CODEWITHSUNDEEP
node.jsredislistenernode-redisioredis
devio
devio

Reputation: 1169

Redis Node to listen to SET events and set a TTL to every request

In my Nodejs app, I use a library that sets keys in my Redis database. So, I need to listen to every request that creates/updates a key and add a ttl on every key (whether it already exists or not).

I have my main Redis client (that add keys to the Redis database) :

const redisClient = createClient({
    url: redisUrl,
    tls: {
        ca: Buffer.from(redisCertBase64, 'base64').toString('utf-8'),
    },
})

And I have added another client that should listen to set events :

const subscriberRedis = redisClient.duplicate()

function done(err) {
    logger.error('Notifications not active')
    if (err) {
        logger.error(err.stack || err.message || err)
    }
}

const eventType = 'notify-keyspace-events'

subscriberRedis.config('get', eventType, (err, conf) => {
    if (err) {
        logger.debug('subscriberRedis:get =>', err.message)
        return done(err)
    }
    logger.debug('conf =>', conf)
    if (conf[1].indexOf('EKx') < 0) {
        subscriberRedis.config('set', eventType, conf[1] + 'EKx', function (err) {
            if (err) {
                logger.debug('subscriberRedis:set =>', err.message)
                return done(err)
            }
        })
    }
})

const EVENT_SET = '__keyevent@0__:set'

subscriberRedis.on('message', function (channel, key) {
    switch (channel) {
        case EVENT_SET:
            logger.info('Key "' + key + '" set!')
            break
    }
})

subscriberRedis.subscribe(EVENT_SET)

When I run this code, I get in the logs subscriberRedis:set => ERR only (P)SUBSCRIBE / (P)UNSUBSCRIBE / PING / QUIT allowed in this context which is logged by the subscriberRedis.config('set',...)

I'm not sure what I'm missing here.

EDIT

I changed the code to this, and it's working now. However, do you think the "race condition" issue is still there when I move to production ?

const redisClient = createClient({
    url: redisUrl,
    tls: {
        ca: Buffer.from(redisCertBase64, 'base64').toString('utf-8'),
    },
})

/**
 * Subscriber listening to `set` events
 **/
const subscriber = redisClient.duplicate()
const EVENT_SET = '__keyevent@0__:set'

subscriber.on('message', function (channel, key) {
    switch (channel) {
        case EVENT_SET:
            redisClient.expire(key, 300)
            logger.debug('Key "'.red + key + '" set!'.yellow)
            break
    }
})
subscriber.subscribe(EVENT_SET)

Upvotes: 1

Views: 1331

Answers (1)

Guy Korland
Guy Korland

Reputation: 9568

The problem is that by the time you call subscriberRedis.config('set' your subscriberRedis has already subscribed on subscriberRedis.subscribe(EVENT_SET).

And, you can't use this connection for subscriberRedis.config('set' while you are subscribed.

Upvotes: 1

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