64 lines
1.8 KiB
TypeScript
64 lines
1.8 KiB
TypeScript
// Copyright 2021 Signal Messenger, LLC
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// SPDX-License-Identifier: AGPL-3.0-only
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import * as durations from './durations';
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const BACKOFF_FACTOR = 1.9;
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const MAX_BACKOFF = 15 * durations.MINUTE;
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const FIRST_BACKOFF = 100 * BACKOFF_FACTOR;
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/**
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* For a given attempt, how long should we sleep (in milliseconds)?
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*
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* The attempt should be a positive integer, and it is 1-indexed. The first attempt is 1,
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* the second is 2, and so on.
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*
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* This is modified from [iOS's codebase][0].
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*
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* [0]: https://github.com/signalapp/Signal-iOS/blob/6069741602421744edfb59923d2fb3a66b1b23c1/SignalServiceKit/src/Util/OWSOperation.swift
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*/
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export type ExponentialBackoffOptionsType = {
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maxBackoffTime: number;
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multiplier: number;
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firstBackoffTime: number;
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};
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export function exponentialBackoffSleepTime(
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attempt: number,
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options: ExponentialBackoffOptionsType = {
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maxBackoffTime: MAX_BACKOFF,
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multiplier: BACKOFF_FACTOR,
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firstBackoffTime: FIRST_BACKOFF,
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}
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): number {
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if (attempt === 1) {
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return 0;
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}
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return Math.min(
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options.maxBackoffTime,
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(options.firstBackoffTime / options.multiplier) *
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options.multiplier ** (attempt - 1)
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);
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}
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/**
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* If I want to retry for X milliseconds, how many attempts is that, roughly? For example,
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* 24 hours (86,400,000 milliseconds) is 111 attempts.
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*
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* `desiredDurationMs` should be at least 1.
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*/
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export function exponentialBackoffMaxAttempts(
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desiredDurationMs: number,
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options?: ExponentialBackoffOptionsType
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): number {
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let attempts = 0;
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let total = 0;
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// There's probably some algebra we could do here instead of this loop, but this is
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// fast even for giant numbers, and is typically called just once at startup.
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do {
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attempts += 1;
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total += exponentialBackoffSleepTime(attempts, options);
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} while (total < desiredDurationMs);
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return attempts;
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}
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