docs: int getRealIndex(int index) throws HpackException {
          //the index is one based, but our table is zero based, hence -1
          //also because of our ring buffer setup the indexes are reversed
          //index = 1 is at position firstSlotPosition + filledSlots
          int newIndex = (firstSlotPosition + (filledTableSlots - index)) % headerTable.length;
          if(newIndex < 0) {
              throw UndertowMessages.MESSAGES.invalidHpackIndex(index);
          }
          return newIndex;
      }