[KAFKA-14967] MockAdminClient throws NullPointerException in CreateTopicsResult

• Type: Bug
• Status: Resolved
• Priority: Major
• Resolution: Fixed
• Affects Version/s: 3.4.0
• Fix Version/s: 3.6.0
• Component/s: clients
• Assignee: James Shaw
• Reporter: James Shaw
• Created: 04/May/23 08:53
• Updated: 28/Jul/23 09:46
• Resolved: 28/Jul/23 09:46

Description

Calling CreateTopicsResult.topicId().get() throws NullPointerException, while KafkaAdminClient correctly returns the topicId.

The NPE appears to be caused by MockAdminClient.createTopics() calling future.complete(null)

Stacktrace:

java.util.concurrent.ExecutionException: java.lang.NullPointerException
	at java.base/java.util.concurrent.CompletableFuture.reportGet(CompletableFuture.java:396)
	at java.base/java.util.concurrent.CompletableFuture.get(CompletableFuture.java:2073)
	at org.apache.kafka.common.internals.KafkaFutureImpl.get(KafkaFutureImpl.java:165)
	at MockAdminClientBug.shouldNotThrowNullPointerException(MockAdminClientBug.java:37)
       [snip]
Caused by: java.lang.NullPointerException
	at org.apache.kafka.common.internals.KafkaFutureImpl.lambda$thenApply$0(KafkaFutureImpl.java:60)
	at java.base/java.util.concurrent.CompletableFuture.uniApplyNow(CompletableFuture.java:684)
	at java.base/java.util.concurrent.CompletableFuture.uniApplyStage(CompletableFuture.java:662)
	at java.base/java.util.concurrent.CompletableFuture.thenApply(CompletableFuture.java:2168)
	at org.apache.kafka.common.internals.KafkaFutureImpl.thenApply(KafkaFutureImpl.java:58)
	at org.apache.kafka.clients.admin.CreateTopicsResult.topicId(CreateTopicsResult.java:82)
	... 85 more

Test case to reproduce:

 
import org.apache.kafka.clients.admin.Admin;
import org.apache.kafka.clients.admin.CreateTopicsResult;
import org.apache.kafka.clients.admin.MockAdminClient;
import org.apache.kafka.clients.admin.NewTopic;
import org.apache.kafka.common.Node;
import org.apache.kafka.common.Uuid;
import org.junit.jupiter.api.Test;

import java.util.Optional;
import java.util.concurrent.ExecutionException;

import static java.util.Collections.singletonList;

public class MockAdminClientBug {
    @Test
    void shouldNotThrowNullPointerException() throws ExecutionException, InterruptedException {
        Node controller = new Node(0, "mock", 0);
        try (Admin admin = new MockAdminClient(singletonList(controller), controller)) {
            CreateTopicsResult result = admin.createTopics(singletonList(new NewTopic("TestTopic", Optional.empty(), Optional.empty())));
            Uuid topicId = result.topicId("TestTopic").get();
            System.out.println(topicId);
        }
    }
}

Issue Links

• links to: GitHub Pull Request #13671