We finished Buttondown’s migration from MDX to Markdoc last week. It went swimmingly, except for one little hitch: our RSS feeds, which sat on top of getServerSideProps and read in the flat .mdoc files, threw 500s in Vercel. (They worked fine locally and in CI, but then those files were purged by Vercel as part of the post-compile deploy.)

I was considering going back to our previous (slightly janky but perfectly reasonable) approach of having a script that generates the RSS files and then just serving them as static asset, but Max Stoiber pointed me in the right direction:

• Create an App Router Route Handler
• Set dynamic="force-static"
• Build the XML in-band.

This means all we had to do was this:

import { createReader } from "@keystatic/core/reader";
import config, { localBaseURL } from "../../../keystatic.config";

const reader = createReader(localBaseURL, config);

export const dynamic = "force-static";

const CHANNEL_METADATA = {
  title: "Buttondown's blog",
  description: "Buttondown's blog — guides, tutorials, and more",
  link: "https://buttondown.com",
};

export async function GET() {
  const slugs = await reader.collections.blog.list();

  const rawPostData = await Promise.all(
    slugs.map(async (slug) => {
      const response = await reader.collections.blog.read(slug, {
        resolveLinkedFiles: true,
      });
      return {
        slug,
        ...response,
      };
    })
  );

  const sortedPostData = rawPostData.sort((a, b) => {
    const coercedADate = new Date(a.date || "");
    const coercedBDate = new Date(b.date || "");
    return coercedBDate.getTime() - coercedADate.getTime();
  });

  const items = sortedPostData.map((post) => ({
    title: post.title,
    description: post.description,
    link: `https://buttondown.com/blog/${post.slug}`,
    pubDate: new Date(post.date || "").toUTCString(),
  }));
  const rssFeed = `<rss version="2.0">
        <channel>
            <title>${CHANNEL_METADATA.title}</title>
            <description>${CHANNEL_METADATA.description}</description>
            <link>${CHANNEL_METADATA.link}</link>
            ${items
              .map(
                (item) => `<item>
                <title>${item.title}</title>
                <description>${item.description}</description>
                <link>${item.link}</link>
                <pubDate>${item.pubDate}</pubDate>
            </item>`
              )
              .join("\n")}
        </channel>
    </rss>`;

  return new Response(rssFeed, {
    headers: {
      "Content-Type": "text/xml",
    },
  });
}

Hopefully, Next will make this all a thing of the past and create a lightweight DSL like they did for sitemaps. In the meantime, though, I hope this helps!