code: public byte[] getPreviewChunkBytes(int chkIdx) {
      if (chkIdx >= nChunks())
        throw new H2OIllegalArgumentException("Asked for chunk index beyond the number of chunks.");
      if (chkIdx == 0)
        return chunkForChunkIdx(chkIdx)._mem;
      else { //must eat partial lines
        // FIXME: a hack to consume partial lines since each preview chunk is seen as cidx=0
        byte[] mem = chunkForChunkIdx(chkIdx)._mem;
        int i = 0, j = mem.length-1;
        while (i < mem.length && mem[i] != CHAR_CR && mem[i] != CHAR_LF) i++;
        while (j > i && mem[j] != CHAR_CR && mem[j] != CHAR_LF) j--;
        if (j-i > 1) return Arrays.copyOfRange(mem,i,j);
        else return null;
      }
    }
docs: Get all the bytes of a given chunk.
  Useful for previewing sections of files.
  
  @param chkIdx index of desired chunk
  @return array of initial bytes