Is it possible to extend IServiceProvider during runtime

Question

TLDR: Is it possible to modify the IServiceProvider after the Startup has ran?

I am running dll's (which implement a interface of me) during run-time. Therefore there's a file listener background job, which waits till the plugin-dll is dropped. Now I want to register classes of this dll to the dependency-injection system. Therefore I added IServiceCollection as a Singleton to the DI inside ConfigureServices to use inside another method.

In therefore I created a test-project and just tried to modify the ServiceCollection in the controller, because it was easier than stripping the background job down.

services.AddSingleton<IServiceCollection>(services);

So I added IServiceCollection to my controller to check if I can add a class to the DI after the Startup class has ran.

[Route("api/v1/test")]
public class TestController : Microsoft.AspNetCore.Mvc.Controller
{
  private readonly IServiceCollection _services;

  public TestController(IServiceCollection services)
  {
    _services = services;

    var myInterface = HttpContext.RequestServices.GetService<IMyInterface>();
    if (myInterface == null)
    {
      //check if dll exist and load it
      //....
      var implementation = new ForeignClassFromExternalDll();
      _services.AddSingleton<IMyInterface>(implementation);
    }
  }

  [HttpGet]
  public IActionResult Test()
  {
    var myInterface = HttpContext.RequestServices.GetService<IMyInterface>();
    return Json(myInterface.DoSomething());
  }
}

public interface IMyInterface { /* ... */ }

public class ForeignClassFromExternalDll : IMyInterface { /* ... */ }

The Service was successfully added to the IServiceCollection, but the change is not persisted yet to HttpContext.RequestServices even after multiple calls the service count increases each time but I don't get the reference by the IServiceProvider.

Now my question is: Is that possible to achieve and yes how. Or should I rather not do that?

Answer 1

Is it possible to modify the IServiceProvider after the Startup has ran?

Short answer: No.

Once IServiceCollection.BuildServiceProvider() has been invoked, any changes to the collection has no effect on the built provider.

Use a factory delegate to defer the loading of the external implementation but this has to be done at start up like the rest of registration.

services.AddSingleton<IMyInterface>(_ => {
    //check if dll exist and load it
    //....
    var implementation = new ForeignClassFromExternalDll();
    return implementation;
});

You can now explicitly inject your interface into the controller constructor

private readonly IMyInterface myInterface;

public MyController(IMyInterface myInterface) {
    this.myInterface = myInterface;
}

[HttpGet]
public IActionResult MyAction() {
    return Json(myInterface.DoSomething());
}

and the load dll logic will be invoked when that interface is being resolved as the controller is resolved.