I am trying to build a simple node.js client using the amqp library, that opens a single connection and then a single channel to a RabbitMQ server. I want to reuse the same connection and channel to send multiple messages. The main problem is, that I don't want to write my entire code inside the callback function of the ceateChannel() function.

How do I reuse the channel outside of the callback function and make sure the callback function has finished before I use the channel?

I've tried both the callback way and the promise way but I can't make either of them work. When using the callback method I run into the described problem.

When using promises, I have the problem that I can't keep a reference of the connection and channel outside of the .then() function because the passed variables get destroyed after setting up the connection and channel.

amqp.connect('amqp://localhost', (err, conn) => {

  if (err !== null) return console.warn(err);
  console.log('Created connection!');

  conn.createChannel((err, ch) => {

    if (err !== null) return console.warn(err);
    console.log('Created channel!');

    //this is where I would need to write the code that uses the variable "ch"
    //but I want to move the code outside of this structure, while making sure
    //this callback pletes before I try using "ch"

  });
});

    amqp.connect('amqp://localhost').then((conn) => {
      return conn.createChannel();
    }).then((ch) => {
      this.channel = ch;
      return ch.assertQueue('', {}).then((ok) => {
        return this.queueName = ok.queue;  
      });
    }).catch(console.warn);

I am trying to build a simple node.js client using the amqp library, that opens a single connection and then a single channel to a RabbitMQ server. I want to reuse the same connection and channel to send multiple messages. The main problem is, that I don't want to write my entire code inside the callback function of the ceateChannel() function.

How do I reuse the channel outside of the callback function and make sure the callback function has finished before I use the channel?

I've tried both the callback way and the promise way but I can't make either of them work. When using the callback method I run into the described problem.

When using promises, I have the problem that I can't keep a reference of the connection and channel outside of the .then() function because the passed variables get destroyed after setting up the connection and channel.

amqp.connect('amqp://localhost', (err, conn) => {

  if (err !== null) return console.warn(err);
  console.log('Created connection!');

  conn.createChannel((err, ch) => {

    if (err !== null) return console.warn(err);
    console.log('Created channel!');

    //this is where I would need to write the code that uses the variable "ch"
    //but I want to move the code outside of this structure, while making sure
    //this callback pletes before I try using "ch"

  });
});

    amqp.connect('amqp://localhost').then((conn) => {
      return conn.createChannel();
    }).then((ch) => {
      this.channel = ch;
      return ch.assertQueue('', {}).then((ok) => {
        return this.queueName = ok.queue;  
      });
    }).catch(console.warn);

• javascript
• node.js
• promise
• rabbitmq
• amqp

Share Improve this question Follow asked Mar 29, 2019 at 12:44 Steve MelonsSteve Melons 8322 silver badges99 bronze badges 3

• why you don't use async\await ? const conn = await amqp.connect('amqp://localhost'); const ch = await conn.createChannel(); // after that you can use ch anywhere – Егор Лебедев Commented Mar 29, 2019 at 13:06
• Where exactly would i use that? I've tried but I don't exactly know how the best way would be. – Steve Melons Commented Mar 29, 2019 at 13:09
• I answered for better format of text – Егор Лебедев Commented Mar 29, 2019 at 13:12

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2 Answers 2

Sorted by: Reset to default 6

why you don't use async\await ?

const conn = await amqp.connect('amqp://localhost');
const ch = await conn.createChannel();
// after that you can use ch anywhere, don't forget to handle exceptions

Also if you use amqplib, don't forget to handle close and internal error events, for example like this:

conn.on('error', function (err) {
    console.log('AMQP:Error:', err);
});
conn.on('close', () => {
    console.log("AMQP:Closed");
});

Try with a class, like this:

RabbitConnection.js

const amqp = require('amqplib');

const RabbitSettings = {
    protocol: 'amqp',
    hostname: 'localhost',
    port: 5672,
    username: 'guest',
    password: 'guest',
    authMechanism: 'AMQPLAIN',
    vhost: '/',
    queue: 'test'
}

class RabbitConnection {

    constructor() {
        RabbitConnection.createConnection();
        this.connection = null;
        this.channel = null;
    }

    static getInstance() {
        if (!RabbitConnection.instance) {
            RabbitConnection.instance = new RabbitConnection();
        }
        return RabbitConnection.instance;
    }
    //create connection to rabbitmq
    static async createConnection() {
        try {
            this.connection = await amqp.connect(`${RabbitSettings.protocol}://${RabbitSettings.username}:${RabbitSettings.password}@${RabbitSettings.hostname}:${RabbitSettings.port}${RabbitSettings.vhost}`);
            this.channel = await this.connection.createChannel();
            this.channel.assertQueue(RabbitSettings.queue);
            console.log('Connection to RabbitMQ established');
        } catch (error) {
            console.log(error);
        }
    }
    //send message to rabbitmq queue
    static async sendMessage(message, queueName) {
        try {
            let msg = await this.channel.sendToQueue(queueName, Buffer.from(message));
            console.log('Message sent to RabbitMQ');
            return msg;
        } catch (error) {
            console.log(error);
        }
    }
}

module.exports = { RabbitConnection };

ServerExpress.js

const express = require('express');
const { RabbitConnection } = require('./RabbitConnection');

const serverUp = () => {
    const app = express();
    app.get('/', (req, res) => {
        RabbitConnection.sendMessage('Hello World', 'test');
        res.send('Hello World!');
    });
    app.listen(3000, () => {
        console.log('Server is running on port 3000');
    });
};

module.exports = { serverUp };

index.js

const { RabbitConnection } = require("./RabbitConnection");
const { serverUp } = require("./ServerExpress");

serverUp();
RabbitConnection.getInstance();