Fileless Activation of WCF Service in .NET 4.0

Every WCF service needs to have a host process.It can be a windows service,IIS or any other .NET program.This host process will create an instance of the System.ServiceModel.ServiceHost class or any custom class deriving from System.ServiceModel.ServiceHostBase.This host class will manage the service configurations, behaviors, channels and make it accessible to the outside world.When a service is hosted in IIS it behaves a little bit differently.Here we need to create a physical file with .svc extension in the virtual directory of the web server.This file actually points to the service class implementing the ServiceContract and System.ServiceModel.Activation.ServiceHostFactory or a derived class System.ServiceModel.Activation.ServiceHostFactoryBase.When IIS receives a request with that .svc file in URI the corresponding ServiceHostFactory creates an instance of the ServiceHost.The markup contained in a .svc file is shown below:

<%@ ServiceHost Language="C#" Debug="true" Factory="System.ServiceModel.Activation.ServiceHostFactory" Service="ServiceRouting.TestService" CodeBehind="TestService.svc.cs" %>

In WCF 4.0 we can create and deploy services in IIS without a physical file in the virtual directory.This can be done using the serviceActivations configuration in the system.serviceModel configuration in web.config as shown below.

<serviceHostingEnvironment >
  <serviceActivations>
    <add factory="System.ServiceModel.Activation.ServiceHostFactory" relativeAddress="./Test.svc" service="ServiceRouting.TestService"/>
  </serviceActivations>
</serviceHostingEnvironment> 

There is no physical file named Test.svc but still I am able to access the service at http://localhost:1182/Test.svc. This is the new Fileless Activation feature introduced in .NET 4.0.

Here we can see that in the relative address we still have to use an extension (here I have used the good old .svc).Going by the design philosophy of REST I will prefer to have the URI as http://localhost:1182/Test .So what happens if I change the relativeAddress attribute to “./Test”.We will get the exception as shown below:

The registered relativeAddress ‘./Test’ under section ‘system.serviceModel/serviceHostingEnvironment/serviceActivations’ in configuration file does not have an extension.

This can be done in a different way using the ASP.NET Routing features provided by the classes in System.Web.Routing namespace.This routing feature was initially introduced with ASP.NET MVC and later was extended to support ASP.NET WebForms as well.Now in .NET 4.0 we have the System.ServiceModel.Activation.ServiceRoute class which allows us to integrate this routing feature with IIS hosted WCF services.To enable this feature we need to do the following:

• Add module and handler reference as shown below:
• IIS 6.0 –

<httpModules>
                        <add name="UrlRoutingModule" type="System.Web.Routing.UrlRoutingModule, System.Web, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a" />
 </httpModules> 

• II7.0

<system.webServer>
  <modules runAllManagedModulesForAllRequests="true">
    <add name="UrlRoutingModule" type="System.Web.Routing.UrlRoutingModule, System.Web, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a" />
  </modules> 

  <handlers>
    <add name="UrlRoutingHandler" preCondition="integratedMode" verb="*" path="UrlRouting.axd"/>
  </handlers> 

</system.webServer>

• Enable ASP.NET Compatibility mode by adding the aspNetCompatibilityEnabled attribute in web.config as shown below.

<serviceHostingEnvironment aspNetCompatibilityEnabled="true" / >

• Add the AspNetCompatibilityRequirements attribute in the service class as shown below:

    [AspNetCompatibilityRequirements(RequirementsMode=AspNetCompatibilityRequirementsMode.Allowed)]
    public class TestService : ITestService
    {
        ///.................
    }

• Register the routes in Application_Start event in the Global.asax.cs file as shown below:

RouteTable.Routes.Add(new ServiceRoute("test", new ServiceHostFactory(), typeof(TestService)));

The constructor of ServiceRoute class accepts three parameters:

• Url Prefix or pattern
• An instance of ServiceHostFactoryBase class or it’s sub classes.
• The type of the class implementing the Service.

It stores this information in an internal cache and uses it later for service activation.

Now we can access the service as http://localhost:1182/test