[NativeAOT] How do I link a static library from a nuget package?

[slxdy]

In my NativeAOT project, I would like the link the static libraries from Microsoft.NETCore.DotNetAppHost.
Is this possible? If yes, how?

[neon-sunset]

It really comes down to specifying DirectPInvoke and NativeLibrary msbuild properties. For specific integrations consumed by .NET itself like ICU - there are separate properties (see https://github.com/dotnet/runtime/blob/main/src/coreclr/nativeaot/docs/compiling.md).

Which library do you want to link to?

[slxdy]

I want to link libnethost.lib from the Microsoft.NETCore.DotNetAppHost nuget package. (Also for some reason, for win-x64 the package contains both nethost.lib and libnethost.lib, though the latter is much bigger)

[AustinWise]

With regards to choosing between nethost.lib and libnethost.lib, it depends on whether you want to statically or dynamically link the nethost library. If you link against the smaller nethost.lib you binary will dynamically link against nethost.dll. If you use the larger libnethost.lib, the contents of the nethost library will be statically linked into your binary.

[slxdy]

Alright thanks, makes sense. Now I just gotta figure out how to link from the nuget package

[slxdy]

To clarify, I know how to link static libs, but I'd like to do so from the nuget package. I don't want to include the lib in my repo

[AustinWise]

I wrote a sample that statically links the nethost API into NativeAOT app. This sample currently only works when published as NativeAOT. If I get more time, I may extend it support dynamic linking so that it can be run as a normal .NET app on CoreCLR.

https://github.com/AustinWise/DotNetHostingAndNativeAot

Drawing on the sample app, instead of using the Microsoft.NETCore.DotNetAppHost package to get the nethost library, this app finds the nethost library from the targeting pack. Typically the .NET SDK includes this.

I tested this solution on Windows 11, Ubuntu 24.04, and macOS 15. On Linux, you might have to do something like apt-get install libstdc++-dev.

I'll reproduce the current state of my solution below:

Project file

<Project Sdk="Microsoft.NET.Sdk">

    <PropertyGroup>
        <OutputType>Exe</OutputType>
        <TargetFramework>net8.0</TargetFramework>
        <ImplicitUsings>enable</ImplicitUsings>
        <Nullable>enable</Nullable>
        <PublishAot>true</PublishAot>
        <InvariantGlobalization>true</InvariantGlobalization>
        <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
    </PropertyGroup>

    <Target Name="PrepareForNativeBuild" AfterTargets="Build">
        <PropertyGroup>
            <NetHostDir>$(NetCoreTargetingPackRoot)/Microsoft.NETCore.App.Host.$(NETCoreSdkRuntimeIdentifier)/$(BundledNETCoreAppPackageVersion)/runtimes/$(NETCoreSdkRuntimeIdentifier)/native</NetHostDir>
            <NetHostName Condition="$([MSBuild]::IsOsPlatform('Windows'))">libnethost.lib</NetHostName>
            <NetHostName Condition="!$([MSBuild]::IsOsPlatform('Windows'))">libnethost.a</NetHostName>
        </PropertyGroup>

        <ItemGroup>
            <NativeLibrary Include="$(NetHostDir)/$(NetHostName)" />
        </ItemGroup>

        <ItemGroup Condition="!$([MSBuild]::IsOsPlatform('Windows'))">
            <!-- This is needed by libnethost.a. -->
            <LinkerArg Include="-lstdc++" />
        </ItemGroup>
    </Target>

</Project>

Code file

This prints the host FXR path:

using System.Runtime.CompilerServices;
using System.Runtime.InteropServices;
using System.Text;

[assembly: DisableRuntimeMarshalling]

partial class Program
{
    static void Main()
    {
        try
        {
            string hostFxrPath = GetHostFxrPath();
            Console.WriteLine($"Got host FXR Path: {hostFxrPath}");
        }
        catch (Exception ex)
        {
            Console.WriteLine($"Failed to get host FXR path: {ex.Message}");
        }
    }

    private static string GetHostFxrPath()
    {
        if (OperatingSystem.IsWindows())
        {
            char[] buffer = new char[1024];
            nint bufferSize = buffer.Length;
            int rc = get_hostfxr_path_windows(buffer, ref bufferSize, IntPtr.Zero);
            if (rc == 0)
            {
                return new string(buffer.AsSpan().Slice(0, (int)bufferSize - 1));
            }
            else
            {
                throw new Exception($"get_hostfxr_path failed: {rc}");
            }
        }
        else
        {
            byte[] buffer = new byte[1024];
            nint bufferSize = buffer.Length;
            int rc = get_hostfxr_path_non_windows(buffer, ref bufferSize, IntPtr.Zero);
            if (rc == 0)
            {
                return Encoding.UTF8.GetString(buffer.AsSpan().Slice(0, (int)bufferSize - 1));
            }
            else
            {
                throw new Exception($"get_hostfxr_path failed: {rc}");
            }
        }
    }

    [LibraryImport("*", EntryPoint = "get_hostfxr_path")]
    private static partial int get_hostfxr_path_windows(char[] buffer, ref nint buffer_size, IntPtr parameters);

    [LibraryImport("*", EntryPoint = "get_hostfxr_path")]
    private static partial int get_hostfxr_path_non_windows(byte[] buffer, ref nint buffer_size, IntPtr parameters);
}

[slxdy]

That is... really smart. Didn't think of getting it from the dotnet sdk itself lol. Thanks a lot