json-serializer | Serialize PHP variables , including objects | JSON Processing library

A quick research shows that I can embed the schema in header before sending the record to topic

If you serialize any object to Avro using BinaryEncoder, that's the default behavior, yes.

the schema again has to be serialized to bytes before embedding on the header

Not sure what you mean "again". For every message, yes, and there's no way around that, but not within the same process of serializing a single record.

What are what are the cons associated with this approach.

There's plenty of documentation about the pros of using a Registry. Cons include maintaining additional infrastructure and not all tools can integrate with it.

How is it possible for confluent to extract schema from the data and store it in schema registry?

Refer source code (extract Schema as text) then POST schema text to the registry to get the ID and embed in the record

Isn't the data serialized before sending to schema registry?

If by "serialized", you mean as Avro, then yes, but the schema is UTF8 serialized

JsonDeserialzier, it deserializes data without any schema and works with JsonNode. Why isn't a similar mechanism possible for Avro?

I think you should be comparing the JsonSchemaDeserializer class. Obviously plain JSON has no concept of schemas. Avro requires a reader schema for deserialization, but there is a similar mechanism - GenericRecord operates similarly to JsonNode

Most likely ItemVM.firstItem is not public (for example, internal), and JSON serializer will only serialize public properties by default (unless you non-public property explicitly to be serialized).

No, the purpose of ServiceStack Messaging is simply to invoke ServiceStack Services via MQ. Any other MQ features is outside the purpose & scope of ServiceStack MQ, you'd need to instead develop against the MQ Provider APIs directly to access their broadcast features.

Server Events is a ServiceStack feature that supports broadcasting messages to subscribers of user-defined channels, but its a completely different implementation that serves a different use-case for sending "server push" real-time events over HTTP or gRPC, e.g. it doesn't use MQ brokers and pub/sub messages aren't persistent (i.e. only subscribers at time messages are sent will receive them).

The generic parameter of the constructor is implied by the T annotation on deserialize. The correct and typesafe syntax is:

That interface only exists in the kafka_2.12 jars.

It appears you somehow have a 2.12 ...-test jar and a 2.13 kafka jar (which is not what your gradle says).

What does gradle dependencies say?

@Ori you can use Utf8json in net core 3.1 projects.

Use

[DataMember(Name = "RoleType")] public string Role_Type { get; set; }

Instead of

[JsonProperty("")]

To use Utf8json formatters in Asp.Net core you need add the formatters as mentioned below.