WCF exception IErrorHandler not getting called

Question

I seem to be having a problem for getting IErrorHandler interface to work. My code is

using System;
using System.Collections.Generic;
using System.Collections.ObjectModel;
using System.Diagnostics;
using System.ServiceModel;
using System.ServiceModel.Channels;
using System.ServiceModel.Configuration;
using System.ServiceModel.Description;
using System.ServiceModel.Dispatcher;

namespace WcfService3
{
    public class Service1 : IService1
    {
        public string GetData(int value)
        {
            throw new Exception("asdf");

        }
    }

    public class MyErrorHandler : IErrorHandler
    {
        public MyErrorHandler()
        {
            string Hello = "";
        }
        public bool HandleError(Exception error)
        {
            return true;
        }

        public void ProvideFault(Exception error, MessageVersion version, ref Message msg)
        {
            var vfc = new MyFault();
            var fe = new FaultException<MyFault>(vfc);
            var fault = fe.CreateMessageFault();
            msg = Message.CreateMessage(version, fault, "http://ns");
        }
    }

    public class ErrorHandlerExtension : BehaviorExtensionElement, IServiceBehavior
    {
        public override Type BehaviorType
        {
            get { return GetType(); }
        }

        protected override object CreateBehavior()
        {
            return this;
        }

        private IErrorHandler GetInstance()
        {
            return new MyErrorHandler();
        }

        void IServiceBehavior.AddBindingParameters(ServiceDescription serviceDescription, ServiceHostBase serviceHostBase, Collection<ServiceEndpoint> endpoints, BindingParameterCollection bindingParameters)
        {
        }

        void IServiceBehavior.ApplyDispatchBehavior(ServiceDescription serviceDescription, ServiceHostBase serviceHostBase)
        {
            IErrorHandler errorHandlerInstance = GetInstance();
            foreach (ChannelDispatcher dispatcher in serviceHostBase.ChannelDispatchers)
            {
                dispatcher.ErrorHandlers.Add(errorHandlerInstance);
            }
        }

        void IServiceBehavior.Validate(ServiceDescription serviceDescription, ServiceHostBase serviceHostBase)
        {
            foreach (ServiceEndpoint endpoint in serviceDescription.Endpoints)
            {
                if (endpoint.Contract.Name.Equals("IMetadataExchange") &&
                    endpoint.Contract.Namespace.Equals("http://schemas.microsoft.com/2006/04/mex"))
                    continue;

                foreach (OperationDescription description in endpoint.Contract.Operations)
                {
                    if (description.Faults.Count == 0)
                    {
                        throw new InvalidOperationException("FaultContractAttribute not found on this method");
                    }
                }
            }
        }
    }
}

My web.config is:

<?xml version="1.0"?>
<configuration>

  <appSettings>
    <add key="aspnet:UseTaskFriendlySynchronizationContext" value="true" />
  </appSettings>
  <system.web>
    <compilation debug="true" targetFramework="4.5" />
    <httpRuntime targetFramework="4.5"/>
  </system.web>
  <system.serviceModel>
      <services>
    <service name="WcfService3.Service1">
      <endpoint address=""
                binding="basicHttpBinding"
                contract="WcfService3.IService1" />
    </service>
  </services>

    <behaviors>
      <serviceBehaviors>
        <behavior>
          <!-- To avoid disclosing metadata information, set the values below to false before deployment -->
          <serviceMetadata httpGetEnabled="true" httpsGetEnabled="true"/>
          <!-- To receive exception details in faults for debugging purposes, set the value below to true.  Set to false before deployment to avoid disclosing exception information -->
          <serviceDebug includeExceptionDetailInFaults="false"/>
        </behavior>
      </serviceBehaviors>
    </behaviors>
      <extensions>
    <behaviorExtensions>
      <add name="errorHandler"
            type="WcfService3.ErrorHandlerExtension, WcfService3, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null" />
    </behaviorExtensions>
  </extensions>

    <protocolMapping>
        <add binding="basicHttpsBinding" scheme="https" />
    </protocolMapping>    
    <serviceHostingEnvironment aspNetCompatibilityEnabled="true" multipleSiteBindingsEnabled="true" />
  </system.serviceModel>
  <system.webServer>
    <modules runAllManagedModulesForAllRequests="true"/>
    <!--
        To browse web app root directory during debugging, set the value below to true.
        Set to false before deployment to avoid disclosing web app folder information.
      -->
    <directoryBrowse enabled="true"/>
  </system.webServer>

</configuration>

My WCF interface is:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Runtime.Serialization;
using System.ServiceModel;
using System.ServiceModel.Web;
using System.Text;

namespace WcfService3
{
    [ServiceContract]
    public interface IService1
    {
        [OperationContract]
        [FaultContract(typeof(MyFault))]
        string GetData(int value);
    }

    [DataContract]
    public class MyFault
    {

    }

}

My question is in IErrorHandler in WCF, if there is any exception during the WCF service call, the HandlerError() function is suppose to get called first like the C# windows application UnhandledException class and then the service should crash right? In the code above, during the service call, an exception is thrown but my HandlerError function is not getting called before the exception is thrown? My goal is to log the error and the WCF service can throw the unhandled exception and crash. I was expecting during the debugging that the breakpoint will visit the HandleError function, but that function is not getting called and just an exception shows up?

Answer 1

In case anyone else comes across this, when I ran across this error, it was because the error was getting thrown in a method that was called from some LINQ expression. The method wasn't actually called until WCF tried to serialize the response, which then threw outside of the service scope. WCF won't pass these errors to the IErrorHandler.

Materializing the list before returning using .ToList() solved this problem for me.

Answer 2

Aren't you missing <errorHandler /> in your behavior section?

<behavior>
    <serviceMetadata httpGetEnabled="true" httpsGetEnabled="true"/>
    <serviceDebug includeExceptionDetailInFaults="false"/>
    <!-- HERE -->
    <errorHandler />
    <!-- HERE -->
</behavior>

The full answer is here. Plus 1 to that answer.