[Bug]: Use system timezone in calculation of share times

[nfebe]

⚠️ 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

A user encountered an issue when attempting to create share links in Nextcloud before 9:00 AM JST (UTC+09:00). After investigation, it appears there is an error in how we calculate share link expiration times, because looking at the code, we always use UTC irrespective of the users timezone.

Steps to reproduce

1. Set the system clock to a time before 9:00 AM JST.
2. Set a default expiration time (which is in number of days).
3. Attempt to create a share link.

Expected behavior

Share links should be created without encountering any issues irrespective of the time of day.

Installation method

None

Nextcloud Server version

26

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

[nfebe]

Likely culprits

server/lib/private/Share20/Manager.php

Lines 432 to 438 in 7d8741c

	$date = new \DateTime();
	$date->setTime(0, 0, 0);
	$date->add(new \DateInterval('P' . $defaultExpireDays . 'D'));
	if ($date < $expirationDate) {
	$message = $this->l->n('Cannot set expiration date more than %n day in the future', 'Cannot set expiration date more than %n days in the future', $defaultExpireDays);
	throw new GenericShareException($message, $message, 404);
	}

and

server/lib/private/Share20/Manager.php

Lines 508 to 514 in 7d8741c

	$date = new \DateTime();
	$date->setTime(0, 0, 0);
	$date->add(new \DateInterval('P' . $this->shareApiLinkDefaultExpireDays() . 'D'));
	if ($date < $expirationDate) {
	$message = $this->l->n('Cannot set expiration date more than %n day in the future', 'Cannot set expiration date more than %n days in the future', $this->shareApiLinkDefaultExpireDays());
	throw new GenericShareException($message, $message, 404);
	}

[nfebe]

Recommended fix :

• Use 'default_timezone'in config file which defaults to 'Europe/Berlin' (or perhaps should default to UTC as the normal php functions)
• User can then set their timezone in config and it would be respected.
• There is TimeZoneService in https://github.com/nextcloud/server/blob/master/apps/dav/lib/CalDAV/TimezoneService.php perhaps we can make it a core service so it is used more widely

[ChristophWurst]

• defaults to 'Europe/Berlin'

Defaults to UTC. Europe/Berlin is an example.