🚀 .NET Generic Host

A lightweight native C++ host for running .NET assemblies without modification. Perfect for hosting WPF applications, console apps, or any .NET DLL with a Main method. 🎯

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✨ Features

• 🔄 Zero Assembly Modification - Run any .NET DLL without changing source code
• 🎨 WPF Support - Full support for WPF applications with proper resource loading
• 🧵 STA Threading - Automatic COM initialization for UI applications
• ⚙️ JSON Configuration - Simple configuration via net-host.json
• 📦 Entry Assembly Support - Properly sets entry assembly for resource loading
• 💬 Command-line Arguments - Pass arguments to the hosted application

🎯 Use Cases

• 🖥️ Host WPF applications from native C++ code
• 📚 Run .NET DLLs as standalone applications
• 🚀 Create custom .NET application launchers
• 🔗 Bridge native and managed code seamlessly

🛠️ Building

Prerequisites

• 🔧 Visual Studio 2022 or later
• 🔷 .NET 8.0 SDK - Download
• ⚡ C++20 support

Build Steps

1. Open net-host.sln in Visual Studio
2. Build the solution (Release/x64 recommended)
3. Output: net-host.exe in x64/Release or x64/Debug

📖 Usage

1️⃣ Create Configuration File

Create net-host.json in the same directory as net-host.exe:

{
  "assemblyPath": "YourApp.dll",
  "typeName": "YourNamespace.Program",
  "methodName": "Main",
  "arguments": []
}

2️⃣ Prepare Your .NET Assembly

Ensure your .NET application has a public static void Main() or public static void Main(string[] args) method:

namespace YourNamespace
{
    public class Program
    {
        public static void Main(string[] args)
        {
            // Your application code
            var app = new App();
            app.Run();
        }
    }
}

3️⃣ Deploy Files

Place in the same directory:

• net-host.exe
• net-host.json
• nethost.dll (from .NET SDK)
• YourApp.dll and all its dependencies
• YourApp.runtimeconfig.json

4️⃣ Run

net-host.exe

⚙️ Configuration Reference

Field	Type	Required	Description
assemblyPath	string	✅ Yes	Path to the .NET DLL (relative or absolute)
typeName	string	✅ Yes	Fully qualified type name (e.g., Namespace.Class)
methodName	string	❌ No	Entry method name (default: Main)
arguments	array	❌ No	Command-line arguments to pass to Main

Example with Arguments

{
  "assemblyPath": "MyApp.dll",
  "typeName": "MyApp.Program",
  "methodName": "Main",
  "arguments": [
    "--config", "production.json",
    "--verbose"
  ]
}

🏗️ How It Works

1. Configuration Loading - Reads net-host.json to get assembly information
2. hostfxr Initialization - Loads .NET hosting library (hostfxr.dll)
3. Runtime Initialization - Initializes .NET runtime using hostfxr_initialize_for_dotnet_command_line
4. COM/STA Setup - Initializes COM in STA mode for WPF support
5. Application Execution - Calls hostfxr_run_app to execute the Main method
6. Entry Assembly Setup - Automatically sets entry assembly for resource loading

🎨 WPF Applications

For WPF applications, the host automatically:

• ✅ Initializes COM in STA (Single-Threaded Apartment) mode
• ✅ Sets up entry assembly for pack:// URI resource loading
• ✅ Handles Application.ResourceAssembly resolution
• ✅ Supports XAML resource loading

No modifications needed to your WPF application!

🐛 Troubleshooting

❌ Assembly Not Found

• ✅ Ensure the DLL path in net-host.json is correct
• ✅ Check that all dependency DLLs are in the same directory
• ✅ Verify the assembly path is relative to net-host.exe location

⚠️ Runtime Initialization Failed

• ✅ Verify .NET 8.0 Runtime is installed
• ✅ Check that runtimeconfig.json exists next to the DLL
• ✅ Ensure rollForward policy in runtimeconfig.json allows runtime version
• ✅ Verify nethost.dll is present in the same directory

🎨 WPF Resource Loading Issues

• ✅ Verify all resource DLLs are present
• ✅ Check that XAML resources are embedded correctly
• ✅ Ensure Build Action for resources is set to Resource
• ✅ Verify pack URIs are correct in your XAML files

🔧 COM Initialization Failed

• ✅ Close other applications that may conflict
• ✅ Run as administrator if necessary
• ✅ Check if COM is already initialized in a different mode

🔧 Technical Details

Architecture

net-host.exe (Native C++)
    ↓ hostfxr API
.NET Runtime
    ↓ load_assembly_and_get_function_pointer
YourApp.dll
    ↓ Main() execution
WPF Application / Console App

Key APIs Used

API	Purpose
hostfxr_initialize_for_dotnet_command_line	Simulates dotnet YourApp.dll
hostfxr_run_app	Executes the application's Main method
CoInitializeEx	Initializes COM for UI threading

📦 Example Projects

Console Application

{
  "assemblyPath": "ConsoleApp.dll",
  "typeName": "ConsoleApp.Program",
  "methodName": "Main",
  "arguments": ["--help"]
}

WPF Application

{
  "assemblyPath": "WpfApp.dll",
  "typeName": "WpfApp.App",
  "methodName": "Main",
  "arguments": []
}

📄 License

This project is licensed under the MIT License - see the LICENSE file for details.

🙏 Acknowledgments

• .NET Hosting APIs - Built with .NET Hosting APIs
• nlohmann/json - JSON for Modern C++

📚 Additional Resources

• hostfxr API Reference
• Write a custom .NET runtime host

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