Merge pull request #632 from lumeland/middleware/hatsu

feat: new middleware `redirect_as2`

middlewares/redirect_as2.ts

@@ -0,0 +1,77 @@
+import type { Middleware } from "../core/server.ts";
+
+export interface Data {
+  /**
+   * User domain.
+   * @default
+   * ```ts
+   * new URL(req.url).host
+   * ```
+   * @example
+   * ```ts
+   * site.options.location.host
+   * ```
+   */
+  host?: URL["host"];
+}
+export interface Options extends Data {
+  /**
+   * Rewrite URL function.
+   * @param url req.url
+   * @returns Rewritten URLs or empty
+   */
+  rewriteUrl: (url: URL, data: Data) => Promise<URL> | URL | undefined | void;
+  /**
+   * User domain.
+   * @default
+   * ```ts
+   * new URL(req.url).host
+   * ```
+   * @example
+   * ```ts
+   * site.options.location.host
+   * ```
+   */
+  host?: URL["host"];
+}
+
+export const hatsu =
+  (instance: URL["host"]): Options["rewriteUrl"] => (url, data) => {
+    const { pathname } = url;
+    const host = data.host ?? url.host;
+    if (url.pathname === "/") {
+      return new URL(`https://${instance}/users/${host}`);
+    } else {
+      return new URL(
+        `https://${host}${pathname}`,
+        `https://${instance}/posts/`,
+      );
+    }
+  };
+
+export const bridgyFed =
+  (instance: URL["host"] = "fed.brid.gy"): Options["rewriteUrl"] =>
+  (url, data) => {
+    const { pathname } = url;
+    const host = data.host ?? url.host;
+    if (pathname === "/") return new URL(`https://${instance}/${host}`);
+    else return new URL(`https://${host}${pathname}`, `https://${instance}/r/`);
+  };
+
+export default (options: Options): Middleware => async (req, next) => {
+  const accept = req.headers.get("accept");
+  if (
+    accept && [
+      "application/activity+json",
+      'application/ld+json;profile="http://www.w3.org/ns/activitystreams"',
+      'application/ld+json; profile="http://www.w3.org/ns/activitystreams"',
+    ].some((type) => (accept.includes(type)))
+  ) {
+    const dest = await options.rewriteUrl(new URL(req.url), {
+      host: options.host,
+    });
+    if (dest) return Response.redirect(dest);
+  }
+
+  return await next(req);
+};