Can not catch exception in ASP.NET MVC

Question

I am currently trying to develop simple web application for my IoT school project. As for now it should only call direct methods from my Raspberry. I am using Azure SDK for C#.

This is how code looks like:

Controller:

    public ActionResult changeState(int? id, bool enable)
    {
        string conn_str = (from u in db.Users join h in db.Hubs on
                u.Hub.HubId equals h.HubId
                where u.UserName == User.Identity.Name select h.connection_str).First();

        Cloud2Device c2d = new Cloud2Device(conn_str);

        if (id == null)
        {
            return new HttpStatusCodeResult(HttpStatusCode.BadRequest);
        }
        Rp rp = db.Rps.SingleOrDefault(r => r.RpId == id);
        if (rp == null)
        {
            return HttpNotFound();
        }
        //IoT stuff
        try
        {
           c2d.EnableRaspberry("myDeviceId").Wait();
        }
        catch(Exception ex)
        {
           //do something
        }
        rp.is_enabled = enable;
        db.SaveChanges();
        return RedirectToAction("Index");
    }

IoT utils:

public class Cloud2Device
{
    private ServiceClient s_serviceClient;

    public Cloud2Device(string conn_str)
    {
        s_serviceClient = ServiceClient.CreateFromConnectionString(conn_str);
    }

    public async Task EnableRaspberry(string deviceId)
    {
        var methodInvocation = new CloudToDeviceMethod("EnableRaspberry") { ResponseTimeout = TimeSpan.FromSeconds(2) };

         var response = await s_serviceClient.InvokeDeviceMethodAsync(deviceId, methodInvocation);
        Debug.WriteLine(response.GetPayloadAsJson());
    }
}

The problem is that from the debug output I can see that exception Microsoft.Azure.Devices.Common.Exceptions.DeviceNotFoundException was thrown however it is not handled by try-catch block.

console output

    Application Insights Telemetry (unconfigured): "name":"Microsoft.ApplicationInsights.Dev.RemoteDependency","time":"2018-05-29T12:04:59.4748528Z","tags":{"ai.internal.sdkVersion":"rddf:2.2.0-738","ai.internal.nodeName":"5CG6455YJ4.ericsson.se","ai.cloud.roleInstance":"5CG6455YJ4.ericsson.se"},"data":{"baseType":"RemoteDependencyData","baseData":{"ver":2,"name":"/twins/myDeviceId/methods","id":"8/ZMgqG4iNc=","data":"https://utiliothub.azure-devices.net/twins/myDeviceId/methods?api-version=2017-10-15","duration":"00:00:01.2380000","resultCode":"404","success":false,"type":"Http","target":"utiliothub.azure-devices.net","properties":{"DeveloperMode":"true"}}}}
    Exception thrown:'Microsoft.Azure.Devices.Common.Exceptions.DeviceNotFoundException' in Microsoft.Azure.Devices.dll
    Exception thrown:'Microsoft.Azure.Devices.Common.Exceptions.DeviceNotFoundException' in mscorlib.dll
    The thread 0x3834 has exited with code 0 (0x0).

Can anyone advise how I can catch and handle this exception in my application ? Thanks in advance for answer.

Answer 1

I'm not sure that error output is actually an exception being thrown up to your code. It could be ApplicationInsights just logging. However, I think the code is frozen due to calling Wait and blocking the return from the async method.

Make the controller method return type Task<ActionResult>, make that method async, then use await c2d.EnableRaspberry("myDeviceId"); to call that method.

See if doing that results in an exception (or success).