joystream/storage-node/packages/util/test/lru.js

/*
 * This file is part of the storage node for the Joystream project.
 * Copyright (C) 2019 Joystream Contributors
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see <https://www.gnu.org/licenses/>.
 */

'use strict'

const expect = require('chai').expect

const lru = require('@joystream/storage-utils/lru')

const DEFAULT_SLEEP = 1
function sleep(ms = DEFAULT_SLEEP) {
  return new Promise((resolve) => {
    setTimeout(resolve, ms)
  })
}

describe('util/lru', function () {
  describe('simple usage', function () {
    it('does not contain keys that were not added', function () {
      const cache = new lru.LRUCache()
      expect(cache.size()).to.equal(0)

      const val = cache.get('something')
      expect(val).to.be.undefined

      expect(cache.has('something')).to.be.false
    })

    it('contains keys that were added', function () {
      const cache = new lru.LRUCache()
      cache.put('something', 'yay!')
      expect(cache.size()).to.equal(1)

      const val = cache.get('something')
      expect(val).to.be.equal('yay!')

      expect(cache.has('something')).to.be.true
    })

    it('does not contain keys that were deleted', function () {
      const cache = new lru.LRUCache()
      cache.put('something', 'yay!')
      expect(cache.size()).to.equal(1)
      let val = cache.get('something')
      expect(val).to.be.equal('yay!')
      expect(cache.has('something')).to.be.true

      cache.del('something')
      expect(cache.size()).to.equal(0)
      val = cache.get('something')
      expect(val).to.be.undefined
      expect(cache.has('something')).to.be.false
    })

    it('can be cleared', function () {
      const cache = new lru.LRUCache()
      cache.put('something', 'yay!')
      expect(cache.size()).to.equal(1)

      cache.clear()
      expect(cache.size()).to.equal(0)
    })
  })

  describe('capacity management', function () {
    it('does not grow beyond capacity', async function () {
      const cache = new lru.LRUCache(2) // Small capacity
      expect(cache.size()).to.equal(0)

      cache.put('foo', '42')
      expect(cache.size()).to.equal(1)

      await sleep()

      cache.put('bar', '42')
      expect(cache.size()).to.equal(2)

      await sleep()

      cache.put('baz', '42')
      expect(cache.size()).to.equal(2) // Capacity exceeded
    })

    it('removes the oldest key when pruning', async function () {
      const cache = new lru.LRUCache(2) // Small capacity
      expect(cache.size()).to.equal(0)

      cache.put('foo', '42')
      expect(cache.size()).to.equal(1)
      expect(cache.has('foo')).to.be.true

      await sleep()

      cache.put('bar', '42')
      expect(cache.size()).to.equal(2)
      expect(cache.has('foo')).to.be.true
      expect(cache.has('bar')).to.be.true

      await sleep()

      cache.put('baz', '42')
      expect(cache.size()).to.equal(2) // Capacity exceeded
      expect(cache.has('bar')).to.be.true
      expect(cache.has('baz')).to.be.true
    })

    it('updates LRU timestamp when reading', async function () {
      const cache = new lru.LRUCache(2) // Small capacity
      expect(cache.size()).to.equal(0)

      cache.put('foo', '42')
      expect(cache.size()).to.equal(1)
      expect(cache.has('foo')).to.be.true

      await sleep()

      cache.put('bar', '42')
      expect(cache.size()).to.equal(2)
      expect(cache.has('foo')).to.be.true
      expect(cache.has('bar')).to.be.true

      await sleep()

      // 'foo' is older than 'bar' right now, so should be pruned first. But
      // if we get 'foo', it would be 'bar' that has to go.
      cache.get('foo')

      // Makes debugging a bit more obvious
      await sleep()

      cache.put('baz', '42')
      expect(cache.size()).to.equal(2) // Capacity exceeded
      expect(cache.has('foo')).to.be.true
      expect(cache.has('baz')).to.be.true
    })
  })
})