Tag Archives: Swarm Eval Kit

Swarm Space – Uplink Payload Formatters revisited

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The approach used in Swarm Space–Uplink Payload Message Creation Time had significant limitations e.g. setting the iothub-creation-time-utc message property.

public interface IFormatterUplink
{
    public Message Evaluate(int organisationId, int deviceId, int deviceType, int userApplicationId, JObject telemetryEvent, JObject payloadJson, string payloadText, byte[] payloadBytes);
}

Uplink payload formatters now return a Microsoft.Azure.Azure.Devices.Client message object to the UplinkController. 

...
JObject telemetryEvent = new JObject
{
    { "packetId", payload.PacketId},
    { "deviceType" , payload.DeviceType},
    { "DeviceID", payload.DeviceId },
    { "organizationId", payload.OrganizationId },
    { "UserApplicationId", payload.UserApplicationId},
    { "ReceivedAtUtc", payload.HiveRxTime.ToString("s", CultureInfo.InvariantCulture) },
    { "DataLength", payload.Len },
    { "Data", payload.Data },
    { "Status", payload.Status },
};

    _logger.LogDebug("Uplink-DeviceId:{0} PacketId:{1} TelemetryEvent before:{0}", payload.DeviceId, payload.PacketId, JsonConvert.SerializeObject(telemetryEvent, Formatting.Indented));

    using (Message ioTHubmessage = swarmSpaceFormatterUplink.Evaluate(payload.OrganizationId, payload.DeviceId, context.DeviceType, payload.UserApplicationId, telemetryEvent, payloadJson, payloadText, payloadBytes))
{
    _logger.LogDebug("Uplink-DeviceId:{0} PacketId:{1} TelemetryEvent after:{0}", payload.DeviceId, payload.PacketId, JsonConvert.SerializeObject(telemetryEvent, Formatting.Indented));

    ioTHubmessage.Properties.Add("PacketId", payload.PacketId.ToString());
    ioTHubmessage.Properties.Add("OrganizationId", payload.OrganizationId.ToString());
    ioTHubmessage.Properties.Add("UserApplicationId", payload.UserApplicationId.ToString());
    ioTHubmessage.Properties.Add("DeviceId", payload.DeviceId.ToString());
    ioTHubmessage.Properties.Add("deviceType", payload.DeviceType.ToString());

    await deviceClient.SendEventAsync(ioTHubmessage);

    _logger.LogInformation("Uplink-DeviceID:{deviceId} PacketId:{1} SendEventAsync success", payload.DeviceId, payload.PacketId);
}
...

The default uplink payload formatter (UserApplicationId 0.cs) returns a Microsoft.Azure.Azure.Devices.Client message object with a serialised TelemetryEvent payload.

public class FormatterUplink : PayloadFormatter.IFormatterUplink
{
    public Message Evaluate(int organisationId, int deviceId, int deviceType, int userApplicationId, JObject telemetryEvent, JObject payloadJson, string payloadText, byte[] payloadBytes)
    {
        Message ioTHubmessage = new Message(Encoding.ASCII.GetBytes(JsonConvert.SerializeObject(telemetryEvent)));

        return ioTHubmessage;
    }
}

The Swarm Eval Kit uplink sample formatter (UserApplicationId 65535.cs) “unpacks” the uplink Javascript ObjectNotation(JSON) message, adds an Azure IoT Central compatible location to the TelemetryEvent and an “iothub-creation-time-utc” message property.

public class FormatterUplink : PayloadFormatter.IFormatterUplink
{
    public Message Evaluate(int organisationId, int deviceId, int deviceType, int userApplicationId, JObject telemetryEvent, JObject payloadJson, string payloadText, byte[] payloadBytes)
    {
        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("a"));

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

        Message ioTHubmessage = new Message(Encoding.ASCII.GetBytes(JsonConvert.SerializeObject(telemetryEvent)));

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

        return ioTHubmessage;
    }
}

If the uplink formatter compilation or execution fails, a detailed exception message is logged to Azure Application Insights

Detailed compilation error message in Application Insights

I need to add some tools to make the creation, modification, deletion and debugging of downlink/uplink formatters easier.

Swarm Space – Uplink Payload Message Creation Time

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The Swarm Space satellite constellation doesn’t have continuous coverage (Jan 2023) so messages sent when there is no coverage are queued (default 48hrs) by the Swarm M138 Modem for transmission when a satellite passes overhead.

Satellite Passes with gap in coverage from 16:18 to 18:42 highlighted

In the Swarm Hive Delivery Method messages from the Swarm Eval Kit and Swarm Tracker in my backyard arriving in “clusters”.

Swarm Hive Delivery Methods webhook calls.

The messages in each “cluster” were processed by a payload formatter then forwarded to Azure IoT Central for processing. All the messages in a cluster had similar event creation times which was “breaking” graphs and device tracking maps. After running the application locally using Telerik Fiddler to try different payloads I realised that the Microsoft.Azure.Azure.Devices.Client message iothub-creation-time-utc property was set to the when the message was received by Swarm Space infrastructure.

_logger.LogDebug("Uplink-DeviceId:{0} PacketId:{1} TelemetryEvent before:{0}", payload.DeviceId, payload.PacketId, JsonConvert.SerializeObject(telemetryEvent, Formatting.Indented));

telemetryEvent = swarmSpaceFormatterUplink.Evaluate(telemetryEvent, payload.Data, payloadBytes, payloadText, payloadJson);

_logger.LogDebug("Uplink-DeviceId:{0} PacketId:{1} TelemetryEvent after:{0}", payload.DeviceId, payload.PacketId, JsonConvert.SerializeObject(telemetryEvent, Formatting.Indented));

// Send the message to Azure IoT Hub
using (Message ioTHubmessage = new Message(Encoding.ASCII.GetBytes(JsonConvert.SerializeObject(telemetryEvent))))
{
   // Ensure the displayed time is the acquired time rather than the uploaded time. 
   ioTHubmessage.Properties.Add("iothub-creation-time-utc", payload.HiveRxTime.ToString("s", CultureInfo.InvariantCulture));
   ioTHubmessage.Properties.Add("PacketId", payload.PacketId.ToString());
   ioTHubmessage.Properties.Add("OrganizationId", payload.OrganizationId.ToString());
   ioTHubmessage.Properties.Add("ApplicationId", payload.UserApplicationId.ToString());
   ioTHubmessage.Properties.Add("DeviceId", payload.DeviceId.ToString());
   ioTHubmessage.Properties.Add("deviceType", payload.DeviceType.ToString());

   await deviceClient.SendEventAsync(ioTHubmessage);

   _logger.LogInformation("Uplink-DeviceID:{deviceId} SendEventAsync success", payload.DeviceId);
}

The Swarm Eval Kit uplink (JSON) message generated by the sample firmware “d” field is the number of seconds since the Unix Epoch that the message payload was constructed.

Swarm Hive Messages with “d” field in the JSON payload highlighted
Online Unix Epoch Convertor displaying Unix Epoch 1672561286 in NZDT and UTC time

The revised 65355.cs payload formatter adds an “iothub-creation-time-utc” field to the TelemetryEvent 

using System;
using System.Globalization;

using Newtonsoft.Json.Linq;

public class FormatterUplink : PayloadFormatter.IFormatterUplink
{
    public JObject Evaluate(JObject telemetryEvent, string payloadBase64, byte[] payloadBytes, string payloadText, JObject payloadJson)
    {
        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("a"));

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

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

        return telemetryEvent;
    }
}

Which, if present is used to populate theMicrosoft.Azure.Azure.Devices.Client message iothub-creation-time-utc property

_logger.LogDebug("Uplink-DeviceId:{0} PacketId:{1} TelemetryEvent before:{0}", payload.DeviceId, payload.PacketId, JsonConvert.SerializeObject(telemetryEvent, Formatting.Indented));

telemetryEvent = swarmSpaceFormatterUplink.Evaluate(telemetryEvent, payload.Data, payloadBytes, payloadText, payloadJson);

.LogDebug("Uplink-DeviceId:{0} PacketId:{1} TelemetryEvent after:{0}", payload.DeviceId, payload.PacketId, JsonConvert.SerializeObject(telemetryEvent, Formatting.Indented));

Send the message to Azure IoT Hub
using (Message ioTHubmessage = new Message(Encoding.ASCII.GetBytes(JsonConvert.SerializeObject(telemetryEvent))))
{
   // Ensure the displayed time is the acquired time rather than the uploaded time. 
   ioTHubmessage.Properties.Add("PacketId", payload.PacketId.ToString());
   ioTHubmessage.Properties.Add("OrganizationId", payload.OrganizationId.ToString());
   ioTHubmessage.Properties.Add("UserApplicationId", payload.UserApplicationId.ToString());
   ioTHubmessage.Properties.Add("DeviceId", payload.DeviceId.ToString());
   ioTHubmessage.Properties.Add("deviceType", payload.DeviceType.ToString());

   if (telemetryEvent.ContainsKey("iothub-creation-time-utc"))
   {
      ioTHubmessage.Properties.Add("iothub-creation-time-utc",telemetryEvent.Value<string>("iothub-creation-time-utc"));
   }

   await deviceClient.SendEventAsync(ioTHubmessage);

   _logger.LogInformation("Uplink-DeviceID:{deviceId} SendEventAsync success", payload.DeviceId);
}

The Azure IoT Central message now had the correct timestamp and “event creation time” values.

AzureIoT Central “Raw Data” with valid timestamp and event creation times

I don’t think this is a good solution

The design of the payload formatters will have to be revisited

Swarm Space – Uplink Payload formatter caching and files

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The payload formatters of my Azure IoT Hub Cloud Identity Translation Gateway use CS-Script and even a simple one was taking more than half a second to compile each time it was called.

using System;
using System.Globalization;

using Newtonsoft.Json.Linq;

public class FormatterUplink : PayloadFormatter.IFormatterUplink
{
    public JObject Evaluate(JObject telemetryEvent, string payloadBase64, byte[] payloadBytes, string payloadText, JObject payloadJson)
    {
        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("a"));

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

        return telemetryEvent;
    }
}

The Swarm Eval Kit default message has a userApplicationId of 65335 

{"ln":123.456,"si":0.0,"bi":0.2,"sv":0.152,"lt":-12.345,"bv":4.032,"d":1671704370,"n":2,"a":9.0,"s":1.0,"c":208.0,"r":-94,"ti":0.032}

The 65355.cs payload formatter adds an Azure IoT Central compatible location to the telemetry payload.

Azure IoT Central uplink telemetry message payload

The formatter files are currently part of the SwarmSpaceAzureIoTConnector project (moving to Azure Blob Storage) so are configured as “content” (bonus syntax highlighting works) and “copy if newer” so they are included in the deployment package.

Visual Studio 2022 Sample payload formatter

I used Alastair Crabtrees’s LazyCache to store compiled payload formatters with Uplink/Downlink + UserApplicationId as the cache key. 

public class FormatterCache : IFormatterCache
{
    private readonly ILogger<FormatterCache> _logger;
    private readonly Models.ApplicationSettings _applicationSettings;
    private readonly static IAppCache _payloadFormatters = new CachingService();

    public FormatterCache(ILogger<FormatterCache>logger, IOptions<Models.ApplicationSettings> applicationSettings)
    {
        _logger = logger;
        _applicationSettings = applicationSettings.Value;
    }

    public async Task<IFormatterUplink> UplinkGetAsync(int userApplicationId)
    {
        IFormatterUplink payloadFormatterUplink = await _payloadFormatters.GetOrAddAsync<PayloadFormatter.IFormatterUplink>($"U{userApplicationId}", (ICacheEntry x) => UplinkLoadAsync(userApplicationId), memoryCacheEntryOptions);

        return payloadFormatterUplink;
    }

    private async Task<IFormatterUplink> UplinkLoadAsync(int userApplicationId)
    {
        string payloadformatterFilePath = $"{_applicationSettings.PayloadFormattersUplinkFilePath}\\{userApplicationId}.cs";

        if (!File.Exists(payloadformatterFilePath))
        {
            _logger.LogInformation("PayloadFormatterUplink- UserApplicationId:{0} PayloadFormatterPath:{1} not found using default:{2}", userApplicationId, payloadformatterFilePath, _applicationSettings.PayloadFormatterUplinkDefault);

            return CSScript.Evaluator.LoadFile<PayloadFormatter.IFormatterUplink>(_applicationSettings.PayloadFormatterUplinkDefault);
        }

        _logger.LogInformation("PayloadFormatterUplink- UserApplicationId:{0} loading PayloadFormatterPath:{1}", userApplicationId, payloadformatterFilePath);

        return CSScript.Evaluator.LoadFile<PayloadFormatter.IFormatterUplink>(payloadformatterFilePath);
    }
...
}

The default uplink and downlink formatters are configured in application settings and are used when a UserApplicationId specific formatter is not configured.

Fiddler Composer illustrating compiled formatter timings before and after caching

Swarm Space – Uplink Payload formatter Proof of Concept(PoC)

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My Azure IoT Hub Cloud Identity Translation Gateway will support the translation of Base64 encoded uplink payloads to Javascript Object Notation (JSON) so they can be processed by Azure IoT Hub client applications and Azure IoT Central. This PoC uses CS-Script by Oleg Shilo to transform the Swarm Eval Kit Base64 encoded JSON uplink messages.

Swarm Hive message list with a message payload

A sample decoded (JSON) Swarm Eval Kit uplink message

{"ln":123.456,"si":0.0,"bi":0.2,"sv":0.152,"lt":-12.345,"bv":4.032,"d":1671704370,"n":2,"a":9.0,"s":1.0,"c":208.0,"r":-94,"ti":0.032}

A Webhook Delivery method forwards uplink messages to my Azure IoT Hub Cloud Identity Translation Gateway.

Swarm Hive Delivery configuration with recent uplink messages

My first hard-coded payload formatter adds an Azure IoT Central compatible location to the telemetry event payload.

const string codeSwarmSpaceUplinkFormatterCode = @"
   using Newtonsoft.Json.Linq;

   public class UplinkFormatter : PayloadFormatter.ISwarmSpaceFormatterUplink
   {
       public JObject Evaluate(JObject telemetryEvent, string payloadBase64, byte[] payloadBytes, string payloadText, JObject payloadJson)
       {
           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(""a""));

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

           return telemetryEvent;
       }
   }";
}

The PayloadFormatter namespace was added to reduce the length of the payload formatter C# interface declarations.

namespace PayloadFormatter 
{
    using Newtonsoft.Json.Linq;

    public interface ISwarmSpaceFormatterUplink
    {
        public JObject Evaluate(JObject telemetry, string payloadBase64, byte[] payloadBytes, string payloadText, JObject payloadJson);
    }

    public interface ISwarmSpaceFormatterDownlink
    {
        public string Evaluate(JObject payloadJson, string payloadText, byte[] payloadBytes, string payloadBase64);
    }
}

namespace devMobile.IoT.SwarmSpace.AzureIoT.Connector
{
    using System.Threading.Tasks;
    using Microsoft.Extensions.Logging;

    using CSScriptLib;

    using PayloadFormatter;

    public interface ISwarmSpaceFormatterCache
    {
        public Task<ISwarmSpaceFormatterUplink> PayloadFormatterGetOrAddAsync(int userApplicationId);

    }

    public class SwarmSpaceFormatterCache : ISwarmSpaceFormatterCache
    {
        private readonly ILogger<SwarmSpaceFormatterCache> _logger;

        public SwarmSpaceFormatterCache(ILogger<SwarmSpaceFormatterCache>logger)
        {
            _logger = logger;
        }

        public async Task<ISwarmSpaceFormatterUplink> PayloadFormatterGetOrAddAsync(int deviceId)
        {
            return CSScript.Evaluator.LoadCode<PayloadFormatter.ISwarmSpaceFormatterUplink>(codeSwarmSpaceUplinkFormatterCode);
        }
...
}

The parameters of the formatter are Base64 encoded, textual and a Newtonsoft JObject representations of the uplink payload and a telemetry event populated with some uplink message metadata.

Azure IoT Central uplink telemetry message payload

The initial “compile” of an uplink formatter was taking approximately 2.1 seconds so they will be “compiled” on demand and cached in a Dictionary with the UserApplicationId as the key. A default uplink formatter will be used when a UserApplicationId specific uplink formatter is not configured.