From 1c769894d773ef6e265638badc6207b9c845df17 Mon Sep 17 00:00:00 2001
From: Claas Augner <caugner@mozilla.com>
Date: Fri, 17 May 2024 19:01:28 -0400
Subject: [PATCH] feat(cloud-function): redirect capitalization

---
 cloud-function/src/app.ts                     |  5 +++
 .../middlewares/redirect-capitalization.ts    | 33 +++++++++++++++++++
 2 files changed, 38 insertions(+)
 create mode 100644 cloud-function/src/middlewares/redirect-capitalization.ts

diff --git a/cloud-function/src/app.ts b/cloud-function/src/app.ts
index 66019a394427..764c55e485b4 100644
--- a/cloud-function/src/app.ts
+++ b/cloud-function/src/app.ts
@@ -22,6 +22,7 @@ import { resolveRunnerHtml } from "./middlewares/resolve-runner-html.js";
 import { proxyRunner } from "./handlers/proxy-runner.js";
 import { stripForwardedHostHeaders } from "./middlewares/stripForwardedHostHeaders.js";
 import { proxyPong } from "./handlers/proxy-pong.js";
+import { redirectCapitalization } from "./middlewares/redirect-capitalization.js";
 
 const router = Router();
 router.use(stripForwardedHostHeaders);
@@ -60,6 +61,7 @@ router.get(
 router.get(
   `/[^/]+/docs/*/*.(${ANY_ATTACHMENT_EXT.join("|")})`,
   requireOrigin(Origin.main, Origin.liveSamples, Origin.play),
+  redirectCapitalization,
   resolveIndexHTML,
   proxyContent
 );
@@ -70,6 +72,7 @@ router.get(
   redirectLocale,
   redirectTrailingSlash,
   redirectMovedPages,
+  redirectCapitalization,
   resolveIndexHTML,
   proxyContent
 );
@@ -78,6 +81,7 @@ router.get(
   requireOrigin(Origin.main),
   redirectLocale,
   redirectEnforceTrailingSlash,
+  redirectCapitalization,
   resolveIndexHTML,
   proxyContent
 );
@@ -93,6 +97,7 @@ router.get(
   redirectFundamental,
   redirectLocale,
   redirectTrailingSlash,
+  redirectCapitalization,
   resolveIndexHTML,
   proxyContent
 );
diff --git a/cloud-function/src/middlewares/redirect-capitalization.ts b/cloud-function/src/middlewares/redirect-capitalization.ts
new file mode 100644
index 000000000000..16d8c6489bc4
--- /dev/null
+++ b/cloud-function/src/middlewares/redirect-capitalization.ts
@@ -0,0 +1,33 @@
+import { NextFunction, Request, Response } from "express";
+
+import { THIRTY_DAYS } from "../constants.js";
+import { redirect } from "../utils.js";
+import { Source, sourceUri } from "../env.js";
+import { slugToFolder } from "@yari-internal/slug-utils";
+
+const target = sourceUri(Source.content);
+
+export async function redirectCapitalization(
+  req: Request,
+  res: Response,
+  next: NextFunction
+) {
+  const url = new URL(req.url, `${req.protocol}://${req.headers.host}`);
+
+  const requestURI = url.pathname;
+  const qs = url.search;
+
+  const metadataURL = `${target}${slugToFolder(requestURI).slice(1).toLowerCase()}/metadata.json`;
+  const tryMetadata = await fetch(metadataURL);
+  if (tryMetadata.ok) {
+    const metadata = await tryMetadata.json();
+    const mdn_url = metadata.mdn_url;
+    if (mdn_url && mdn_url !== requestURI) {
+      return redirect(res, mdn_url + qs, {
+        cacheControlSeconds: THIRTY_DAYS,
+      });
+    }
+  }
+
+  next();
+}