The Things Network MQTT Client

Another option for I had been looking at for connecting an Azure IoT Hub and The Things Network(TTN) was a Message Queue Telemetry Transport(MQTT) integration.

To trial this approach I build a .Net Core console application which sent message to and received messages from an application running on a GHI Electronics TinyCLRV2 Fezduino with RakWireless Wisduino Evaluation Board(EVB).

The console application uses MQTTNet to connect to TTN. It subscribes to to the TTN application device uplink topic (did try subscribing to the uplink messages for all the devices in the application but this was to noisy), and the downlink message scheduled, sent and acknowledged topics. To send messages to the device I published them on the device downlink topic.

//string uplinktopic = $"{applicationId}/devices/+/up";
string uplinktopic = $"{applicationId}/devices/{deviceId}/up";
await mqttClient.SubscribeAsync(uplinktopic, MQTTnet.Protocol.MqttQualityOfServiceLevel.AtLeastOnce);

string downlinkAcktopic = $"{applicationId}/devices/{deviceId}/events/down/acks";
await mqttClient.SubscribeAsync(downlinkAcktopic, MQTTnet.Protocol.MqttQualityOfServiceLevel.AtLeastOnce);

string downlinkScheduledtopic = $"{applicationId}/devices/{deviceId}/events/down/scheduled";
await mqttClient.SubscribeAsync(downlinkScheduledtopic, MQTTnet.Protocol.MqttQualityOfServiceLevel.AtLeastOnce);

string downlinkSenttopic = $"{applicationId}/devices/{deviceId}/events/down/sent";
await mqttClient.SubscribeAsync(downlinkSenttopic, MQTTnet.Protocol.MqttQualityOfServiceLevel.AtLeastOnce);

string downlinktopic = $"{applicationId}/devices/{deviceId}/down";

I used the classes from one of my earlier blog posts to deserialise the uplink message payload so I could display a subset of the fields.

MQTTNet based .Net Core console client
Things Network Device Data view

In the TTN Device data tab I could see messages being sent, to and received from from the device.

Visual Studio 2019 Tiny CLR debugger Output

In the Visual Studio 2019 debugger output window I could see messages being sent and received by the Fezduino.

Malformed TTN downlink payload

I had some problems with the downlink messages silently failing as the TTN sample payload JSON was malformed and I had copied it without noticing.

I have a working TTN HTTP Integration (uplink messages only) but have been exploring alternatives using TTN MQTT and Azure IoT Hub AMQP clients.

The next step is to build an Azure IoT Hub client (using native AMQP) then join them together.

AllThingsTalk with MQTTnet

As I’m testing my Message Queue Telemetry Transport(MQTT) LoRa gateway I’m building a proof of concept(PoC) .Net core console application for each IoT platform I would like to support.

This PoC was to confirm that I could connect to the AllThingsTalk MQTT API then format topics and payloads correctly.

MQTTNet Console Client

The AllThingsTalk MQTT broker, username, and device ID are required command line parameters.

namespace devmobile.Mqtt.TestClient.AllThingsTalk
{
	using System;
	using System.Diagnostics;
	using System.Threading;
	using System.Threading.Tasks;

	using MQTTnet;
	using MQTTnet.Client;
	using MQTTnet.Client.Disconnecting;
	using MQTTnet.Client.Options;
	using MQTTnet.Client.Receiving;

	using Newtonsoft.Json;
	using Newtonsoft.Json.Linq;

	class Program
	{
		private static IMqttClient mqttClient = null;
		private static IMqttClientOptions mqttOptions = null;
		private static string server;
		private static string username;
		private static string deviceID;

		static void Main(string[] args)
		{
			MqttFactory factory = new MqttFactory();
			mqttClient = factory.CreateMqttClient();

			if ((args.Length != 3))
			{
				Console.WriteLine("[MQTT Server] [UserName] [ClientID]");
				Console.WriteLine("Press <enter> to exit");
				Console.ReadLine();
				return;
			}

			server = args[0];
			username = args[1];
			deviceID = args[2];

			Console.WriteLine($"MQTT Server:{server} DeviceID:{deviceID}");

			// AllThingsTalk formatted device state update topic
			string topicD2C = $"device/{deviceID}/state";

			mqttOptions = new MqttClientOptionsBuilder()
				.WithTcpServer(server)
				.WithCredentials(username, "HighlySecurePassword")
				.WithClientId(deviceID)
				.WithTls()
				.Build();

			mqttClient.UseDisconnectedHandler(new MqttClientDisconnectedHandlerDelegate(e => MqttClient_Disconnected(e)));
			mqttClient.UseApplicationMessageReceivedHandler(new MqttApplicationMessageReceivedHandlerDelegate(e => MqttClient_ApplicationMessageReceived(e)));
			mqttClient.ConnectAsync(mqttOptions).Wait();

			// AllThingsTalk formatted device command with wildcard topic
			string topicC2D = $"device/{deviceID}/asset/+/command";

			mqttClient.SubscribeAsync(topicC2D, MQTTnet.Protocol.MqttQualityOfServiceLevel.AtLeastOnce).GetAwaiter().GetResult();

			while (true)
			{
				JObject payloadJObject = new JObject();

				double temperature = 22.0 + (DateTime.UtcNow.Millisecond / 1000.0);
				temperature = Math.Round( temperature, 1 );
				double humidity = 50 + (DateTime.UtcNow.Millisecond / 100.0);
				humidity = Math.Round(humidity, 1);

				JObject temperatureJObject = new JObject
				{
					{ "value", temperature }
				};
				payloadJObject.Add("Temperature", temperatureJObject);

				JObject humidityJObject = new JObject
				{
					{ "value", humidity }
				};
				payloadJObject.Add("Humidity", humidityJObject);

				string payload = JsonConvert.SerializeObject(payloadJObject);
				Console.WriteLine($"Topic:{topicD2C} Payload:{payload}");

				var message = new MqttApplicationMessageBuilder()
					.WithTopic(topicD2C)
					.WithPayload(payload)
					.WithAtMostOnceQoS()
//					.WithAtLeastOnceQoS()
					.Build();

				Console.WriteLine("PublishAsync start");
				mqttClient.PublishAsync(message).Wait();
				Console.WriteLine("PublishAsync finish");

				Thread.Sleep(15100);
			}
		}

		private static void MqttClient_ApplicationMessageReceived(MqttApplicationMessageReceivedEventArgs e)
		{
			Console.WriteLine($"ClientId:{e.ClientId} Topic:{e.ApplicationMessage.Topic} Payload:{e.ApplicationMessage.ConvertPayloadToString()}");
		}

		private static async void MqttClient_Disconnected(MqttClientDisconnectedEventArgs e)
		{
			Debug.WriteLine("Disconnected");
			await Task.Delay(TimeSpan.FromSeconds(5));

			try
			{
				await mqttClient.ConnectAsync(mqttOptions);
			}
			catch (Exception ex)
			{
				Debug.WriteLine("Reconnect failed {0}", ex.Message);
			}
		}
	}

The AllThingsTalk device configuration was relatively easy but I need to investigate “Gateway” functionality and configuration further.

Configuring an Asset
Configuration a watchdog to check for sensor data
Sending a command to an actuator
Processing a command on the client

The ability to look at message payloads in the Debug tab would be very helpful when working out why a payload was not being processed as expected.

Asset debug information

Overall the AllThingsTalk configuration went fairly smoothly, though I need to investigate the “Gateway” configuration and functionality further. The way that assets are name by the system could make support in my MQTT Gateway more complex.

Azure IoT Hub MQTT+TLS Overheads

An Azure IoT Hub has a series of metrics and one I had been using was “Total Device Data Usage”. To better understand what it was displaying I modified my Azure IoT Hub MQTT Test Application to display the size of the JOSN payload.

MQTTNet based client displaying payload length

The size of the packets sent and the total device data appeared to map pretty well but I was also interested in the Transport Layer Security (TLS) and Messaging Queuing Telemetry Transport (MQTT) overheads.

Azure IoT Hub Metrics

To get an idea of the overheads I fired up LiveTcpUdpWatch by Nirsoft and noted down the traffic measure on port 8883.

Conenction LiveTcpUdpWatch main screen

Launching the MQTTNet client sending every 30 seconds resulted in traffic like this

4179b - Establishing connection
4284b - 105b
4317b - 33b
4386b - 69b
4455b - 69b
4524b - 69b
4593b - 69b
4662b - 69b
4731b - 69b
4800b - 69b
4869b - 69b
4938b - 69b
5007b - 69b
5076b - 69b
5145b - 69b
5214b - 69b
5288b - 69b

So it looks like my very rough numbers are close to the numbers discussed in the above article. I need to explore the impact of keep-alive messages and other background operations.

Bosch IoT Suite with MQTTnet

As I’m testing my Message Queue Telemetry Transport(MQTT) LoRa gateway I’m building a proof of concept(PoC) .Net core console application for each IoT platform I would like to support.

This PoC was to confirm that I could connect to the Bosch IoT Suite MQTT API then format topics and payloads correctly.

MQTTNet Console Client

The Bosch IoT Hub MQTT broker, username, password, and clientID are the required command line parameters. For this PoC I ran out of time to get cloud to device (C2D) messaging or any presentation functionality working.

/*
    Copyright ® 2019 December devMobile Software, All Rights Reserved
 
    MIT License

    Permission is hereby granted, free of charge, to any person obtaining a copy
    of this software and associated documentation files (the "Software"), to deal
    in the Software without restriction, including without limitation the rights
    to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
    copies of the Software, and to permit persons to whom the Software is
    furnished to do so, subject to the following conditions:

    The above copyright notice and this permission notice shall be included in all
    copies or substantial portions of the Software.

    THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
    IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
    FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
    AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
    LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
    OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
    SOFTWARE

	 A quick and dirty test client to explore how BoschIoT Suite MQTT connectivity works
 */
namespace devMobile.Mqtt.TestClient.BoschIoTSuite
{
   using System;
   using System.Diagnostics;
   using System.Threading;
   using System.Threading.Tasks;

   using MQTTnet;
   using MQTTnet.Client;
   using MQTTnet.Client.Disconnecting;
   using MQTTnet.Client.Options;
   using MQTTnet.Client.Receiving;
   using Newtonsoft.Json;
   using Newtonsoft.Json.Linq;

   class Program
   {
      private static IMqttClient mqttClient = null;
      private static IMqttClientOptions mqttOptions = null;
      private static string server;
      private static string username;
      private static string password;
      private static string clientId;

      static void Main(string[] args)
      {
         MqttFactory factory = new MqttFactory();
         mqttClient = factory.CreateMqttClient();

         if (args.Length != 4) 
         {
            Console.WriteLine("[MQTT Server] [UserName] [Password] [ClientID]");
            Console.WriteLine("Press <enter> to exit");
            Console.ReadLine();
            return;
         }

         server = args[0];
         username = args[1];
         password = args[2];
         clientId = args[3];

         mqttOptions = new MqttClientOptionsBuilder()
            .WithTcpServer(server)
            .WithCredentials(username, password)
            .WithClientId(clientId)
            .WithTls()
            .Build();

         mqttClient.UseDisconnectedHandler(new MqttClientDisconnectedHandlerDelegate(e => MqttClient_Disconnected(e)));
         mqttClient.UseApplicationMessageReceivedHandler(new MqttApplicationMessageReceivedHandlerDelegate(e => MqttClient_ApplicationMessageReceived(e)));
         mqttClient.ConnectAsync(mqttOptions).Wait();

         string topicD2C = "telemetry";

         while (true)
         {
            JObject payloadJObject = new JObject();

            payloadJObject.Add("OfficeTemperature", "22." + DateTime.UtcNow.Millisecond.ToString());
            payloadJObject.Add("OfficeHumidity", (DateTime.UtcNow.Second + 40).ToString());

            string payload = JsonConvert.SerializeObject(payloadJObject);
            Console.WriteLine($"Topic:{topicD2C} Payload:{payload}");

            var message = new MqttApplicationMessageBuilder()
               .WithTopic(topicD2C)
               .WithPayload(payload)
               .WithAtMostOnceQoS() // Anthing but this causes timeout
               .WithRetainFlag()
            .Build();

            Console.WriteLine("PublishAsync start");
            mqttClient.PublishAsync(message).Wait();
            Console.WriteLine("PublishAsync finish");

            Thread.Sleep(30100);
         }
      }

      private static void MqttClient_ApplicationMessageReceived(MqttApplicationMessageReceivedEventArgs e)
      {
         Console.WriteLine($"ClientId:{e.ClientId} Topic:{e.ApplicationMessage.Topic} Payload:{e.ApplicationMessage.ConvertPayloadToString()}");
      }

      private static async void MqttClient_Disconnected(MqttClientDisconnectedEventArgs e)
      {
         Debug.WriteLine("Disconnected");
         await Task.Delay(TimeSpan.FromSeconds(5));

         try
         {
            await mqttClient.ConnectAsync(mqttOptions);
         }
         catch (Exception ex)
         {
            Debug.WriteLine("Reconnect failed {0}", ex.Message);
         }
      }
   }
}

The bosch IoT Hub device configuration was via a swagger API but I need to spend some more time figuring out how to configure the data analysis and presentation tools.

I adapted the steps in the IoT Hub Documentation for Sending Device Data using MQTT. The first step was to create a free Hub subscription.

IoT Hub Subscription

Then using the device registry swagger UI page to add a new device.

Device Registry Swagger UI

After a couple of failed attempts I worked out the format of the Authorisation details (I think the username format in the online documentation might be wrong)

Swagger UI Authorisation form
Querying the available devices

Of the 10+ SaaS IoT services I have setup the Bosch IoT Suite was the hardest to get working. I think this was becuase it is meant to be managed via the API from a in-house application. In a future post I’ll get configure the cloud to device messaging, plus analysis and display functionality.

wolkabout with MQTTnet

As I’m testing my Message Queue Telemetry Transport(MQTT) LoRa gateway I’m building a proof of concept(PoC) .Net core console application for each IoT platform I would like to support.

This PoC was to confirm that I could connect to the walkabout MQTT API then format topics and payloads correctly.

MQTTNet Console Client

The walkabout MQTT broker, username, API Key, and device ID are the required command line parameters. For this PoC I couldn’t get cloud to device (C2D) or Transport Layer Security(TLS) working so will have to do some more research.

namespace devmobile.Mqtt.TestClient.WolkAbout
{
   using System;
   using System.Diagnostics;
   using System.Threading;
   using System.Threading.Tasks;

   using MQTTnet;
   using MQTTnet.Client;
   using MQTTnet.Client.Disconnecting;
   using MQTTnet.Client.Options;

   using Newtonsoft.Json;
   using Newtonsoft.Json.Linq;

   class Program
   {
      private static IMqttClient mqttClient = null;
      private static IMqttClientOptions mqttOptions = null;
      private static string server;
      private static string username;
      private static string apiKey;
      private static string clientID;

      static void Main(string[] args)
      {
         MqttFactory factory = new MqttFactory();
         mqttClient = factory.CreateMqttClient();

         if ((args.Length != 4) )
            {
            Console.WriteLine("[MQTT Server] [UserName] [APIKey] [ClientID]");
            Console.WriteLine("Press <enter> to exit");
            Console.ReadLine();
            return;
         }

         server = args[0];
         username = args[1];
         apiKey = args[2];
         clientID = args[3];

         Console.WriteLine($"MQTT Server:{server} Username:{username} ClientID:{clientID}");

         // wolkabout formatted client state update topic
         string topicD2C = $"readings/{username}/";

         mqttOptions = new MqttClientOptionsBuilder()
            .WithTcpServer(server)
            .WithCredentials(username, apiKey)
            .WithClientId(clientID)
            //.WithTls()
            .Build();

         mqttClient.UseDisconnectedHandler(new MqttClientDisconnectedHandlerDelegate(e => MqttClient_Disconnected(e)));
         mqttClient.ConnectAsync(mqttOptions).Wait();

         while (true)
         {
            JObject payloadJObject = new JObject();

            double temperature = 22.0 + (DateTime.UtcNow.Millisecond / 1000.0);
            double humidity = 50 + (DateTime.UtcNow.Millisecond / 100.0);

            payloadJObject.Add("Temperature", temperature);
            payloadJObject.Add("Humidity", humidity);

            string payload = JsonConvert.SerializeObject(payloadJObject);
            Console.WriteLine($"Topic:{topicD2C} Payload:{payload}");

            var message = new MqttApplicationMessageBuilder()
               .WithTopic(topicD2C)
               .WithPayload(payload)
               .WithAtLeastOnceQoS()
               .Build();

            Console.WriteLine("PublishAsync start");
            mqttClient.PublishAsync(message).Wait();
            Console.WriteLine("PublishAsync finish");

            Thread.Sleep(30100);
         }
      }

      private static async void MqttClient_Disconnected(MqttClientDisconnectedEventArgs e)
      {
         Debug.WriteLine("Disconnected");
         await Task.Delay(TimeSpan.FromSeconds(5));

         try
         {
            await mqttClient.ConnectAsync(mqttOptions);
         }
         catch (Exception ex)
         {
            Debug.WriteLine("Reconnect failed {0}", ex.Message);
         }
      }
   }

The walkabout device configuration was relatively easy but I need watch the instructional videos again to better understand the device and data semantics relationship.

Data semantics configuration
Devices setup
Device Setup
My first dashboard

SmartWorks with MQTTnet

As I’m testing my Message Queue Telemetry Transport(MQTT) LoRa gateway I’m building a proof of concept(PoC) .Net core console application for each IoT platform I would like to support.

This PoC was to confirm that I could connect to the SmartWorks (formerly Carriots) MQTT API then format topics and payloads correctly.

MQTTNet Console Client

The SmartWorks MQTT broker, username, and device ID are the required command line parameters. I didn’t notice any configuration options for cloud to device (C2D) messaging which maybe due to my device configuration or the free trial I was using.

namespace devMobile.Mqtt.TestClient.SmartWorks
{
   using System;
   using System.Diagnostics;
   using System.Threading;
   using System.Threading.Tasks;

   using MQTTnet;
   using MQTTnet.Client;
   using MQTTnet.Client.Disconnecting;
   using MQTTnet.Client.Options;
   using MQTTnet.Client.Receiving;
   using Newtonsoft.Json;
   using Newtonsoft.Json.Linq;

   class Program
   {
      private static IMqttClient mqttClient = null;
      private static IMqttClientOptions mqttOptions = null;
      private static string server;
      private static string username;
      private static string clientId;
      private static string commandTopic;
      private static string groupname;
      private static string feedname;

      static void Main(string[] args)
      {
         MqttFactory factory = new MqttFactory();
         mqttClient = factory.CreateMqttClient();

         if (args.Length != 3) 
         {
            Console.WriteLine("[MQTT Server] [UserName] [ClientID]");
            Console.WriteLine("Press <enter> to exit");
            Console.ReadLine();
            return;
         }

         server = args[0];
         username = args[1];
         clientId = args[2];

         mqttOptions = new MqttClientOptionsBuilder()
            .WithTcpServer(server)
            .WithCredentials(username, "")
            .WithClientId(clientId)
            .WithTls()
            .Build();

         mqttClient.UseDisconnectedHandler(new MqttClientDisconnectedHandlerDelegate(e => MqttClient_Disconnected(e)));
         mqttClient.ConnectAsync(mqttOptions).Wait();

         // Adafruit.IO format for topics which are called feeds
         string topicD2C = $"{username}/streams";

         while (true)
         {
            JObject payloadJObject = new JObject();

            payloadJObject.Add("at", "now");
            payloadJObject.Add("device", clientId);
            payloadJObject.Add("protocol", "v2");

            double temperature = 22.0 + (DateTime.UtcNow.Millisecond / 1000.0);
            double humidity = 50 + (DateTime.UtcNow.Millisecond / 100.0);

            JObject dataJObject = new JObject();
            dataJObject.Add("OfficeTemperature", temperature);
            dataJObject.Add("OfficeHumidity", humidity);

            payloadJObject.Add("data", dataJObject);

            string payload = JsonConvert.SerializeObject(payloadJObject);
            Console.WriteLine($"Topic:{topicD2C} Payload:{payload}");

            var message = new MqttApplicationMessageBuilder()
               .WithTopic(topicD2C)
               .WithPayload(payload)
               .WithAtLeastOnceQoS()
            .Build();

            Console.WriteLine("PublishAsync start");
            mqttClient.PublishAsync(message).Wait();
            Console.WriteLine("PublishAsync finish");

            Thread.Sleep(30100);
         }
      }

      private static async void MqttClient_Disconnected(MqttClientDisconnectedEventArgs e)
      {
         Debug.WriteLine("Disconnected");
         await Task.Delay(TimeSpan.FromSeconds(5));

         try
         {
            await mqttClient.ConnectAsync(mqttOptions);
         }
         catch (Exception ex)
         {
            Debug.WriteLine("Reconnect failed {0}", ex.Message);
         }
      }
   }
}

The ThingsBoard device configuration was relatively easy with convenient buttons to copy the Device ID (Client ID in test client) and Access Token (UserName in test client). I need to revisit the Device and Group configuration to see if I can make the automatically generated names more user friendly.

Devices configuration

The Device configuration form has a tab which has a link for the “Data Streams” form which was useful for debugging.

Device configuration

I have emailed SmartWorks support about a free trial of their dashboard product as it is not available in the free trial.

Device data stream query form

Overall the initial configuration went smoothly but the lack of any dashboard functionality in the free trial was quite limiting.

Azure IoT Hub SAS Tokens revisited yet again

Based my previous post on SAS Token Expiry I wrote a test harness to better understand DateTimeOffset

using System;

namespace UnixEpochTester
{
   class Program
   {
      static void Main(string[] args)
      {
         Console.WriteLine($"DIY                {new DateTime(1970, 1, 1, 0, 0, 0, DateTimeKind.Utc)}");
         Console.WriteLine($"DateTime.UnixEpoch {DateTime.UnixEpoch} {DateTime.UnixEpoch.Kind}");
         Console.WriteLine();

         TimeSpan fromUnixEpochNow = DateTime.UtcNow - DateTime.UnixEpoch;
         Console.WriteLine($"Epoc now {fromUnixEpochNow} {fromUnixEpochNow.TotalSeconds.ToString("f0")} sec");
         Console.WriteLine();

         TimeSpan fromUnixEpochFixed = new DateTime(2019, 11, 30, 2, 0, 0, DateTimeKind.Utc) - DateTime.UnixEpoch;
         Console.WriteLine($"Epoc  {fromUnixEpochFixed} {fromUnixEpochFixed.TotalSeconds.ToString("f0")} sec");
         Console.WriteLine();

         DateTimeOffset dateTimeOffset = new DateTimeOffset( new DateTime( 2019,11,30,2,0,0, DateTimeKind.Utc));
         Console.WriteLine($"Epoc DateTimeOffset {fromUnixEpochFixed} {dateTimeOffset.ToUnixTimeSeconds()}");
         Console.WriteLine();

         TimeSpan fromEpochStart = new DateTime(2019, 11, 30, 2, 0, 0, DateTimeKind.Utc) - DateTime.UnixEpoch;
         Console.WriteLine($"Epoc DateTimeOffset {fromEpochStart} {fromEpochStart.TotalSeconds.ToString("F0")}");
         Console.WriteLine();


         // https://www.epochconverter.com/ matches
         // https://www.unixtimestamp.com/index.php matches

         Console.WriteLine("Press ENTER to exit");
         Console.ReadLine();
      }
   }
}

I validated my numbers against a couple of online calculators and they matched which was a good start.

DateTimeOffset test harness

As I was testing my Azure MQTT Test Client I had noticed some oddness with MQTT connection timeouts.

string token = generateSasToken($"{server}/devices/{clientId}", password, "", new TimeSpan(0,5,0));
1/12/2019 1:29:52 PM> Device: [MQTTLoRa915MHz], Data:[{"OfficeTemperature":"22.391","OfficeHumidity":"93"}]
1/12/2019 1:30:22 PM> Device: [MQTTLoRa915MHz], Data:[{"OfficeTemperature":"22.29","OfficeHumidity":"64"}]
...
1/12/2019 1:43:56 PM> Device: [MQTTLoRa915MHz], Data:[{"OfficeTemperature":"22.591","OfficeHumidity":"98"}]
1/12/2019 1:44:26 PM> Device: [MQTTLoRa915MHz], Data:[{"OfficeTemperature":"22.754","OfficeHumidity":"68"}]


string token = generateSasToken($"{server}/devices/{clientId}", password, "", new TimeSpan(0,5,0));
1/12/2019 1:29:52 PM> Device: [MQTTLoRa915MHz], Data:[{"OfficeTemperature":"22.391","OfficeHumidity":"93"}]
1/12/2019 1:30:22 PM> Device: [MQTTLoRa915MHz], Data:[{"OfficeTemperature":"22.29","OfficeHumidity":"64"}]
...
1/12/2019 2:01:37 PM> Device: [MQTTLoRa915MHz], Data:[{"OfficeTemperature":"22.334","OfficeHumidity":"79"}]
1/12/2019 2:02:07 PM> Device: [MQTTLoRa915MHz], Data:[{"OfficeTemperature":"22.503","OfficeHumidity":"49"}]


string token = generateSasToken($"{server}/devices/{clientId}", password, "", new TimeSpan(0,5,0));
2/12/2019 9:27:21 PM> Device: [MQTTLoRa915MHz], Data:[{"OfficeTemperature":"22.196","OfficeHumidity":"61"}]
2/12/2019 9:27:51 PM> Device: [MQTTLoRa915MHz], Data:[{"OfficeTemperature":"22.788","OfficeHumidity":"91"}]
...
2/12/2019 9:36:24 PM> Device: [MQTTLoRa915MHz], Data:[{"OfficeTemperature":"22.670","OfficeHumidity":"64"}]
2/12/2019 9:36:54 PM> Device: [MQTTLoRa915MHz], Data:[{"OfficeTemperature":"22.836","OfficeHumidity":"94"}]


string token = generateSasToken($"{server}/devices/{clientId}", password, "", new TimeSpan(0,5,0));
2/12/2019 9:40:52 PM> Device: [MQTTLoRa915MHz], Data:[{"OfficeTemperature":"22.46","OfficeHumidity":"92"}]
2/12/2019 9:41:22 PM> Device: [MQTTLoRa915MHz], Data:[{"OfficeTemperature":"22.443","OfficeHumidity":"62"}]
...
2/12/2019 9:50:55 PM> Device: [MQTTLoRa915MHz], Data:[{"OfficeTemperature":"22.742","OfficeHumidity":"95"}]


string token = generateSasToken($"{server}/devices/{clientId}", password, "", new TimeSpan(0,10,0));
approx 15min as only 30 sec resolution
1/12/2019 12:50:23 PM> Device: [MQTTLoRa915MHz], Data:[{"OfficeTemperature":"22.630","OfficeHumidity":"65"}]
1/12/2019 12:50:53 PM> Device: [MQTTLoRa915MHz], Data:[{"OfficeTemperature":"22.798","OfficeHumidity":"95"}]
...
1/12/2019 1:03:59 PM> Device: [MQTTLoRa915MHz], Data:[{"OfficeTemperature":"22.677","OfficeHumidity":"41"}]
1/12/2019 1:04:30 PM> Device: [MQTTLoRa915MHz], Data:[{"OfficeTemperature":"22.26","OfficeHumidity":"72"}]


string token = generateSasToken($"{server}/devices/{clientId}", password, "", new TimeSpan(0,10,0));
approx 15min as only 30 sec resolution
1/12/2019 1:09:30 PM> Device: [MQTTLoRa915MHz], Data:[{"OfficeTemperature":"22.106","OfficeHumidity":"72"}]
1/12/2019 1:10:00 PM> Device: [MQTTLoRa915MHz], Data:[{"OfficeTemperature":"22.463","OfficeHumidity":"42"}]
...
1/12/2019 1:23:35 PM> Device: [MQTTLoRa915MHz], Data:[{"OfficeTemperature":"22.366","OfficeHumidity":"77"}]
1/12/2019 1:24:05 PM> Device: [MQTTLoRa915MHz], Data:[{"OfficeTemperature":"22.537","OfficeHumidity":"47"}]

The dataset with the 5 minute expiry which remained connected for approximately 30 mins was hopefully a configuration issue.

The updated SAS Token code not uses ToUnixTimeSeconds to eliminate the scope for local vs. UTC issues.

      public static string generateSasToken(string resourceUri, string key, string policyName, TimeSpan timeToLive)
      {
         DateTimeOffset expiryDateTimeOffset = new DateTimeOffset(DateTime.UtcNow.Add(timeToLive));

         string expiryEpoch = expiryDateTimeOffset.ToUnixTimeSeconds().ToString();
         string stringToSign = WebUtility.UrlEncode(resourceUri) + "\n" + expiryEpoch;

         HMACSHA256 hmac = new HMACSHA256(Convert.FromBase64String(key));
         string signature = Convert.ToBase64String(hmac.ComputeHash(Encoding.UTF8.GetBytes(stringToSign)));

         string token = $"SharedAccessSignature sr={WebUtility.UrlEncode(resourceUri)}&sig={WebUtility.UrlEncode(signature)}&se={expiryEpoch}";

         if (!String.IsNullOrEmpty(policyName))
         {
            token += "&skn=" + policyName;
         }

         return token;
      }

I need to test the expiry of my SAS Tokens some more especially with the client running on my development machine (NZT which is currently UTC+13) and in Azure (UTC timezone)

ThingsBoard with MQTTnet

As I’m testing my Message Queue Telemetry Transport(MQTT) LoRa gateway I’m building a proof of concept(PoC) .Net core console application for each IoT platform I would like to support.

This PoC was to confirm that I could connect to the ThingsBoard MQTT API then format topics and payloads correctly.

MQTTNet Console Client

The ThingsBoard MQTT broker, username, and client ID are the minimum command line options required with the CommandTopic optional.

   class Program
   {
      private static IMqttClient mqttClient = null;
      private static IMqttClientOptions mqttOptions = null;
      private static string server;
      private static string username;
      private static string clientId;
      private const string telemetryTopic = "v1/devices/me/telemetry";
      private static string commandTopic;

      static void Main(string[] args)
      {
         MqttFactory factory = new MqttFactory();
         mqttClient = factory.CreateMqttClient();

         if ((args.Length != 3) && (args.Length != 4))
         {
            Console.WriteLine("[MQTT Server] [UserName] [ClientID]");
            Console.WriteLine("[MQTT Server] [UserName] [ClientID] [CommandTopic]");
            Console.WriteLine("Press <enter> to exit");
            Console.ReadLine();
            return;
         }

         server =  args[0];
         username = args[1];
         clientId =  args[2];
         
         if (args.Length == 3)
         {
            Console.WriteLine($"MQTT Server:{server} ClientID:{clientId}");
         }

         if (args.Length == 4)
         {
            commandTopic = args[3];
            Console.WriteLine($"MQTT Server:{server} ClientID:{clientId} CommandTopic:{commandTopic}");
         }

         mqttOptions = new MqttClientOptionsBuilder()
            .WithTcpServer(server)
            .WithCredentials(username, "")
            .WithClientId(clientId)
            //.WithTls() blows up if this enabled, need to do more research on certificate config.
            .Build();

         mqttClient.UseDisconnectedHandler(new MqttClientDisconnectedHandlerDelegate(e => MqttClient_Disconnected(e)));
         mqttClient.UseApplicationMessageReceivedHandler(new MqttApplicationMessageReceivedHandlerDelegate(e => MqttClient_ApplicationMessageReceived(e)));
         mqttClient.ConnectAsync(mqttOptions).Wait();

         if (args.Length == 4)
         {
            mqttClient.SubscribeAsync(commandTopic, MQTTnet.Protocol.MqttQualityOfServiceLevel.AtLeastOnce).GetAwaiter().GetResult();
         }

         while (true)
         {
            JObject payloadJObject = new JObject();

            payloadJObject.Add("OfficeTemperature", "22." + DateTime.UtcNow.Millisecond.ToString());
            payloadJObject.Add("OfficeHumidity", (DateTime.UtcNow.Second + 40).ToString());

            string payload = JsonConvert.SerializeObject(payloadJObject);
            Console.WriteLine($"Topic:{telemetryTopic} Payload:{payload}");

            var message = new MqttApplicationMessageBuilder()
               .WithTopic(telemetryTopic)
               .WithPayload(payload)
               .WithAtLeastOnceQoS()
            .Build();

            Console.WriteLine("PublishAsync start");
            mqttClient.PublishAsync(message).Wait();
            Console.WriteLine("PublishAsync finish");

            Thread.Sleep(30100);
         }
      }

      private static void MqttClient_ApplicationMessageReceived(MqttApplicationMessageReceivedEventArgs e)
      {
         Console.WriteLine($"ClientId:{e.ClientId} Topic:{e.ApplicationMessage.Topic} Payload:{e.ApplicationMessage.ConvertPayloadToString()}");
      }

      private static async void MqttClient_Disconnected(MqttClientDisconnectedEventArgs e)
      {
         Debug.WriteLine("Disconnected");
         await Task.Delay(TimeSpan.FromSeconds(5));

         try
         {
            await mqttClient.ConnectAsync(mqttOptions);
         }
         catch (Exception ex)
         {
            Debug.WriteLine("Reconnect failed {0}", ex.Message);
         }
      }

The ThingsBoard device configuration was relatively easy with convenient buttons to copy the Device ID (Client ID in test client) and Access Token (UserName in test client). After looking at the source code for some of the other samples I figured out the ThingsBoard MQTT setup does not use the password field.

Device setup

The Device configuration form has a tab which displays the last telemetry which was useful for debugging. (I need to investigate the MQTT API support for claiming devices)

Device Telemetry display

To get telemetry data displayed on my dashboard I “added” it to my dashboard from the Entity configuration form. (I need to spend some more time watching the video tutorials to understand this process).

Device Entity View Setup

The dashboard designer had a number of “widgets” and what appeared to be the ability to add custom ones. Most forms also had “customer” option which appeared to be for multi-tenant support.

Selecting a dashboard graph widget
Configuring the y Axis Range for graph widget
Dashboard display home office Humidity & Temperature Information

Overall the initial configuration went smoothly after I figured out that the password was not required, and that Transport Layer Security(TLS) required some additional configuration.

Azure IoT Hub MQTT LoRa Field Gateway

Back in April I started working on an MQTT LoRa Field gateway which was going to support a selection of different Software as a service(SaaS) Internet of Things IoT) platforms.

I now have a working Azure IoT Hub plug-in (Azure IoT Central support as planned as well) with the first iteration focused on Device to Cloud (D2C) messaging. In a future iteration I will add Cloud to Device messaging(C2D).

My applications use a lightweight, easy to implemented protocol which is intended for hobbyist and educational use rather than commercial applications (I have been working on a more secure version as yet another side project)

I have a number of sample Arduino with Dragino LoRa Shield for Arduino, MakerFabs Maduino, Dragino LoRa Mini Dev, M2M Low power Node and Netduino with Elecrow LoRa RFM95 Shield etc. clients. These work with both my platform specific (Adafruit.IO, Azure IoT Hub/Central) gateways and protocol specific field gateways.

Azure IoT Hub Device Explorer Data Display

When the application is first started it creates a minimal configuration file which should be downloaded, the missing information filled out, then uploaded using the File explorer in the Windows device portal.

{
  "MQTTUserName": "YourIoTHubHub.azure-devices.net/MQTTLoRa915MHz/api-version=2018-06-30",
  "MQTTPassword": "SharedAccessSignature sr=YourIoTHubHub.azure-devices.net%2Fdevices%2FMQTTLoRa915MHz&sig=123456789012345678901234567890123456789012345%3D&se=1574673583",
  "MQTTClientID": "MQTTLoRa915MHz",
  "MQTTServer": "YourIoTHubHub.azure-devices.net",
  "Address": "LoRaIoT1",
  "Frequency": 915000000.0,
  "MessageHandlerAssembly": "Mqtt.IoTCore.FieldGateway.LoRa.AzureIoTHub",
  "PlatformSpecificConfiguration": ""
}

The application logs debugging information to the Windows 10 IoT Core ETW logging Microsoft-Windows-Diagnostics-LoggingChannel

MQTT LoRa Gateway with Azure IoT Hub plug-in

The message handler uploads all values in an inbound messages in one MQTT message.

namespace devMobile.Mqtt.IoTCore.FieldGateway
{
   using System;
   using System.Diagnostics;
   using System.Text;
   using Windows.Foundation.Diagnostics;

   using devMobile.IoT.Rfm9x;
   using MQTTnet;
   using MQTTnet.Client;
   using Newtonsoft.Json.Linq;
   using Newtonsoft.Json;

   public class MessageHandler : IMessageHandler
   {
      private LoggingChannel Logging { get; set; }
      private IMqttClient MqttClient { get; set; }
      private Rfm9XDevice Rfm9XDevice { get; set; }
      private string PlatformSpecificConfiguration { get; set; }

      void IMessageHandler.Initialise(LoggingChannel logging, IMqttClient mqttClient, Rfm9XDevice rfm9XDevice, string platformSpecificConfiguration)
      {
         LoggingFields processInitialiseLoggingFields = new LoggingFields();

         this.Logging = logging;
         this.MqttClient = mqttClient;
         this.Rfm9XDevice = rfm9XDevice;
         this.PlatformSpecificConfiguration = platformSpecificConfiguration;
      }

      async void IMessageHandler.Rfm9XOnReceive(Rfm9XDevice.OnDataReceivedEventArgs e)
      {
         LoggingFields processReceiveLoggingFields = new LoggingFields();
         char[] sensorReadingSeparators = { ',' };
         char[] sensorIdAndValueSeparators = { ' ' };

         processReceiveLoggingFields.AddString("PacketSNR", e.PacketSnr.ToString("F1"));
         processReceiveLoggingFields.AddInt32("PacketRSSI", e.PacketRssi);
         processReceiveLoggingFields.AddInt32("RSSI", e.Rssi);

         string addressBcdText = BitConverter.ToString(e.Address);
         processReceiveLoggingFields.AddInt32("DeviceAddressLength", e.Address.Length);
         processReceiveLoggingFields.AddString("DeviceAddressBCD", addressBcdText);

         string messageText;
         try
         {
            messageText = UTF8Encoding.UTF8.GetString(e.Data);
            processReceiveLoggingFields.AddString("MessageText", messageText);
         }
         catch (Exception ex)
         {
            processReceiveLoggingFields.AddString("Exception", ex.ToString());
            this.Logging.LogEvent("PayloadProcess failure converting payload to text", processReceiveLoggingFields, LoggingLevel.Warning);
            return;
         }

         // Chop up the CSV text
         string[] sensorReadings = messageText.Split(sensorReadingSeparators, StringSplitOptions.RemoveEmptyEntries);
         if (sensorReadings.Length < 1)
         {
            this.Logging.LogEvent("PayloadProcess payload contains no sensor readings", processReceiveLoggingFields, LoggingLevel.Warning);
            return;
         }

         JObject payloadJObject = new JObject();

         JObject feeds = new JObject();

         // Chop up each sensor read into an ID & value
         foreach (string sensorReading in sensorReadings)
         {
            string[] sensorIdAndValue = sensorReading.Split(sensorIdAndValueSeparators, StringSplitOptions.RemoveEmptyEntries);

            // Check that there is an id & value
            if (sensorIdAndValue.Length != 2)
            {
               this.Logging.LogEvent("PayloadProcess payload invalid format", processReceiveLoggingFields, LoggingLevel.Warning);
               return;
            }

            string sensorId = string.Concat(addressBcdText, sensorIdAndValue[0]);
            string value = sensorIdAndValue[1];

            feeds.Add(sensorId.ToLower(), value);
         }
         payloadJObject.Add("feeds", feeds);

         string topic = $"devices/{MqttClient.Options.ClientId}/messages/events/";

         try
         {
            var message = new MqttApplicationMessageBuilder()
               .WithTopic(topic)
               .WithPayload(JsonConvert.SerializeObject(payloadJObject))
               .WithAtLeastOnceQoS()
               .Build();
            Debug.WriteLine(" {0:HH:mm:ss} MQTT Client PublishAsync start", DateTime.UtcNow);
            await MqttClient.PublishAsync(message);
            Debug.WriteLine(" {0:HH:mm:ss} MQTT Client PublishAsync finish", DateTime.UtcNow);

            this.Logging.LogEvent("PublishAsync Azure IoTHub payload", processReceiveLoggingFields, LoggingLevel.Information);
         }
         catch (Exception ex)
         {
            processReceiveLoggingFields.AddString("Exception", ex.ToString());
            this.Logging.LogEvent("PublishAsync Azure IoTHub payload", processReceiveLoggingFields, LoggingLevel.Error);
         }
      }

      void IMessageHandler.MqttApplicationMessageReceived(MqttApplicationMessageReceivedEventArgs e)
      {
         LoggingFields processReceiveLoggingFields = new LoggingFields();

         processReceiveLoggingFields.AddString("ClientId", e.ClientId);
#if DEBUG
         processReceiveLoggingFields.AddString("Payload", e.ApplicationMessage.ConvertPayloadToString());
#endif
         processReceiveLoggingFields.AddString("QualityOfServiceLevel", e.ApplicationMessage.QualityOfServiceLevel.ToString());
         processReceiveLoggingFields.AddBoolean("Retain", e.ApplicationMessage.Retain);
         processReceiveLoggingFields.AddString("Topic", e.ApplicationMessage.Topic);

         this.Logging.LogEvent("MqttApplicationMessageReceived topic not processed", processReceiveLoggingFields, LoggingLevel.Error);
      }

      void IMessageHandler.Rfm9xOnTransmit(Rfm9XDevice.OnDataTransmitedEventArgs e)
      {
      }
   }
}

The formatting of the username and generation of password are password are a bit awkward and will be fixed in a future refactoring. Along with regenerating the SAS connection token just before it is due to expire.

Azure IoT Hub SAS Tokens revisited again

This post has been edited (2019-11-24) my original assumption about how DateTime.Kind unspecified was handled were incorrect.

As I was testing my Azure MQTT Test Client I noticed some oddness with MQTT connection timeouts and this got me wondering about token expiry times. So, I went searching again and found this Azure IoT Hub specific sample code

public static string generateSasToken(string resourceUri, string key, string policyName, int expiryInSeconds = 3600)
{
    TimeSpan fromEpochStart = DateTime.UtcNow - new DateTime(1970, 1, 1);
    string expiry = Convert.ToString((int)fromEpochStart.TotalSeconds + expiryInSeconds);

    string stringToSign = WebUtility.UrlEncode(resourceUri) + "\n" + expiry;

    HMACSHA256 hmac = new HMACSHA256(Convert.FromBase64String(key));
    string signature = Convert.ToBase64String(hmac.ComputeHash(Encoding.UTF8.GetBytes(stringToSign)));

    string token = String.Format(CultureInfo.InvariantCulture, "SharedAccessSignature sr={0}&sig={1}&se={2}", WebUtility.UrlEncode(resourceUri), WebUtility.UrlEncode(signature), expiry);

    if (!String.IsNullOrEmpty(policyName))
    {
        token += "&skn=" + policyName;
    }

    return token;
}

This code worked first time and was more flexible than mine which was a bonus. Though while running my MQTTNet based client I noticed the connection would drop after approximately 10mins (EDIT this was probably an unrelated networking issue).

A long time ago (25 years) I had issues sharing a Unix time value between an applications written with Borland C and Microsoft Visual C which made me wonder about Unix epoch base offsets.

So to test my theory I built a Unix epoch test harness console application

using System;

namespace UnixEpocTest
{
   class Program
   {
      static void Main(string[] args)
      {
         TimeSpan ttl = new TimeSpan(0, 0, 0);

         Console.WriteLine("Current time");
         Console.WriteLine($"Local     {DateTime.Now} {DateTime.Now.Kind}");
         Console.WriteLine($"UTC       {DateTime.UtcNow} {DateTime.UtcNow.Kind}");
         Console.WriteLine($"Unix DIY  {new DateTime(1970, 1, 1)} {new DateTime(1970, 1, 1).Kind}");
         Console.WriteLine($"Unix DIY+ {new DateTime(1970, 1, 1).ToUniversalTime()} {new DateTime(1970, 1, 1).ToUniversalTime().Kind}");
         Console.WriteLine($"Unix DIY  {new DateTime(1970, 1, 1, 0,0,0, DateTimeKind.Utc)}");
         Console.WriteLine($"Unix      {DateTime.UnixEpoch} {DateTime.UnixEpoch.Kind}");
         Console.WriteLine();

         TimeSpan fromEpochStart = DateTime.UtcNow - new DateTime(1970, 1, 1);
         TimeSpan fromEpochStartUtc = DateTime.UtcNow - new DateTime(1970, 1, 1,0,0,0, DateTimeKind.Utc);
         TimeSpan fromEpochStartUnixEpoch = DateTime.UtcNow - DateTime.UnixEpoch;

         Console.WriteLine("Epoch comparison");
         Console.WriteLine($"Local {fromEpochStart} {fromEpochStart.TotalSeconds.ToString("f0")} sec");
         Console.WriteLine($"UTC   {fromEpochStartUtc} {fromEpochStartUtc.TotalSeconds.ToString("f0")} sec");
         Console.WriteLine($"Epoc  {fromEpochStartUnixEpoch} {fromEpochStartUnixEpoch.TotalSeconds.ToString("f0")} sec");
         Console.WriteLine();

         TimeSpan afterEpoch = DateTime.UtcNow.Add(ttl) - new DateTime(1970, 1, 1);
         TimeSpan afterEpochUtC = DateTime.UtcNow.Add(ttl) - new DateTime(1970, 1, 1).ToUniversalTime();
         TimeSpan afterEpochEpoch = DateTime.UtcNow.Add(ttl) - DateTime.UnixEpoch;

         Console.WriteLine("Epoch calculation");
         Console.WriteLine($"Local {afterEpoch}");
         Console.WriteLine($"UTC   {afterEpochUtC}");
         Console.WriteLine($"Epoch {afterEpochEpoch}");
         Console.WriteLine();

         Console.WriteLine("Epoch DateTime");
         Console.WriteLine($"Local :{new DateTime(1970, 1, 1)}");
         Console.WriteLine($"UTC   :{ new DateTime(1970, 1, 1).ToUniversalTime()}");

         Console.WriteLine("Press ENTER to exit");
         Console.ReadLine();

         Console.WriteLine("Hello World!");
      }
   }
}

EDIT: I now think the UtcNow to “unspecified” kind mathematics was being handled correctly. I have updated the code to use the DateTime.UnixEpoch constant so the code is more readable.

public static string generateSasToken(string resourceUri, string key, string policyName, int expiryInSeconds = 900)
      {
         TimeSpan fromEpochStart = DateTime.UtcNow - DateTime.UnixEpoch;
         string expiry = Convert.ToString((int)fromEpochStart.TotalSeconds + expiryInSeconds);

         string stringToSign = WebUtility.UrlEncode(resourceUri) + "\n" + expiry;

         HMACSHA256 hmac = new HMACSHA256(Convert.FromBase64String(key));
         string signature = Convert.ToBase64String(hmac.ComputeHash(Encoding.UTF8.GetBytes(stringToSign)));

         string token = String.Format(CultureInfo.InvariantCulture, "SharedAccessSignature sr={0}&sig={1}&se={2}", WebUtility.UrlEncode(resourceUri), WebUtility.UrlEncode(signature), expiry);

         if (!String.IsNullOrEmpty(policyName))
         {
            token += "&skn=" + policyName;
         }

         return token;
      }

I need to test the expiry of my SAS Tokens some more especially with the client running on my development machine (NZT which is currently UTC+13) and in Azure (UTC timezone)