[CalDAV] Nextcloud returns HTTP 500 instead of 403 when POSTing an event without valid instances

### Steps to reproduce
Upload a recurring CalDAV event that does not contain any valid instances. For instance, that could be daily event with 3 instances (`RRULE:FREQ=DAILY;COUNT=5`) where all three instances are excluded by `EXDATE`:

```
$ cat 1.ics 
BEGIN:VCALENDAR
VERSION:2.0
PRODID:DAVx5/4.1 ical4j/3.1.1
BEGIN:VEVENT
DTSTAMP:20220106T192417Z
UID:188ffa89-91d7-4efd-aa3e-87e83b037901
SEQUENCE:3
SUMMARY:Test
DTSTART;TZID=Europe/Vienna:20220105T150000
DTEND;TZID=Europe/Vienna:20220105T160000
RRULE:FREQ=DAILY;WKST=SU;COUNT=2;INTERVAL=1
EXDATE;TZID=Europe/Vienna:20220106T150000
EXDATE;TZID=Europe/Vienna:20220105T150000
CLASS:PUBLIC
END:VEVENT
END:VCALENDAR

$ curl -inT 1.ics https://cloud.bitfire.at/remote.php/dav/calendars/test/79/188ffa89-91d7-4efd-aa3e-87e83b037901.ics
HTTP/2 500 
[…]

<?xml version="1.0" encoding="utf-8"?>
<d:error xmlns:d="DAV:" xmlns:s="http://sabredav.org/ns">
  <s:exception>Sabre\VObject\Recur\NoInstancesException</s:exception>
  <s:message>This recurrence rule does not generate any valid instances</s:message>
</d:error>
```

### Expected behaviour
If the server rejects an event because it's invalid, it should return a semantic HTTP error instead of 500 Internal server error, which would indicate the problem is on the server side.

As far as I can see, HTTP [403](https://datatracker.ietf.org/doc/html/rfc4791#section-1.3) with [(CALDAV:valid-calendar-object-resource)](https://datatracker.ietf.org/doc/html/rfc4791#section-5.3.2.1) would be the most appropriate (but maybe there's something better).

### Actual behaviour
Nextcloud returns 500 Internal server error.

### Server configuration

**Operating system:** Linux

**Web server:** nginx

**Database:** MySQL

**PHP version:** 8.0

**Nextcloud version:** 23.0.0

**List of activated apps:**
<details>
<summary>App list</summary>

```
Enabled:
  - accessibility: 1.9.0
  - activity: 2.15.0
  - calendar: 3.0.4
  - circles: 23.0.0
  - cloud_federation_api: 1.6.0
  - comments: 1.13.0
  - contacts: 4.0.7
  - contactsinteraction: 1.4.0
  - dashboard: 7.3.0
  - dav: 1.21.0
  - federatedfilesharing: 1.13.0
  - files: 1.18.0
  - files_rightclick: 1.2.0
  - files_sharing: 1.15.0
  - files_trashbin: 1.13.0
  - files_versions: 1.16.0
  - files_videoplayer: 1.12.0
  - firstrunwizard: 2.12.0
  - impersonate: 1.10.0
  - integration_twitter: 1.0.2
  - logreader: 2.8.0
  - lookup_server_connector: 1.11.0
  - mail: 1.11.5
  - nextcloud_announcements: 1.12.0
  - notifications: 2.11.1
  - oauth2: 1.11.0
  - password_policy: 1.13.0
  - photos: 1.5.0
  - privacy: 1.7.0
  - provisioning_api: 1.13.0
  - serverinfo: 1.13.0
  - settings: 1.5.0
  - sharebymail: 1.13.0
  - sociallogin: 4.9.7
  - spreed: 13.0.1
  - support: 1.6.0
  - survey_client: 1.11.0
  - talk_matterbridge: 1.23.2
  - tasks: 0.14.2
  - text: 3.4.0
  - theming: 1.14.0
  - twofactor_backupcodes: 1.12.0
  - updatenotification: 1.13.0
  - user_status: 1.3.1
  - viewer: 1.7.0
  - weather_status: 1.3.0
  - workflowengine: 2.5.0
Disabled:
  - admin_audit
  - duplicatefinder
  - encryption
  - federation
  - files_external
  - files_pdfviewer
  - recommendations
  - systemtags
  - user_ldap
```
</details>

**Nextcloud configuration:**
<details>
<summary>Config report</summary>

```
{
    "system": {
        "instanceid": "***REMOVED SENSITIVE VALUE***",
        "passwordsalt": "***REMOVED SENSITIVE VALUE***",
        "secret": "***REMOVED SENSITIVE VALUE***",
        "trusted_domains": [
            "***REMOVED SENSITIVE VALUE***"
        ],
        "datadirectory": "***REMOVED SENSITIVE VALUE***",
        "overwrite.cli.url": "***REMOVED SENSITIVE VALUE***",
        "dbtype": "mysql",
        "version": "23.0.0.10",
        "dbname": "***REMOVED SENSITIVE VALUE***",
        "dbhost": "***REMOVED SENSITIVE VALUE***",
        "dbport": "",
        "dbtableprefix": "oc_",
        "dbuser": "***REMOVED SENSITIVE VALUE***",
        "dbpassword": "***REMOVED SENSITIVE VALUE***",
        "installed": true,
        "default_phone_region": "AT",
        "mail_from_address": "***REMOVED SENSITIVE VALUE***",
        "mail_smtpmode": "sendmail",
        "mail_smtpauthtype": "LOGIN",
        "mail_domain": "***REMOVED SENSITIVE VALUE***",
        "mysql.utf8mb4": true,
        "mail_sendmailmode": "smtp",
        "updater.release.channel": "stable",
        "activity_expire_days": 14,
        "filelocking.enabled": true,
        "memcache.locking": "\\OC\\Memcache\\Redis",
        "memcache.local": "\\OC\\Memcache\\Redis",
        "redis": {
            "host": "***REMOVED SENSITIVE VALUE***",
            "port": -1,
            "password": "***REMOVED SENSITIVE VALUE***"
        },
        "maintenance": false,
        "theme": "",
        "loglevel": 2
    }
}
```
</details>

**Are you using external storage, if yes which one:** no

**Are you using encryption:** no

**Are you using an external user-backend, if yes which one:** no
</details>

### Logs

#### Nextcloud log (data/nextcloud.log)
<details>
<summary>Nextcloud log</summary>

```
…
{"reqId":"wB6m5behGQYI0jXRHywf","level":4,"time":"2022-01-06T19:27:29+00:00","remoteAddr":"xxxxxxxxxxx","user":"test","app":"webdav","method":"PUT","url":"/remote.php/dav/calendars/test/79/188ffa89-91d7-4efd-aa3e-87e83b037901.ics","message":"This recurrence rule does not generate any valid instances","userAgent":"curl/7.74.0","version":"23.0.0.10","exception":{"Exception":"Sabre\\VObject\\Recur\\NoInstancesException","Message":"This recurrence rule does not generate any valid instances","Code":0,"Trace":[{"file":"/nextcloud/apps/dav/lib/CalDAV/CalDavBackend.php","line":2761,"function":"__construct","class":"Sabre\\VObject\\Recur\\EventIterator","type":"->"},{"file":"/nextcloud/apps/dav/lib/CalDAV/CalDavBackend.php","line":1355,"function":"getDenormalizedData","class":"OCA\\DAV\\CalDAV\\CalDavBackend","type":"->"},{"file":"/nextcloud/3rdparty/sabre/dav/lib/CalDAV/CalendarObject.php","line":103,"function":"updateCalendarObject","class":"OCA\\DAV\\CalDAV\\CalDavBackend","type":"->","args":["*** sensitive parameters replaced ***"]},{"file":"/nextcloud/3rdparty/sabre/dav/lib/DAV/Server.php","line":1137,"function":"put","class":"Sabre\\CalDAV\\CalendarObject","type":"->"},{"file":"/nextcloud/3rdparty/sabre/dav/lib/DAV/CorePlugin.php","line":492,"function":"updateFile","class":"Sabre\\DAV\\Server","type":"->","args":["*** sensitive parameters replaced ***"]},{"file":"/nextcloud/3rdparty/sabre/event/lib/WildcardEmitterTrait.php","line":89,"function":"httpPut","class":"Sabre\\DAV\\CorePlugin","type":"->"},{"file":"/nextcloud/3rdparty/sabre/dav/lib/DAV/Server.php","line":472,"function":"emit","class":"Sabre\\DAV\\Server","type":"->"},{"file":"/nextcloud/3rdparty/sabre/dav/lib/DAV/Server.php","line":253,"function":"invokeMethod","class":"Sabre\\DAV\\Server","type":"->"},{"file":"/nextcloud/3rdparty/sabre/dav/lib/DAV/Server.php","line":321,"function":"start","class":"Sabre\\DAV\\Server","type":"->"},{"file":"/nextcloud/apps/dav/lib/Server.php","line":339,"function":"exec","class":"Sabre\\DAV\\Server","type":"->"},{"file":"/nextcloud/apps/dav/appinfo/v2/remote.php","line":35,"function":"exec","class":"OCA\\DAV\\Server","type":"->"},{"file":"/nextcloud/remote.php","line":166,"args":["/nextcloud/apps/dav/appinfo/v2/remote.php"],"function":"require_once"}],"File":"/nextcloud/3rdparty/sabre/vobject/lib/Recur/EventIterator.php","Line":192,"CustomMessage":"--"}}

```
</details>


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[CalDAV] Nextcloud returns HTTP 500 instead of 403 when POSTing an event without valid instances #30514

rfc2822
openedon Jan 6, 2022

Steps to reproduce

Expected behaviour

Actual behaviour

Server configuration

Logs

Nextcloud log (data/nextcloud.log)

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