##API Rate Limiter This is an npm module that will allow you to instantiate a RateLimiter object in your node.js or io.js server. The object exposes the public methods documented below and is designed to be used for rate limiting incoming or outgoing API calls. Rate limiter is designed to be fast and scalable, so it uses a redis database to keep track of per-user and global requests.

N.B. Rate_Limiter is not yet production-ready. If you would like to help make it production-ready, submit a pull request!

###Installation and Dependencies Place the APIRateLimiter folder into your project folder, or use npm:

$ npm install --save rate_limiter

Next, install and run redis on your server. Quickstart Guide

Once redis is installed, you can run it with:

$ redis-server

It is fastest to use a redis instance running locally to your server. If you do this, and do not change redis default port, the example redisPORT and redisIP arguments given below to the RateLimiter() constructor will be the redis defaults.

##Usage

###Incoming/outgoing

APIRateLimiter is capable of tracking both incoming or outgoing requests. In fact, it can be used to limit the rate of anything if you're clever.

###Require rateLimiter and the RateLimiter Constructor: In your server or your API client, require rateLimiter.js and instantiate a rateLimiter:

var RL = require('rate_limiter');

Constructor:

####RateLimiter(redisPORT:<integer>, redisIP:<string>, redisOptions:<object>)

Instantiate a new rateLimiter object.

var rateLimiter = new RL.RateLimiter(6379, "localhost", {});

Any argument can be null to accept redis defaults. To accept all redis defaults (Port: 6379, ip: localhost, no options), use constructor with no arguments.

#####redisOptions

The third parameter of the RateLimiter constructor takes a javascript object with the following notable property:

• "auth_pass" : <string> If your redis database is secured, place the password here.

Other available properties can be found here: https://www.npmjs.com/package/redis in the API documentation of the npm redis module. They should mirror the options available in the redis API for server and connection options.

###rateLimiter Object Public Methods

####rateLimiter.authorizeRequest(APIname:<string>, user:<string>, callback:<function(error<error>, isAuthorized<boolean>)>)

This function takes the name of an API being limited, a string associated with the user making the request. (This will likely be an IP, or an API account key), and finally, a callback.

If you are only limiting global calls, passing null in the place of a user string for the second argument is fine.

The third parameter takes a callback function which will be called asynchronously once the rate limiter has cleared or rejected a request, or if an error has occured. The first argument to the callback will be the error or null; The second argument will be a boolean: true if the request would not exceed the set limit, or false if it would. You should pass a function that will handle either sending, queueing, or simply discarding the request once it is approved or denied.

Depending on how you use rate_limiter, you may find it necessary to pass a closure to maintain access to the request object in question. This will be fixed soon with express.js middleware handling, or perhaps sooner, an optional fourth argument to authorizeRequest() that will accept a raw request object which it will pass untouched to the callback.

####rateLimiter.setPerUserLimit(APIname:<string>, limit:<integer>, timeWindow:<integer>)

To initiate limit tracking for an API, use this function on its own or along with rateLimiter.setGlobalLimit(). A new API tracker will be created if APIname hasn't been added before.

timeWindow should be in milliseconds.

limit should be an integer. such that the system will allow: limit requests per user per timeWIndow

####rateLimiter.setGlobalLimit(APIname:<string>, limit:<integer>, timeWindow:<integer>)

To initiate limit tracking for an API, use this function on its own or along with rateLimiter.setPerUserLimit().

timeWindow should be in milliseconds.

limit should be an integer, such that the system will allow: limit global requests per timeWindow

##Testing

To run tests, be sure your redis server is running($ redis-server), then in another shell, from the rate_limiter project directory:

$ npm test

For the purposes of testing, and example, a small test API server and a test API harvester can be found at test/examples/. This server serves as an example for integrating a rateLimiter object into your node server for limitting incoming requests. The harvester uses a very similar pattern to rate limit outgoing requests--the same limiter object works either way.

The server and harvester work in concert to demonstrate the rateLimiter. To run them, run the following three commands in order, in three separate shells:

$ redis-server

$ node rate_limiter/test/examples/exampleAPIServer.js

$ node rate_limiter/test/examples/exampleAPIHarvester.js

##Roadmap *Separate code into incoming and outgoing rate limiters. Expose specialized objects. Create express middlewre for incoming limiters.

*Add ability to handle request queueing in OutgoingRateLimiter.

*Create express/restify middleware.

*Simplify and streamline timeWindow parameter to allow for wide range of times in easier format. Perhaps create a specialized datatype with ints of either seconds, minutes, hours, or days.

*Incorporate status reports as parameter to callback for authorizeRequest() so that reason for denial (global limit exceeded or user limit exceeded) is available to handling code.