GNU bug report logs - #21270
gzip huge filesize problem

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Message #13 received at 21270-done <at> debbugs.gnu.org (full text, mbox):

From: Jim Meyering <jim <at> meyering.net>
To: Mark Adler <madler <at> alumni.caltech.edu>
Cc: Alexander Kleinsorge <aleks <at> physik.tu-berlin.de>,
 21270-done <at> debbugs.gnu.org
Subject: Re: bug#21270: gzip huge filesize problem
Date: Sun, 16 Aug 2015 21:44:54 -0600

tags 21270 notabug
thanks

On Sun, Aug 16, 2015 at 1:58 AM, Mark Adler <madler <at> alumni.caltech.edu> wrote:
> Alexander,
>
> Thank you for your report.  This is a well-known limitation of the gzip format.  The -l function makes use of the uncompressed length stored in the last four bytes of a gzip stream.  Therein lies the rub, since four bytes can represent no more than 4 GB - 1.
>
> There is another problem with that approach, in that a valid gzip file may consist of a series of concatenated gzip streams, in which case -l will report only on the last one.  In that case, even if the entire stream decompresses to less than 4 GB, the result will still be incorrect.
>
> The only reliable way to determine the uncompressed size of a gzip file is to decompress the entire file (which can be done without storing the result).  This in fact is what "pigz -lt file.gz" does.  It will correctly report the uncompressed length, but takes much longer than "gzip -l".
>
> -l remains useful however in most cases, so it remains a gzip and pigz option.

Thank you for replying Mark.
I've marked this as "notabug" with the in-line comment above, and am
closing the auto-created issue with the "-done" part of the debbugs
email recipient address.

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