Url ze souborové cesty - problém se subdoménou

function pathToURL($relPath) {
    $filePathName = realpath($relPath);
    $filePath = realpath(dirname($relPath));
    $basePath = realpath($_SERVER['DOCUMENT_ROOT']);
   
    // can not create URL for directory lower than DOCUMENT_ROOT
    if (strlen($basePath) > strlen($filePath)) {
        return '';
    }
   
    return 'http://' . $_SERVER['HTTP_HOST'] . substr($filePathName, strlen($basePath));
}