ubuntu-phone team mailing list archive

[Thomas Voß <thomas.voss@xxxxxxxxxxxxx>]

On Tue, Nov 12, 2013 at 3:56 PM, Gerry Boland
<gerry.boland@xxxxxxxxxxxxx> wrote:
> 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.
>

What is the underlying technology used for the cache and how will it
be exposed to the rest of the system?

> 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.
>

If we want to standardize, I would propose to look at the
implementation that is the most toolkit-/runtime-agnostic one, with
the fewest dependencies to make sure that higher levels of the stack
can easily consume it. Ideally something with a very simple API (and
desktop file parsing is not rocket science, so it should be fairly
small).

Thomas

> 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
>
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