External Plugins in GNOME Software (3)

Lots of nice feedback from my last post, so here’s some new stuff. Up now is downloading new metadata and updates in plugins.

The plugin loader supports a gs_plugin_refresh() vfunc that is called in various situations. To ensure plugins have the minimum required metadata on disk it is called at startup, but with a cache age of infinite. This basically means the plugin must just ensure that any data exists no matter what the age.

Usually once per day, we’ll call gs_plugin_refresh() but with the correct cache age set (typically a little over 24 hours) which allows the plugin to download new metadata or payload files from remote servers. The gs_utils_get_file_age() utility helper can help you work out the cache age of file, or the plugin can handle it some other way.

For the Flatpak plugin we just make sure the AppStream metadata exists at startup, which allows us to show search results in the UI. If the metadata did not exist (e.g. if the user had added a remote using the commandline without gnome-software running) then we would show a loading screen with a progress bar before showing the main UI. On fast connections we should only show that for a couple of seconds, but it’s a good idea to try any avoid that if at all possible in the plugin.
Once per day the gs_plugin_refresh() method is called again, but this time with GS_PLUGIN_REFRESH_FLAGS_PAYLOAD set. This is where the Flatpak plugin would download any ostree trees (but not doing the deloy step) so that the applications can be updated live in the details panel without having to wait for the download to complete. In a similar way, the fwupd plugin downloads the tiny LVFS metadata with GS_PLUGIN_REFRESH_FLAGS_METADATA and then downloads the large firmware files themselves only when the GS_PLUGIN_REFRESH_FLAGS_PAYLOAD flag is set.

If the @app parameter is set for gs_plugin_download_file() then the progress of the download is automatically proxied to the UI elements associated with the application, for instance the install button would show a progress bar in the various different places in the UI. For a refresh there’s no relevant GsApp to use, so we’ll leave it NULL which means something is happening globally which the UI can handle how it wants, for instance showing a loading page at startup.

gs_plugin_refresh (GsPlugin *plugin,
                   guint cache_age,
                   GsPluginRefreshFlags flags,
                   GCancellable *cancellable,
                   GError **error)
  const gchar *metadata_fn = "/var/cache/example/metadata.xml";
  const gchar *metadata_url = "http://www.example.com/new.xml";

  /* this is called at startup and once per day */
    g_autoptr(GFile) file = g_file_new_for_path (metadata_fn);

    /* is the metadata missing or too old */
    if (gs_utils_get_file_age (file) > cache_age) {
      if (!gs_plugin_download_file (plugin,
                                    error)) {
        /* it's okay to fail here */
        return FALSE;
      g_debug ("successfully downloaded new metadata");

  /* this is called when the session is idle */
  if ((flags & GS_PLUGIN_REFRESH_FLAGS_PAYLOAD) == 0) {
    // FIXME: download any required updates now

  return TRUE;

Note, if the downloading fails it’s okay to return FALSE; the plugin loader continues to run all plugins and just logs an error to the console. We’ll be calling into gs_plugin_refresh() again in only a few hours, so there’s no need to bother the user. For actions like gs_plugin_app_install we also do the same thing, but we also save the error on the GsApp itself so that the UI is free to handle that how it wants, for instance showing a GtkDialog window for example.

External Plugins in GNOME Software (2)

After quite a lot of positive feedback from my last post I’ll write some more about custom plugins. Next up is returning custom applications into the installed list. The use case here is a proprietary software distribution method that installs custom files into your home directory, but you can use your imagination for how this could be useful.

The example here is all hardcoded, and a true plugin would have to derive the details about the GsApp, for example reading in an XML file or YAML config file somewhere. So, code:

#include <gnome-software.h>

gs_plugin_initialize (GsPlugin *plugin)
  gs_plugin_add_rule (plugin, GS_PLUGIN_RULE_RUN_BEFORE, "icons");

gs_plugin_add_installed (GsPlugin *plugin,
                         GsAppList *list,
                         GCancellable *cancellable,
                         GError **error)
  g_autofree gchar *fn = NULL;
  g_autoptr(GsApp) app = NULL;
  g_autoptr(AsIcon) icon = NULL;

  /* check if the app exists */
  fn = g_build_filename (g_get_home_dir (), "chiron", NULL);
  if (!g_file_test (fn, G_FILE_TEST_EXISTS))
    return TRUE;

  /* the trigger exists, so create a fake app */
  app = gs_app_new ("example:chiron.desktop");
  gs_app_set_management_plugin (app, "example");
  gs_app_set_kind (app, AS_APP_KIND_DESKTOP);
  gs_app_set_state (app, AS_APP_STATE_INSTALLED);
  gs_app_set_name (app, GS_APP_QUALITY_NORMAL,
  gs_app_set_summary (app, GS_APP_QUALITY_NORMAL,
                      "A teaching application");
  gs_app_set_description (app, GS_APP_QUALITY_NORMAL,
        "Chiron is the name of an application.\n\n"
        "It can be used to demo some of our features");

  /* these are all optional */
  gs_app_set_version (app, "1.2.3");
  gs_app_set_size_installed (app, 2 * 1024 * 1024);
  gs_app_set_size_download (app, 3 * 1024 * 1024);
  gs_app_set_origin_ui (app, "The example plugin");
  gs_app_add_category (app, "Game");
  gs_app_add_category (app, "ActionGame");
  gs_app_add_kudo (app, GS_APP_KUDO_INSTALLS_USER_DOCS);
  gs_app_set_license (app, GS_APP_QUALITY_NORMAL,
                      "GPL-2.0+ and LGPL-2.1+");

  /* create a stock icon (loaded by the 'icons' plugin) */
  icon = as_icon_new ();
  as_icon_set_kind (icon, AS_ICON_KIND_STOCK);
  as_icon_set_name (icon, "input-gaming");
  gs_app_set_icon (app, icon);

  /* return new app */
  gs_app_list_add (list, app);

  return TRUE;

This shows a lot of the plugin architecture in action. Some notable points:

  • The application ID (example:chiron.desktop) has a prefix of example which means we can co-exist with any package or flatpak version of the Chiron application, not setting the prefix would make the UI confused if more than one chiron.desktop got added.
  • Setting the management plugin means we can check for this string when working out if we can handle the install or remove action.
  • Most applications want a kind of AS_APP_KIND_DESKTOP to be visible as an application.
  • The origin is where the application originated from — usually this will be something like Fedora Updates.
  • The GS_APP_KUDO_INSTALLS_USER_DOCS means we get the blue “Documentation” award in the details page; there are many kudos to award to deserving apps.
  • Setting the license means we don’t get the non-free warning — removing the 3rd party warning can be done using AS_APP_QUIRK_PROVENANCE
  • The icons plugin will take the stock icon and convert it to a pixbuf of the correct size.

To show this fake application just compile and install the plugin, touch ~/chiron and then restart gnome-software.

Screenshot from 2016-05-20 21-22-38

By filling in the optional details (which can also be filled in using gs_plugin_refine_app() (to be covered in a future blog post) you can also make the details page a much more exciting place. Adding a set of screenshots is left as an exercise to the reader.

Screenshot from 2016-05-20 21-22-46

For anyone interested, I’m also slowly writing up these blog posts into proper docbook and uploading them with the gtk-doc files here. I think this documentation would have been really useful for the Endless and Ubuntu people a few weeks ago, so if anyone sees any typos or missing details please let me know.

External plugins in GNOME Software

I’ve just pushed a set of patches to gnome-software master that allow people to compile out-of-tree gnome-software plugins.

In general, building things out-of-tree isn’t something that I think is a very good idea; the API and ABI inside gnome-software is still changing and there’s a huge benefit to getting plugins upstream where they can undergo review and be ported as the API adapts. I’m also super keen to provide configurability in GSettings for doing obviously-useful things, the sort of thing Fleet Commander can set for groups of users. However, now we’re shipping gnome-software in enterprise-class distros we might want to allow customers to ship thier own plugins to make various business-specific changes that don’t make sense upstream. This might involve querying a custom LDAP server and changing the suggested apps to reflect what groups the user is in, or might involve showing a whole new class of applications that does not conform to the Linux-specific “application is a desktop-file” paradigm. This is where a plugin makes sense, and something I’d like to support in future updates to RHEL 7.

At this point it probably makes sense to talk a bit about how the architecture of gnome-software works. At its heart it’s just a big plugin loader that has some GTK UI that gets created for various result types. The idea is we have lots of small plugins that each do one thing and then pass the result onto the other plugins. These are ordered by dependencies against each other at runtime and each one can do things like editing an existing application or adding a new application to the result set. This is how we can add support for things like firmware updating, Steam, GNOME Shell web-apps and flatpak bundles without making big changes all over the source tree.

There are broadly 3 types of plugin methods:

  • Actions: Do something on a specific GsApp; install gimp.desktop
  • Refine: Get details about a specific GsApp; is firefox.desktop installed? or get reviews for inkscape.desktop
  • Adopt: Can this plugin handle this GsApp; can fwupd handle com.hughski.ColorHug2.firmware

You only need to define the vfuncs that the plugin needs, and the name is taken automatically from the suffix of the .so file. So, lets look at a sample plugin one chunk at a time, taking it nice and slow. First the copyright and licence (it only has to be GPLv2+ if it’s headed upstream):

 * Copyright (C) 2016 Richard Hughes 
 * Licensed under the GNU General Public License Version 2

Then, the magic header that sucks in everything that’s exported:

#include <gnome-software.h>

Then we have to define when our plugin is run in reference to other plugins, as we’re such a simple plugin we’re relying on another plugin to run after us to actually make the GsApp “complete”, i.e. adding icons and long descriptions:

gs_plugin_initialize (GsPlugin *plugin)
  gs_plugin_add_rule (plugin, GS_PLUGIN_RULE_RUN_BEFORE, "appstream");

Then we can start to do something useful. In this example I want to show GIMP as a result (from any provider, e.g. flatpak or a distro package) when the user searches exactly for fotoshop. There is no prefixing or stemming being done for simplicity.

gs_plugin_add_search (GsPlugin *plugin,
                      gchar **values,
                      GsAppList *list,
                      GCancellable *cancellable,
                      GError **error)
  guint i;
  for (i = 0; values[i] != NULL; i++) {
    if (g_strcmp0 (values[i], "fotoshop") == 0) {
      g_autoptr(GsApp) app = gs_app_new ("gimp.desktop");
      gs_app_add_quirk (app, AS_APP_QUIRK_MATCH_ANY_PREFIX);
      gs_app_list_add (list, app);
  return TRUE;

We can then easily build and install the plugin using:

gcc -shared -o libgs_plugin_example.so gs-plugin-example.c -fPIC \
 `pkg-config --libs --cflags gnome-software` \
 sudo cp libgs_plugin_example.so `pkg-config gnome-software --variable=plugindir`

Screenshot from 2016-05-19 10-39-53

I’m going to be cleaning up the exported API and adding some more developer documentation before I release the next tarball, but if this is useful to you please let me know and I’ll do some more blog posts explaining more how the internal architecture of gnome-software works, and how you can do different things with plugins.

3rd Party Fedora Repositories and AppStream

I was recently asked how to make 3rd party repositories add apps to GNOME Software. This is relevant if you run a internal private repo for employee tools, or are just kind enough to provide a 3rd party repo for Fedora or RHEL users for your free or non-free applications.

In most cases people are already running something like this to generate the repomd metadata files on a directory of RPM files:

createrepo_c --no-database --simple-md-filenames SRPMS/
createrepo_c --no-database --simple-md-filenames x86_64/

So, we need to actually generate the AppStream XML. This works by exploding any interesting .rpm files and merging together the .desktop file, the .appdata.xml file and preprocessing some icons. Only applications installing AppData files will be shown in GNOME Software, so you might need to fix before you start.

appstream-builder			\
	--origin=yourcompanyname	\
	--basename=appstream		\
	--cache-dir=/tmp/asb-cache	\
	--enable-hidpi			\
	--max-threads=1			\
	--min-icon-size=32		\
	--output-dir=/tmp/asb-md	\
	--packages-dir=x86_64/		\

This takes a second or two (or 40 minutes if you’re trying to process the entire Fedora archive…) and spits out some files to /tmp/asb-md — you probably want to change some things there to make more sense for your build server.

We then have to take the generated XML and the tarball of icons and add it to the repomd.xml master document so that GNOME Software (via PackageKit) automatically downloads the content for searching. This is as simple as doing:

modifyrepo_c				\
	--no-compress			\
	--simple-md-filenames		\
	/tmp/asb-md/appstream.xml.gz	\
modifyrepo_c				\
	--no-compress			\
	--simple-md-filenames		\
	/tmp/asb-md/appstream-icons.tar.gz	\

Any questions, please ask. If you’re using a COPR then all these steps are done for you automatically. If you’re using xdg-app already, then this is all magically done for you as well, and automatically downloaded by GNOME Software.

Upgrading Fedora 23 to 24 using GNOME Software

I’ve spent the last couple of days fixing up all the upgrade bugs in GNOME Software and backporting them to gnome-3-20. The idea is that we backport gnome-software plus a couple of the deps into Fedora 23 so that we can offer a 100% GUI upgrade experience. It’s the first time we’ve officially transplanted a n+1 GNOME component into an older release (ignoring my unofficial Fedora 20 whole-desktop backport COPR) and so we’re carefully testing for regressions and new bugs.

If you do want to test upgrading from F23 to F24, first make sure you’ve backed up your system. Then, install and enable this COPR and update gnome-software. This should also install a new libhif, libappstream-glib, json-glib and PackageKit and a few other bits. If you’ve not done the update offline using [the old] GNOME Software, you’ll need to reboot at this stage as well.

Fire up the new gnome-software and look at the new UI. Actually, there’s not a lot new to see as we’ve left new features like the ODRS reviewing service and xdg-app as F24-only features, so it should be mostly the same as before but with better search results. Now go to the Updates page which will show any updates you have pending, and it will also download the list of possible distro upgrades to your home directory.

As we’re testing upgrading to a pre-release, we have to convince gnome-software that we’re living in the future. First, open ~/.cache/gnome-software/3.20/upgrades/fedora.json and search for f24. Carefully change the Under Development string to Active then save the file. Log out, back in and the launch gnome-software again or wait for the notification from the shell. If all has gone well you should see a banner telling you about the new upgrade. If you click Download go and get a coffee and start baking a cake, as it’s going to take a long time to download all that new goodness. Once complete just click Install, which prompts a reboot where the packages will be installed. For this step you’ll probably want to bake another cake. We’re not quite in an atomic instant-apply world yet, although I’ll be talking a lot more about that for Fedora 25.

With a bit of luck, after 30 minutes staring at a progressbar the computer should reboot itself into a fresh new Fedora 24 beta installation. Success!


If you spot any problems or encounter any bugs, please let me know either in bugzilla, email or or IRC. I’ve not backported all the custom CSS for the upgrade banner just yet, but this should be working soon. Thanks!

Age Ratings in GNOME Software: Introducing OARS?

In GNOME Software we show lots of applications ranging from games aimed at pre-schoolers to applications explicitly designed to download, well, porn. A concept that is fairly well understood by parents is age ratings, and there are well known and trusted ratings bodies such as the ESRB and PEGI, as well as other country-specific schemes. Parents can use the ratings to control what kind of content is available to install, and vendors can use the ratings as a legal (or common-sense) control who gets to purchase what.

The ratings systems between countries are varied, varying from descriptions such as “M” which will be familiar for US users, “R” for Australian users to the slightly more obvious “18+” rating for European users. The differing ratings authorities define what is allowed in each category in slightly different way, some allowing mild profanity for a “7+” rating, and others none at all. Some countries consider drug taking in a video game to be no more dangerous as to mild cursing, other countries consider this on the same level as sexual violence.


So, we’re sunk, right? Nearly. There exists a group called “International Age Rating Coalition” which allows developers to register (sometimes for free), answer a simple questionnaire and out pops the ratings they should use for various countries. The IARC is made up of the regulatory bodies all over the planet, and so you can use the actual trademarked age rating images for your product. ish.

If you want to build a a software center, say GNOME Software for example, you have to pay a license fee. A $100,000 annual fee, plus extra per application shown in the software center. This is prohibitive for us, and would mean we couldn’t have the same functionality in other software center interfaces.

We could easily provide in the AppData files details about the application/game. This can be combined with a rule engine specific to the country of viewing, which would pop out a rating. I think the ESRB would be hard pushed to trademark “M” as an age rating, although I completely agree they have correctly and sensibly trademarked the stylized logo for the PG rating, along with the “ESRB” name itself. I don’t think this should stop us using an “PG” or “M” rating in the software center as long as we avoid these trademarks and copyrights.

I’m happy to work on a new system to both generate the AppData upstream information from a questionaire, and the rule engines that processes these rules and pops out a rating. The question then becomes, is this useful? Is this something that people would actually want? Comments welcome.

p.s. OARS: “Open Age Rating System”, name is work in process.

Moderate reviews in GNOME Software

I’m pondering adding something like this for GNOME Software:

Screenshot from 2016-02-11 20-31-28

The idea is it would be launched using a special geeky-user-only gnome-software --mode=moderate command line, so that someone can up or down-vote any reviews that are compatible with their country code. This would be used by super-users using community distros like Fedora, and perhaps people in a QA team for distros like RHEL. The reason I wanted to try to use gnome-software rather than just doing it in a web-app was that you have access to the user machine hash, so you can hide reviews the user has already voted on without requiring a username and password that has to be matched to the local machine. We also have all the widgets and code in place, so it is really just a couple of hundred lines of code for this sekret panel. The server keeps track of who voted on what and so reviewers can just close the app, open it a few weeks later and just continue only moderating the reviews that came in since then.

I can’t imagine the tool would be used by many people, but it does make reviewing comments easy. Comments welcome.

Comments are live

With a huge amount of help from Robert Ancell for a lot of the foundations for the new code, I’ve pushed a plugin today to allow anonymous rating of applications.

Screenshot from 2016-02-10 17-16-04

If people abuse or spam this I’ll take the feature away until we can have OpenID logins in GNOME Online Accounts, but I’m kinda hoping people won’t be evil. The server is live and accepting reviews and votes, but the API isn’t set in stone.

Anonymous reviews in GNOME Software

Choosing an application to install is hard when there are lots of possible projects matching a specific search term. We already list applications based on the integration level and with useful metrics like “is it translated in my language” and this makes sure that high quality applications are listed near the top of the results. For more information about an application we often want a more balanced view than the PR speak or unfounded claims of the upstream project. This is where user-contributed reviews come in.


To get a user to contribute a review (which takes time) we need to make the process as easy as possible. Making the user create a user account on yet-another-webservice will make this much harder and increase the barrier to participation to the point that very few people would contribute reviews. If anonymous reviewing does not work the plan is to use some kind of attestation service so you can use a GMail or Facebook for confirming your identity. At this point I’m hoping people will just be nice to each other and not abuse the service although this reviewing facility will go away if it starts being misused.

Designing an anonymous service is hard when you have to be resilient against a socially awkward programmer with specific political ideologies. If you don’t know any people that match this description you have obviously never been subscribed to fedora-devel or memo-list.

Obviously when contacting a web service you share your IP address. This isn’t enough to uniquely identify a machine and user, which we want for the following reasons:

  • Allowing users to retract only their own reviews
  • Stopping users up or down-voting the same review multiple times

A compromise would be to send a hash of two things that identify the user and machine. In GNOME Software we’re using a SHA1 hash of the machine-id and the UNIX username along with a salt, although this “user_id” is only specified as a string and the format is not checked.

For projects like RHEL where we care very much what comments are shown to paying customers we definitely want reviews to be pre-approved and checked before showing to customers. For distros like Fedora we don’t have this luxury and so we’re going to rely on the community to self-regulate reviews. Reviews are either up-voted or down-voted according how useful they are along with the nuclear option of marking the review as abusive.


By specifying the users current locale we can sort the potential application reviews according to a heuristic that we’re still working on. Generally we want to prefer useful reviews in the users locale and hide ones that have been marked as abusive, and we also want to indicate the users self-review so they can remove it later if required. We also want to prioritize reviews for the current application version compared to really old versions of these applications.

Comments welcome!

AppData and the gettext domain

When users are searching for software in GNOME Software it is very important to answer the the question “Is this localized in my language?” If you can only speak Swedish then an application talking just in American English is not much use at all. The way we calculate this in the AppStream builder is to look at the compiled .mo files, breaking them apart and then using statistics to work out what locales are included.

When we’re processing distro packages we usually extract them one at a time. We first try for a gettext domain (the .mo file name) of the distro package name, and if that’s not found then we just try and find the first .mo file in any of the locale directories. This works about 70% of the time (which is good) but fails about 30% of the time (which is bad). For xdg-app we build the application in a special prefix, along with any dependent libraries. We don’t have a distro package name for the bundle (only the application ID) and so the “first .mo file we can find” heuristic fails more often that it works. We clearly need some more information about the gettext domain from the upstream project.

AppData to the rescue. By adding this in the AppData file informs the AppStream generation code in the xdg-app builder what gettext domain to use for an application. To use this you just need to add:

  <translation type="gettext">the_gettext_domain_here</translation>

under the <component> tag. The gettext domain is normally set in the configure.ac file with the GETTEXT_PACKAGE define. If you don’t have this extra data in your application then appstream-util validate is soon going to fail, and your application isn’t going to get the language metadata and so will be lower in the search results for users using GNOME Software in a non-C locale. If your GNOME application is available in jhbuild the good news is that I’ve automatically added the <translation> tag to 104 projects semi-automatically today. For XFCE and KDE I’m going to be sending emails to the development mailing lists tomorrow. For all other applications I’m going to be using the <update_contact> email address set in the AppData file for another mass-emailing.

Although it seems I’m asking people to do more things again and again I can assure you that slowly we’re putting the foundations in place for an awesome software installer experience. Just today I merged in the xdg-app branch into gnome-software and so I’m hoping to have a per-user xdg-app preview available in Fedora 24. Exciting times. :)