Detect default application for opening PDFs

[apyrgio]

Dangerzone has some logic for detecting which application (*.desktop file) can open a PDF:

dangerzone/dangerzone/gui/logic.py

Lines 97 to 123 in 65776d8

	def _find_pdf_viewers(self) -> Dict[str, str]:
	pdf_viewers: Dict[str, str] = {}
	if platform.system() == "Linux":
	# Find all .desktop files
	for search_path in [
	"/usr/share/applications",
	"/usr/local/share/applications",
	os.path.expanduser("~/.local/share/applications"),
	]:
	try:
	for filename in os.listdir(search_path):
	full_filename = os.path.join(search_path, filename)
	if os.path.splitext(filename)[1] == ".desktop":
	# See which ones can open PDFs
	desktop_entry = DesktopEntry(full_filename)
	if (
	"application/pdf" in desktop_entry.getMimeTypes()
	and "dangerzone" not in desktop_entry.getName().lower()
	):
	pdf_viewers[desktop_entry.getName()] = (
	desktop_entry.getExec()
	)
	except FileNotFoundError:
	pass
	return pdf_viewers

The result on Tails 6.2 is the following application list:

However, what's missing here is to present to the user the default application for opening PDFs. Instead, the first choice is picked up at random. Here, it's GIMP, whereas it should be Document Viewer.

[apyrgio]

On almost all Linux distros, we can use xdg-mime to find the default application for a mime type. On Tails, it returns the correct application:

$ xdg-mime query default application/pdf
org.gnome.Evince.desktop

We can improve this list by putting at the top the desktop file that xdg-mime returns. If xdg-mime is not present, or returns no results, we can keep the list order as is.