Question

I just noticed something particular. I have an internal stock service which is published through basicHttpBinding, and a customBinding (http+binary) for which metadata is enabled. I also included a mex endpoint for http. We use Visual Studio 2008 & VB.NET

Just recently we noticed that we were unable to succesfully add a service reference to this service in our other projects. All that it would generate was the first custom exception we included through a FaultContract (actually, there was only 1 type). if I’d add a simple web reference it would work correctly as well. Also, the WcfClient.exe had no problems either in loading the services. Just VS.NET add service reference wouldn’t work.

In the service this exception inherits from Exception and is marked as serializable. That’s all you’re supposed to do, no?

Anyway, this had me baffled. If I remove the FaultContract for this custom exception everything works fine. I can add a service reference, no problem. But is there a way I can still have my custom exceptions? Is this a known problem?

Answer 1

I ran into this myself today. The solution was to use an object not inheriting from Exception in the FaultContract. If you look at the MSDN docs for FaultException and FaultContract you will see that the official examples use plain classes (with DataContact attributes) rather than classes extending Exception for FaultException.Detail. I’m not sure why Exception causes the Add Service Reference to fail, but I suspect it has to do with the serializing or retrieving the type information for custom exceptions. I have included before and after example implementations to demonstrate the working approach.

Before (didn’t work):

[ServiceContract]
public interface IMyService
{
    [OperationContract]
    [FaultContract(typeof(MyException))]
    MyResults MyServiceOperation(string myParameter);
}

[Serializable]
public class MyException : Exception
{
    public string CustomData { get; set; }
}

[ErrorHandlerBehavior(typeof(MyErrorHandler))]
public class MyService : IMyService
{
    public MyResults MyServiceOperation(string myParameter)
    {
        ...
        throw new MyModelException { CustomData = "42" };
        ...
    }
}

public class MyErrorHandler : IErrorHandler
{
    public bool HandleError(Exception error) { return false; }

    public void ProvideFault(Exception error, MessageVersion version, ref Message fault)
    {
        try { throw error; }
        catch (MyModelException ex)
        {
            var faultEx = new FaultException<MyException>(new MyException { CustomData = ex.CustomData });
            fault = Message.CreateMessage(version, faultEx.CreateMessageFault(), faultEx.Action);
        }
        catch { /* Supress all others */ }
    }
}

After (worked):

[ServiceContract]
public interface IMyService
{
    [OperationContract]
    [FaultContract(typeof(MyFault))]
    MyResults MyServiceOperation(string myParameter);
}

[DataContract]
public class MyFault
{
    [DataMember]
    public string CustomData { get; set; }
}

[ErrorHandlerBehavior(typeof(MyErrorHandler))]
public class MyService : IMyService
{
    public MyResults MyServiceOperation(string myParameter)
    {
        ...
        throw new MyModelException { CustomData = "42" };
        ...
    }
}

public class MyErrorHandler : IErrorHandler
{
    public bool HandleError(Exception error) { return false; }

    public void ProvideFault(Exception error, MessageVersion version, ref Message fault)
    {
        try { throw error; }
        catch (MyModelException ex)
        {
            var faultEx = new FaultException<MyFault>(new MyFault { CustomData = ex.CustomData });
            fault = Message.CreateMessage(version, faultEx.CreateMessageFault(), faultEx.Action);
        }
        catch { /* Supress all others */ }
    }
}

Source: Max Strini for the use of his code and help in finding the solution to this issue.