downloadFromFs.js

const DIR = os.homedir() + '/.foo';

// adapted from  https://stackoverflow.com/a/24977085/3183756
const downloadFromFs = (req, res) => {
  const { name } = req.params;
  const filePath = path.join(DIR, name);
  fs.stat(filePath, (err, stats) => {
    if (err) {
      if (err.code === 'ENOENT') {
        // 404 Error if file not found
        return res.status(404).end();
      }
      return res.status(400).end(err.message);
    }
    const range = req.headers.range;

    let headers = {
      'Content-Disposition': `inline; filename=${name}`,
      'Accept-Ranges': 'bytes',
      'Content-Length': stats.size,
      'Content-Type': mime.getType(name),
    };
    let status = 200;
    let streamOpts;

    if (range) {
      status = 206;
      const positions = range.replace(/bytes=/, '').split('-');
      const start = parseInt(positions[0], 10);
      const total = stats.size;
      const end = Math.max(start, positions[1] ? parseInt(positions[1], 10) : total - 1);
      const chunkSize = end - start + 1;

      Object.assign(headers, {
        'Content-Range': 'bytes ' + start + '-' + end + '/' + total,
        'Content-Length': chunkSize,
      });
      streamOpts = { start, end };
    }

    res.writeHead(status, headers);

    const stream = fs
      .createReadStream(filePath, streamOpts)
      .on('open', () => {
        stream.pipe(res);
      })
      .on('error', err => {
        res.end(err.message);
      });
  });
};