getFileSize.js

const express = require('express');

const app = express();

app.post('/file', (req, res, next) => {
    let first = true;

    req.on('data', chunk => {
        if (!first) {
            return;
        }

        console.log('file extension is', chunk.slice(1, 4).toString());
        console.log('PNG width is', chunk.readUIntBE(16, 4));
        console.log('PNG height is', chunk.readUIntBE(20, 4));
        first = false;
    });

    req.on('end', () => {
        res.send('done');
    })

    req.on('error', next);
});

app.use((err, req, res, next) => {
    res.send('error' + JSON.stringify(err));
});

app.listen('3000');