Question

Consider the following very basic WCF service implementation:

public enum TransactionStatus 
{
    Success = 0,
    Error = 1
}

public class TransactionResponse
{
    public TransactionStatus Status { get; set; }
    public string Message { get; set; }
}


[ServiceContract]
[XmlSerializerFormat]
public interface ITestService
{
    [OperationContract]
    TransactionResponse DoSomething(string data);
}   

public class TestService : ITestService
{
    public TransactionResponse DoSomething(string data)
    {
        var result = ProcessData(data); // may throw InvalidOperationException
        return new TransactionResponse() 
        {
            Status = TransactionStatus.Success,
            Message = result                
        };            
    }

    private string ProcessData(string data) 
    {
        if (data = "foobar")
            throw new InvalidOperationException();

        return data;        
    }        
}

In the instance that the DoSomething method does throw an InvalidOperationException, I would like to intercept the fault and return a TransactionResponse object, rather than have WCF raise a FaultException with the client. How can I do this without surrounding each method body in a huge try catch statement? Is there some where I can hook into? Can I do this with some sort of attribute or something? An example of how I would like to handle it can be demonstrated using ASP.NET MVC:

public class ApiController : BaseController
{
    protected override void OnException(ExceptionContext filterContext)
    {
        var ex = filterContext.Exception;
        var message = HttpContext.IsDebuggingEnabled ? ex.ToString() : ex.Message;

        _logger.Error("Error processing request for controller {0}, action {1}",
            filterContext.RequestContext.RouteData.Values["controller"],
            filterContext.RequestContext.RouteData.Values["action"]);

        _logger.Error(ex.ToString());
        filterContext.ExceptionHandled = true;
        filterContext.Result = ToXml(new ApiResult(false)
        {
            Message = message
        });
    }

    // ...
}

Using the above method in MVC, I can ensure that no matter which controller action throws an exception, I can handle it and return an appropriately formatted ActionResult containing the necessary info. Is there a way to do this kind of thing with WCF?

Answer 1

Check out the WCF IErrorHandler interface – it allows you to centrally define one way in your service implementation to catch all exceptions and either swallow them, or convert them to WCF-friendly SOAP exceptions. This will make sure the channel between the client and the server isn’t faulted, e.g. it can still be used after this call failed.

I don’t understand why you’d want to “catch” the SOAP faults and convert those to something else, though…. nor do I know of any support that WCF would give you. The basic assumption is: catch .NET exceptions and convert them into interoperable SOAP faults