Node mini-server that extracts thumbnail images from Flipnote Studio PPM or KWZ animation files

flipnoteThumbnailServer.js

// requires promise-fs, gm and flipnote.js and imagemagick
// npm i promise-fs gm flipnote.js
// https://imagemagick.org/index.php

const http = require('http');
const path = require('path');
const url = require('url');
const fs = require('promise-fs');
const flipnote = require('flipnote.js/dist/node');
const gm = require('gm').subClass({imageMagick: true});

// may wanna change this or make it configurable from cli args or something
const PORT = 4000;
const USER_CONTENT_PATH = './';

const server = http.createServer();

server.on('request', (req, res) => {
  const parts = url.parse(req.url, true);
  const query = parts.query;

  const filename = query['filename'];
  const format = query['format'];

  if (!filename) {
    res.statusCode = 500;
    res.end('No filename specified');
    return;
  }

  // may wanna do extra santitisation but this should prevent path traversal bs
  const filepath = path.normalize(path.join(USER_CONTENT_PATH, filename));

  if (!fs.existsSync(filepath)) {
    res.statusCode = 500;
    res.end('File not found');
    return;
  }

  fs.readFile(filepath)
    .then(file => flipnote.parseSource(file.buffer))
    .then(note => {
      const gif = flipnote.gifEncoder.fromFlipnoteFrame(note, note.thumbFrameIndex);
      const gifBuffer = Buffer.from(gif.getBuffer());
      res.statusCode = 200;
      switch (format) {
        case 'png':
          res.setHeader('Content-Type', 'image/png');
          gm(gifBuffer, 'image.gif')
            .stream('png')
            .pipe(res);
          break;
        // gif is fastest but discord is shit at displaying them :(
        case 'gif':
        default:
          res.setHeader('Content-Type', 'image/gif');
          res.end(gifBuffer);
          break;
      }
    })
    .catch(err => {
      console.error(err);
      res.statusCode = 500;
      res.end('Could not generate thumbnail');
    });
})

server.listen(PORT, () => {
  console.log(`Server running at http://localhost:${ PORT }/`)
});