how to remove subscription callbacks in redis? - redis

Question

I have a subscriber redis client instance that is performing a callback when entries in the db expire.. I tried adding an initial unsubscribe call to remove previous any existing listeners, but it does not seem to be working:
const setOnExpire = (onExpire) => {
client.config('set', 'notify-keyspace-events', 'Ex', () => {
subscriber.unsubscribe('__keyevent#0__:expired', 0); // <-- this does not seem to be doing what I was hoping it would...
subscriber.subscribe('__keyevent#0__:expired', () => {
subscriber.on('message', function (channel, key) {
onExpire(key);
});
});
});
};
setOnExpire(() => { console.log('foo'); });
setOnExpire(() => { console.log('bar'); }); // my intention is to replace the callback that logs "foo"
client.hmsetAsync(someKey, someAttrs).then(() => {
client.expireAsync(someKey, 5);
});
I run this, hoping to only see "bar" get logged when the record expires in 5 seconds, however instead, I see "foo" and "bar."
How can I properly remove the pre-existing subscriber.on('message') listeners?

Answer 1

If I understand your question correctly. I think this is not a Redis related problem, it's just an application-level problem. You only need to call subscriber.subscribe once to set up a subscription. You want to support only one callback, so store that callback internally. And every time setOnExpire get called, just replace the callback with a new one. I'm not a JavaScript expert, bellow code snippet works fine on my computer:
var redis = require("redis");
var bluebird = require('bluebird');
bluebird.promisifyAll(redis);
var client = redis.createClient();
var subscriber = redis.createClient();
const setOnExpire = function() {
var notify_on = false;
var promise;
var callback = function(key) { };
return (onExpire) => {
if (notify_on) {
promise.then(()=> {
callback = onExpire;
});
} else {
promise = new Promise((resolve, reject) => {
notify_on = true;
client.config('set', 'notify-keyspace-events', 'Ex', () => {
resolve();
});
});
promise.then(() => {
subscriber.subscribe('__keyevent#0__:expired', () => {
subscriber.on('message', function (channel, key) {
callback(key);
});
});
});
}
};
}();
setOnExpire(() => { console.log('foo'); });
setOnExpire(() => { console.log('bar'); }); // my intention is to replace the callback that logs "foo"
client.hmsetAsync('hello', 'yesl', 'thankyou').then(() => {
client.expireAsync('hello', 5);
});