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feat: Implement caching and rate limiting for API requests

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This commit is contained in:
Zakhar Timoshenko
2026-10-18 17:20:29 +03:00
parent 3dc6cc4e9e
commit 6b68cec34a
12 changed files with 282 additions and 27 deletions
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42
server/source.js
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@@ -21,8 +21,22 @@ const arr = (value) => (value ? (Array.isArray(value) ? value : [value]) : []);
const DISCOVERY_TTL = 15 * 60 * 1000,
CATALOG_TTL = 15 * 60 * 1000,
CALENDAR_TTL = 6 * 60 * 60 * 1000;
// A forced refresh (?refresh=1, the PWA's "Обновить") reaches the university at most this often;
// sooner, the copy just read is the answer. Anyone can send the request, and one catalog crawl
// is up to 180 listings of the university's Nextcloud.
export const MIN_REFRESH = 2 * 60 * 1000;
const CALENDAR_MIN_REFRESH = 10 * 60 * 1000;
/** Milliseconds since an ISO time; Infinity for a missing or broken one. */
const ageOf = (iso) => {
const age = Date.now() - new Date(iso).getTime();
return Number.isFinite(age) ? age : Infinity;
};
let catalogue, pending, calendar, calendarPending, sources, sourcesPending;
const status = { catalogError: null, calendarError: null };
// When the university last failed to answer: background refreshes back off for MIN_REFRESH,
// so a down source is not crawled again on every request.
const failedAt = { catalog: 0, calendar: 0 };
const backingOff = (what) => Date.now() - failedAt[what] < MIN_REFRESH;
export async function request(path, method = "GET") {
// Only the university share is reachable; listings and catalog entries supply the paths.
@@ -232,15 +246,17 @@ export async function getCatalog(refresh = false) {
const y = academicStartYear(todayIso());
return `${y}–${y + 1}`;
})();
const age = catalogue ? ageOf(catalogue.updatedAt) : Infinity;
// A cached catalog of last year is refreshed as soon as the new year begins.
const fresh =
catalogue &&
Date.now() - new Date(catalogue.updatedAt).getTime() < CATALOG_TTL &&
(catalogue.year === expected || catalogue.currentYear === false);
if (!refresh && fresh) return catalogue;
const thisYear =
catalogue && (catalogue.year === expected || catalogue.currentYear === false);
const forced = refresh && age >= MIN_REFRESH;
if (thisYear && age < CATALOG_TTL && !forced) return catalogue;
if (thisYear && !forced && backingOff("catalog")) return catalogue;
if (!pending)
pending = crawl()
.catch((error) => {
failedAt.catalog = Date.now();
status.catalogError = error.message;
if (catalogue)
return {
@@ -253,6 +269,9 @@ export async function getCatalog(refresh = false) {
.finally(() => {
pending = null;
});
// Stale-while-revalidate: an outdated copy of this year answers at once and the crawl runs
// behind it. Only a first start, a new academic year or a forced refresh wait for the crawl.
if (thisYear && !forced) return catalogue;
return pending;
}
export async function documentFor(id) {
@@ -324,15 +343,14 @@ async function readCalendarCache() {
}
export async function getCalendar(refresh = false) {
await readCalendarCache();
if (
!refresh &&
calendar &&
Date.now() - new Date(calendar.updatedAt).getTime() < CALENDAR_TTL
)
return calendar;
const age = calendar ? ageOf(calendar.updatedAt) : Infinity;
const forced = refresh && age >= CALENDAR_MIN_REFRESH;
if (calendar && age < CALENDAR_TTL && !forced) return calendar;
if (calendar && !forced && backingOff("calendar")) return calendar;
if (!calendarPending)
calendarPending = loadCalendar()
.catch((error) => {
failedAt.calendar = Date.now();
status.calendarError = error.message;
if (calendar) return { ...calendar, stale: true, error: error.message };
throw error;
@@ -340,6 +358,8 @@ export async function getCalendar(refresh = false) {
.finally(() => {
calendarPending = null;
});
// As with the catalog, a saved week table answers while the new one loads.
if (calendar && !forced) return calendar;
return calendarPending;
}