ksqlDB error when deserilaizing jeager spans from protobuf

Question

I am trying to get ksqlDB to deserialize protobuf messages with not much success I am afraid.

More specifically, I have Jaeger spans published to a Kafka broker by Jaeger Collector and have successfully register the Jaeger protobuf schema model with schema registry under /subjects/jaeger-spans-value/ route and the schema string is properly escaped.

The Collector is configured to publish Kafka: KAFKA_PRODUCER_ENCODING: 'protobuf', while spans generated by the HotROD app are published directly to the Collector over HTTP at jaeger-collector:14268/api/traces.

KsqlDB always returns a deserialization error when I am trying to register any stream against that topic:

ERROR {"type":0,"deserializationError":{"target":"value","errorMessage":"Error deserializing message from topic: jaeger-spans","recordB64":null,"cause":["Failed to deserialize data for topic jaeger-spans to Protobuf: ","Error deserializing Protobuf message for id -1","Unknown magic byte!"],"topic":"jaeger-spans"},"recordProcessingError":null,"productionError":null,"serializationError":null,"kafkaStreamsThreadError":null} (processing.transient_STR_SPANS_MODEL_8922992258591230941.KsqlTopic.Source.deserializer:44)

It is worth noting that all this are running inside a docker compose stack, but I have tested the same setup with JSON as the Jaeger span encoding format and works like a dream. ksqlDB successfully communicates with the schema registry.

Any ideas/feedback would be highly appreciated.

~GS