C# Language Exception Handling Implementing IErrorHandler for WCF Services
Example
Implementing IErrorHandler for WCF services is a great way to centralize error handling and logging. The implementation shown here should catch any unhandled exception that is thrown as a result of a call to one of your WCF services. Also shown in this example is how to return a custom object, and how to return JSON rather than the default XML.
Implement IErrorHandler:
using System.ServiceModel.Channels;
using System.ServiceModel.Dispatcher;
using System.Runtime.Serialization.Json;
using System.ServiceModel;
using System.ServiceModel.Web;
namespace BehaviorsAndInspectors
{
public class ErrorHandler : IErrorHandler
{
public bool HandleError(Exception ex)
{
// Log exceptions here
return true;
} // end
public void ProvideFault(Exception ex, MessageVersion version, ref Message fault)
{
// Get the outgoing response portion of the current context
var response = WebOperationContext.Current.OutgoingResponse;
// Set the default http status code
response.StatusCode = HttpStatusCode.InternalServerError;
// Add ContentType header that specifies we are using JSON
response.ContentType = new MediaTypeHeaderValue("application/json").ToString();
// Create the fault message that is returned (note the ref parameter) with BaseDataResponseContract
fault = Message.CreateMessage(
version,
string.Empty,
new CustomReturnType { ErrorMessage = "An unhandled exception occurred!" },
new DataContractJsonSerializer(typeof(BaseDataResponseContract), new List<Type> { typeof(BaseDataResponseContract) }));
if (ex.GetType() == typeof(VariousExceptionTypes))
{
// You might want to catch different types of exceptions here and process them differently
}
// Tell WCF to use JSON encoding rather than default XML
var webBodyFormatMessageProperty = new WebBodyFormatMessageProperty(WebContentFormat.Json);
fault.Properties.Add(WebBodyFormatMessageProperty.Name, webBodyFormatMessageProperty);
} // end
} // end class
} // end namespace
In this example we attach the handler to the service behavior. You could also attach this to IEndpointBehavior, IContractBehavior, or IOperationBehavior in a similar way.
Attach to Service Behaviors:
using System;
using System.Collections.ObjectModel;
using System.ServiceModel;
using System.ServiceModel.Channels;
using System.ServiceModel.Configuration;
using System.ServiceModel.Description;
using System.ServiceModel.Dispatcher;
namespace BehaviorsAndInspectors
{
public class ErrorHandlerExtension : BehaviorExtensionElement, IServiceBehavior
{
public override Type BehaviorType
{
get { return GetType(); }
}
protected override object CreateBehavior()
{
return this;
}
private IErrorHandler GetInstance()
{
return new ErrorHandler();
}
void IServiceBehavior.AddBindingParameters(ServiceDescription serviceDescription, ServiceHostBase serviceHostBase, Collection<ServiceEndpoint> endpoints, BindingParameterCollection bindingParameters) { } // end
void IServiceBehavior.ApplyDispatchBehavior(ServiceDescription serviceDescription, ServiceHostBase serviceHostBase)
{
var errorHandlerInstance = GetInstance();
foreach (ChannelDispatcher dispatcher in serviceHostBase.ChannelDispatchers)
{
dispatcher.ErrorHandlers.Add(errorHandlerInstance);
}
}
void IServiceBehavior.Validate(ServiceDescription serviceDescription, ServiceHostBase serviceHostBase) { } // end
} // end class
} // end namespace
Configs in Web.config:
...
<system.serviceModel>
<services>
<service name="WebServices.MyService">
<endpoint binding="webHttpBinding" contract="WebServices.IMyService" />
</service>
</services>
<extensions>
<behaviorExtensions>
<!-- This extension if for the WCF Error Handling-->
<add name="ErrorHandlerBehavior" type="WebServices.BehaviorsAndInspectors.ErrorHandlerExtensionBehavior, WebServices, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null" />
</behaviorExtensions>
</extensions>
<behaviors>
<serviceBehaviors>
<behavior>
<serviceMetadata httpGetEnabled="true"/>
<serviceDebug includeExceptionDetailInFaults="true"/>
<ErrorHandlerBehavior />
</behavior>
</serviceBehaviors>
</behaviors>
....
</system.serviceModel>
...
Here are a few links that may be helpful on this topic:
https://msdn.microsoft.com/en-us/library/system.servicemodel.dispatcher.ierrorhandler(v=vs.100).aspx
Other Examples:
IErrorHandler returning wrong message body when HTTP status code is 401 Unauthorized
IErrorHandler doesn't seem to be handling my errors in WCF .. any ideas?
How to make custom WCF error handler return JSON response with non-OK http code?
How do you set the Content-Type header for an HttpClient request?
