feat: implement middleware for VST Search subdomain HTML rewriting

functions/_middleware.js

@@ -0,0 +1,55 @@
+// Cloudflare Pages middleware.
+//
+// Both softwaremanager.xyz and vstsearch.softwaremanager.xyz serve the same
+// index.html. Crawlers (Discord, Twitter, etc.) read the raw HTML and do NOT
+// run JavaScript, so we rewrite the <title> and Open Graph / Twitter meta tags
+// server-side when the request is for the VST Search subdomain. This gives the
+// subdomain its own link embed without a separate deploy.
+
+const VST = {
+  title: "VST Search - SoftwareManager",
+  description: "Search for plugins easily",
+  url: "https://vstsearch.softwaremanager.xyz/",
+};
+
+class AttributeSetter {
+  constructor(attribute, value) {
+    this.attribute = attribute;
+    this.value = value;
+  }
+  element(element) {
+    element.setAttribute(this.attribute, this.value);
+  }
+}
+
+class ContentSetter {
+  constructor(value) {
+    this.value = value;
+  }
+  element(element) {
+    element.setInnerContent(this.value);
+  }
+}
+
+export async function onRequest(context) {
+  const { request, next } = context;
+  const response = await next();
+
+  const onVstDomain = new URL(request.url).hostname.startsWith("vstsearch.");
+  const contentType = response.headers.get("content-type") || "";
+
+  // Leave everything untouched on the main domain and for non-HTML responses.
+  if (!onVstDomain || !contentType.includes("text/html")) {
+    return response;
+  }
+
+  return new HTMLRewriter()
+    .on("title", new ContentSetter(VST.title))
+    .on("meta[name='description']", new AttributeSetter("content", VST.description))
+    .on("meta[property='og:title']", new AttributeSetter("content", VST.title))
+    .on("meta[property='og:description']", new AttributeSetter("content", VST.description))
+    .on("meta[property='og:url']", new AttributeSetter("content", VST.url))
+    .on("meta[name='twitter:title']", new AttributeSetter("content", VST.title))
+    .on("meta[name='twitter:description']", new AttributeSetter("content", VST.description))
+    .transform(response);
+}