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https://github.com/jhurliman/node-rate-limiter

A generic rate limiter for node.js. Useful for API clients, web crawling, or other tasks that need to be throttled
https://github.com/jhurliman/node-rate-limiter

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A generic rate limiter for node.js. Useful for API clients, web crawling, or other tasks that need to be throttled

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README 

        
# limiter



[![Build Status](https://travis-ci.org/jhurliman/node-rate-limiter.png)](https://travis-ci.org/jhurliman/node-rate-limiter)

[![NPM Downloads](https://img.shields.io/npm/dm/limiter.svg?style=flat)](https://www.npmjs.com/package/limiter)



Provides a generic rate limiter for the web and node.js. Useful for API clients,

web crawling, or other tasks that need to be throttled. Two classes are exposed, 

RateLimiter and TokenBucket. TokenBucket provides a lower level interface to 

rate limiting with a configurable burst rate and drip rate. RateLimiter sits on

top of the token bucket and adds a restriction on the maximum number of tokens

that can be removed each interval to comply with common API restrictions such as

"150 requests per hour maximum".



## Installation



    yarn add limiter



## Usage



A simple example allowing 150 requests per hour:



```javascript

import { RateLimiter } from "limiter";



// Allow 150 requests per hour (the Twitter search limit). Also understands

// 'second', 'minute', 'day', or a number of milliseconds

const limiter = new RateLimiter({ tokensPerInterval: 150, interval: "hour" });



async function sendRequest() {

  // This call will throw if we request more than the maximum number of requests

  // that were set in the constructor

  // remainingRequests tells us how many additional requests could be sent

  // right this moment

  const remainingRequests = await limiter.removeTokens(1);

  callMyRequestSendingFunction(...);

}

```



Another example allowing one message to be sent every 250ms:



```javascript

import { RateLimiter } from "limiter";



const limiter = new RateLimiter({ tokensPerInterval: 1, interval: 250 });



async function sendMessage() {

  const remainingMessages = await limiter.removeTokens(1);

  callMyMessageSendingFunction(...);

}

```



The default behaviour is to wait for the duration of the rate limiting that's

currently in effect before the promise is resolved, but if you pass in

`"fireImmediately": true`, the promise will be resolved immediately with

`remainingRequests` set to -1:



```javascript

import { RateLimiter } from "limiter";



const limiter = new RateLimiter({

  tokensPerInterval: 150,

  interval: "hour",

  fireImmediately: true

});



async function requestHandler(request, response) {

  // Immediately send 429 header to client when rate limiting is in effect

  const remainingRequests = await limiter.removeTokens(1);

  if (remainingRequests < 0) {

    response.writeHead(429, {'Content-Type': 'text/plain;charset=UTF-8'});

    response.end('429 Too Many Requests - your IP is being rate limited');

  } else {

    callMyMessageSendingFunction(...);

  }

}

```



A synchronous method, tryRemoveTokens(), is available in both RateLimiter and

TokenBucket. This will return immediately with a boolean value indicating if the

token removal was successful.



```javascript

import { RateLimiter } from "limiter";



const limiter = new RateLimiter({ tokensPerInterval: 10, interval: "second" });



if (limiter.tryRemoveTokens(5))

  console.log('Tokens removed');

else

  console.log('No tokens removed');

```



To get the number of remaining tokens **outside** the `removeTokens` promise,

simply use the `getTokensRemaining` method.



```javascript

import { RateLimiter } from "limiter";



const limiter = new RateLimiter({ tokensPerInterval: 1, interval: 250 });



// Prints 1 since we did not remove a token and our number of tokens per

// interval is 1

console.log(limiter.getTokensRemaining());

```



Using the token bucket directly to throttle at the byte level:



```javascript

import { TokenBucket } from "limiter";



const BURST_RATE = 1024 * 1024 * 150; // 150KB/sec burst rate

const FILL_RATE = 1024 * 1024 * 50; // 50KB/sec sustained rate



// We could also pass a parent token bucket in to create a hierarchical token

// bucket

// bucketSize, tokensPerInterval, interval

const bucket = new TokenBucket({

  bucketSize: BURST_RATE,

  tokensPerInterval: FILL_RATE,

  interval: "second"

});



async function handleData(myData) {

  await bucket.removeTokens(myData.byteLength);

  sendMyData(myData);

}

```



## Additional Notes



Both the token bucket and rate limiter should be used with a message queue or 

some way of preventing multiple simultaneous calls to removeTokens(). 

Otherwise, earlier messages may get held up for long periods of time if more 

recent messages are continually draining the token bucket. This can lead to 

out of order messages or the appearance of "lost" messages under heavy load.



## License



MIT License