c# – Sparkplug B and metrics specification in MQTT

I finally found the solution!

If you send a NCMD message to the topic spBv1.0/ClientEU1/NCMD/27352352 with a SparkPlug B payload (not json payload, it should be SparkPlug B) as the following:

using System;
using System.Text;
using System.Threading.Tasks;
using MQTTnet;
using MQTTnet.Client;
using Google.Protobuf;
using Org.Eclipse.Tahu.Protobuf;
using Newtonsoft.Json;

......

 var payload = new Payload
 {
     Timestamp = (ulong)DateTimeOffset.UtcNow.ToUnixTimeMilliseconds(),
     Seq = 0
 };

 payload.Metrics.Add(new Payload.Types.Metric
 {
     Name = "Node Control/Rebirth",
     Alias = 1,
     Datatype = 11,
     BooleanValue = true
 });


 byte[] payloadBytes;
 using (var stream = new System.IO.MemoryStream())
 {
     payload.WriteTo(stream);
     payloadBytes = stream.ToArray();
 }

 var message = new MqttApplicationMessageBuilder()
     .WithTopic("spBv1.0/CustomerA/NCMD/27352352") 
     .WithPayload(payloadBytes)
     .WithQualityOfServiceLevel(MQTTnet.Protocol.MqttQualityOfServiceLevel.ExactlyOnce)
     .WithRetainFlag(false)
     .Build();

 await mqttClient.PublishAsync(message);

then, you will get a response at spBv1.0/ClientEU1/DBIRTH/27352352/HART0 with full details of all your metrics like the following:
You need to listen to spBv1.0/ClientEU1/DBIRTH/27352352/HART0. I used MQTT Explorer while running the code, so it got the response from the broker:

{
  "timestamp" : 1722607594070,
  "metrics" : [ 
{
    "name" : "Tag",
    "alias" : 135,
    "timestamp" : 1722607594070,
    "dataType" : "String",
    "properties" : {
      "Quality" : {
        "type" : "Int32",
        "value" : 192
      }
    },
    "value" : "SENSOR  "
  }, {
    "name" : "Manufacturer ID",
    "alias" : 136,
    "timestamp" : 1722607594070,
    "dataType" : "UInt8",
    "properties" : {
      "Quality" : {
        "type" : "Int32",
        "value" : 192
      }
    },
    "value" : 42
  }, 

 {
    "name" : "Temperature",
    "alias" : 141,
    "timestamp" : 1722607594070,
    "dataType" : "Float",
    "properties" : {
      "engUnit" : {
        "type" : "String",
        "value" : "%"
      },
      "Quality" : {
        "type" : "Int32",
        "value" : 192
      }
    },
    "value" : 86.20619
  }, 
{
    "name" : "Flow Value",
    "alias" : 143,
    "timestamp" : 1722607594070,
    "dataType" : "Float",
    "properties" : {
      "engUnit" : {
        "type" : "String",
        "value" : "m"
      },
      "Quality" : {
        "type" : "Int32",
        "value" : 192
      }
    },
    "value" : 12.930929
  }, 

 {
    "name" : "Pressure Variable",
    "alias" : 145,
    "timestamp" : 1722607594070,
    "dataType" : "Float",
    "properties" : {
      "engUnit" : {
        "type" : "String",
        "value" : "dB"
      },
      "Quality" : {
        "type" : "Int32",
        "value" : 192
      }
    },
    "value" : 37.0
  }, 

 {
    "name" : "Electron Variable",
    "alias" : 147,
    "timestamp" : 1722607594070,
    "dataType" : "Float",
    "properties" : {
      "engUnit" : {
        "type" : "String",
        "value" : "m"
      },
      "Quality" : {
        "type" : "Int32",
        "value" : 192
      }
    },
    "value" : 2.069071
  }
 ],
  "seq" : 1
}