[Bug]: preview generation fails with S3 storage: "Parent folder not in filecache"

[bazaah]

⚠️ 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

When generating a preview via the OC\Preview\Generator->generatePreviews code path for a S3 backed nextcloud instance, previews will sometimes fail to generate with a stack trace like this:

Stack Trace

2025-10-03T14:23:20+00:00 In Cache.php line 274:
2025-10-03T14:23:20+00:00
2025-10-03T14:23:20+00:00   [Exception]
2025-10-03T14:23:20+00:00   Parent folder not in filecache for 0/b
2025-10-03T14:23:20+00:00
2025-10-03T14:23:20+00:00
2025-10-03T14:23:20+00:00 Exception trace:
2025-10-03T14:23:20+00:00   at /var/www/html/lib/private/Files/Cache/Cache.php:274
2025-10-03T14:23:20+00:00  OC\Files\Cache\Cache->insert() at /var/www/html/lib/private/Files/Cache/Cache.php:239
2025-10-03T14:23:20+00:00  OC\Files\Cache\Cache->put() at /var/www/html/lib/private/Files/ObjectStore/ObjectStoreStorage.php:109
2025-10-03T14:23:20+00:00  OC\Files\ObjectStore\ObjectStoreStorage->mkdir() at /var/www/html/lib/private/Files/ObjectStore/ObjectStoreStorage.php:94
2025-10-03T14:23:20+00:00  OC\Files\ObjectStore\ObjectStoreStorage->mkdir() at /var/www/html/lib/private/Files/ObjectStore/ObjectStoreStorage.php:94
2025-10-03T14:23:20+00:00  OC\Files\ObjectStore\ObjectStoreStorage->mkdir() at /var/www/html/lib/private/Files/ObjectStore/ObjectStoreStorage.php:94
2025-10-03T14:23:20+00:00  OC\Files\ObjectStore\ObjectStoreStorage->mkdir() at /var/www/html/lib/private/Files/ObjectStore/ObjectStoreStorage.php:94
2025-10-03T14:23:20+00:00  OC\Files\ObjectStore\ObjectStoreStorage->mkdir() at /var/www/html/lib/private/Files/Storage/Wrapper/Wrapper.php:58
2025-10-03T14:23:20+00:00  OC\Files\Storage\Wrapper\Wrapper->mkdir() at /var/www/html/lib/private/Files/View.php:1210
2025-10-03T14:23:20+00:00  OC\Files\View->basicOperation() at /var/www/html/lib/private/Files/View.php:211
2025-10-03T14:23:20+00:00  OC\Files\View->mkdir() at /var/www/html/lib/private/Files/Node/Folder.php:129
2025-10-03T14:23:20+00:00  OC\Files\Node\Folder->newFolder() at /var/www/html/lib/private/Files/AppData/AppData.php:129
2025-10-03T14:23:20+00:00  OC\Files\AppData\AppData->newFolder() at /var/www/html/lib/private/Preview/Storage/Root.php:56
2025-10-03T14:23:20+00:00  OC\Preview\Storage\Root->newFolder() at /var/www/html/lib/private/Preview/Generator.php:584
2025-10-03T14:23:20+00:00  OC\Preview\Generator->getPreviewFolder() at /var/www/html/lib/private/Preview/Generator.php:110
2025-10-03T14:23:20+00:00  OC\Preview\Generator->generatePreviews() at /var/www/html/lib/private/PreviewManager.php:188
2025-10-03T14:23:20+00:00  OC\PreviewManager->generatePreviews() at /var/www/html/apps/previewgenerator/lib/Command/Generate.php:210
2025-10-03T14:23:20+00:00  OCA\PreviewGenerator\Command\Generate->parseFile() at /var/www/html/apps/previewgenerator/lib/Command/Generate.php:192
2025-10-03T14:23:20+00:00  OCA\PreviewGenerator\Command\Generate->parseFolder() at /var/www/html/apps/previewgenerator/lib/Command/Generate.php:190
2025-10-03T14:23:20+00:00  OCA\PreviewGenerator\Command\Generate->parseFolder() at /var/www/html/apps/previewgenerator/lib/Command/Generate.php:190
2025-10-03T14:23:20+00:00  OCA\PreviewGenerator\Command\Generate->parseFolder() at /var/www/html/apps/previewgenerator/lib/Command/Generate.php:161
2025-10-03T14:23:20+00:00  OCA\PreviewGenerator\Command\Generate->generatePathPreviews() at /var/www/html/apps/previewgenerator/lib/Command/Generate.php:109
2025-10-03T14:23:20+00:00  OCA\PreviewGenerator\Command\Generate->execute() at /var/www/html/3rdparty/symfony/console/Command/Command.php:326
2025-10-03T14:23:20+00:00  Symfony\Component\Console\Command\Command->run() at /var/www/html/3rdparty/symfony/console/Application.php:1078
2025-10-03T14:23:20+00:00  Symfony\Component\Console\Application->doRunCommand() at /var/www/html/3rdparty/symfony/console/Application.php:324
2025-10-03T14:23:20+00:00  Symfony\Component\Console\Application->doRun() at /var/www/html/3rdparty/symfony/console/Application.php:175
2025-10-03T14:23:20+00:00  Symfony\Component\Console\Application->run() at /var/www/html/lib/private/Console/Application.php:187
2025-10-03T14:23:20+00:00  OC\Console\Application->run() at /var/www/html/console.php:87
2025-10-03T14:23:20+00:00  require_once() at /var/www/html/occ:33

This one was generate via a oc preview:generate-all call, but you can get the same thing calling oc preview:generate <the file path> on the buggy file, or just scrolling the photos or memories apps. This has existed for (at least) server versions 29, 30 and 31. The files it happens to are seemingly random, but it will consistently happen for a file once you find one.

The only commonality I can find is that the error's mentioned file path (e.g Parent folder not in filecache for <file path>) always has a zero 0 character in it.

Steps to reproduce

1. Use an S3 backed Nextcloud server
2. Attempt to generate a preview (e.g via oc or just browsing in the files or photos apps)
3. Note the stack trace (or 503 in web tools) on some of the photos

Expected behavior

The preview should be generated

Nextcloud Server version

31

Operating system

Debian/Ubuntu

PHP engine version

PHP 8.3

Web server

Apache (supported)

Database engine version

PostgreSQL

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

Updated from a MINOR version (ex. 32.0.1 to 32.0.2)

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": {
        "passwordsalt": "***REMOVED SENSITIVE VALUE***",
        "secret": "***REMOVED SENSITIVE VALUE***",
        "trusted_domains": [
            "***REMOVED SENSITIVE VALUE***"
        ],
        "dbtype": "pgsql",
        "dbhost": "***REMOVED SENSITIVE VALUE***",
        "dbname": "***REMOVED SENSITIVE VALUE***",
        "dbuser": "***REMOVED SENSITIVE VALUE***",
        "dbpassword": "***REMOVED SENSITIVE VALUE***",
        "dbtableprefix": "oc_",
        "dbpersistent": true,
        "default_language": "en",
        "default_locale": "en_US",
        "knowledgebaseenabled": true,
        "knowledgebase.embedded": false,
        "allow_user_to_change_display_name": true,
        "remember_login_cookie_lifetime": 691200,
        "session_lifetime": 86400,
        "davstorage.request_timeout": 30,
        "session_relaxed_expiry": true,
        "session_keepalive": true,
        "auto_logout": true,
        "token_auth_enforced": true,
        "token_auth_activity_update": 60,
        "auth.bruteforce.protection.enabled": true,
        "auth.storeCryptedPassword": true,
        "hide_login_form": false,
        "mail_domain": "***REMOVED SENSITIVE VALUE***",
        "mail_from_address": "***REMOVED SENSITIVE VALUE***",
        "mail_smtpmode": "smtp",
        "mail_smtphost": "***REMOVED SENSITIVE VALUE***",
        "mail_smtpport": 25,
        "mail_smtptimeout": 10,
        "mail_template_class": "\\OC\\Mail\\EMailTemplate",
        "mail_send_plaintext_only": false,
        "htaccess.RewriteBase": "\/",
        "allow_local_remote_servers": true,
        "trashbin_retention_obligation": "90, 365",
        "versions_retention_obligation": "auto, 90",
        "appcodechecker": true,
        "updatechecker": true,
        "updater.release.channel": "stable",
        "config_is_read_only": false,
        "log_type": "file",
        "log_type_audit": "file",
        "logfilemode": 416,
        "loglevel": 2,
        "logtimezone": "UTC",
        "log_rotate_size": 67108864,
        "profiler": false,
        "defaultapp": "dashboard,files",
        "appstoreenabled": false,
        "enable_previews": true,
        "preview_concurrency_all": 8,
        "preview_concurrency_new": 4,
        "preview_max_filesize_image": 25,
        "preview_max_memory": 128,
        "enabledPreviewProviders": [
            "OC\\Preview\\BMP",
            "OC\\Preview\\GIF",
            "OC\\Preview\\JPEG",
            "OC\\Preview\\Krita",
            "OC\\Preview\\MarkDown",
            "OC\\Preview\\MP3",
            "OC\\Preview\\OpenDocument",
            "OC\\Preview\\PNG",
            "OC\\Preview\\TXT",
            "OC\\Preview\\XBitmap",
            "OC\\Preview\\Imaginary",
            "OC\\Preview\\ImaginaryPDF"
        ],
        "maintenance": false,
        "maintenance_window_start": 1,
        "memcache.local": "\\OC\\Memcache\\APCu",
        "memcache.distributed": "\\OC\\Memcache\\Redis",
        "redis": {
            "host": "***REMOVED SENSITIVE VALUE***",
            "port": "***REMOVED SENSITIVE VALUE***",
            "timeout": 5,
            "read_timeout": 5,
            "dbindex": 0
        },
        "objectstore_multibucket": {
            "class": "OC\\Files\\ObjectStore\\S3",
            "arguments": {
                "region": "***REMOVED SENSITIVE VALUE***",
                "bucket": "***REMOVED SENSITIVE VALUE***",
                "num_buckets": 256,
                "autocreate": true,
                "key": "***REMOVED SENSITIVE VALUE***",
                "secret": "***REMOVED SENSITIVE VALUE***",
                "hostname": "***REMOVED SENSITIVE VALUE***",
                "use_ssl": true,
                "use_path_style": true
            }
        },
        "objectstore.multibucket.preview-distribution": true,
        "sharing.enable_mail_link_password_expiration": true,
        "sharing.mail_link_password_expiration_interval": 3600,
        "sharing.minSearchStringLength": 2,
        "files_external_allow_create_new_local": false,
        "filesystem_cache_readonly": false,
        "trusted_proxies": "***REMOVED SENSITIVE VALUE***",
        "forwarded_for_headers": [
            "HTTP_X_FORWARDED_FOR",
            "HTTP_X_REAL_IP"
        ],
        "max_filesize_animated_gifs_public_sharing": 10,
        "filelocking.enabled": true,
        "filelocking.ttl": 3600,
        "memcache.locking": "\\OC\\Memcache\\Redis",
        "upgrade.disable-web": true,
        "upgrade.cli-upgrade-link": "",
        "documentation_url.server_logs": "",
        "simpleSignUpLink.shown": false,
        "version": "31.0.4.1",
        "instanceid": "***REMOVED SENSITIVE VALUE***",
        "installed": true,
        "overwrite.cli.url": "***REMOVED SENSITIVE VALUE***",
        "datadirectory": "***REMOVED SENSITIVE VALUE***",
        "memories.db.triggers.fcu": true,
        "memories.exiftool": "\/var\/www\/html\/apps\/memories\/bin-ext\/exiftool-amd64-glibc",
        "memories.vod.path": "\/var\/www\/html\/apps\/memories\/bin-ext\/go-vod-amd64",
        "overwriteprotocol": "https",
        "memories.gis_type": 2,
        "default_phone_region": "US",
        "preview_imaginary_url": "***REMOVED SENSITIVE VALUE***",
        "preview_imaginary_key": "***REMOVED SENSITIVE VALUE***"
    }
}

List of activated Apps

Enabled:
  - activity: 4.0.0
  - app_api: 5.0.2
  - bruteforcesettings: 4.0.0
  - calendar: 5.5.5
  - 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
  - logreader: 4.0.0
  - lookup_server_connector: 1.19.0
  - memories: 7.6.2
  - nextcloud_announcements: 3.0.0
  - notes: 4.12.3
  - notifications: 4.0.0
  - oauth2: 1.19.1
  - password_policy: 3.0.0
  - photos: 4.0.0-dev.1
  - previewgenerator: 5.10.0
  - privacy: 3.0.0
  - profile: 1.0.0
  - provisioning_api: 1.21.0
  - recommendations: 4.0.0
  - related_resources: 2.0.0
  - richdocuments: 8.7.5
  - serverinfo: 3.0.0
  - settings: 1.14.0
  - sharebymail: 1.21.0
  - snappymail: 2.38.2
  - support: 3.0.0
  - survey_client: 3.0.0
  - systemtags: 1.21.1
  - tasks: 0.16.1
  - text: 5.0.0
  - theming: 2.6.1
  - 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
  - encryption: 2.19.0
  - files_external: 1.23.0
  - suspicious_login: 9.0.1
  - twofactor_nextcloud_notification: 5.0.0
  - user_ldap: 1.22.0

Nextcloud Signing status

Nextcloud Logs

Error    no app in context  Parent folder not in filecache for 0/2                                                             2025-10-03T15:39:38+00:00

  Error    no app in context  Parent folder not in filecache for 0/1                                                             2025-10-03T15:39:42+00:00

  Error    no app in context  Parent folder not in filecache for 0/2                                                             2025-10-03T15:39:42+00:00

  Error    no app in context  Parent folder not in filecache for 0/8                                                             2025-10-03T15:39:41+00:00

  Error    no app in context  Parent folder not in filecache for 0/1                                                             2025-10-03T15:39:42+00:00

  Error    no app in context  Parent folder not in filecache for 0/5                                                             2025-10-03T15:40:24+00:00

  Error    no app in context  Parent folder not in filecache for 0/5                                                             2025-10-03T15:40:24+00:00

  Error    no app in context  Parent folder not in filecache for 0/b                                                             2025-10-03T15:43:50+00:00

  Error    no app in context  Parent folder not in filecache for 0/0                                                             2025-10-03T15:43:23+00:00

  Error    no app in context  Parent folder not in filecache for 0/b                                                             2025-10-03T15:43:50+00:00

  Error    no app in context  Parent folder not in filecache for 0/4                                                             2025-10-03T15:43:50+00:00

Additional info

I am using docker.io/library/nextcloud:31.0.4 as the nextcloud image, docker.io/valkey/valkey:8 for redis and postgres 17 for my database.

[joshtrichards]

The only commonality I can find is that the error's mentioned file path (e.g Parent folder not in filecache for ) always has a zero 0 character in it.

Hmm. Might be #49987 (or similar cause but elsewhere in that area).

    "version": "31.0.4.1",

P.S. This is missing a a lot of maintenance releases (31.0.9 is latest).

[bazaah]

Yeah, its on my todo list for this weekend

[bazaah]

So, taking the hint from 49987, it seems normalizePath is (maybe?) the issue.

I'm not familiar with PHP, so please excuse any mistakes on my end. Throwing that function into an interpreter^1:

<?php

function normalizePath(string $path): string {
		$path = trim($path, '/');
		//FIXME why do we sometimes get a path like 'files//username'?
		$path = str_replace('//', '/', $path);

		// dirname('/folder') returns '.' but internally (in the cache) we store the root as ''
		if (!$path || $path === '.') {
			$path = '';
		}

		return $path;
	}
	
$multipart = "0/a";
$singlePartNotZero = "a";
$singlePartZero = "0";

$nM = normalizePath($multipart);
$nNZ = normalizePath($singlePartNotZero);
$nZ = normalizePath($singlePartZero);

echo "multipart ($multipart) -> '$nM'\n";
echo "singlePartNotZero ($singlePartNotZero) -> '$nNZ'\n";
echo "singlePartZero ($singlePartZero) -> '$nZ'\n";

Gives this, using php 8.3.23:

multipart (0/a) -> '0/a'
singlePartNotZero (a) -> 'a'
singlePartZero (0) -> ''

Which I think is an issue in the singlePartZero case?

[bazaah]

This one line change does seem to fix it, for me:

-		if (!$path || $path === '.') {
+		if (!isset($path) || $path === '.') {

[mrsakrano]

New reply to your ticket #11444 Title: Re: [nextcloud/server] [Bug]: preview generation fails with S3 storage: "Parent folder not in filecache" (Issue #55530) Message: Hello,we received your message and our support will reach out to you as soon as possible.

[bazaah]

Is there anything more I can do here? I can confirm that the oneline fix above seems to fully fix the issue for my installation. I'm happy to open a PR with it, though I am admittedly not very experienced with PHP, so I may need some help with CI :)