ramanathan1504 opened a new pull request, #4081:
URL: https://github.com/apache/logging-log4j2/pull/4081
Issue #3660
### Root cause (what was going wrong)
There were three related edge cases:
1. **Strict-after boundary in `getTimeAfter`**
- `getTimeAfter` must move to the *next second* before evaluation.
- Using `+1ms` can collapse back to the same second after millisecond
truncation and return the same fire time again.
2. **Millisecond input handling in `getPrevFireTime`**
- On rollover/restart paths, file timestamps often include milliseconds
(e.g. `...00.201`).
- Without compensating for that, `getPrevFireTime` could resolve to the
previous day around DST fallback boundaries, which can trigger an extra
rollover.
3. **Spring-forward (23-hour day) reverse-search step**
- Day-level reverse search used a fixed 24h step.
- On 23h DST days, that can skip over a valid previous fire time.
### Fix implemented
In
`log4j-core/src/main/java/org/apache/logging/log4j/core/util/CronExpression.java`:
- `getTimeAfter(...)`: keep strict next-second behavior (`+1000` ms).
- `getPrevFireTime(...)`: for inputs with millisecond fraction, shift by
`+999ms` before delegating to `getTimeBefore(...)`.
- `findMinIncrement()`: for day-level fallback increment, use 23h minimum
step to remain DST-safe on spring-forward days.
### Validation
`log4j-core-test/src/test/java/org/apache/logging/log4j/core/util/CronExpressionTest.java`
now includes/contains DST cases for:
- fallback at 2AM (`Australia/Sydney`)
- fallback at midnight (`America/Santiago`)
- spring-forward 23h day (`Australia/Sydney`)
Current result locally:
- `CronExpressionTest`: **16 run, 0 failures**
This addresses the “twice-a-year” DST rollover corruption path you
described, including both fallback ambiguity and spring-forward short-day
behavior.
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