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Authored an e-book named “ASP.NET Web Forms Cheat Sheet”
OWIN stands for Open Web Interface for .NET that decouples the Web Application from Web Server through an interface. In this article I will try to show some basic example of creating custom OWIN middle ware component and using it in self-host console application. The idea is to clarify the working of OWIN and what we can achieve with this new paradigm.
OWIN classifies web application into 4 parts
| ASP.Net MVC web application | Fully OWIN compatible web applications | |
| Host | IIS | Any application Console App, Windows Service, IIS etc. |
| Server | IIS | An application that hooks up the HTTP Listener to listen for a request. |
| Middleware | IHTTP Modules | OWIN Middleware |
| Application | ASP.NET MVC 5 in IIS | ASP.NET vNext, Web API 2 etc. |
How is the request processed by OWIN Host?
When the request comes in to the OWIN server, the request properties like query string, path, content type, and so many others added into the IDictionary<string, object> object. This dictionary object is then sent to the request pipeline and then middleware components in the request pipeline can use this dictionary object and process accordingly.
OWIN expose following interface
System.Func<System.Collections.Generic.IDictionary<string, object>, System.Threading.Tasks.Task>;
Func is a new way of defining delegates in .NET framework. The first parameter denotes the input parameter and second as a return parameter. Here we have IDictionary<string,object> as input and Task as the resultant output.
When the request comes to the server, OWIN host calls the Invoke method of all the middleware components defined in order and pass the dictionary object. Each middleware component gets the complete request properties as dictionary object.
Startup.cs class is an entry point to build the request pipeline. In the Startup class, Configuration method is mandatory that takes IAppBuilder as a parameter. Using IAppBuilder you can add the OWIN based middleware and define the request pipeline. Developers can develop their own pipeline for incoming request. In IIS there are many components configured through which the request is passed through and for simple or mid-sized applications that seems to be an overkill. With OWIN based host it is quite easy to use only those OWIN extensions or middleware components that are required for your web application.
In order to elaborate, let’s create a simple OWIN middleware that logs the incoming request message into the console application and host the OWIN server in console application itself.
public void Configuration(IAppBuilder app){ }
7. Now let’s create a custom logging component to log incoming HTTP Request
public class LoggingMiddleware
{
private AppFunc appFunc;
public LoggingMiddleware(System.Func<System.Collections.Generic.IDictionary<string, object>, System.Threading.Tasks.Task> func)
{
this.appFunc = func;
}
public async Task Invoke(IDictionary<string,object> env)
{
Console.WriteLine(“Request method is “+ env[“owin.RequestMethod”]);
var task = appFunc.Invoke(env);
}
}
8. Add this logging middleware in the configuration method using IAppBuilder use method
public void Configuration(IAppBuilder app)
{
app.Use<LoggingMiddleware>();
}
9. In the Main method of console app start the server using following WebApp.Start
Microsoft.Owin.Hosting.WebApp.Start<Startup>(“http://localhost:12345”);
Console.ReadLine();
Following is a complete code
public class Startup
{
public void Configuration(IAppBuilder app)
{
app.Use<LoggingMiddleware>();
}
}
public class LoggingMiddleware
{
private AppFunc appFunc;
public LoggingMiddleware(System.Func<System.Collections.Generic.IDictionary<string, object>, System.Threading.Tasks.Task> func)
{
this.appFunc = func;
}
public async Task Invoke(IDictionary<string,object> env)
{
Console.WriteLine(“Request method is “+ env[“owin.RequestMethod”]);
var task = appFunc.Invoke(env);
}
}
class Program
{
static void Main()
{
Microsoft.Owin.Hosting.WebApp.Start<Startup>(“http://localhost:12345”);
Console.ReadLine();
}
}
}
10. Now run the application and access the URL http://localhost:5555
11. You will see the logging on your console app.
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