@sebspark/promise-cache v3.10.0

@sebspark/promise-cache

Simple caching wrapper

PromiseCache implementation

Features

• PromiseCache: Simple caching wraper for promises

• Persistor: Simple Key/Value caching wrapper, can be used with redis or with local memory.

Installation

To install promise-cache, use yarn:

yarn install @sebspark/promise-cache

Usage

PromiseCache Class

import { PromiseCache } from '@sebspark/promise-cache'

// with redis
const cacheInRedis = new PromiseCache<T>({
  redis: REDIS_URL,
  ttlInSeconds: ttl,
  caseSensitive: true
})

// without redis
const cacheLocalMemory = new PromiseCache<T>({
  ttlInSeconds: ttl,
  caseSensitive: true
})

PromiseCache Methods

// Wrap
/* Simple promise cache wrapper
 * @param key Cache key.
 * @param delegate The function to execute if the key is not in the cache.
 * @param ttlInSeconds Time to live in seconds.
 * @param ttlKeyInSeconds The key in the response object that contains the TTL.
 * @returns The result of the delegate function.
*/
const ttl = 5 // 5 seconds
const delegate = new Promise((reject, resolve) => { resolve(123)})
const response = await cacheInRedis.wrap('Key', delegate, ttl)
expect(response).toBe(123)

// Size
/*
* Cache size
* @returns The number of entries in the cache
*/

const entries = await cacheInRedis.size()
expect(entries).toBe(1)

// Find
 /**
* Get a value from the cache.
* @param key Cache key.
*/

const cachedValue = await cacheInRedis.find('Key')
expect(cachedValue).toBe(123)

// Override
/**
 * Set a value in the cache.
 * @param key Cache key.
 * @param value Cache value.
 * @param ttlInSeconds? Time to live in seconds.
 */

await cacheInRedis.override('Key', 234) // keep the same ttl
const cached = cacheInRedis.find('Key')
expect(cached).toBe(234)

Persistor Class

import { Persistor } from '@sebspark/promise-cache'

// with redis
const store = new Persistor<T>({
  redis: REDIS_URL,
})

// without redis
const store = new Persistor<T>()

Persistor Methods

/**
* Size
* @returns The number of entries in the cache
*/

const size = await store.size()
expect(size).toBe(0)

/**
* Set
* Set a value in the cache.
* @param key Cache key.
* @param object.value Value to set in the cache.
* @param object.ttl Time to live in seconds.
* @param object.timestamp Timestamp
*/

await store.set<number>('MyKey', {
  value: 123,
  ttl: 10               // In seconds, default undefined
  timestamp: Date.now() // default Date.now()
})

/**
 * Get a value from the cache.
 * @param key Cache key.
 * @returns GetType<T> value
 */

const cached = await store.get('MyKey')
expect(cached).toBe({
  value: 43,
  ttl: 10,
  timestamp: // The timestamp
})

/**
 * Delete a value from the cache.
 * @param key Cache key
 */

await store.delete('MyKey')
expect(await store.get('MyKey').toBe(null)

Cache implementation

The basic functionality of this new implementation is:

1. You create a persistor to store your cached data. This can be the built in InMemoryPersistor or a Redis client
2. You create a cache by calling createCache(persistor, 'optional-prefix')
3. You call the cache's wrap function to wrap your original function(s)
4. You call the wrapped function(s) instead of the originals

Why the change?

When trying to add support for caching to a specified time in addition to for a specified time, it tuyrned out to be hard given the original implementation. Changing the implementation proved hard without breaking changes. So a new implementation is is.

How to use it

import { createClient } from 'redis'
import { createCache } from '@sebspark/promise-cache'
import { myFunction } from './some_function'

const run = async () => {
  // Create your persistor
  const persistor = createClient({ url: 'redis' })
  await persistor.connect() // This is not handled by the cache

  // Create your cache and give it a prefix
  const cache = createCache(persistor, 'my-prefix')
  
  // wrap your function
  const myCachedFunction = cache.wrap(myFunction, {
    key: 'my-function', // cached data will be stored with the key 'my-prefix:my-function'
    expiry: 100, // ttl will be 100 ms
  })

  // call the wrapped function
  const response = await myCachedFunction() // the wrapped function will have the same signature as the original
}

run()

Keys

Keys can be constructed in two ways: as a fixed string or as a function that generates a string. The generator will accept the arguments of the wrapped function.

const cache = createCache(persistor, 'api')

const getById = async (id: string): Promise<Data> => {
  // Something gets called
}

const cachedGetById = cache.wrap(myApiCall, {
  key: (id) => `getById:${id}`
})

const result = await cachedGetById('foo')

// key will be 'api:getById:foo'

Expiry

Expiration can be set as either a number (number of milliseconds from now) or a Date (exact expiry time). It can be set either as a value (number | Date) or as a function that generates a value (number | Date). The generator will accept the arguments and the response of the wrapped function.

const cache = createCache(persistor, 'api')

type Data = {
  value: number
  expires: string // ISO6501 date time string
}

const getById = async (id: string): Promise<Data> => {
  // Something gets called
}

const cachedGetById = cache.wrap(myApiCall, {
  key: (id) => `getById:${id}`,
  expires: ([id], data) => new Date(data.expires),
})

const result = await cachedGetById('foo')

There are also helpers for setting time or manipulating dates

import { createCache, time } from '@sebspark/promise-cache'

const cache = createCache(persistor, 'api')

type Data = {
  value: number
  lastUpdated: string // ISO6501 date time string. Data is updated every 30 minutes.
}

const getById = async (id: string): Promise<Data> => {
  // Something gets called
}

// Computed from response
const cachedGetById = cache.wrap(myApiCall, {
  key: (id) => `getById:${id}`,
  expires: ([id], data) => time.add(new Date(data.lastUpdated), { minutes: 30 })
})

// Fixed at 20 seconds
const cachedGetById = cache.wrap(myApiCall, {
  key: (id) => `getById:${id}`,
  expires: time.seconds(100),
})

// Fixed at today 20:00:00 UTC
const cachedGetById = cache.wrap(myApiCall, {
  key: (id) => `getById:${id}`,
  expires: time.today(20),
})

// Fixed at tomorrow 00:00:00
const cachedGetById = cache.wrap(myApiCall, {
  key: (id) => `getById:${id}`,
  expires: time.tomorrow(),
})

If expiry is not set or yields an unusable value, it will default to 1 sec.