Grab Tesseract's trained models from GitHub, instead of from the Alpine
Linux repos. Over the past few months, the models in the Alpine Linux
repos did not remain stable, leading to CI issues.
Since the models are already pre-trained and available through
Tesseract's repo on GitHub, we can use the release tarball that they
offer to install them in the container image, which is basically what
the upstream packages are doing as well.
In order to make sure that we have no regressions, at the time of this
commit we ensured that the hashes of the models offered through the
Alpine Linux repos and the models offered from the GitHub release are
the same. Also, in order to detect future regressions or foul play, we
check the downloaded models against a known checksum. Given that these
models change every few years, updating the checksum should not be an
issue.
Fix#357
Some documents were reporting the following error when running them
over pdftoppm:
Syntax Error: Missing language pack for 'Adobe-Japan1' mapping
This did not necessarily make the document fail but it could be
that some fonts were not properly rendered due to the missing package.
Commit d7be28ec2a assumed that OpenJDK was
required for the PDFtk package, which is no longer installed in the
Dangerzone image, and thus was removed.
Turns out that while LibreOffice does not depend on OpenJDK, it may
produce corrupted PDFs if installed without it, and will not abort the
operation.
Reinstate OpenJDK to fix the issue of corrupted PDFs.
Fixes#315
default-jre and java dependencies dependencies had been added initially
[1] because of libreoffice-java-common, which is no longer present.
Then, when the image was changed from ubuntu to alpine [2], default-jre
was replaced with openjdk-8.
If java is still a dependency for libreoffice, then it should be pulled
automatically.
[1] 9ecdb9e995
[2] 650ae6eee1
PDFtk actually isn't needed. It was being used for breaking a PDF
into pages but this is something that be replaced by the already present
'pdftoppm'. Furthermore, by removing this dependency we contribute to
reproducible builds and overall supply chain security because it was
obtained from gitlab with no signature verification or version pinning.
The replacement 'pdftoppm' enabled us to do a shortcut:
- before: PDF -> PDF pages -> PNG images -> RGB images
- after: PDF -> PPM images -> RGB images
And this last conversion step is trivial since the RGB format we were
using is just a PPM file without the metadata in its header.
