On: Decompressing a Gzip File by Hand

[thomastay]

Wow! This program is really cool and I'm honestly not surprised it's written by Mark Adler, the guy who wrote zlib, that guy is an amazing programmer.

Thanks, this would have saved me a bunch of time and I wish I'd known this before writing this article. I'll add it in as a footnote later on.

For anyone who's curious, here's the output of the infgen program on the gzip file in the article (I remade the file so the timestamp is different)

  $ cat test.out.gz | ./infgen -ddis
  ! infgen 2.6 output
  !
  time 1637813470 ! UTC Thu Nov 25 04:11:10 2021
  name 'test.out
  gzip
  !
  last                    ! 1
  fixed                   ! 01
  literal 'a              ! 10010001
  literal 'a              ! 10010001
  match 6 1               ! 00000 0000100
  literal 10              ! 00111010
  end                     ! 0000000
  ! stats literals 8.0 bits each (24/3)
  ! stats matches 66.7% (1 x 6.0)
  ! stats inout 5:6 (4) 9 0
                          ! 00
  ! stats total inout 5:6 (4) 9
  ! stats total block average 9.0 uncompressed
  ! stats total block average 4.0 symbols
  ! stats total literals 8.0 bits each
  ! stats total matches 66.7% (1 x 6.0)
  !
  crc
  length

[cesarb → thomastay]

> (I remade the file so the timestamp is different)

That's why you should always use "gzip -n". Having the file name and timestamp in the compressed file header was IMO a mistake, and newer single-file compressors (bzip2, xz, zstd) AFAIK don't even have these fields in their native file format.

[Rendello → thomastay]

Woah! I didn't even notice it was him. Most of the accepted answers relating to anything Deflate are by him on Stack Overflow, so I shouldn't be surprised.

[tinus_hn → thomastay]

If you use the < operator you don’t need to spawn a ‘cat’ process that does nothing but copy around the contents of the file.