GNU bug report logs - #43597
28.0.50; arc-mode.el fails to display a ZIP file

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From: Stephen Berman <stephen.berman <at> gmx.net>
To: Andreas Schwab <schwab <at> linux-m68k.org>
Cc: 43597 <at> debbugs.gnu.org
Subject: bug#43597: 28.0.50; arc-mode.el fails to display a ZIP file
Date: Thu, 24 Sep 2020 23:58:51 +0200

On Thu, 24 Sep 2020 22:40:15 +0200 Stephen Berman <stephen.berman <at> gmx.net> wrote:

> On Thu, 24 Sep 2020 22:25:23 +0200 Andreas Schwab <schwab <at> linux-m68k.org> wrote:
>
>> On Sep 24 2020, Stephen Berman wrote:
>>
>>> In case it helps, here is the final byte sequence in the file (I've
>>> replace the control characters and raw bytes by ASCII representations):
>>>
>>> PK^E^F\377\377\377\377%^@%^@\377\377\377\377\377\377\377\377^@^@
>>
>> That means the archive is in ZIP64 format.  See
>> <https://pkware.cachefly.net/webdocs/casestudies/APPNOTE.TXT>.  The real
>> values are contained in the zip64 end of central directory record, which
>> has "PK\6\6" as the signature.
>
> Thanks.  But then it seems that arc-mode.el doesn't handle this format
> correctly: archive-zip-summarize has this code:
>
>   (let ((p (archive-l-e (+ (point) 16) 4))
>         files)
>     (when (= p -1)
>       ;; If the offset of end-of-central-directory is -1, this is a
>       ;; Zip64 extended ZIP file format, and we need to glean the info
>       ;; from Zip64 records instead.
>
> But the first value returned by archive-l-e for this file is 255, not
> -1, and on each iteration the value increases, so the ZIP64 code in the
> body of the when-clause is never executed.

I've confirmed that changing the when-clause condition to (= p
4294967295) (that's octal 37777777777, hex ffffffff) makes the body get
executed and the contents of the problematic ZIP file are correctly
displayed in archive-mode.  Is that the correct fix?

Steve Berman

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