How to catch a custom FaultException in WCF

Question

I am testing WCF for potentially implementing an API for remote controlling a device that runs our Controller-Software (C#/.Net 4.6.1) on Windows.

I am currently trying to figure out how to throw and catch a FaultException from my service and catch it from a .Net client.

The problem I am having is that when running the code (in Debug-mode on VS 2015), the exception is not caught by the client, but VS ends up showing me the exception inside VS at the code-location of the service (Service.cs), where it is being thrown. The exception message is:

An exception of type 'System.ServiceModel.FaultException`1' occurred in WcfService.dll but was not handled in user code

Additional information: The argument value was not 1

where The argument value was not 1 is the custom message provide by me. Here are the relevant parts of my code. I hope somebody can spot, what I am doing wrong:

IService.cs:

[ServiceContract(CallbackContract = typeof(IMyEvents))]
public interface IService
{
    [OperationContract]
    [FaultContract(typeof(InvalidValueFault))]
    string ThrowsFaultIfArgumentValueIsNotOne(int value);

    ...
}

[DataContract]
public class InvalidValueFault
{
    private string _message;

    public InvalidValueFault(string message)
    {
        _message = message;
    }

    [DataMember]
    public string Message { get { return _message; } set { _message = value; } }
}

Service.cs: [ServiceBehavior(ConcurrencyMode = ConcurrencyMode.Reentrant, InstanceContextMode = InstanceContextMode.Single)] public class Service : IService { private string defaultString;

    public Service(string ctorTestValue)
    {
        this.defaultString = ctorTestValue;
    }

    public string ThrowsFaultIfArgumentValueIsNotOne(int value)
    {
        if (value == 1)
            return string.Format("Passed value was correct: {0}", value);

        // this is where the box with the exception is shown inside Visual Studio
        throw new FaultException<InvalidValueFault>(new InvalidValueFault("The argument value was not 1"), new FaultReason("The argument value was not 1"));
    }

    ...
}

Server.cs: public class Server { private ServiceHost svh; private Service service;

    public Server()
    {
        service = new Service("A fixed ctor test value that the service should return.");
        svh = new ServiceHost(service);
    }

    public void Open(string ipAdress, string port)
    {
        svh.AddServiceEndpoint(
        typeof(IService),
        new NetTcpBinding(),
        "net.tcp://"+ ipAdress + ":" + port);
        svh.Open();
    }

    public void Close()
    {
        svh.Close();
    }
}

Client.cs:

public class Client : IMyEvents
{
    ChannelFactory<IService> scf;
    IService s;

    public void OpenConnection(string ipAddress, string port)
    {
        var binding = new NetTcpBinding();

        scf = new DuplexChannelFactory<IService>(
        new InstanceContext(this),
        binding,
        "net.tcp://" + ipAddress + ":" + port);
        s = scf.CreateChannel();
    }

    public void CloseConnection()
    {
        scf.Close();
    }

    public string ThrowsFaultIfArgumentValueIsNotOne(int value)
    {
        try
        {
            return s.ThrowsFaultIfArgumentValueIsNotOne(value);
        }

        catch (System.ServiceModel.FaultException<InvalidValueFault> fault)
        {
            Console.WriteLine("Exception thrown by ThrowsFaultIfArgumentValueIsNotOne(2):");
            Console.WriteLine("Exception message: " + fault.Message);
            //throw;
            return "Exception happend.";
        }
    }

    ...
}

Program.cs (Test Program using the server and the client):

class Program
{
    static void Main(string[] args)
    {
        // start server
        var server = new Server();
        server.Open("localhost", "6700");
        Console.WriteLine("Server started.");

        var client = new Client();
        client.OpenConnection("localhost", "6700");

        Console.ReadLine();
        Console.WriteLine("Result for client.ThrowsFaultIfArgumentValueIsNotOne(1): {0}", client.ThrowsFaultIfArgumentValueIsNotOne(1));

        Console.ReadLine();
        Console.WriteLine("Result for client.ThrowsFaultIfArgumentValueIsNotOne(2): {0}", client.ThrowsFaultIfArgumentValueIsNotOne(2));

        Console.ReadLine();
        client.CloseConnection();
        Thread.Sleep(1000);
        server.Close();
    }
}

Tomas Smagurauskas Tomas Smagurauskas · Accepted Answer · 2016-09-07T11:56:50

If you generated your SOAP code from wsdl using vs tools then FaultException that is being thrown here is generic FaultException - meaning it is FaultException<fault_contract>. You what generic type exception that is by checking your service reference code and inspecting [System.ServiceModel.FaultContractAttribute()] attribute. This attribute has Type parameter which is you generic type.

So if you it looks something like this

[System.ServiceModel.FaultContractAttribute(typeof(MyFaultContract)]
[System.ServiceModel.OperationContractAttribute(Action = "SoapAction", ReplyAction = "*")]
SoapResponse SoapAction(SoapRequest request);

then your catch clause should look like this

try {
    soapClient.SoapAction(new SoapRequest());
}
catch (FaultException<MyFaultContract> e) {

}

How to catch a custom FaultException in WCF

3 Answers