Simple microservice with Seneca and Express

Microservice implementation

Installing microservice dependencies

mkdir mathms
cd mathms
npm init
npm i seneca -S

Seneca 'Math' plugin

File mathms/MathPlugin.js:

module.exports = function MathPlugin(options) {
    this.add('role:math,cmd:sum', sum);
    this.add('role:math,cmd:product', product);

    // middleware for 'role:math,*' pins, that prepares values and calls actions themselves
    this.wrap('role:math', function (msg, respond) {
        msg.left = Number(msg.left).valueOf();
        msg.right = Number(msg.right).valueOf();

        // execute previously matched action
        this.prior(msg, respond);
    });

    function sum(msg, respond) {
        respond(null, {answer: msg.left + msg.right});
    }

    function product(msg, respond) {
        respond(null, {answer: msg.left * msg.right});
    }
};

Seneca 'Math' microservice

File mathms/MathMS.js:

require('seneca')()
    .use('MathPlugin') // equal to .use(require('./MathPlugin'))
    .listen({
        type: 'tcp', // communicate via TCP
        pin: 'role:math' // listen only this pin pattern
    });

Running the microservice

Run our mathms/MathMS.js with the following command:

node MathMS

Sample output looks like to this:

2016-04-26T08:21:53.579Z iqpuwz8vca8t/1461658913554/2348/- INFO hello   Seneca/2.0.1/iqpuwz8vca8t/1461658913554/2348/-
2016-04-26T08:21:54.924Z iqpuwz8vca8t/1461658913554/2348/- INFO listen  {type:tcp,pin:role:math}

Express application implementation

Installing application dependencies

mkdir myapp
cd myapp
npm init
npm i express body-parser seneca -S

Seneca 'MathAPI' plugin

File myapp/MathAPI.js:

module.exports = function MathAPI(options) {

    // valid operations list
    var valid_ops = {sum: 'sum', product: 'product'};

    this.add('role:api,path:calculate', function (msg, respond) {
        // talking to the microservice
        this.act('role:math', {
            cmd: valid_ops[msg.operation],
            left: msg.left,
            right: msg.right
        }, respond);
    });

    // plugin initialization
    this.add('init:MathAPI', function (msg, respond) {
        // http://localhost:3000/api/calculate/sum?left=2&right=3
        //                       ^      ^       ^   ^-------^
        //                  prefix action operation arguments
        this.act('role:web', {
            use: {
                prefix: '/api',
                pin: 'role:api,path:*',
                map: {
                    calculate: {GET: true, suffix: '/:operation'}
                }
            }
        }, respond);
    });
};

Express application

File myapp/server.js:

var seneca = require('seneca')()
    .use('MathAPI') // equal to .use(require('./MathAPI'))
    .client({type: 'tcp', pin: 'role:math'});

var app = require('express')()
    .use(require('body-parser').json())
    .use(seneca.export('web'))
    .listen(3000);

Running the express application

node server.js

Sample output looks like to this:

2016-04-26T08:24:40.571Z obe5f3hoxbu4/1461659080545/7820/- INFO hello   Seneca/2.0.1/obe5f3hoxbu4/1461659080545/7820/-
2016-04-26T08:24:40.944Z obe5f3hoxbu4/1461659080545/7820/- INFO client  {type:tcp,pin:role:math}

Testing express application

Send GET requests to the following URLs or open them in a web browser:

• http://localhost:3000/api/calculate/sum?left=2&right=3 outputs {answer: 5}
• http://localhost:3000/api/calculate/product?left=2&right=3 outputs {answer: 6}

Resources

• Seneca
• Seneca Web Server Integration example
• Express