Add encryption toggles

.gitignore

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 /target
+bin
+obj

csharp/DirectIpNet.Native/DirectIpNet.Native.csproj

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+<Project Sdk="Microsoft.NET.Sdk">
+  <PropertyGroup>
+    <TargetFramework>net8.0</TargetFramework>
+    <Nullable>enable</Nullable>
+    <OutputType>Library</OutputType>
+    <PublishAot>true</PublishAot>
+  </PropertyGroup>
+  <ItemGroup>
+    <ProjectReference Include="../DirectIpNet/SBDDirectIP.csproj" />
+  </ItemGroup>
+</Project>

csharp/DirectIpNet.Native/Exports.cs

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+using System;
+using System.Runtime.InteropServices;
+using System.Threading.Tasks;
+using SBDDirectIP;
+
+namespace SBDDirectIP.Native;
+
+public static unsafe class Exports
+{
+    [StructLayout(LayoutKind.Sequential)]
+    public struct ConfirmationInfo
+    {
+        public uint ClientMsgId;
+        public uint IdReference;
+        public MessageStatus Status;
+    }
+
+    [UnmanagedCallersOnly(EntryPoint = "directip_send_mt")]
+    public static int SendMt(byte* host, int port, uint clientMsgId, byte* imei, byte* payload, int payloadLen, ConfirmationInfo* confirmation)
+    {
+        try
+        {
+            var hostStr = Marshal.PtrToStringUTF8((IntPtr)host)!;
+            var imeiStr = Marshal.PtrToStringUTF8((IntPtr)imei)!;
+            var data = new byte[payloadLen];
+            if (payload != null && payloadLen > 0)
+            {
+                Marshal.Copy((IntPtr)payload, data, 0, payloadLen);
+            }
+
+            var client = new DirectIpClient(hostStr, port);
+            var msg = MTMessage.Builder()
+                .ClientMsgId(clientMsgId)
+                .Imei(imeiStr)
+                .Payload(data)
+                .Build();
+
+            Task<Confirmation> task = client.SendAsync(msg);
+            task.Wait();
+            Confirmation conf = task.Result;
+
+            if (confirmation != null)
+            {
+                confirmation->ClientMsgId = conf.ClientMsgId;
+                confirmation->IdReference = conf.IdReference;
+                confirmation->Status = conf.Status;
+            }
+
+            return 0;
+        }
+        catch
+        {
+            return -1;
+        }
+    }
+}

csharp/DirectIpNet.Native/README.md

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+# DirectIpNet.Native
+
+This project exposes the `SBDDirectIP` API as a native C library. It uses
+`UnmanagedCallersOnly` so the resulting binary can be consumed from any language
+that can call C functions.
+
+## Building
+
+Use `dotnet publish` with NativeAOT enabled to produce a shared library:
+
+```shell
+cd csharp/DirectIpNet.Native
+dotnet publish -c Release -r linux-x64
+```
+
+The compiled library will be placed under `bin/Release/net8.0/linux-x64/native`.
+
+## Usage
+
+Include `directip.h` in your C or C++ project and link against the produced
+library. Example:
+
+```c
+#include "directip.h"
+
+int main() {
+    ConfirmationInfo conf;
+    const char payload[] = "Hello";
+    int rc = directip_send_mt("127.0.0.1", 10800, 1,
+                              "012345678901234",
+                              (const uint8_t*)payload, sizeof(payload)-1,
+                              &conf);
+    return rc;
+}
+```

csharp/DirectIpNet.Native/directip.h

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+#ifndef DIRECTIP_H
+#define DIRECTIP_H
+
+#include <stdint.h>
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+typedef struct {
+    uint32_t ClientMsgId;
+    uint32_t IdReference;
+    int32_t Status;
+} ConfirmationInfo;
+
+int directip_send_mt(const char* host,
+                     int port,
+                     uint32_t client_msg_id,
+                     const char* imei,
+                     const uint8_t* payload,
+                     int payload_len,
+                     ConfirmationInfo* confirmation);
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif // DIRECTIP_H

csharp/DirectIpNet/DirectIpClient.cs

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+using System;
+using System.Net.Sockets;
+using System.Threading.Tasks;
+
+namespace SBDDirectIP;
+
+public class DirectIpClient
+{
+    private readonly string _host;
+    private readonly int _port;
+
+    public DirectIpClient(string host, int port)
+    {
+        _host = host;
+        _port = port;
+    }
+
+    public async Task<Confirmation> SendAsync(MTMessage message)
+    {
+        using var client = new TcpClient();
+        await client.ConnectAsync(_host, _port);
+        using var stream = client.GetStream();
+        var data = message.ToArray();
+        await stream.WriteAsync(data, 0, data.Length);
+        var buffer = new byte[56];
+        int bytesRead = await stream.ReadAsync(buffer, 0, buffer.Length);
+        return Confirmation.FromArray(buffer.AsSpan(3));
+    }
+}