Developing a server for the game, where to start?

Question

Programming

Hello.
Such a question, how are servers for games created? For example, there is a GTA SA game, as I understand it, third-party developers have made a client that somehow interacts with the game, transmits data, etc., I seem to understand, but how does the client still affect the game? I'm VERY excited about the idea of ​​making a server for GTA 5, making mods for it, etc. , but I can't figure out where to start. How do I manage the game client? I seem to represent the server part, a question-answer.
For example, making a minecraft server is not a problem. I downloaded, configured, launched, I didn’t find it here :( But in fact I don’t need this, I want to make my server from 0 and my mods, bring my ideas to life!
Who has experience, tell me!

Answer 1

For example, there is a GTA SA game, as I understand it, third-party developers made a client

Not certainly in that way. Any multiplayer game consists of two parts - client and server, and they do not work without each other (there are serverless games, but in such cases usually one of the clients becomes a server, this is how it works in Doom / Quake / UT). In GTA, both the client and the server were made by Rockstar Games, not individual developers. And even - more, Rockstar Games tried to hide the interaction protocol - so that hackers and crackers do not hack the game, gaining game benefits in non-game ways. "Make a GTA server" with which the GTA client will work will not work, at least the price of such development will be comparable to the price of working on GTA (which cost tens of millions of dollars).
What a third party developer can do is make mods for the finished server, using the tools that the developer suggested, or trying to "rob" the interaction protocol. There are server and client mods, and are only possible if you have access to a computer running the server and client (you always have a client, and most mods do this).
Minecraft is noticeably easier than GTA. If only because minecraft was made by one person, and GTA was made by dozens of programmers. And for minecraft, you can make your own server, not a mod (although there are mods for it too). For example, great article. .
"Downloaded, configured, launched" - this is not "server development", it took what someone had already developed.
PS Everything written - IMHO. I'm not a fan of GTA and I don't know the market for unofficial GTA servers, I just know that there are (sort of). But personally, I think that hardly anyone can write a server if there is either no source code (steal it), or the developers make tools for developing mods.

Answer 2

From the study of the client-server data exchange protocol.