Modding:SaveGame Data Storage: Difference between revisions

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__FORCETOC__
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{{GameVersion|1.12}}


Before starting, you should have a development environment set up. If you don't have one already you should read the tutorial [[Setting up your Development Environment]]. Furthermore, we assume that you have a basic understanding of the C# language and Object Oriented Programming. Let's get started!
Before starting, you should have a development environment set up. If you don't have one already you should read the tutorial [[Setting up your Development Environment]]. Furthermore, we assume that you have a basic understanding of the C# language and Object Oriented Programming. Let's get started!
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== Preparation ==
== Preparation ==


Let's start by creating a new .cs file for this mod, and adding our imports and the <code>VintageStory.ServerMods</code> namespace to wrap our class in. Additionally, we'll declare the class <code>LookingForGroup</code> that will inheret from <code>ModSystem</code> which is the base class for mod systems. You can read more about this [http://apidocs.vintagestory.at/api/Vintagestory.API.Common.ModSystem.html here].
Let's start by creating a new .cs file for this mod, and adding our imports and the <code>VintageStory.ServerMods</code> namespace to wrap our class in. Additionally, we'll declare the class <code>LookingForGroup</code> that will inherit from <code>ModSystem</code> which is the base class for mod systems. You can read more about this [http://apidocs.vintagestory.at/api/Vintagestory.API.Common.ModSystem.html here].


<syntaxhighlight lang="c#">
<syntaxhighlight lang="c#">
Line 32: Line 33:
     {
     {
         ICoreServerAPI serverApi;
         ICoreServerAPI serverApi;
        List<string> lfgList;
         public override void StartServerSide(ICoreServerAPI api)
         public override void StartServerSide(ICoreServerAPI api)
         {
         {
             serverApi = api;
             serverApi = api;
            api.Event.SaveGameLoaded += OnSaveGameLoading;
            api.Event.GameWorldSave += OnSaveGameSaving;


             api.RegisterCommand("lfg", "List or join the lfg list", "[list|join|leave]", OnLfg);
             api.RegisterCommand("lfg", "List or join the lfg list", "[list|join|leave]", OnLfg);
Line 44: Line 50:
In this class, we create an override for the <code>StartServerSide</code> method. This method of the <code>ModSystem</code> is called for all mods on the Server side by the game.
In this class, we create an override for the <code>StartServerSide</code> method. This method of the <code>ModSystem</code> is called for all mods on the Server side by the game.


When the Server side starts, we register a command that players will use to access our list of those looking for group. This will be <code>/lfg</code> with the arguments list, join or leave.
The Core Server API contains an additional API for <code>Event</code> registration; this, in turn, contains two very important events (among others): <code>SaveGameLoaded</code> and <code>GameWorldSave</code>. These events are fired when the game is loaded, and when the game saves, respectively. We can assign delegates that will be called when the events fire by assigning these to the event with the <code>+=</code> operator.
 
When the Server side starts, we add two event delegates that will retrieve our list from the <code>SaveGame</code> when the we game loads, and that will save the list when the game saves. We also register a command that players will use to access our list of those looking for group. This will be <code>/lfg</code> with the arguments list, join or leave.


Let's create the delegate <code>OnLfg</code> that will be called when a player enters this command.
Let us now define the event delegates!


== Storing and Retrieving the List ==
== Retrieving and Storing the List ==


Right after our <code>StartServerSide</code> override, let's create our <code>/lfg</code> command delegate:
When the game loads, <code>OnSaveGameLoading</code> gets called and attempts to get our list of players looking for group. The Core Server Api has a member called <code>WorldManager</code> which we use to access everything World related, including our <code>SaveGame</code>.


<syntaxhighlight lang="c#">
<syntaxhighlight lang="c#">
         private void OnLfg(IServerPlayer player, int groupId, CmdArgs args)
         private void OnSaveGameLoading()
         {
         {
             if (args.Length < 1)
             byte[] data = serverApi.WorldManager.SaveGame.GetData("lfg");
            {
                player.SendMessage(groupId, "/lfg [list|join|leave]", EnumChatType.CommandError);
                return;
            }


            lfgList = data == null ? new List<string>() : SerializerUtil.Deserialize<List<string>>(data);
         }
         }
</syntaxhighlight>
</syntaxhighlight>


This has three parameters: the player issuing the command, the group in which this command was entered, and the arguments sent for the command.
We attempt to get our list by exposing the <code>GetData</code> method and passing it an identifier for our custom data, in this case our "lfg" list.
 
'''Hint''': If nothing is found stored under the key we provide, the <code>GetData</code> method returns null. In our mod example, this will happen until at least one player enters the list!


The first thing we do is check that there is at least an argument given, with <code>if (args.Length < 1)</code>. If there isn't, we show the player the list of possible arguments and we go no further.
<code>byte[] data = serverApi.WorldManager.SaveGame.GetData("lfg");</code>


Next, we'll attempt to get our list of players looking for group. The Core Server Api has a member called <code>WorldManager</code> which we use to access everything World related, including our <code>SaveGame</code>.
As you can see, we're retrieving an array of bytes, which is the data type we actually store on the <code>SaveGame</code>. Let's convert it to a <code>List</code> of strings:


<syntaxhighlight lang="c#">
<code>lfgList = data == null ? new List<string>() : SerializerUtil.Deserialize<List<string>>(data);</code>
        private void OnLfg(IServerPlayer player, int groupId, CmdArgs args)
        {
            if (args.Length < 1)...


            byte[] data = serverApi.WorldManager.SaveGame.GetData("lfg");
Here we use a ternary operator to assign our <code>lfgList</code> field a new <code>List<string></code> if there was nothing stored under the "lfg" key.


            List<string> players = data == null ? new List<string>() : SerializerUtil.Deserialize<List<string>>(data);
If <code>data</code> is not null, we expose the <code>Deserialize<T></code> method of the <code>SerializerUtil</code> class. This method will deserialize an array of bytes into an instance of the type argument we pass it. Now that we have a delegate that fetches our list of players "lfg", let's create the delegate that stores this list when the Game World is saved:


<syntaxhighlight lang="c#">
        private void OnSaveGameSaving()
        {
            serverApi.WorldManager.SaveGame.StoreData("lfg", SerializerUtil.Serialize(lfgList));
         }
         }
</syntaxhighlight>
</syntaxhighlight>


We attempt to get our list by exposing the <code>GetData</code> method and passing it an identifier for our custom data, in this case our "lfg" list.
Here we call the <code>StoreData</code> method to save our list under the "lfg" key for later retrieval! Because we can only store data in the form of <code>byte[]</code>, we use the <code>Serialize</code> method of the <code>SerializerUtil</code> class to turn <code>lfgList</code> back to an array of bytes, which we pass as the second argument.  
 
'''Hint''': If nothing is found stored under the identifier, the <code>GetData</code> method returns null. In our mod example, this will happen until at least one player enters the list!
 
<code>byte[] data = serverApi.WorldManager.SaveGame.GetData("lfg");</code>
 
As you can see, we're retrieving an array of bytes, which is data type we actually store on the SaveGame. Let's convert it to a <code>List</code> of strings:
 
List<string> players = data == null ? new List<string>() : SerializerUtil.Deserialize<List<string>>(data);


Here we use a ternary operator to assign our <code>players</code> list a new <code>List<string></code> if there was nothing stored under the "lfg" key.
We now have implemented a way to assign our list from storageto <code>lfgList</code> when the <code>SaveGame</code> is loaded, and a way to store this list once the game is saved. In between these two events, we want players to be added or removed from <code>lfgList</code> via our command. Let's create our command delegate!


If <code>data</code> is not null, we expose the <code>Deserialize<T></code> method of the <code>SerializerUtil</code> class. This method will deserialize an array of bytes into an instance of the type argument we pass it.
== Handling the Command ==


Now that we have our list of players "lfg", let's handle the possible arguments of the command.
Server chat commands have three parameters: the player issuing the command, the group in which this command was entered, and the arguments sent for the command.


<syntaxhighlight lang="c#">
<syntaxhighlight lang="c#">
         private void OnLfg(IServerPlayer player, int groupId, CmdArgs args)
         private void OnLfg(IServerPlayer player, int groupId, CmdArgs args)
         {
         {
            if (args.Length < 1)...
            byte[] data = serverApi.WorldManager.SaveGame.GetData("lfg");
            List<string> players = data == null ? new List<string>() : SerializerUtil.Deserialize<List<string>>(data);
             string cmd = args.PopWord();
             string cmd = args.PopWord();
             switch (cmd)
             switch (cmd)
             {
             {
Line 127: Line 120:
</syntaxhighlight>
</syntaxhighlight>


We use the <code>PopWord</code> of our <code>CmdArgs</code> parameter to collect the first argument passed (ignoring anything subsequent). We then start a switch statement for our valid arguments, and default to showing these to the player if none of them match.
We use the <code>PopWord</code> of our <code>CmdArgs</code> parameter to collect the first argument passed (ignoring anything subsequent). We then start a switch statement for our valid arguments, and default to showing these to the player if none of them match or <code>cmd</code> is null.


Let's handle each of these:
Let's handle each of these:
Line 133: Line 126:
<syntaxhighlight lang="c#">
<syntaxhighlight lang="c#">
                 case "join":
                 case "join":
                     if (players.Contains(player.PlayerUID))
                     if (lfgList.Contains(player.PlayerUID))
                     {
                     {
                         player.SendMessage(groupId, "You're already in this list!", EnumChatType.Notification);
                         player.SendMessage(groupId, "You're already in the list!", EnumChatType.CommandError);
                     }
                     }
                     else
                     else
                     {
                     {
                         players.Add(player.PlayerUID);
                         lfgList.Add(player.PlayerUID);
                        data = SerializerUtil.Serialize(players);
                         player.SendMessage(groupId, "Successfully joined.", EnumChatType.CommandSuccess);
 
                        serverApi.WorldManager.SaveGame.StoreData("lfg", data);
 
                         player.SendMessage(groupId, "Successfully joined!", EnumChatType.Notification);
                     }
                     }
                     break;
                     break;
</syntaxhighlight>
</syntaxhighlight>


If <code>/lfg join</code> was entered, we'll first check if the player is already on the "lfg" list, letting the player know if so. Alternatively, we add the player's unique identifier to the list, and use the <code>Serialize</code> method to turn the updated players <code>List<string></code> back to an array of byte.
If <code>/lfg join</code> was entered, we'll first check if the player is already on the "lfg" list, letting the player know if so. Alternatively, we add the player's unique identifier to the list and show a success message.  


After, we use the <code>StoreData</code> method to save our new serialized list under the "lfg" key for later retrieval! Upon completion, we let the player know that he is now in the list.
'''Hint:''' We do not want to store player names directly. This is because player names may change, therefore our list could become inaccurate.


Now let's handle <code>/lfg leave</code>:
Next we handle <code>/lfg leave</code>:


<syntaxhighlight lang="c#">
<syntaxhighlight lang="c#">
                 case "leave":
                 case "leave":
                     if (!players.Remove(player.PlayerUID))
                     if (!lfgList.Remove(player.PlayerUID))
                     {
                     {
                         player.SendMessage(groupId, "You're not in the list!", EnumChatType.Notification);
                         player.SendMessage(groupId, "You're not in the list!", EnumChatType.CommandError);
                     }
                     }
                     else
                     else
                     {
                     {
                        data = SerializerUtil.Serialize(players);
                         player.SendMessage(groupId, "Successfully left.", EnumChatType.CommandSuccess);
 
                        serverApi.WorldManager.SaveGame.StoreData("lfg", data);
 
                         player.SendMessage(groupId, "Successfully left!", EnumChatType.Notification);
                     }
                     }
                     break;
                     break;
</syntaxhighlight>
</syntaxhighlight>


The <code>Remove</code> method returns false if nothing matching the argument passed to it was found to be removed, and true if it was. If the player was in the list, we serialize the updated list, and store the data to the <code>SaveGame</code>, letting the player know their request was successful.
The <code>Remove</code> method returns false if nothing matching the argument passed to it was found and removed, and true if it was. We let the player know if they were not on the list, or if they were and got successfully taken out of it.


Finally, we handle <code>/lfg list</code>:
Finally, we handle <code>/lfg list</code>:
Line 178: Line 163:
<syntaxhighlight lang="c#">
<syntaxhighlight lang="c#">
                 case "list":
                 case "list":
                     if (players.Count == 0)
                     if (lfgList.Count == 0)
                     {
                     {
                         player.SendMessage(groupId, "Noone is looking for group!", EnumChatType.Notification);
                         player.SendMessage(groupId, "Noone is looking for a group.", EnumChatType.CommandSuccess);
                        break;
                     }
                     }
 
                     else
                     string lfgList = "Players looking for group:";
                    players.ForEach((playerUid) =>
                     {
                     {
                         lfgList += "\n" + serverApi.World.PlayerByUid(playerUid).PlayerName;
                        string response = "Players looking for group:";
                    });
                         lfgList.ForEach((playerUid) =>
                        {
                            response += "\n" + serverApi.World.PlayerByUid(playerUid).PlayerName;
                        });


                    player.SendMessage(groupId, lfgList, EnumChatType.Notification);
                        player.SendMessage(groupId, response, EnumChatType.CommandSuccess);
                    }
                     break;
                     break;
</syntaxhighlight>
</syntaxhighlight>


In this case we simply let the player know if are no players in the "lfg" list, and if there are then we build a string with all the player names on the list!
In this case we simply let the player know if there is noone on the list, but if there are we build a string with all the player names on the list.


== Conclusion ==
== Conclusion ==
Line 211: Line 197:
     {
     {
         ICoreServerAPI serverApi;
         ICoreServerAPI serverApi;
        List<string> lfgList;
         public override void StartServerSide(ICoreServerAPI api)
         public override void StartServerSide(ICoreServerAPI api)
         {
         {
             serverApi = api;
             serverApi = api;


             api.RegisterCommand("lfg", "List or join the lfg list", "[list|join|leave]", OnLfg);
            api.Event.SaveGameLoaded += OnSaveGameLoading;
            api.Event.GameWorldSave += OnSaveGameSaving;
 
             api.RegisterCommand("lfg", "Access the lfg list.", "[list|join|leave]", OnLfg);
         }
         }


         private void OnLfg(IServerPlayer player, int groupId, CmdArgs args)
         private void OnSaveGameLoading()
         {
         {
            if (args.Length < 1)
            {
                player.SendMessage(groupId, "/lfg [list|join|leave]", EnumChatType.CommandError);
                return;
            }
             byte[] data = serverApi.WorldManager.SaveGame.GetData("lfg");
             byte[] data = serverApi.WorldManager.SaveGame.GetData("lfg");


             List<string> players = data == null ? new List<string>() : SerializerUtil.Deserialize<List<string>>(data);
             lfgList = data == null ? new List<string>() : SerializerUtil.Deserialize<List<string>>(data);
        }
        private void OnSaveGameSaving()
        {
            serverApi.WorldManager.SaveGame.StoreData("lfg", SerializerUtil.Serialize(lfgList));
        }


        private void OnLfg(IServerPlayer player, int groupId, CmdArgs args)
        {
             string cmd = args.PopWord();
             string cmd = args.PopWord();
             switch (cmd)
             switch (cmd)
             {
             {
                 case "join":
                 case "join":
                     if (players.Contains(player.PlayerUID))
                     if (lfgList.Contains(player.PlayerUID))
                     {
                     {
                         player.SendMessage(groupId, "You're already in this list!", EnumChatType.Notification);
                         player.SendMessage(groupId, "You're already in the list!", EnumChatType.CommandError);
                     }
                     }
                     else
                     else
                     {
                     {
                         players.Add(player.PlayerUID);
                         lfgList.Add(player.PlayerUID);
                        data = SerializerUtil.Serialize(players);
                         player.SendMessage(groupId, "Successfully joined.", EnumChatType.CommandSuccess);
 
                        serverApi.WorldManager.SaveGame.StoreData("lfg", data);
 
                         player.SendMessage(groupId, "Successfully joined!", EnumChatType.Notification);
                     }
                     }
                     break;
                     break;


                 case "leave":
                 case "leave":
                     if (!players.Remove(player.PlayerUID))
                     if (!lfgList.Remove(player.PlayerUID))
                     {
                     {
                         player.SendMessage(groupId, "You're not in the list!", EnumChatType.Notification);
                         player.SendMessage(groupId, "You're not in the list!", EnumChatType.CommandError);
                     }
                     }
                     else
                     else
                     {
                     {
                        data = SerializerUtil.Serialize(players);
                         player.SendMessage(groupId, "Successfully left.", EnumChatType.CommandSuccess);
 
                        serverApi.WorldManager.SaveGame.StoreData("lfg", data);
 
                         player.SendMessage(groupId, "Successfully left!", EnumChatType.Notification);
                     }
                     }
                     break;
                     break;


                 case "list":
                 case "list":
                     if (players.Count == 0)
                     if (lfgList.Count == 0)
                     {
                     {
                         player.SendMessage(groupId, "Noone is looking for group!", EnumChatType.Notification);
                         player.SendMessage(groupId, "Noone is looking for a group.", EnumChatType.CommandSuccess);
                        break;
                     }
                     }
 
                     else
                     string lfgList = "Players looking for group:";
                    players.ForEach((playerUid) =>
                     {
                     {
                         lfgList += "\n" + serverApi.World.PlayerByUid(playerUid).PlayerName;
                        string response = "Players looking for group:";
                    });
                         lfgList.ForEach((playerUid) =>
                        {
                            response += "\n" + serverApi.World.PlayerByUid(playerUid).PlayerName;
                        });


                    player.SendMessage(groupId, lfgList, EnumChatType.Notification);
                        player.SendMessage(groupId, response, EnumChatType.CommandSuccess);
                    }
                     break;
                     break;
 
                   
                case null:
                 default:
                 default:
                     player.SendMessage(groupId, "/lfg [list|join|leave]", EnumChatType.CommandError);
                     player.SendMessage(groupId, "/lfg [list|join|leave]", EnumChatType.CommandError);
                     break;
                     return;
             }
             }
         }
         }
     }
     }
}
}
</syntaxhighlight>
</syntaxhighlight>



Revision as of 14:11, 10 May 2020

This page was last verified for Vintage Story version 1.12.


Before starting, you should have a development environment set up. If you don't have one already you should read the tutorial Setting up your Development Environment. Furthermore, we assume that you have a basic understanding of the C# language and Object Oriented Programming. Let's get started!

Introduction

VintageStory allows you to set and retrieve custom data to the world's game save as well as individual chunks. The way it works is actually quite simple!

Custom data is stored as an array of bytes to save space, but we can easily convert any valid C# type to byte[] with a very convenient class in the VintageStory API: SerializerUtil. This class provides us with two static methods that allow us to quickly Serialize into byte arrays, and Deserialize<T> them into other types.

You can check out the methods for storing and retrieving these arrays of bytes for Chunks and for SaveGame

Custom Data in SaveGame

Let us show you this powerful set of tools by making an example mod in which we implement an open list of players currently looking for a group to play with ingame.

This list will be a List<string> of players which will be stored to the world's SaveGame. Anyone can join it, leave it, or see who needs a group. We'll store this list as an array of bytes, and it can be accessed by the key "lfg".

Preparation

Let's start by creating a new .cs file for this mod, and adding our imports and the VintageStory.ServerMods namespace to wrap our class in. Additionally, we'll declare the class LookingForGroup that will inherit from ModSystem which is the base class for mod systems. You can read more about this here.

using System.Collections.Generic;
using Vintagestory.API.Common;
using Vintagestory.API.Server;
using Vintagestory.API.Util;

namespace Vintagestory.ServerMods
{
    class LookingForGroup : ModSystem
    {
        ICoreServerAPI serverApi;
        List<string> lfgList;

        public override void StartServerSide(ICoreServerAPI api)
        {
            serverApi = api;

            api.Event.SaveGameLoaded += OnSaveGameLoading;
            api.Event.GameWorldSave += OnSaveGameSaving;

            api.RegisterCommand("lfg", "List or join the lfg list", "[list|join|leave]", OnLfg);
        }
    }
}

In this class, we create an override for the StartServerSide method. This method of the ModSystem is called for all mods on the Server side by the game.

The Core Server API contains an additional API for Event registration; this, in turn, contains two very important events (among others): SaveGameLoaded and GameWorldSave. These events are fired when the game is loaded, and when the game saves, respectively. We can assign delegates that will be called when the events fire by assigning these to the event with the += operator.

When the Server side starts, we add two event delegates that will retrieve our list from the SaveGame when the we game loads, and that will save the list when the game saves. We also register a command that players will use to access our list of those looking for group. This will be /lfg with the arguments list, join or leave.

Let us now define the event delegates!

Retrieving and Storing the List

When the game loads, OnSaveGameLoading gets called and attempts to get our list of players looking for group. The Core Server Api has a member called WorldManager which we use to access everything World related, including our SaveGame.

        private void OnSaveGameLoading()
        {
            byte[] data = serverApi.WorldManager.SaveGame.GetData("lfg");

            lfgList = data == null ? new List<string>() : SerializerUtil.Deserialize<List<string>>(data);
        }

We attempt to get our list by exposing the GetData method and passing it an identifier for our custom data, in this case our "lfg" list.

Hint: If nothing is found stored under the key we provide, the GetData method returns null. In our mod example, this will happen until at least one player enters the list!

byte[] data = serverApi.WorldManager.SaveGame.GetData("lfg");

As you can see, we're retrieving an array of bytes, which is the data type we actually store on the SaveGame. Let's convert it to a List of strings:

lfgList = data == null ? new List<string>() : SerializerUtil.Deserialize<List<string>>(data);

Here we use a ternary operator to assign our lfgList field a new List<string> if there was nothing stored under the "lfg" key.

If data is not null, we expose the Deserialize<T> method of the SerializerUtil class. This method will deserialize an array of bytes into an instance of the type argument we pass it. Now that we have a delegate that fetches our list of players "lfg", let's create the delegate that stores this list when the Game World is saved:

        private void OnSaveGameSaving()
        {
            serverApi.WorldManager.SaveGame.StoreData("lfg", SerializerUtil.Serialize(lfgList));
        }

Here we call the StoreData method to save our list under the "lfg" key for later retrieval! Because we can only store data in the form of byte[], we use the Serialize method of the SerializerUtil class to turn lfgList back to an array of bytes, which we pass as the second argument.

We now have implemented a way to assign our list from storageto lfgList when the SaveGame is loaded, and a way to store this list once the game is saved. In between these two events, we want players to be added or removed from lfgList via our command. Let's create our command delegate!

Handling the Command

Server chat commands have three parameters: the player issuing the command, the group in which this command was entered, and the arguments sent for the command.

        private void OnLfg(IServerPlayer player, int groupId, CmdArgs args)
        {
            string cmd = args.PopWord();
            switch (cmd)
            {
                case "join":
                    break;

                case "leave":
                    break;

                case "list":
                    break;

                default:
                    player.SendMessage(groupId, "/lfg [list|join|leave]", EnumChatType.CommandError);
                    break;
            }
        }

We use the PopWord of our CmdArgs parameter to collect the first argument passed (ignoring anything subsequent). We then start a switch statement for our valid arguments, and default to showing these to the player if none of them match or cmd is null.

Let's handle each of these:

                case "join":
                    if (lfgList.Contains(player.PlayerUID))
                    {
                        player.SendMessage(groupId, "You're already in the list!", EnumChatType.CommandError);
                    }
                    else
                    {
                        lfgList.Add(player.PlayerUID);
                        player.SendMessage(groupId, "Successfully joined.", EnumChatType.CommandSuccess);
                    }
                    break;

If /lfg join was entered, we'll first check if the player is already on the "lfg" list, letting the player know if so. Alternatively, we add the player's unique identifier to the list and show a success message.

Hint: We do not want to store player names directly. This is because player names may change, therefore our list could become inaccurate.

Next we handle /lfg leave:

                case "leave":
                    if (!lfgList.Remove(player.PlayerUID))
                    {
                        player.SendMessage(groupId, "You're not in the list!", EnumChatType.CommandError);
                    }
                    else
                    {
                        player.SendMessage(groupId, "Successfully left.", EnumChatType.CommandSuccess);
                    }
                    break;

The Remove method returns false if nothing matching the argument passed to it was found and removed, and true if it was. We let the player know if they were not on the list, or if they were and got successfully taken out of it.

Finally, we handle /lfg list:

                case "list":
                    if (lfgList.Count == 0)
                    {
                        player.SendMessage(groupId, "Noone is looking for a group.", EnumChatType.CommandSuccess);
                    }
                    else
                    {
                        string response = "Players looking for group:";
                        lfgList.ForEach((playerUid) =>
                        {
                            response += "\n" + serverApi.World.PlayerByUid(playerUid).PlayerName;
                        });

                        player.SendMessage(groupId, response, EnumChatType.CommandSuccess);
                    }
                    break;

In this case we simply let the player know if there is noone on the list, but if there are we build a string with all the player names on the list.

Conclusion

If you followed the steps correctly, you should have the following code:

using System.Collections.Generic;
using Vintagestory.API.Common;
using Vintagestory.API.Server;
using Vintagestory.API.Util;

namespace Vintagestory.ServerMods
{
    class LookingForGroup : ModSystem
    {
        ICoreServerAPI serverApi;
        List<string> lfgList;
        public override void StartServerSide(ICoreServerAPI api)
        {
            serverApi = api;

            api.Event.SaveGameLoaded += OnSaveGameLoading;
            api.Event.GameWorldSave += OnSaveGameSaving;

            api.RegisterCommand("lfg", "Access the lfg list.", "[list|join|leave]", OnLfg);
        }

        private void OnSaveGameLoading()
        {
            byte[] data = serverApi.WorldManager.SaveGame.GetData("lfg");

            lfgList = data == null ? new List<string>() : SerializerUtil.Deserialize<List<string>>(data);
        }
        private void OnSaveGameSaving()
        {
            serverApi.WorldManager.SaveGame.StoreData("lfg", SerializerUtil.Serialize(lfgList));
        }

        private void OnLfg(IServerPlayer player, int groupId, CmdArgs args)
        {
            string cmd = args.PopWord();
            switch (cmd)
            {
                case "join":
                    if (lfgList.Contains(player.PlayerUID))
                    {
                        player.SendMessage(groupId, "You're already in the list!", EnumChatType.CommandError);
                    }
                    else
                    {
                        lfgList.Add(player.PlayerUID);
                        player.SendMessage(groupId, "Successfully joined.", EnumChatType.CommandSuccess);
                    }
                    break;

                case "leave":
                    if (!lfgList.Remove(player.PlayerUID))
                    {
                        player.SendMessage(groupId, "You're not in the list!", EnumChatType.CommandError);
                    }
                    else
                    {
                        player.SendMessage(groupId, "Successfully left.", EnumChatType.CommandSuccess);
                    }
                    break;

                case "list":
                    if (lfgList.Count == 0)
                    {
                        player.SendMessage(groupId, "Noone is looking for a group.", EnumChatType.CommandSuccess);
                    }
                    else
                    {
                        string response = "Players looking for group:";
                        lfgList.ForEach((playerUid) =>
                        {
                            response += "\n" + serverApi.World.PlayerByUid(playerUid).PlayerName;
                        });

                        player.SendMessage(groupId, response, EnumChatType.CommandSuccess);
                    }
                    break;
                    
                case null:
                default:
                    player.SendMessage(groupId, "/lfg [list|join|leave]", EnumChatType.CommandError);
                    return;
            }
        }
    }
}

Testing

Let's test our mod. Once you're ingame, try entering /lfg join. Now quit the game and join back in. Upon entering /lfg list, you should see your name on the list; this means that your custom data has persisted in the SaveGame!

Distribution

To distribute this mod, you may run the following command in the modtools cli pack <your mod id>, then copy the .zip file into your VintageStory mods folder.

Here are the official versions: