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

    protected function extractAssetContent($asset)
    {
        $assetSettings = $this->extractAssetSettings($asset);
        $fileRelativePathAndFilename = $assetSettings['path'];
        $fileRelativePath = dirname($assetSettings['path']);
        $absolutePathAndFilename = GeneralUtility::getFileAbsFileName($fileRelativePathAndFilename);
        $isExternal = true === isset($assetSettings['external']) && true === (bool) $assetSettings['external'];
        $isFluidTemplate = true === isset($assetSettings['fluid']) && true === (bool) $assetSettings['fluid'];
        if (false === empty($fileRelativePathAndFilename)) {
            if (false === $isExternal && false === file_exists($absolutePathAndFilename)) {
                throw new \RuntimeException('Asset "' . $absolutePathAndFilename . '" does not exist.');
            }
            if (true === $isFluidTemplate) {
                $content = $this->renderAssetAsFluidTemplate($asset);
            } else {
                $content = $this->buildAsset($asset);
            }
        } else {
            $content = $this->buildAsset($asset);
        }
        if ('css' === $assetSettings['type'] && true === (bool) $assetSettings['rewrite']) {
            $content = $this->detectAndCopyFileReferences($content, $fileRelativePath);
        }
        return $content;
    }