code: function _btoh (bytes) {
     if (bytes) {
        var res = '';
        for (var i = 0; i < bytes.length; ++i) {
           res += ('0' + (bytes[i] & 0xFF).toString(16)).slice(-2);
        }
        return res;
     } else {
        return null;
     }
  }
docs: / Convert array of bytes to hex string.