@Override
    public final CompletableFuture<Boolean> renderResponse(OutputStream stream, Result response, Execution execution, Request request) {
        Writer writer = null;
        try {
            writer = createWriter(stream, response);
            render(writer, response);
        }
        catch (IOException e) {
            throw new RuntimeException(e);
        }
        finally {
            if (writer != null)
                try { writer.close(); } catch (IOException e2) {};
        }
        CompletableFuture<Boolean> completed = new CompletableFuture<>();
        completed.complete(true);
        return completed;
    }
Renders synchronously and returns when rendering is complete.

@return a future which is always completed to true
container-search/src/main/java/com/yahoo/search/rendering/Renderer.java