GNU bug report logs - #55166
28.1; tar-mode doesn't re-compress when saving remote files

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Message #14 received at 55166 <at> debbugs.gnu.org (full text, mbox):

From: Dan McCarthy <daniel.c.mccarthy <at> gmail.com>
To: Michael Albinus <michael.albinus <at> gmx.de>
Cc: 55166 <at> debbugs.gnu.org, Lars Ingebrigtsen <larsi <at> gnus.org>
Subject: Re: bug#55166: 28.1;
 tar-mode doesn't re-compress when saving remote files
Date: Tue, 3 May 2022 14:02:41 -0400

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It works perfectly. Thanks a lot!

On Tue, May 3, 2022 at 8:36 AM Michael Albinus <michael.albinus <at> gmx.de>
wrote:

> Lars Ingebrigtsen <larsi <at> gnus.org> writes:
>
> Hi,
>
> >> dan <at> solstice:/tmp$ touch a b c
> >> dan <at> solstice:/tmp$ tar cf test.tar a b c
> >> dan <at> solstice:/tmp$ bzip2 -z test.tar
> >> dan <at> solstice:/tmp$ file test.tar.bz2
> >> test.tar.bz2: bzip2 compressed data, block size = 900k
> >>
> >> If you visit that remote file and save it, the result will have the .bz2
> >> extension but won't actually be compressed:
> >>
> >> dan <at> solstice:/tmp$ file test.tar.bz2
> >> test.tar.bz2: POSIX tar archive (GNU)
> >>
> >> This doesn't happen with compressed remote files which aren't tar
> archives.
> >
> > I can reproduce this problem with Emacs 29, too.  (And if I edit the
> > file locally instead of via tramp, the tar file is saved compressed, so
> > it seems to be tramp-related.)
>
> Well, the problem seems to exist since Emacs 27, likely due to some
> subtle changes in basic-save-buffer-1 or basic-save-buffer-2. I haven't
> poked further there, because it looks like saving the buffer with this
> constellation happened twice in Emacs 26, which looks not optimal.
>
> The problem is an exotic feature of write-region, which first looks for
> a file name handler in FILENAME, and if there isn't one, it checks
> VISIT.
>
> write-region of the compressed remote tar file in the scenario above is
> called like
>
> --8<---------------cut here---------------start------------->8---
>   ...
>   tramp-file-name-handler(write-region nil nil
> "/ssh:detlef:/tmp/tmpfSxlA9" nil "/ssh:detlef:/tmp/test.tar.bz2"
> "/ssh:detlef:/tmp/test.tar.bz2" nil)
>   write-region(nil nil "/ssh:detlef:/tmp/tmpfSxlA9" nil
> "/ssh:detlef:/tmp/test.tar.bz2" "/ssh:detlef:/tmp/test.tar.bz2")
>   basic-save-buffer-2()
>   basic-save-buffer-1()
>   basic-save-buffer(t)
>   save-buffer(1)
>   funcall-interactively(save-buffer 1)
>   call-interactively(save-buffer nil nil)
>   command-execute(save-buffer)
> --8<---------------cut here---------------end--------------->8---
>
> That is, a remote temporary file ("/ssh:detlef:/tmp/tmpfSxlA9") is
> written, and the magic extension of the remote VISIT argument
> "/ssh:detlef:/tmp/test.tar.bz2" is ignored.
>
> When FILENAME is a local temporary file, the handler for VISIT
> (jka-compr-handler) is triggered. That's the second test Lars has applied.
>
> I've pushed a fix to master, which shall fix this. Dan, could you pls
> check?
>
> In parallel I'll try to write a test case for this problem. But that's
> unrelated to closing this bug.
>
> Best regards, Michael.
>

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