[PR] [ISSUE #9728] Fix correctMinOffset handling of incomplete consume queue records [rocketmq]

["daguimu (via GitHub)" <gi...@apache.org>]

daguimu opened a new pull request, #10211:
URL: https://github.com/apache/rocketmq/pull/10211

   ## Problem
   
   In `ConsumeQueue.correctMinOffset()`, the size check at line 616 only guards against completely empty buffers (`result.getSize() == 0`). When a consume queue mapped file contains a partially written record (1-19 bytes, less than `CQ_STORE_UNIT_SIZE` = 20), the subsequent `buffer.getLong()` call throws `BufferUnderflowException`.
   
   This can happen when:
   1. The last mapped file in a consume queue has a partially written record due to async flush
   2. CommitLog messages are lost during restart (async-flush + sync-master)
   3. The broker does not truncate the incomplete record during recovery
   
   ## Root Cause
   
   The check `result.getSize() == 0` does not cover the case where `result.getSize()` is between 1 and 19 (less than one complete CQ unit of 20 bytes). A partial record cannot be meaningfully processed.
   
   Note: PR #10109 previously added a guard for the last mapped file check (lines 564-570), which resolved the main startup crash. This PR addresses the remaining edge case in the binary search section where a partially written record could still cause a `BufferUnderflowException`.
   
   ## Fix
   
   Changed the size check from:
   ```java
   if (result.getSize() == 0) {
   ```
   to:
   ```java
   if (result.getSize() < ConsumeQueue.CQ_STORE_UNIT_SIZE) {
   ```
   
   This properly handles both empty buffers and incomplete records.
   
   ## Tests Added
   
   No new tests needed — existing `ConsumeQueueTest` (13 tests covering `correctMinOffset` with various offset scenarios) all pass. The fix is a one-line defensive check improvement.
   
   ## Impact
   
   - Prevents `BufferUnderflowException` on partially written consume queue records
   - No behavioral change for normal consume queues (all valid records are >= 20 bytes)
   - Minimal, single-line change with no risk of side effects
   
   Fixes #9728


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