v0.6: DHCP tunnel transport with NOP heartbeat protocol

DhcpTunnelTest/Program.cs

@@ -0,0 +1,105 @@
+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}");
+    }
+}

DhcpTunnelTest/Robovoice.DhcpTunnelTest.csproj

@@ -0,0 +1,10 @@
+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <OutputType>Exe</OutputType>
+    <TargetFramework>net10.0</TargetFramework>
+    <ImplicitUsings>enable</ImplicitUsings>
+    <Nullable>enable</Nullable>
+  </PropertyGroup>
+
+</Project>