Open Web Interface for .NET (OWIN)

ASP.NET Core supports the Open Web Interface for .NET (OWIN). OWIN allows web apps to be decoupled from web servers. It defines a standard way for middleware to be used in a pipeline to handle requests and associated responses. ASP.NET Core applications and middleware can interoperate with OWIN-based applications, servers, and middleware.

Use OWIN

ASP.NET Core's OWIN support is deployed as part of the Microsoft.AspNetCore.Owin package.

OWIN middleware conforms to the OWIN specification, which requires a Func<IDictionary<string, object>, Task> interface, and specific keys be set (such as owin.ResponseBody).

public Task OwinHello(IDictionary<string, object> environment)
{
    string responseText = "Hello World via OWIN";
    byte[] responseBytes = Encoding.UTF8.GetBytes(responseText);

    // OWIN Environment Keys: https://owin.org/spec/spec/owin-1.0.0.html
    var responseStream = (Stream)environment["owin.ResponseBody"];
    var responseHeaders = (IDictionary<string, string[]>)environment["owin.ResponseHeaders"];

    responseHeaders["Content-Length"] = new string[] { responseBytes.Length.ToString(CultureInfo.InvariantCulture) };
    responseHeaders["Content-Type"] = new string[] { "text/plain" };

    return responseStream.WriteAsync(responseBytes, 0, responseBytes.Length);
}

To add the OwinHello middleware (shown above) to the ASP.NET Core pipeline use the UseOwin extension method:

public void Configure(IApplicationBuilder app)
{
    app.UseOwin(pipeline =>
    {
        pipeline(next => OwinHello);
    });
}

OWIN-based servers can host ASP.NET Core apps. One such server is Nowin, a .NET OWIN web server:

services.AddSingleton<IServer, NowinServer>();