Rendering twig blocks directly from outside a twig render call, for email purpose

TwigRenderer.php

<?php

namespace Incenteev\MailerBundle\Mailer;

class TwigRenderer implements RendererInterface
{
    private $twig;
    private $styleInliner;

    /**
     * @param \Twig_Environment     $twig
     * @param StyleInlinerInterface $styleInliner
     */
    public function __construct(\Twig_Environment $twig, StyleInlinerInterface $styleInliner)
    {
        $this->twig = $twig;
        $this->styleInliner = $styleInliner;
    }

    /**
     * {@inheritDoc}
     *
     * The template must define 3 blocks: subject, body_text and body_html.
     */
    public function render(Message $message)
    {
        /** @var $template \Twig_Template */
        $template = $this->twig->loadTemplate($message->getTemplate());
        $context = $this->twig->mergeGlobals($message->getContext());

        $subject = $this->renderBlock($template, 'subject', $context);
        $textBody = $this->renderBlock($template, 'body_text', $context);
        $htmlBody = $this->renderBlock($template, 'body_html', $context);

        $htmlBody = $this->styleInliner->inlineStyle($htmlBody);

        return array(
            'subject' => $subject,
            'text' => $textBody,
            'html' => $htmlBody,
        );
    }

    /**
     * Renders a Twig block with error handling.
     *
     * This avoids getting some leaked buffer when an exception occurs.
     * Twig blocks are not taking care of it as they are not meant to be rendered directly.
     *
     * @param \Twig_Template $template
     * @param string         $block
     * @param array          $context
     *
     * @return string
     *
     * @throws \Exception
     */
    private function renderBlock(\Twig_Template $template, $block, array $context)
    {
        $level = ob_get_level();
        ob_start();
        try {
            $rendered = $template->renderBlock($block, $context);
            ob_end_clean();

            return $rendered;
        } catch (\Exception $e) {
            while (ob_get_level() > $level) {
                ob_end_clean();
            }

            throw $e;
        }
    }
}