Neon/Snap

Reading Material

Snap & Snapcraft Documentation: https://docs.snapcraft.io
Snap Guide: Guidelines_and_HOWTOs/Snap
Content Snap: Neon/Snap/KF5Content
Current notes on state of Snaps https://notes.kde.org/p/neon-snaps

Usage

To use them

https://apachelog.wordpress.com/2017/01/30/kde-applications-in-ubuntu-snap-store/

sudo snap install kblocks

No sudo

To drop the requirement to have to sudo everything you need to login using ubuntu login credentials first.

sudo snap login

After that you should have a ~/.snap/auth.json file and snap should work without sudo.

Building

The snapcraft.yamls we have in our packaging repositories are generally meant to be built via our tooling and the respective Jenkins jobs. Generally they can however also be built manually as the tooling only extends them a bit to build from git and install suitable packages for the current content-snap SDK. By and large this is optional though.

To build you need a working snapd (for containerized use LXD is recommended because it has native systemd support). You'll also want latest snapcraft: snap install --classic snapcraft

Building is done by running

snap run snapcraft --destructive-mode

It's destructive because it needs to change your system. By default snapcraft since 2019 would try to throw builds in a VM, since snaps mostly need neon's repos to build that isn't useful for us in its current form.

Snapd Problems

(upstream issues ought to be filed/subscribed to and mentioned here)

Theming [is kind of addressed by XDG Settings portal]
1. How to get theme settings from the host into the snap?
2. QtStyles are binary plugins and so even when we know which style is configured on the host we cannot just load it
3. Icon themes in /usr/share and ~/.local cannot be accessed from inside snaps
4. Same for mouse cursor themes
5. Same for fonts
6. upstream is aware and working on it
7. https://bugs.launchpad.net/ubuntu/+source/snapd/+bug/1585332
Hard to debug applications
1. We have huge wrapper scripts that are required for applications to run properly
  1. https://cgit.kde.org/scratch/apol/kf5-snap-env.git/tree/
  2. https://forum.snapcraft.io/t/custom-environment-variables-for-parts/1639/10
2. It's hard to reach out to debugging tools
  1. should be easy-ish to use gdb-server
  2. gdb/valgrind/strace need to be in the snap to be reachable
3. Possibly needs a way to catch and send cores and then retrace them server-side with (externally) generated debug symbol dumps?
Discover Software Center integration isn't at the level of PackageKit or Flatpak. Mostly boils down to some appstream support
1. we are lacking appstream ids, useful for de-duplication
2. cannot use snaps for the featured applications list (apps are listed as appstream ids)
3. AppStream ID as id for reviews https://forum.snapcraft.io/t/best-way-to-key-a-snap-for-reviewing/854/2
4. https://forum.snapcraft.io/t/support-for-appstream-id/2327
No source code storage/retrieval for snaps
1. https://bugs.launchpad.net/snapcraft/+bug/1711333
2. https://forum.snapcraft.io/t/use-a-separate-manifest-file-or-save-everything-in-snap-snapcraft-yaml/1152

Snapcraft Problems

No real way to run unit tests through snapcraft
1. Talking with snapcraft developers, they suggested using "install: ctest ." much like in here: https://snapcraft.io/docs/build-snaps/node
2. Implemented here: https://cgit.kde.org/scratch/apol/kf5-snap-env.git/plain/README.md
Content snap has problems
1. Make sure that on cleanbuilds we get the deps from the Neon repo instead of ubuntu (for the things Neon implements)
2. Related https://bugs.kde.org/show_bug.cgi?id=385062
3. https://bugs.launchpad.net/snapcraft/+bug/1719928
Lack of Appstream support
1. Substantial metadata duplication. snap metadata excessively duplicates appstream metadata such as license, summary, version, icon. Makes it undesirable to maintain the data in snapcraft.yaml so it will simply go out of date at some point.
  1. https://forum.snapcraft.io/t/extracting-existing-data-from-projects-to-feed-into-snap-yaml/2285
  2. https://github.com/snapcore/snapcraft/issues/1694
2. Should be extracting the icon and desktop file from the package. Now it's copied in the packaging.
GPG verification of incoming content is not supported. This breaks the signing chain from tag -> tarball -> pkg -> user. Only applies to tarballs. [Supposedly the tarball is somewhere in the build tree, so we could build custom rigging to download the gpg after snapcraft ran and verify the tarball snapcraft got is the signed one and abort if not]