Intro
OWIN (Open Web Interface for .NET) is a standard for an interface between .NET Web applications and Web servers. Nancy is lightweight framework for building HTTP based services on .NET. This post will contain two main points, first creating simple OWIN pipline, and second implementing Nancy on top of it.
Creating simple OWIN pipeline
To make this as simple as we can, we will use ASP.NET empty template. The empty template comes with a bare minimum dependencies and web.config. In order for this to be OWIN-based application we need to add some references, specifically OWIN server so we can host it in IIS.
Install Microsoft.Owin.Host.SystemWeb from NuGet.
Install-Package Microsoft.Owin.Host.SystemWeb
Now in order to make our application to be OWIN-application we need to have startup class to serve as entry point in the pipeline. We have few approaches of connecting the startup class with the runtime:
- Naming Convention: just create Startup class in base of the project with namespace that matches assembly name or the global namespace.
- OwinStartup Attribute: create class with any name and add OwinStartup attribute to it, where type is the namespace of our class.
[assembly: OwinStartup(typeof(TestProject.Startup2))] - appSettings: add new key owin:appStartup in appSettings section and set the value to the namespace of the class i.e:
<add key="owin:appStartup" value="TestProject.Startup2" />
I will use the first approach with naming convention.
Now that we are connected with the runtime, we will need a way to configure OWIN pipeline and register new middleware. OWIN makes this possible with method called Configuration(IAppBuilder) that we need to implement in our Startup class.
// Startup.cs
namespace TestEmpty {
public class Startup {
public void Configuration(IAppBuilder app) {
}
}
}
We will register simple middleware that will return simple Hello World! message for every request.
// context: IOwinContext with request and response fields
// next: AppFunc with next middleware that should be executed
app.Use((context, next) => { return context.Response.WriteAsync("Hello World!"); });
Now if we run our application we will receive Hello World! message in the browser.
Adding Nancy to our OWIN application
Nancy doesn’t have any dependencies on existing frameworks so we will need to reference Nancy and also Nancy.Owin so we can register it as OWIN middleware.
Installing Nancy
We can install Nancy.Owin package and it will automatically install Nancy as a dependency.
Install-Package Nancy.Owin
Creating modules
Modules are the lynchpin of any given Nancy application. Create folder named Modules, and create new class, i.e. TestModule class. In order for Nancy to recognize our class as a valid Nancy module we need to declare it public and inherit from NancyModule. Now we need to define what routes this module will handle.
public class TestModule : NancyModule {
public TestModule() {
Get["/test"] = parameters => "Hello World from Nancy!";
}
}
Now if we run our application we will see Hello World! insted of Hello World from Nancy! this is because we didn’t register Nancy in the OWIN pipeline. Nancy provides very simple helper method UseNancy that we can put in our Startup class in the configuration.
public class Startup {
public void Configuration(IAppBuilder app) {
app.UseNancy();
app.Use((context, next) => { return context.Response.WriteAsync("Hello World!"); });
}
}
Now if we run our project, and go to the defined route localhost:35641/test we will receive our message from Nancy. But now if we try to go on another route we will get 404 - NotFound this is because Nancy collects every request and stops executing other middleware that comes after, and if there is no route defined in any of the modules we get 404 error. But luckily there are few options to let request through Nancy into other middleware.
Mapping specific route to Nancy
We can map Nancy middleware to be executed only on specific route.
public class Startup {
public void Configuration(IAppBuilder app) {
// Every request that comes to /nfx will be handled with Nancy
app.Map("/nfx", mapped => { mapped.UseNancy(); });
app.Use((context, next) => { return context.Response.WriteAsync("Hello World!"); });
}
}
Using PassThroughWhenStatusCodesAre from Nancy.Owin
We can use PassThroughWhenStatusCodesAre function from Nancy.Owin.
public class Startup {
public void Configuration(IAppBuilder app) {
// this will let every request through if Nancy returns
// Not Found (404) status for that route
app.UseNancy(conf => { conf.PassThroughWhenStatusCodesAre(Nancy.HttpStatusCode.NotFound); });
app.Use((context, next) => { return context.Response.WriteAsync("Hello World!"); });
}
}