Myriota Connector – Uplink Payload formatters revisited

The myriota Azure IoT Hub Cloud Identity Translation Gateway payload formatters use compiled C# code to convert uplink packet payloads to JSON.

namespace PayloadFormattercode
{
    using System.Collections.Generic;

    using Newtonsoft.Json.Linq;

    public interface IFormatterUplink
    {
        public JObject Evaluate(IDictionary<string, string> properties, string application, string terminalId, DateTime timestamp, JObject payloadJson, string payloadText, byte[] payloadBytes);
    }
..
}

The myriota uplink packet payload is only 20 bytes long so it is very unlikely that the payloadText and payloadJSON parameters would ever be populated so I removed them from the interface. The uplink message handler interface has been updated and the code to convert (if possible) the payload bytes to text and then to JSON deleted.

namespace PayloadFormatter
{
    using System.Collections.Generic;

    using Newtonsoft.Json.Linq;

    public interface IFormatterUplink
    {
        public JObject Evaluate(IDictionary<string, string> properties, string application, string terminalId, DateTime timestamp, byte[] payloadBytes);
    }
...
}

All of the sample payload formatters have been updated to reflect the updated parameters. The sample Tracker.cs payload formatter unpacks a message from Myriota Dev Kit running the Tracker sample and returns an Azure IoT Central compatible location telemetry payload.

/*
myriota tracker payload format

typedef struct {
  uint16_t sequence_number;
  int32_t latitude;   // scaled by 1e7, e.g. -891234567 (south 89.1234567)
  int32_t longitude;  // scaled by 1e7, e.g. 1791234567 (east 179.1234567)
  uint32_t time;      // epoch timestamp of last fix
} __attribute__((packed)) tracker_message; 

*/ 
using System;
using System.Collections.Generic;
using System.Globalization;

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


public class FormatterUplink : PayloadFormatter.IFormatterUplink
{
    public JObject Evaluate(IDictionary<string, string> properties, string application, string terminalId, DateTime timestamp, byte[] payloadBytes)
    {
        JObject telemetryEvent = new JObject();

        if (payloadBytes is null)
        {
            return telemetryEvent;
        }

        telemetryEvent.Add("SequenceNumber", BitConverter.ToUInt16(payloadBytes));

        JObject location = new JObject();

        double latitude = BitConverter.ToInt32(payloadBytes, 2) / 10000000.0;
        location.Add("lat", latitude);

        double longitude = BitConverter.ToInt32(payloadBytes, 6) / 10000000.0;
        location.Add("lon", longitude);

        location.Add("alt", 0);

        telemetryEvent.Add("DeviceLocation", location);

        UInt32 packetimestamp = BitConverter.ToUInt32(payloadBytes, 10);

        DateTime fixAtUtc = DateTime.UnixEpoch.AddSeconds(packetimestamp);

        telemetryEvent.Add("FixAtUtc", fixAtUtc);

        properties.Add("iothub-creation-time-utc", fixAtUtc.ToString("s", CultureInfo.InvariantCulture));

        return telemetryEvent;
    }
}

If a message payload is text or JSON it can still be converted in the payload formatter.

Myriota Connector – Azure IoT Hub DTDL Support

The Myriota connector supports the use of Digital Twin Definition Language(DTDL) for Azure IoT Hub Connection Strings and the Azure IoT Hub Device Provisioning Service(DPS).

{
  "ConnectionStrings": {
    "ApplicationInsights": "...",
    "UplinkQueueStorage": "...",
    "PayloadFormattersStorage": "..."
  },
  "AzureIoT": {
   ...
 "ApplicationToDtdlModelIdMapping": {
   "tracker": "dtmi:myriotaconnector:Tracker_2lb;1",
     }
  }
 ...    
}

The Digital Twin Definition Language(DTDL) configuration used when a device is provisioned or when it connects is determined by the payload application which is based on the Myriota Destination endpoint.

The Azure Function Configuration of Application to DTDL Model ID

BEWARE – They application in ApplicationToDtdlModelIdMapping is case sensitive!

Azure IoT Central Device Template Configuration

I used Azure IoT Central Device Template functionality to create my Azure Digital Twin definitions.

Azure IoT Hub Device Connection String

The DeviceClient CreateFromConnectionString method has an optional ClientOptions parameter which specifies the DTLDL model ID for the duration of the connection.

private async Task<DeviceClient> AzureIoTHubDeviceConnectionStringConnectAsync(string terminalId, string application, object context)
{
    DeviceClient deviceClient;

    if (_azureIoTSettings.ApplicationToDtdlModelIdMapping.TryGetValue(application, out string? modelId))
    {
        ClientOptions clientOptions = new ClientOptions()
        {
            ModelId = modelId
        };

        deviceClient = DeviceClient.CreateFromConnectionString(_azureIoTSettings.AzureIoTHub.ConnectionString, terminalId, TransportSettings, clientOptions);
    }
    else
    { 
        deviceClient = DeviceClient.CreateFromConnectionString(_azureIoTSettings.AzureIoTHub.ConnectionString, terminalId, TransportSettings);
    }

    await deviceClient.OpenAsync();

    return deviceClient;
}
Azure IoT Explorer Telemetry message with DTDL Model ID

Azure IoT Hub Device Provisioning Service

The ProvisioningDeviceClient RegisterAsync method has an optional ProvisionRegistrationAdditionalData parameter. The PnpConnection CreateDpsPayload is used to generate the JsonData property which specifies the DTLDL model ID used when the device is initially provisioned.

private async Task<DeviceClient> AzureIoTHubDeviceProvisioningServiceConnectAsync(string terminalId, string application, object context)
{
    DeviceClient deviceClient;

    string deviceKey;
    using (var hmac = new HMACSHA256(Convert.FromBase64String(_azureIoTSettings.AzureIoTHub.DeviceProvisioningService.GroupEnrollmentKey)))
    {
        deviceKey = Convert.ToBase64String(hmac.ComputeHash(Encoding.UTF8.GetBytes(terminalId)));
    }

    using (var securityProvider = new SecurityProviderSymmetricKey(terminalId, deviceKey, null))
    {
        using (var transport = new ProvisioningTransportHandlerAmqp(TransportFallbackType.TcpOnly))
        {
            DeviceRegistrationResult result;

            ProvisioningDeviceClient provClient = ProvisioningDeviceClient.Create(
                _azureIoTSettings.AzureIoTHub.DeviceProvisioningService.GlobalDeviceEndpoint,
                _azureIoTSettings.AzureIoTHub.DeviceProvisioningService.IdScope,
                securityProvider,
            transport);

            if (_azureIoTSettings.ApplicationToDtdlModelIdMapping.TryGetValue(application, out string? modelId))
            {
                ClientOptions clientOptions = new ClientOptions()
                {
                    ModelId = modelId
                };

                ProvisioningRegistrationAdditionalData provisioningRegistrationAdditionalData = new ProvisioningRegistrationAdditionalData()
                {
                    JsonData = PnpConvention.CreateDpsPayload(modelId)
                };
                result = await provClient.RegisterAsync(provisioningRegistrationAdditionalData);
            }
            else
            {
                result = await provClient.RegisterAsync();
            }
  
            if (result.Status != ProvisioningRegistrationStatusType.Assigned)
            {
                _logger.LogWarning("Uplink-DeviceID:{0} RegisterAsync status:{1} failed ", terminalId, result.Status);

                throw new ApplicationException($"Uplink-DeviceID:{0} RegisterAsync status:{1} failed");
            }

            IAuthenticationMethod authentication = new DeviceAuthenticationWithRegistrySymmetricKey(result.DeviceId, (securityProvider as SecurityProviderSymmetricKey).GetPrimaryKey());

            deviceClient = DeviceClient.Create(result.AssignedHub, authentication, TransportSettings);
        }
    }

    await deviceClient.OpenAsync();

    return deviceClient;
}
Azure IoT Central Device Connection Group configuration

An Azure IoT Central Device connection groups can be configured to “automagically” provision devices.

Myriota Connector – Azure IoT Hub Connectivity

The Myriota connector supports the use of Azure IoT Hub Connection Strings and the Azure IoT Hub Device Provisioning Service(DPS) for device management. I use Alastair Crabtree’s LazyCache to store Azure IoT Hub connections which are opened the first time they are used.

 public async Task<DeviceClient> GetOrAddAsync(string terminalId, object context)
 {
     DeviceClient deviceClient;

     switch (_azureIoTSettings.AzureIoTHub.ConnectionType)
     {
         case Models.AzureIotHubConnectionType.DeviceConnectionString:
             deviceClient = await _azuredeviceClientCache.GetOrAddAsync(terminalId, (ICacheEntry x) => AzureIoTHubDeviceConnectionStringConnectAsync(terminalId, context));
             break;
         case Models.AzureIotHubConnectionType.DeviceProvisioningService:
             deviceClient = await _azuredeviceClientCache.GetOrAddAsync(terminalId, (ICacheEntry x) => AzureIoTHubDeviceProvisioningServiceConnectAsync(terminalId, context));
             break;
         default:
             _logger.LogError("Uplink- Azure IoT Hub ConnectionType unknown {0}", _azureIoTSettings.AzureIoTHub.ConnectionType);

             throw new NotImplementedException("AzureIoT Hub unsupported ConnectionType");
     }

     return deviceClient;
 }

The IAzureDeviceClientCache.GetOrAddAsync method returns an open Azure IoT Hub DeviceClient connection or uses the method specified in the application configuration.

Azure IoT Hub Device Connection String

The Azure IoT Hub delegate uses a Device Connection String which is retrieved from the application configuration.

{
  "ConnectionStrings": {
    "ApplicationInsights": "...",
    "UplinkQueueStorage": "...",
    "PayloadFormattersStorage": "..."
  },
  "AzureIoT": {
    "AzureIoTHub": {
      "ConnectionType": "DeviceConnectionString",
      "connectionString": "HostName=....azure-devices.net;SharedAccessKeyName=device;SharedAccessKey=...",
        }
   }
 ...    
}
Azure Function with IoT Hub Device connection string configuration
private async Task<DeviceClient> AzureIoTHubDeviceConnectionStringConnectAsync(string terminalId, object context)
{
    DeviceClient deviceClient = DeviceClient.CreateFromConnectionString(_azureIoTSettings.AzureIoTHub.ConnectionString, terminalId, TransportSettings);

    await deviceClient.OpenAsync();

    return deviceClient;
 }
Azure IoT Hub Device Shared Access Policy for Device Connection String

One of my customers uses an Azure Logic Application to manage Myriota and Azure IoT Connector configuration.

Azure IoT Hub manual Device configuration

Azure IoT Hub Device Provisioning Service

The Azure IoT Hub Device Provisioning Service(DPS) delegate uses Symmetric Key Attestation with the Global Device Endpoint, ID Scope and Group Enrollment Key retrieved from the application configuration.

{
  "ConnectionStrings": {
    "ApplicationInsights": "...",
    "UplinkQueueStorage": "...",
    "PayloadFormattersStorage": "..."
  },
  "AzureIoT": {
      "ConnectionType": "DeviceProvisioningService",
      "DeviceProvisioningServiceIoTHub": {
        "GlobalDeviceEndpoint": "global.azure-devices-provisioning.net",
        "IDScope": ".....",
        "GroupEnrollmentKey": "...."
      }
   }
}
Azure IoT Function with Azure IoT Hub Device Provisioning Service(DPS) configuration

Symmetric key attestation with the Azure IoT Hub Device Provisioning Service(DPS) is performed using the same security tokens supported by Azure IoT Hubs to securely connect devices. The symmetric key of an enrollment group isn’t used directly by devices in the provisioning process. Instead, devices that provision through an enrollment group do so using a derived device key.

private async Task<DeviceClient> AzureIoTHubDeviceProvisioningServiceConnectAsync(string terminalId, object context)
{
    DeviceClient deviceClient;

    string deviceKey;
    using (var hmac = new HMACSHA256(Convert.FromBase64String(_azureIoTSettings.AzureIoTHub.DeviceProvisioningService.GroupEnrollmentKey)))
    {
        deviceKey = Convert.ToBase64String(hmac.ComputeHash(Encoding.UTF8.GetBytes(terminalId)));
    }

    using (var securityProvider = new SecurityProviderSymmetricKey(terminalId, deviceKey, null))
    {
        using (var transport = new ProvisioningTransportHandlerAmqp(TransportFallbackType.TcpOnly))
        {
            DeviceRegistrationResult result;

            ProvisioningDeviceClient provClient = ProvisioningDeviceClient.Create(
                _azureIoTSettings.AzureIoTHub.DeviceProvisioningService.GlobalDeviceEndpoint,
                _azureIoTSettings.AzureIoTHub.DeviceProvisioningService.IdScope,
                securityProvider,
                transport);

            result = await provClient.RegisterAsync();
  
            if (result.Status != ProvisioningRegistrationStatusType.Assigned)
            {
                _logger.LogWarning("Uplink-DeviceID:{0} RegisterAsync status:{1} failed ", terminalId, result.Status);

                throw new ApplicationException($"Uplink-DeviceID:{0} RegisterAsync status:{1} failed");
            }

            IAuthenticationMethod authentication = new DeviceAuthenticationWithRegistrySymmetricKey(result.DeviceId, (securityProvider as SecurityProviderSymmetricKey).GetPrimaryKey());

            deviceClient = DeviceClient.Create(result.AssignedHub, authentication, TransportSettings);
        }
    }

    await deviceClient.OpenAsync();

    return deviceClient;
}

The derived device key is a hash of the device’s registration ID and is computed using the symmetric key of the enrollment group. The device can then use its derived device key to sign the SAS token it uses to register with DPS.

Azure Device Provisioning Service Adding Enrollment Group Attestation
Azure Device Provisioning Service Add Enrollment Group IoT Hub(s) selection.
Azure Device Provisioning Service Manager Enrollments

For initial development and testing I ran the function application in the desktop emulator and simulated Myriota Device Manager webhook calls with Azure Storage Explorer and modified sample payloads.

Azure Storage Explorer Storage Account Queued Messages

I then used Azure IoT Explorer to configure devices, view uplink traffic etc.

Azure IoT Explorer Devices

When I connected to my Azure IoT Hub shortly after starting the Myriota Azure IoT Connector Function my test devices started connecting as messages arrived.

Azure IoT Explorer Device Telemetry

I then deployed my function to Azure and configured the Azure IoT Hub connection string, Azure Application Insights connection string etc.

Azure Portal Myriota Resource Group
Azure Portal Myriota IoT Hub Metrics

There was often a significant delay for the Device Status to update. which shouldn’t be a problem.

Myriota – Uplink Payload formatters and caching

My myriota Azure IoT Hub Cloud Identity Translation Gateway payload formatters uses C# code (compiled with CS-Script cached with Alastair Crabtrees’s LazyCache) to convert uplink packet payloads to JSON.

I have found that putting the C/C++ structure for the uplink payload at the top of the convertor really helpful.

/*
myriota tracker payload format

typedef struct {
  uint16_t sequence_number;
  int32_t latitude;   // scaled by 1e7, e.g. -891234567 (south 89.1234567)
  int32_t longitude;  // scaled by 1e7, e.g. 1791234567 (east 179.1234567)
  uint32_t time;      // epoch timestamp of last fix
} __attribute__((packed)) tracker_message; 

*/ 
using System;
using System.Collections.Generic;

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


public class FormatterUplink : PayloadFormatter.IFormatterUplink
{
    public JObject Evaluate(IDictionary<string, string> properties, string application, string terminalId, DateTime timestamp, JObject payloadJson, string payloadText, byte[] payloadBytes)
    {
        JObject telemetryEvent = new JObject();

        telemetryEvent.Add("SequenceNumber", BitConverter.ToUInt16(payloadBytes));

        double latitude = BitConverter.ToInt32(payloadBytes, 2) / 10000000.0;
        telemetryEvent.Add("Latitude", latitude);

        double longitude = BitConverter.ToInt32(payloadBytes, 6) / 10000000.0;
        telemetryEvent.Add("Longitude", longitude);

        UInt32 packetimestamp = BitConverter.ToUInt32(payloadBytes, 10);
        DateTime lastFix = DateTime.UnixEpoch.AddSeconds(packetimestamp);

       properties.Add("iothub-creation-time-utc", lastFix .ToString("s", CultureInfo.InvariantCulture));

       return telemetryEvent;
    }
}

The sample Tracker.cs payload formatter unpacks a message from Myriota Dev Kit running the Tracker sample and returns an Azure IoT Central compatible location telemetry payload.

BEWARE : I think the Azure IoT Central Position lat, lon + alt values might be case sensitive.

Azure IoT Explorer displaying Tracker.cs payload formatter output

The identity payload formatter to use is configured as part of the Destination webhook Uniform Resource Locator (URL).

Myriota Destination configuration application name URL configuration
namespace devMobile.IoT.MyriotaAzureIoTConnector.Connector.Models
{
    public class UplinkPayloadQueueDto
    {
        public string Application { get; set; }
        public string EndpointRef { get; set; }
        public DateTime PayloadReceivedAtUtc { get; set; }
        public DateTime PayloadArrivedAtUtc { get; set; }
        public QueueData Data { get; set; }
        public string Id { get; set; }
        public Uri CertificateUrl { get; set; }
        public string Signature { get; set; }
    }

    public class QueueData
    {
        public List<QueuePacket> Packets { get; set; }
    }

    public class QueuePacket
    {
        public string TerminalId { get; set; }

        public DateTime Timestamp { get; set; }

        public string Value { get; set; }
    }
}

A pair of Azure Blob Storage containers are used to store the uplink/downlink (coming soon) formatter files. The compiled payload formatters are cached with Uplink/Downlink + Application (from the UplinkPayloadQueueDto) as the key.

Azure IoT Storage Explorer uplink payload formatters

The default uplink and downlink formatters used when there is no payload formatter for “Application” are configured in the application settings.

.NET nanoFramework RAK11200 – Brownout Voltage Revisited

The voltage my test setup was calculating looked wrong, then I realised that the sample calculation in the RAK Wireless forums wasn’t applicable to my setup.

I reassembled my RAK11200 WisBlock WiFi Module, RAK19001 WisBlock Base Board, RAK1901 WisBlock Temperature and Humidity Sensor, 1200mAH Lithium Polymer (LiPo) battery, SKU920100 Solar Board test setup, put a new 9V battery (I had forgotten to turn it off last-time) in my multimeter then collected some data. A=ReadValue(), C= ReadRatio(), E= measured battery voltage.

Excel spreadsheet for calculating ratio

I updated the formula used to calculate the battery voltage and deployed the application

public static void Main()
{
    Debug.WriteLine($"{DateTime.UtcNow:HH:mm:ss} devMobile.IoT.RAK.Wisblock.AzureIoTHub.RAK11200.PowerSleep starting");

    Thread.Sleep(5000);

    try
    {
        double batteryVoltage;

        Configuration.SetPinFunction(Gpio.IO04, DeviceFunction.I2C1_DATA);
        Configuration.SetPinFunction(Gpio.IO05, DeviceFunction.I2C1_CLOCK);

        Debug.WriteLine($"{DateTime.UtcNow:HH:mm:ss} Battery voltage measurement");

        // Configure Analog input (AIN0) port then read the "battery charge"
        AdcController adcController = new AdcController();

        using (AdcChannel batteryVoltageAdcChannel = adcController.OpenChannel(AdcControllerChannel))
        {
            batteryVoltage = batteryVoltageAdcChannel.ReadValue() / 723.7685;

            Debug.WriteLine($" BatteryVoltage {batteryVoltage:F2}");

            if (batteryVoltage < Config.BatteryVoltageBrownOutThreshold)
            {
                Sleep.EnableWakeupByTimer(Config.FailureRetryInterval);
                Sleep.StartDeepSleep();
            }
        }
        catch (Exception ex)
        {
...    
}

To test the accuracy of the voltage calculation I am going to run my setup on the office windowsill for a week regularly measuring the voltage. Then, turn the solar panel over (so the battery is not getting charged) and monitor the battery discharging until the RAK11200 WisBlock WiFi Module won’t connect to the network.

.NET nanoFramework RAK11200 – Brownout Voltage

My test setup was a RAK11200 WisBlock WiFi Module, RAK19001 WisBlock Base Board, RAK1901 WisBlock Temperature and Humidity Sensor, 1200mAH Lithium Polymer (LiPo) battery and SKU920100 Solar Board. The test setup uploads temperature, humidity and battery voltage telemetry to an Azure IoT Hub every 5 minutes (short delay so battery life reduced).

The first step was to check that I could get a “battery voltage” value for the RAKWireless RAK11200 WisBlock WiFi Module on a RAK19001 WisBlock Base Board for managing “brownouts” and send to my Azure IoT Hub.

RAK19001 Power supply schematic

The RAK19001 WisBlock Base Board has a voltage divider (R4&R5 with output ADC_VBAT) which is connected to pin 21(AIN0) on the CPU slot connector.

RAK19001 connector schematic

The RAK19001 WisBlock Base Board has quite a low leakage current so the majority of the power consumption should be the RAK11200 WisBlock WiFi Module.

RAK19001 leakage current from specifications

I used AdcController + AdcChannel to read AIN0 and modified the code using the formula (for a RAK4631 module) in the RAK Wireless forums to calculate the battery voltage. (UPDATE This calculation is not applicable to my scenario)

RAK11200 Schematic with battery voltage analog input highlighted

When “slept” the RAK11200 WisBlock WiFi Module power consumption is very low

RAK11200 low power current from specifications
public static void Main()
{
    Debug.WriteLine($"{DateTime.UtcNow:HH:mm:ss} devMobile.IoT.RAK.Wisblock.AzureIoTHub.RAK11200.PowerSleep starting");

    Thread.Sleep(5000); // This do debugger can attach consider removing in realease version

    try
    {
        double batteryVoltage;

        Configuration.SetPinFunction(Gpio.IO04, DeviceFunction.I2C1_DATA);
        Configuration.SetPinFunction(Gpio.IO05, DeviceFunction.I2C1_CLOCK);

        Debug.WriteLine($"{DateTime.UtcNow:HH:mm:ss} Battery voltage measurement");

        // Configure Analog input (AIN0) port then read the "battery charge"
        AdcController adcController = new AdcController();

        using (AdcChannel batteryVoltageAdcChannel = adcController.OpenChannel(AdcControllerChannel))
        {

            // https://forum.rakwireless.com/t/custom-li-ion-battery-voltage-calculation-in-rak4630/4401/7
            // When I checked with multimeter I had to increase 1.72 to 1.9
            batteryVoltage = batteryVoltageAdcChannel.ReadValue() * (3.0 / 4096) * 1.9;

            Debug.WriteLine($" BatteryVoltage {batteryVoltage:F2}");

            if (batteryVoltage < Config.BatteryVoltageBrownOutThreshold)
            {
                Sleep.EnableWakeupByTimer(Config.FailureRetryInterval);
                Sleep.StartDeepSleep();
            }
        }

        Debug.WriteLine($"{DateTime.UtcNow:HH:mm:ss} Wifi connecting");

        if (!WifiNetworkHelper.ConnectDhcp(Config.Ssid, Config.Password, requiresDateTime: true))
        {
            if (NetworkHelper.HelperException != null)
            {
                Debug.WriteLine($"{DateTime.UtcNow:HH:mm:ss} WifiNetworkHelper.ConnectDhcp failed {NetworkHelper.HelperException}");
            }

            Sleep.EnableWakeupByTimer(Config.FailureRetryInterval);
            Sleep.StartDeepSleep();
        }
        Debug.WriteLine($"{DateTime.UtcNow:HH:mm:ss} Wifi connected");

        // Configure the SHTC3 
        I2cConnectionSettings settings = new(I2cDeviceBusID, Shtc3.DefaultI2cAddress);

        string payload ;

        using (I2cDevice device = I2cDevice.Create(settings))
        using (Shtc3 shtc3 = new(device))
        {
            if (shtc3.TryGetTemperatureAndHumidity(out var temperature, out var relativeHumidity))
            {
                Debug.WriteLine($" Temperature {temperature.DegreesCelsius:F1}°C Humidity {relativeHumidity.Value:F0}% BatteryVoltage {batteryVoltage:F2}");

                payload = $"{{\"RelativeHumidity\":{relativeHumidity.Value:F0},\"Temperature\":{temperature.DegreesCelsius:F1}, \"BatteryVoltage\":{batteryVoltage:F2}}}";
            }
            else
            {
                Debug.WriteLine($" BatteryVoltage {batteryVoltage:F2}");

                payload = $"{{\"BatteryVoltage\":{batteryVoltage:F2}}}";
            }

#if SLEEP_SHT3C
            shtc3.Sleep();
#endif
        }

        // Configure the HttpClient uri, certificate, and authorization
        string uri = $"{Config.AzureIoTHubHostName}.azure-devices.net/devices/{Config.DeviceID}";

        HttpClient httpClient = new HttpClient()
        {
            SslProtocols = System.Net.Security.SslProtocols.Tls12,
            HttpsAuthentCert = new X509Certificate(Config.DigiCertBaltimoreCyberTrustRoot),
            BaseAddress = new Uri($"https://{uri}/messages/events?api-version=2020-03-13"),
        };
        httpClient.DefaultRequestHeaders.Add("Authorization", SasTokenGenerate(uri, Config.Key, DateTime.UtcNow.Add(Config.SasTokenRenewFor)));

        Debug.WriteLine($"{DateTime.UtcNow:HH:mm:ss} Azure IoT Hub device {Config.DeviceID} telemetry update start");

        HttpResponseMessage response = httpClient.Post("", new StringContent(payload));

        Debug.WriteLine($"{DateTime.UtcNow:HH:mm:ss} Response code:{response.StatusCode}");

        response.EnsureSuccessStatusCode();
    }
    catch (Exception ex)
    {
        Debug.WriteLine($"{DateTime.UtcNow:HH:mm:ss} Azure IoT Hub telemetry update failed:{ex.Message} {ex?.InnerException?.Message}");

        Sleep.EnableWakeupByTimer(Config.FailureRetryInterval);
        Sleep.StartDeepSleep();
    }

    Sleep.EnableWakeupByTimer(Config.TelemetryUploadInterval);
#if SLEEP_LIGHT
    Sleep.StartLightSleep();
#endif
#if SLEEP_DEEP
    Sleep.StartDeepSleep();
#endif
}

The nanoFramework.Hardware.Esp32.Sleep functionality supports LightSleep and DeepSleep states. The ESP32 device can be “woken up” by GPIO pin(s), Touch pad activity or by a Timer.

RAK11200+RAK19007+RAK1901+ LiPo battery test rig

After some “tinkering” I found the voltage calculation was surprisingly accurate (usually within 0.01V) for my RAK19001 and RAK19007 base boards.

When the battery voltage was close to its minimum working voltage of the ESP32 device it would reboot when the WifiNetworkHelper.ConnectDhcp method was called. This would quickly drain the battery flat even when the solar panel was trying to charge the battery.

Now, before trying to connect to the wireless network the battery voltage is checked and if too low (more experimentation required) the device goes into a deep sleep for a configurable period (more experimentation required). This is so the solar panel can charge the battery to a level where wireless connectivity will work.

Swarm Space – Asset Tracker Payload Formatter

After writing Swarm Space – Payload Formatter Debugging I then tested it creating a new payload formatter for my new Swarm Asset Tracker.

Swarm Asset Tracker device

The Swarm Asset Tracker has a slightly different payload to the Swarm Eval Kit which is detailed in the product manual.

Swarm Asset Tracker JSON payload

The first message sent shortly after I powered up the device had the latitude and longitude of Null Island

The Asset Tracker UserApplicationId is 65002 and the payload is similar to the Swarm Eval Kit. I created some message payloads (location of Christchurch Cathedral) for testing.

The JSON payload sent by my Swarm Asset Tracker

{
  "dt": 1677396395,
  "lt": -43.5333,
  "ln": 172.6333,
  "al": 25,
  "sp": 0,
  "hd": 126,
  "gj": 92,
  "gs": 1,
  "bv": 4103,
  "tp": 20,
  "rs": -110,
  "tr": -107,
  "ts": 3,
  "td": 1677396357,
  "hp": 166,
  "vp": 187,
  "tf": 36526
}

The Base64 representation of the payload sent by my Swarm Asset Tracker

ew0KICAiZHQiOiAxNjc3Mzk2Mzk1LA0KICAibHQiOiAtNDMuNTMzMywNCiAgImxuIjogMTcyLjYzMzMsDQogICJhbCI6IDI1LA0KICAic3AiOiAwLA0KICAiaGQiOiAxMjYsDQogICJnaiI6IDkyLA0KICAiZ3MiOiAxLA0KICAiYnYiOiA0MTAzLA0KICAidHAiOiAyMCwNCiAgInJzIjogLTExMCwNCiAgInRyIjogLTEwNywNCiAgInRzIjogMywNCiAgInRkIjogMTY3NzM5NjM1NywNCiAgImhwIjogMTY2LA0KICAidnAiOiAxODcsDQogICJ0ZiI6IDM2NTI2DQp9

The initial version of my payload formatter

using System;
using System.Collections.Generic;
using System.Globalization;
using Newtonsoft.Json.Linq;

public class FormatterUplink : PayloadFormatter.IFormatterUplink
{
    public JObject Evaluate(IDictionary<string, string> properties, uint organisationId, uint deviceId, byte deviceType, ushort userApplicationId, JObject payloadJson, string payloadText, byte[] payloadBytes)
    {
        JObject telemetryEvent = new JObject();

        if ((payloadText != "") && (payloadJson != null))
        {
            JObject location = new JObject();

            location.Add("lat", payloadJson.GetValue("lt"));
            location.Add("lon", payloadJson.GetValue("ln"));
            location.Add("alt", payloadJson.GetValue("al"));

            telemetryEvent.Add("DeviceLocation", location);
        }

        // Course & speed
        telemetryEvent.Add("Course", payloadJson.GetValue("hd"));
        telemetryEvent.Add("Speed", payloadJson.GetValue("sp"));

        // Battery voltage
        telemetryEvent.Add("BatteryVoltage", payloadJson.GetValue("bv"));

        // RSSI
        telemetryEvent.Add("RSSI", payloadJson.GetValue("rs"));

        properties.Add("iothub-creation-time-utc", DateTimeOffset.FromUnixTimeSeconds((long)payloadJson.GetValue("dt")).ToString("s", CultureInfo.InvariantCulture));

        return telemetryEvent;
    }
}

The PayloadFormatterMaintenanceApplication command line I used for testing my Swarm Asset Tracker payload formatter

The console output of my Swarm Asset Tracker payload formatter

The PayloadFormatterMaintenanceApplication is better than trying to debug a payload formatter in a staging/production environment.

Currently the payload formatters still have to be manually uploaded to the application’s Azure Blob Storage for final testing.

Swarm Space – Payload Formatter Debugging

After Swarm Space – Uplink Payload Formatters revisited I wrote a couple of payload formatters and they were easy to get wrong and the Azure Application Insights error messages were unhelpful.

namespace PayloadFormatter // Additional namespace for shortening interface when usage in formatter code
{
    using System.Collections.Generic;

    using Newtonsoft.Json.Linq;

    public interface IFormatterUplink
    {
        public JObject Evaluate(IDictionary<string, string> properties, uint organisationId, uint deviceId, byte deviceType, ushort userApplicationId, JObject payloadJson, string payloadText, byte[] payloadBytes);
    }

    public interface IFormatterDownlink
    {
        public byte[] Evaluate(IDictionary<string, string> properties, uint organisationId, uint deviceId, byte deviceType, ushort userApplicationId, JObject payloadJson, string payloadText, byte[] payloadBytes);
    }
}

The definitions of the uplink & downlink payload formatter evaluator interfaces have been updated and shifted to a new project.

Visual Studio 2022 Solution with payloadformatter maintenance application

I built a console application to help with developing and debugging uplink or downlink formatters. The application has a number of command line parameters which specify the formatter to be used, UserApplicationId, OrganizationId, DeviceType etc.

public class CommandLineOptions
{
    [Option('d', "Direction", Required = true, HelpText = "Test Uplink or DownLink formatter")]
	public string Direction { get; set; }

    [Option('p', "filename", HelpText = "Uplink or Downlink Payload file name")]
    public string PayloadFilename { get; set; } = string.Empty;

    [Option('o', "OrganisationId", Required = true, HelpText = "Organisation unique identifier")]
    public uint OrganizationId { get; set; }

    [Option('i', "DeviceId", Required = true, HelpText = "Device unique identitifer")]
    public uint DeviceId { get; set; }

    [Option('t', "DeviceType", Required = true, HelpText = "Device type number")]
    public byte DeviceType { get; set; }

    [Option('u', "UserApplicationId", Required = true, HelpText = "User Application Id")]
    public ushort UserApplicationId { get; set; }

    [Option('h', "SwarmHiveReceivedAtUtc", HelpText = "Swarm Hive received at time UTC")]
    public DateTime? SwarmHiveReceivedAtUtc { get; set; }

    [Option('w', "UplinkWebHookReceivedAtUtc", HelpText = "Webhook received at time UTC")]
    public DateTime? UplinkWebHookReceivedAtUtc { get; set; }

    [Option('s', "Status", HelpText = "Uplink local file system file name")]
    public byte? Status { get; set; }

    [Option('c', "Client", HelpText = "Uplink local file system file name")]
    public string Client { get; set; } 
 }

The downlink formatter (similar approach for uplink) loads the sample file as an array of bytes, then tries to convert it to text, and finally to JSON. Then the formatter code is “compiled” and the executed with the file payload and command line parameters.

private static async Task DownlinkFormatterCore(CommandLineOptions options)
{
    Dictionary<string, string> properties = new Dictionary<string, string>();

    string formatterFolder = Path.Combine(Environment.CurrentDirectory, "downlink");
    Console.WriteLine($"Downlink- uplinkFormatterFolder: {formatterFolder}");

    string formatterFile = Path.Combine(formatterFolder, $"{options.UserApplicationId}.cs");
    Console.WriteLine($"Downlink- UserApplicationId: {options.UserApplicationId}");
    Console.WriteLine($"Downlink- Payload formatter file: {formatterFile}");

    PayloadFormatter.IFormatterDownlink evalulator;
    try
    {
        evalulator = CSScript.Evaluator.LoadFile<PayloadFormatter.IFormatterDownlink>(formatterFile);
     }
    catch (CSScriptLib.CompilerException cex)
    {
        Console.Write($"Loading or compiling file:{formatterFile} failed Exception:{cex}");
        return;
    }

    string payloadFilename = Path.Combine(formatterFolder, options.PayloadFilename);
    Console.WriteLine($"Downlink- payloadFilename:{payloadFilename}");
    byte[] uplinkBytes;

    try
    {
        uplinkBytes = File.ReadAllBytes(payloadFilename);
    }
    catch (DirectoryNotFoundException dex)
    {
        Console.WriteLine($"Uplink payload filename directory {formatterFolder} not found:{dex}");
        return;
    }
    catch (FileNotFoundException fnfex)
    {
        Console.WriteLine($"Uplink payload filename {payloadFilename} not found:{fnfex}");
        return;
    }
    catch (FormatException fex)
    {
        Console.WriteLine($"Uplink payload file invalid format {payloadFilename} not found:{fex}");
        return;
    }

    // See if payload can be converted to a string
    string uplinkText = string.Empty;
    try
    {
        uplinkText = Encoding.UTF8.GetString(uplinkBytes);
    }
    catch (FormatException fex)
    {
        Console.WriteLine("Encoding.UTF8.GetString failed:{0}", fex.Message);
    }

    // See if payload can be converted to JSON
    JObject uplinkJson;
    try
    {
        uplinkJson = JObject.Parse(uplinkText);
    }
    catch (JsonReaderException jrex)
    {
        Console.WriteLine("JObject.Parse failed Exception:{1}", jrex);

        uplinkJson = new JObject();
    }

    Console.WriteLine("Properties");
    foreach (var property in properties)
    {
        Console.WriteLine($"{property.Key}:{property.Value}");
    }

    // Transform the byte and optional text and JSON payload
    Byte[] payload;
    try
    {
        payload = evalulator.Evaluate(properties, options.OrganizationId, options.DeviceId, options.DeviceType, options.UserApplicationId, uplinkJson, uplinkText, uplinkBytes);
    }
    catch (Exception ex)
    {
        Console.WriteLine($"evalulatorUplink.Evaluate failed Exception:{ex}");
        return;
    }

    Console.WriteLine("Payload");
    Console.WriteLine(Convert.ToBase64String(payload));
}

The sample JSON payload is what would be sent by Azure IoT Central to a device to configure the fan speed

Azure IoT Central M138 Breakout device template with the Fan Status command selected
{
  "FanStatus": 2
}

If the downlink payload formatter is compiled and executes successfully the Base64 representation output is displayed

using System;
using System.Collections.Generic;
using Newtonsoft.Json.Linq;

public class FormatterDownlink : PayloadFormatter.IFormatterDownlink
{
    public byte[] Evaluate(IDictionary<string, string> properties, uint organisationId, uint deviceId, byte deviceType, ushort userApplicationId, JObject payloadJson, string payloadText, byte[] payloadBytes)
    {
        byte? status = payloadJson.Value<byte?>("FanStatus");

        if ( status.HasValue ) 
        { 
            return new byte[] { status.Value };
        }

        return new byte[]{};
    }
}

If the downlink payload formatter syntax is incorrect e.g. { status.Value ; }; an error message with the line and column is displayed.

using System;
using System.Collections.Generic;
using Newtonsoft.Json.Linq;

public class FormatterDownlink : PayloadFormatter.IFormatterDownlink
{
    public byte[] Evaluate(IDictionary<string, string> properties, uint organisationId, uint deviceId, byte deviceType, ushort userApplicationId, JObject payloadJson, string payloadText, byte[] payloadBytes)
    {
        byte? status = payloadJson.Value<byte?>("FanStatus");

        if ( status.HasValue ) 
        {
            return new byte[] { status.Value ; };
        }

        return new byte[]{};
    }
}

If the downlink payload formatter syntax is correct but execution fails (in the example code division by zero) an error message is displayed.

using System;
using System.Collections.Generic;
using Newtonsoft.Json.Linq;

public class FormatterDownlink : PayloadFormatter.IFormatterDownlink
{
    public byte[] Evaluate(IDictionary<string, string> properties, uint organisationId, uint deviceId, byte deviceType, ushort userApplicationId, JObject payloadJson, string payloadText, byte[] payloadBytes)
    {
        byte? status = payloadJson.Value<byte?>("FanStatus");

        if ( status.HasValue ) 
        {
            int divideByZero = 10;

            divideByZero = divideByZero / 0;

            return new byte[] { status.Value };
        }

        return new byte[]{};
    }
}

The PayloadFormatterMaintenanceApplication makes it significantly easier to develop formatters. Currently the payload formatters have to be manually uploaded to the application’s Azure Blob Storage for final testing.

Swarm Space – Replacing the OpenAPI Client

At the start of this project I used NSwag and Open API Swagger definition file (provided by Swarm Space technical support) to generate a Swarm Space Bumble bee hive client and the core of a simulator.

Swarm Space Bumble hive classes in Visual Studio 2022

My SwarmSpaceAzureIoTConnector project only needed to login, get a list of devices and send messages so all the additional functionality was never going to be used. The method to send a message didn’t work, the class used for the payload (UserMessage) appears to be wrong.

OpenAPI Swagger docs for sending a message

The Open API Swagger definition for sending a message to a device

"post": {
        "tags": [ "messages" ],
        "summary": "POST user messages",
        "description": "<p>This endpoint submits a JSON formatted UserMessage object for delivery to a Swarm device. A JSON object is returned with a newly assigned <code>packetId</code> and <code>status</code> of<code>OK</code> on success, or <code>ERROR</code> (with a description of the error) on failure.</p><p>The current user must have access to the <code>userApplicationId</code> and <code>device</code> given inside the UserMessage JSON. The device must also have the ability to receive messages from the Hive (\"two-way communication\") enabled. If these conditions are not met, a response with status code 403 (Forbidden) will be returned.</p><p>Note that the <code>data</code> field is the <b>Base64-encoded</b> version of the data to be sent. This allows the sending of binary, as well as text, data.</p>",
        "operationId": "addApplicationMessage",
        "requestBody": {
          "content": { "application/json": { "schema": { "$ref": "#/components/schemas/UserMessage" } } },
          "required": true
        },
        "responses": {
          "401": {
            "description": "Unauthorized",
            "content": { "*/*": { "schema": { "$ref": "#/components/schemas/ApiError" } } }
          },
          "403": {
            "description": "Forbidden",
            "content": { "*/*": { "schema": { "$ref": "#/components/schemas/ApiError" } } }
          },
          "400": {
            "description": "Bad Request",
            "content": { "*/*": { "schema": { "$ref": "#/components/schemas/ApiError" } } }
          },
          "200": {
            "description": "OK",
            "content": { "application/json": { "schema": { "$ref": "#/components/schemas/PacketPostReturn" } } }
          }
        }
      }
    },

The Open API Swagger definition for a UserMessage

[System.CodeDom.Compiler.GeneratedCode("NJsonSchema", "13.17.0.0 (NJsonSchema v10.8.0.0 (Newtonsoft.Json v13.0.0.0))")]
    public partial class UserMessage
    {
        /// <summary>
        /// Swarm packet ID
        /// </summary>
        [Newtonsoft.Json.JsonProperty("packetId", Required = Newtonsoft.Json.Required.Always)]
        public long PacketId { get; set; }

        /// <summary>
        /// Swarm message ID. There may be multiple messages for a single message ID. A message ID represents an intent to send a message, but there may be multiple Swarm packets that are required to fulfill that intent. For example, if a Hive -&gt; device message fails to reach its destination, automatic retry attempts to send that message will have the same message ID.
        /// </summary>
        [Newtonsoft.Json.JsonProperty("messageId", Required = Newtonsoft.Json.Required.DisallowNull, NullValueHandling = Newtonsoft.Json.NullValueHandling.Ignore)]
        public long MessageId { get; set; }

        /// <summary>
        /// Swarm device type
        /// </summary>
        [Newtonsoft.Json.JsonProperty("deviceType", Required = Newtonsoft.Json.Required.Always)]
        public int DeviceType { get; set; }

        /// <summary>
        /// Swarm device ID
        /// </summary>
        [Newtonsoft.Json.JsonProperty("deviceId", Required = Newtonsoft.Json.Required.Always)]
        public int DeviceId { get; set; }

        /// <summary>
        /// Swarm device name
        /// </summary>
        [Newtonsoft.Json.JsonProperty("deviceName", Required = Newtonsoft.Json.Required.DisallowNull, NullValueHandling = Newtonsoft.Json.NullValueHandling.Ignore)]
        public string DeviceName { get; set; }

        /// <summary>
        /// Direction of message
        /// </summary>
        [Newtonsoft.Json.JsonProperty("direction", Required = Newtonsoft.Json.Required.Always)]
        public int Direction { get; set; }

        /// <summary>
        /// Message data type, always = 6
        /// </summary>
        [Newtonsoft.Json.JsonProperty("dataType", Required = Newtonsoft.Json.Required.Always)]
        public int DataType { get; set; }

        /// <summary>
        /// Application ID
        /// </summary>
        [Newtonsoft.Json.JsonProperty("userApplicationId", Required = Newtonsoft.Json.Required.Always)]
        public int UserApplicationId { get; set; }

        /// <summary>
        /// Organization ID
        /// </summary>
        [Newtonsoft.Json.JsonProperty("organizationId", Required = Newtonsoft.Json.Required.Always)]
        public int OrganizationId { get; set; }

        /// <summary>
        /// Length of data (in bytes) before base64 encoding
        /// </summary>
        [Newtonsoft.Json.JsonProperty("len", Required = Newtonsoft.Json.Required.DisallowNull, NullValueHandling = Newtonsoft.Json.NullValueHandling.Ignore)]
        public int Len { get; set; }

        /// <summary>
        /// Base64 encoded data string
        /// </summary>
        [Newtonsoft.Json.JsonProperty("data", Required = Newtonsoft.Json.Required.Always)]
        [System.ComponentModel.DataAnnotations.Required(AllowEmptyStrings = true)]
        public byte[] Data { get; set; }

        /// <summary>
        /// Swarm packet ID of acknowledging packet from device
        /// </summary>
        [Newtonsoft.Json.JsonProperty("ackPacketId", Required = Newtonsoft.Json.Required.DisallowNull, NullValueHandling = Newtonsoft.Json.NullValueHandling.Ignore)]
        public long AckPacketId { get; set; }

        /// <summary>
        /// Message status. Possible values:
        /// <br/>0 = incoming message (from a device)
        /// <br/>1 = outgoing message (to a device)
        /// <br/>2 = incoming message, acknowledged as seen by customer. OR a outgoing message packet is on groundstation
        /// <br/>3 = outgoing message, packet is on satellite
        /// <br/>-1 = error
        /// <br/>-3 = failed to deliver, retrying
        /// <br/>-4 = failed to deliver, will not re-attempt
        /// <br/>
        /// </summary>
        [Newtonsoft.Json.JsonProperty("status", Required = Newtonsoft.Json.Required.DisallowNull, NullValueHandling = Newtonsoft.Json.NullValueHandling.Ignore)]
        public int Status { get; set; }

        /// <summary>
        /// Time that the message was received by the Hive
        /// </summary>
        [Newtonsoft.Json.JsonProperty("hiveRxTime", Required = Newtonsoft.Json.Required.Always)]
        [System.ComponentModel.DataAnnotations.Required(AllowEmptyStrings = true)]
        public System.DateTimeOffset HiveRxTime { get; set; }

        private System.Collections.Generic.IDictionary<string, object> _additionalProperties;

        [Newtonsoft.Json.JsonExtensionData]
        public System.Collections.Generic.IDictionary<string, object> AdditionalProperties
        {
            get { return _additionalProperties ?? (_additionalProperties = new System.Collections.Generic.Dictionary<string, object>()); }
            set { _additionalProperties = value; }
        }

    }

After several attempts I gave up and have rebuilt the required Bumble bee hive integration with RestSharp

public async Task SendAsync(uint organisationId, uint deviceId, byte deviceType, ushort userApplicationId, byte[] data, CancellationToken cancellationToken)
{
    await TokenRefresh(cancellationToken);

    _logger.LogInformation("SendAsync: OrganizationId:{0} DeviceType:{1} DeviceId:{2} UserApplicationId:{3} Data:{4} Enabled:{5}", organisationId, deviceType, deviceId, userApplicationId, Convert.ToBase64String(data), _bumblebeeHiveSettings.DownlinkEnabled);

    Models.MessageSendRequest message = new Models.MessageSendRequest()
    {
        OrganizationId = (int)organisationId,
        DeviceType = deviceType,
        DeviceId = (int)deviceId,
        UserApplicationId = userApplicationId,
        Data = data,
    };

    RestClientOptions restClientOptions = new RestClientOptions()
    {
        BaseUrl = new Uri(_bumblebeeHiveSettings.BaseUrl),
        ThrowOnAnyError = true,
    };

    using (RestClient client = new RestClient(restClientOptions))
    {
        RestRequest request = new RestRequest("api/v1/messages", Method.Post);

        request.AddBody(message);

        request.AddHeader("Authorization", $"bearer {_token}");

        // To save the limited monthly allocation of mesages downlinks can be disabled
        if (_bumblebeeHiveSettings.DownlinkEnabled)
        {
           var response = await client.PostAsync<Models.MessageSendResponse>(request, cancellationToken);

            _logger.LogInformation("SendAsync-Result:{Status} PacketId:{PacketId}", response.Status, response.PacketId);
        }
    }
}

The new Data Transfer Objects(DTOs) were “inspired” by the NSwag generated ones.

public partial class MessageSendRequest
{
    /// <summary>
    /// Swarm device type
    /// </summary>
    [Newtonsoft.Json.JsonProperty("deviceType", Required = Newtonsoft.Json.Required.Always)]
    public int DeviceType { get; set; }

    /// <summary>
    /// Swarm device ID
    /// </summary>
    [Newtonsoft.Json.JsonProperty("deviceId", Required = Newtonsoft.Json.Required.Always)]
    public int DeviceId { get; set; }

    /// <summary>
    /// Application ID
    /// </summary>
    [Newtonsoft.Json.JsonProperty("userApplicationId", Required = Newtonsoft.Json.Required.Always)]
    public int UserApplicationId { get; set; }

    /// <summary>
    /// Organization ID
    /// </summary>
    [Newtonsoft.Json.JsonProperty("organizationId", Required = Newtonsoft.Json.Required.Always)]
    public int OrganizationId { get; set; }

    /// <summary>
    /// Base64 encoded data string
    /// </summary>
    [Newtonsoft.Json.JsonProperty("data", Required = Newtonsoft.Json.Required.Always)]
    [System.ComponentModel.DataAnnotations.Required(AllowEmptyStrings = true)]
    public byte[] Data { get; set; }
}

public class MessageSendResponse
{
    /// <summary>
    /// Swarm packet ID.
    /// </summary>
    [Newtonsoft.Json.JsonProperty("packetId", Required = Newtonsoft.Json.Required.Always)]
    public long PacketId { get; set; }

    /// <summary>
    /// Submission status, "OK" or "ERROR" with a description of the error.
    /// </summary>
    [Newtonsoft.Json.JsonProperty("status", Required = Newtonsoft.Json.Required.Always)]
    [System.ComponentModel.DataAnnotations.Required(AllowEmptyStrings = true)]
    public string Status { get; set; }
}

The RestSharp based approach is significantly smaller and less complex….

Swarm Space – Underlying Architecture sorted

After figuring out that calling an Azure Http Trigger function to load the cache wasn’t going to work reliably, I have revisited the architecture one last time and significantly refactored the SwarmSpaceAzuureIoTConnector project.

Visual Studio 2022 solution

The application now has a StartUpService which loads the Azure DeviceClient cache (Lazy Cache) in the background as the application starts up. If an uplink message is received from a SwarmDevice before, it has been loaded by the FunctionsStartup the DeviceClient information is cached and another connection to the Azure IoT Hub is not established.

...
using Microsoft.Azure.Functions.Extensions.DependencyInjection;

[assembly: FunctionsStartup(typeof(devMobile.IoT.SwarmSpaceAzureIoTConnector.Connector.StartUpService))]
namespace devMobile.IoT.SwarmSpaceAzureIoTConnector.Connector
{
...
    public class StartUpService : BackgroundService
    {
        private readonly ILogger<StartUpService> _logger;
        private readonly ISwarmSpaceBumblebeeHive _swarmSpaceBumblebeeHive;
        private readonly Models.ApplicationSettings _applicationSettings;
        private readonly IAzureDeviceClientCache _azureDeviceClientCache;

        public StartUpService(ILogger<StartUpService> logger, IAzureDeviceClientCache azureDeviceClientCache, ISwarmSpaceBumblebeeHive swarmSpaceBumblebeeHive, IOptions<Models.ApplicationSettings> applicationSettings)//, IOptions<Models.AzureIoTSettings> azureIoTSettings)
        {
            _logger = logger;
            _azureDeviceClientCache = azureDeviceClientCache;
            _swarmSpaceBumblebeeHive = swarmSpaceBumblebeeHive;
            _applicationSettings = applicationSettings.Value;
        }

        protected override async Task ExecuteAsync(CancellationToken cancellationToken)
        {
            await Task.Yield();

            _logger.LogInformation("StartUpService.ExecuteAsync start");

            try
            {
                _logger.LogInformation("BumblebeeHiveCacheRefresh start");

                foreach (SwarmSpace.BumblebeeHiveClient.Device device in await _swarmSpaceBumblebeeHive.DeviceListAsync(cancellationToken))
                {
                    _logger.LogInformation("BumblebeeHiveCacheRefresh DeviceId:{DeviceId} DeviceName:{DeviceName}", device.DeviceId, device.DeviceName);

                    Models.AzureIoTDeviceClientContext context = new Models.AzureIoTDeviceClientContext()
                    {
                        OrganisationId = _applicationSettings.OrganisationId,
                        DeviceType = (byte)device.DeviceType,
                        DeviceId = (uint)device.DeviceId,
                    };

                    await _azureDeviceClientCache.GetOrAddAsync(context.DeviceId, context);
                }

                _logger.LogInformation("BumblebeeHiveCacheRefresh finish");
            }
            catch (Exception ex)
            {
                _logger.LogError(ex, "StartUpService.ExecuteAsync error");

                throw;
            }

            _logger.LogInformation("StartUpService.ExecuteAsync finish");
        }
    }
}

The uplink and downlink payload formatters are stored in Azure Blob Storage are compiled (CS-Script) as they are loaded then cached (Lazy Cache)

Azure Storage explorer displaying list of uplink payload formatter blobs.
Azure Storage explorer displaying list of downlink payload formatter blobs.
private async Task<IFormatterDownlink> DownlinkLoadAsync(int userApplicationId)
{
    BlobClient blobClient = new BlobClient(_payloadFormatterConnectionString, _applicationSettings.PayloadFormattersDownlinkContainer, $"{userApplicationId}.cs");

    if (!await blobClient.ExistsAsync())
    {
        _logger.LogInformation("PayloadFormatterDownlink- UserApplicationId:{0} Container:{1} not found using default:{2}", userApplicationId, _applicationSettings.PayloadFormattersUplinkContainer, _applicationSettings.PayloadFormatterUplinkBlobDefault);

        blobClient = new BlobClient(_payloadFormatterConnectionString, _applicationSettings.PayloadFormatterDownlinkBlobDefault, _applicationSettings.PayloadFormatterDownlinkBlobDefault);
    }

    BlobDownloadResult downloadResult = await blobClient.DownloadContentAsync();

    return CSScript.Evaluator.LoadCode<PayloadFormatter.IFormatterDownlink>(downloadResult.Content.ToString());
}

The uplink and downlink formatters can be edited in Visual Studio 2022 with syntax highlighting (currently they have to be manually uploaded).

The SwarmSpaceBumbleebeehive module no longer has public login or logout methods.

    public interface ISwarmSpaceBumblebeeHive
    {
        public Task<ICollection<Device>> DeviceListAsync(CancellationToken cancellationToken);

        public Task SendAsync(uint organisationId, uint deviceId, byte deviceType, ushort userApplicationId, byte[] payload);
    }

The DeviceListAsync and SendAsync methods now call the BumblebeeHive login method after configurable period of inactivity.

public async Task<ICollection<Device>> DeviceListAsync(CancellationToken cancellationToken)
{
        if ((_TokenActivityAtUtC + _bumblebeeHiveSettings.TokenValidFor) < DateTime.UtcNow)
        {
            await Login();
        }

        using (HttpClient httpClient = _httpClientFactory.CreateClient())
       {
            Client client = new Client(httpClient);

            client.BaseUrl = _bumblebeeHiveSettings.BaseUrl;

            httpClient.DefaultRequestHeaders.Add("Authorization", $"bearer {_token}");

            return await client.GetDevicesAsync(null, null, null, null, null, null, null, null, null, cancellationToken);
        }
}

I’m looking at building a webby user interface where users an interactivity list, create, edit, delete formatters with syntax highlighter support, and the executing the formatter with sample payloads.

Swarm Space Azure IoT Connector Identity Translation Gateway Architecture

This approach uses most of the existing building blocks, and that’s it no more changes.