Create an Application for Producing Messages

Use the following code to create a manifest.yml file that binds your application to the messaging service.

You need to add domain, messaging service and your queue name in the indicated spaces.

applications:
      - name: producer
        host: producer-host
        domain: <REPLACE WITH YOUR DOMAIN>
        buildpack: https://github.com/cloudfoundry/nodejs-buildpack
        memory: 256M
        health-check-type: none
        path: .
        command: node producer.js
        services:
        - <REPLACE WITH YOUR MESSAGING SERVICE>

env:
      SAP_JWT_TRUST_ACL: "[{\"clientid\":\"*\",\"identityzone\":\"*\"}]"
      SAP_XBEM_BINDINGS: >
        {
          "inputs": {},
          "outputs": {
            "myOutA" : {
              "service": "<REPLACE WITH YOUR MESSAGING SERVICE>,
              "address": "topic:<REPLACE WITH YOUR TOPIC>",
              "reliable": false
            },
            "myOutB" : {
              "service": "<REPLACE WITH YOUR MESSAGING SERVICE>,
              "address": "topic:<REPLACE WITH YOUR TOPIC>",
              "reliable": false
            }
          }
        }

Create a package.json file to list the packages your project depends on and to specify versions of a package that your project can use. This makes your build reproducible, and therefore easier to share with other developers.

{
        "name": "producer",
        "description": "Simple NodeJS Application producing messages",
        "version": "0.0.1",
        "engines": {
                "node": ">=6.9.1"
        },
        "dependencies": {
                "@sap/xb-msg": ">=0.2.4",
                "@sap/xb-msg-amqp-v100": "^0.9.17",
                "@sap/xb-msg-env": ">=0.2.1",
                "@sap/xsenv": "1.2.8"
        },
        "scripts": {
                "start": "node producer.js"
        }
}

Use the following code to create a producer.js file. This file holds the actual application. Find descriptions of what it does as comments in the coding.

On a higher level you do the following:

1. Perform settings in respect to Node.js modules and to messaging.

2. Get the messaging options from the environment.

3. The messaging client is instantiated using the options.

4. Client and stream handler methods are defined.

As a result, the application sends messages to the defined topic and writes a quick info including a counter into the log file.

use strict;

//------------------------------------------------------------------------------------------------------------------
//  Basic setup in respect to modules, messaging settings and getting messaging options
//------------------------------------------------------------------------------------------------------------------

const msg = require('@sap/xb-msg');
const env = require('@sap/xb-msg-env');
const xsenv = require('@sap/xsenv');
const service = '<REPLACE WITH YOUR MESSAGING SERVICE>';
const taskList = {
    myOutA : { topic: '<REPLACE WITH YOUR TOPIC>' , timerMin: 1, timerMax: 11 },
    myOutB : { topic: '<REPLACE WITH YOUR TOPIC>' , timerMin: 5, timerMax:  8 }
};
var counter = 1;

xsenv.loadEnv();

//------------------------------------------------------------------------------------------------------------------
// Start messaging client
//------------------------------------------------------------------------------------------------------------------

const client = new msg.Client(env.msgClientOptions(service, [], ['myOutA', 'myOutB']));


function setupOptions(tasks, options) {
    Object.getOwnPropertyNames(tasks).forEach((id) => {
        const task = tasks[id];
        options.destinations[0].ostreams[id] = {
            channel: 1,
            exchange: 'amq.topic',
            routingKey: task.topic
        };
    });
    return options;
}

function getRandomInt(min, max) {
    min = Math.ceil(min);
    max = Math.floor(max);
    return (Math.floor(Math.random() * (max - min + 1)) + min) * 1000;
}

function initTasks(tasks, client) {
    Object.getOwnPropertyNames(tasks).forEach((id) => {
        const task = tasks[id];
        const stream = client.ostream(id);

        const handler = () => {
            console.log('publishing message number ' + counter + ' to topic ' + task.topic);

            const message = {
                target: { address: 'topic:' + task.topic },
                payload: Buffer.from("Message Number " + counter)

            };
            if (!stream.write(message)) {
                console.log('wait');
                return;
            }
            setTimeout(handler, getRandomInt(task.timerMin, task.timerMax));
            counter++;
        };

        stream.on('drain', () => {
            setTimeout(handler, getRandomInt(task.timerMin, task.timerMax));
        });

        setTimeout(handler, getRandomInt(task.timerMin, task.timerMax));
    });
}

//------------------------------------------------------------------------------------------------------------------
// Messaging client handler methods
//------------------------------------------------------------------------------------------------------------------

client
    .on('connected', () => {
        console.log('connected');
        initTasks(taskList, client);
    })
    .on('drain', () => {
        console.log('continue');
    })
    .on('error', (error) => {
        console.log(error);
    });

client.connect();