[Bug]: Absence event starts one day too early and is always set to UTC

[ChristophWurst]

⚠️ This issue respects the following points: ⚠️

• This is a bug, not a question or a configuration/webserver/proxy issue.
• This issue is not already reported on Github OR Nextcloud Community Forum (I've searched it).
• Nextcloud Server is up to date. See Maintenance and Release Schedule for supported versions.
• I agree to follow Nextcloud's Code of Conduct.

Bug description

Despite #41703, setting an out of office with 28 RC3 leads to a calendar event that starts one day too early and is drifting for timezones with an offset due to the event being set to UTC.

Steps to reproduce

1. Log into Nextcloud
2. Configure an absence
3. Open Calendar

Expected behavior

Absence events starts 00:00 of my first day of absence and ends 00:00 of the first day I'm back.

Installation method

None

Nextcloud Server version

28

Operating system

None

PHP engine version

None

Web server

None

Database engine version

None

Is this bug present after an update or on a fresh install?

None

Are you using the Nextcloud Server Encryption module?

None

What user-backends are you using?

• Default user-backend (database)
• LDAP/ Active Directory
• SSO - SAML
• Other

Configuration report

No response

List of activated Apps

No response

Nextcloud Signing status

No response

Nextcloud Logs

No response

Additional info

No response

[ChristophWurst]

Debugging

• Login timezone: browser sends correct timezone during login ✔️
• Actual value in database: Europe/Vienna ✔️
• Time during absence configuration: correct, not a day early. ✔️
• Calendar timezone in oc_calendars: NULL ⚠️

[ChristophWurst]

The day drift is fixable easily.

The time drift only happens if the calendar has no timezone set. Other code uses better sources for the timezone anyway, so we should migrate this too. The problem created is that we will only have the timezone id, not the full VTIMEZONE component.