code: async function gzip(input, dst, level=4){
      // is input a filename or stream ?
      if (typeof input === 'string'){
          input = await _fileInputStream(input);
      }
  
      // compress
      const gzipStream = input.pipe(_zlib.createGzip({
          level: level
      }));
  
      // write content to file
      return _fileOutputStream(gzipStream, dst);
  }
docs: compress a file