function addXSetMember (key, timestamp, field, value, res, next) {
  let redisConnection = res.locals.connection;
  myutil.decodeHTMLEntities(field, function (decodedField) {
    myutil.decodeHTMLEntities(value, function (decodedValue) {
      redisConnection.xadd(key, timestamp, decodedField, decodedValue, function (err) {
        if (err) {
          console.error('addXSetMember', err);
          return next(err);
        }
        return res.send('ok');
      });
    });
  });
}
Stream related functions (XSet) - only add and delete allowed, no edit