fix: reject non-finite (NaN/inf) TTL to prevent immortal cache entries

[27Bslash6]

Summary

Fixes #158. A NaN or inf TTL slipped past every TTL guard because they all use a < comparison and IEEE-754 comparisons against NaN/inf are False. The result was a cache entry whose expiry never triggers — stale data served indefinitely (DATA IS SACRED).

Changes

All three TTL guard sites now reject non-finite values:

• config/decorator.py: DecoratorConfig validation rejects a non-finite ttl up front via math.isfinite, before the existing < 0 check — so @cache(ttl=float("nan")) fails loud at decoration.
• l1_cache.py: put() skips caching when the computed expiry is non-finite (alongside the existing too-short-TTL guard), so no immortal L1 entry can form from a NaN/inf redis_ttl or expires_at.
• object_cache.py: put() rejects a non-finite ttl alongside the existing ttl < 1 check.

Tests

Unit tests (run on PRs) cover all three sites with both NaN and inf:

• test_decorator_config.py: non-finite ttl raises at validation
• test_l1_memory_bounds.py: non-finite redis_ttl/expires_at are not stored
• test_object_cache.py: non-finite ttl raises

Verification

• ruff clean, basedpyright 0 errors, 52 unit tests pass across the three touched test files.

Summary by CodeRabbit

• Bug Fixes

  • Strengthened TTL validation across caching so non-finite values (NaN, ±inf) are rejected in addition to existing negative/zero checks, preventing invalid cache entries.

• Tests

  • Added unit tests covering non-finite TTL handling for decorator config, L1 cache and object cache to ensure correct rejection and safe memory accounting.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Path: .coderabbit.yaml

Review profile: ASSERTIVE

Plan: Pro

Run ID: 371e812b-6bf8-4169-b921-e9beea09623a

📥 Commits

Reviewing files that changed from the base of the PR and between 8978c10 and 5721515.

📒 Files selected for processing (3)

• tests/unit/config/test_decorator_config.py
• tests/unit/test_l1_memory_bounds.py
• tests/unit/test_object_cache.py

---

Walkthrough

This pull request adds non-finite TTL validation across three cache layers: DecoratorConfig, L1Cache, and ObjectCache. Each layer imports math and applies isfinite() checks to reject NaN and infinity at configuration, put operations, and expiry computation, preventing immortal cache entries.

Changes

Non-finite TTL validation across cache layers

Layer / File(s)	Summary
DecoratorConfig TTL finite-value validation src/cachekit/config/decorator.py, tests/unit/config/test_decorator_config.py	DecoratorConfig._validate_config() now imports math and validates ttl is finite before checking non-negativity, raising ValueError for NaN/inf. Parametrised test verifies rejection of both values.
L1Cache expiry guard for non-finite values src/cachekit/l1_cache.py, tests/unit/test_l1_memory_bounds.py	L1Cache.put() imports math and updates the expiry guard to reject non-finite effective expiry times. New test class verifies non-finite redis_ttl and expires_at values are not stored and leave memory accounting at zero.
ObjectCache put TTL finite-value validation src/cachekit/object_cache.py, tests/unit/test_object_cache.py	ObjectCache.put() imports math and enforces finite TTL before the >= 1 check, updating the error message to reference "finite number" and using repr formatting. Parametrised test verifies NaN and inf are rejected.

Estimated code review effort

🎯 3 (Moderate) | ⏱️ ~20 minutes

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 75.00% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly and concisely summarizes the main change: rejecting non-finite TTL values (NaN/inf) to prevent immortal cache entries.
Description check	✅ Passed	The PR description covers the problem, motivation, changes across all three sites, tests added, and verification results. All key sections are present and complete.
Linked Issues check	✅ Passed	All coding requirements from issue #158 are met: non-finite TTLs are rejected in config validation, skipped in L1Cache.put, and rejected in ObjectCache.put, with comprehensive test coverage.
Out of Scope Changes check	✅ Passed	All changes directly address issue #158's objectives of preventing non-finite TTLs from bypassing guards and creating immortal entries. No out-of-scope changes detected.

_{✏️ Tip: You can configure your own custom pre-merge checks in the settings.}

✨ Finishing Touches

📝 Generate docstrings

• Create stacked PR
• Commit on current branch

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch fix/nonfinite-ttl-guard

---

_{Comment @coderabbitai help to get the list of available commands and usage tips.}

[coderabbitai]

Actionable comments posted: 3

🤖 Prompt for all review comments with AI agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

Inline comments:
In `@tests/unit/config/test_decorator_config.py`:
- Around line 97-101: The parameterized test test_non_finite_ttl_rejected
currently checks float("nan") and float("inf") but misses negative infinity;
update the param list for bad_ttl in that test (the DecoratorConfig(ttl=bad_ttl)
assertion) to include negative infinity (e.g., float("-inf") or -float("inf"))
so the test asserts both +inf and -inf are rejected as non-finite TTLs.

In `@tests/unit/test_l1_memory_bounds.py`:
- Around line 71-79: The parameterized tests
test_non_finite_redis_ttl_not_stored and test_non_finite_expires_at_not_stored
only cover float("nan") and float("inf"); update both
`@pytest.mark.parametrize`("bad_ttl", [...]) decorators to also include negative
infinity (e.g. float("-inf")) so the tests cover ±inf; locate the decorators
above the functions test_non_finite_redis_ttl_not_stored and
test_non_finite_expires_at_not_stored and add float("-inf") to the list of
bad_ttl cases.

In `@tests/unit/test_object_cache.py`:
- Around line 76-81: Update the parameterized inputs for
test_non_finite_ttl_raises so it includes negative infinity as well as NaN and
positive infinity: modify the `@pytest.mark.parametrize` call that sets "bad_ttl"
in function test_non_finite_ttl_raises to include float("-inf") along with
float("nan") and float("inf"), ensuring the test rejects NaN/±inf TTLs when
calling ObjectCache.put("k", "value", ttl=bad_ttl).

🪄 Autofix (Beta)

Fix all unresolved CodeRabbit comments on this PR:

• Push a commit to this branch (recommended)
• Create a new PR with the fixes

---

ℹ️ Review info

⚙️ Run configuration

Configuration used: Path: .coderabbit.yaml

Review profile: ASSERTIVE

Plan: Pro

Run ID: a41184f3-9ddf-4cf7-8ed9-78b416948b96

📥 Commits

Reviewing files that changed from the base of the PR and between 82d0417 and 8978c10.

📒 Files selected for processing (7)

• .secrets.baseline
• src/cachekit/config/decorator.py
• src/cachekit/l1_cache.py
• src/cachekit/object_cache.py
• tests/unit/config/test_decorator_config.py
• tests/unit/test_l1_memory_bounds.py
• tests/unit/test_object_cache.py

[codecov]

Codecov Report

❌ Patch coverage is 83.33333% with 2 lines in your changes missing coverage. Please review.
✅ All tests successful. No failed tests found.

Files with missing lines	Patch %	Lines
src/cachekit/config/decorator.py	66.66%	1 Missing and 1 partial ⚠️

📢 Thoughts on this report? Let us know!