Handle exceptions in web services with Elmah

Question

Hi

Is there a way to globally handle exceptions in regular ASP.NET Web Service (asmx) using ELMAH like we do it in ASP.NET web site ?

Thanks

Answer 1

ASP.NET web services never fire Application_Error event and exceptions cannot be handled globally by ELMAH like in ASP.NET apps. But we can "manually" log exceptions using ELMAH:

public int WebServiceMethod() {
  try {
   ...
  }
  catch (Excetion ex) {
    Elmah.ErrorLog.GetDefault(
      HttpContext.Current).Log(new Elmah.Error(ex, HttpContext.Current));
  }
}

Answer 2

You can use a SoapExtension to do this :

using System;
using System.Web.Services.Protocols;

namespace MyNamespace
{
    class ELMAHExtension : SoapExtension
    {
        public override object GetInitializer(Type serviceType)
        { return null; }

        public override object GetInitializer(LogicalMethodInfo methodInfo, SoapExtensionAttribute attribute)
        { return null; }

        public override void Initialize(object initializer)
        { }

        public override void ProcessMessage(SoapMessage message)
        {
            if (message.Stage == SoapMessageStage.AfterSerialize &&
                message.Exception != null)
            {
                // Log exception here
            }
        }
    }
}

You register this in the web.config with the following lines :

<system.web>
  <webServices>
    <soapExtensionTypes>
      <add type="MyNamespace.ELMAHExtension, MyDLL" priority="1" group="1" />
    </soapExtensionTypes>
  </webServices>
</system.web>

This will give you access to the HttpContext and SoapMessage objects which should give you all of the details you need about what was being called. I think the exception you retrieve at this stage will always be a SoapException and that the bit you are interested in is probably the inner exception.