bug#27563: [PATCH v3 0/2] Make ghostscript reproducible.

[Danny Milosavljevic]

So this is what's needed to finally make ghostscript, netpbm and groff
reproducible.  Groff just finished its 38th build on my machine and it
finally compared the rounds as equal.

I'm posting those here in order to make sure we all agree that this is
the way to go.

The patchset patches PDF creation in ghostscript.  It's for core-updates.

The PDF file has a trailer field "/ID" which is required only when
encrypting.  But ghostscript derives it from the current time.
So I figured leaving it off if allowed would be the easiest fix.
If it's not there then it can't change :P

Also, newer PDF files have an RDF header specifying some extra information
in an XML-like format.  For example there's an instance UUID (PDF/A specifies
that it's recommended to set this to an empty string), and a document UUID.
The latter again is time-based.

This patchset
* removes the RDF tag which contains the document UUID and
* sets the instance UUID to "" and
* removes the ID tag if allowed (i.e. if not encrypting).

Because of the printf-style functions, it has to split up the printfs a bit,
but really it just makes one of the parts printed optional - in multiple
places (because PDF trailers can be chained).

Danny Milosavljevic (2):
  gnu: ghostscript: Don't write document UUID; use "" as instance UUID.
  gnu: ghostscript: Write document ID only when encrypting.

 gnu/local.mk                                       |  2 +
 gnu/packages/ghostscript.scm                       |  4 +-
 .../patches/ghostscript-no-header-id.patch         | 47 ++++++++++++++++++++++
 .../patches/ghostscript-no-header-uuid.patch       | 28 +++++++++++++
 4 files changed, 80 insertions(+), 1 deletion(-)
 create mode 100644 gnu/packages/patches/ghostscript-no-header-id.patch
 create mode 100644 gnu/packages/patches/ghostscript-no-header-uuid.patch