A Simple Node.js Microservice Module

Captain-MS which means Captain MicroService is a simple module which provides a basic setup for a microservice project.

Installation

npm install @halagram/captain-ms --save

Optionally, you can also install the CLI tool for setting up Services easily using

npm install -g @halagram/captain-ms-cli

Creating a Service

    const captain = require('@halagram/captain-ms'); // require the module
    
    // instantiate the service
    let service = new captain.Service({
        name: "App Service",
        port: 3000
    }, new captain.Logger('AppServiceTag') /** An app logger instance **/);

    // create a router
    let router = require('express').Router();
    router.all('/greet', (req, res) => {
        res.send('Hello Captain!');
    });

    // set the service routes. This is produces app.use('/key', value);
    service.setRoutes({
        '': router
    });

    // start the service
    service.start();

You can also enable JWT for a router

    service.enableJWT({
        encryptionKey: password,
        secret: secret,
        allowed : {
            modelName : modelObject //allowed models that will access this route or service
        }
    });

    service.start();

Also, you can limit requests from same IPs

    service.enableRateLimiter({ 
        host: '127.0.0.1',
        port: 6379,
        environment: 'development',
        freeRetries: 2, // number of requests before delays
        minWait: 10 * 1000, // 10 seconds
    });

    service.start();

Message Queues

Message Queues are supported in captain-ms. Captain-ms uses ZeroMQ for its messages. The following types are supported:

• Request-Reply (req-rep)
• Publish-Subscribe (pub-sub)
• Push-Pull (push-pull)

Create a simple req-rep message broker like the sample below

const {StartReqRepBroker} = require('@halagram/captain-ms').MessageQueue

StartReqRepBroker(
    {port : 3001, identity : `Central Requester`},
    {port : 3002, identity : `Central Responder`}
);

To create a pub-sub broker,

const {StartPubSubBroker} = require('@halagram/captain-ms').MessageQueue

StartPubSubBroker(
    {port : 3003, identity : `Central Publisher`},
    {port : 3004, identity : `Central Subsciber`}
);

Then, you can create a requester and responder to connect to the req-rep broker and publisher and subscriber to connect to the pub-sub broker..

const { Requester, Responder, xSubscriber, xPublisher } = require('@halagram/captain-ms').MessageQueue;

let requester = Requester({port : 3001, identity : `Requester`});
let responder = Responder({port : 3002, identity : `Responder`});
let publisher = xPublisher({port : 3003, identity : `Publisher`});
let subscriber = xSubscriber({port : 3004, identity : `Subscriber`});

NOTE: You can also create a direct connection between the subscriber and publisher by using

const { Subscriber, Publisher } = require('@halagram/captain-ms').MessageQueue;

Sending and replying messages

You send messages via a requester then, the responder acts on and replies the message. Example is given below

let MSG_TYPE = 'TWO_ADDER';

requester.request({type: MSG_TYPE, number: 7}, (response) => {
    logger.debug(response); // prints '9' on the console
});

responder.$on(MSG_TYPE, (msg) => {
    let result = msg.number + 2;
    responder.reply(result); // sends the response back to the requester
});

...

Middlewares

File upload middlewares

File uploads are done by middlewares and throws errors if any occurs

    captain.Validator.files({}, 'files'); // this uploads files to a 'files' base directory

Usage:

    router.post('/upload', captain.Validator.files({avatar :{
        folder : 'media', // the folder to store the files
        required : true, // this file is not optional
        max: 3, // allow a maximum of 3 files
        len : 2, // allow only 2 files
        min : 1, // allow a minimum of 1 file
        exclude : null, // array of file types to reject
        include : ["video", "image"] // allow image/* and video/*
    }}, 'files'), (req, res, next) => {
        req.uploads.upload(); // to perform an upload
        req.uploads.rollback(); // to perform a rollback
        res.json(req.uploads.files);
    });

Utilities

Using the Crypto Utility class

This class can be used to generates hashes, compare them to raw texts, encrypt and decrypt data. Ex

    // to perfprm a hash
    captain.Crypto.hash('text');

    // to compare a hash
    captain.Crypto.compare('text', 'hash-of-text');

The above methods return promises; where the hash method resolves a hash and the compare method resolves true if the hash matches the text

    // to encrypt an object or string
    let encrypted = captain.Crypto.encrypt('encryption-key', 'password');

    // to decrypt an encrypted object or string
    let decrypted = captain.Crypto.decrypt('encryption-key', 'encrypted-value');

Generating tokens

Use the JWT utility class to generate tokens and make sure you decrypt them by using the jwt().decrypt middleware

    let token = captain.JWT.getToken({ name: 'captain', lang: 'nodejs' }, 'secret', 'encryption-key');

Using the Logger

The Logger has a constructor which receives two arguments; the first is the log tag while the second is the environment which could be 'development' or 'production'. The development environment permits logging while the production does not, as console logging is done synchronously.

    /** This logs some text on the console **/
    let logger = new captain.Logger('CaptainTag', 'development');
    logger.debug('log some debug text');

    /** This does NOT log any text on the console **/
    let logger = new captain.Logger('CaptainTag');
    logger.debug('log some debug text');

The Logger has five methods:

    logger.debug('log some debug text');

    logger.success('connection accepted on port 8080');

    logger.warn('log some warning text', 'WarningTag'); // logs some value with the custom tag

    logger.error('log some error text');

    logger.trace('log some trace');

Using the Validator Middlewares

    // to perform a validation on the request body, use the body method while passing a JOI schema
    router.all('/', captain.Validator.body(schema), (req, res, next) => {
        res.send('Validation passed');
    });