Enable Support for Discoverable CSM Servers

[vrnhgd]

I play CS1 every once in a blue moon. Have always wanted to be able to play a proper multiplayer game via CSM, but it's so challenging to find somebody else that's technical enough to get everything set up (and match extensions).

The set of changes described here implements the following:

1. support MS Visual Studio 18 / 2026 (a194bed) and search for Cities Skylines in various install directories (i.e. I'm lazy and don't want to have to type in the install dir every time and it's in an expected place 99% of the time) (e8885f7)
2. adds convenience scripts for running the game server via PowerShell and deploying DLLs to a secondary test host via SSH/SCP (e8885f7, 13f97d9, ad961de)
3. Update data model for server naming and host discoverability (2e25e18)
4. Update UI to expose discoverability settings (2181fec)
5. add HTTP endpoints to the game server to allow users to query public APIs (7dd005a)
6. use a custom Json parser... JsonUtility wasn't playing nicely and neither was Newtonsot.Json (67bc06c, 6f087bb)

[vrnhgd]

How it works:

1. A host creates a server the same way that you would using existing CSM mods:

2. If host has set the game to discoverable, the core API server will actually advertise existence of the server in its server list

{
  "Servers": [
    {
      "Name": "roond's world",
      "CurrentPlayers": 0,
      "MaxPlayers": 0,
      "HasPassword": true,
      "Address": "100.66.251.86:4230"
    }
  ]
}

3. Host gets notification that their process is available

4. Non-Host Player can either directly type in the IP address etc. OR they can now browse available public matches

6. If there's a public available match, you can click "join" and it will auto-populate the relevant IP address/port combo required. Note that passwords are still required

[vrnhgd]

improvements that I could use help with because I don't really have experience:

• some kind of fail2ban/jail for users who spam public servers or the API server

some improvements that could be made as future pull requests:

• IP address/port shouldn't be exposed to the user at all in the UI when connecting to a public game (a smart enough user could reasonably use WireShark or something, so the point of this is to remove irrelevant info for non-technical users)
• users should be able to compute point-to-point host ping time and all-player max ping time to determine if they're comfortable with the RTT. we should probably set reasonable limits on maximum latency before CSM won't support multiplayer
• current/maximum player count needs to be displayed

[kaenganxt]

Thank you for your contribution, that is really appreciated!

I would have one request: Could you maybe use the existing LiteNetLib protocol to retrieve the server list from the GS instead of HTTP?

I think the HTTP implementation is quite some overhead (including JSON parsing) and needs some extra considerations on the hosting side as well (port forwarding).

About your questions:

some kind of fail2ban/jail for users who spam public servers or the API server

that's usually part of the hosting side and not of the application, so doesn't need to be done in the GS

IP address/port shouldn't be exposed to the user at all in the UI when connecting to a public game (a smart enough user could reasonably use WireShark or something, so the point of this is to remove irrelevant info for non-technical users)

Using the token instead of the IP address to connect should be fine. This is the same then as connecting through the Steam overlay.

I've added some comments already to the code, but didn't have time to test it yet.

[vrnhgd]

I have zero experience using LiteNetLib but I'll take a stab at it. Do you have ideas of a different way that I can do ser-des for the server information? if not, JSON deserialization still will be required though since the Server objects are JSON.

I've made the other changes that you suggested on the review!

[kaenganxt]

While testing, I found some UI issues with this patch:

Maybe you can make the panel a bit higher.

I think a line break should work.

[vrnhgd]

I won't be able to modify the position of the UI panel as I don't have access to my machine that runs CSM... can't test it locally. I've completed your other items though. If you'd like to make the change to move the panel up a bit I'm happy to include it!