More elaborate fetcher API's

src/fetchers/simpleProxy.ts

@@ -9,9 +9,28 @@ const headerMap: Record<string, string> = {
   origin: 'X-Origin',
 };
 
+const responseHeaderMap: Record<string, string> = {
+  'x-set-cookie': 'Set-Cookie',
+};
+
 export function makeSimpleProxyFetcher(proxyUrl: string, f: FetchLike): Fetcher {
-  const fetcher = makeStandardFetcher(f);
   const proxiedFetch: Fetcher = async (url, ops) => {
+    const fetcher = makeStandardFetcher(async (a, b) => {
+      const res = await f(a, b);
+
+      // set extra headers that cant normally be accessed
+      res.extraHeaders = new Headers();
+      Object.entries(responseHeaderMap).forEach((entry) => {
+        const value = res.headers.get(entry[0]);
+        if (!value) return;
+        res.extraHeaders?.set(entry[0].toLowerCase(), value);
+      });
+
+      // set correct final url
+      res.extraUrl = res.headers.get('X-Final-Destination') ?? res.url;
+      return res;
+    });
+
     const fullUrl = makeFullUrl(url, ops);
 
     const headerEntries = Object.entries(ops.headers).map((entry) => {