volos-quota-memory/lib/memoryquota.js

In-memory provider for Quota enforcement in the Volos system.

/****************************************************************************
 The MIT License (MIT)

 Copyright (c) 2013 Apigee Corporation

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 of this software and associated documentation files (the "Software"), to deal
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'use strict';

var assert = require('assert');

var Quota = require('volos-quota-common');

/*
 * This is a quota implementation that uses buckets in memory. Each quota bucket is simply
 * an object with an expiration time.
 */

var create = function(options) {
  return new Quota(MemoryQuotaSpi, options);
};
module.exports.create = create;


function MemoryQuotaSpi(options) {
  this.options = options;
  this.buckets = {};

  assert(options.timeInterval);
  if (options.startTime) {
    assert.equal(typeof options.startTime, 'number');
  }

  var self = this;
  this.timer = setInterval(function() {
    trimTokens(self);
  }, options.timeInterval);
}

MemoryQuotaSpi.prototype.destroy = function() {
  clearTimeout(this.timer);
};

MemoryQuotaSpi.prototype.apply = function(options, cb) {
  var bucket = this.buckets[options.identifier];
  var now = Date.now();

  if (!bucket) {
    bucket = {
      count: 0,
      expires: this.calculateExpiration(now)
    };
    this.buckets[options.identifier] = bucket;
  }

  if (now > bucket.expires) {
    // Quota bucket has expired. The timer also runs but only periodically
    bucket.count = 0;
    bucket.expires = this.calculateExpiration(now);
  }

  bucket.count += options.weight;

  var allow = options.allow || this.options.allow;

  var result = {
    allowed: allow,
    used: bucket.count,
    isAllowed: (bucket.count <= allow),
    expiryTime: bucket.expires - now
  };
  cb(undefined, result);
};

// Separate this out for white-box unit testing

MemoryQuotaSpi.prototype.calculateExpiration = function(now) {
  assert.equal(typeof now, 'number');

  if (this.options.startTime) {
    // "calendar" start quota -- calculate time until the end of the bucket
    var remaining = (now - this.options.startTime) % this.options.timeInterval;
    return now + this.options.timeInterval - remaining;

  } else {

    if ('month' === this.options.timeUnit) {

      var date = new Date(now);
      return new Date(date.getFullYear(), date.getMonth() + 1, 1) - 1; // last ms of this month

    } else {

      // Default quota type -- start counting from now
      return now + this.options.timeInterval;
    }
  }
};

/*
 * Quotas always obey their expiration times (which prevents us from having to register a huge
 * number of individual timeouts) but we still want to periodically clean them up to prevent memory
 * issues. This job runs once per time interval (minute, hour, day, or week) and removes expired tokens.
 */
function trimTokens(self) {
  var now = Date.now();
  for (var b in Object.keys(self.buckets)) {
    if (now > b.expires) {
      delete self.buckets.b;
    }
  }
}