Full blown example.

src/pages/api/v1/rom.ts

@@ -0,0 +1,44 @@
+import { NextApiHandler } from "next";
+import * as fs from 'fs';
+import * as path from 'path';
+
+const PATH_ROMS = path.resolve('.', 'data', 'games');
+
+const handler:NextApiHandler = async (req, res) => {
+  if (req.method !== 'GET') {
+    res.setHeader('Allow', ['GET']);
+    res.status(405).end(`Method Not Allowed`);
+    return;
+  }
+
+  // ID query param
+  if(!req.query.id || typeof req.query.id !== 'string') {
+    res.status(404).end(`Not Found`);
+    return;
+  }
+
+  const { id } = req.query;
+  if(!id) {
+    res.status(404).end(`Not Found`);
+    return;
+  }
+
+  // Does rom exist?
+  const pathRom = path.resolve(PATH_ROMS, `${id}.bin`);
+  if(!fs.existsSync(pathRom)) {
+    res.status(404).end(`Not Found`);
+    return;
+  }
+
+  // Read rom
+  try {
+    const romStream = fs.createReadStream(pathRom);
+    res.setHeader('Content-Type', 'application/octet-stream');
+    res.setHeader('Content-Disposition', `attachment; filename="${id}.bin"`);
+    romStream.pipe(res);
+  } catch (error) {
+    res.status(500).end(`Internal Server Error`);
+  }
+};
+
+export default handler;