Classes/Slots/FileUpload.php
public function sanitizeFileName($fileName, \TYPO3\CMS\Core\Resource\Folder $folder)
    {
        $slotArguments = func_get_args();
        // Last parameter is the signal name itself and is not actually part of the arguments
        array_pop($slotArguments);

        $storageConfiguration = $folder->getStorage()->getConfiguration();
        $storageRecord = $folder->getStorage()->getStorageRecord();
        if ($storageRecord['driver'] !== 'Local') {
            // Unfortunately unsupported yet
            return;
        }

        $targetDirectory = $storageConfiguration['pathType'] === 'relative' ? PATH_site : '';
        $targetDirectory .= rtrim(rtrim($storageConfiguration['basePath'], '/') . $folder->getIdentifier(), '/');

        $processedFileName = static::$imageResizer->getProcessedFileName(
            $targetDirectory . '/' . $fileName,
            $GLOBALS['BE_USER']
        );
        if ($processedFileName !== null) {
            static::$originalFileName = $fileName;
            $slotArguments[0] = PathUtility::basename($processedFileName);

            return $slotArguments;
        }
    }
public function sanitizeFileName($fileName, \TYPO3\CMS\Core\Resource\Folder $folder)
    {
        $slotArguments = func_get_args();
        // Last parameter is the signal name itself and is not actually part of the arguments
        array_pop($slotArguments);

        $storageConfiguration = $folder->getStorage()->getConfiguration();
        $storageRecord = $folder->getStorage()->getStorageRecord();
        if ($storageRecord['driver'] !== 'Local') {
            // Unfortunately unsupported yet
            return;
        }

        $targetDirectory = $storageConfiguration['pathType'] === 'relative' ? PATH_site : '';
        $targetDirectory .= rtrim(rtrim($storageConfiguration['basePath'], '/') . $folder->getIdentifier(), '/');

        $processedFileName = static::$imageResizer->getProcessedFileName(
            $targetDirectory . '/' . $fileName,
            $GLOBALS['BE_USER']
        );
        if ($processedFileName !== null) {
            static::$originalFileName = $fileName;
            $slotArguments[0] = PathUtility::basename($processedFileName);

            return $slotArguments;
        }
    }
Sanitizes the file name.

@param string $fileName
@param \TYPO3\CMS\Core\Resource\Folder $folder
@return void|array