Survey not shown on mobile (iOS 15, iPhone < 8)

[ilsd]

Please use the 👍 reaction to show that you are affected by the same issue. Please don't comment if you have no relevant information to add!

Issue

When sharing a survey created with Forms via a link (anonymous answers) users of mobile browsers (at least on iPhone7, iOS 15.8.2 ) do not see the survey at all.

Other users (e.g. Firefox on Desktop) see and are able to complete the survey (it just works).

Steps to replicate it:

1. Open this link with a a mobile browser: https://cloud.lantschner.name/index.php/apps/forms/s/YmMTjH4YsPzbjKedEHTNAfAo
2. See a screen w/o any form

Sumary

All users of iPhone < 8 can not participate in any survey.

Seems the problem is the lookbehind, which is only supported starting iOS 16.4 (Lookbehind in JS regular expressions | Can I use... Support tables for HTML5, CSS3, etc 1)

TODO: It needs to be checked if the current regex can be rewritten without a lookbehind.

Discussion

https://help.nextcloud.com/t/forms-survey-not-shown-at-all-on-mobile-ios-if-shared-via-link/186261

May be related to

https://help.nextcloud.com/t/forms-nextcloud-app-gui-fehler/166702
sounds similar although, in their case, the user was obviously at least able to start the survey.

Context

Nextcloud version : Nextcloud Hub 7 (28.0.3)
Operating system and version: Debian 4.19.304-1
Apache or nginx version : Apache/2.4.38 (Debian)
PHP version: PHP 8.2.17

[Chartman123]

@susnux following the investigation in the forum I think it comes from this line here: https://github.com/nextcloud/forms/blob/main/src%2Futils%2FRegularExpression.js#L30

Is there an easy fix for it? If not I think that we shouldn't set this on highest priority given that the devices only receive security fixes from Apple and all modern browsers support this code.

[susnux]

I think we could use (?:^|[^\\])(?:\\\\)*\/ as a regex, it only matches for non escaped slashes, so for checking it works.

[Chartman123]

So you mean that in our case it doesn't matter if it also matches preceeding characters? If yes, fine for me. Should I create a PR for that or do you want to do it yourself?

[susnux]

Yes we do not care, as we just use it for testing not sanitizing. If you want create a PR, happy to review :)