Subscriber on Mosquitto MQTT ContentType is Null

Question

I'm trying to publish a serialized message and sending the ContentType of that object type, so when I receive the message on the subscriber I know which type I can deserialize back to.

Here is the publish code:

public async Task PublishByTopicAsync<T>(string topic, T payload)
    {
        var payloadInBytes = _serializer.SerializeObject(payload);
        var message = new MqttApplicationMessage()
        {
            Topic = topic,
            PayloadFormatIndicator = MqttPayloadFormatIndicator.CharacterData,
            ContentType = "json",//payload?.GetType().FullName,
            Payload = payloadInBytes,
            QualityOfServiceLevel = MqttQualityOfServiceLevel.AtMostOnce
        };
        await _mqttClient.Value.Result.EnqueueAsync(message);
    }

On the receiving side I get this:

Any idea how can I send the type of object on publishing, and receive it on the subscriber?

What MQTT version are you connecting to the broker with? Only messages sent via MQTT v5 will have a PayloadFormatIndicator — hardillb, Aug 03 '22 at 12:19
I am using MQTTnet.Extensions.ManagedClient" Version="4.0.2.221. How do I know which MQTT protocol is used? — João Antunes, Aug 03 '22 at 13:29
Ok I've added ".WithProtocolVersion(MqttProtocolVersion.V500)" on the WithClientOptions and it now works :) thanks for the help! — João Antunes, Aug 03 '22 at 13:48

score 1 · Accepted Answer · answered Aug 03 '22 at 13:59

1

As described in the comments, PayloadFormatIndicator is only available when both clients are connected to the broker with MQTT v5

answered Aug 03 '22 at 13:59

hardillb

54,545
11
67
105

Subscriber on Mosquitto MQTT ContentType is Null

1 Answers1