DateTime.Now:HH:mm:ss.fff}] SEND FAILED: {ex.Message}");
    }

    try { Thread.Sleep(intervalMs); }
    catch (OperationCanceledException) { break; }
}

cts.Cancel();
await recvTask;

static string? GetLanInterfaceIp()
{
    foreach (var nic in NetworkInterface.GetAllNetworkInterfaces())
    {
        if (nic.OperationalStatus != OperationalStatus.Up)
            continue;
        if (nic.NetworkInterfaceType == NetworkInterfaceType.Loopback)
            continue;
        if (nic.Description.Contains("WireGuard", StringComparison.OrdinalIgnoreCase))
            continue;

        foreach (var addr in nic.GetIPProperties().UnicastAddresses)
        {
            if (addr.Address.AddressFamily == AddressFamily.InterNetwork)
            {
                var ip = addr.Address.ToString();
                if (ip.StartsWith("192.168.") || ip.StartsWith("10.") || ip.StartsWith("172."))
                    return ip;
            }
        }
    }
    return null;
}

static void ReceiveLoop(Socket sock, CancellationToken ct)
{
    byte[] buffer = new byte[4096];
    EndPoint fromEp = new IPEndPoint(IPAddress.Any, 0);

    while (!ct.IsCancellationRequested)
    {
        int received;
        try
        {
            if (!sock.Poll(500_000, SelectMode.SelectRead))
                continue;
            received = sock.ReceiveFrom(buffer, ref fromEp);
        }
        catch (Exception ex)
        {
            Console.WriteLine($"[{DateTime.Now:HH:mm:ss.fff}] RECV ERROR: {ex.Message}");
            continue;
        }

        string text = Encoding.UTF8.GetString(buffer, 0, received).TrimEnd('\n', '\r');
        if (!text.StartsWith("HKMSTR"))
        {
            Console.WriteLine($"[{DateTime.Now:HH:mm:ss.fff}] RECV {received} bytes from {fromEp} (no magic)");
            continue;
        }

        Console.WriteLine($"[{DateTime.Now:HH:mm:ss.fff}] RECV {received} bytes from {fromEp}: {text}");
    }
}