agmission/Development/server/helpers/job_queue.js

const
  debug = require('debug')('agm:job-queuer'),
  amqp = require('amqplib/callback_api'),
  utils = require('./utils'),
  env = require('./env');

let amqpConn = null;
let connTimer;

const JOB_QUEUE = env.PRODUCTION ? env.QUEUE_NAME_JOBS : 'dev_jobs'
const GDATA_QUEUE = 'gdata';

function JobQueuer(ops = {}) {
  this._conOps = {
    protocol: ops.protocol || 'amqp',
    hostname: ops.hostname || env.QUEUE_HOST,
    port: ops.port || env.QUEUE_PORT || 5672,
    username: ops.username || env.QUEUE_USR,
    password: ops.password || env.QUEUE_PWD,
    vhost: ops.vhost || env.QUEUE_VHOST || '/',
    hearbeat: ops.heartbeat || env.QUEUE_HEARTBEAT || 0
  };
}

// Rabbitmq connection. If the connection is closed or fails to be established at all, we will reconnect
JobQueuer.prototype.start = function start() {
  if (amqpConn)
    closeOnErr('force_close_reconnect');

  amqp.connect(JobQueuer.instance._conOps, function (err, conn) {
    if (err) {
      console.error("[AMQP]", err.message);
      connTimer = setTimeout(start, 5000);
      return;
    }
    conn.on("error", function (err) {
      if (err.message !== "Connection closing") {
        console.error("[AMQP] conn error", err.message);
      }
    });
    conn.on("close", function () {
      console.error("[AMQP] reconnecting");
      connTimer = setTimeout(start, 5000);
      return;
    });

    amqpConn = conn;
    process.once('SIGINT', () => {
      closeOnErr('force_close_SIGINT');
    });

    whenConnected();
  });
}

function whenConnected() {
  debug("[AMQP] Job Queuer connected");
  startPublisher();
}

/**
 * Rabbitmq message queue testing section
 */
let pubChannel = null;
let offlinePubQueue = [];
function startPublisher() {
  amqpConn.createConfirmChannel(function (err, ch) {
    if (closeOnErr(err)) return;

    ch.on("error", function (err) {
      console.error("[AMQP] channel error", err.message);
    });
    ch.on("close", function () {
      console.error("[AMQP] channel closed");
    });

    pubChannel = ch;
    // Start processing for the pending offline queue items left on the queue if any
    let m;
    while ((m = offlinePubQueue.shift())) {
      if (!m) break;
      pubChannel.publish(m[0], m[1], m[2]);
    }
  });
}

/**
 * Enqueue a new task to the background task queue
 * @param {*} exchange then exchange name, default direct exchange to be ''
 * @param {*} routingKey the queue name, '', default will be the jobs queue
 * @param {*} content the item binary content. i.e.: Buffer.from(JSON.stringify(importTask))
 */
JobQueuer.prototype.publish = function publish(exchange, routingKey, content, cb) {
  if (!pubChannel) {
    debug("Publish channel for the Job Queue is not valid !");
    return;
  }

  pubChannel.publish(exchange, !routingKey ? JOB_QUEUE : routingKey, content, { persistent: true }, function (err) {
    if (err) {
      debug(err);
      offlinePubQueue.push([exchange, routingKey, content]);
      closeOnErr(err);
      cb && cb(err);
    }
    cb && cb();
    // debug(' [.] Published %s', content.toString());
  });
}

JobQueuer.prototype.publishJobTask = function publish(content, cb) {
  this.publish('', JOB_QUEUE, content, cb);
}

JobQueuer.prototype.publishLocTask = function publish(content, cb) {
  this.publish('', GDATA_QUEUE, content, cb);
}

function closeOnErr(err) {
  if (connTimer) clearTimeout(connTimer);
  if (!err) return false;
  console.error("[AMQP] error", err);
  if (amqpConn) {
    try {
      amqpConn.close();
    } catch (ignore) { }
  }
  return true;
}

/* ************************************************************************
SINGLETON CLASS DEFINITION
************************************************************************ */
JobQueuer.instance = null;

/**
* Singleton getInstance definition
* @return singleton class
*/
module.exports = {
  getInstance(ops) {
    // TODO: Add connection options to set connection params from the caller; refactor to ES6 class (optional)
    if (JobQueuer.instance === null) {
      debug("Created a new JobQueuer");
      JobQueuer.instance = new JobQueuer(ops);
    }
    return JobQueuer.instance;
  }
}