What is OWIN?

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. For more information please visit the official website at http://owin.org/

Katana

Katana is OWIN implementations for Microsoft servers and frameworks.

Katana - ASP.NET Host

Note: Assumes your project is an ASP.NET project with Nancy.dll referenced and without any Nancy.Hosting.xxxxx.dll referenced.

• Install package using Nuget

Install-Package Microsoft.Owin.Host.SystemWeb
Install-Package Nancy.Owin

• Add the following key in web.config. (This is required for the current v1.0.1 for SystemWeb OWIN host and is likely to be removed in future versions.)

<appSettings>
    <add key="owin:HandleAllRequests" value="true"/>
</appSettings>

• Create an OWIN startup file

using Owin;
using Nancy.Owin;

public class Startup
{
    public void Configuration(IAppBuilder app)
    {
        app.UseNancy();
    }
}

Note: You must keep the Startup file‘s namespace the same as your application name or it will return a 403.14 - Forbidden.

• Edit web.config Only if you are using PUT, HEAD or DELETE verbs

<system.webServer>
<handlers>
      <remove name="ExtensionlessUrlHandler-Integrated-4.0" />
      <remove name="OPTIONSVerbHandler" />
      <remove name="TRACEVerbHandler" />
      <add name="ExtensionlessUrlHandler-Integrated-4.0" path="*." verb="*" type="System.Web.Handlers.TransferRequestHandler" preCondition="integratedMode,runtimeVersionv4.0" />
</handlers>
</system.webServer>

NOTE! You might have to perform an extra step to get custom static content conventions and diagnostics to work:

• See Extra steps required when using Microsoft.Owin.Host.SystemWeb

Katana - HttpListener (SelfHost)

• Install packages using NuGet

Install-Package Microsoft.Owin.Hosting
Install-Package Microsoft.Owin.Host.HttpListener
Install-Package Nancy.Owin

• Create an OWIN startup file

using Owin;

public class Startup
{
    public void Configuration(IAppBuilder app)
    {
        app.UseNancy();
    }
}

• Main Entry Point

using Microsoft.Owin.Hosting;

class Program
{
    static void Main(string[] args)
    {
        var url = "http://+:8080";

        using (WebApp.Start<Startup>(url))
        {
            Console.WriteLine("Running on {0}", url);
            Console.WriteLine("Press enter to exit");
            Console.ReadLine();
        }
    }
}

• Run Visual Studio or the compiled executable in admin mode.

Running without Admin mode

Note that on Windows hosts a HttpListenerException may be thrown with an Access Deniedmessage. To resolve this the URL has to be added to the ACL.

On Windows Vista/Server 2008 or later, execute the following in PowerShell or CMD running as administrator:

netsh http add urlacl url=http://+:8080/ user=DOMAIN\username

Replace DOMAIN\username with your domain and username or your computer name and username if you are not joined to a domain. See http://msdn.microsoft.com/en-us/library/ms733768.aspx for more information. You can find the user with whoami command.

You can remove the urlacl using the following command.

netsh http delete urlacl url=http://+:8080/

Also but the port may need to be opened on the machine or corporate firewall to allow access to the service.

Accessing OWIN environment variables

public class HomeModule : NancyModule
{
    public HomeModule()
    {
      Get["/"] = x => {
            var env                 = this.Context.GetOwinEnvironment();

            var requestBody         = (Stream)env["owin.RequestBody"];
            var requestHeaders      = (IDictionary<string, string[]>)env["owin.RequestHeaders"];
            var requestMethod       = (string)env["owin.RequestMethod"];
            var requestPath         = (string)env["owin.RequestPath"];
            var requestPathBase     = (string)env["owin.RequestPathBase"];
            var requestProtocol     = (string)env["owin.RequestProtocol"];
            var requestQueryString  = (string)env["owin.RequestQueryString"];
            var requestScheme       = (string)env["owin.RequestScheme"];

            var responseBody        = (Stream)env["owin.ResponseBody"];
            var responseHeaders     = (IDictionary<string, string[]>)env["owin.ResponseHeaders"];

            var owinVersion         = (string)env["owin.Version"];
            var cancellationToken   = (CancellationToken)env["owin.CallCancelled"];

            var uri = (string)env["owin.RequestScheme"] + "://" + requestHeaders["Host"].First() +
              (string)env["owin.RequestPathBase"] + (string)env["owin.RequestPath"];

            if (env["owin.RequestQueryString"] != "")
              uri += "?" + (string)env["owin.RequestQueryString"];

            return string.Format("{0} {1}", requestMethod, uri);
      };
    }
}

Conditional pass-through

Nancy in an OWIN pipeline is, by default, terminating. That is, when it fails to resolve a handler or static content, it will complete the request and return a 404. Subsequent middleware will not be invoked. For example, given this Startup...

using Owin;

public class Startup
{
    public void Configuration(IAppBuilder app)
    {
        app
          .UseNancy()
          .UseOtherMiddleware();
    }
}

...the Middleware UseOtherMiddleware will never be invoked.

In order to configure Nancy to pass-through, you can supply a delegate that is invoked on a per-request basis, after it has been initially handled by Nancy:

using Owin;
using Nancy;

public class Startup
{
    public void Configuration(IAppBuilder app)
    {
        app
          .UseNancy(options =>
              options.PerformPassThrough = context =>
                  context.Response.StatusCode == HttpStatusCode.NotFound)
          .UseOtherMiddleware();
    }
}

Here, when Nancy is responding with a 404, the request is passed-through to UseOtherMiddlewareand Nancy‘s response (any headers and body) is discarded.

There is also an extension helper make it more succinct if you are just dealing with StatusCodes for pass-through:

using Owin;
using Nancy;

// Needed to use extension helper.
using Nancy.Owin;

public class Startup
{
    public void Configuration(IAppBuilder app)
    {
        app
          .UseNancy(options => options.PassThroughWhenStatusCodesAre(
              HttpStatusCode.NotFound,
              HttpStatusCode.InternalServerError))
          .UseOtherMiddleware();
    }
}

Extra steps required when usingMicrosoft.Owin.Host.SystemWeb

When you are hosting Nancy using Microsoft.Owin.Host.SystemWeb you need some additional configuration to get it working in IIS.

First of all, in your OWIN Startup.cs you will need to addapp.UseStageMarker(PipelineStage.MapHandler), for example:

using Microsoft.Owin.Extensions;
using Owin;

public class Startup
{
    public void Configuration(IAppBuilder app)
    {
        app.UseNancy();
        app.UseStageMarker(PipelineStage.MapHandler);
    }
}

You will also have to add the following to your Web.config:

<system.webServer>
    <modules runAllManagedModulesForAllRequests="true" />
</system.webServer>

Without this additional configuration, the StaticFileModule from OWIN would intercept the request and return a 404.