Dose preview mode only work with file-system based router?

[P233]

I am using the next.js custom server with koa in my project and trying to turn off useFileSystemPublicRoutes. But then I could not make the preview mode works properly.

In the custom server file I have this router for api/preview.

app.prepare().then(() => {
  const server = new Koa();
  const router = new Router();

  router.get("/api/preview", async (ctx) => {
    await app.render(ctx.req, ctx.res, "/api/preview", ctx.query);
    ctx.respond = false;
  });  
  ...
});

This is the /api/preview.ts file:

export default async (req, res) => {
  res.setPreviewData({
    previewToken: req.query.token
  });
  ...
}

I got TypeError: res.setPreviewData is not a function and the req value is {}.

Now I have to use both custom server and enable useFileSystemPublicRoutes. Did I miss anything?

[timneutkens]

Would recommend not using a custom server and building around API routes to begin with