fix(spa): handle HTML redirects for aliases (#1680)

quartz/components/scripts/util.ts

@@ -24,3 +24,22 @@ export function removeAllChildren(node: HTMLElement) {
     node.removeChild(node.firstChild)
   }
 }
+
+// AliasRedirect emits HTML redirects which also have the link[rel="canonical"]
+// containing the URL it's redirecting to.
+// Extracting it here with regex is _probably_ faster than parsing the entire HTML
+// with a DOMParser effectively twice (here and later in the SPA code), even if
+// way less robust - we only care about our own generated redirects after all.
+const canonicalRegex = /<link rel="canonical" href="([^"]*)">/
+
+export async function fetchCanonical(url: URL): Promise<Response> {
+  const res = await fetch(`${url}`)
+  if (!res.headers.get("content-type")?.startsWith("text/html")) {
+    return res
+  }
+  // reading the body can only be done once, so we need to clone the response
+  // to allow the caller to read it if it's was not a redirect
+  const text = await res.clone().text()
+  const [_, redirect] = text.match(canonicalRegex) ?? []
+  return redirect ? fetch(redirect) : res
+}