Random wanderings through Microsoft Azure esp. the IoT bits, AI on Micro controllers, .NET nanoFramework, .NET Core on *nix, and GHI Electronics TinyCLR
While debugging my AzureIoTSmartEdgeCamera application I kept on getting file locked errors when the image from the security camera downloading which was a bit odd. So, I went back to basics and started with only the compiler directives required to build a “minimalist” version of the application.
Console output of minimalist application
If I had been paying attention, I would have noticed the issue here. I had missed that in the first block of System.Console.Writelines that the image download finished after the YoloV5 inferencing started.
#if CAMERA_SECURITY
private void SecurityCameraImageCapture()
{
_logger.LogTrace("Security Camera Image download start");
NetworkCredential networkCredential = new NetworkCredential()
{
UserName = _securityCameraSettings.CameraUserName,
Password = _securityCameraSettings.CameraUserPassword,
};
using (WebClient client = new WebClient())
{
client.Credentials = networkCredential;
client.DownloadFile(_securityCameraSettings.CameraUrl, _applicationSettings.ImageCameraFilepath);
}
_logger.LogTrace("Security Camera Image download done");
}
#endif
#if CAMERA_SECURITY
private async Task SecurityCameraImageCapture()
{
_logger.LogTrace("Security Camera Image download start");
using (Stream cameraStream = await _httpClient.GetStreamAsync(_securityCameraSettings.CameraUrl))
using (Stream fileStream = File.Create(_applicationSettings.ImageCameraFilepath))
{
await cameraStream.CopyToAsync(fileStream);
}
_logger.LogTrace("Security Camera Image download done");
}
#endif
If I had been paying attention, I would have also noticed the issue here..
Console output of maximalist application
When I changed the compiler definitions to turn on pretty much every feature the issue became really really obvious because the “Security Camera Image download done” message wasn’t displayed.
class Program
{
private static string payload;
static async Task Main(string[] args)
{
string filename;
string azureIoTHubconnectionString;
DeviceClient azureIoTHubClient;
if (args.Length != 2)
{
Console.WriteLine("[JOSN file] [AzureIoTHubConnectionString]");
Console.WriteLine("Press <enter> to exit");
Console.ReadLine();
return;
}
filename = args[0];
azureIoTHubconnectionString = args[1];
try
{
payload = File.ReadAllText(filename);
// Open up the connection
azureIoTHubClient = DeviceClient.CreateFromConnectionString(azureIoTHubconnectionString, TransportType.Mqtt);
//azureIoTHubClient = DeviceClient.CreateFromConnectionString(azureIoTHubconnectionString, TransportType.Mqtt_Tcp_Only);
//azureIoTHubClient = DeviceClient.CreateFromConnectionString(azureIoTHubconnectionString, TransportType.Mqtt_WebSocket_Only);
await azureIoTHubClient.OpenAsync();
await azureIoTHubClient.SetMethodDefaultHandlerAsync(MethodCallbackDefault, null);
Timer MessageSender = new Timer(TimerCallback, azureIoTHubClient, new TimeSpan(0, 0, 10), new TimeSpan(0, 0, 10));
Console.WriteLine("Press <enter> to exit");
Console.ReadLine();
}
catch (Exception ex)
{
Console.WriteLine(ex.Message);
Console.WriteLine("Press <enter> to exit");
Console.ReadLine();
}
}
public static async void TimerCallback(object state)
{
DeviceClient azureIoTHubClient = (DeviceClient)state;
try
{
// I know having the payload as a global is a bit nasty but this is a demo..
using (Message message = new Message(Encoding.ASCII.GetBytes(JsonConvert.SerializeObject(payload))))
{
Console.WriteLine(" {0:HH:mm:ss} AzureIoTHubDeviceClient SendEventAsync start", DateTime.UtcNow);
await azureIoTHubClient.SendEventAsync(message);
Console.WriteLine(" {0:HH:mm:ss} AzureIoTHubDeviceClient SendEventAsync finish", DateTime.UtcNow);
}
}
catch (Exception ex)
{
Console.WriteLine(ex.Message);
}
}
private static async Task<MethodResponse> MethodCallbackDefault(MethodRequest methodRequest, object userContext)
{
Console.WriteLine($"Default handler method {methodRequest.Name} was called.");
return new MethodResponse(200);
}
}
I configured an Azure IoT hub then used Azure IoT explorer to create a device and get the connections string for my application. After fixing up the application’s command line parameters I could see the timer code was successfully sending telemetry messages to my Azure IoT Hub. I also explored the different MQTT connections options TransportType.Mqtt, TransportType.Mqtt_Tcp_Only, and TransportType.Mqtt_WebSocket_Only which worked as expected.
MQTT Console application displaying sent telemetryAzure IoT Hub displaying received telemetry
I could also initiate Direct Method calls to my console application from Azure IoT explorer.
Azure IoT Explorer initiating a Direct Method MQTT console application displaying direct method call.
I then changed the protocol to AMQP
class Program
{
private static string payload;
static async Task Main(string[] args)
{
string filename;
string azureIoTHubconnectionString;
DeviceClient azureIoTHubClient;
Timer MessageSender;
if (args.Length != 2)
{
Console.WriteLine("[JOSN file] [AzureIoTHubConnectionString]");
Console.WriteLine("Press <enter> to exit");
Console.ReadLine();
return;
}
filename = args[0];
azureIoTHubconnectionString = args[1];
try
{
payload = File.ReadAllText(filename);
// Open up the connection
azureIoTHubClient = DeviceClient.CreateFromConnectionString(azureIoTHubconnectionString, TransportType.Amqp);
//azureIoTHubClient = DeviceClient.CreateFromConnectionString(azureIoTHubconnectionString, TransportType.Amqp_Tcp_Only);
//azureIoTHubClient = DeviceClient.CreateFromConnectionString(azureIoTHubconnectionString, TransportType.Amqp_WebSocket_Only);
await azureIoTHubClient.OpenAsync();
await azureIoTHubClient.SetMethodDefaultHandlerAsync(MethodCallbackDefault, null);
//MessageSender = new Timer(TimerCallbackAsync, azureIoTHubClient, new TimeSpan(0, 0, 10), new TimeSpan(0, 0, 10));
MessageSender = new Timer(TimerCallbackSync, azureIoTHubClient, new TimeSpan(0, 0, 10), new TimeSpan(0, 0, 10));
#if MESSAGE_PUMP
Console.WriteLine("Press any key to exit");
while (!Console.KeyAvailable)
{
await Task.Delay(100);
}
#else
Console.WriteLine("Press <enter> to exit");
Console.ReadLine();
#endif
}
catch (Exception ex)
{
Console.WriteLine(ex.Message);
Console.WriteLine("Press <enter> to exit");
Console.ReadLine();
}
}
public static async void TimerCallbackAsync(object state)
{
DeviceClient azureIoTHubClient = (DeviceClient)state;
try
{
// I know having the payload as a global is a bit nasty but this is a demo..
using (Message message = new Message(Encoding.ASCII.GetBytes(JsonConvert.SerializeObject(payload))))
{
Console.WriteLine(" {0:HH:mm:ss} AzureIoTHubDeviceClient SendEventAsync start", DateTime.UtcNow);
await azureIoTHubClient.SendEventAsync(message);
Console.WriteLine(" {0:HH:mm:ss} AzureIoTHubDeviceClient SendEventAsync finish", DateTime.UtcNow);
}
}
catch (Exception ex)
{
Console.WriteLine(ex.Message);
}
}
public static void TimerCallbackSync(object state)
{
DeviceClient azureIoTHubClient = (DeviceClient)state;
try
{
// I know having the payload as a global is a bit nasty but this is a demo..
using (Message message = new Message(Encoding.ASCII.GetBytes(JsonConvert.SerializeObject(payload))))
{
Console.WriteLine(" {0:HH:mm:ss} AzureIoTHubDeviceClient SendEventAsync start", DateTime.UtcNow);
azureIoTHubClient.SendEventAsync(message).GetAwaiter();
Console.WriteLine(" {0:HH:mm:ss} AzureIoTHubDeviceClient SendEventAsync finish", DateTime.UtcNow);
}
}
catch (Exception ex)
{
Console.WriteLine(ex.Message);
}
}
private static async Task<MethodResponse> MethodCallbackDefault(MethodRequest methodRequest, object userContext)
{
Console.WriteLine($"Default handler method {methodRequest.Name} was called.");
return new MethodResponse(200);
}
}
In the first version of my console application I could see the SendEventAsync method was getting called but was not returning
AMQP Console application displaying sent telemetry failure
Even though the SendEventAsync call was not returning the telemetry messages were making it to my Azure IoT Hub.
Azure IoT Hub displaying AMQP telemetry
When I tried to initiate a Direct Method call from Azure IoT Explorer it failed after a while with a timeout.
Azure IoT Explorer initiating a Direct Method
The first successful approach I tried was to change the Console.Readline to a “message pump” (flashbacks to Win32 API programming).
Console.WriteLine("Press any key to exit");
while (!Console.KeyAvailable)
{
await Task.Delay(100);
}
After some more experimentation I found that changing the timer method from asynchronous to synchronous also worked.
public static void TimerCallbackSync(object state)
{
DeviceClient azureIoTHubClient = (DeviceClient)state;
try
{
// I know having the payload as a global is a bit nasty but this is a demo..
using (Message message = new Message(Encoding.ASCII.GetBytes(JsonConvert.SerializeObject(payload))))
{
Console.WriteLine(" {0:HH:mm:ss} AzureIoTHubDeviceClient SendEventAsync start", DateTime.UtcNow);
azureIoTHubClient.SendEventAsync(message).GetAwaiter();
Console.WriteLine(" {0:HH:mm:ss} AzureIoTHubDeviceClient SendEventAsync finish", DateTime.UtcNow);
}
}
catch (Exception ex)
{
Console.WriteLine(ex.Message);
}
}
I also had to change the method declaration and modify the SendEventAsync call to use a GetAwaiter.
AMQP Console application displaying sent telemetryAzure IoT Hub displaying received telemetryAzure IoT Explorer initiating a Direct MethodMQTT console application displaying direct method call.
It took a while to figure out enough about what was going on so I could do a search with the right keywords (DeviceClient AMQP async await SendEventAsync) to confirm my suspicion that MQTT and AMQP clients did behave differently.
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