Re: make git ignore the timestamp embedded in PDFs

From: Andreas Leha <andreas.leha@med.uni-goettingen.de>
Date: May 18, 2013, 18:09 UTC
Message-ID: <87ip2ggnx9.fsf@med.uni-goettingen.de>
In-Reply-To: <5197AD3A.5050500@kdbg.org>

Johannes Sixt <j6t@kdbg.org> writes:

Show 31 quoted lines

> Am 18.05.2013 09:42, schrieb Andreas Leha:
>>> Am 14.05.2013 15:17, schrieb Andreas Leha:
>>>> Hi all,
>>>>
>>>> how can I make git ignore the time stamp(s) in a PDF.  Two PDFs that
>>>> differ only in these time stamps should be considered identical.
>>>> ...
>>>> What I tried is a filter:
>>>> ,----[ ~/.gitconfig ]
>>>> | [filter "pdfresetdate"]
>>>> |         clean = pdfresetdate
>>>> `----
>>>>
>>>> This 'works' as far as the committed pdf indeed has the date reset to my
>>>> default value.
>>>>
>>>> However, when I re-checkout the files, they are marked modified by git.
>>>
>>> I'm using cleaned files every now and then, but not on Linux. I have
>>> never observed this behavior recently.
>>>
>>> If you 'git add' the file, does it keep its modified state? Does 'git
>> 
>> yes.
>> 
>>> diff' tell a difference?
>> 
>> no.
>
> I do not believe you. I'm sure that "Binary files differ" was
> reported.

You are correct, of course. I had forgotten that I also had enabled a special diff for pdf files, that reports the difference in the pdfinfo output.

Show 9 quoted lines

> The reason is that your pdfresetdate script is not idempotent. Look:
>
> $ pdfresetdate < x.pdf > y.pdf
> $ pdfresetdate < y.pdf > z.pdf
> $ md5sum x.pdf y.pdf z.pdf
> c46a7097574a035e89d1a46d93c83528  x.pdf
> 8e6d942b4cc7d8a4dfe6898867573617  y.pdf
> e6333bc0f8ab9781d3e1d811a392d516  z.pdf
>

Thanks for that. I had not noticed due to the non-binary diff I had enabled.

> A file that was already cleaned by the clean filter must not be
> modified, i.e., the y.pdf and z.pdf should be identical. But they are not.
>
> Fix your clean filter.

I will (try to) do.  Anyway, git seems unresponsible for my issue.

Thanks for that clear analysis!

Regards, Andreas