Support byte for byte identical compression - #361
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Identical input data should produce identical output date.
mattviasat
commented
Aug 27, 2026
| # --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" |
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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)
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GZIP_CMDnow passes--no-nameto gzip, so it stops embedding a fresh timestamp in the compressed archive's header on every packaging run.With this change, we will always see the same output if we receive the same input. This helps when diffing the output of makeself.