Mark an operation with the FaultContractAttribute attribute to declare one or more specific exception conditions that are added to the Web Service Description Language (WSDL) description of the service operation as explicit SOAP fault messages returned by the operation.

In all managed applications, processing errors are represented by Exception objects. In SOAP-based applications such as Windows Communication Foundation (WCF) applications, service methods communicate processing error information using SOAP fault messages. Because WCF applications execute under both types of error systems, any managed exception information that must be sent to the client must be converted from exceptions into SOAP faults. You can use the default service exception behaviors, or you can explicitly control whether -- and how -- exceptions are mapped to fault messages. For an overview of exceptions and SOAP faults in WCF applications, see Specifying and Handling Faults in Contracts and Services.

It is recommended that service operations use the FaultContractAttribute to formally specify all SOAP faults that a client can expect to receive in the normal course of an operation. It is also recommended that only that information a client must know is returned in a SOAP fault to minimize information disclosure.

• The Action property controls the action of the fault message.

• The DetailType property gets the type of the detail object serialized in the fault message.

• The Name and Namespace properties control the name and namespace, respectively, of the fault message.

• The HasProtectionLevel indicates whether the fault message has a protection level specified, and if so, the ProtectionLevel property controls that level of protection.

Caution:
If a fault message carries information that is sensitive or can lead to security problems, it is strongly recommended that the ProtectionLevel property be set.

• If you set the ProtectionLevel explicitly to either ProtectionLevel..::.Sign or ProtectionLevel..::.EncryptAndSign, then you must use a binding with security enabled using the System.ServiceModel..::.SecurityMode property on the binding or an exception is thrown.

• If you select a binding that enables security and you do not set the ProtectionLevel property anywhere on the contract, all application data will be encrypted and signed.

• If you select a binding that does not have security enabled (for example, the System.ServiceModel..::.BasicHttpBinding has security disabled by default), and the ProtectionLevel is not explicitly set, then none of the application data will be protected.

For many scenarios setting ProtectionLevel to EncryptAndSign for fault messages is sufficient. For more details, see Understanding Protection Level.

To return a specified fault from an operation marked with FaultContractAttribute, throw a FaultException<(Of <(TDetail>)>) (where the type parameter is the serializable error information) when the managed exception occurs during the operation. WCF client applications surface the SOAP fault as the same type as was thrown in the client implementation -- that is, as a FaultException<(Of <(TDetail>)>) (where the typeparameter is the serializable error information). The FaultContractAttribute can be used only to specify SOAP faults for two-way service operations and for asynchronous operation pairs; one-way operations do not support SOAP faults and therefore do not support FaultContractAttribute.

Note:
You can use any serializable type to convey error information. The only restriction in this version of WCF is that types specified in a FaultContractAttribute must be serializable by the System.Runtime.Serialization..::.DataContractSerializer. For the serialization support the DataContractSerializer provides, see Data Contract Serializer.

For example, to specify that clients can expect a SOAP fault that contains an Int32, place that type parameter in the FaultContractAttribute on your service method.

Note:
The following code examples do not set the ProtectionLevel, Name, or Namespace properties.

  <OperationContractAttribute(), FaultContractAttribute(GetType(Integer))> _
    Function Divide(ByVal arg1 As Integer, ByVal arg2 As Integer) As Integer
End Interface 'FCADemonstration

[OperationContractAttribute]
[FaultContractAttribute(typeof(int))]
int Divide(int arg1, int arg2);

Then, in your service method, throw a new FaultException<(Of <(TDetail>)>) where the type parameter is the type that contains the error information (in the above case, a Int32). For example:

Throw New FaultException(Of Integer)(4)

throw new FaultException<int>(4);

The preceding example is very basic; almost any information can be passed using an System..::.Int32 code, so this detail type is not the most useful. Typically, WCF applications specify SOAP faults with detail types specific to the error information requirements of the client. For a more complete example, see the Example section.

Note:

If you specify a FaultException<(Of <(TDetail>)>) where the type parameter is a System..::.String, the string value is assigned to the Detail property in the client application; clients cannot retrieve that string by calling the FaultException<(Of <(TDetail>)>)..::.ToString method. To have the string value returned when the client application calls Exception..::.ToString, throw a System.ServiceModel..::.FaultException exception inside the operation and pass the string to the constructor.

To explicitly control the behavior of the application when an exception or FaultException<(Of <(TDetail>)>) is thrown, implement the System.ServiceModel.Dispatcher..::.IErrorHandler interface on an System.ServiceModel.Description..::.IServiceBehavior, System.ServiceModel.Description..::.IContractBehavior or System.ServiceModel.Description..::.IEndpointBehavior and assign it to the ChannelDispatcherErrorhandlers()()() property. IErrorHandlerenables you to explicitly control the SOAP fault that is generated and whether to send it back to the client.

To facilitate debugging, set the ServiceBehaviorAttribute..::.IncludeExceptionDetailInFaults to true in code or you can use the ServiceDebugBehavior..::.IncludeExceptionDetailInFaults in an application configuration file. When enabled, the service automatically returns exception information to the caller. These faults appear to the client as FaultException exceptions.

Important Note:

Because managed exceptions can expose internal application information, setting ServiceBehaviorAttribute..::.IncludeExceptionDetailInFaults or ServiceDebugBehavior..::.IncludeExceptionDetailInFaults to true can permit WCF clients to obtain information about internal service operation exceptions, including personally identifiable or other sensitive information. Therefore, setting ServiceBehaviorAttribute..::.IncludeExceptionDetailInFaults or ServiceDebugBehavior..::.IncludeExceptionDetailInFaults to true is only recommended as a way of temporarily debugging a service application. In addition, the WSDL for a method that returns unhandled managed exceptions in this way does not contain the contract for the FaultException<(Of <(TDetail>)>) of type String. Clients must expect the possibility of an unknown SOAP fault (returned to WCF clients as System.ServiceModel..::.FaultException objects) to obtain the debugging information properly.

The following code example shows the use of FaultContractAttribute to specify that the SampleMethod operation can return a SOAP fault with the detail type of GreetingFault.

using System;
using System.Collections.Generic;
using System.Net.Security;
using System.Runtime.Serialization;
using System.ServiceModel;
using System.Text;

namespace Microsoft.WCF.Documentation
{
  [ServiceContract(Namespace="http://microsoft.wcf.documentation")]
  public interface ISampleService{
    [OperationContract]
    [FaultContractAttribute(
      typeof(GreetingFault),
      Action="http://www.contoso.com/GreetingFault",
      ProtectionLevel=ProtectionLevel.EncryptAndSign
      )]
    string SampleMethod(string msg);
  }

  [DataContractAttribute]
  public class GreetingFault
  { 
    private string report;

    public GreetingFault(string message)
    {
      this.report = message;
    }

    [DataMemberAttribute]
    public string Message
    {
      get { return this.report; }
      set { this.report = value; }
    }
  }

  class SampleService : ISampleService
  {
  #region ISampleService Members

  public string  SampleMethod(string msg)
  {
    Console.WriteLine("Client said: " + msg);
    // Generate intermittent error behavior.
    Random rand = new Random(DateTime.Now.Millisecond);
    int test = rand.Next(5);
    if (test % 2 != 0)
      return "The service greets you: " + msg; 
    else
      throw new FaultException<GreetingFault>(new GreetingFault("A Greeting error occurred. You said: " + msg));
  }

  #endregion
  }
}

The following code example shows that WCF clients of ISampleService experience this SOAP fault as a FaultException<(Of <(TDetail>)>) of type GreetingFault.

using System;
using System.ServiceModel;
using System.ServiceModel.Channels;
using Microsoft.WCF.Documentation;

public class Client
{
  public static void Main()
  {
    // Picks up configuration from the config file.
    SampleServiceClient wcfClient = new SampleServiceClient();
    try
    {
      // Making calls.
      Console.WriteLine("Enter the greeting to send: ");
      string greeting = Console.ReadLine();
      Console.WriteLine("The service responded: " + wcfClient.SampleMethod(greeting));

      Console.WriteLine("Press ENTER to exit:");
      Console.ReadLine();

      // Done with service. 
      wcfClient.Close();
      Console.WriteLine("Done!");
    }
    catch (TimeoutException timeProblem)
    {
      Console.WriteLine("The service operation timed out. " + timeProblem.Message);
      Console.ReadLine();
      wcfClient.Abort();
    }
    catch (FaultException<GreetingFault> greetingFault)
    {
      Console.WriteLine(greetingFault.Detail.Message);
      Console.ReadLine();
      wcfClient.Abort();
    }
    catch (FaultException unknownFault)
    {
      Console.WriteLine("An unknown exception was received. " + unknownFault.Message);
      Console.ReadLine();
      wcfClient.Abort();
    }
    catch (CommunicationException commProblem)
    {
      Console.WriteLine("There was a communication problem. " + commProblem.Message + commProblem.StackTrace);
      Console.ReadLine();
      wcfClient.Abort();
    }
  }
}

Windows 7, Windows Vista, Windows XP SP2, Windows Server 2008 R2, Windows Server 2008, Windows Server 2003

.NET Framework

Reference