urltomarkdown/node_modules/express-rate-limit

Express Rate Limit

Basic rate-limiting middleware for Express. Use to limit repeated requests to public APIs and/or endpoints such as password reset. Plays nice with express-slow-down.

Alternate Rate Limiters

This module does not share state with other processes/servers by default. If you need a more robust solution, I recommend using an external store. See the stores section below for a list of external stores.

This module was designed to only handle the basics and didn't even support external stores initially. These other options all are excellent pieces of software and may be more appropriate for some situations:

• rate-limiter-flexible
• express-brute
• rate-limiter

Installation

From the npm registry:

# Using npm
> npm install express-rate-limit
# Using yarn or pnpm
> yarn/pnpm add express-rate-limit

From Github Releases:

# Using npm
> npm install https://github.com/nfriedly/express-rate-limit/releases/download/v{version}/express-rate-limit.tgz
# Using yarn or pnpm
> yarn/pnpm add https://github.com/nfriedly/express-rate-limit/releases/download/v{version}/express-rate-limit.tgz

Replace {version} with the version of the package that you want to your, e.g.: 6.0.0.

Usage

Importing

This library is provided in ESM as well as CJS forms, and works with both Javascript and Typescript projects.

This package requires you to use Node 14 or above.

Import it in a CommonJS project (type: commonjs or no type field in package.json) as follows:

const rateLimit = require('express-rate-limit')

Import it in a ESM project (type: module in package.json) as follows:

import rateLimit from 'express-rate-limit'

Examples

To use it in an API-only server where the rate-limiter should be applied to all requests:

import rateLimit from 'express-rate-limit'

const limiter = rateLimit({
	windowMs: 15 * 60 * 1000, // 15 minutes
	max: 100, // Limit each IP to 100 requests per `window` (here, per 15 minutes)
	standardHeaders: true, // Return rate limit info in the `RateLimit-*` headers
	legacyHeaders: false, // Disable the `X-RateLimit-*` headers
})

// Apply the rate limiting middleware to all requests
app.use(limiter)

To use it in a 'regular' web server (e.g. anything that uses express.static()), where the rate-limiter should only apply to certain requests:

import rateLimit from 'express-rate-limit'

const apiLimiter = rateLimit({
	windowMs: 15 * 60 * 1000, // 15 minutes
	max: 100, // Limit each IP to 100 requests per `window` (here, per 15 minutes)
	standardHeaders: true, // Return rate limit info in the `RateLimit-*` headers
	legacyHeaders: false, // Disable the `X-RateLimit-*` headers
})

// Apply the rate limiting middleware to API calls only
app.use('/api', apiLimiter)

To create multiple instances to apply different rules to different endpoints:

import rateLimit from 'express-rate-limit'

const apiLimiter = rateLimit({
	windowMs: 15 * 60 * 1000, // 15 minutes
	max: 100, // Limit each IP to 100 requests per `window` (here, per 15 minutes)
	standardHeaders: true, // Return rate limit info in the `RateLimit-*` headers
	legacyHeaders: false, // Disable the `X-RateLimit-*` headers
})

app.use('/api/', apiLimiter)

const createAccountLimiter = rateLimit({
	windowMs: 60 * 60 * 1000, // 1 hour
	max: 5, // Limit each IP to 5 create account requests per `window` (here, per hour)
	message:
		'Too many accounts created from this IP, please try again after an hour',
	standardHeaders: true, // Return rate limit info in the `RateLimit-*` headers
	legacyHeaders: false, // Disable the `X-RateLimit-*` headers
})

app.post('/create-account', createAccountLimiter, (request, response) => {
	//...
})

To use a custom store:

import rateLimit from 'express-rate-limit'
import MemoryStore from 'express-rate-limit/memory-store.js'

const apiLimiter = rateLimit({
	windowMs: 15 * 60 * 1000, // 15 minutes
	max: 100, // Limit each IP to 100 requests per `window` (here, per 15 minutes)
	standardHeaders: true, // Return rate limit info in the `RateLimit-*` headers
	store: new MemoryStore(),
})

// Apply the rate limiting middleware to API calls only
app.use('/api', apiLimiter)

Note: most stores will require additional configuration, such as custom prefixes, when using multiple instances. The default built-in memory store is an exception to this rule.

Troubleshooting Proxy Issues

If you are behind a proxy/load balancer (usually the case with most hosting services, e.g. Heroku, Bluemix, AWS ELB, Nginx, Cloudflare, Akamai, Fastly, Firebase Hosting, Rackspace LB, Riverbed Stingray, etc.), the IP address of the request might be the IP of the load balancer/reverse proxy (making the rate limiter effectively a global one and blocking all requests once the limit is reached) or undefined. To solve this issue, add the following line to your code (right after you create the express application):

app.set('trust proxy', numberOfProxies)

Where numberOfProxies is the number of proxies between the user and the server. To find the correct number, create a test endpoint that returns the client IP:

app.set('trust proxy', 1)
app.get('/ip', (request, response) => response.send(request.ip))

Go to /ip and see the IP address returned in the response. If it matches your IP address (which you can get by going to http://ip.nfriedly.com/ or https://api.ipify.org/), then the number of proxies is correct and the rate limiter should now work correctly. If not, then keep increasing the number until it does.

For more information about the trust proxy setting, take a look at the official Express documentation.

Request API

A request.rateLimit property is added to all requests with the limit, current, and remaining number of requests and, if the store provides it, a resetTime Date object. These may be used in your application code to take additional actions or inform the user of their status.

The property name can be configured with the configuration option requestPropertyName

Configuration options

windowMs

Time frame for which requests are checked/remembered. Also used in the Retry-After header when the limit is reached.

Note: with non-default stores, you may need to configure this value twice, once here and once on the store. In some cases the units also differ (e.g. seconds vs miliseconds)

Defaults to 60000 ms (= 1 minute).

max

Max number of connections during windowMs milliseconds before sending a 429 response.

May be a number, or a function that returns a number or a promise. If max is a function, it will be called with request and response params.

Defaults to 5. Set to 0 to disable.

Example of using a function:

import rateLimit from 'express-rate-limit'

const isPremium = (request) => {
	// ...
}

const limiter = rateLimit({
	// `max` could also be an async function or return a promise
	max: (request, response) => {
		if (isPremium(request)) return 10
		else return 5
	},
	// ...
})

// Apply the rate limiting middleware to all requests
app.use(limiter)

message

Error message sent to user when max is exceeded.

May be a string, JSON object, or any other value that Express's response.send method supports.

Defaults to 'Too many requests, please try again later.'

statusCode

HTTP status code returned when max is exceeded.

Defaults to 429.

legacyHeaders

Enable headers for request limit (X-RateLimit-Limit) and current usage (X-RateLimit-Remaining) on all responses and time to wait before retrying (Retry-After) when max is exceeded.

Defaults to true.

Renamed in 6.x from headers to legacyHeaders.

standardHeaders

Enable headers conforming to the ratelimit standardization draft adopted by the IETF: RateLimit-Limit, RateLimit-Remaining, and, if the store supports it, RateLimit-Reset. May be used in conjunction with, or instead of the legacyHeaders option.

This setting also enables the Retry-After header when max is exceeded.

Defaults to false (for backward compatibility), but recommended to use.

Renamed in 6.x from draft_polli_ratelimit_headers to standardHeaders.

keyGenerator

Function used to generate keys.

Defaults to request.ip, similar to this:

const keyGenerator = (request /*, response*/) => request.ip

handler

The function to handle requests once the max limit is exceeded. It receives the request and the response objects. The next param is available if you need to pass to the next middleware/route. Finally, the options param has all of the options that originally passed in when creating the current limiter and the default values for other options.

The request.rateLimit object has limit, current, and remaining number of requests and, if the store provides it, a resetTime Date object.

Defaults to:

const handler = (request, response, next, options) => {
	response.status(options.statusCode).send(options.message)
}

requestWasSuccessful

Function that is called when skipFailedRequests and/or skipSuccessfulRequests are set to true. May be overridden if, for example, a service sends out a 200 status code on errors.

Defaults to

const requestWasSuccessful = (request, response) => response.statusCode < 400

skipFailedRequests

When set to true, failed requests won't be counted. Request considered failed when:

• response status >= 400
• requests that were cancelled before last chunk of data was sent (response close event triggered)
• response error event was triggered by response

(Technically they are counted and then un-counted, so a large number of slow requests all at once could still trigger a rate-limit. This may be fixed in a future release.)

Defaults to false.

skipSuccessfulRequests

When set to true successful requests (response status < 400) won't be counted. (Technically they are counted and then un-counted, so a large number of slow requests all at once could still trigger a rate-limit. This may be fixed in a future release.)

Defaults to false.

skip

Function used to skip (whitelist) requests. Returning true, or a promise that resolves with true, from the function will skip limiting for that request.

Defaults to always false (count all requests):

const skip = (/*request, response*/) => false

requestPropertyName

The name of the property that contains the rate limit information to add to the request object.

Defaults to rateLimit.

store

The storage to use when persisting rate limit attempts.

By default, the memory store is used.

Available data stores are:

• memory-store: (default) Simple in-memory option. Does not share state when app has multiple processes or servers.
• rate-limit-redis: A Redis-backed store, more suitable for large or demanding deployments.
• rate-limit-memcached: A Memcached-backed store.
• rate-limit-mongo: A MongoDB-backed store.
• precise-memory-rate-limit - A memory store similar to the built-in one, except that it stores a distinct timestamp for each IP rather than bucketing them together.

You may also create your own store. It must implement the Store interface as follows:

import rateLimit, {
	Store,
	Options,
	IncrementResponse,
} from 'express-rate-limit'

/**
 * A {@link Store} that stores the hit count for each client.
 *
 * @public
 */
class SomeStore implements Store {
	/**
	 * Some store-specific parameter.
	 */
	customParam!: string
	/**
	 * The duration of time before which all hit counts are reset (in milliseconds).
	 */
	windowMs!: number

	/**
	 * @constructor for {@link SomeStore}. Only required if the user needs to pass
	 * some store specific parameters. For example, in a Mongo Store, the user will
	 * need to pass the URI, username and password for the Mongo database.
	 *
	 * @param customParam {string} - Some store-specific parameter.
	 */
	constructor(customParam: string) {
		this.customParam = customParam
	}

	/**
	 * Method that actually initializes the store. Must be synchronous.
	 *
	 * @param options {Options} - The options used to setup the middleware.
	 *
	 * @public
	 */
	init(options: Options): void {
		this.windowMs = options.windowMs

		// ...
	}

	/**
	 * Method to increment a client's hit counter.
	 *
	 * @param key {string} - The identifier for a client
	 *
	 * @returns {IncrementResponse} - The number of hits and reset time for that client
	 *
	 * @public
	 */
	async increment(key: string): Promise<IncrementResponse> {
		// ...

		return {
			totalHits,
			resetTime,
		}
	}

	/**
	 * Method to decrement a client's hit counter.
	 *
	 * @param key {string} - The identifier for a client
	 *
	 * @public
	 */
	async decrement(key: string): Promise<void> {
		// ...
	}

	/**
	 * Method to reset a client's hit counter.
	 *
	 * @param key {string} - The identifier for a client
	 *
	 * @public
	 */
	async resetKey(key: string): Promise<void> {
		// ...
	}

	/**
	 * Method to reset everyone's hit counter.
	 *
	 * @public
	 */
	async resetAll(): Promise<void> {
		// ...
	}
}

export default SomeStore

Instance API

resetKey(key)

Resets the rate limiting for a given key. An example use case is to allow users to complete a captcha or whatever to reset their rate limit, then call this method.

Issues and Contributing

If you encounter a bug or want to see something added/changed, please go ahead and open an issue! If you need help with something, feel free to start a discussion!

If you wish to contribute to the library, thanks! First, please read the contributing guide. Then you can pick up any issue and fix/implement it!

License

MIT © Nathan Friedly