Fault Exceptions in WCF

Exceptions thrown by WCF service are treated as Fault exceptions. As a developer we should gracefully handle these kind of exceptions. Let's take a look at this by an example/

Service Contract -

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[ServiceContract] public interface IService2 { [OperationContract] [FaultContract(typeof(MyException))] [DebuggerStepThrough] MyException GetData(int value); } [DataContract] public class MyException { [DataMember] public bool Result { get; set; } [DataMember] public string ErrorMessage { get; set; } [DataMember] public Exception MyInnerException { get; set; } [DataMember] public string ClientMessage { get; set; } }

Service Implementation -

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public class Service1 : IService2 { public MyException GetData(int value) { MyException mx = new MyException(); try { double a = 44; if (value == 0) { throw new DivideByZeroException(); } double res = a / value; mx.ClientMessage = "Everything is well"; mx.Result = true; return mx; } catch (DivideByZeroException dvex) { mx.Result = true; mx.ClientMessage = "Divide by zero"; mx.MyInnerException = dvex; mx.ErrorMessage = dvex.StackTrace; throw new FaultException<MyException>(mx, dvex.ToString()); } } }

Client (aspx.cs page) -

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try { FaultContractsDemo.ServiceReference1.Service2Client o = new ServiceReference1.Service2Client(); MyException data = o.GetData(0); if (data.Result) lblMessage.Text = "All is well"; } catch (FaultException<MyException> ex) { lblMessage.Text = ex.Detail.ClientMessage; }

The service layer throws an exception, but client never recieves any. I am getting unhandled exception like,

The underlying connection was closed: The connection was closed unexpectedly.

 WCF does not like serializing the DivideByZeroException or any root exception caused at service layer, which is necessary to get it across the wire. Commenting out this would work as expected.

Can multiple catch blocks be executed ?

One of my acquaintance asked this question. Initially I got confused that is it really possible.
The answer to this question is "NO". Here is a program in support with this answer.

    class Program
    {
        static void Main(string[] args)
        {
            try
            {
                int numerator = 20;
                int denominator = 0;
                int result = numerator / denominator;
            }
            catch (DivideByZeroException de)
            {
                Console.WriteLine("You are trying to divide by number 0");
            }
            catch (Exception ex)
            {
                Console.WriteLine("This is a general exception.");
            }
            finally
            {
                Console.WriteLine("You are in finally block.");
            }
        }
    }

The output of this program is;
You are trying to divide by number 0
You are in finally block.

This means that when an exception occurs, and is handled with the specific type it executes the statements in the catch block and leaves the control to finally block, if exists.

It is not possible to execute multiple catch blocks.

Returning from finally

Can we return from finally block? If your answer is yes, take a look at this code.
We have a function body as ;

try
{  
   return "From try"; 
}
catch (Exception ex)
{ 
   return "From Catch"; 
}
finally
{
   return "From Finally"; 
}

If this is enclosed in a function and we are giving call to the function,

what will be the return value of this statement?

And the answer is, it will give a compilation error, as we cannot return from finally block.