Help understanding the content interface

snapcraft
1

I’ve been trying to make a PoC of the content interface https://github.com/joedborg/snap-content-interface-test

Very basically, I’m trying to get a file snapped in the provider (hippo-food) to appear in the consumer (hungry-hippo). In this instance, it’s food.

I can see the food file is in the hippo-food snap:

➜ ll -h /snap/hippo-food/current/
total 1.0M
-rw-rw-r-- 1 root root 1.0M Jun  9 15:00 food

But, when I connect the interface

snap connect hungry-hippo:mouth hippo-food:food

…the file does not seem to end up in $SNAP_COMMON, as specified here https://github.com/joedborg/snap-content-interface-test/blob/master/consumer/snap/snapcraft.yaml#L14

➜ ll -h /var/snap/hungry-hippo/common
total 0

Have I misunderstood how this is meant to work? On top of this, I’d like to know if I can specify a hook to act upon the file, in the consuming snap, when the connection is made.

Many thanks,
Joe

2

The content interface is only effective for the snap itself, i.e. you need to be in the snap’s mount namespace. So if you did

snap run --shell hungry-hippo -c 'ls -h $SNAP_COMMON'

I think you would see the food.

3

Ah thanks Ian! That’s working, however on the first attempt, I got this warning before it listed:

update.go:85: cannot change mount namespace according to change mount (/snap/hippo-food/x1/food /var/snap/hungry-hippo/common/food/food none bind,ro 0 0): cannot use "/snap/hippo-food/x1/food" as bind-mount source: not a directory

Should I log that?

4

Can you show the snapcraft.yaml before you file a bug? It looks like you might have a layout error, perhaps using bind instead of bind-file?

5

Sure,
Consumer https://github.com/joedborg/snap-content-interface-test/blob/master/consumer/snap/snapcraft.yaml
Provider https://github.com/joedborg/snap-content-interface-test/blob/master/provider/snap/snapcraft.yaml