How can you just get server side rendering result on nextjs?

Question

In a api route of my nextjs server, I want to request the server itself for a page where it will perform validation and return the result(whether it's validate or not), and I'll do next step depending on the result.

I need this flow because I want to use same validation codes on both client side and server side, and the codes depend on hooks(like redux selector).

Is it possible? Or is there any work around to meet what I intend to do? I hope there is at least a way to redirect in component during server side rendering as workaround.

If it's possible, would there be a way for a nextjs to return just a simple text message as the page result? So I can easily see if validation has gone ok.