Fix DST caching bug by using strict timestamp arithmetic and add regression test

[Kevinrob]

Description

This PR resolves issue #194, where cache entries could be incorrectly cached for nearly an hour during the Daylight Saving Time (DST) transition (Summer -> Winter).

Changes

• Core Fix: Replaced \DateTimeImmutable::modify() with direct timestamp manipulation (setTimestamp()) for relative dates. This avoids the ambiguity of local time during DST transitions, as UNIX timestamps are absolute.
• Regression Test: Added testDstTransitionDoesNotIncorrectlyCache in PrivateCacheTest. It mocks the system time precisely during the transition point in the Europe/Berlin timezone to ensure the fix works as expected.
• Improved Test Isolation: Ensured the global Clock is reset to a NativeClock after time-sensitive tests.

Verification

• Successfully reproduced the potential for error locally and verified that the new logic correctly identifies entries as stale during the critical transition window.
• All 81 tests passed on PHP 8.5.

[gemini-code-assist]

Summary of Changes

Hello, 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 addresses a critical bug where cache entries could be incorrectly marked as valid or stale for an extended period during Daylight Saving Time transitions. The fix involves a fundamental change in how cache expiration times are calculated, moving from potentially ambiguous date modifications to precise, absolute timestamp arithmetic. A dedicated regression test has been added to prevent future recurrences of this issue, ensuring robust caching behavior across time zone changes.

Highlights

• DST Caching Fix: Replaced \DateTimeImmutable::modify() with direct timestamp manipulation (setTimestamp()) to prevent incorrect cache expiration during Daylight Saving Time transitions.
• Regression Test: Introduced testDstTransitionDoesNotIncorrectlyCache in PrivateCacheTest to validate the fix by simulating a DST transition scenario.
• Test Isolation Improvement: Ensured the global Clock is consistently reset to a NativeClock after time-sensitive tests to maintain test environment integrity.

Changelog

• src/Strategy/GreedyCacheStrategy.php
  • Changed how cache entry expiration is calculated from Clock::now()->modify() to Clock::now()->setTimestamp($now->getTimestamp() + $ttl).
• src/Strategy/PrivateCacheStrategy.php
  • Updated cache entry creation for 'no-cache' responses to use setTimestamp() for expiration.
  • Modified cache entry creation based on Cache-Control headers to use setTimestamp() for expiration.
  • Adjusted default cache entry creation to use setTimestamp() for expiration.
• tests/PrivateCacheTest.php
  • Added testDstTransitionDoesNotIncorrectlyCache to simulate a DST transition and assert correct cache entry staleness.
  • Ensured the default timezone is restored and the Clock is reset to NativeClock in a finally block after the DST test.

Activity

• No human activity (comments, reviews, etc.) has occurred on this pull request yet.

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[gemini-code-assist]

Code Review

This pull request correctly addresses a bug related to Daylight Saving Time transitions by using UNIX timestamps for cache expiration calculations instead of relative date modifications. The changes in GreedyCacheStrategy.php and PrivateCacheStrategy.php are sound. The addition of the regression test testDstTransitionDoesNotIncorrectlyCache is excellent, as it specifically targets the fixed bug and ensures it doesn't reappear. My feedback includes a couple of suggestions to further improve test isolation and code maintainability.