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| 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 | 3x 70x 70x 70x 2x 68x 1x 1x 1x 1x 1x 67x 66x 66x 65x | /**
* Tiny in-memory stale-while-revalidate cache for slow server routes.
*
* - First call for a key blocks until the loader resolves.
* - Subsequent calls within TTL return the cached value immediately.
* - After TTL expires, callers receive the stale value and a background
* refresh fires; the next caller after refresh sees the new value.
*
* In-memory only — fine for single-replica ACA Container Apps. If we ever
* scale the UI horizontally we should swap this for a shared cache (Redis
* or NATS-backed). The caller-supplied key should encode anything that
* varies per request (auth role, query params).
*/
interface CacheEntry<T> {
value: T;
freshUntil: number; // epoch ms
refreshing?: Promise<T>;
}
const cache = new Map<string, CacheEntry<unknown>>();
export async function cached<T>(
key: string,
ttlMs: number,
loader: () => Promise<T>,
): Promise<T> {
const now = Date.now();
const entry = cache.get(key) as CacheEntry<T> | undefined;
if (entry && entry.freshUntil > now) {
return entry.value;
}
// Stale-but-present: serve stale, kick off background refresh once.
if (entry) {
Eif (!entry.refreshing) {
entry.refreshing = loader()
.then((v) => {
cache.set(key, { value: v, freshUntil: Date.now() + ttlMs });
return v;
})
.catch((err) => {
// Refresh failed — keep the stale entry so callers don't get a
// stampede of failures. Reset the refreshing flag so a later
// caller can retry.
if (entry) entry.refreshing = undefined;
throw err;
});
}
return entry.value;
}
// Cold cache: must wait for the loader.
const value = await loader();
cache.set(key, { value, freshUntil: Date.now() + ttlMs });
return value;
}
/** Test-only helper to clear the cache between specs. */
export function __resetCacheForTests() {
cache.clear();
}
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