User application Snap plugging "cups" does not set CUPS_SERVER

[Till Kamppeter]

See also

https://forum.snapcraft.io/t/cups-interface-merged-into-snapd-additional-steps-to-complete/

for some background information.

I am on Jammy, amd64.

For the development of the new "cups" interface of snapd I did the following test:

1. Install snapd Snap from edge, gave me version 2.54.4+git1072.g87e5a7c

2. Get CUPS Snap from GIT repo: https://github.com/OpenPrinting/cups-snap, apply following patch:

----------
--- a/snapcraft.yaml
+++ b/snapcraft.yaml
@@ -59,6 +59,7 @@ slots:
     interface: cups-control
   cups:
     interface: cups
+ cups-socket-directory: $SNAP_COMMON/run

 apps:

----------

Build the Snap with "snapcraft snap" and install it with "sudo snap install --dangerous SNAPFILE"

3. Get test-snapd-cups-consumer from GIT: https://github.com/snapcore/test-snapd-cups-consumer/
Build and install this Snap, as you did with the CUPS Snap, no patches needed here.

4. Connect the "cups" interface:

sudo snap connect test-snapd-cups-consumer:cups cups:cups

Now you should have all set up. So run the application of the test Snap:

test-snapd-cups-consumer.cups

It starts a shell inside the Snap harness so that you can do tests there. CUPS command line tools are installed there.

In the shell run:

$ echo $CUPS_SERVER
$ lpstat -H
$ lpstat -v
$ exit

You see that the CUPS_SERVER environment variable is no set and the lpstat commands refer themselves to the system's CUPS (/run/cups/cups.sock) and not to the Snap's CUPS (/var/cups/cups.sock).

$ snap list
Name Version Rev Tracking Publisher Notes
bare 1.0 5 latest/stable canonical✓ base
chromium 99.0.4844.51 1926 latest/stable canonical✓ -
core 16-2.54.3 12725 latest/stable canonical✓ core
core18 20211215 2284 latest/stable canonical✓ base
core20 20220304 1376 latest/edge canonical✓ base
cups 2.4.1-3 x22 - - -
cups-admin-test 0.1.0 x5 - - -
cups-admin-test-no-control 0.1.0 x10 - - -
ghostscript-printer-app 1.0 x130 - - -
gimp 2.10.28 383 latest/stable snapcrafters -
gnome-3-28-1804 3.28.0-19-g98f9e67.98f9e67 161 latest/stable canonical✓ -
gnome-3-34-1804 0+git.3556cb3 77 latest/stable/… canonical✓ -
gnome-3-38-2004 0+git.1f9014a 99 latest/stable canonical✓ -
gtk-common-themes 0.1-59-g7bca6ae 1519 latest/stable/… canonical✓ -
gutenprint-printer-app 1.0 x35 - - -
hplip-printer-app 1.0 x3 latest/edge - -
ipp-usb 0.9.19+git7.72a1620 x3 - - -
kde-frameworks-5-core18 5.61.0 32 latest/stable kde✓ -
kde-frameworks-5-qt-5-15-core20 5.79.0 14 latest/stable kde✓ -
multipass 1.8.0 6130 latest/stable canonical✓ -
ps-printer-app 1.0 x76 latest/edge - -
rasterview 1.8 222 latest/stable michaelrsweet -
snap-store 3.38.0-66-gbd5b8f7 558 latest/stable/… canonical✓ -
snapcraft 6.0.2 7010 latest/stable canonical✓ classic
snapd 2.54.4+git1072.g87e5a7c 15211 latest/edge canonical✓ snapd
telegram-desktop 3.4.3 3544 latest/stable telegram.desktop -
test-snapd-cups-consumer 1.0 x2 latest/edge - -
zoom-client 5.9.6.2225 170 latest/stable ogra -

$ snap connections | grep cups
avahi-control cups:avahi-control :avahi-control manual
avahi-observe cups-admin-test-no-control:avahi-observe :avahi-observe manual
avahi-observe cups-admin-test:avahi-observe :avahi-observe manual
cups cups-admin-test-no-control:cups cups:cups manual
cups test-snapd-cups-consumer:cups cups:cups manual
cups-control chromium:cups-control :cups-control -
cups-control cups-admin-test:cups-control :cups-control manual
cups-control cups:cups-internal cups:cups-control manual
home cups-admin-test-no-control:home :home -
home cups-admin-test:home :home -
home cups:home :home -
network cups-admin-test-no-control:network :network -
network cups-admin-test:network :network -
network cups:network :network -
network test-snapd-cups-consumer:network :network -
network-bind cups:network-bind :network-bind -
network-manager-observe cups:network-manager-observe :network-manager-observe manual
raw-usb cups:raw-usb :raw-usb manual
system-files cups:etc-cups :system-files manual

$

[Till Kamppeter (till-kamppeter)]

$ snap version
snap 2.54.4+git1072.g87e5a7c
snapd 2.54.4+git1072.g87e5a7c
series 16
ubuntu 22.04
kernel 5.15.0-18-generic

[Ian Johnson (anonymouse67)]

I can't reproduce this in a jammy VM when building the test-snapd-cups-consumer snap from git revision 4f25c2f7cff6ba1d13149c19d52177004615ebaf with the cups snap on edge (revision 664):

ubuntu@sparkling-zebu:~/test-snapd-cups-consumer$ snapcraft snap
...
Snapping |
Snapped test-snapd-cups-consumer_1.0_amd64.snap
ubuntu@sparkling-zebu:~/test-snapd-cups-consumer$ sudo snap install cups --edge
cups (edge) 2.4.1-3 from OpenPrinting✓ installed
ubuntu@sparkling-zebu:~/test-snapd-cups-consumer$ sudo snap install --dangerous test-snapd-cups-consumer_1.0_amd64.snap
2022-03-11T08:45:56-06:00 INFO failed to update "cups", will not have required content "foo": snap has no updates available
test-snapd-cups-consumer 1.0 installed
ubuntu@sparkling-zebu:~/test-snapd-cups-consumer$ snap connections test-snapd-cups-consumer
Interface Plug Slot Notes
content test-snapd-cups-consumer:foo-install-cups - -
cups test-snapd-cups-consumer:cups cups:cups -
cups-control test-snapd-cups-consumer:cups-control - -
network test-snapd-cups-consumer:network :network -
ubuntu@sparkling-zebu:~/test-snapd-cups-consumer$ test-snapd-cups-consumer.cups
To run a command as administrator (user "root"), use "sudo <command>".
See "man sudo_root" for details.

ubuntu@sparkling-zebu:/home/ubuntu/test-snapd-cups-consumer$ echo $CUPS_SERVER
/var/cups/cups.sock
ubuntu@sparkling-zebu:/home/ubuntu/test-snapd-cups-consumer$ ^C
ubuntu@sparkling-zebu:/home/ubuntu/test-snapd-cups-consumer$ exit
ubuntu@sparkling-zebu:~/test-snapd-cups-consumer$ snap list cups
Name Version Rev Tracking Publisher Notes
cups 2.4.1-3 664 latest/edge openprinting✓ -
ubuntu@sparkling-zebu:~/test-snapd-cups-consumer$ snap version
snap 2.54.4+git1079.gbf8d25c
snapd 2.54.4+git1079.gbf8d25c
series 16
ubuntu 22.04
kernel 5.15.0-18-generic

[Ian Johnson (anonymouse67)]

Till confirmed to me that he cannot reproduce this anymore either, so I'm going to close this bug.