Using node app inside an express js server

Question

I have an Express js server endpoint with the following directory structure:

app.js
node_modules
package-lock.json
package.json
mrz-detection

The mrz-detection directory, contains a node app which I would normally call from the command line like this node run/getMrz.js --file passport.jpg

My app.js looks like this

const { getMrz } = require('./mrz-detection');
const fs = require('fs');
const app = express()
const port = 3000
const bodyParser = require('body-parser');
app.use(bodyParser.json({limit: '10mb', extended: true}));
var passportsArr = [];


app.post('/', function(req, res) {
    var passport = req.body;
    let buff = new Buffer(passport.data, 'base64');
    fs.writeFileSync('passport.png', buff);
    // send passport photo to mrz-detection app here
})

app.listen(port, () => console.log(`Mrz detection app listening at http://localhost:${port}`))

I need to call the mrz-detection app from my post route in the app.js

How would I do that?

Does this answer your question? [Node.js spawn child process and get terminal output live](https://stackoverflow.com/questions/14332721/node-js-spawn-child-process-and-get-terminal-output-live) — Ayush Gupta, Apr 11 '20 at 17:22
mrz-detection is a package :/ implement it in the post method, the code in `run` folder is just wrapping it for cli — Lawrence Cherone, Apr 11 '20 at 17:33

score 0 · Answer 1 · answered Apr 11 '20 at 17:27

There are two ways I can think of to do this:

Call the other program command-line-style as explained by a commentor
Refactor your code so that you can simply import a function from your other file and use it. I would recommend this more because it allows for complex parameters to potentially be passed without having to serialize and deserialize them in the command line.

score 0 · Answer 2 · answered Apr 11 '20 at 17:34

You could you start the app as a child process:

https://nodejs.org/api/child_process.html

There are a few different 'child_process' functions for spawning child processes

execFile spawn fork

With fork, sending messages between parent and child works automatically

const fork = require('child_process').fork;
const child = fork('/path/to/app.js', ['optional', 'arguments']);

// message from child
child.on('message', (msg) => {
    console.log('message from child ' + msg);
}

// send message to child
child.send({hi:'hi from parent'});

Using node app inside an express js server

2 Answers2