Tag Archives: Azure Function

Myriota – Uplink Payload formatters and caching

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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.