app.js

/**
 * Captcha PNG img generator
 * @Author: Chakshu Gautam
 * @Email: chaks.gautam@gmail.com
 * @Version: 2.0
 * @Date: 2020-08-18
 * @license http://www.opensource.org/licenses/bsd-license.php BSD License
 */
const {v1: uuid} = require('uuid');

const captchapng = require('./captchapng');
const cors = require('cors')

const express = require('express');
const app = express()
const port = process.env.PORT || 9000

const low = require('lowdb');
const FileSync = require('lowdb/adapters/FileSync');
const adapter = new FileSync('db.json');
const db = low(adapter);
app.use(cors({
    origin: '*',
    optionsSuccessStatus: 200,
}));

db.defaults({ captchas: []}).write();

app.listen(port, () => console.log(`listening on port: ${port}`))

app.get('/', (request, response) => {

    const captchaParsed = parseInt(Math.random()*900000+100000);
    var p = new captchapng(120, 30, captchaParsed); // width,height,numeric captcha
    p.color(0, 0, 0, 0);  // First color: background (red, green, blue, alpha)
    p.color(80, 80, 80, 255); // Second color: paint (red, green, blue, alpha)

    var img = p.getBase64();
    var imgbase64 = new Buffer(img,'base64');

    const token = uuid();
    db.get('captchas').push({token, captchaParsed, timestamp: Math.floor(Date.now() / 1000)}).write();
    console.log({token});

    response.header({
        'Content-Type': 'image/png',
        token,
        'access-control-expose-headers': 'token'
    });

    // Request token
    response.send(imgbase64);
});

const removeOldCaptchas = () => {
    // Delete all captchas that are more than 600 seconds old.
    const now = Math.floor(Date.now() / 1000);
    const allData = db.get('captchas').value();

    console.log({now});
    allData.filter(captcha => now - captcha.timestamp > 600).forEach(filteredCaptcha => {
        db.get('captchas').remove({ token: filteredCaptcha.token }).write();
    })
}

app.get('/verify', (request, response) => {

    removeOldCaptchas();

    try{
        const userResponse = request.query.captcha;
        const token = request.query.token;
        const captcha = db.get('captchas').find({ token: token }).value();
        
        if(!captcha) {response.status(400).send({status: "Token Not Found"}); return;}
        
        deleteUsedCaptcha(token); 
        if (parseInt(userResponse) === (captcha && captcha.captchaParsed)) {
            response.status(200).send({status: "Success"});
        }else {
            response.status(400).send({status: "Code Incorrect"});
        }
    }catch(err){
        console.log({err});
        response.status(500).send({status: "Internal Server Error"});
    }
});
function deleteUsedCaptcha(token) {
    db.get('captchas').remove({ token: token }).write();
}