[Bug]: Content Security Policy (CSP) Error for preview-service-worker.js in files_sharing

⚠️ 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

Bug #39849 is about a problem where the Content-security-policy header does not include permission to load the right worker scripts.

In the activity your can see that the problem happens in configurations that do not include often-used addins like the Talk or Maps app and then it is fixed in the Files app. However, in the files_sharing app, the app that hosts files for external users that follow a share link, it is unfortunately not fixed.

That's rather unfortunate, as it isn't a great look if you show Nextcloud to external users and it doesn't work properly.

In the console you see messages like

Refused to load https://nextcloud.sitename/index.php/apps/files/preview-service-worker.js because it does not appear in the worker-src directive of the Content Security Policy.

I noticed this problem when I was researching why flipping through photos does not work on a share, I don't know if it would be resolved if this problem is resolved but it stands to reason. I don't really know where to add the patch from #39849 in the files_sharing app, otherwise I could try. But if someone is more knowledgeable with the source I hope it's not a hard problem.

Steps to reproduce

1. Go to a share link (starts with https://nextcloud.sitename/s )
2. Look in the web console

Expected behavior

No error messages

Nextcloud Server version

31

Operating system

Debian/Ubuntu

PHP engine version

PHP 8.3

Web server

Nginx

Database engine version

PostgreSQL

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

None

Are you using the Nextcloud Server Encryption module?

Encryption is Disabled

What user-backends are you using?

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

Configuration report

{
    "system": {
        "instanceid": "***REMOVED SENSITIVE VALUE***",
        "passwordsalt": "***REMOVED SENSITIVE VALUE***",
        "secret": "***REMOVED SENSITIVE VALUE***",
        "trusted_domains": [
            "nextcloud.***",
            "nextcloud.***2"
        ],
        "overwritehost": "nextcloud.***",
        "trusted_proxies": "***REMOVED SENSITIVE VALUE***",
        "datadirectory": "***REMOVED SENSITIVE VALUE***",
        "dbtype": "pgsql",
        "version": "31.0.9.1",
        "overwrite.cli.url": "https:\/\/nextcloud.***",
        "dbname": "***REMOVED SENSITIVE VALUE***",
        "dbhost": "***REMOVED SENSITIVE VALUE***",
        "dbport": "",
        "dbtableprefix": "oc_",
        "dbuser": "***REMOVED SENSITIVE VALUE***",
        "dbpassword": "***REMOVED SENSITIVE VALUE***",
        "default_phone_region": "NL",
        "installed": true,
       "mail_smtpmode": "smtp",
        "mail_sendmailmode": "smtp",
        "mail_from_address": "***REMOVED SENSITIVE VALUE***",
        "mail_domain": "***REMOVED SENSITIVE VALUE***",
        "mail_smtphost": "***REMOVED SENSITIVE VALUE***",
        "maintenance": false,
        "data-fingerprint": "***",
        "theme": "",
        "loglevel": 0,
        "memcache.local": "\\OC\\Memcache\\APCu",
        "mail_smtpport": "1465",
        "mail_smtpauthtype": "PLAIN",
        "mail_smtpauth": 1,
        "mail_smtpsecure": "ssl",
        "mail_smtpname": "***REMOVED SENSITIVE VALUE***",
        "mail_smtppassword": "***REMOVED SENSITIVE VALUE***",
        "filelocking.enabled": true,
        "memcache.locking": "\\OC\\Memcache\\Redis",
        "redis": {
            "host": "***REMOVED SENSITIVE VALUE***",
            "port": 0,
            "timeout": 0,
            "password": "***REMOVED SENSITIVE VALUE***"
        },
        "maintenance_window_start": 100,
        "memories.db.triggers.fcu": true,
        "memories.exiftool": "\/var\/www\/nextcloud\/apps\/memories\/bin-ext\/exiftool-amd64-glibc",
        "memories.vod.path": "\/var\/www\/nextcloud\/apps\/memories\/bin-ext\/go-vod-amd64",
        "enabledPreviewProviders": [
            "OC\\Preview\\Image",
            "OC\\Preview\\HEIC"
        ],
        "memories.gis_type": 2,
        "app_install_overwrite": [
            "gpxpod"
        ]
    }
}

List of activated Apps

Enabled:
  - activity: 4.0.0
  - app_api: 5.0.2
  - circles: 31.0.0
  - cloud_federation_api: 1.14.0
  - comments: 1.21.0
  - contacts: 7.3.2
  - contactsinteraction: 1.12.0
  - dashboard: 7.11.0
  - dav: 1.33.0
  - federatedfilesharing: 1.21.0
  - federation: 1.21.0
  - files: 2.3.1
  - files_downloadlimit: 4.0.0
  - files_pdfviewer: 4.0.0
  - files_reminders: 1.4.0
  - files_sharing: 1.23.1
  - files_trashbin: 1.21.0
  - files_versions: 1.24.0
  - firstrunwizard: 4.0.0
  - gpxpod: 7.0.4
  - logreader: 4.0.0
  - lookup_server_connector: 1.19.0
  - memories: 7.6.2
  - nextcloud_announcements: 3.0.0
  - notifications: 4.0.0
  - oauth2: 1.19.1
  - password_policy: 3.0.0
  - photos: 4.0.0
  - previewgenerator: 5.10.0
  - privacy: 3.0.0
  - profile: 1.0.0
  - provisioning_api: 1.21.0
  - recognize: 9.0.7
  - recommendations: 4.0.0
  - related_resources: 2.0.0
  - serverinfo: 3.0.0
  - settings: 1.14.0
  - sharebymail: 1.21.0
  - support: 3.0.0
  - survey_client: 3.0.0
  - systemtags: 1.21.1
  - text: 5.0.0
  - theming: 2.6.1
  - twofactor_admin: 4.8.0
  - twofactor_backupcodes: 1.20.0
  - twofactor_totp: 13.0.0-dev.0
  - updatenotification: 1.21.0
  - user_status: 1.11.0
  - viewer: 4.0.0
  - weather_status: 1.11.0
  - webhook_listeners: 1.2.0
  - workflowengine: 2.13.0
Disabled:
  - admin_audit: 1.21.0
  - bruteforcesettings: 4.0.0 (installed 2.4.0)
  - camerarawpreviews: 0.8.7 (installed 0.8.7)
  - encryption: 2.19.0
  - files_external: 1.23.0
  - files_rightclick: 0.15.1 (installed 1.6.0)
  - suspicious_login: 9.0.1
  - twofactor_nextcloud_notification: 5.0.0
  - user_ldap: 1.22.0

Nextcloud Signing status

No errors have been found.

Nextcloud Logs

Additional info

No response

Compare the files_sharing share-link response with the Content Security Policy fix from bug #39849 in the Files app, focusing on preview-service-worker.js and the worker-src directive. Reproduce the issue from a share link in the browser console; done means the worker loads without a CSP error and the affected preview behavior works.