Reversing Client and buiding a server from it

Question

I have this very old online game client (MMO) that has gone offline, and I want to make a server to this client.

I saw a lot of this kind of servers like World of Warcraft private servers.

I think that is not illegal do this to this with this client because the company is long gone, and I will not distribute...

So, how do I start reversing this client to make a server? Do I need to capture the database requests and build a database based on the requests? I think that probably this go way further. Can you help me?

Can you give some examples?

Thanks everyone.

Answer 1

There was a good post on reverse engineering subreddit about this a little bit ago.

There are a few links with peoples experiences. Effectively you will play the game of trying to make your client happy by "answering" packets with your server if you dont have packet captures to go after. I would first identify packet parsing logic within the client. A good way of doing this is tracing recv() calls backwards and generally you will find a giant function (or a few functions) that contain a switch statement. Hopefully you'll find some useful strings, else you're just going to be playing the "keep the client happy" guessing game.