code: public HpackHeaderField getEntry(int index) {
          if (index <= 0 || index > length()) {
              throw new IndexOutOfBoundsException();
          }
          int i = head - index;
          if (i < 0) {
              return hpackHeaderFields[i + hpackHeaderFields.length];
          } else {
              return hpackHeaderFields[i];
          }
      }
docs: Return the header field at the given index. The first and newest entry is always at index 1,
  and the oldest entry is at the index length().