FluidTYPO3\Vhs\Service\AssetService::getFileIntegrity PHP Method

    protected function getFileIntegrity($file)
    {
        if (isset($GLOBALS['TSFE']->tmpl->setup['plugin.']['tx_vhs.']['assets.']['tagsAddSubresourceIntegrity'])) {
            // Note: 3 predefined hashing strategies (the ones suggestes in the rfc sheet)
            if (0 < $GLOBALS['TSFE']->tmpl->setup['plugin.']['tx_vhs.']['assets.']['tagsAddSubresourceIntegrity'] && $GLOBALS['TSFE']->tmpl->setup['plugin.']['tx_vhs.']['assets.']['tagsAddSubresourceIntegrity'] < 4) {
                if (false === file_exists($file)) {
                    return '';
                }
                $integrityMethod = ['sha256', 'sha384', 'sha512'][$GLOBALS['TSFE']->tmpl->setup['plugin.']['tx_vhs.']['assets.']['tagsAddSubresourceIntegrity'] - 1];
                $integrityFile = sprintf('typo3temp/vhs-assets-%s.%s', str_replace('vhs-assets-', '', pathinfo($file, PATHINFO_BASENAME)), $integrityMethod);
                if (false === file_exists($integrityFile) || 0 === filemtime($integrityFile) || true === isset($GLOBALS['BE_USER']) || true === (bool) $GLOBALS['TSFE']->no_cache || true === (bool) $GLOBALS['TSFE']->page['no_cache']) {
                    if (extension_loaded('hash') && function_exists('hash_file')) {
                        $integrity = base64_encode(hash_file($integrityMethod, $file, true));
                    } elseif (extension_loaded('openssl') && function_exists('openssl_digest')) {
                        $integrity = base64_encode(openssl_digest(file_get_contents($file), $integrityMethod, true));
                    } else {
                        return '';
                        // Sadly, no integrity generation possible
                    }
                    $this->writeFile($integrityFile, $integrity);
                }
                return sprintf('%s-%s', $integrityMethod, $integrity ?: file_get_contents($integrityFile));
            }
        }
        return '';
    }