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…der (LAB-557) GET 200s carry the entry's remaining freshness in whole seconds (server-clock delta; 0 on stale-window responses; omitted for no-expiry entries and by pre-signal servers) so SDK local caches can bound L1 backfill to min(local_ttl, fresh_for) instead of restarting the freshness clock at time-of-read. Additive and backward compatible; not emitted on HEAD. Re-serving tiers must decay or omit — never replay an undecayed value beyond their documented coherence window. Origin: CodeRabbit outside-diff finding on cachekit-py#233.
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WalkthroughThe SaaS API specification adds remaining-freshness headers, tenant-partitioned caching, mandatory response headers, freshness bounds, stale-read restrictions, and no-expiry lifecycle rules. The changelog and feature matrix document these changes and planned Python support. ChangesSaaS API freshness and lifecycle
Priority: ➖ Normal Estimated code review effort: 1 (Trivial) | ~5 minutes Change: Feature Merge Risk: 🟡 Moderate · up to A bounded entry with unknown remaining freshness can be locally backfilled for the SDK’s full configured TTL, allowing it to be served past the server freshness bound. Clarify the tier rule before merge. 🚥 Pre-merge checks | ✅ 5✅ Passed checks (5 passed)
✨ Finishing Touches🧪 Generate unit tests (beta)
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In `@spec/saas-api.md`:
- Line 111: Update the L1 backfill contract to prevent client-side stale serving
beyond the server’s evict_at boundary: either prohibit stale-while-revalidate
service for server-bounded entries once fresh_for expires, including fresh_for =
0, or define and apply a remaining-eviction signal that caps stale service
through evict_at. Ensure the behavior remains consistent with the server
eviction rule in Line 253.
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…reshness bound (LAB-2531) CodeRabbit (PR #51): X-CacheKit-Fresh-For reports remaining freshness (fresh_until), not remaining eviction time (evict_at), so an L1 with client-side SWR could serve its copy as locally-stale past the server's evict_at — contradicting the Reading-a-stale-entry bound. Close the gap by prohibiting any local service past fresh_for (and any backfill at fresh_for = 0): stale service is the server's job, which owns the stale window through evict_at. A remaining-eviction signal is deliberately not added — it would let clients replicate the stale window invisibly to server-side revalidation and metering.
…el review (LAB-2531) Expert-panel follow-up to the fresh_for hard-service-bound rule: - Reading-a-stale-entry: stale-flagged responses MUST NOT be backfilled at all (not merely 'not as fresh'), with or without Fresh-For — closes the backfill-as-locally-stale reading against Freshness-only servers. - Edge tiers MUST emit Fresh-For: 0 when remaining freshness is unknown, never omit — omission reads as 'no freshness bound' and silently restores the unbounded backfill this header exists to kill. - Header absence licenses fresh service only; local stale service of server-backed entries is prohibited unconditionally. - HEAD MUST NOT create/refresh/extend any local entry's service bound. - Value grammar: non-ASCII-digit or > 2,592,000 (30-day cap) treated as 0, same as unparseable/negative. - Documented revocation propagation: an issued fresh_for is a snapshot; DELETE/PATCH-shorten reaches L1s only within the largest outstanding fresh_for — secure caches size TTL to revocation tolerance. Also disambiguated that serving server-returned stale bytes per Reading-a-stale-entry is unaffected (only the local copy is governed), and cut the clause restating the section preamble.
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# Conflicts: # CHANGELOG.md
…, mandate Cache-Control: no-store (LAB-2531) Blockers: the deployment-specific '<=5 s' coherence figure contradicted the deployed tiers (L0 5 s + colo 5 s compose to ~10 s, colo hits re-stamp a full undecayed L0 TTL) — replaced with the general rule that coherence windows compound across composed tiers that re-stamp rather than decay. And the spec's first contemplation of intermediary caches had no HTTP cache directives while the cache key carries no tenant: byte-identical URLs across tenants make RFC 9111 heuristic caching a cross-tenant read — servers MUST now emit Cache-Control: no-store on every response, and CacheKit-operated tiers MUST partition internal caches by tenant. Majors: fresh + Fresh-For: 0 documented as legal (final sub-second floors to 0); dead 'no expiry' emission branch removed (TTL is mandatory, so the branch failed open into pre-signal legacy behavior); local deadlines SHOULD use a suspend-counting clock (guidance, not wire contract).
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Resolved the merge conflict in Same push carries the second expert-panel round's remediation (
All local verify legs green (stdlib suite, 8/8). |
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In `@spec/saas-api.md`:
- Line 119: Update the revocation-bound statement near the “fresh_for” semantics
to account for in-flight response transit and clock or suspend errors, or remove
the absolute “at most” guarantee. Ensure the documented bound matches the
client’s behavior of starting its local deadline after response transit.
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… error (LAB-2531) The previous sentence claimed revocation reaches L1s within 'at most the largest outstanding fresh_for' — an absolute bound contradicted two bullets earlier (transit overstates remaining freshness) and one bullet earlier (suspend-blind clocks serve past the deadline). A GET already in flight when the DELETE lands is backfilled on arrival and served for its full local bound, so the true bound is the largest applied local bound plus transit plus clock error. Take CodeRabbit's wording, name the in-flight mechanism explicitly.
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Inline comments:
In `@spec/saas-api.md`:
- Line 119: Update the revocation-bound statement in the “fresh_for” semantics
paragraph to include the applicable sum of serving-tier coherence windows, in
addition to the largest locally applied bound, in-flight response transit, and
clock or suspend error. Preserve the distinction that already-backfilled copies
remain unaffected and ensure the security-sensitive cache TTL guidance reflects
the complete bound.
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…ndows (LAB-557) A re-stamping tier may compliantly hand out a copy it cached before the origin DELETE — that copy was never in flight, yet is backfilled for its full local bound. The bound therefore adds the path's compounded coherence windows to the local bound, transit, and clock terms; without it the security-sensitive TTL guidance understated revocation exposure. CodeRabbit finding on protocol#51.
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…uthorization (LAB-557, LAB-2531) Third expert-panel round on the remaining-freshness header. Every finding applied; the two design calls are decided here rather than parked: F1 (HIGH) — the re-stamp/backfill rules were an enumeration with three escapes: `fresh` + `Fresh-For: 0` was mislabelled `stale` by the passthrough clause, an unrecognized freshness token with a positive value was undefined, and SDK backfill was not gated on the label. Both sides are now fail-closed: a positive value is legal only on a `fresh`-labelled response that itself carried a positive value; every other shape is emitted as `0` with the label passed through unchanged; SDK backfill requires `fresh` (or absent) — a positive value on `stale` is a server bug, not a licence. F2 — decided past the panel's "clamp to evict_at" option: the header MUST decay and MUST NOT be re-stamped, under any label. A clamp needs an evict_at signal between tiers that the deployed path does not carry; decay needs nothing — saas#325's L0/colo tiers already decay — and it keeps a pre-DELETE copy's local service inside the entry's fresh_until. Bytes coherence (deployment-documented, compounding) is unchanged; the header is now stricter than the bytes. evict_at is stated as the store's bound, with the end-to-end revocation bound kept in Remaining Freshness. F3 — Vary: Authorization joins Cache-Control: no-store as a mandatory response header. One static header; an independent second control against cross-tenant disclosure for a cache that ignores no-store but honours Vary. F4 — value grammar is length-guarded (1–7 ASCII digits) before the range check, so a wrapping fixed-width parse cannot land an over-cap value in range. Minors: coherence window and signal-capable server defined at first use (and stated independent of SWR support); decay floors at 0; unknown remaining freshness is `0`, never omitted; absent-header legacy rule scoped to GET 200 OK; the no-local-stale-service rationale is stated once and cross-referenced from the stale-read rule.
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Panel round applied — c2fc531Per finding, with the two design calls decided rather than parked (Ray's direction on LAB-557):
Side finding while checking F2 against the implementation: cachekit-io/saas#325 omits Verification: the nine stdlib verify legs pass locally; CHANGELOG carries the round. CodeRabbit has not yet reviewed |
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Inline comments:
In `@CHANGELOG.md`:
- Around line 48-52: Update the changelog summary around the `fresh_until` rules
to state that positive values and SDK backfill are allowed for responses
labelled `fresh` or with no freshness label, where the absent label is treated
as the pre-SWR `fresh` default; preserve the existing behavior for all other
labels and invalid values.
In `@spec/saas-api.md`:
- Line 262: Update the evict_at requirement in the local caching rules so it
applies only to responses with a usable server freshness bound, or remove the
legacy rule that preserves the full local TTL when X-CacheKit-Fresh-For is
absent. Align the wording near Remaining Freshness and the line 262 rule so
unsignaled responses may retain the documented legacy behavior while
signal-capable responses cannot be served past evict_at.
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…(LAB-2531) CodeRabbit round five on protocol#51 (c2fc531): - spec/saas-api.md 'Reading a stale entry': the local-cache 'MUST NOT extend service past evict_at' rule contradicted the legacy absent-header rule in Remaining Freshness (a pre-signal response keeps the configured local TTL, which can outlive evict_at). Scope the MUST NOT to responses carrying X-CacheKit-Fresh-For and name the pre-signal case as the origin gap the header closes. No behaviour change: line 119 already governed absence. - CHANGELOG third-round entry said positive values and SDK backfill require the 'fresh' label; the spec accepts 'fresh' OR unlabelled (pre-SWR default). Align the summary so a literal reader does not emit 0 / skip backfill on valid unlabelled signal responses. Record the evict_at scoping in the same entry.
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…GET /ttl returns null (LAB-557)
Ray's ruling on the Feature Design review (option A, LAB-557 2026-09-13):
admit immortal entries and amend the spec to match shipped reality.
The spec asserted "there is no no-expiry entry" on the strength of a
tenant-default TTL that no server implements — saas has stored
`expires_at NULL` for an omitted X-CacheKit-TTL since day one, and Redis,
Memcached and File all admit unbounded entries. Three rounds of this PR
built rules on that fiction.
- PUT: omitted X-CacheKit-TTL means no expiry (no fresh_until, no
evict_at, served fresh until deleted or overwritten, never stale).
Servers MUST NOT substitute a hidden default — the existing rule that
validation must not depend on defaults clients cannot see.
- Remaining Freshness: the header is omitted for no-expiry entries. The
server bound is unbounded, so min(local_ttl, ∞) is the SDK's configured
local TTL — exactly the absent-header path, so "no-expiry" and
"pre-signal server" are indistinguishable to the client by design and
produce the same action.
- Re-serving tiers: "unknown means 0, never absent" splits into "no bound
→ omit, mirroring the store" and "bound unknown → 0". A tier MUST record
at populate whether a copy is unbounded or merely unhinted; one that
cannot tell MUST emit 0. Matches what saas#350 already does after
Helly R's review.
- GET /v1/cache/{key}/ttl: a no-expiry key returns 200 {"ttl": null},
never 404 (the key exists) and never a negative sentinel. null was
chosen over Redis's -1 because the field is typed as seconds and all
three SDKs already model no expiry as null/None/Option::None — ts types
the body `{ ttl: number | null }`, rs has `TtlResponse { ttl: Option<u64> }`
with a null-parsing test, py returns the JSON value with "None = no
expiry" in its docstring. PATCH /ttl on a no-expiry entry bounds it.
- The 30-day maximum is restated as a bound on a stated TTL's value range,
not a storage-lifetime ceiling — a client could never ask for 31 days
but always got forever by omitting the header; the rationale now says so.
CHANGELOG entries for the earlier rounds are corrected in place (they are
unreleased) rather than contradicted by a new one.
481b1b8
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Inline comments:
In `@spec/saas-api.md`:
- Line 108: Update the re-serving-tier rule for Remaining Freshness so tiers
implementing it emit X-CacheKit-Fresh-For: 0 when the upstream copy’s expiry
status or remaining freshness is unknown; allow absent-header pass-through only
for tiers that do not implement Remaining Freshness or when the tier knows the
copy has no expiry.
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…n bound (LAB-2531) Panel round on 481b1b8 (Mark S + CodeRabbit r4001310558), no-expiry follow-through: B1 — lines 108/111 stated two MUSTs for one situation: a tier fronting a pre-signal store 'passes the absence through' (omit) vs a tier that 'cannot tell unbounded from unhinted MUST emit 0'. Omitting lets the SDK apply its full local TTL to a bounded entry — the origin gap. Rule is now single and fail-closed: a tier MAY omit only on positive knowledge of no expiry (a signal-capable store below omitted, or the copy came from a write with no TTL); everything else, a pre-signal store below included, is 0. Matches saas#350, where tiers omit only when the DO reported a null bound. B2 — line 123 claimed the local revocation term is 'decayed, so it ends no later than fresh_until'. A no-expiry entry has no fresh_until; its local term is the full configured local TTL, re-anchored per read, with no server ceiling. Stated honestly, incl. the formerly-no-expiry PATCH/DELETE case, and revocation-sensitive keys MUST carry an explicit X-CacheKit-TTL. MEDs — GET /ttl null is not transparent to pre-null readers (mixed-reader rule added, mirroring stale_ttl); revalidation PUT MUST re-send TTL or it immortalizes a bounded key; the 30-day cap rationale says storage accumulation is unbounded by this spec (LAB-279). One-line note: a mispartitioned no-expiry copy never self-heals. CHANGELOG no-expiry bullet corrected in place (unreleased).
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Defines the
X-CacheKit-Fresh-Forremaining-freshness response header (LAB-557) so SDK local caches can bound L1 backfill tomin(local_ttl, fresh_for)instead of restarting the freshness clock at time-of-read — an entry read near the end of its server-side window could previously be served fresh from L1 for up to another full TTL, pastfresh_until(and, with a stale window, pastevict_at).Spec semantics (
spec/saas-api.md#remaining-freshness):200only;max(0, floor(fresh_until − now))on the server clock;0on stale reads; omitted for no-expiry entries and by pre-signal servers. Not emitted on HEAD.Also adds the sdk-feature-matrix row (🚧 LAB-557 for py — flips to ✅ per the matrix's released-artifact verification rules once a cachekit-py release ships it) and a CHANGELOG entry.
Companions: cachekit-io/saas (emission), cachekit-io/cachekit-py (consumption), cachekit-io/docs (public API doc).
Expert-panel review (4 agents, high stakes): FIX-FIRST → all surviving findings applied in the companion repos; spec text itself had no surviving findings. Origin: CodeRabbit outside-diff finding on cachekit-py#233 (LAB-506).
Summary by CodeRabbit
X-CacheKit-Fresh-Forresponse header, including freshness limits, expiry, stale-response handling andHEADexclusions.Cache-Control: no-storeandVary: Authorizationheaders, with tenant-isolated internal caching.Summary
This PR strengthens the specification for the
X-CacheKit-Fresh-Forresponse header, which communicates an entry's remaining freshness so SDK-side local caches (L1) can bound how long they serve a backfilled copy.Key Changes
Mandatory second anti-cross-tenant control
Vary: Authorizationin addition toCache-Control: no-storeon every response. This provides an independent second defense against cross-tenant HTTP caching: even if a cache wrongly stores a response despiteno-store, honoringVaryprevents it from serving tenant A's copy to tenant B's request.Fail-closed rules for re-serving tiers (edge/colo caches)
The emission rules are reframed from enumerated cases into strict, fail-closed principles:
0), never a larger value under any label. This keeps a pre-DELETEcopy's local service inside the entry'sfresh_until.0, never absent — when remaining freshness is unknown, emit0; never omit the header (omission signals "pre-signal server" and reopens unbounded backfill).fresh+ positive — a positive value is legal only when the underlying response was labelledfreshwith a strictly positive value; every other shape (stale,0, unrecognized token, missing header) must be emitted as0with its freshness label passed through unchanged.SDK consumption tightening
freshlabel — astaleor unrecognized label forbids backfill regardless of the numeric value.2,592,000(the 30-day TTL cap). The length check must run before the range check to prevent a wrapping fixed-width integer conversion from landing an over-cap value back in range.Clarified revocation and store bounds
evict_atis now explicitly stated as the store's service bound, not an end-to-end one — copies already handed to re-serving tiers or backfilled locally run to their own bounded lifetimes.Documentation consolidation
These are specification-only changes (no code); the CHANGELOG notes the deployed tiers already decay, so the rules impose zero implementation cost on conforming servers.
Summary
This PR refines the specification for the
X-CacheKit-Fresh-Forremaining-freshness response header, clarifying the behavior boundary between signal-capable servers and pre-signal (legacy) servers.Changes
Scoping the
evict_atlocal-cache rule to responses carrying the headerThe core change narrows the "never serve past
evict_at" rule so that it applies only to responses that actually carry theX-CacheKit-Fresh-Forheader. Previously the rule was stated unconditionally.The updated spec now clarifies two distinct paths:
evict_at. The header is the mechanism enabling local caches to honor this bound for fresh-labelled reads near the freshness boundary.evict_at. This is explicitly identified as the origin gap the header is designed to close.Extending positive-value legality to unlabelled responses
The CHANGELOG update broadens the rule for when a positive
X-CacheKit-Fresh-Forvalue is legal: it now applies tofresh-labelled responses and unlabelled responses (the pre-SWRfreshdefault). Correspondingly, SDK backfill is now gated on thefreshlabel or an unlabelled response.Purpose
These changes ensure backward compatibility with pre-signal servers by explicitly documenting that legacy TTL behavior is preserved when the header is absent, while defining the stricter revocation guarantees that apply once the header is present.
Summary
This PR introduces the
X-CacheKit-Fresh-Forremaining-freshness response header to the CacheKit Protocol Specification and, as part of the same effort, corrects the spec to properly admit no-expiry entries — reconciling the spec with what every server implementation (saas, Redis, Memcached, File) has always done.Key Changes
X-CacheKit-Fresh-Forremaining-freshness headerGET /v1/cache/{key}200 OKresponses, carrying the entry's remaining freshness in whole seconds (computed against the server's clock).min(local_ttl, fresh_for)instead of restarting the freshness clock at time-of-read, preventing an entry near the end of its server-side window from being served fresh locally beyond that window.Fresh-For: 0;fresh+Fresh-For: 0is documented as legal (serve, don't backfill).fresh+ positive responses, and value grammar guarded to 1–7 ASCII digits capped at 2,592,000.No-expiry entries admitted (Ray's ruling on the Feature Design review)
The spec previously described a tenant-default TTL that no server actually implements. This PR corrects that:
PUTwithoutX-CacheKit-TTLnow means "no expiry" — nofresh_until, noevict_at, servedfreshuntil deleted or overwritten, never stale. Servers MUST NOT substitute a hidden default (aligning validation with the same principle already applied toX-CacheKit-Stale-TTL).X-CacheKit-Fresh-Foris omitted for no-expiry entries — the server bound is unbounded, so the SDK's configured local TTL (the absent-header path) is the correct bound.0"; a tier that cannot distinguish the two MUST emit0.GET /v1/cache/{key}/ttlreturns200 OKwith{"ttl": null}for a no-expiry key — never404, never a negative sentinel. SDKs MUST acceptnulland surface it as their no-expiry value.PATCH /ttlon a no-expiry entry bounds it (fresh_until = now + ttl).TTL=0rationale:0is an error to prevent silent data loss (Redis/HTTP reading) or an unintended no-expiry entry (Memcached reading) — no expiry is requested only by omitting the header.Files Changed
CHANGELOG.md— documents both the header addition and the no-expiry admission.spec/saas-api.md— normative spec updates for header emission/consumption, TTL validation, SWR write semantics, and the/ttlendpoints.Summary
This PR refines the specification for the
X-CacheKit-Fresh-Forremaining-freshness response header, closing a cache-coherence gap and clarifying revocation behavior for no-expiry entries.Key Changes
Re-serving tier rule hardened (fail-closed)
The previous rule ("no bound → omit, mirroring the store; bound unknown →
0") is replaced with "omit only on positive knowledge of no expiry; otherwise0". A tier may now omit the header only when it can positively confirm a copy has no expiry — either a signal-capable store below omitted it, or the tier populated the copy from a write carrying noX-CacheKit-TTL.Critically, a tier fronting a pre-signal store must now emit
0rather than passing the absence through. The prior pass-through behavior re-opened the origin gap for bounded entries behind such a tier, silently restoring the unbounded local backfill this header exists to prevent. The trade-off is no local backfill behind that tier until the store signals — the correct fail-closed posture for a mixed deployment.Revocation bound for no-expiry entries documented
The spec now clarifies that no-expiry entries (and any read served without the header) have no server-side revocation ceiling: the local term is the reader's full configured local TTL, re-anchored on every read. A revoked no-expiry value can therefore outlive its
DELETEby the largest local TTL in the fleet. New normative guidance requires revocation-sensitive keys to be stored with an explicitX-CacheKit-TTL.Revalidation
PUTmust re-send TTLA revalidation
PUTmust now re-send bothX-CacheKit-TTLand the stale window. OmittingX-CacheKit-TTLon a recompute does not carry the previous bound forward — it silently stores a no-expiry entry, immortalizing a formerly-bounded key.Mixed-reader caveat for
GET /ttlreturningnullAdded a warning that the
{"ttl": null}response for no-expiry entries is not transparent to older SDKs that assert an integer or coerce non-integers to0(which would read an immortal key as missing or expiring now). Deployments must not store no-expiry entries for keys whose/ttlreaders predatenullsupport.Storage hygiene note
Clarified that nothing in the spec bounds how long or how many no-expiry entries accumulate — storage hygiene is an operator concern (tracked as LAB-279). Also notes that a mispartitioned no-expiry copy never self-heals, making the tenant-partitioning rule its only control.