etherpad-lite/src/node/utils/MinifyWorker.js

'use strict';
/**
 * Worker thread to minify JS & CSS files out of the main NodeJS thread
 */

const CleanCSS = require('clean-css');
const Terser = require('terser');
const path = require('path');
const Threads = require('threads');

const compressJS = (content) => Terser.minify(content);

const compressCSS = (filename, ROOT_DIR) => new Promise((res, rej) => {
  try {
    const absPath = path.join(ROOT_DIR, filename);

    /*
       * Changes done to migrate CleanCSS 3.x -> 4.x:
       *
       * 1. Rework the rebase logic, because the API was simplified (but we have
       *    less control now). See:
       *    https://github.com/jakubpawlowicz/clean-css/blob/08f3a74925524d30bbe7ac450979de0a8a9e54b2/README.md#important-40-breaking-changes
       *
       *    EXAMPLE:
       *        The URLs contained in a CSS file (including all the stylesheets
       *        imported by it) residing on disk at:
       *            /home/muxator/etherpad/src/static/css/pad.css
       *
       *        Will be rewritten rebasing them to:
       *            /home/muxator/etherpad/src/static/css
       *
       * 2. CleanCSS.minify() can either receive a string containing the CSS, or
       *    an array of strings. In that case each array element is interpreted as
       *    an absolute local path from which the CSS file is read.
       *
       *    In version 4.x, CleanCSS API was simplified, eliminating the
       *    relativeTo parameter, and thus we cannot use our already loaded
       *    "content" argument, but we have to wrap the absolute path to the CSS
       *    in an array and ask the library to read it by itself.
       */

    const basePath = path.dirname(absPath);

    new CleanCSS({
      rebase: true,
      rebaseTo: basePath,
    }).minify([absPath], (errors, minified) => {
      if (errors) return rej(errors);

      return res(minified.styles);
    });
  } catch (error) {
    // on error, just yield the un-minified original, but write a log message
    console.error(`Unexpected error minifying ${filename} (${absPath}): ${error}`);
    callback(null, content);
  }
});

Threads.expose({
  compressJS,
  compressCSS,
});