safe-memory-cache

safe-memory-cache

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

Updated with defensive coding (for prototype poisoning immunity)

Why another cache package?

• Is lightweight and has trivial API
• Can't be broken by a malicious key (__proto__) or a prototype poisoning of intrinsics
• 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

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
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
retainUsed	boolean	N	Keep items longer than the maxTTL if they are used

What limit should I set ?

If you expect N keys to be used most frequently, (limit/buckets) >= 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

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 The implementation uses defensive coding to avoid relying on intrinsics that could be modified later.

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

delete keyword removes fields from objects, but changes the hidden class aka shape 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.

There's only one interval created per cache instance.