Unable to link results to sheets

[sheyaln]

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Describe the bug

"Create spreadsheet" from the Results page of a form always fails with "There was an error while linking the file" when Nextcloud uses S3 as primary storage. I am not a php developer, so take this analysis with a grain of salt:

The server log shows PhpOffice\PhpSpreadsheet\Reader\Exception: Unable to identify a reader for this file. The issue seems to be $node->newFile() on S3 objectstore creates a file containing a single space character (0x20) instead of a truly empty file. The Forms app then treats this as an existing spreadsheet and tries to load it with PhpSpreadsheet, which fails on the 1-byte content. Since the error fires before putContent() runs, the broken file persists and every retry hits the same failure.

The code I believe is relevant, found in SubmissionService::exportData():

if ($file && $file->getContent()) {
    // reached because " " (space) is truthy in PHP
    $existentFile = $this->tempManager->getTemporaryFile($fileFormat);
    file_put_contents($existentFile, $file->getContent());
    $spreadsheet = IOFactory::load($existentFile);  // fails — 1 byte is not valid XLSX/ODS/CSV
} else {
    $spreadsheet = new Spreadsheet();  // intended path for new files, never reached
}

To Reproduce

1. Use Nextcloud with S3 as primary object storage
2. Create a form and collect at least one submission
3. Go to the form's Results tab
4. Click the export menu → "Create spreadsheet"
5. Select any directory in the file picker and click "Create XLSX" (or ODS/CSV)
6. See error: "There was an error while linking the file"

Expected behavior

A new spreadsheet is created in the selected directory containing the form submissions, and the file is linked to the form for automatic sync.

Nextcloud (please complete the following information):

• Nextcloud-Version: 32.0.6.1
• Forms-Version: 5.2.4

Desktop (please complete the following information):

• OS: macOS
• Browser: Firefox
• Version: 147

Browser log

PATCH /ocs/v2.php/apps/forms/api/v3/forms/8 → 500

Server log

{
  "level": 3,
  "time": "2026-02-18T12:04:51+00:00",
  "app": "no app in context",
  "method": "PATCH",
  "url": "/ocs/v2.php/apps/forms/api/v3/forms/8",
  "message": "Unable to identify a reader for this file",
  "exception": {
    "Exception": "PhpOffice\\PhpSpreadsheet\\Reader\\Exception",
    "Message": "Unable to identify a reader for this file",
    "File": "/var/www/html/custom_apps/forms/vendor/phpoffice/phpspreadsheet/src/PhpSpreadsheet/IOFactory.php",
    "Line": 205
  }
}