Fix unhandled exception in KafkaIO SDF (#37449)

[junaiddshaukat]

Summary

PR #34659 introduced a "fail fast" feature using checkState() in GenerateKafkaSourceDescriptor and WatchForKafkaTopicPartitions. However, when Kafka returns null or an empty partition list for a topic, checkState() throws IllegalStateException inside DoFns. Since DoFns automatically retry on exceptions, this causes infinite retries instead of cleanly stopping the pipeline — the opposite of the intended "fail fast" behavior.

Fix

Replaced checkState() assertions with LOG.warn() + continue in both classes. When a topic has no available partitions:

• A warning is logged so operators can investigate the Kafka configuration
• The topic is skipped gracefully, allowing the pipeline to continue processing other valid topics
• No exception is thrown, preventing the infinite retry loop

What I changed

File	Change
KafkaIO.java	Replaced checkState / if-else branching with null/empty check, LOG.warn, and continue in GenerateKafkaSourceDescriptor.processElement()
WatchForKafkaTopicPartitions.java	Replaced checkState with LOG.warn and continue in getAllTopicPartitions(). Added SLF4J Logger.
WatchForKafkaTopicPartitionsTest.java	Added 3 unit tests: null partition info, empty partition info, and partial topic availability (one missing, one valid)

Testing

• All existing WatchForKafkaTopicPartitionsTest tests pass
• 3 new tests verify the graceful handling:
  • testGetAllTopicPartitionsWithNullPartitionInfo — returns empty list, no exception
  • testGetAllTopicPartitionsWithEmptyPartitionInfo — returns empty list, no exception
  • testGetAllTopicPartitionsSkipsMissingTopics — skips missing topic, returns valid topic's partitions
• spotlessApply passes (code formatting verified)

Fixes #37449

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[gemini-code-assist]

Summary of Changes

Hello @junaiddshaukat, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request resolves a critical flaw in KafkaIO's error handling for topic partition discovery. Previously, if Kafka returned no partition information for a topic, an IllegalStateException would be thrown, causing DoFns to enter an infinite retry loop. The changes introduce a more robust mechanism that logs warnings and skips problematic topics, ensuring pipeline resilience and continuous operation even when facing transient or misconfigured Kafka topics.

Highlights

• Bug Fix: Infinite Retries in KafkaIO: Addresses an issue where checkState() in KafkaIO's DoFns would throw IllegalStateException when Kafka returned null or empty partition lists, leading to infinite retries and pipeline stalls.
• Graceful Error Handling: Replaced checkState() assertions with LOG.warn() and continue statements. This allows the pipeline to log a warning for topics with no available partitions and gracefully skip them, continuing to process other valid topics.
• New Unit Tests: Added three new unit tests in WatchForKafkaTopicPartitionsTest.java to specifically verify the graceful handling of null partition information, empty partition information, and scenarios with partial topic availability.

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Changelog

• sdks/java/io/kafka/src/main/java/org/apache/beam/sdk/io/kafka/KafkaIO.java
  • Modified GenerateKafkaSourceDescriptor.processElement() to replace checkState with a null/empty check, LOG.warn, and continue for handling missing partition info.
• sdks/java/io/kafka/src/main/java/org/apache/beam/sdk/io/kafka/WatchForKafkaTopicPartitions.java
  • Removed the checkState import.
  • Added an SLF4J Logger instance.
  • Updated getAllTopicPartitions() to replace checkState with LOG.warn and continue when partition information is null or empty.
• sdks/java/io/kafka/src/test/java/org/apache/beam/sdk/io/kafka/WatchForKafkaTopicPartitionsTest.java
  • Added assertTrue and Collections imports.
  • Introduced testGetAllTopicPartitionsWithNullPartitionInfo to verify handling of null partition info.
  • Added testGetAllTopicPartitionsWithEmptyPartitionInfo to test handling of empty partition lists.
  • Created testGetAllTopicPartitionsSkipsMissingTopics to ensure topics with missing partitions are skipped while others are processed.

Activity

• The pull request addresses and fixes issue [Bug]: Unhandled exception in KafkaIO SDF #37449.
• The author has confirmed that the appropriate issue is mentioned in the description.
• All existing WatchForKafkaTopicPartitionsTest tests pass.
• Three new tests have been added and pass, verifying graceful handling of various partition info scenarios.
• spotlessApply has passed, indicating code formatting compliance.

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