index.js

const config = require('./config');

const escpos = require('escpos');
escpos.USB = require('escpos-usb');

const express = require('express');
const compression = require('compression');
const cors = require('cors');
const multer = require('multer');

const log = (m) => {
    config.enableLogs && console.log(m);
}

const logError = (m) => {
    log('ERROR: ' + m);
}

const initPrinter = () => {
    return new Promise((resolve, reject) => {
        const device = new escpos.USB(config.usbVendorId, config.usbProductId);
        const printer = new escpos.Printer(device);

        device.open(err => {
           if (err) {
               logError(err);
               reject(err);
           }
           else {
               resolve(printer);
           }
        });
    });
};

const printImage = (printer, url) => {
    return new Promise((resolve, reject) => {
        escpos.Image.load(url, async (image) => {
            if (!(image instanceof escpos.Image)) {
                const e = 'Couldnt convert the supplied image blob to escpos.Image';
                logError(e);
                reject(e);
                return;
            }
    
            try {
                await printer.image(image);
                printer.cut().close();
                resolve();
            }
            catch (err) {
                logError(err);
                reject(err);
            }
        });
    });
}

const handlePrint = async (req, res) => {
    if (!req.file) {
        logError('No blob attached');
        res.status(400).send('No blob attached');
        return;
    }

    if (!config.enableUsb) {
        log('Skipped print')
        res.send('Skipped');
        return;
    }

    try {
        const printer = await initPrinter();
        await printImage(printer, req.file.path);
        
        log('Completed print');
        res.send('OK');
    }
    catch (err) {
        logError(err);
        res.status(500).send(err);
    }
};

const app = express();

app.use(compression());
app.use(cors());
app.use(express.static(__dirname + '/public'));

const upload = multer({ 
    fileFilter: (req, file, cb) => {
        cb(null, file && file.mimetype == "image/png");
    },
    storage: multer.diskStorage({
        destination: (req, file, cb) => {
            cb(null, __dirname + '/uploads');
        },
        filename: (req, file, cb) => {
            const uniqueSuffix = Date.now() + '-' + Math.round(Math.random() * 1E9);
            cb(null, uniqueSuffix + '.png');
        }
    })
});


app.post('/print', upload.single('blob'), handlePrint);

app.listen(config.port, () => {
    log(`Listening at port ${config.port}...`);
});