Serve short URLs

package.json

@@ -11,6 +11,7 @@
   "dependencies": {
     "compression": "^1.7.1",
     "modern-normalize": "^1.0.0",
+    "node-fetch": "^2.6.1",
     "polka": "next",
     "sirv": "^1.0.0"
   },

src/server.js

@@ -1,15 +1,45 @@
 import sirv from 'sirv';
 import polka from 'polka';
+import fetch from 'node-fetch';
 import compression from 'compression';
 import * as sapper from '@sapper/server';
 
 const { PORT, NODE_ENV } = process.env;
 const dev = NODE_ENV === 'development';
 
+const shortenerBase = process.env.SHORTENER_BASE || 'https://link.nanao.moe';
+
+var linksCache = {}
+
+const links = async function(req, res, next) {
+	if(linksCache[req.path]) {
+		if(linksCache[req.path] == 'none') {
+			next();
+		} else {
+			res.writeHead(301, { Location: linksCache[req.path] });
+			res.end();
+		}
+		return;
+	}
+
+	fetch(shortenerBase+req.path, {
+		redirect: 'manual',
+	}).then(function(fetchres){
+		var unshortenedUrl = fetchres.headers.get('Location');
+		if(unshortenedUrl == shortenerBase+"/") {
+			linksCache[req.path] = "none";
+			next()
+		} else {
+			res.writeHead(301, { Location: unshortenedUrl });
+			res.end();
+		}
+	})
+}
 polka() // You can also use Express
 	.use(
 		compression({ threshold: 0 }),
 		sirv('static', { dev }),
+		links,
 		sapper.middleware()
 	)
 	.listen(PORT, err => {

yarn.lock

@@ -1984,6 +1984,11 @@ no-case@^2.2.0:
   dependencies:
     lower-case "^1.1.1"
 
+node-fetch@^2.6.1:
+  version "2.6.1"
+  resolved "https://registry.yarnpkg.com/node-fetch/-/node-fetch-2.6.1.tgz#045bd323631f76ed2e2b55573394416b639a0052"
+  integrity sha512-V4aYg89jEoVRxRb2fJdAg8FHvI7cEyYdVAh94HH0UIK8oJxUfkjlDQN9RbMx+bEjP7+ggMiFRprSti032Oipxw==
+
 node-gyp@^7.1.0:
   version "7.1.2"
   resolved "https://registry.yarnpkg.com/node-gyp/-/node-gyp-7.1.2.tgz#21a810aebb187120251c3bcec979af1587b188ae"