in timebase-kafka-connector/src/main/java/deltix/kafka/connect/RawMessageDeserializer.java [138:150]
public SourceRecord deserialize(RawMessage message, Map<String,String> partition, long messageTimestamp, long messageCounter) {
Map<String, Object> values = getValues(message);
Struct value = buildStruct(null, getSchema(message.type), values);
long msgOffset = (tbMessageId == null) ? messageCounter : (Long) values.get(tbMessageId);
HashMap<String, Long> offset = new HashMap<>(2);
offset.put(TIMESTAMP_ATTR, messageTimestamp);
offset.put(OFFSET_ATTR, msgOffset);
String key = buildKey(values, messageTimestamp, msgOffset);
return new SourceRecord(partition, offset, topic, Schema.STRING_SCHEMA, key, value.schema(), value);
}