Look on my works, ye Mighty, and despair!

Normally when developing an ASP.NET application I add fall back logging for any unhandled exceptions in Global.asax.cs:

public class Global : HttpApplication
{
    private ILog _logger;
    
    protected void Application_Start(object sender, EventArgs e)
    {
        XmlConfigurator.Configure();
        _logger = LogManager.GetLogger(typeof(Global));
    }

    protected void Application_Error(object sender, EventArgs e)
    {
        var error = Server.GetLastError();
        _logger.Error("Unhandled error", error);
    }
}

This means any YSODs are logged.

When developing applications with Nancy this no longer works, as Nancy has it’s own error handling pipeline.

The solution is to implement a handler to log any unhandled errors:

public class LoggingErrorHandler : IErrorHandler
{
    private readonly ILog _logger = LogManager.GetLogger(typeof(LoggingErrorHandler));

    public bool HandlesStatusCode(HttpStatusCode statusCode)
    {
        return statusCode == HttpStatusCode.InternalServerError;
    }

    public void Handle(HttpStatusCode statusCode, NancyContext context)
    {
        object errorObject;
        context.Items.TryGetValue(NancyEngine.ERROR_EXCEPTION, out errorObject);
        var error = errorObject as Exception;

        _logger.Error("Unhandled error", error);
    }
}

And, as of 0.10.0, there’s no longer any need to register it. Any IErrorHandler implementations will be picked up, auto-magically.