FileNotFoundException when trying to load Autofac as an embedded assembly

Question

Previous versions of Autofac worked, but since they switched to making it a Portable Class Library it won't load.

I tried applying the fix listed here (KB2468871) but it told me that it was not needed.

The error goes away when I move the Autofac.dll file into the same location as the executable. When it loads it from the external DLL it loads fine.

Why won't it work as an embedded DLL?

Here is the exception:

        System.IO.FileNotFoundException: Could not load file or assembly 'System.Core, Version=2.0.5.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e, Retargetable=Yes' or one of its dependencies. The system cannot find the file specified.

        Stack trace: 
           at Autofac.Core.Registration.ComponentRegistration..ctor(Guid id, IInstanceActivator activator, IComponentLifetime lifetime, InstanceSharing sharing, InstanceOwnership ownership, IEnumerable`1 services, IDictionary`2 metadata)
           at Autofac.Core.Container..ctor()
           at Autofac.ContainerBuilder.Build(ContainerBuildOptions options)
           at MyApp.Configuration.Bootstrapper.Run(String[] args) in c:\Dev\MyApp\App\Configuration\Bootstrapper.cs:line 25
           at MyApp.Configuration.EntryPoint.Main(String[] args) in c:\Dev\MyApp\App\Configuration\EntryPoint.cs:line 22

If it helps, here is the part of the .csproj file that embeds the DLLs into the executable:

  <Target Name="AfterResolveReferences">
<ItemGroup>
  <EmbeddedResource Include="@(ReferenceCopyLocalPaths)" Condition="'%(ReferenceCopyLocalPaths.Extension)' == '.dll'">
    <LogicalName>%(ReferenceCopyLocalPaths.DestinationSubDirectory)%(ReferenceCopyLocalPaths.Filename)%(ReferenceCopyLocalPaths.Extension)</LogicalName>
  </EmbeddedResource>
</ItemGroup>

... and here is the EntryPoint class:

internal static class EntryPoint
{
    [STAThread]
    private static void Main(params string[] args)
    {
        AppDomain.CurrentDomain.AssemblyResolve += (sender, e) => loadEmbeddedAssembly(e.Name);
        Bootstrapper.Run(args); // must call separate class when using embedded assemblies
    }

    private static Assembly loadEmbeddedAssembly(string name)
    {
        var container = Assembly.GetExecutingAssembly();
        var path = new AssemblyName(name).Name + ".dll";

        using (var stream = container.GetManifestResourceStream(path))
        {
            if (stream == null)
            {
                return null;
            }

            var bytes = new byte[stream.Length];
            stream.Read(bytes, 0, bytes.Length);
            return Assembly.Load(bytes);
        }
    }
}

Answer 1

I could easily repro your problem by using Assembly.Load(byte[]) on a PCL library that targeted Silverlight and used a System.Core type, this problem isn't specific to Autofac. It is a rather evil way to load an assembly, about as bad as Assembly.LoadFile(). Not having a loading context is a recipe for DLL Hell.

The CLR has an unenviable job to do with these PCL library references, it needs to magically map the retargetable assembly references to a real one. In other words, the 2.0.5.0 reference needs to be mapped to the correct one for the runtime version, 4.0.0.0 in your case. It can only do this if it has a good idea what the actual runtime version is, not having a loading context makes that difficult. Clearly it doesn't attempt to do so, it fires the AssemblyResolve event again for the 2.0.5.0 reference.

Which is the solution, remarkable simple in hind-sight. Just intercept the resolve request for the retargetable assembly references and use Assembly.Load() to let the CLR sort it out from the loading context of your AppDomain. Alter your AssemblyResolve event handler like this:

private static Assembly loadEmbeddedAssembly(string name)
{
    if (name.EndsWith("Retargetable=Yes")) {
        return Assembly.Load(new AssemblyName(name));
    }
    // Rest of your code
    //...
}

This worked well in my test app, I trust it will solve your problem with Autofac as well.