code: public Slice readSlice(int length)
      {
          Slice newSlice = slice.slice(position, length);
          position += length;
          return newSlice;
      }
docs: Returns a new slice of this buffer's sub-region starting at the current
  {@code position} and increases the {@code position} by the size
  of the new slice (= {@code length}).
  
  @param length the size of the new slice
  @return the newly created slice
  @throws IndexOutOfBoundsException if {@code length} is greater than {@code this.available()}