Consuming messages one by one in NodeJS

[András Szabó]

By default, the consume() function consumes all the messages that are in the queue, but I need pop only one message from the queue, and with the next consume() call pop the second message from the queue, etc. I have this code:

rabbit.js (in this file I have implemented the sending to and receiving from the queue):

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

amqp.connect('amqp://localhost', function(err, conn) {
  conn.createChannel(function(err, channel) {    
    ch = channel;
  });
});

module.exports.queueSend = function(msg) {
    var q = 'hello';

    ch.assertQueue(q, {durable: false});
    ch.sendToQueue(q, new Buffer(msg));
    console.log(" [x] Sent %s", msg);
}

module.exports.queueReceive = function() {
    var q = 'hello';

    ch.assertQueue(q, {durable: false});
    console.log(" [*] Waiting for messages in %s. To exit press CTRL+C", q);
    ch.consume(q, function(msg) {
      console.log(" [x] Received %s", msg.content.toString());
    }, {noAck: false});
}

rabbit_test.js (in this file I have tested the functionality of the previous code):

var rabbit = require("./rabbit");

setTimeout(function() {
    rabbit.queueSend("01C");
    rabbit.queueSend("02C");
    rabbit.queueReceive();
}, 2000);

When I call the queueReceive() function, it prints out the "01C" and "02C" messages too, not only the "01C". I need print out only the "01C" and with a next queueReceive() call the "02C".

P.S.: I tried this code too in rabbit.js for function queueReceive():

module.exports.queueReceive = function() {
    var q = 'hello';

    ch.prefetch(1);
    ch.assertQueue(q, {durable: false});
    console.log(" [*] Waiting for messages in %s. To exit press CTRL+C", q);
    ch.consume(q, function(msg) {
      ch.ack(msg);
      console.log(" [x] Received %s", msg.content.toString());
    }, {noAck: false});
}

I added the ch.ack(msg) and ch.prefetch(1) parts, but it doesn't works neither.

How can i get this working? Thank you in advance!

[Luke Bakken]

Hello András -

I don't know the amqplib API off the top of my head, but I bet there's a channel.get() method you can use instead of channel.consume()

Luke

On Tuesday, December 5, 2017 at 3:58:20 PM UTC-8, András Szabó wrote:

By default, the consume() function consumes all the messages that are in the queue, but I need pop only one message from the queue, and with the next consume() call pop the second message from the queue, etc. I have this code:

[András Szabó]

Thanks Luke! It works for me. :)

[András Szabó]

An another question: is it possible to get given amount of messages from queue? The get() method gets one message, the consume() gets the all messages, but is there a method for getting a given amount (e.g. three) of messages? Thanks!

[Luke Bakken]

Hi András -

Please do not follow up a question with a new question in the same discussion. The reason is that people will probably not notice your new question.

[Michael Klishin]

The "how do I know how many messages are in the queue" question has been discussed numerous times all over the Internet

in the last few years. Please do some research.

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MK

Staff Software Engineer, Pivotal/RabbitMQ