feat: generate og:image when there isn't one

src/pages/post/[...slug].astro

@@ -3,6 +3,10 @@ import Layout from '../../layouts/Layout.astro';
 import { getCollection } from 'astro:content';
 import Comments from "../../components/Comments.astro";
 import {getImage} from "astro:assets";
+import { unified } from "unified";
+import { select } from "unist-util-select";
+import remarkMdx from "remark-mdx";
+import remarkParse from "remark-parse";
 
 export async function getStaticPaths() {
   const blogEntries = await getCollection('posts');
@@ -14,16 +18,19 @@ export async function getStaticPaths() {
 const { entry } = Astro.props;
 const { Content } = await entry.render();
 
-
 const slug = Astro.params.slug;
+
+// get featured image and use it as og:image
+// use the custom cover image if it exists, otherwise use the featured image file in the same directory
 const featuredImages = import.meta.glob(`/src/content/posts/*/featured.*`,{import:'default',eager:true});
+const customFeaturedImage = entry.data.cover?.src
 const matchedImage = Object.keys(featuredImages).find(path => path.includes(slug));
 let matchedImage_src;
-if (matchedImage) {
+if (matchedImage && !customFeaturedImage) {
     matchedImage_src = await getImage({src: featuredImages[matchedImage], format: 'webp'}) || null;
 }
-const cover = entry.data.cover || matchedImage_src?.src || `/post/${slug}/og.webp`;
-//|| `/posts/${slug}/featured.webp` || `/posts/${slug}/featured.png` || `/posts/${slug}/featured.jpg`
+
+const cover = customFeaturedImage || matchedImage_src?.src || `/post/${slug}/featured.png` || '';
 ---
 
 <Layout

src/pages/post/[slug]/featured.png.js

@@ -0,0 +1,62 @@
+import { getCollection } from 'astro:content';
+import sharp from 'sharp';
+import {getImage} from "astro:assets";
+
+export async function getStaticPaths() {
+  const blogEntries = await getCollection('posts');
+  return blogEntries.map(post => ({
+    params: { slug: post.slug }, props: { post },
+  }));
+}
+
+// get the post has a external featured.* image files
+async function getExternalImage(post) {
+  const featuredImages = import.meta.glob(`/src/content/posts/*/featured.*`, {import: 'default', eager: true});
+  const matchedImage = Object.keys(featuredImages).find(path => path.includes(post.slug));
+  let matchedImage_src;
+  if (matchedImage) {
+    matchedImage_src = await getImage({src: featuredImages[matchedImage], format: 'webp'}) || null;
+  }
+  return matchedImage_src;
+}
+
+// This function dynamically generates og:images for posts that don't have a featured image
+export async function GET({ props }) {
+  const {post} = props;
+  try {
+    // Check if a custom cover image already exists
+    if (post.data.cover && await getExternalImage(post)) {
+      // Redirect to the existing image
+      return new Response(null);
+    }
+
+    // Generate an image with post title and description
+    const width = 1280;
+    const height = 720;
+
+    // Create a simple image with text
+    const svg = `
+      <svg width="${width}" height="${height}" xmlns="http://www.w3.org/2000/svg">
+        <rect width="${width}" height="${height}" fill="#2e3440"/>
+        <text x="50%" y="40%" font-family="JetBrains Mono, monospace" font-size="50" text-anchor="middle" fill="#eceff4">${post.data.title}</text>
+        <text x="50%" y="60%" font-family="JetBrains Mono, monospace" font-size="30" text-anchor="middle" fill="#81a1c1">${post.data.description}</text>
+      </svg>
+    `;
+
+    // Convert SVG to WebP
+    const buffer = await sharp(Buffer.from(svg))
+      .toFormat('webp')
+      .toBuffer();
+
+    // Return the image
+    return new Response(buffer, {
+      headers: {
+        'Content-Type': 'image/png',
+        'Cache-Control': 'public, max-age=31536000'
+      }
+    });
+  } catch (error) {
+    console.error('Error generating image:', error);
+    return new Response('Error generating image', { status: 500 });
+  }
+}