[CAMEL-13878] Message is forwarded to the wrong Kafka Topic

• Type: Bug
• Status: Resolved
• Priority: Major
• Resolution: Fixed
• Affects Version/s: 2.24.1
• Fix Version/s: 3.0.0.RC2, 3.0.0
• Component/s: camel-kafka
• Estimated Complexity: Unknown
• Assignee: Claus Ibsen
• Reporter: Klearchos Klearchou
• Created: 19/Aug/19 21:18
• Updated: 01/Oct/19 10:20
• Resolved: 01/Oct/19 10:20

Description

I have 3 Apache Spring Boot applications and 3 topics.

Let's call them Topic A, B and C and the Spring Boot applications FirstApp, SecondApp and ThridApp. I use Java DSL for the Kafka configuration.

The FirstApp creates a message to Kafka Topic A.

The SecondApp reads from Topic A makes transformations and passes each value to Topic B.

The ThirdApp reads from Topic B and after transformations tries to pass it to Topic C.

At this point through the debugger I saw that at the class  org.apache.camel.component.kafka.KafkaProducer and at the method 

protected Iterator<ProducerRecord> createRecorder(Exchange exchange) something strange is happening.
The headerTopic (line 140) from the following line:

String headerTopic = exchange.getIn().getHeader(KafkaConstants.TOPIC, String.class);

contains the topic A! The correct topic that I have clearly set through the Java DSL can be found under the line 137: 

String topic = endpoint.getConfiguration().getTopic();

As a workaround I have entered the following line inside a processor at the SecondProgram:

exchange.getIn().setHeader(KafkaConstants.TOPIC, null);

This has the side-effect that the headerTopic at line 140 is empty and thus the correct topic from line 137 is used.

I believe that since I have clearly set the destination topic at the ThirdProgram to Topic C then Apache Camel should not override this with Topic A.

It looks like a bug since from the method description I understand that we try to avoid circular loops.