Extend the base isolation provider to immediately convert each page to
a PDF, and optionally use OCR. In contract with the way we did things
previously, there are no more two separate stages (document to pixels,
pixels to PDF). We now handle each page individually, for two main
reasons:
1. We don't want to buffer pixel data, either on disk or in memory,
since they take a lot of space, and can potentially leave traces.
2. We can perform these operations in parallel, saving time. This is
more evident when OCR is not used, where the time to convert a page
to pixels, and then back to a PDF are comparable.
The PyMuPDF package was previously mainly used within the Dangerzone
container, as well as on Qubes. With on-host conversion, PyMuPDF will be
used in all supported platforms by default. For this reason, we can
promote it to a main dependency.
Add a new way to detect where the Tesseract data are stored in a user's
system. On Linux, the Tesseract data should be installed via the package
manager. On macOS and Windows, they should be bundled with the
Dangerzone application.
There is also the exception of running Dangerzone locally, where even
on Linux, we should get the Tesseract data from the Dangerzone share/
folder.
Add a Python script that can run in all supported platforms, and can
download and extract the Tesseract language data from GitHub, while
also:
1. Checking that the expected hash matches.
2. Informing the user if the language data have already been downloaded.
3. Extracting only the subset of language data that Dangerzone needs
Install PyMuPDF under ./dangerzone/vendor, right before we build the
.deb package. We vendor PyMuPDF just for Debian, since the provided
versions don't have OCR support enabled.
Currently, we don't use PyMuPDf on the host, but this will change once
we fully implement the on-host conversion feature.
Refs #625
Add a script that installs PyMuPDF under ./dangerzone/vendor. This will
be useful in subsequent commits, for vendoring PyMuPDF when building
Debian packages.
