WCF Zero-Config in .NET 3.5! (Part I)

WCF configuration is, in my mind, the biggest misstep made within WCF (prior to .NET 4.0), compared to ASMX web services. For someone getting starting with web services, their first steps should “just work”. My early successes with ASMX web services allowed me to build confidence. WCF, on the other hand, forces one to immediately deal with System.ServiceModel XML configuration hell. This can scare developers away, especially with the incredibly configurable and extensible WCF. Fortunately .NET 4.0 does allow zero-config WCF, but what about .NET 3.5? This post shows part of how to accomplish this within ASP.NET.

I don’t want to advocate config-less use of WCF in production, but it is sure convenient to have this available in testing. When I first worked with WCF, I was not aware of the WCF Service Configuration Tool (SvcConfigEditor.exe) which has a GUI to more safely edit the System.ServiceModel part of a config file. This caused a lot of teeth-gnashing indeed.

The first big step to making WCF just work was POCO (plain old CLR object) support added to .NET 3.5 SP1. This brings back the ASMX default serialization of including all public fields and properties in a class for serialization. In WCF before 3.5 SP1, a class would have the DataContract attribute applied to it.

In this post I explain how to use a custom ServiceHost and ServiceHostFactory to automatically add HTTP-based metadata exchange (MEX) support for any given service hosted within ASP.NET. This code is reuseable, requiring only the Factory attribute to be added to the service directive line in the .svc. The .svc Factory refers to a custom service host factory. The custom factory simply has code to reference the custom ServiceHost.

The ServiceHost class inherits from the default ServiceHost class. It calls the base class for all functionality and then adds the mex-specific logic. Identifying which extensibility hook is needed is the hard part. From there it simply a matter of mirroring the config file entries to enable mex with programmatic setup. As with the config file, a behavior must be added to set HttpGetEnabled = “true” and add a Mex Endpoint to the service. Note that this example covers HTTP based metadata exchange, not HTTPS, although the concepts are similar.

Step 1: Add the ServiceHost and ServiceHostFactory to a new file within your web site.

 Imports System.Collections  
 Imports System.Collections.Generic  
 Imports System.ServiceModel.Channels  
 Imports System.ServiceModel.Description  
 Imports System.ServiceModel.Dispatcher  
 Imports System.Xml.Schema  
 Imports ServiceDescription = System.Web.Services.Description.ServiceDescription  
 Imports System.ServiceModel.Activation  
 Public Class AutoMexServiceHost  
   Inherits ServiceHost  
   Public Sub New()  
     ConditionallyAddMexEndpoint()  
   End Sub  
   Public Sub ConditionallyAddMexEndpoint()  
     Dim mb As ServiceMetadataBehavior  
     mb = Me.Description.Behaviors.Find(Of ServiceMetadataBehavior)()  
     If (mb Is Nothing) Then  
       mb = New ServiceMetadataBehavior()  
       mb.HttpGetEnabled = True  
       Me.Description.Behaviors.Add(mb)  
       Me.AddServiceEndpoint(ServiceMetadataBehavior.MexContractName, _  
             MetadataExchangeBindings.CreateMexHttpBinding(), _  
             "mex")  
     End If  
   End Sub  
   Public Sub New(ByVal serviceType As Type, ByVal ParamArray baseAddresses As Uri())  
     MyBase.New(serviceType, baseAddresses)  
     ConditionallyAddMexEndpoint()  
   End Sub  
   Public Sub New(ByVal singletonInstance As Object, ByVal ParamArray baseAddresses As Uri())  
     MyBase.New(singletonInstance, baseAddresses)  
     ConditionallyAddMexEndpoint()  
   End Sub  
 End Class  
 Public NotInheritable Class AutoMexServiceHostFactory  
   Inherits ServiceHostFactory  
   Public Overrides Function CreateServiceHost(ByVal constructorString As String, ByVal baseAddresses As Uri()) As ServiceHostBase  
     Return MyBase.CreateServiceHost(constructorString, baseAddresses)  
   End Function  
   Protected Overrides Function CreateServiceHost(ByVal serviceType As Type, ByVal baseAddresses As Uri()) As ServiceHost  
     Return New AutoMexServiceHost(serviceType, baseAddresses)  
   End Function  
 End Class  

Step 2: Add Factory to your existing .svc file
For example,

<%@ ServiceHost Language="VB" Debug="true" Service="WcfNoodler.Service1" CodeBehind="Service1.svc.vb" Factory="WcfNoodler.AutoMexServiceHostFactory"%>