Redis Key expiry notification

sample.ts

export namespace RedisExpiryNotification {
  const callbackMap: any = {}
  const PREFIX = '__keyspace@?__:'

  redisClient.send_command(
    'config',
    // ['set', 'notify-keyspace-events', 'Ex'],
    ['set', 'notify-keyspace-events', 'Kx'],
    RedisExpiryNotification.onRedisKeyExpiredCallback
  )

  redisClient.on('pmessage', onRedisKeyExpiredCallback)

  export function onExpiry(key: string, callback: () => void) {
    log.info('Subscribing to expiry updates on', key)

    if (!(key in callbackMap)) {
      callbackMap[key] = []
    }

    callbackMap[key].push(callback)
    const expired_subKey = `${PREFIX}${key}`
    redisClient.psubscribe(expired_subKey)
  }

  export function onRedisKeyExpiredCallback(
    chan: string,
    pattern: string,
    event: string
  ) {
    const key = pattern.substring(PREFIX.length)
    if (key in callbackMap) {
      const callbacks = callbackMap[key]
      callbacks.forEach((cb: any) => {
        cb(null)
      })

      delete callbackMap[key]
    }
  }
}