Function rateLimit

source/rate-limit.ts:345–582

(
	passedOptions?: Partial<Options>,
)

 * @public
 */
const rateLimit = (
	passedOptions?: Partial<Options>,
): RateLimitRequestHandler => {
	// Parse the options and add the default values for unspecified options
	const config = parseOptions(passedOptions ?? {})
	const options = getOptionsFromConfig(config)

	// The limiter shouldn't be created in response to a request (usually)
	config.validations.creationStack(config.store)
	// The store instance shouldn't be shared across multiple limiters
	config.validations.unsharedStore(config.store)

	// Call the `init` method on the store, if it exists
	if (typeof config.store.init === 'function') {
		// If store.init() throws or rejects, we'll catch and log it
		// Use .catch() rather than await, because we need to return synchronously
		try {
			const storeInit = config.store.init(options)
			if (storeInit instanceof Promise) {
				storeInit.catch((error) =>
					config.logger.error(
						error,
						'express-rate-limit: async error during store initialization.',
					),
				)
			}
		} catch (error) {
			config.logger.error(
				error,
				'express-rate-limit: error during store initialization.',
			)
		}
	}

	// Then return the actual middleware
	const middleware = handleAsyncErrors(
		async (request: Request, response: Response, next: NextFunction) => {
			// Attach event listeners immediately — before ANY async work — so events
			// that fire during skip/key/increment awaits are never missed.
			const closePromise =
				config.skipFailedRequests &&
				new Promise<void>((resolve) => response.once('close', resolve))

			const finishPromise =
				(config.skipFailedRequests || config.skipSuccessfulRequests) &&
				new Promise<void>((resolve) => response.once('finish', resolve))

			const errorPromise =
				config.skipFailedRequests &&
				new Promise<void>((resolve) => response.once('error', resolve))

			// First check if we should skip the request
			const skip = await config.skip(request, response)
			if (skip) {
				next()
				return
			}