How do I check a port for an RDP service?

I'm trying to make a simple port scanner like NMAP, and in this part I'm on I need to check if a port is using the RDP service. I think the rdp-rs crate can help, but im confused where to look. I know i should start with something having to do with TPKT. but basically my final goal is to return a boolean if the port is rdp or not

I don't know anything about RDP, but just reading the README of rdp-rs, there are multiple authentication methods, and you'd have to know which one to use.

If your goal is simply to tell if a port is RDP or not, maybe just pick one authentication method, and hopefully the error message will show you that the port is RDP, even though it didn't connect successfully.

nah, i know there's a way to make a handshake or something