Embedding .NET Assemblies inside .NET Assemblies

There are times when you create an assembly executable that has dependencies on other assemblies. You may want pass this assembly around without having the need for it to be installed however; if you have to copy DLL’s around with the EXE, there could be a chance that they are forgotten or the wrong versions are copied.

The topic of this post is to explain how we can embed DLL assemblies within our EXE assembly and load them at execution time.

Referencing an Assembly

Take a look at this little console app. It does nothing useful other than serialize an object to JSON. It does however; have a dependency on Newtonsoft.Json.dll, the most popular JSON library.

class Program
{
    static void Main(string[] args)
    {
        Console.WriteLine();

        var aa = JsonConvert.SerializeObject(GetPeople());

        Console.WriteLine($"{aa}\n\n");

        //Output: [{"Name":"Denham","Age":21},{"Name":"Wifey","Age":102}]
    }

    static List<Person> GetPeople()
    {
        return new List<Person>()
        {
            new Person() {Name = "Denham", Age = 21 },
            new Person() {Name = "Wifey", Age = 102 }
        };
    }
}

class Person
{
    public string Name { get; set; }
    public int Age { get; set; }
}

If we take a look in the output folder we can see the referenced assembly copied at build time.

If we delete that assembly and execute the EmbedAssembly.exe app we get the “Could not load file or assembly” error.

So when passing this assembly around we must ensure Newtonsoft.Json.dll is passed as well and in some scenarios, a specific version of it.

Embedding an Assembly within an Assembly

Let’s look at how we can embed Newtonsoft.Json.dll inside EmbedAssembly.exe.

  • Within my solution I created an EmbeddedAssemblies folder and copied the Newtonsoft.Json.dll from the output folder into it.
  • I right clicked the folder and selected Add -> Existing Item and added the DLL.
  • I then highlighted Newtonsoft.Json.dll and in the Properties pane I changed Build Action to Embedded Resource and Copy to Output Directory to Do not copy.
  • You can then remove the NewtonSoft nuget package and add a reference to the DLL in the EmbeddedAssemblies folder.

Now we have our assembly embedded, we need to know how to reference it. There is a logical path to a resource however; a simple way is by adding the following method to output all the embedded resources to the Output log. Run the app in debug mode to view the output.

static void ListEmbeddedResourceNames()
{
    Trace.WriteLine("Listing Embedded Resource Names");

    foreach (var resource in Assembly.GetExecutingAssembly().GetManifestResourceNames())
        Trace.WriteLine("Resource: " + resource);
}

The Resource listed is the full name to our resource which corresponds to the namespace.folder.assembly. Make a note of this name. If you do not see the resource listed, check the steps above were completed.

The last step is to add the following code highlighted below.

  • In our Main method I set up an AssemblyResolve event listener.
  • I had to move the code that does JsonConvert.SerializeObject into another method. The reason being is that the .NET loader will try and load the Newtonsoft.Json.dll before the event handler is wired up.
  • When the .NET loader tries to load Newtonsoft.Json.dll, the event will fire and execute the CurrentDomain_AssemblyResolve method. This method takes care of pulling out the assembly and loading it.
static void Main(string[] args)
{
    ListEmbeddedResourceNames();
    AppDomain.CurrentDomain.AssemblyResolve += CurrentDomain_AssemblyResolve;
    Run();
}

static void Run()
{
    Console.WriteLine();

    var aa = JsonConvert.SerializeObject(GetPeople());

    Console.WriteLine($"{aa}\n\n");

    //Output: [{"Name":"Denham","Age":21},{"Name":"Wifey","Age":102}]
}

static Assembly CurrentDomain_AssemblyResolve(object sender, ResolveEventArgs args)
{
    using (var stream = Assembly.GetExecutingAssembly().GetManifestResourceStream("EmbedAssembly.EmbeddedAssemblies.Newtonsoft.Json.dll"))
    {
        var assemblyData = new Byte[stream.Length];
        stream.Read(assemblyData, 0, assemblyData.Length);
        return Assembly.Load(assemblyData);
    }
}

That’s it. Let’s compile and test it. As you can see the folder does not contain Newtonsoft.Json.dll however; the exe runs without the failure we first had above.

A nice simple way of carrying around your dependencies.

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