fix(files): extract extension from basename in ObjectStoreStorage::fopen

[Bytepie]

Summary

Fixes an issue in ObjectStoreStorage::fopen() where the file extension is extracted using strrpos($path, '.') across the entire relative path instead of basename($path).

Problem

When an extensionless file is located inside a folder containing a dot (e.g. 0. Projects/Subfolder/hit), $ext is assigned the entire subpath string after the dot:

$ext = ". Projects/Subfolder/hit"

When TempManager::getTemporaryFile($ext) is called, directory separators are stripped:

/tmp/oc_tmp_<32_chars>. ProjectsSubfolderhit

How we encountered it

In our production case, a user had deeply nested folders with Cyrillic names. Because Linux's NAME_MAX limit is 255 bytes (and Cyrillic takes 2 bytes per character in UTF-8), the flattened filename easily exceeded 255 bytes, causing Linux to reject it with ENAMETOOLONG.

TempManager returned false, and fopen(false, $mode) crashed with:

ValueError: Path must not be empty

This fatal error killed the PHP process while the write lock was active, leaving behind orphaned exclusive locks in Redis.

Solution

1. Use basename($path) when extracting the file extension in ObjectStoreStorage::fopen().
2. Guard against false return from getTemporaryFile() before invoking fopen().
3. Added unit test testFopenWriteInDottedDirectoryWithoutExtension to ObjectStoreStorageTest.php.

Tests

Tested against live Nextcloud container where I had this issue during migration of data from GlusterFS to S3 (Ceph), and verified with PHPUnit in nextcloud-docker-dev environment.

Checklist

• Code is properly formatted
• Sign-off message is added to all commits
• Tests (unit, integration, api and/or acceptance) are included
• Screenshots before/after for front-end changes
• Documentation (manuals or wiki) has been updated or is not required
• Backports requested where applicable (ex: critical bugfixes)
• Labels added where applicable (ex: bug/enhancement, 3. to review, feature component)
• Milestone added for target branch/version (ex: 32.x for stable32)

AI (if applicable)

• The content of this PR was partly or fully generated using AI