interfaces/repo: validate slot/plug names

[stolowski]

It's seems that by an oversight or an error in refactoring we don't validate slot and plug names coming from snap yaml on installation anymore. This allows names such as ttyS5 go through, which then causes an error on interface hooks ("error: cannot perform the following tasks:- Prepare connection of slot caracalla:ttyS4 (internal error: no registered handlers for hook "prepare-slot-ttyS4"), because they are strict on names.

This PR adds validation (back?) to AddSnap. Note that it may break (according to morhpis, it actually will break) some existing snaps, so I'm open to discussion what we can do to workaround/mitigate, other than relaxing this validation.

[zyga]

I think this code is good and should land but we need a way to migrate systems that used wrong plugs / slot names to alternate names.

One idea is to ship a core snap that can rename interfaces according to gadget hints. Following that release a gadget that assumes: snapdXX which contains such definitions.

[mvo5]

Code looks fine, mitigation for existing user is something we need to discuss, ideally with @niemeyer

[pedronis]

marked as Blocked until we discuss the path forward for preexisting snaps/revisions with the issue

[stolowski]

Regarding existing snaps affected by this change... I think they are broken already anyway - if they use capital letters in plugs (slots), they will fail on hooks (even if they don't have hooks) - that would need to be checked with @morphis who originally experienced this issue.

[morphis]

@stolowski We mainly have those plugs on gadget snaps but we can work around this problem when we coordinate a release of the core snap and the gadget snap to happen with the same OTA.

[niemeyer]

@morphis Thanks for the flexibility there, it's appreciated. I suggest going ahead right now and replacing the plugs/slot names so that they are lowercase. This was never intended to be accepted, and there are likely areas in the code already that will blow up if they see such names.

I've got a list of snap.yaml files from Celso today. It's not complete, but it comprises 663 snaps that are classic or strict and released in stable. Missing from the set from stable are only very old snaps released before the store started collecting snap.yaml into the database.

The result is that none of them have uppercase slot or plug names. If you're curious, this is the list: http://paste.ubuntu.com/24186301/

We can try to gather more data, but I consider this and @morphis willingness to address the issue with existing gadgets as good evidence that we can go ahead and fix the bug.

[morphis]

Sounds good to me. I will cross check that with others today but that should be our easiest way forward.

[morphis]

@niemeyer Btw. your list doesn't cover branded stores as I miss specific product ones which are definitely there. Can you cross-check those too?

[zyga]

We cannot land this as core has duplicated plug/slot name and it may have unexpected consequences.

[niemeyer]

This looks completely unrelated to that issue. Let's please discuss in:

https://forum.snapcraft.io/t/duplicate-plug-slot-names-inside-the-core-snap/184

[niemeyer]

I'm tentatively merging this targeting 2.24.

@mvo5 @morphis Let's keep an eye on potential side effects here.