[ISSUE #10578] Fix master election maxOffset comparator overflow

[Aias00]

What changed

Fix DefaultElectPolicy master-election ordering to avoid integer overflow when comparing broker maxOffset values.

The election comparator previously used subtraction and cast the long offset delta to int:

(int) (o2.getMaxOffset() - o1.getMaxOffset())

When two brokers have the same epoch and their maxOffset difference exceeds Integer.MAX_VALUE, the comparator can overflow and return the wrong ordering. That may cause the controller to elect a broker with a lower offset as master.

This PR replaces subtraction-based comparisons with Integer.compare and Long.compare, preserving the existing ordering rules:

1. Higher epoch first
2. Higher max offset first
3. Lower election priority first

Fixes #10578

Why

Master election is a control-plane correctness path. A comparator overflow here can select a stale replica when broker offsets diverge by more than Integer.MAX_VALUE.

Tests

Added DefaultElectPolicyTest covering the overflow case:

• two brokers with the same epoch
• offset delta greater than Integer.MAX_VALUE
• verifies the broker with the higher offset is elected

Verified locally:

mvn -q -pl controller -DskipTests=false -Dtest=DefaultElectPolicyTest -Djacoco.skip=true test
mvn -q -pl controller -DskipTests compile -Dspotbugs.skip=true -Dcheckstyle.skip=true
mvn -q -DskipTests compile -Dspotbugs.skip=true -Dcheckstyle.skip=true

Notes

checkstyle:check was not used as a gating signal because the controller module currently reports existing unrelated checkstyle violations. The targeted test and compile checks pass.

[Copilot]

Pull request overview

Fixes a correctness bug in the controller master-election ordering by replacing overflow-prone subtraction/casting in DefaultElectPolicy’s comparator with safe Integer.compare / Long.compare comparisons, and adds a focused regression test for the overflow scenario described in #10578.

Changes:

• Replace subtraction-based epoch/maxOffset/priority comparisons in the election comparator with Integer.compare/Long.compare to prevent overflow and preserve intended ordering.
• Add DefaultElectPolicyTest to cover the case where maxOffset deltas exceed Integer.MAX_VALUE and ensure the higher-offset broker is elected.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
controller/src/main/java/org/apache/rocketmq/controller/elect/impl/DefaultElectPolicy.java	Updates the broker ordering comparator to avoid overflow and keep deterministic ordering rules (epoch desc, offset desc, priority asc).
controller/src/test/java/org/apache/rocketmq/controller/elect/impl/DefaultElectPolicyTest.java	Adds a regression test ensuring election prefers the higher maxOffset when the offset difference exceeds Integer.MAX_VALUE.

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[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 48.14%. Comparing base (8242c1e) to head (cc9c594).

Additional details and impacted files

@@              Coverage Diff              @@
##             develop   #10579      +/-   ##
=============================================
- Coverage      48.26%   48.14%   -0.12%     
+ Complexity     13433    13400      -33     
=============================================
  Files           1378     1378              
  Lines         100817   100820       +3     
  Branches       13040    13041       +1     
=============================================
- Hits           48660    48542     -118     
- Misses         46211    46310      +99     
- Partials        5946     5968      +22     

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