Wcf async pattern doesn't throw Fault Exception - wcf

Question

I have a service that implement the Async pattern:
[OperationContract(AsyncPattern = true)]
IAsyncResult BeginLoadDocument(Byte[] value, AsyncCallback callback, object state);
Boolean EndLoadDocument(IAsyncResult asyncResult);
The "BeginLoadDocument" run a private method "CallBack" in the service side using a ThreadPool:
public IAsyncResult BeginLoadDocument(string id, AsyncCallback callback, object state)
{
PendingAsyncResult<string> asyncResult =
new PendingAsyncResult<string>(id, callback, state);
ThreadPool.QueueUserWorkItem(new WaitCallback(Callback), asyncResult);
return asyncResult;
}
the Callback method load the document and set the result for the "EndLoadDocument".
So far so good, but how I can handle the exceptions?
If I throw an excetion in the server side, I get a FaultedException'1 wasn't handled.
I did try to use the attribute [FaultContract(typeof(InforError))] where "InfoError" is my custum DataMember, but it does not work.
I am building the proxy using the svcutil /a http:....

Answer 1

You can catch an exception client-side as follows:
try {
MyClient.MyCall();
}
catch (FaultException<IOException> exc) {
// Log and handle exception
}
Where the real exception thrown was, in this example, an IOException.
You'll also need a FaultContract, as you indicated you are, on the Service Interface, as such:
[ServiceContract]
public interface IMyService {
[OperationContract]
[FaultContract(typeof(IOException))]
void MyCall();
}
**** EDIT ****
I'm a little fuzzy on something you wrote:
[FaultContract(typeof(InforError))] where "InfoError" is my custum DataMember
What do you mean by 'DataMember'? What's the definition for InfoError?
The [FaultContract] should be defined on the service interface method... in your post you sound like you're trying to add it to the client side; this is not correct. If I modify your example code, it would look like:
[ServiceContract]
public interface IMyService {
[OperationContract(AsyncPattern = true)]
[FaultContract(typeof(InfoErrorException))]
IAsyncResult BeginLoadDocument(Byte[] value, AsyncCallback callback, object state);
string EndLoadDocument(IAsyncResult asyncResult);
If your service interface is decorated as such, the client should be able to receive FaultExceptions when you call EndLoadDocument (provided the exception that was thrown was an InfoErrorException exception).
On the server side, you have to trap exceptions, then wrap them in a FaultException, as such:
catch (IOException exp) {
InfoErrorException myException = new InfoErrorException();
myException.Reason = "I failed: " + exp.Message;
throw new FaultException<InfoErrorException>(myException);
}
I believe (but would have to double-check) that you can also catch a FaultException on the client side without specifying the type... similar to catching the generic System.Exception.
Your try...catch for the FaultException should be in your callback, around the statement to call EndLoadDocument().

Answer 2

Looks like you are using Silverlight.
Problem is that WCF service returns HTTP Status different to 200, so browser do not provide additional data about response to Silverlight Runtime.
The solution is to use custom ErrorHandler to provide necessary HTTP Code:
/// <summary>Sets the HTTP code to 200 for faults.</summary>
public class HttpStatusCode200ErrorHandler : IErrorHandler
{
public Type ServiceType { get; set; }
public HttpStatusCode200ErrorHandler(Type serviceType)
{
ServiceType = serviceType;
}
public bool HandleError(Exception error)
{
return false;
}
public virtual void ProvideFault(Exception error, MessageVersion version, ref Message fault)
{
fault.Properties[HttpResponseMessageProperty.Name] =
new HttpResponseMessageProperty { StatusCode = System.Net.HttpStatusCode.OK };
}
}
You can attach it to your service using following ServiceBehavior attribute:
/// <summary>Applies HttpStatusCode200ErrorHandler.</summary>
[AttributeUsage(AttributeTargets.Class)]
public class HttpStatusCode200BehaviorAttribute : Attribute, IServiceBehavior
{
public void AddBindingParameters(ServiceDescription serviceDescription, ServiceHostBase serviceHostBase, System.Collections.ObjectModel.Collection<ServiceEndpoint> endpoints, System.ServiceModel.Channels.BindingParameterCollection bindingParameters)
{
}
public void ApplyDispatchBehavior(ServiceDescription serviceDescription, ServiceHostBase serviceHostBase)
{
foreach (ChannelDispatcher dispatcher in serviceHostBase.ChannelDispatchers)
{
dispatcher.ErrorHandlers.Add(new HttpStatusCode200ErrorHandler(serviceDescription.ServiceType));
}
}
public void Validate(ServiceDescription serviceDescription, ServiceHostBase serviceHostBase)
{
}
}
For more details look at Understanding WCF Faults in Silverlight.