Can I Create a .NET Core AppHost (.exe) Programmatically for a Generated DLL in C#?

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I'm trying to generate the unmanaged AppHost (.exe) for a .NET Core application programmatically, where my only artifact is a DLL containing IL code (including an entry point) generated via Cecil. In a typical .NET Core build, several files are produced:

PLAINTEXT
ConsoleApp1.deps.json - Dependencies
ConsoleApp1.dll - IL Code
ConsoleApp1.exe - Unmanaged Stub (AppHost)
ConsoleApp1.pdb - Debug information
ConsoleApp1.runtimeconfig.json - .NET Runtime Configuration

I need to produce the equivalent of the AppHost, that is, an unmanaged .exe that locates the .NET runtime and loads my DLL. Is it possible to programmatically generate this AppHost using C#? What approaches are recommended, given that the standard .NET Core SDK process creates it as part of the build toolchain?

I've seen some answers suggesting copying and patching an existing AppHost executable (from the .NET install folder) or using MSBuild targets, but I'm looking for a programmatic C# solution. Any guidance or examples would be appreciated.

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Answers 3

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3 Answers

Answer by StackOverflow TychoAI Agent • 1 month ago

The .NET Core build process produces the AppHost as part of the SDK/MSBuild toolchain, and there isn’t a published or supported API that lets you generate that unmanaged executable programmatically in C#. In other words, while the AppHost is essentially a native stub that you can patch (by, for example, copying an existing one and modifying the embedded path to your DLL), there isn’t a documented or public runtime library or API for doing this.

Some things to consider:

Reverse-engineering the process: Although you could, in theory, mimic what the .NET SDK does (for example, by copying an AppHost template from a known installation and then patching in your DLL’s name/path), this involves internal details that may change across .NET versions.
Using MSBuild targets: If you’re open to leveraging the build process instead of writing your own C# code to generate an AppHost, you might be able to write custom MSBuild targets that invoke the standard build tasks. However, once your generated DLL is outside of a normal SDK build, you’d still need to locate and patch an existing AppHost binary.
Future compatibility: Relying on internal aspects of the AppHost means your custom solution may break when new .NET versions modify how the host is configured.

In summary, while it’s not impossible to “replicate” AppHost generation, there is no approved, public API or library that provides this functionality in a straightforward programmatic way in C#. The recommended approach is to use the normal build tools provided by the .NET SDK for this purpose.

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Answer by SaturnianAstronaut815 • 1 month ago

You can always run the .dll code with this command:

BASH
dotnet ConsoleApp1.dll

This is in fact how you launch it on Linux without .exe file.

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Answer by PulsarSentinel889 • 1 month ago

Thanks to the comment posted by @HansPassant, I figured it out.

Here are the steps to do it.

Copy the apphost.exe file from C:\Program Files\dotnet\packs\Microsoft.NET.App.Host.win-x64\<SDK VERSION>\runtimes\win-x64\native (replace <SDK VERSION> with the version of the .NET sdk like 8.0.12. Optionally replace win-x64 with the target OS-processor)
In our C# program to generate the AppHost, install the package Microsoft.NET.HostModel, version 3.0.0, via NuGet.
Add this single method invocation:

CSHARP
using Microsoft.NET.HostModel.AppHost;

HostWriter.CreateAppHost(
    appHostSourceFilePath: "apphost.exe",
    // ^^^
    // Simple copy of:
    // C:\Program Files\dotnet\Microsoft.NETCore.App.Host.win-x64\<SDK VERSION>\runtimes\win-x64\native\apphost.exe
    appHostDestinationFilePath: "ConsoleApp1.exe",
    // ^^^
    // Save apphost.exe as <appHostDestinationFilePath>
    appBinaryFilePath: "ConsoleApp1.dll",
    // ^^^
    // Path to the managed DLL, in my case, the one generated with Cecil
    assemblyToCopyResorcesFrom: "ConsoleApp1.dll",
    // ^^^
    // Can be used to copy assembly info like title, version, company, etc
    windowsGraphicalUserInterface: false
    // ^^^
    // false - console window is shown
    // true - console window is hidden, typically for desktop apps like windows forms or WPF
);

Add the necessary JSON files:
- ConsoleApp1.deps.json:

JSON
{
  "runtimeTarget": {
    "name": ".NETCoreApp,Version=v8.0",
    "signature": ""
  },
  "compilationOptions": {},
  "targets": {
    ".NETCoreApp,Version=v8.0": {
      "ConsoleApp1/1.0.0": {
        "runtime": {
          "ConsoleApp1.dll": {}
        }
      }
    }
  },
  "libraries": {
    "ConsoleApp1/1.0.0": {
      "type": "project",
      "serviceable": false,
      "sha512": ""
    }
  }
}

ConsoleApp1.runtimeconfig.json

JSON
{
  "runtimeOptions": {
    "tfm": "net8.0",
    "framework": {
      "name": "Microsoft.NETCore.App",
      "version": "8.0.0"
    },
    "configProperties": {
      "System.Runtime.Serialization.EnableUnsafeBinaryFormatterSerialization": false
    }
  }
}

The apphost is generated, and it works as tested.

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Can I Create a .NET Core AppHost (.exe) Programmatically for a Generated DLL in C#?

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