GNU bug report logs - #35145
additional fields like for comments by gzip

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Message #5 received at submit <at> debbugs.gnu.org (full text, mbox):

From: Jörg Jenderek <joerg.jen.der.ek <at> gmx.net>
To: mailing list bug-gzip <bug-gzip <at> gnu.org>
Subject: additional fields like for comments by gzip
Date: Thu, 4 Apr 2019 15:23:37 +0200

Hello,
According to rfc1952 a gzip compressed file could contain additional
fields like a comment-field at the beginning. But i saw no option in
gzip command to create such fields. I have tried gzip version 1.3.12,
1.6, 1.9 on Windows, Linux and Raspian systems.

Does there exist in gzip command an option to create such fields or
is this feature not implemented? And if not can this implemented?

Thanks for advices and answers
Jörg Jenderek
--
Jörg Jenderek

Message #8 received at 35145 <at> debbugs.gnu.org (full text, mbox):

From: Paul Eggert <eggert <at> cs.ucla.edu>
To: Jörg Jenderek <joerg.jen.der.ek <at> gmx.net>,
 35145 <at> debbugs.gnu.org
Subject: Re: bug#35145: additional fields like for comments by gzip
Date: Thu, 4 Apr 2019 14:45:09 -0700

On 4/4/19 6:23 AM, Jörg Jenderek wrote:
> Does there exist in gzip command an option to create such fields or
> is this feature not implemented? And if not can this implemented?

As far as I know gzip has no such feature. Of course it could be
implemented, as a wishlist item. What would be the use case?

Message #11 received at 35145 <at> debbugs.gnu.org (full text, mbox):

From: Paul Eggert <eggert <at> cs.ucla.edu>
To: Jörg Jenderek <joerg.jen.der.ek <at> gmx.net>
Cc: 35145 <at> debbugs.gnu.org
Subject: Re: bug#35145: additional fields like for comments by gzip
Date: Sun, 7 Apr 2019 21:52:00 -0700

Jörg Jenderek wrote:

> normally files compressed with gzip have filename extension "gz" and
> mime type "application/gzip". When compressing tar archives often
> these get file name extension "tgz".
> The VirtualBox Extension Packs seems to be also gzipped tar archives.
> But these get their own file name extension "vbox-extpack" and mime
> type "application/x-virtualbox-vbox-extpack" at least for
> VirtualBox 6.0.4 on Windows systems.
> I am trying to refine definitions for file identifying utilies TrID
> ( http://mark0.net/soft-trid-e.html) and file (
> ftp://ftp.astron.com/pub/file ). Such utilities simply use some
> characteristics byte patterns to identify file types. As far as i can
> see, it is not possible at the moment for both utilities to
> distinguish gzipped tar files from VirtualBox extension packages. If
> the gzipped file would contain a comment field or other extra field,
> it would be possible to distinguish such different file types.

OK, I see; you're trying to improve TrID etc., since they're not smart enough to 
uncompress the file to figure out its file type. However, can't these utilities 
use file name extensions? If so, I suggest using some extension like ".vep" for 
VirtualBox Extension Packs, as that won't require changing gzip and other 
programs that accept and consume gzip files.

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