Merge branch 'exponential-backoff' into sse-branc
This commit is contained in:
22
source/errors.ts
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22
source/errors.ts
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/**
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* Error thrown when the maximum number of retries is hit in an exponential backoff
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*/
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export class ExponentialBackoffMaxRetriesHitError extends Error {
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constructor(errors: Array<Error>) {
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super('Exponential backoff: Max retries hit', { cause: errors });
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this.name = 'ExponentialBackoffMaxRetriesHitError';
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}
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}
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/**
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* Error thrown when the exponential backoff retries are stopped
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*/
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export class ExponentialBackoffStoppedRetriesError extends Error {
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constructor(reason: unknown) {
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// Convert the reason to an error if it is not an error
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const reasonError = reason instanceof Error ? reason : new Error(`${reason}`);
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super(`Exponential backoff was aborted: "${reasonError.message}"`, { cause: reasonError });
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this.name = 'ExponentialBackoffStoppedRetriesError';
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}
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}
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275
source/exponential-backoff.ts
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source/exponential-backoff.ts
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import { ExponentialBackoffStoppedRetriesError, ExponentialBackoffMaxRetriesHitError } from './errors.ts';
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/**
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* Exponential backoff is a technique used to retry a function after a delay.
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*
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* The delay increases exponentially with each attempt, up to a maximum delay.
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*
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* The jitter is a random amount of time subtracted from the delay to prevent thundering herd problems.
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*
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* The growth rate is the factor by which the delay increases with each attempt.
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*/
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export class ExponentialBackoff {
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readonly #options: ExponentialBackoffOptions;
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/**
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* Creates a new exponential-backoff instance.
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*
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* Unspecified options use the defaults listed below.
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*
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* @param options - Exponential-backoff configuration overrides.
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* @param options.maxDelay - Maximum delay between retries. Default: `10_000` ms.
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* @param options.maxAttempts - Maximum number of attempts; `0` retries indefinitely. Default: `10`.
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* @param options.baseDelay - Delay used as the basis for the first retry. Default: `1_000` ms.
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* @param options.growthRate - Multiplier applied to the delay after each attempt. Default: `2`.
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* @param options.jitter - Maximum proportional reduction subtracted from each delay (0–1). Default: `0.1`.
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*/
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constructor(options: Partial<ExponentialBackoffOptions> = {}) {
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this.#options = {
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maxDelay: 10_000,
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maxAttempts: 10,
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baseDelay: 1_000,
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growthRate: 2,
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jitter: 0.1,
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...options,
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};
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ExponentialBackoff.validateOptions(this.#options);
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}
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/**
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* Create a new ExponentialBackoff instance
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*
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* @param config - The configuration for the exponential backoff
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* @returns The ExponentialBackoff instance
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*/
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static from(config?: Partial<ExponentialBackoffOptions>): ExponentialBackoff {
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const backoff = new ExponentialBackoff(config);
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return backoff;
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}
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/**
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* Run the function with exponential backoff
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*
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* @param taskFn - The function to run
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* @param onError - The callback to call when an error occurs
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* @param options - The configuration for the exponential backoff
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*
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* @throws An {@link ExponentialBackoffMaxRetriesHitError} with all the errors that were thrown by the task function
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* @throws An {@link ExponentialBackoffStoppedRetriesError} if the abort signal is activated
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*
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* @returns The result of the function
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*/
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static run<T>(
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taskFn: (callbackParameters: ExponentialBackoffCallbackParameters) => Promise<T>,
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onError = (_error: Error): void => {},
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options?: Partial<ExponentialBackoffOptions>,
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): Promise<T> {
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const backoff = ExponentialBackoff.from(options);
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return backoff.run(taskFn, onError);
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}
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/**
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* Calculate the delay before we should attempt to retry
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*
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* @param options - The configuration for the exponential backoff
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* @param attempt - The current attempt number
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* @returns The time in milliseconds before another attempt should be made
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*/
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public static calculateDelay(options: ExponentialBackoffOptions, attempt: number): number {
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// Get the power of the growth rate
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const power = options.growthRate ** attempt;
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// Get the delay before jitter or limit
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const rawDelay = options.baseDelay * power;
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// Cap the delay to the maximum. Do this before the jitter so jitter does not become larger than delay
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const cappedDelay = Math.min(rawDelay, options.maxDelay);
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// Get a random number for the amount to "jitter" the delay by
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const jitterAmount = Math.random();
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// Calculate the jitter
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const jitter = jitterAmount * options.jitter * cappedDelay;
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// Subtract the jitter from the delay
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return cappedDelay - jitter;
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}
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/**
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* Validate the options for the exponential backoff
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*
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* @param options - The options to validate
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*
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* @throws An error if the options are invalid
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*/
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public static validateOptions(options: ExponentialBackoffOptions): void {
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// Validate the max delay is a finite number not less than 0
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if (!Number.isFinite(options.maxDelay)) {
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throw new Error('maxDelay must be a finite number');
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}
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if (options.maxDelay < 0) {
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throw new Error('maxDelay must be not less than 0');
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}
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// Validate the max attempts is a finite number not less than 0
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if (!Number.isFinite(options.maxAttempts)) {
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throw new Error('maxAttempts must be a finite number');
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}
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if (options.maxAttempts < 0) {
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throw new Error('maxAttempts must be not less than 0');
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}
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// Validate the base delay is a finite number not less than 0
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if (!Number.isFinite(options.baseDelay)) {
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throw new Error('baseDelay must be a finite number');
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}
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if (options.baseDelay < 0) {
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throw new Error('baseDelay must be not less than 0');
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}
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// Validate the growth rate is a finite number not less than 0
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if (!Number.isFinite(options.growthRate)) {
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throw new Error('growthRate must be a finite number');
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}
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if (options.growthRate < 0) {
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throw new Error('growthRate must be not less than 0');
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}
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// Validate the jitter is a finite number not less than 0 or greater than 1
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if (!Number.isFinite(options.jitter)) {
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throw new Error('jitter must be a finite number');
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}
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if (options.jitter < 0 || options.jitter > 1) {
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throw new Error('jitter must be not less than 0 or greater than 1');
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}
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}
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/**
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* Run the function with exponential backoff
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*
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* If the function fails but we have not hit the max attempts, the error will be passed to the onError callback
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* and the function will be retried with an exponential delay
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*
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* If the function fails and we have hit the max attempts, an ExponentialBackoffMaxRetriesHitError will be thrown with all the errors that were thrown by the task function
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*
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* @param taskFn - The function to run
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* @param onError - The callback to call when an error occurs
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*
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* @throws An {@link ExponentialBackoffMaxRetriesHitError} with all the errors that were thrown by the task function
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* @throws An {@link ExponentialBackoffStoppedRetriesError} if the abort signal is activated
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*
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* @returns The result of the function
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*/
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async run<T>(
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taskFn: (callbackParameters: ExponentialBackoffCallbackParameters) => Promise<T>,
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onError = (_error: Error): void => {},
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): Promise<T> {
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// Initialize an abort signal to allow the task function to be aborted
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const abortController = new AbortController();
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const stopRetries = abortController.abort.bind(abortController);
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// Initialize an empty array to store the errors
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const errors: Error[] = [];
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// Initialize the attempt counter
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let attempt = 0;
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// If the max attempts is 0, we should continue indefinitely.
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const unlimitedAttempts = this.#options.maxAttempts === 0;
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// Loop until we succeed, hit the max attempts, or the abort signal is activated
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while (true) {
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try {
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// Await the promise before returning so its execution context remains in the try-catch
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// If we didn't await, this `run` function would successfully return and any errors would not be caught here.
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return await taskFn({ stopRetries });
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} catch (error) {
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// Store the error in case we fail every attempt
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const errorInstance = error instanceof Error ? error : new Error(`${error}`);
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onError(errorInstance);
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// If we have unlimited attempts, don't append this to the errors array to prevent a memory leak.
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if (!unlimitedAttempts) {
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errors.push(errorInstance);
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}
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}
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// Calculate the count for next attempt. Do this now so we can exit before waiting and before running the next attempt.
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const nextAttemptCount = attempt + 1;
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const nextAttemptExceedsMaxAttempts = nextAttemptCount >= this.#options.maxAttempts;
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// If the next attempt exceeds the max attempts, break out of the loop
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if (!unlimitedAttempts && nextAttemptExceedsMaxAttempts) {
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break;
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}
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// Check if the abort signal has been aborted
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if (abortController.signal.aborted) {
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// Throw an error if the abort signal has been aborted
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throw new ExponentialBackoffStoppedRetriesError(abortController.signal.reason);
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}
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// Wait before going to the next attempt
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const delay = ExponentialBackoff.calculateDelay(this.#options, attempt);
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await new Promise((resolve) => setTimeout(resolve, delay));
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attempt++;
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}
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// We completed the loop without ever succeeding. Throw an ExponentialBackoffMaxRetriesHitError with all the errors we got
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throw new ExponentialBackoffMaxRetriesHitError(errors);
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}
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}
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export type ExponentialBackoffOptions = {
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/**
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* The maximum delay between attempts in milliseconds
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*/
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maxDelay: number;
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/**
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* The maximum number of attempts. Passing 0 will result in infinite attempts.
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*/
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maxAttempts: number;
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/**
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* The base delay between attempts in milliseconds
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*/
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baseDelay: number;
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/**
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* The growth rate of the delay
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*/
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growthRate: number;
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/**
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* The jitter of the delay as a percentage of growthRate. The jitter is subtracted from the delay.
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*/
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jitter: number;
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};
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/**
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* The function to call to stop the retries.
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* This mimics the AbortSignal.abort function by taking in a reason for stopping
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*
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* @param reason - The reason for stopping the retries.
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*/
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export type ExponentialBackoffStopRetriesFunction = (reason: unknown) => void;
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/**
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* The parameters for the task function
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*
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* @param stopRetries - The function to call to stop the retries
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*/
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export type ExponentialBackoffCallbackParameters = {
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stopRetries: ExponentialBackoffStopRetriesFunction;
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};
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@@ -1,3 +1,4 @@
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export * from './exponential-backoff.ts';
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export * from './extended-json.ts';
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export * from './script.ts';
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export * from './sse-session/index.ts';
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