IErrorHandler Interface (System.ServiceModel.Dispatcher)

IErrorHandler Interface

.NET Framework Class Library

IErrorHandler Interface

Allows an implementer to control the fault message returned to the caller and optionally perform custom error processing such as logging.

Namespace: System.ServiceModel.Dispatcher
Assembly: System.ServiceModel (in System.ServiceModel.dll)

Syntax

Visual Basic (Declaration)

Public Interface IErrorHandler

Visual Basic (Usage)

Dim instance As IErrorHandler

public interface IErrorHandler

Visual C++

public interface class IErrorHandler

JScript

public interface IErrorHandler

Remarks

To explicitly control the behavior of the application when an exception is thrown, implement the IErrorHandler interface and add it to the ErrorHandlers property. IErrorHandler enables you to explicitly control the SOAP fault generated, decide whether to send it back to the client, and perform associated tasks, such as logging. Error handlers are called in the order in which they were added to the ErrorHandlers property.

Implement the ProvideFault method to control the fault message that is returned to the client.

Implement the HandleError method to ensure error-related behaviors, including error logging, assuring a fail fast, shutting down the application, and so on.

Note:
Because the HandleError method can be called from many different places there are no guarantees made about which thread the method is called on. Do not depend on HandleError method being called on the operation thread.

All ProvideFault implementations are called first, prior to sending a response message. When all ProvideFault implementations have been called and return, and if fault is non-nullNothingnullptra null reference (Nothing in Visual Basic), it is sent back to the client according to the operation contract. If fault is nullNothingnullptra null reference (Nothing in Visual Basic) after all implementations have been called, the response message is controlled by the ServiceBehaviorAttribute..::.IncludeExceptionDetailInFaults property value.

Note:
Exceptions can occur after all ProvideFault implementations are called and a response message is handed to the channel. If a channel exception occurs (for example, difficulty serializing the message) IErrorHandler objects are not notified. In this case, you should make sure that your development environment catches and displays such exceptions to you or makes use of tracing to discover the problem. For more information about tracing, see Using Tracing to Troubleshoot Your Application.

Note:

Exceptions can occur after all ProvideFault implementations are called and a response message is handed to the channel. If a channel exception occurs (for example, difficulty serializing the message) IErrorHandler objects are not notified. In this case, you should make sure that your development environment catches and displays such exceptions to you or makes use of tracing to discover the problem. For more information about tracing, see Using Tracing to Troubleshoot Your Application.

After the response message has been sent, all HandleError implementations are called in the same order.

Typically, an IErrorHandler implementation is added to the ErrorHandlers property on the service (and the client in the case of duplex communication).

You can add the IErrorHandler to the runtime by implementing a behavior (either an System.ServiceModel.Description..::.IServiceBehavior, System.ServiceModel.Description..::.IEndpointBehavior, System.ServiceModel.Description..::.IContractBehavior, or System.ServiceModel.Description..::.IOperationBehavior object) and use the behavior programmatically, from a configuration file or with a custom attribute to attach your IErrorHandler.

For more information about using behaviors to modify the runtime, see Attaching Extensions Using Behaviors.

Examples

The following code example demonstrates a service that implements IErrorHandler that returns only FaultException<(Of <(TDetail>)>) of type GreetingFault when a service method throws a managed exception.

#region IErrorHandler Members
public bool HandleError(Exception error)
{
  Console.WriteLine("HandleError called.");
  // Returning true indicates you performed your behavior.
  return true;
}

// This is a trivial implementation that converts Exception to FaultException<GreetingFault>.
public void ProvideFault(
  Exception error,
  MessageVersion ver,
  ref Message msg
)
{
  Console.WriteLine("ProvideFault called. Converting Exception to GreetingFault....");
  FaultException<GreetingFault> fe 
    = new FaultException<GreetingFault>(new GreetingFault(error.Message));
  MessageFault fault = fe.CreateMessageFault();
  msg = Message.CreateMessage(
    ver, 
    fault, 
    "http://microsoft.wcf.documentation/ISampleService/SampleMethodGreetingFaultFault"
  );
}
#endregion

The following code example shows how to use a service behavior to add the IErrorHandler implementation to the ErrorHandlers property.

// This behavior modifies no binding parameters.
#region IServiceBehavior Members
public void AddBindingParameters(
  ServiceDescription description, 
  ServiceHostBase serviceHostBase, 
  System.Collections.ObjectModel.Collection<ServiceEndpoint> endpoints, 
  System.ServiceModel.Channels.BindingParameterCollection parameters
)
{
  return;
}

// This behavior is an IErrorHandler implementation and 
// must be applied to each ChannelDispatcher.
public void ApplyDispatchBehavior(ServiceDescription description, ServiceHostBase serviceHostBase)
{
  Console.WriteLine("The EnforceGreetingFaultBehavior has been applied.");
  foreach(ChannelDispatcher chanDisp in serviceHostBase.ChannelDispatchers)
  {
    chanDisp.ErrorHandlers.Add(this);      
  }
}

// This behavior requires that the contract have a SOAP fault with a detail type of GreetingFault.
public void Validate(ServiceDescription description, ServiceHostBase serviceHostBase)
{
  Console.WriteLine("Validate is called.");
  foreach (ServiceEndpoint se in description.Endpoints)
  {
    // Must not examine any metadata endpoint.
    if (se.Contract.Name.Equals("IMetadataExchange")
      && se.Contract.Namespace.Equals("http://schemas.microsoft.com/2006/04/mex"))
      continue;
    foreach (OperationDescription opDesc in se.Contract.Operations)
    {
      if (opDesc.Faults.Count == 0)
        throw new InvalidOperationException(String.Format(
          "EnforceGreetingFaultBehavior requires a "  
          + "FaultContractAttribute(typeof(GreetingFault)) in each operation contract.  "
          + "The \"{0}\" operation contains no FaultContractAttribute.",
          opDesc.Name)
        );
      bool gfExists = false;
      foreach (FaultDescription fault in opDesc.Faults)
      {
        if (fault.DetailType.Equals(typeof(GreetingFault)))
        {
          gfExists = true;
          continue;
        }
      }
      if (gfExists == false)
      {
        throw new InvalidOperationException(
"EnforceGreetingFaultBehavior requires a FaultContractAttribute(typeof(GreetingFault)) in an operation contract."
        );
      }
    }
  }
}
#endregion

The following code example shows how to configure the service to load the service behavior using an application configuration file. For more details about how to expose a service behavior in a configuration file, see IServiceBehavior.

xml

<configuration>
  <system.serviceModel>
    <services>
      <service 
        name="Microsoft.WCF.Documentation.SampleService"
        behaviorConfiguration="metaAndErrors">
        <host>
          <baseAddresses>
            <add baseAddress="http://localhost:8080/SampleService"/>
          </baseAddresses>
        </host>
        <endpoint
          address=""
          binding="wsHttpBinding"
          contract="Microsoft.WCF.Documentation.ISampleService"
         />
        <endpoint
          address="mex"
          binding="mexHttpBinding"
          contract="IMetadataExchange"
         />
      </service>
    </services>
    <behaviors>
      <serviceBehaviors>
        <behavior name="metaAndErrors">
          <serviceDebug includeExceptionDetailInFaults="true"/>
          <serviceMetadata httpGetEnabled="true"/>
          <enforceGreetingFaults />
        </behavior>
      </serviceBehaviors>
    </behaviors>
    <extensions>
      <behaviorExtensions>
        <add 
          name="enforceGreetingFaults" 
          type="Microsoft.WCF.Documentation.EnforceGreetingFaultBehavior, HostApplication, Version=0.0.0.0, Culture=neutral, PublicKeyToken=null"
        />
      </behaviorExtensions>
    </extensions>
  </system.serviceModel>
</configuration>

Platforms

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

The .NET Framework and .NET Compact Framework do not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.

Version Information

.NET Framework

Supported in: 3.5, 3.0

Reference

IErrorHandler Members

System.ServiceModel.Dispatcher Namespace