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update the age header when responding from cache #15052

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update the age header when responding from cache #15052

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d6511d3
update the age header when responding from cache
Aug 6, 2026
27891cd
Age in seconds, not milliseconds
asharpe Aug 6, 2026
02e1337
update type
Aug 6, 2026
d71f861
increment the age by the duration of time in cache
Aug 6, 2026
ed09902
add changeset
Aug 6, 2026
869414f
auto-format
asharpe Aug 6, 2026
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6 changes: 6 additions & 0 deletions .changeset/increment-cache-response-age.md
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Original file line number Diff line number Diff line change
@@ -0,0 +1,6 @@
---
"miniflare": patch
---

Increment the Age response header when responding from cache.

8 changes: 8 additions & 0 deletions packages/miniflare/src/workers/cache/cache.worker.ts
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Expand Up @@ -30,6 +30,7 @@ interface CacheMetadata {
headers: string[][];
status: number;
size: number;
stored?: number;
}

type CacheRouteHandler = RouteHandler<
Expand Down Expand Up @@ -302,6 +303,12 @@ export class CacheObject extends MiniflareDurableObject {
// time we don't do this is when the entry isn't found, or expired, in which
// case, we just threw a `CacheMiss`)
assert(resHeaders !== undefined);
const now = this.timers.now();
const age = parseInt(resHeaders.get("age") || "0", 10);
const cachedDuration = Math.round(
(now - (cached.metadata.stored || now)) / 1000
);
resHeaders.set("Age", String(age + cachedDuration));
resHeaders.set("CF-Cache-Status", "HIT");
resRanges ??= [];

Expand Down Expand Up @@ -356,6 +363,7 @@ export class CacheObject extends MiniflareDurableObject {
headers: Object.entries(headers),
status: res.status,
size,
stored: this.timers.now(),
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@devin-ai-integration devin-ai-integration Bot Aug 6, 2026

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🟡 Cached responses can report an age that is too young for slow or large uploads

The time a cached item was saved is recorded (this.timers.now() at packages/miniflare/src/workers/cache/cache.worker.ts:366) only after the whole body has finished being written, rather than when the item was received, so slow or large responses are later reported as newer than they are.
Impact: Clients can be told a cached response is fresher than it really is, which can make them hold on to stale content longer.

Why the timestamp lands late: metadata promise resolves after the blob write

metadata is a promise created from sizePromise (packages/miniflare/src/workers/cache/cache.worker.ts:355-367). KeyValueStorage.put() first awaits this.#blob.put(entry.value) and only then awaits entry.metadata (packages/miniflare/src/workers/shared/keyvalue.worker.ts:208-223), so this.timers.now() inside the .then() executes after the entire body has been streamed. By contrast, the entry's expiration is computed synchronously at request time (packages/miniflare/src/workers/cache/cache.worker.ts:372), so stored and expiration use different clocks. Capturing the timestamp once, before starting the stream, and reusing it for both would keep them consistent.

Prompt for agents 
In packages/miniflare/src/workers/cache/cache.worker.ts, the `put` handler records `stored: this.timers.now()` inside the metadata promise (`sizePromise.then(...)`). Because `KeyValueStorage.put()` awaits the blob write before awaiting the metadata promise (packages/miniflare/src/workers/shared/keyvalue.worker.ts), this timestamp is taken after the whole response body has been streamed, not when the response was received. The `expiration` passed to `storage.put` is computed synchronously at request time, so the two values are based on different clock readings; for large or slow bodies the entry's recorded store time is later than its effective expiry basis, making the Age header computed in `match` too small. Consider capturing a single `now` value before starting the stream and using it for both `stored` and `expiration`.
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}));

await this.storage.put({
Expand Down