LibreOffice uses a number of external libraries, and most of them can be configured to use a bundled version or a system version. libxmlsec was an exception previously (only the bundled version was usable), but LibreOffice master (towards 6.0) doesn’t have this limitation anymore.

Using a bundled version is a good choice in case:

Using a system version is a good thing in case:

With that in mind, let’s have a look what blocked using system-xmlsec in the past:

If you are a Linux distro packager then --with-system-libs already implies --with-system-xmlsec, so you probably don’t have to do anything. If you build LO for static analysis (e.g. Coverity) then this should be also useful, so not relevant issues in 3rd-party code don’t have to be ignored manually.

Last weekend I attended the LibreOffice Perugia HackFest 2017, with the primary goal of mentoring students (together with Eike and Christian): provided they manage to contribute at least one non-trivial easy hack, they get university credits for their work.

I worked with Arianna, Claudio, Francesco and Gian, all of them managed to achieve something by the end of the third day.

When I was not helping others, I also fixed a few bugs:

Some photos I took during the event are available.

Thanks the organizers for the great event, also kudos to Collabora, Red Hat and TDF for allowing mentors to come! :-)

This post summarizes the plumbing work around ODF/OOXML digital signatures that I did on LibreOffice master after the 5.3 branch-off up to now. The big thing is the integration of the libxmlsec 1.2.24 release. Among other things, this contains 2 larger changes that I contributed upstream triggered by the needs of LibreOffice:

After the release I also noticed that creating signatures on Windows was broken, this is now fixed on xmlsec master and also backported to LibreOffice.

All this is available in LibreOffice master, towards 5.4.

This is a follow-up to the previous post that described how it is now possible to insert a PDF file as an image in LibreOffice and export that back to PDF, while keeping the original PDF contents. I’ve recently improved this feature so the resulting file is smaller and the vector image can be viewed in more viewers. First, thanks to PMG who made this work possible.

Let’s look at the previously mentioned front page of a magazine sample when it’s viewed in okular. (A KDE pdf viewer, i.e. something that’s not Adobe Acrobat). The previously used reference XObject PDF markup is not handled by it, so the bitmap fallback was displayed:

Compare it with the new result:

Notice the sharp text in the first line.

Also the size of this sample is smaller now, since we don’t write a large bitmap, and the not shown second page of the PDF image: 2 385 984 → 1 605 558 bytes (about one third of the output is avoided).

Both techniques have pros and cons, here is a summary:

Nevertheless, the new approach seems like a much better default, so LibreOffice no longer writes the reference XObject approach unless you explicitly request it in the PDF export dialog.

Some perhaps interesting details:

All this is available in LibreOffice master, towards 5.4.

pdfium is the rendering library used in Chromium’s pdf viewer. It’s based on the foxit pdf renderer and its rendering quality is much better compared to the pre-existing "convert PDF to ODG, then to an image" code when it comes to just viewing a PDF file. First, thanks to PMG who made this work possible.

Let’s look at a few samples that compare the old pdfimport rendering result and the new pdfium-based one. One important feature is that embedded fonts are handled. This is how this inserted PDF looked like previously:

Compare it with the new result:

Now let’s see the front page of a magazine, you can see 4 unexpected artifacts:

New result:

Finally a problem with pdfium was that LibreOffice got bitmaps from it, so in case you re-exported to PDF, the quality of these PDF images were worse than in the original PDF file. The PDF specification has a reference XObject feature that helps in this case: it allows the PDF export to still write the bitmap to the exported PDF, but in case the reader supports this feature, the vector-based original file will be shown, not the bitmap.

Here is a simple hand-crafted star in a PDF file, as it looked initially:

This is how it looks after LibreOffice’s PDF export learned to emit reference XObjects:

All this is available in LibreOffice master, towards 5.4.

Last month a LibreOffice bugreport was filed, as the ODF signature created with Hungarian citizen eID cards is not something LibreOffice can verify. After a bit of research it seemed that LibreOffice and NSS (what we use for crypto work on Linux/macOS) is not a problem, but xmlsec’s NSS backend does not recognize ECDSA keys (RSA or DSA keys work fine).

The xmlsec improvements happened in these pull requests:

After this the xmlsec code looked good enough. I had to request an update of the bugdoc in the TDF bug twice, as the signature itself looked also incorrect initially:

Finally a warning still remains: while trying to parse the text of the <X509IssuerName> element, the dotted decimal form is still not parsed (see this NSS bugreport). The bug is confirmed on the mailing list, but no other progress have been made so far.

Oh, and of course: Windows is still untouched, there a bigger problem remains: we use CryptoAPI (not CNG) there, and that does not support ECDSA at all. Hooray for open-source libs where you can add such support yourself. ;-)

I rarely write about work did by others, but given that in the previous post I mentioned that linked videos (when they are a http:// URL) are not working, I had a very positive experience which is worth noting. :-)

I got a private mail nagging me to file a bug and just 3 days later it got fixed!

Thanks to both Oliver for the nagging and to Albert for the actual fix.

PDF supports screen annotations, which means it’s possible to play embedded and linked videos on top of a static image. Given that LibreOffice also supports videos, it made sense to add support for this in our PDF export filter. First, thanks to PMG who made this work possible. This is currently added for Writer and Impress.

FOSDEM 2017 is here this weekend, and as Michael Stahl pointed out, this (together with the LibreOffice annual conference) are two time periods each year when lots of Impress bugfixes are made, as people start dogfooding. ;-) So below you can read about a pair of Impress bugs I fixed recently.

As mentioned in the blog post of Mike already, last month we were allowed to hack on anything we want in LibreOffice for a few days. I used this time to progress with 3 different topics.