audiobookshelf/server/managers/ApiCacheManager.js

const { LRUCache } = require('lru-cache')
const Logger = require('../Logger')
const Database = require('../Database')

class ApiCacheManager {

  defaultCacheOptions = { max: 1000, maxSize: 10 * 1000 * 1000, sizeCalculation: item => (item.body.length + JSON.stringify(item.headers).length) }
  defaultTtlOptions = { ttl: 30 * 60 * 1000 }

  constructor(cache = new LRUCache(this.defaultCacheOptions), ttlOptions = this.defaultTtlOptions) {
    this.cache = cache
    this.ttlOptions = ttlOptions
  }

  init(database = Database) {
    let hooks = ['afterCreate', 'afterUpdate', 'afterDestroy', 'afterBulkCreate', 'afterBulkUpdate', 'afterBulkDestroy', 'afterUpsert']
    hooks.forEach(hook => database.sequelize.addHook(hook, (model) => this.clear(model, hook)))
  }

  clear(model, hook) {
    Logger.debug(`[ApiCacheManager] ${model.constructor.name}.${hook}: Clearing cache`)
    this.cache.clear()
  }

  get middleware() {
    return (req, res, next) => {
      const key = { user: req.user.username, url: req.url }
      const stringifiedKey = JSON.stringify(key)
      Logger.debug(`[ApiCacheManager] count: ${this.cache.size} size: ${this.cache.calculatedSize}`)
      const cached = this.cache.get(stringifiedKey)
      if (cached) {
        Logger.debug(`[ApiCacheManager] Cache hit: ${stringifiedKey}`)
        res.set(cached.headers)
        res.status(cached.statusCode)
        res.send(cached.body)
        return
      }
      res.originalSend = res.send
      res.send = (body) => {
        Logger.debug(`[ApiCacheManager] Cache miss: ${stringifiedKey}`)
        const cached = { body, headers: res.getHeaders(), statusCode: res.statusCode }
        if (key.url.search(/^\/libraries\/.*?\/personalized/) !== -1) {
          Logger.debug(`[ApiCacheManager] Caching with ${this.ttlOptions.ttl} ms TTL`)
          this.cache.set(stringifiedKey, cached, this.ttlOptions)
        } else {
          this.cache.set(stringifiedKey, cached)
        }
        res.originalSend(body)
      }
      next()
    }
  }
}
module.exports = ApiCacheManager