safe-memory-cache

safe-memory-cache

Secure and size-limited in-memory cache for Node.js and browsers.

Why another cache package?

• Is lightweight and has trivial API
• Can't be broken by a malicious key (__proto__)
• Can't be affected by modifications to native prototypes
• Limits the number of items without the use of delete (and no memory leaks caused by delete), plays well with garbage collector. But also doesn't drop the whole cache when full, frees up gradually
• Doesn't waste your eventloop ticks with timeouts set to remove single items from cache, but still deletes oldest items first

Usage

var safeMemoryCache = require('safe-memory-cache')
var cache = safeMemoryCache(options)

cache.set("key1","value1")
cache.get("key1") == "value1"

cache.clear()
cache.get("key1") == undefined

cache.destroy() //only needed if you use maxTTL

If your engine supports Map, you can use the map based version. It doesn't need (nor have) sanitization on keys and it uses Maps as buckets for storage.

const safeMemoryCache = require('safe-memory-cache/map')

options:

name	type	required	description
limit	number	Y	Maximum number of items to store in cache. When cache length is close to the limit, oldest items are removed to make more room.
maxTTL	number	N	Time in miliseconds within which an element should no longer be in cache if it was not accessed. Actual time is approximate and will be less or equal maxTTL
strongSanitizer	bool	N	When set to true sanitizes keys to prevent memory issues in older JS engines. Defaults to false. No sanitization if you use the Map based version.
buckets	number	N	Overrides the number of buckets used internally. Default is 2
cleanupListener	function	N	Calls the function with a storage bucket that's been removed

What limit should I set ?

If you expect N keys to be used most frequently, limit/buckets should be at least N.

What is it fit for?

Caching in general. When you need to cache results of some long running process or a lot of them and you don't have a strong requirement to keep every item until its exact expiry time.

Technicalities

What's the point of strongSanitizer?

Some older JavaScript engines had memory leaks triggered by object keys which contain control characters like - or . strongSanitizer:true makes sure the keys are converted to alphanumeric characters only.

Prevents any potential hacks like overwriting __proto__ too.

Default sanitizer is only preventing __proto__ key from breaking the functionality.

How do you know items added to native prototypes won't affect the cache?

Objects used for storing key/value pairs don't inherit from any of the native prototypes, nor Object

What's with the memory leaks, buckets and delete?

delete keyword removes fields from objects, but changes the hidden class of the object which takes up some memory. As a result, adding and deleting unique fields to a plain JavaScript object may cause memory consumption to grow. Some JavaScript engines had it leak memory in various ways.

Then how do you remove old items from cache if you can't use delete?

Cache consists of a number of buckets and the oldest bucket is removed when new room is needed. Therefore the oldest (1/buckets) of entries gets removed.