| commit | 23fcf8b09f5baee0a24bb39ad24263541333a759 | [log] [tgz] |
|---|---|---|
| author | René Scharfe <l.s.r@web.de> | Wed Jun 15 19:04:09 2022 +0200 |
| committer | Junio C Hamano <gitster@pobox.com> | Wed Jun 15 13:19:47 2022 -0700 |
| tree | a2cfad69c3f51a44ffef7f3784510193127a0ee8 | |
| parent | 76d7602631a9d0cb67cc1b848d580b862dc5de8b [diff] |
archive-tar: use OS_CODE 3 (Unix) for internal gzip
gzip(1) encodes the OS it runs on in the 10th byte of its output. It
uses the following OS_CODE values according to its tailor.h [1]:
0 - MS-DOS
3 - UNIX
5 - Atari ST
6 - OS/2
10 - TOPS-20
11 - Windows NT
The gzip.exe that comes with Git for Windows uses OS_CODE 3 for some
reason, so this value is used on practically all supported platforms
when generating tgz archives using gzip(1).
Zlib uses a bigger set of values according to its zutil.h [2], aligned
with section 4.4.2 of the ZIP specification, APPNOTE.txt [3]:
0 - MS-DOS
1 - Amiga
3 - UNIX
4 - VM/CMS
5 - Atari ST
6 - OS/2
7 - Macintosh
8 - Z-System
10 - Windows NT
11 - MVS (OS/390 - Z/OS)
13 - Acorn Risc
16 - BeOS
18 - OS/400
19 - OS X (Darwin)
Thus the internal gzip implementation in archive-tar.c sets different
OS_CODE header values on major platforms Windows and macOS. Git for
Windows uses its own zlib-based variant since v2.20.1 by default and
thus embeds OS_CODE 10 in tgz archives.
The tar archive for a commit is generated consistently on all systems
(by the same Git version). The OS_CODE in the gzip header does not
influence extraction. Avoid leaking OS information and make tgz
archives constistent and reproducable (with the same Git and libz
versions) by using OS_CODE 3 everywhere.
At least on macOS 12.4 this produces the same output as gzip(1) for the
examples I tried:
# before
$ git -c tar.tgz.command='git archive gzip' archive --format=tgz v2.36.0 | shasum
3abbffb40b7c63cf9b7d91afc682f11682f80759 -
# with this patch
$ git -c tar.tgz.command='git archive gzip' archive --format=tgz v2.36.0 | shasum
dc6dc6ba9636d522799085d0d77ab6a110bcc141 -
$ git archive --format=tar v2.36.0 | gzip -cn | shasum
dc6dc6ba9636d522799085d0d77ab6a110bcc141 -
[1] https://git.savannah.gnu.org/cgit/gzip.git/tree/tailor.h
[2] https://github.com/madler/zlib/blob/master/zutil.h
[3] https://pkware.cachefly.net/webdocs/casestudies/APPNOTE.TXT
Helped-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Signed-off-by: René Scharfe <l.s.r@web.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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