Store manifest in memory so it does not need to be generated for every page request (#1433)

Co-authored-by: Dessalines <dessalines@users.noreply.github.com>

src/server/handlers/manifest-handler.ts

@@ -0,0 +1,28 @@
+import type { Request, Response } from "express";
+import { LemmyHttp } from "lemmy-js-client";
+import { getHttpBaseInternal } from "../../shared/env";
+import { wrapClient } from "../../shared/services/HttpService";
+import generateManifestJson from "../utils/generate-manifest-json";
+import { setForwardedHeaders } from "../utils/set-forwarded-headers";
+
+let manifest: Awaited<ReturnType<typeof generateManifestJson>> | undefined =
+  undefined;
+
+export default async (req: Request, res: Response) => {
+  if (!manifest) {
+    const headers = setForwardedHeaders(req.headers);
+    const client = wrapClient(new LemmyHttp(getHttpBaseInternal(), headers));
+    const site = await client.getSite({});
+
+    if (site.state === "success") {
+      manifest = await generateManifestJson(site.data);
+    } else {
+      res.sendStatus(500);
+      return;
+    }
+  }
+
+  res.setHeader("content-type", "application/manifest+json");
+
+  res.send(manifest);
+};