fix(dav): Allow underscores on custom links

[solracsf]

• Resolves: [Bug]: Custom Public Link containing underscores "_" stopped working on upgrade to 31.0.2 #51714
• Completes fix(dav): Fix share token pattern for base uri extraction #51365

Checklist

• Code is properly formatted
• Sign-off message is added to all commits
• Tests (unit, integration, api and/or acceptance) are included
• Screenshots before/after for front-end changes
• Documentation (manuals or wiki) has been updated or is not required
• Backports requested where applicable (ex: critical bugfixes)

[solracsf]

/backport to stable31

[provokateurin]

This doesn't make sense, because creating custom links with underscores is not allowed in the first place:

server/apps/files_sharing/lib/Controller/ShareAPIController.php

Line 1381 in 78b31ca

if (!preg_match('/^[a-z0-9-]+$/i', $token)) {

[solracsf]

Hum. Then 2 ways here, either allow it (I don't see a valid reason why not, but correct me), or validate input and clearly states that _ is not allowed.

See Kate's comment

[provokateurin]

Well I'm wondering how we even received such a bug report, given that it's not allowed to create custom links with underscores. To me it only makes sense if we either miss the validation in some cases (maybe when updating the share?) or the report manually edited the database (and thus created an invalid report).

I'm fine with allowing underscores though, I don't see why we should allow them.

[susnux]

I agree with Kate and think we should do both

1. Properly validate the input -> Bugfix and backport.
2. Allow underscore (this PR) -> Feature for 32.

[kesselb]

Properly validate the input -> Bugfix and backport.

Those links were created with the 3rdparty app before 31 (#51714 (comment)).

[solracsf]

@kesselb comment also says:

Share links with underscore can still be created in my v. 31.0.2 without complaint from Nextcloud.

[kesselb]

I believe the user meant that they can still create share links with underscores using the cfg_share_links app. This app is available for Nextcloud 31 and is enabled according to the system report. The custom share link feature is disabled by default, so the user might not have realized they were using the app instead of the built-in approach.

I wanted to clarify that the input validation for our custom share link feature is not broken and doesn't need fixing. If we want to allow underscores, continuing with this PR should be fine.

[provokateurin]

I agree with @kesselb, but since there is nothing against allowing underscores we should just merge this PR.

[szaimen]

LGTM but did not test