TYPO3 11: convert t3 file uri into file identifier - typo3

Question

How can I convert the TYPO3 file uri t3://file?uid=54 to be usable for other TYPO3 methods which need a file identifier?
The file uri is returned by a flexform which selects a XML file. This XML file should be read.
However I cannot find a useful API function in the TYPO3 Core.
$paramTestFile = 't3://file?uid=54';
$xmlString = GeneralUtility::getURL($paramTestFile);
The above code fails for TYPO3 URIs.
The file reference with uid=54 is at "fileadmin/example.xml".
The Filelist backend module shows the details of this file.
However I need this file path also in the PHP code in order to read in the file.
use TYPO3\CMS\Core\LinkHandling\FileLinkHandler;
$fileHandler = GeneralUtility::makeInstance(FileLinkHandler::class);
$fileInfo = $fileHandler->asString($paramTestFile);
It is not possible to use $paramTestFile in the above example.
The class FileLinkHandler and its method asString does exactly the opposite of what I need.
$content = #file_get_contents($url);
However the absolute file path is needed for the read method . How can I convert the FAL file URI into the file identifier?
use TYPO3\CMS\Core\Resource\StorageRepository;
$storageRepository = GeneralUtility::makeInstance(StorageRepository::class);
$defaultStorage = $storageRepository->getDefaultStorage();
$fileInfo = $defaultStorage->getFileByIdentifier($paramTestFileIdentifier);

Answer 1

To resolve a t3://file... URN use TYPO3\CMS\Core\LinkHandling\LinkService::resolve(). This method will return an array with a key file containing a TYPO3\CMS\Core\Resource\FileInterface. This also works for other URNs but will return another array structure.
Then use the getContents() method of the FileInterface to finally get the content of the file.
The documentation is not very detailed for this part of the core so I have linked you directly to the related sources.