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Fix OCR bug in Qubes Fedora 38 templates

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Provide a fix for an OCR bug that affected Fedora 38 templates of Qubes
OS. In that specific configuration, the PyMuPDF version accepts the
Tesseract data directory only from the `TESSDATA_PREFIX` environment
variable. Our mistake was that we were setting this environment variable
in a dev script, instead of setting it for all configurations.

In this commit, we set an attribute in the fitz.fitz module, so that
both dev scripts and end-user installations can work. This is hacky, but
it targets an old PyMuPDF release after all, so we don't expect things
to break in the long run.

Fixes #737
This commit is contained in:
Alex Pyrgiotis 2024-03-04 16:41:55 +02:00
parent d35eb56b4b
commit f75d471ec8
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2 changed files with 26 additions and 6 deletions
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28
dangerzone/conversion/pixels_to_pdf.py
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@ -64,8 +64,32 @@ class PixelsToPDF(DangerzoneConverter):
tessdata=get_tessdata_dir(),
)
else:
# XXX method signature changed in v1.22.5 to add tessdata arg
# TODO remove after oldest distro has PyMuPDF >= v1.22.5
# XXX: In PyMuPDF v1.22.5, the function signature of
# `pdfocr_tobytes()` / `pdfocr_save()` was extended with an argument
# to explicitly set the Tesseract data dir [1].
#
# In earlier versions, the PyMuPDF developers recommend setting this
# path via the TESSDATA_PREFIX environment variable. In practice,
# this environment variable is read at import time, so subsequent
# changes to the environment variable are not tracked [2].
#
# To make things worse, any attempt to alter the internal attribute
# (`fitz.TESSDATA_PREFIX`) makes no difference as well, when using
# the OCR functions. That's due to the way imports work in `fitz`,
# where somehow the internal `fitz.fitz` module is shadowed.
#
# A hacky solution is to grab the `fitz.fitz` module from
# `sys.modules`, and set there the TESSDATA_PREFIX variable. We can
# get away with this hack because we have a proper solution for
# subsequent PyMuPDF versions, and we know that nothing will change
# in older versions.
#
# TODO: Remove after oldest distro has PyMuPDF >= v1.22.5
#
# [1]: https://pymupdf.readthedocs.io/en/latest/pixmap.html#Pixmap.pdfocr_save
# [2]: https://github.com/pymupdf/PyMuPDF/blob/0368e56cfa6afb55bcf6c726e7f51a2a16a5ccba/fitz/fitz.i#L308
sys.modules["fitz.fitz"].TESSDATA_PREFIX = get_tessdata_dir() # type: ignore [attr-defined]
page_pdf_bytes = pixmap.pdfocr_tobytes(
compress=True,
language=ocr_lang,

4
dev_scripts/dangerzone
View file

@ -4,10 +4,6 @@
import os
import sys
# XXX workaround lack of tessdata path arg for PyMuPDF < v1.22.5
# for context see https://github.com/freedomofpress/dangerzone/issues/682
os.environ["TESSDATA_PREFIX"] = os.environ.get("TESSDATA_PREFIX", "/usr/share/tesseract/tessdata")
# Load dangerzone module and resources from the source code tree
sys.path.insert(0, os.path.dirname(os.path.dirname(os.path.abspath(__file__))))
sys.dangerzone_dev = True