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Support byte for byte identical compression #360

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81efff4
stops embedding a timestamp in gzip header
mattviasat Aug 27, 2026
5ff0624
enable testByteforbyte on GNU tar
mattviasat Aug 27, 2026
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5 changes: 4 additions & 1 deletion makeself.sh
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Original file line number Diff line number Diff line change
Expand Up @@ -499,7 +499,10 @@ fi

case $COMPRESS in
gzip)
GZIP_CMD="gzip -c$COMPRESS_LEVEL"
# --no-name: omit the filename/timestamp from the gzip member
# header. Without it, the compressed output differ on every run even
# when the input is byte-for-byte identical.
GZIP_CMD="gzip --no-name -c$COMPRESS_LEVEL"
GUNZIP_CMD="gzip -cd"
;;
pigz)
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7 changes: 3 additions & 4 deletions test/datetest
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Expand Up @@ -94,10 +94,9 @@ testByteforbyte()
{
date='Sat Mar 3 19:35:21 EST 2016'

# bsdtar does not have option --mtime
# TODO: unstable test: first second differ: char 242, line 10

startSkipping
# GNU tar supports --tar-extra's --mtime option used below.
# bsdtar (Mac/BSD) does not.
tar --version 2>/dev/null | grep -q GNU || startSkipping

@mattviasat mattviasat Aug 27, 2026

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We can enable this test when we are using GNU tar now.

Mac /opt/homebrew/bin/gtar

bash datetest -- testByteforbyte # /opt/homebrew/bin/gtar
testByteforbyte
Header is 772 lines long

About to compress 4 KB of data...
Adding files to archive named "src.sh"...
/opt/homebrew/bin/gtar: Option --mtime: Treating date '20160303' as 2016-03-03 00:00:00
./startup.sh
CRC: 1520247960
MD5: 21a99f115e4b3125a76fef4d4d203432

Self-extractable archive "src.sh" successfully created.
Header is 772 lines long

About to compress 4 KB of data...
Adding files to archive named "src.sh"...
/opt/homebrew/bin/gtar: Option --mtime: Treating date '20160303' as 2016-03-03 00:00:00
./startup.sh
CRC: 1520247960
MD5: 21a99f115e4b3125a76fef4d4d203432

Self-extractable archive "src.sh" successfully created.

Ran 1 test.

OK

It still does not work on bsdtar.

Mac /usr/bin/bsdtar

bash datetest -- testByteforbyte
testByteforbyte
Header is 772 lines long

About to compress 4 KB of data...
Adding files to archive named "src.sh"...
bsdtar: Option --mtime is not supported
Usage:
  List:    bsdtar -tf <archive-filename>
  Extract: bsdtar -xf <archive-filename>
  Create:  bsdtar -cf <archive-filename> [filenames...]
  Help:    bsdtar --help
ERROR: failed to create temporary archive: /var/folders/2x/mv56x8w15pb0lv1ql29c99lm0000gp/T//mkself69625.tar
mv: rename src.sh to first: No such file or directory
Header is 772 lines long

About to compress 4 KB of data...
Adding files to archive named "src.sh"...
bsdtar: Option --mtime is not supported
Usage:
  List:    bsdtar -tf <archive-filename>
  Extract: bsdtar -xf <archive-filename>
  Create:  bsdtar -cf <archive-filename> [filenames...]
  Help:    bsdtar --help
ERROR: failed to create temporary archive: /var/folders/2x/mv56x8w15pb0lv1ql29c99lm0000gp/T//mkself69649.tar
mv: rename src.sh to second: No such file or directory
cmp: first: No such file or directory
ASSERT:expected:<2> but was:<0>
shunit2:ERROR testByteforbyte() returned non-zero return code.

Ran 1 test.

FAILED (failures=1)


# Exercise
${SUT} --packaging-date "${date}" --tar-extra "--mtime 20160303" \
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