From: "René Scharfe" <l.s.r@web.de>
To: git@vger.kernel.org
Cc: "Junio C Hamano" <gitster@pobox.com>,
"Johannes Schindelin" <johannes.schindelin@gmx.de>,
"Rohit Ashiwal" <rohit.ashiwal265@gmail.com>,
"Ævar Arnfjörð Bjarmason" <avarab@gmail.com>,
"Jeff King" <peff@peff.net>,
"brian m . carlson" <sandals@crustytoothpaste.net>
Subject: [PATCH v3 4/5] archive-tar: use OS_CODE 3 (Unix) for internal gzip
Date: Sun, 12 Jun 2022 08:18:20 +0200 [thread overview]
Message-ID: <0a6877c3-07f2-b0e2-f23c-9ea4c588e8a5@web.de> (raw)
In-Reply-To: <217a2f4d-4fc2-aaed-f5c2-1b7e134b046d@web.de>
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.
NB: The function deflateSetHeader() was introduced by zlib 1.2.2.1,
released 2004-10-31.
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
Signed-off-by: René Scharfe <l.s.r@web.de>
---
Perhaps makes sense for remote-curl as well (out of scope of this
series)?
archive-tar.c | 9 +++++++++
1 file changed, 9 insertions(+)
diff --git a/archive-tar.c b/archive-tar.c
index 53d0ef685c..bf7e321e0e 100644
--- a/archive-tar.c
+++ b/archive-tar.c
@@ -460,6 +460,14 @@ static void tgz_write_block(const void *data)
static const char internal_gzip_command[] = "git archive gzip";
+static void tgz_set_os(git_zstream *strm, int os)
+{
+#if ZLIB_VERNUM >= 0x1221
+ struct gz_header_s gzhead = { .os = os };
+ deflateSetHeader(&strm->z, &gzhead);
+#endif
+}
+
static int write_tar_filter_archive(const struct archiver *ar,
struct archiver_args *args)
{
@@ -473,6 +481,7 @@ static int write_tar_filter_archive(const struct archiver *ar,
if (!strcmp(ar->filter_command, internal_gzip_command)) {
write_block = tgz_write_block;
git_deflate_init_gzip(&gzstream, args->compression_level);
+ tgz_set_os(&gzstream, 3); /* Unix, for reproducibility */
gzstream.next_out = outbuf;
gzstream.avail_out = sizeof(outbuf);
--
2.36.1
next prev parent reply other threads:[~2022-06-12 6:18 UTC|newest]
Thread overview: 74+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-04-12 23:04 [PATCH 0/2] Avoid spawning gzip in git archive Johannes Schindelin via GitGitGadget
2019-04-12 23:04 ` [PATCH 1/2] archive: replace write_or_die() calls with write_block_or_die() Rohit Ashiwal via GitGitGadget
2019-04-13 1:34 ` Jeff King
2019-04-13 5:51 ` Junio C Hamano
2019-04-14 4:36 ` Rohit Ashiwal
2019-04-26 14:29 ` Johannes Schindelin
2019-04-26 23:44 ` Junio C Hamano
2019-04-29 21:32 ` Johannes Schindelin
2019-05-01 18:09 ` Jeff King
2019-05-02 20:29 ` René Scharfe
2019-05-05 5:25 ` Junio C Hamano
2019-05-06 5:07 ` Jeff King
2019-04-14 4:34 ` Rohit Ashiwal
2019-04-14 10:33 ` Junio C Hamano
2019-04-26 14:28 ` Johannes Schindelin
2019-05-01 18:07 ` Jeff King
2019-04-12 23:04 ` [PATCH 2/2] archive: avoid spawning `gzip` Rohit Ashiwal via GitGitGadget
2019-04-13 1:51 ` Jeff King
2019-04-13 22:01 ` René Scharfe
2019-04-15 21:35 ` Jeff King
2019-04-26 14:51 ` Johannes Schindelin
2019-04-27 9:59 ` René Scharfe
2019-04-27 17:39 ` René Scharfe
2019-04-29 21:25 ` Johannes Schindelin
2019-05-01 17:45 ` René Scharfe
2019-05-01 18:18 ` Jeff King
2019-06-10 10:44 ` René Scharfe
2019-06-13 19:16 ` Jeff King
2019-04-13 22:16 ` brian m. carlson
2019-04-15 21:36 ` Jeff King
2019-04-26 14:54 ` Johannes Schindelin
2019-05-02 20:20 ` Ævar Arnfjörð Bjarmason
2019-05-03 20:49 ` Johannes Schindelin
2019-05-03 20:52 ` Jeff King
2019-04-26 14:47 ` Johannes Schindelin
[not found] ` <pull.145.v2.git.gitgitgadget@gmail.com>
[not found] ` <4ea94a8784876c3a19e387537edd81a957fc692c.1556321244.git.gitgitgadget@gmail.com>
2019-05-02 20:29 ` [PATCH v2 3/4] archive: optionally use zlib directly for gzip compression René Scharfe
[not found] ` <ac2b2488a1b42b3caf8a84594c48eca796748e59.1556321244.git.gitgitgadget@gmail.com>
2019-05-02 20:30 ` [PATCH v2 2/4] archive-tar: mark RECORDSIZE/BLOCKSIZE as unsigned René Scharfe
2019-05-08 11:45 ` Johannes Schindelin
2019-05-08 23:04 ` Jeff King
2019-05-09 14:06 ` Johannes Schindelin
2019-05-09 18:38 ` Jeff King
2019-05-10 17:18 ` René Scharfe
2019-05-10 21:20 ` Jeff King
2022-06-12 6:00 ` [PATCH v3 0/5] Avoid spawning gzip in git archive René Scharfe
2022-06-12 6:03 ` [PATCH v3 1/5] archive: rename archiver data field to filter_command René Scharfe
2022-06-12 6:05 ` [PATCH v3 2/5] archive-tar: factor out write_block() René Scharfe
2022-06-12 6:08 ` [PATCH v3 3/5] archive-tar: add internal gzip implementation René Scharfe
2022-06-13 19:10 ` Junio C Hamano
2022-06-12 6:18 ` René Scharfe [this message]
2022-06-12 6:19 ` [PATCH v3 5/5] archive-tar: use internal gzip by default René Scharfe
2022-06-13 21:55 ` Junio C Hamano
2022-06-14 11:27 ` Johannes Schindelin
2022-06-14 15:47 ` René Scharfe
2022-06-14 15:56 ` René Scharfe
2022-06-14 16:29 ` Johannes Schindelin
2022-06-14 20:04 ` René Scharfe
2022-06-15 16:41 ` Junio C Hamano
2022-06-14 11:28 ` [PATCH v3 0/5] Avoid spawning gzip in git archive Johannes Schindelin
2022-06-14 20:05 ` René Scharfe
2022-06-30 18:55 ` Johannes Schindelin
2022-07-01 16:05 ` Johannes Schindelin
2022-07-01 16:27 ` Jeff King
2022-07-01 17:47 ` Junio C Hamano
2022-06-15 16:53 ` [PATCH v4 0/6] " René Scharfe
2022-06-15 16:58 ` [PATCH v4 1/6] archive: update format documentation René Scharfe
2022-06-15 16:59 ` [PATCH v4 2/6] archive: rename archiver data field to filter_command René Scharfe
2022-06-15 17:01 ` [PATCH v4 3/6] archive-tar: factor out write_block() René Scharfe
2022-06-15 17:02 ` [PATCH v4 4/6] archive-tar: add internal gzip implementation René Scharfe
2022-06-15 20:32 ` Ævar Arnfjörð Bjarmason
2022-06-16 18:55 ` René Scharfe
2022-06-24 11:13 ` Ævar Arnfjörð Bjarmason
2022-06-24 20:24 ` René Scharfe
2022-06-15 17:04 ` [PATCH v4 5/6] archive-tar: use OS_CODE 3 (Unix) for internal gzip René Scharfe
2022-06-15 17:05 ` [PATCH v4 6/6] archive-tar: use internal gzip by default René Scharfe
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