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std/async/retry.ts

Deno standard library
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// Copyright 2018-2024 the Deno authors. All rights reserved. MIT license.// This module is browser compatible.
import { assert } from "../assert/assert.ts";import { exponentialBackoffWithJitter } from "./_util.ts";
/** * Error thrown in {@linkcode retry} once the maximum number of failed attempts * has been reached. */export class RetryError extends Error { /** * Constructs a new {@linkcode RetryError} instance. * * @example * ``` * import { RetryError } from "https://deno.land/std@$STD_VERSION/async/retry.ts"; * * throw new RetryError({ foo: "bar" }, 3); * ``` */ constructor(cause: unknown, attempts: number) { super(`Retrying exceeded the maxAttempts (${attempts}).`); this.name = "RetryError"; this.cause = cause; }}
/** Options for {@linkcode retry}. */export interface RetryOptions { /** * How much to backoff after each retry. * * @default {2} */ multiplier?: number; /** * The maximum milliseconds between attempts. * * @default {60000} */ maxTimeout?: number; /** * The maximum amount of attempts until failure. * * @default {5} */ maxAttempts?: number; /** * The initial and minimum amount of milliseconds between attempts. * * @default {1000} */ minTimeout?: number; /** * Amount of jitter to introduce to the time between attempts. This is `1` * for full jitter by default. * * @default {1} */ jitter?: number;}
const defaultRetryOptions: Required<RetryOptions> = { multiplier: 2, maxTimeout: 60000, maxAttempts: 5, minTimeout: 1000, jitter: 1,};
/** * Calls the given (possibly asynchronous) function up to `maxAttempts` times. * Retries as long as the given function throws. If the attempts are exhausted, * throws a {@linkcode RetryError} with `cause` set to the inner exception. * * The backoff is calculated by multiplying `minTimeout` with `multiplier` to the power of the current attempt counter (starting at 0 up to `maxAttempts - 1`). It is capped at `maxTimeout` however. * How long the actual delay is, depends on `jitter`. * * When `jitter` is the default value of `1`, waits between two attempts for a * randomized amount between 0 and the backoff time. With the default options * the maximal delay will be `15s = 1s + 2s + 4s + 8s`. If all five attempts * are exhausted the mean delay will be `9.5s = ½(4s + 15s)`. * * When `jitter` is `0`, waits the full backoff time. * * @example * ```ts * import { retry } from "https://deno.land/std@$STD_VERSION/async/retry.ts"; * const req = async () => { * // some function that throws sometimes * }; * * // Below resolves to the first non-error result of `req` * const retryPromise = await retry(req, { * multiplier: 2, * maxTimeout: 60000, * maxAttempts: 5, * minTimeout: 100, * jitter: 1, * }); * ``` * * @example * ```ts * import { retry } from "https://deno.land/std@$STD_VERSION/async/retry.ts"; * const req = async () => { * // some function that throws sometimes * }; * * // Make sure we wait at least 1 minute, but at most 2 minutes * const retryPromise = await retry(req, { * multiplier: 2.34, * maxTimeout: 80000, * maxAttempts: 7, * minTimeout: 1000, * jitter: 0.5, * }); * ``` */export async function retry<T>( fn: (() => Promise<T>) | (() => T), opts?: RetryOptions,): Promise<T> { const options: Required<RetryOptions> = { ...defaultRetryOptions, ...opts, };
assert(options.maxTimeout >= 0, "maxTimeout is less than 0"); assert( options.minTimeout <= options.maxTimeout, "minTimeout is greater than maxTimeout", ); assert(options.jitter <= 1, "jitter is greater than 1");
let attempt = 0; while (true) { try { return await fn(); } catch (error) { if (attempt + 1 >= options.maxAttempts) { throw new RetryError(error, options.maxAttempts); }
const timeout = exponentialBackoffWithJitter( options.maxTimeout, options.minTimeout, attempt, options.multiplier, options.jitter, ); await new Promise((r) => setTimeout(r, timeout)); } attempt++; }}