ubuntu-phone team mailing list archive

[Gerry Boland <gerry.boland@xxxxxxxxxxxxx>]

Hi folks,
Ryan Lortie and Lars Ubernickel were at this years FreeDesktop Summit
[1]. One thing they've mentioned to me is the fact that it was decided
to have a binary cache of desktop files, to improve access and searching
of that data.

This reminded me that our desktop file parsing situation is a bit of a
mess. Right now we have multiple approaches:
- unity (Qt) launcher uses QSettings ini file parser [should be standard
compliant]
- unity-mir/qtubuntu (Qt) has it's own super-basic parser, which needs
to be replaced
- upstart-app-launch (bash/C) has a tiny C util to read the "Exec"
strong from a desktop file
- click lenses (Vala) use GLib.KeyFile, another ini file parser
[standard compliant]
and there's probably more. Since we use many GTK-based tools,
GDesktopAppInfo is often used too.

The cache is generated by the tool that can be found at [5].

The main point of the cache is answering complex questions like "give me
the apps associated with application/pdf", though it will also probably
speed up single .desktop-file key-value data reads since the cache will
most probably be kept in memory or disk cache.

A desktop file reader could benefit if it supports this new cache. So
having a custom parser, or just using ini file parsers, would not ideal
if we want to use this cache in future.

I think a logical approach is to standardize (as much as possible) on a
single desktop file parser implementation ASAP. Should we later want to
use the cache, we can add it to our chosen parser, and thus all its
users will immediately benefit.

Here are possible solutions:

1. GDesktopAppInfo [2]
- will support the new cache shortly.
- we would need to wrap this for easy use with Qt however.
- pulls in GIO
- usable though Vala too.
- it will be well tested and used by more than just us.

2. KDE frameworks 5 [3]
- cache support not landed yet.
- whole framework is not released and thus not packaged for Ubuntu. We
would have to help the KDE guys out on this.
- would integrate nicely with Qt.
- will be well tested with many users aside from us.
- not usable with Vala.

3. QtXDG [4]
- no plans to support cache currently. Would need extending to support
the cache.
- packaged for Ubuntu, but Qt4 only. It does build and work on Qt5
however. Would need the Qt5 version to be packaged.
- integrates nicely with Qt.
- not many users, nor well tested.
- not usable with Vala.

4. Make something home-grown
- Antii Kaijanmäki has written a desktop file parser in Qt5 [6]. It
would need to be split into a separate library, and be packaged.
- no plans to support cache currently.
- integrates nicely with Qt.
- We would be the sole users, and this having less "in the wild" testing.
- not usable with Vala, without significant changes.

What do people think? Are there alternatives I'm missing?
Thanks
-Gerry




[1] https://en.opensuse.org/openSUSE:2013_Desktop_Summit#Agenda
[2]
https://developer.gnome.org/gio/unstable/gio-Desktop-file-based-GAppInfo.html
[3]
http://quickgit.kde.org/?p=kdelibs.git&a=tree&h=96b05b9b35e395ef2de16dc2188bbfd8eb190de7&hb=c2e988586e7b8788030195dbec625a21c1dd03af&f=tier1%2Fkconfig%2Fsrc%2Fcore
[4]
https://github.com/hawaii-desktop/qtxdg/blob/master/src/xdg/qdesktopfile.h
[5] https://github.com/desrt/desktop-file-index
[6]
https://code.launchpad.net/~kaijanmaki/unity8/launcher-backend/+merge/179663