"System.IO.Ports is currently only supported on Windows" when dynamically loading assembly on a Windows machine

Question

A console application dynamically loads an assembly containing a class that refers System.IO.Ports.

Both the application and the class library target net8.0-windows.

I get the exception System.IO.Ports is currently only supported on Windows., even though the command OperatingSystem.IsWindows() returns true.

If I add a reference to the class library from console application the error disappears.

I guess that during dynamic loading the information about the target runtime is lost.

Adding

<RuntimeIdentifiers>win-x64</RuntimeIdentifiers> 

to projects does not help.

A minimal reproducible example is available on GitHub.

Console application project file:

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

<PropertyGroup>
    <OutputType>Exe</OutputType>
    <TargetFramework>net8.0-windows</TargetFramework>
    <ImplicitUsings>enable</ImplicitUsings>
    <Nullable>enable</Nullable>
</PropertyGroup>

Class library project file:

<PropertyGroup>
    <TargetFramework>net8.0-windows</TargetFramework>
    <ImplicitUsings>enable</ImplicitUsings>
    <Nullable>enable</Nullable>
    <CopyLocalLockFileAssemblies>true</CopyLocalLockFileAssemblies>
</PropertyGroup>

<ItemGroup>
    <PackageReference Include="System.IO.Ports" Version="8.0.0" />
</ItemGroup>

Program.cs:

using System.Reflection;

try
{
    var serialPortPath = "..\\..\\..\\..\\SerialPort\\bin\\Debug\\net8.0-windows\\SerialPort.dll";
    var serialAssembly = Assembly.LoadFrom(serialPortPath);
    var serialPort = Activator.CreateInstance(serialAssembly.GetType("SerialPort.SerialPort"));
}
catch    
{
    // Do nothing
}

SerialPort.cs:

namespace SerialPort
{
    public class SerialPort
    {
        public SerialPort()
        {
            var serial = new System.IO.Ports.SerialPort();
        }
    }
}

The exception throws at

var serial = new System.IO.Ports.SerialPort();

EDIT: I'm aware of LoadContext, but I don't understand the root of the problem yet: if I directly refer the assembly it correctly finds the Windows dll, why the information about target platform is lost when loading via Assembly.LoadFrom?

Answer 1

Because SerialPort.dll depends on System.IO.Ports.dll, when you load SerialPort.dll, the runtime automatically loads System.IO.Ports.dll from the same folder, but unfortunately this is a wrong assembly file, the right assembly file to load is located in runtimes\win\lib\net8.0\ folder. To resolve the dependency path, you need to create a custom AssemblyLoadContext and an AssemblyDependencyResolver, also ensure that SerialPort.deps.json is generated along with SerialPort.dll:

var customALC = new CustomALC();
....
var serialAssembly = customALC.Load(serialPortPath);
....

class CustomALC : AssemblyLoadContext
{
    private AssemblyDependencyResolver? _resolver;

    protected override Assembly? Load(AssemblyName assemblyName)
    {
        var path = _resolver?.ResolveAssemblyToPath(assemblyName);
        return path != null ? LoadFromAssemblyPath(path) : null;
    }

    public Assembly Load(string path)
    {
        path = Path.GetFullPath(path);
        _resolver = new AssemblyDependencyResolver(path);
        return LoadFromAssemblyPath(path);
    }
}