Proper catching of specific exceptions through web service

Question

I am currently using a C# .NET Service in our client program. As part of the server design, several custom made exceptions are thrown to indicate specific errors (as in any

Answer 1

The proper way would be to define fault contracts. For example in your web service you could do the following:

[DataContract]
public class NoRoomsAvailableFaultContract
{
    [DataMember]
    public string Message { get; set; }
}

Next you declare this contract for a given service operation

[ServiceContract]
public interface IMyServiceContract
{
    [OperationContract]
    [FaultContract(typeof(NoRoomsAvailableFaultContract))]
    void MyOperation();
}

And you implement it like so:

public class MyService : IMyServiceContract 
{
    public void MyOperation()
    {
        if (somethingWentWrong)
        {
            var faultContract = new NoRoomsAvailableFaultContract()
            {
                Message = "ERROR MESSAGE"
            };
            throw new FaultException<NoRoomsAvailableFaultContract>(faultContract);
        }
    }
}

In this case the NoRoomsAvailableFaultContract will be exposed in the WSDL and svcutil.exe could generate a proxy class. Then you could catch this exception:

try
{
    myServiceProxy.MyOperation();
}
catch (FaultException<NoRoomsAvailableFaultContract> ex)
{
    Console.WriteLine(ex.Message);
}

Answer 2

darin has the correct answer. I'll only say explicitly what he implies: web services do not pass exceptions. They return SOAP Faults. If you define your faults properly, as he does, then you get to throw FaultException<fault>. This will become a SOAP Fault with fault in the detail element. In the case of a .NET client, this will then be turned into a FaultException<fault>, which you can catch.

Other platforms may handle this somewhat differently. I've seen IBM's Rational Web Developer generate Java proxy code that creates a separate exception for each declared fault. That was a version before Java generics, so maybe by now it does the same thing as .NET does.