source: frontend/node_modules/gzip-size/index.js

'use strict';
const fs = require('fs');
const stream = require('stream');
const zlib = require('zlib');
const {promisify} = require('util');
const duplexer = require('duplexer');

const getOptions = options => ({level: 9, ...options});
const gzip = promisify(zlib.gzip);

module.exports = async (input, options) => {
        if (!input) {
                return 0;
        }

        const data = await gzip(input, getOptions(options));
        return data.length;
};

module.exports.sync = (input, options) => zlib.gzipSync(input, getOptions(options)).length;

module.exports.stream = options => {
        const input = new stream.PassThrough();
        const output = new stream.PassThrough();
        const wrapper = duplexer(input, output);

        let gzipSize = 0;
        const gzip = zlib.createGzip(getOptions(options))
                .on('data', buf => {
                        gzipSize += buf.length;
                })
                .on('error', () => {
                        wrapper.gzipSize = 0;
                })
                .on('end', () => {
                        wrapper.gzipSize = gzipSize;
                        wrapper.emit('gzip-size', gzipSize);
                        output.end();
                });

        input.pipe(gzip);
        input.pipe(output, {end: false});

        return wrapper;
};

module.exports.file = (path, options) => {
        return new Promise((resolve, reject) => {
                const stream = fs.createReadStream(path);
                stream.on('error', reject);

                const gzipStream = stream.pipe(module.exports.stream(options));
                gzipStream.on('error', reject);
                gzipStream.on('gzip-size', resolve);
        });
};

module.exports.fileSync = (path, options) => module.exports.sync(fs.readFileSync(path), options);