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bug#27563: [PATCH v3 2/2] gnu: ghostscript: Write document ID only when

From: Danny Milosavljevic
Subject: bug#27563: [PATCH v3 2/2] gnu: ghostscript: Write document ID only when encrypting.
Date: Fri, 7 Jul 2017 18:42:25 +0200

Hi Leo,

On Fri, 7 Jul 2017 12:21:51 -0400
Leo Famulari <address@hidden> wrote:

> > That leaves the document UUID - and upstream, in some of the other
> I think the lowest risk is to do nothing to Ghostscript and move the PDF
> documentation to a separate 'doc' output. Then, we could have
> reproducible binaries and ignore the PDF issues for now. Does anyone
> know how many packages include PDF documentation built with Ghostscript?

Aren't the derivations of the doc outputs still a problem?  For example, Hydra 
will run out of space sooner or later because it keeps building them, right?

> 2) At least some of the patches in the related Ghostscript discussions
> seem to be proof of concepts rather than finished code:
> https://bugs.ghostscript.com/show_bug.cgi?id=697484#c3
> So, if these patches came from there, we'd want to be extra careful.

No, I wrote the ones here without external sources (except for the direct 
discussion on my newish upstream bug report, and the PDF and XMP specifications 
- whatever worth they have).

> By the way, this is the patch used for Debian's latest Ghostscript
> package:
> https://anonscm.debian.org/git/printing/ghostscript.git/tree/debian/patches/2010_add_build_timestamp_setting.patch?id=e2bf3ad7026afe13636d4937430c3fdae7854078
> That patch was not reviewed on a public forum, at least nothing I can
> find with Google. Again, I'd want to get the Ghostscript team's advice.

On such an approach they advised that we should only generate *unique* UUIDs.  
But the UUIDs are generated from these times.  So that linked patch would 
generate multiple non-unique uuids on systems.

That's why I removed the entire UUID and Time sections and actually didn't 
fiddle with the ghostscript-internal times at all.  Builds reproducibly.

I wonder how many packages actually use the ghostscript pdf writer too.  How to 
find that out?

Note that groff itself also fails to build reproducibly without the patches.

In any case, the patch 2/2 is quite tame (it looks scary because of the printf 
splitting, but it's actually just either leaving "/ID[...]" off or not, 

But I understand that it would be even easier to do nothing.  Wouldn't make the 
stuff reproducible, though.

I'd vote for an environment variable to disable UUID printing and also Time 
header printing.  That way it would do everything normally in regular usage - 
but when used in packages, it would just not *print* the problematic stuff.  No 
internal state is changed at all by the patches.

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