index.js

var assert = require("assert");
var microtime = require("microtime-nodejs");

function RateLimiter (options) {
  var redis           = options.redis,
    interval        = options.interval * 1000, // in microseconds
    maxInInterval   = options.maxInInterval,
    minDifference   = options.minDifference ? 1000 * options.minDifference : null, // also in microseconds
    namespace       = options.namespace || (options.redis && (`rate-limiter-${ Math.random().toString(36).slice(2)}`)) || null;

  assert(interval > 0, "Must pass a positive integer for `options.interval`");
  assert(maxInInterval > 0, "Must pass a positive integer for `options.maxInInterval`");
  assert(!(minDifference < 0), "`options.minDifference` cannot be negative");

  if (!options.redis) {
    var storage = {};
    var timeouts = {};
  }

  if (redis) {
    // If redis is going to be potentially returning buffers OR an array from
    // ZRANGE, need a way to safely convert either of these types to an array
    // of numbers.  Otherwise, we can just assume that the result is an array
    // and safely map over it.
    var zrangeToUserSet;
    if (redis.options.return_buffers || redis.options.detect_buffers) {
      zrangeToUserSet = function(str) {
        return String(str).split(",").map(Number);
      };
    } else {
      zrangeToUserSet = function(arr) {
        return arr.map(Number);
      };
    }

    return function(id, cb) {
      if (!cb) {
        cb = id;
        id = "";
      }


      assert.equal(typeof cb, "function", "Callback must be a function.");

      var now = microtime.now();
      var key = namespace + id;
      var clearBefore = now - interval;

      var batch = redis.multi();
      batch.zremrangebyscore(key, 0, clearBefore);
      batch.zrange(key, 0, -1);
      batch.zadd(key, now, now);
      batch.expire(key, Math.ceil(interval / 1000000)); // convert to seconds, as used by redis ttl.
      batch.exec(function(err, resultArr) {
        if (err) return cb(err);

        var userSet = zrangeToUserSet(resultArr[1]);

        var tooManyInInterval = userSet.length >= maxInInterval;
        var timeSinceLastRequest = now - userSet[userSet.length - 1];

        var result;
        var remaining = maxInInterval - userSet.length - 1;

        if (tooManyInInterval || timeSinceLastRequest < minDifference) {
          result = Math.max(tooManyInInterval ? userSet[userSet.length - maxInInterval] - now + interval : 0, minDifference ? minDifference : 0);
          result = Math.floor(result / 1000); // convert to miliseconds for user readability.
        } else {
          result = 0;
        }

        return cb(null, result, remaining);
      });
    };
  } else {
    return function() {
      var args = Array.prototype.slice.call(arguments);
      var cb = args.pop();
      var id;
      if (typeof cb === "function") {
        id = args[0] || "";
      } else {
        id = cb || "";
        cb = null;
      }

      var now = microtime.now();
      var clearBefore = now - interval;

      clearTimeout(timeouts[id]);
      delete timeouts[id];

      var userSet = storage[id] = (storage[id] || []).filter(function(timestamp) {
        return timestamp > clearBefore;
      });

      var tooManyInInterval = userSet.length >= maxInInterval;
      var timeSinceLastRequest = now - userSet[userSet.length - 1];

      var result;
      var remaining = maxInInterval - userSet.length - 1;

      if (tooManyInInterval || timeSinceLastRequest < minDifference) {
        result = Math.max(tooManyInInterval ? userSet[userSet.length - maxInInterval] - now + interval : 0, minDifference ? minDifference : 0);
        result = Math.floor(result / 1000); // convert from microseconds for user readability.
      } else {
        result = 0;
      }
      userSet.push(now);
      timeouts[id] = setTimeout(function() {
        delete storage[id];
        delete timeouts[id];
      }, interval / 1000); // convert to miliseconds for javascript timeout

      if (cb) {
        return process.nextTick(function() {
          cb(null, result, remaining);
        });
      } else {
        return result;
      }
    };
  }
}

module.exports = RateLimiter;