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@ChisholmKyle
Created February 11, 2016 08:05
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General purpose rate limiters using Redis and ioredis in node.js
var Ioredis = require('ioredis');
var redis = new Ioredis();
// Rolling window rate limiter
//
// key is a unique identifier for the process or function call being limited
// exp is the expiry in milliseconds
// maxnum is the number of function calls allowed before expiry
var redis_limiter_rolling = function(key, maxnum, exp, next) {
redis.multi([
['incr', 'limiter:num:' + key],
['time']
]).exec(function(err, results) {
if (err) {
next(err);
} else {
// unique incremented list number for this key
var listnum = results[0][1];
// current time
var tcur = (parseInt(results[1][1][0], 10) * 1000) + Math.floor(parseInt(results[1][1][1], 10) / 1000);
// absolute time of expiry
var texpiry = tcur - exp;
// get number of transacation in the last expiry time
var listkey = 'limiter:list:' + key;
redis.multi([
['zadd', listkey, tcur.toString(), listnum],
['zremrangebyscore', listkey, '-inf', texpiry.toString()],
['zcard', listkey]
]).exec(function(err, results) {
if (err) {
next(err);
} else {
// num is the number of calls in the last expiry time window
var num = parseInt(results[2][1], 10);
if (num <= maxnum) {
// does not reach limit
next(null, false, num, exp);
} else {
// limit surpassed
next(null, true, num, exp);
}
}
});
}
});
};
// Lockout window rate limiter
//
// key is a unique identifier for the process or function call being limited
// exp is the expiry in milliseconds
// maxnum is the number of function calls allowed within expiry time
var util_limiter_lockout = function(key, maxnum, exp, next) {
// lockout rate limiter
var idkey = 'limiter:lock:' + key;
redis.incr(idkey, function(err, result) {
if (err) {
next(err);
} else {
if (result <= maxnum) {
// still within number of allowable calls
// - reset expiry and allow next function call
redis.expire(idkey, exp, function(err) {
if (err) {
next(err);
} else {
next(null, false, result);
}
});
} else {
// too many calls, user must wait for expiry of idkey
next(null, true, result);
}
}
});
};
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