Date: Thu, 8 Dec 2005 18:56:42 -0500 From: Brian Fundakowski Feldman <green@freebsd.org> To: Dan Nelson <dnelson@allantgroup.com> Cc: Steven Hartland <killing@multiplay.co.uk>, freebsd-stable@freebsd.org Subject: Re: bsdtar / libarchive bug? Message-ID: <20051208235642.GG98704@green.homeunix.org> In-Reply-To: <20051208234540.GB95420@dan.emsphone.com> References: <00c701c5fc1c$e6db4220$b3db87d4@multiplay.co.uk> <20051208225404.GF98704@green.homeunix.org> <20051208234540.GB95420@dan.emsphone.com>
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On Thu, Dec 08, 2005 at 05:45:40PM -0600, Dan Nelson wrote:
> In the last episode (Dec 08), Brian Fundakowski Feldman said:
> > On Thu, Dec 08, 2005 at 05:29:06PM -0000, Steven Hartland wrote:
> > > It seems bsdtar can create files it cant read. i.e. it will happily create
> > > empty tar.gz files but when it comes to read them the following error
> > > is output:
> > > tar: Unrecognized archive format: Inappropriate file type or format
> > >
> > > Having a look at libarchive shows the following code:
> > > /* An empty archive is a serious error. */
> > > if (bytes_read == 0) {
> > > archive_set_error(a, ARCHIVE_ERRNO_FILE_FORMAT,
> > > "Empty input file");
> > > return (ARCHIVE_FATAL);
> > > }
> > >
> > > Which is where I expect the issue is, why would an empty archive
> > > be fatal? I can see any reason for this, yes its strange but there's
> > > nothing fatal about it imo.
> >
> > I don't think it will "happily create empty tar.gz files", even where
> > by empty you mean the tar itself inside of the gz.
> >
> > {"/home/green" green@green}$ tar cfv x.tar
> > tar: no files or directories specified
> > {"/home/green" green@green}$ tar cfvz x.tar.gz
> > tar: no files or directories specified
> > {"/home/green" green@green}$ ls -l x.ta*
> > ls: x.ta*: No such file or directory
>
> I managed to make it create 0-byte files:
>
> $ touch a
> $ tar cvf b.tar --exclude a a
> $ tar zcvf b.tar.gz --exclude a a
> $ ls -la b.tar*
> -rw-r--r-- 1 dan wheel 0 Dec 8 17:37 b.tar
> -rw-r--r-- 1 dan wheel 20 Dec 8 17:37 b.tar.gz
> $ gunzip -vl b.tar.gz
> method crc date time compressed uncompr. ratio uncompressed_name
> defla 00000000 Dec 8 17:37 20 0 0.0% b.tar
>
> This works because at the time tar creates the output file, it doesn't
> know that I have excluded all the listed files.
>
> I am leaning towards an empty archive being legal, though, since it
> makes scripting easier. There may be cases where you are archiving
> files generated daily, and you want to distinguish "no data today" from
> "the archiver didn't run". At worst it should print a warning.
Just don't let it accept a 0-length gzip.
--
Brian Fundakowski Feldman \'[ FreeBSD ]''''''''''\
<> green@FreeBSD.org \ The Power to Serve! \
Opinions expressed are my own. \,,,,,,,,,,,,,,,,,,,,,,\
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