source: binary-improvements/7dtd-server-fixes/src/PersistentData/PersistentContainer.cs

using System;
using System.IO;
using System.Runtime.Serialization;
using System.Runtime.Serialization.Formatters.Binary;

namespace AllocsFixes.PersistentData {
        [Serializable]
        public class PersistentContainer {
                private const string persistentDataFileName = "/AllocsPersistentData.bin";
                
                private Players players;
                [OptionalField] private Attributes attributes;

                public Players Players => players ??= new Players ();

                public Attributes Attributes => attributes ??= new Attributes ();

                private static PersistentContainer instance;

                public static PersistentContainer Instance => instance ??= new PersistentContainer ();

                private PersistentContainer () {
                }
                
                public void Save () {
                        lock (fileLockObject) {
                                using Stream stream = File.Open ($"{GameIO.GetSaveGameDir ()}{persistentDataFileName}", FileMode.Create);
                                BinaryFormatter bFormatter = new BinaryFormatter ();
                                bFormatter.Serialize (stream, this);
                        }
                }

                public static bool Load () {
                        var filePath = $"{GameIO.GetSaveGameDir ()}{persistentDataFileName}";
                        
                        if (!File.Exists (filePath)) {
                                return false;
                        }

                        try {
                                PersistentContainer obj;
                                lock (fileLockObject) {
                                        using Stream stream = File.Open (filePath, FileMode.Open);
                                        BinaryFormatter bFormatter = new BinaryFormatter ();
                                        obj = (PersistentContainer)bFormatter.Deserialize (stream);
                                }

                                instance = obj;
                                return true;
                        } catch (Exception e) {
                                Log.Error ("Exception in PersistentContainer.Load");
                                Log.Exception (e);
                        }

                        return false;
                }

                private static readonly object fileLockObject = new();
        }
}