RabbitMQ with NodeJS - using amqplib to get message count

Question

How do I get the number of messages currently en-queued?

My code is basically the following:

function readQueue() {
    var open = require('amqplib').connect(config.rabbitServer);

    open.then(function (conn) {
        var ok = conn.createChannel();
        ok = ok.then(function (ch) {
            ch.prefetch(config.bulkSize);

            setInterval(function () {
                handleMessages();
            }, config.bulkInterval);

            ch.assertQueue(config.inputQueue);
            ch.consume(config.inputQueue, function (msg) {
                if (msg !== null) {
                    pendingMessages.push(msg);
                }
            });
        });
        return ok;
    }).then(null, console.warn);
}

I found nothing in the documentation or while debugging, and I did see a different library that allows this, so wondering if amqplib supports this as well.

Answer 1

You can get the queue-length with amqplib.

In my case the queue has the feature 'durable:true'. You have to pass it as an option.

var amqp = require('amqplib/callback_api');

amqp.connect(amqp_url, function(err, conn) {
  conn.createChannel(function(err, ch) {
    var q = 'task2_queue';

    ch.assertQueue(q, {durable: true}, function(err, ok) {
      console.log(ok);
    });
  });
});

It will return an object like this:

{ queue: 'task2_queue', messageCount: 34, consumerCount: 2 }

For more information: https://www.squaremobius.net/amqp.node/channel_api.html#channel_assertQueue

Answer 2

I think the assertQueue method call will return an object that contains the current message count. I don't remember the exact property name off-hand, but it should be in there.

The real trick, though, is that this number will never be updated once you call assertQueue. The only way to get an updated message count is to call assertQueue again. This can have some performance implications if you're checking it too frequently.