Build the Astro site UI

src/pages/rss.xml.ts

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+import rss from '@astrojs/rss';
+import type { APIRoute } from 'astro';
+import { experimental_AstroContainer as AstroContainer } from 'astro/container';
+import { render } from 'astro:content';
+import ogDefault from '../assets/og-default.jpg';
+import {
+  absoluteUrl,
+  articlePath,
+  getPublishedPosts,
+  optimizeOgImage,
+  site,
+} from '../lib/site';
+
+// Escape characters that would otherwise break XML parsing inside text nodes
+// (the `customData` strings are inserted as-is by @astrojs/rss).
+function escapeXml(value: string) {
+  return value
+    .replace(/&/g, '&')
+    .replace(/</g, '&lt;')
+    .replace(/>/g, '&gt;')
+    .replace(/"/g, '&quot;')
+    .replace(/'/g, '&apos;');
+}
+
+// Rewrite root-relative URLs to absolute so RSS readers (which load the HTML
+// outside any page context) can still resolve assets and links.
+function absolutizeUrls(html: string, baseUrl: string) {
+  return html
+    .replace(/(<(?:a|link)\b[^>]*\bhref=")(\/[^"]*)(")/g, `$1${baseUrl}$2$3`)
+    .replace(
+      /(<(?:img|source|video|audio)\b[^>]*\bsrc=")(\/[^"]*)(")/g,
+      `$1${baseUrl}$2$3`
+    )
+    .replace(/(\bsrcset=")([^"]+)(")/g, (_, prefix, value, suffix) => {
+      const rewritten = value
+        .split(',')
+        .map((candidate: string) => {
+          const trimmed = candidate.trim();
+          if (!trimmed.startsWith('/')) return trimmed;
+          return baseUrl + trimmed;
+        })
+        .join(', ');
+      return prefix + rewritten + suffix;
+    });
+}
+
+export const GET: APIRoute = async () => {
+  const posts = await getPublishedPosts();
+  const feedUrl = absoluteUrl('/rss.xml');
+  const channelImage = await optimizeOgImage(ogDefault);
+  const channelImageUrl = absoluteUrl(channelImage.src);
+  const creator = escapeXml(site.name);
+  const container = await AstroContainer.create();
+
+  const items = await Promise.all(
+    posts.map(async (post) => {
+      const url = absoluteUrl(articlePath(post));
+      const updated = post.data.updated
+        ? `<atom:updated>${post.data.updated.toISOString()}</atom:updated>`
+        : '';
+      const { Content } = await render(post);
+      const html = await container.renderToString(Content);
+      // @astrojs/rss XML-escapes the `content` string and emits it inside
+      // <content:encoded>. RSS readers decode the escaped HTML the same as if
+      // it were wrapped in CDATA, so escaping is fine and safer to author.
+      const content = absolutizeUrls(html, site.url);
+      return {
+        title: post.data.title,
+        description: post.data.description,
+        pubDate: post.data.date,
+        link: url,
+        author: `${site.email} (${site.name})`,
+        categories: [...post.data.tags],
+        content,
+        customData: [`<dc:creator>${creator}</dc:creator>`, updated]
+          .filter(Boolean)
+          .join('\n'),
+      };
+    })
+  );
+
+  return rss({
+    title: site.name,
+    description: site.description,
+    site: site.url,
+    xmlns: {
+      atom: 'http://www.w3.org/2005/Atom',
+      content: 'http://purl.org/rss/1.0/modules/content/',
+      dc: 'http://purl.org/dc/elements/1.1/',
+    },
+    customData: [
+      '<language>en-us</language>',
+      `<lastBuildDate>${new Date().toUTCString()}</lastBuildDate>`,
+      `<atom:link href="${feedUrl}" rel="self" type="application/rss+xml" />`,
+      '<image>',
+      `  <url>${channelImageUrl}</url>`,
+      `  <title>${escapeXml(site.name)}</title>`,
+      `  <link>${site.url}</link>`,
+      '</image>',
+    ].join('\n'),
+    items,
+  });
+};