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fix(overpass): reserve singleflight before disk cache reads

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Said committed 2026-10-20 01:12:36 +01:00
1 parent 84d96971df
commit 5980a08533
4 files changed
+96 -71
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server/providers/overpass.js
+34 -59
View File
@@ -164,6 +164,30 @@ function overpassProxy({ routing = {} } = {}) {
readDisk: () =>
readOverpassDisk(cacheKey, overpassDiskTtlMs(cacheKey)),
allowUpstream: () => _overpassRateLimiter(clientKey(req)),
loadUpstream: async () => {
if (_overpassConcurrent >= OVERPASS_MAX_CONCURRENT)
return {
status: 503,
contentType: 'application/json',
retryAfterMs: 2000,
body: JSON.stringify({
error: 'Overpass proxy busy — try again shortly',
}),
};
_overpassConcurrent++;
try {
const payload = await fetchOverpassPayload(safeBody);
if (overpassPayloadIsData(payload)) {
const entry = { ...payload, cachedAt: Date.now() };
_overpassCache.set(cacheKey, entry);
trimOverpassCache();
writeOverpassDisk(cacheKey, entry);
}
return payload;
} finally {
_overpassConcurrent--;
}
},
});
if (preflight.source === 'RATE_LIMITED') {
res.writeHead(429, {
@@ -173,71 +197,22 @@ function overpassProxy({ routing = {} } = {}) {
res.end(JSON.stringify({ error: 'Rate limit exceeded' }));
return;
}
if (preflight.source !== 'UPSTREAM') {
// A coalesced caller sees the same failure as the original request
// and must get the same last-good fallback, not the raw refusal.
if (!overpassPayloadIsData(preflight.payload)) {
const stale = await readStaleOverpass(cacheKey);
if (stale) {
sendOverpassResponse(res, stale, 'STALE');
return;
}
}
if (preflight.source === 'DISK') {
_overpassCache.set(cacheKey, preflight.payload);
trimOverpassCache();
}
sendOverpassResponse(res, preflight.payload, preflight.source);
return;
}
// From here onward the request is genuinely upstream-bound and has
// consumed one local limiter slot. Cache and dedupe hits above do not.
if (_overpassConcurrent >= OVERPASS_MAX_CONCURRENT) {
res.writeHead(503, {
'Content-Type': 'application/json',
'Retry-After': '2',
});
res.end(
JSON.stringify({
error: 'Overpass proxy busy — try again shortly',
}),
);
return;
}
_overpassConcurrent += 1;
const requestPromise = fetchOverpassPayload(safeBody)
.then((payload) => {
// Only a 2xx is data. `< 500` cached every 4xx, so one mirror's
// refusal was written to memory AND disk — and boundary-class
// queries hold a month-long TTL, so a single 406 outlived the
// outage that caused it.
if (overpassPayloadIsData(payload)) {
const entry = { ...payload, cachedAt: Date.now() };
_overpassCache.set(cacheKey, entry);
trimOverpassCache();
writeOverpassDisk(cacheKey, entry);
}
return payload;
})
.finally(() => {
_overpassConcurrent -= 1;
_overpassInFlight.delete(cacheKey);
});
_overpassInFlight.set(cacheKey, requestPromise);
const payload = await requestPromise;
// Degraded upstream (rate-limited on every mirror / 5xx / runtime
// error): last-good roads beat an empty layer — serve stale from
// memory or disk at ANY age before surfacing the failure.
if (!overpassPayloadIsData(payload)) {
if (!overpassPayloadIsData(preflight.payload)) {
const stale = await readStaleOverpass(cacheKey);
if (stale) {
sendOverpassResponse(res, stale, 'STALE');
return;
}
}
sendOverpassResponse(res, payload, 'MISS');
if (preflight.source === 'DISK') {
_overpassCache.set(cacheKey, preflight.payload);
trimOverpassCache();
}
sendOverpassResponse(
res,
preflight.payload,
preflight.source === 'UPSTREAM' ? 'MISS' : preflight.source,
);
} catch (e) {
// Every mirror threw (network-level). Same serve-stale rule.
const stale = cacheKey ? await readStaleOverpass(cacheKey) : null;