lru cache

Created: 2020-09-09 09:30:04 -0700 Modified: 2020-09-09 09:30:41 -0700

Code to serialize and deserialize an LRU

Note: I wrote this for Bot Land and didn’t know if it would come in handy in the future, so here it is:

/**
 * This file exists because the Node module "lru-cache" has dump/load functions,
 * but it won't serialize/deserialize the objects in the LRU for me, so I've
 * replaced it with serializeLru and deserializeLru.
 */
const LRU = require('lru-cache');
const _ = require('lodash');

/**
 * Serializes an LRU as long as each entry has a "serialize" function on it.
 * @param {LRU} lru
 * @return {Array<Object>} - serialized entries that have 'k' and 'v' properties
 */
function serializeLru(lru) {
  const serializedEntries = [];
  lru.rforEach((value, key, cache) => {
    serializedEntries.push({
      k: key,
      v: value.serialize(),
    });
  });

  return serializedEntries;
}

/**
 * The converse of serializeLru.
 * @param {Array<Object>} serializedLruEntries - the return value from
 * serializeLru
 * @param {Function} deserializationFn - the function to use to deserialize
 * each entry
 * @param {number} maxEntries - the max number of entries to have in the new
 * LRU
 * @return {LRU}
 */
function deserializeLru(serializedLruEntries, deserializationFn, maxEntries) {
  const lru = new LRU({
    max: maxEntries,
  });

  _.forEach(serializedLruEntries, (serializedEntry) => {
    lru.set(serializedEntry.k, deserializationFn(serializedEntry.v));
  });

  return lru;
}

module.exports = {
  serializeLru,
  deserializeLru,
};