Classes/Utility/FAL.php
protected static function findExistingFile($fileName)
    {
        $file = null;
        $relativePath = substr(PathUtility::dirname($fileName), strlen(PATH_site));
        $resourceFactory = \TYPO3\CMS\Core\Resource\ResourceFactory::getInstance();
        $targetFolder = $resourceFactory->retrieveFileOrFolderObject($relativePath);

        $storageConfiguration = $targetFolder->getStorage()->getConfiguration();
        if (isset($storageConfiguration['basePath'])) {
            $basePath = rtrim($storageConfiguration['basePath'], '/') . '/';
            $basePath = GeneralUtility::getFileAbsFileName($basePath);
            $identifier = substr($fileName, strlen($basePath) - 1);

            $row = GeneralUtility::makeInstance(ConnectionPool::class)
                ->getConnectionForTable('sys_file')
                ->select(
                    ['uid'],
                    'sys_file',
                    [
                        'storage' => $targetFolder->getStorage()->getUid(),
                        'identifier' => $identifier,
                    ]
                )
                ->fetch();

            if (!empty($row['uid'])) {
                /** @var \TYPO3\CMS\Core\Resource\FileRepository $fileRepository */
                $fileRepository = GeneralUtility::makeInstance(\TYPO3\CMS\Core\Resource\FileRepository::class);
                $file = $fileRepository->findByUid($row['uid']);
            }
        }

        return $file;
    }
protected static function findExistingFile($fileName)
    {
        $file = null;
        $relativePath = substr(PathUtility::dirname($fileName), strlen(PATH_site));
        $resourceFactory = \TYPO3\CMS\Core\Resource\ResourceFactory::getInstance();
        $targetFolder = $resourceFactory->retrieveFileOrFolderObject($relativePath);

        $storageConfiguration = $targetFolder->getStorage()->getConfiguration();
        if (isset($storageConfiguration['basePath'])) {
            $basePath = rtrim($storageConfiguration['basePath'], '/') . '/';
            $basePath = GeneralUtility::getFileAbsFileName($basePath);
            $identifier = substr($fileName, strlen($basePath) - 1);

            $row = GeneralUtility::makeInstance(ConnectionPool::class)
                ->getConnectionForTable('sys_file')
                ->select(
                    ['uid'],
                    'sys_file',
                    [
                        'storage' => $targetFolder->getStorage()->getUid(),
                        'identifier' => $identifier,
                    ]
                )
                ->fetch();

            if (!empty($row['uid'])) {
                /** @var \TYPO3\CMS\Core\Resource\FileRepository $fileRepository */
                $fileRepository = GeneralUtility::makeInstance(\TYPO3\CMS\Core\Resource\FileRepository::class);
                $file = $fileRepository->findByUid($row['uid']);
            }
        }

        return $file;
    }
Finds an existing file.

@param string $fileName
@return \TYPO3\CMS\Core\Resource\AbstractFile|null