#Owin

About

OWIN defines a standard interface between .NET web servers and web applications. The goal of the OWIN interface is to decouple server and application, encourage the development of simple modules for .NET web development, and, by being an open standard, stimulate the open source ecosystem of .NET web development tools.

Katana - OWIN implementations for Microsoft servers and frameworks.

What Is Katana?

The seeds of the Katana project were actually sown outside of Microsoft with an open source project called the Open Web Inter­face for .NET (OWIN), a specification that defines the interactions between Web servers and application components (see owin.org). Because the goal of the specification is to stimulate a broad and vibrant ecosystem of Microsoft .NET Framework-based Web servers and application components, it reduces all interactions between servers and applications to a small set of types and a single function signature known as the application delegate, or AppFunc:

using AppFunc = Func<IDictionary<string, object>, Task>;

Every component in an OWIN-based application supplies an application delegate to a server. The components are then chained together into a pipeline into which an OWIN-based server pushes requests. In order to use resources efficiently, all components in the pipeline should be asynchronous, and this is reflected in the application delegate returning a Task object.

All states, including application state, request state, server state and so forth, are held in the IDictionary<string, object> object specified on the application delegate. This data structure, known as the environment dictionary, is passed from component to component as a request progresses through the pipeline. While any key/value data may be inserted into the environment dictionary, the OWIN specification defines keys for some core elements of HTTP.

Katana components can be viewed through the architectural stack depicted in:

The stack consists of the following layers:

• Host: The process that runs the application and can be anything from IIS or a standalone executable, to your own custom program. The host is responsible for startup, loading of other OWIN components and shutting down gracefully.
• Server: Responsible for binding to a TCP port, constructing the environment dictionary and processing requests through an OWIN pipeline.
• Middleware: The name given to all of the components that handle requests in an OWIN pipeline. It can range from a simple compression component to a complete framework such as ASP.NET Web API, though from the server’s perspective, it’s simply a component that exposes the application delegate.
• Application: This is your code. Because Katana is not a replacement for ASP.NET but rather a new way to compose and host components, existing ASP.NET Web API and SignalR applications remain unchanged, as those frameworks can participate in an OWIN pipeline. In fact, for these kinds of applications, Katana components will be visible only in a small configuration class.

Additional Information:

https://msdn.microsoft.com/en-us/magazine/dn451439.aspx

Use OWIN to Self-Host ASP.NET Web API 2:

http://www.asp.net/web-api/overview/hosting-aspnet-web-api/use-owin-to-self-host-web-api