Spring Cloud Stream w/Kafka + Confluent Schema Registry Client broken? - spring

Question

Curious if anyone has got this working as I'm currently struggling.
I have created simple Source and Sink applications to send and receive an Avro schema based message. The schema for the message is held in a Confluent Schema Registry. Both apps are configured to use the ConfluentSchemaRegistryClient class but I think there might be a bug in here somewhere. Here's what I see that makes me wonder.
If I interact with the Confluent registry's REST API I can see that there is only one version of the schema in question (lightly edited to obscure what I'm working on):
$ curl -i "http://schemaregistry:8081/subjects/somesubject/versions"
HTTP/1.1 200 OK
Date: Fri, 05 May 2017 16:13:37 GMT
Content-Type: application/vnd.schemaregistry.v1+json
Content-Length: 3
Server: Jetty(9.2.12.v20150709)
[1]
When the Source app sends off its message over Kafka I noticed that the version in the header looked a bit funky:
contentType"application/octet-stream"originalContentType/"application/vnd.somesubject.v845+avro"
I'm not 100% clear about why the application/vnd.somesubject.v845+avro content type is wrapped up in application/octet-stream but ignoring that, note that it is saying version 845 not version 1.
Looking at the ConfluentSchemaRegistryClient implementation I see that it POSTs to /subjects/(string: subject)/versions and returns the id of the schema not the version. This then gets put into SchemaReference's version field: https://github.com/spring-cloud/spring-cloud-stream/blob/master/spring-cloud-stream-schema/src/main/java/org/springframework/cloud/stream/schema/client/ConfluentSchemaRegistryClient.java#L81
When the Sink app tries to fetch the schema for the message based upon the header it fails because it tries to fetch version 845 that its plucked out of the header: https://github.com/spring-cloud/spring-cloud-stream/blob/master/spring-cloud-stream-schema/src/main/java/org/springframework/cloud/stream/schema/client/ConfluentSchemaRegistryClient.java#L87
Anyone have thoughts on this? Thanks in advance.
** UPDATE **
OK pretty convinced this is a bug. Took the ConfluentSchemaRegistryClient and modified the register method slightly to POST to /subjects/(string: subject) (i.e. dropped the trailing /versions) which per Confluent REST API docs returns a payload with the version in it. Works like a charm:
public SchemaRegistrationResponse register(String subject, String format, String schema) {
Assert.isTrue("avro".equals(format), "Only Avro is supported");
String path = String.format("/subjects/%s", subject);
HttpHeaders headers = new HttpHeaders();
headers.put("Accept",
Arrays.asList("application/vnd.schemaregistry.v1+json", "application/vnd.schemaregistry+json",
"application/json"));
headers.add("Content-Type", "application/json");
Integer version = null;
try {
String payload = this.mapper.writeValueAsString(Collections.singletonMap("schema", schema));
HttpEntity<String> request = new HttpEntity<>(payload, headers);
ResponseEntity<Map> response = this.template.exchange(this.endpoint + path, HttpMethod.POST, request,
Map.class);
version = (Integer) response.getBody().get("version");
}
catch (JsonProcessingException e) {
e.printStackTrace();
}
SchemaRegistrationResponse schemaRegistrationResponse = new SchemaRegistrationResponse();
schemaRegistrationResponse.setId(version);
schemaRegistrationResponse.setSchemaReference(new SchemaReference(subject, version, "avro"));
return schemaRegistrationResponse;
}