Struct EffectiveExpiry 

pub struct EffectiveExpiry;

Stateless calculator for effective expiry decisions.

All methods are pure: they take inputs by value/reference, do no I/O, and never read the system clock. The caller is responsible for supplying a monotonically-correct now_unix_ms.

Implementations

impl EffectiveExpiry

pub fn compute( hard_expires_at_unix_ms: Option<u64>, now_unix_ms: u64, last_access_unix_ms: u64, extended: &ExtendedTtlPolicy, ) -> ExpiryDecision

Compute the effective expiry decision for a cache entry.

Arguments

• hard_expires_at_unix_ms — pre-computed hard expiry from the base BlobCachePolicy. None means “no hard expiry” (entry never hard-expires; only idle TTL can kill it).
• now_unix_ms — current time, supplied by caller.
• last_access_unix_ms — wall-clock time of the most recent access.
• extended — extended policy knobs.

Decision Order

1. Idle TTL — if configured and now - last_access > idle_ttl, return Expired regardless of hard expiry. Idle is checked first because an idle-killed entry is dead even within its hard window.
2. No hard expiry — if hard_expires_at_unix_ms is None, the only remaining gate is idle (already passed) → Fresh.
3. Within hard expiry — now <= hard → Fresh.
4. Within SWR window — now <= hard + stale_serve_ms → Stale.
5. Otherwise → Expired.

pub fn jittered_ttl_ms(base_ttl_ms: u64, jitter_pct: u8, seed: u64) -> u64

Compute a jittered TTL given a base TTL, a jitter percentage, and a deterministic seed.

Returns base_ttl_ms + base_ttl_ms * offset / 100 where offset is in [0, jitter_pct] (clamped to 0..=100). When jitter_pct == 0 the result is exactly base_ttl_ms.

Uses a small LCG (Numerical Recipes constants) so callers can supply any u64 seed (entry hash, write timestamp, etc.) without needing rand. Same seed + same inputs → same result, always.

Saturates on overflow rather than panicking.