app/lib/search/ask-pacing.mjs

Functions

Imports

It imports no other module of this repo. Imported by app/lib/search/ask-guard.server.ts.

Source

1// Paced rather than a flat cap: a flat cap is a cliff a distributed caller spends in minutes, denying
2// Ask until UTC midnight. Paced, the denial ends when the abuse does. The bill is bounded either way.
3
4/**
5 * Never above dailyLimit, so this only ever refuses earlier than the flat cap would.
6 *
7 * @param {number} dailyLimit total answers permitted in a UTC day
8 * @param {number} burst units available on top of the paced share
9 * @param {Date} now
10 * @returns {number} the ceiling to enforce at this instant
11 */
12export function pacedAllowance(dailyLimit, burst, now) {
13  const SECONDS_PER_DAY = 86400;
14
15  const elapsed =
16    now.getUTCHours() * 3600 + now.getUTCMinutes() * 60 + now.getUTCSeconds();
17
18  // floor, not ceil: at 00:00:00 the allowance must be exactly burst.
19  const paced = Math.floor((dailyLimit * elapsed) / SECONDS_PER_DAY);
20
21  return Math.min(dailyLimit, paced + burst);
22}
23
24/**
25 * The honest Retry-After under pacing; seconds-until-midnight would send readers away for a day.
26 *
27 * @param {number} dailyLimit
28 * @returns {number} seconds, at least 1
29 */
30export function secondsPerPacedUnit(dailyLimit) {
31  if (dailyLimit <= 0) return 86400;
32  return Math.max(1, Math.round(86400 / dailyLimit));
33}