[Bug]: Validation error in iCalendar: TRIGGER MUST appear exactly once in a VALARM component

⚠️ 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

Frequently getting a message in the server log:

Validation error in iCalendar: TRIGGER MUST appear exactly once in a VALARM component

But as far as I can tell, the calendar entry that it's reporting about conforms to the validation requirement:

BEGIN:VCALENDAR
VERSION:2.0
CALSCALE:GREGORIAN
PRODID:-//Sabre//Sabre VObject 4.5.4//EN
BEGIN:VEVENT
UID:f9b5b6ca42cf624b1c11bff4d206a686
DTSTART:20240416T120000
DTEND:20240416T130000
SUMMARY:[redacted]
DESCRIPTION:[redacted]
CREATED:20240411T134539Z
DTSTAMP:20240411T134539Z
BEGIN:VALARM
ACTION:DISPLAY
DESCRIPTION:[redacted]
TRIGGER;RELATED=START:-PT15M
END:VALARM
BEGIN:VALARM
ACTION:DISPLAY
DESCRIPTION:[redacted]
TRIGGER;RELATED=START:-PT1D
END:VALARM
END:VEVENT
END:VCALENDAR

That looks to me like TRIGGER is only appearing exactly once in each of those VALARM components.

Steps to reproduce

Not entirely clear. Just create a calendar event with the same structure as above I suppose.

Expected behavior

Should not emit invalid warnings.

Installation method

Other Community project

Nextcloud Server version

29

Operating system

RHEL/CentOS

PHP engine version

PHP 8.0

Web server

Apache (supported)

Database engine version

MySQL

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

Updated from a MINOR version (ex. 22.1 to 22.2)

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

{
    "system": {
        "log_type": "syslog",
        "datadirectory": "***REMOVED SENSITIVE VALUE***",
        "updatechecker": false,
        "check_for_working_htaccess": false,
        "asset-pipeline.enabled": false,
        "assetdirectory": "\/var\/lib\/nextcloud",
        "preview_libreoffice_path": "\/usr\/bin\/libreoffice",
        "apps_paths": [
            {
                "path": "\/usr\/share\/nextcloud\/apps",
                "url": "\/apps",
                "writable": false
            },
            {
                "path": "\/var\/lib\/nextcloud\/apps",
                "url": "\/apps-appstore",
                "writable": true
            }
        ],
        "instanceid": "***REMOVED SENSITIVE VALUE***",
        "passwordsalt": "***REMOVED SENSITIVE VALUE***",
        "secret": "***REMOVED SENSITIVE VALUE***",
        "trusted_domains": [
            "owncloud.example.com",
            "www.example.com"
        ],
        "overwrite.cli.url": "http:\/\/owncloud.example.com\/",
        "dbtype": "mysql",
        "dbname": "***REMOVED SENSITIVE VALUE***",
        "dbhost": "***REMOVED SENSITIVE VALUE***",
        "dbuser": "***REMOVED SENSITIVE VALUE***",
        "dbpassword": "***REMOVED SENSITIVE VALUE***",
        "version": "29.0.0.19",
        "installed": true,
        "theme": "",
        "maintenance": false,
        "forcessl": false,
        "loglevel": 1,
        "log_authfailip": true,
        "mail_from_address": "***REMOVED SENSITIVE VALUE***",
        "mail_smtpmode": "smtp",
        "mail_domain": "***REMOVED SENSITIVE VALUE***",
        "mail_smtphost": "***REMOVED SENSITIVE VALUE***",
        "trashbin_retention_obligation": "auto",
        "htaccess.RewriteBase": "\/",
        "appstore.experimental.enabled": true,
        "mysql.utf8mb4": true
    }
}

List of activated Apps

Enabled:
  - activity: 2.21.1
  - calendar: 4.7.3
  - circles: 29.0.0-dev
  - cloud_federation_api: 1.12.0
  - comments: 1.19.0
  - contacts: 6.0.0
  - contactsinteraction: 1.10.0
  - dashboard: 7.9.0
  - dav: 1.30.1
  - federatedfilesharing: 1.19.0
  - federation: 1.19.0
  - files: 2.1.0
  - files_downloadlimit: 2.0.0
  - files_pdfviewer: 2.10.0
  - files_reminders: 1.2.0
  - files_sharing: 1.21.0
  - files_trashbin: 1.19.0
  - files_versions: 1.22.0
  - firstrunwizard: 2.18.0
  - logreader: 2.14.0
  - lookup_server_connector: 1.17.0
  - nextcloud_announcements: 1.18.0
  - notes: 4.10.0
  - notifications: 2.17.0
  - oauth2: 1.17.0
  - password_policy: 1.19.0
  - photos: 2.5.0
  - privacy: 1.13.0
  - provisioning_api: 1.19.0
  - recommendations: 2.1.0
  - related_resources: 1.4.0
  - serverinfo: 1.19.0
  - settings: 1.12.0
  - sharebymail: 1.19.0
  - support: 1.12.0
  - survey_client: 1.17.0
  - systemtags: 1.19.0
  - text: 3.10.0
  - theming: 2.4.0
  - twofactor_backupcodes: 1.18.0
  - updatenotification: 1.19.1
  - user_status: 1.9.0
  - viewer: 2.3.0
  - weather_status: 1.9.0
  - workflowengine: 2.11.0
Disabled:
  - admin_audit: 1.19.0
  - bruteforcesettings: 2.9.0
  - encryption: 2.17.0
  - files_external: 1.21.0
  - files_rightclick: 0.15.1 (installed 1.6.0)
  - files_texteditor: 2.15.1 (installed 2.15.1)
  - suspicious_login: 7.0.0
  - twofactor_totp: 11.0.0-dev
  - user_ldap: 1.20.0 (installed 1.14.1)

Nextcloud Signing status

No response

Nextcloud Logs

{"reqId":"Zkd8EYMn0F7rKyEDPu20pwAAAAQ","level":3,"time":"2024-05-17T15:47:30+00:00","remoteAddr":"10.75.22.132","user":"brian","app":"webdav","method":"PUT","url":"/remote.php/dav/calendars/brian/private/[redacted].ics","message":"{\"Exception\":\"Sabre\\\\DAV\\\\Exception\\\\UnsupportedMediaType\",\"Message\":\"Validation error in iCalendar: TRIGGER MUST appear exactly once in a VALARM component\",\"Code\":0,\"Trace\":[{\"file\":\"/usr/share/nextcloud/3rdparty/sabre/dav/lib/CalDAV/Plugin.php\",\"line\":739,\"function\":\"validateICalendar\",\"class\":\"Sabre\\\\CalDAV\\\\Plugin\",\"type\":\"->\",\"args\":[\"*** sensitive parameters replaced ***\",\"*** sensitive parameters replaced ***\",false,[\"Sabre\\\\HTTP\\\\Request\"],[\"Sabre\\\\HTTP\\\\Response\"],false]},{\"file\":\"/usr/share/nextcloud/3rdparty/sabre/event/lib/WildcardEmitterTrait.php\",\"line\":89,\"function\":\"beforeWriteContent\",\"class\":\"Sabre\\\\CalDAV\\\\Plugin\",\"type\":\"->\",\"args\":[\"*** sensitive parameters replaced ***\",[\"OCA\\\\DAV\\\\CalDAV\\\\CalendarObject\"],\"*** sensitive parameters replaced ***\",false]},{\"file\":\"/usr/share/nextcloud/3rdparty/sabre/dav/lib/DAV/Server.php\",\"line\":1133,\"function\":\"emit\",\"class\":\"Sabre\\\\DAV\\\\Server\",\"type\":\"->\",\"args\":[\"beforeWriteContent\",[\"*** sensitive parameters replaced ***\",[\"OCA\\\\DAV\\\\CalDAV\\\\CalendarObject\"],\"*** sensitive parameters replaced ***\",false]]},{\"file\":\"/usr/share/nextcloud/3rdparty/sabre/dav/lib/DAV/CorePlugin.php\",\"line\":492,\"function\":\"updateFile\",\"class\":\"Sabre\\\\DAV\\\\Server\",\"type\":\"->\",\"args\":[\"*** sensitive parameters replaced ***\"]},{\"file\":\"/usr/share/nextcloud/3rdparty/sabre/event/lib/WildcardEmitterTrait.php\",\"line\":89,\"function\":\"httpPut\",\"class\":\"Sabre\\\\DAV\\\\CorePlugin\",\"type\":\"->\",\"args\":[[\"Sabre\\\\HTTP\\\\Request\"],[\"Sabre\\\\HTTP\\\\Response\"]]},{\"file\":\"/usr/share/nextcloud/3rdparty/sabre/dav/lib/DAV/Server.php\",\"line\":472,\"function\":\"emit\",\"class\":\"Sabre\\\\DAV\\\\Server\",\"type\":\"->\",\"args\":[\"method:PUT\",[[\"Sabre\\\\HTTP\\\\Request\"],[\"Sabre\\\\HTTP\\\\Response\"]]]},{\"file\":\"/usr/share/nextcloud/3rdparty/sabre/dav/lib/DAV/Server.php\",\"line\":253,\"function\":\"invokeMethod\",\"class\":\"Sabre\\\\DAV\\\\Server\",\"type\":\"->\",\"args\":[[\"Sabre\\\\HTTP\\\\Request\"],[\"Sabre\\\\HTTP\\\\Response\"]]},{\"file\":\"/usr/share/nextcloud/3rdparty/sabre/dav/lib/DAV/Server.php\",\"line\":321,\"function\":\"start\",\"class\":\"Sabre\\\\DAV\\\\Server\",\"type\":\"->\",\"args\":[]},{\"file\":\"/usr/share/nextcloud/apps/dav/lib/Server.php\",\"line\":374,\"function\":\"exec\",\"class\":\"Sabre\\\\DAV\\\\Server\",\"type\":\"->\",\"args\":[]},{\"file\":\"/usr/share/nextcloud/apps/dav/appinfo/v2/remote.php\",\"line\":35,\"function\":\"exec\",\"class\":\"OCA\\\\DAV\\\\Server\",\"type\":\"->\",\"args\":[]},{\"file\":\"/usr/share/nextcloud/remote.php\",\"line\":172,\"args\":[\"/usr/share/nextcloud/apps/dav/appinfo/v2/remote.php\"],\"function\":\"require_once\"}],\"File\":\"/usr/share/nextcloud/3rdparty/sabre/dav/lib/CalDAV/Plugin.php\",\"Line\":873,\"message\":\"Validation error in iCalendar: TRIGGER MUST appear exactly once in a VALARM component\",\"exception\":{},\"CustomMessage\":\"Validation error in iCalendar: TRIGGER MUST appear exactly once in a VALARM component\"}","userAgent":"Evolution/3.52.1","version":"29.0.0.19"}

Additional info

No response

Start at 3rdparty/sabre/dav/lib/CalDAV/Plugin.php around lines 739 and 873, then trace the PUT path shown through apps/dav/lib/Server.php. Reproduce validation with the supplied iCalendar payload and Evolution context; done means the reported validation behavior is explained and covered by an appropriate test or confirmed as an external dependency issue.