createrepo_as is a tool that allows us to create AppStream metadata from a directory of packages. It is typically used when generating distribution metadata, usually at the same time as modifyrepo or createrepo.

What this tool does:

• Searches a directory of packages and reads just the RPM header of each.
• If a package contains an interesting file, just the relevant files are decompressed from the package archive.
• A set of plugins are run on the extracted files, and if these match certain criteria CraApplication objects are created.
• Any screenshots referenced are downloaded to a local cache. This is optional and can be disabled with --nonet.
• When all the packages are processed, some of the CraApplication objects are merged into single applications. This is how fonts are collected.
• The CraApplication objects are serialized to XML and written to a compressed archive.
• Any application icons or screenshots referenced are written to a .tar archive.

To run createrepo_as you either need to install the package containing the binary and data files, or you can build a local copy. To do the latter just do:

dnf install automake autoconf libtool rpm-devel \
            gtk3-devel sqlite-devel libsoup-devel
./autogen.sh
make

To actually run the extractor you can do:

./createrepo_as --verbose   \
                --max-threads=8 \
                --log-dir=/tmp/logs \
                --packages-dir=/mnt/archive/Megarpms/21/Packages \
                --temp-dir=/mnt/ssd/AppStream/tmp \
                --output-dir=./repodata \
                --screenshot-url=http://megarpms.org/screenshots/ \
                --basename="megarpms-21"

This will output a lot of progress text. Now, go and make a cup of tea and wait patiently if you have a lot of packages to process. After this is complete you should finally see:

Writing ./repodata/megarpms-21.xml.gz
Writing ./repodata/megarpms-21-icons.tar
Done!

You now have two choices what to do with these files. You can either upload them with the rest of the metadata you ship (e.g. in the same directory as repomd.xml and primary.sqlite.bz2) which will work with Fedora 21.

For Fedora 20, you have to actually install these files, so you can do something like this in the megarpms-release.spec file:

Source1:   http://www.megarpms.org/temp/megarpms-20.xml.gz
Source2:   http://www.megarpms.org/temp/megarpms-20-icons.tar.gz

%install
mkdir -p %{buildroot}%{_datadir}/app-info/xmls
cp %{SOURCE1} %{buildroot}%{_datadir}/app-info/xmls
mkdir -p %{buildroot}%{_datadir}/app-info/icons/megarpms-20
tar xvzf %{SOURCE2}
cd -

or, if your distro ships a new enough libappstream-glib:

%install
DESTDIR=%{buildroot} appstream-util install %{SOURCE1} %{SOURCE2}

This ensures that gnome-software can access both data files when starting up.

Applications are defined in the context of AppStream as such:

• Installs a desktop file and would be visible in a desktop
• Has an metadata extractor (e.g. src/plugins/cra-plugin-gstreamer.c) and includes an AppData file

These guidelines explain how we filter applications from a package set.

First, some key words:

• SHOULD: The application should do this if possible
• MUST: The application or addon must do this to be included
• CANNOT: the application or addon must not do this

The current rules of inclusion are thus:

• Icons MUST be installed in /usr/share/pixmaps/*, /usr/share/icons/*, /usr/share/icons/hicolor/*/apps/*, or /usr/share/${app_name}/icons/*
• Desktop files MUST be installed in /usr/share/applications/ or /usr/share/applications/kde4/
• Desktop files MUST have Name, Comment and Icon entries
• Valid applications with NoDisplay=true MUST have an AppData file.
• Applications with Categories=Settings, Categories=ConsoleOnly or Categories=DesktopSettings MUST have an AppData file.
• Applications MUST have had an upstream release in the last 5 years or have an AppData file.
• Application icon MUST be available in 48x48 or larger
• Applications must have at least one main or additional category listed in the desktop file or supply an AppData file. See http://standards.freedesktop.org/menu-spec/latest/apa.html and http://standards.freedesktop.org/menu-spec/latest/apas02.html for the full Categories list.
• Codecs MUST have an AppData file
• Input methods MUST have an AppData file
• If included, AppData files MUST be valid XML
• AppData files MUST be installed into /usr/share/appdata
• Application icons CANNOT use XPM or ICO format
• Applications CANNOT use obsolete toolkits such as GTK+-1.2 or QT3
• Applications that ship a desktop file SHOULD include an AppData file.
• Screenshots SHOULD be in 16:9 aspect ratio
• Application icons SHOULD have an alpha channel
• Applications SHOULD ship a 64x64 PNG format icon or SVG
• AppData files SHOULD include translations
• Desktop files SHOULD include translations

GPLv2+