salix/modules/invoiceOut/back/methods/invoiceOut/downloadZip.js

const JSZip = require('jszip');
const fs = require('fs-extra');
const UserError = require('vn-loopback/util/user-error');

module.exports = Self => {
    Self.remoteMethodCtx('downloadZip', {
        description: 'Download a zip file with multiple invoices pdfs',
        accessType: 'READ',
        accepts: [
            {
                arg: 'ids',
                type: 'string',
                description: 'The invoices ids',
            }
        ],
        returns: [
            {
                arg: 'body',
                type: 'file',
                root: true
            }, {
                arg: 'Content-Type',
                type: 'string',
                http: {target: 'header'}
            }, {
                arg: 'Content-Disposition',
                type: 'string',
                http: {target: 'header'}
            }
        ],
        http: {
            path: '/downloadZip',
            verb: 'GET'
        },
        accessScopes: ['DEFAULT', 'read:multimedia']
    });

    Self.downloadZip = async function(ctx, ids, options) {
        const models = Self.app.models;
        const myOptions = {};
        const zip = new JSZip();

        if (typeof options == 'object')
            Object.assign(myOptions, options);

        const zipConfig = await models.ZipConfig.findOne(null, myOptions);
        let totalSize = 0;
        ids = ids.split(',');

        for (let id of ids) {
            if (zipConfig && totalSize > zipConfig.maxSize) throw new UserError('Files are too large');
            const invoiceOutPdf = await models.InvoiceOut.download(ctx, id, myOptions);
            const fileName = extractFileName(invoiceOutPdf[2]);
            const body = invoiceOutPdf[0];
            const sizeInBytes = (await fs.promises.stat(body.path)).size;
            const sizeInMegabytes = sizeInBytes / (1024 * 1024);
            totalSize += sizeInMegabytes;
            zip.file(fileName, body);
        }

        const stream = zip.generateNodeStream({streamFiles: true});

        return [stream, 'application/zip', `filename="download.zip"`];
    };

    function extractFileName(str) {
        const matches = str.match(/"(.*?)"/);
        return matches ? matches[1] : str;
    }
};