Logging to elmah.io from WCF

ELMAH (the open-source project) and WCF aren't exactly known to go hand in hand. But, with a bit of custom code, logging exceptions from WCF to elmah.io is possible.

Let's get started. Install elmah.io into your WCF project using NuGet:

Install-Package Elmah.Io

dotnet add package Elmah.Io

<PackageReference Include="Elmah.Io" Version="5.*" />

paket add Elmah.Io

During the installation, you will be asked for your API key (Where is my API key?) and log ID (Where is my log ID?).

Add a new class named HttpErrorHandler:

public class HttpErrorHandler : IErrorHandler
{
    public bool HandleError(Exception error)
    {
        return false;
    }

    public void ProvideFault(Exception error, MessageVersion version, ref Message fault)
    {
        if (error != null)
        {
            Elmah.ErrorSignal.FromCurrentContext().Raise(error);
        }
    }
}

This is an implementation of WCF's IErrorHandler that instructs WCF to log any errors to ELMAH, using the Raise-method on ErrorSignal.

Then create an attribute named ServiceErrorBehaviourAttribute:

public class ServiceErrorBehaviourAttribute : Attribute, IServiceBehavior
{
    Type errorHandlerType;

    public ServiceErrorBehaviourAttribute(Type errorHandlerType)
    {
        this.errorHandlerType = errorHandlerType;
    }

    public void Validate(ServiceDescription description, ServiceHostBase serviceHostBase)
    {
    }

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

    public void ApplyDispatchBehavior(ServiceDescription description, ServiceHostBase serviceHostBase)
    {
        IErrorHandler errorHandler;
        errorHandler = (IErrorHandler)Activator.CreateInstance(errorHandlerType);
        foreach (ChannelDispatcherBase channelDispatcherBase in serviceHostBase.ChannelDispatchers)
        {
            ChannelDispatcher channelDispatcher = channelDispatcherBase as ChannelDispatcher;
            channelDispatcher.ErrorHandlers.Add(errorHandler);
        }
    }
}

We'll use the ServiceErrorBehaviourAttribute class for decorating endpoints which we want logging uncaught errors to ELMAH. Add the new attribute to your service implementation like this:

[ServiceErrorBehaviour(typeof(HttpErrorHandler))]
public class Service1 : IService1
{
    // ...
}

That's it. Services decorated with the ServiceErrorBehaviourAttribute now logs exceptions to ELMAH.

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