adapters.md

System.Web Adapters

The main use case of the adapters in this repo is to help developers who have taken a reliance on System.Web types within their class libraries as they want to move to ASP.NET Core.

Let's take a look at an example using the proposed adapters moving from .NET Framework to ASP.NET Core.

ASP.NET Framework

Consider a controller that does something such as:

public class SomeController : Controller
{
  public ActionResult Index()
  {
    SomeOtherClass.SomeMethod(HttpContext.Current);
  }
}

which then has logic in a separate assembly passing that HttpContext around until finally, some inner method does some logic on it such as:

public class Class2
{
  public bool PerformSomeCheck(HttpContext context)
  {
    return context.Request.Headers["SomeHeader"] == "ExpectedValue";
  }
}

ASP.NET Core

In order to run the above logic in ASP.NET Core, a developer will need to add the Microsoft.AspNetCore.SystemWebAdapters package, that will enable the projects to work on both platforms.

The libraries would need to be updated to understand the adapters, but it will be as simple as adding the package and recompiling. If these are the only dependencies a system has on System.Web.dll, then the libraries will be able to target .NET Standard to facilitate a simpler building process while migrating.

The controller in ASP.NET Core will now look like this:

public class SomeController : Controller
{
  [Route("/")]
  public IActionResult Index()
  {
    SomeOtherClass.SomeMethod(Context);
  }
}

Notice that since there's a Controller.Context property, they can pass that through, but it generally looks the same. Using implicit conversions, the Microsoft.AspNetCore.Http.HttpContext can be converted into the adapter that could then be passed around through the levels utilizing the code in the same way.