Keep track of game object by UniqueID

. Add ObjectHolder which does just that
- ObjectHolder is accessible though Game.Objects
- UniqueID replaces "sync ID"
- Move DeSerializer classes to IO folder

src/EscapeMenuMultiplayer.cs

@@ -135,12 +135,15 @@ public class EscapeMenuMultiplayer : Container
 
         if (IntegratedServer != null) {
             IntegratedServer.Server.Stop();
+            // TODO: Have a single method to "reset" the state?
+            IntegratedServer.Server.Objects.Clear();
             IntegratedServer.Server.Sync.Clear();
             IntegratedServer.GetParent().RemoveChild(IntegratedServer);
             IntegratedServer.QueueFree();
             IntegratedServer = null;
 
             client.Disconnect();
+            client.Objects.Clear();
             client.Sync.Clear();
         }
 
@@ -156,6 +159,7 @@ public class EscapeMenuMultiplayer : Container
             client.Connect(address, port);
         } else {
             client.Disconnect();
+            client.Objects.Clear();
             client.Sync.Clear();
         }
     }

src/IO/DeSerializer.Impl.cs

@@ -205,26 +205,26 @@ public class DictionaryDeSerializerGenerator
     }
 }
 
-public class SyncedObjectDeSerializerGenerator
+public class NodeDeSerializerGenerator
     : IDeSerializerGenerator
 {
     public IDeSerializer GenerateFor(Type type)
     {
-        if (!typeof(Node).IsAssignableFrom(type) || (type.GetCustomAttribute<SyncObjectAttribute>() == null)) return null;
-        var deSerializerType = typeof(SyncedObjectDeSerializer<>).MakeGenericType(type);
+        if (!typeof(Node).IsAssignableFrom(type)) return null;
+        var deSerializerType = typeof(NodeDeSerializer<>).MakeGenericType(type);
         return (IDeSerializer)Activator.CreateInstance(deSerializerType);
     }
 
-    private class SyncedObjectDeSerializer<TObj>
+    private class NodeDeSerializer<TObj>
             : DeSerializer<TObj>
         where TObj : Node
     {
         public override void Serialize(Game game, BinaryWriter writer, TObj value)
-            => writer.Write(game.Sync.GetStatusOrThrow(value).SyncID);
+            => writer.Write(game.Objects.GetSyncID(value).Value);
         public override TObj Deserialize(Game game, BinaryReader reader)
         {
-            var id    = reader.ReadUInt32();
-            var value = (TObj)game.Sync.GetStatusOrThrow(id).Object;
+            var id    = new UniqueID(reader.ReadUInt32());
+            var value = (TObj)game.Objects.GetNodeByID(id);
             if (value == null) throw new Exception($"Could not find synced object of type {typeof(TObj)} with ID {id}");
             return value;
         }

src/IO/DeSerializerRegistry.cs

@@ -38,7 +38,7 @@ public static class DeSerializerRegistry
         RegisterGenerator(new ArrayDeSerializerGenerator());
         RegisterGenerator(new CollectionDeSerializerGenerator());
         RegisterGenerator(new DictionaryDeSerializerGenerator());
-        RegisterGenerator(new SyncedObjectDeSerializerGenerator());
+        RegisterGenerator(new NodeDeSerializerGenerator());
     }
 
     public static void Register<T>(Action<BinaryWriter, T> serialize, Func<BinaryReader, T> deserialize)

src/IO/Save.cs

@@ -0,0 +1,7 @@
+using System;
+
+[AttributeUsage(AttributeTargets.Property)]
+public class SaveAttribute : Attribute
+{
+
+}

src/Network/Sync.cs

@@ -9,17 +9,17 @@ using Godot;
 public class Sync
 {
     protected Game Game { get; }
-    protected Dictionary<uint, SyncStatus> StatusBySyncID { get; } = new Dictionary<uint, SyncStatus>();
+    protected Dictionary<UniqueID, SyncStatus> StatusByID { get; } = new Dictionary<UniqueID, SyncStatus>();
     protected Dictionary<Node, SyncStatus> StatusByObject { get; } = new Dictionary<Node, SyncStatus>();
 
     static Sync() => DeSerializerRegistry.Register(new SyncPacketObjectDeSerializer());
     public Sync(Game game) => Game = game;
 
-    public SyncStatus GetStatusOrNull(uint syncID)
-        => StatusBySyncID.TryGetValue(syncID, out var value) ? value : null;
-    public SyncStatus GetStatusOrThrow(uint syncID)
-        => GetStatusOrNull(syncID) ?? throw new Exception(
-            $"No {nameof(SyncStatus)} found for ID {syncID}");
+    public SyncStatus GetStatusOrNull(UniqueID id)
+        => StatusByID.TryGetValue(id, out var value) ? value : null;
+    public SyncStatus GetStatusOrThrow(UniqueID id)
+        => GetStatusOrNull(id) ?? throw new Exception(
+            $"No {nameof(SyncStatus)} found for ID {id}");
 
     public SyncStatus GetStatusOrNull(Node obj)
     {
@@ -39,23 +39,23 @@ public class Sync
             node.QueueFree();
         }
 
+        StatusByID.Clear();
         StatusByObject.Clear();
-        StatusBySyncID.Clear();
     }
 }
 
 
 public class SyncStatus
 {
-    public uint SyncID { get; }
+    public UniqueID ID { get; }
     public Node Object { get; }
     public SyncObjectInfo Info { get; }
 
     public int DirtyProperties { get; set; }
     public SyncMode Mode { get; set; }
 
-    public SyncStatus(uint syncID, Node obj, SyncObjectInfo info)
-        { SyncID = syncID; Object = obj; Info = info; }
+    public SyncStatus(UniqueID id, Node obj, SyncObjectInfo info)
+        { ID = id; Object = obj; Info = info; }
 }
 
 public enum SyncMode
@@ -73,11 +73,11 @@ public class SyncPacket
     public class Object
     {
         public ushort InfoID { get; }
-        public uint SyncID { get; }
+        public UniqueID ID { get; }
         public SyncMode Mode { get; }
         public List<(byte, object)> Values { get; }
-        public Object(ushort infoID, uint syncID, SyncMode mode, List<(byte, object)> values)
-            { InfoID = infoID; SyncID = syncID; Mode = mode; Values = values; }
+        public Object(ushort infoID, UniqueID id, SyncMode mode, List<(byte, object)> values)
+            { InfoID = infoID; ID = id; Mode = mode; Values = values; }
     }
 }
 
@@ -87,7 +87,7 @@ internal class SyncPacketObjectDeSerializer
     public override void Serialize(Game game, BinaryWriter writer, SyncPacket.Object value)
     {
         writer.Write(value.InfoID);
-        writer.Write(value.SyncID);
+        writer.Write(value.ID.Value);
         writer.Write((byte)value.Mode);
         writer.Write((byte)value.Values.Count);
 
@@ -103,7 +103,7 @@ internal class SyncPacketObjectDeSerializer
     public override SyncPacket.Object Deserialize(Game game, BinaryReader reader)
     {
         var infoID = reader.ReadUInt16();
-        var syncID = reader.ReadUInt32();
+        var id     = new UniqueID(reader.ReadUInt32());
         var mode   = (SyncMode)reader.ReadByte();
         var count  = reader.ReadByte();
 
@@ -124,6 +124,6 @@ internal class SyncPacketObjectDeSerializer
             values.Add((propID, deSerializer.Deserialize(game, reader)));
         }
 
-        return new SyncPacket.Object(infoID, syncID, mode, values);
+        return new SyncPacket.Object(infoID, id, mode, values);
     }
 }

src/Network/SyncClient.cs

@@ -14,25 +14,28 @@ public class SyncClient : Sync
     {
         foreach (var packetObj in packet.Changes) {
             var info   = SyncRegistry.Get(packetObj.InfoID);
-            var status = GetStatusOrNull(packetObj.SyncID);
+            var status = GetStatusOrNull(packetObj.ID);
 
             if (status == null) {
                 if (packetObj.Mode != SyncMode.Spawn) throw new Exception(
-                    $"Unknown synced object {info.Name} (ID {packetObj.SyncID})");
+                    $"Unknown synced object {info.Name} (ID {packetObj.ID})");
 
                 var obj = info.Scene.Init<Node>();
-                status  = new SyncStatus(packetObj.SyncID, obj, info);
-                StatusBySyncID.Add(status.SyncID, status);
+                Client.Objects.Add(packetObj.ID, obj);
+
+                status = new SyncStatus(packetObj.ID, obj, info);
+                StatusByID.Add(status.ID, status);
                 StatusByObject.Add(status.Object, status);
+
                 Client.GetNode("World").AddChild(obj);
             } else {
                 if (packetObj.Mode == SyncMode.Spawn) throw new Exception(
-                    $"Spawning object {info.Name} with ID {packetObj.SyncID}, but it already exists");
+                    $"Spawning object {info.Name} with ID {packetObj.ID}, but it already exists");
                 if (info != status.Info) throw new Exception(
                     $"Info of synced object being modified doesn't match ({info.Name} != {status.Info.Name})");
 
                 if (packetObj.Mode == SyncMode.Destroy) {
-                    StatusBySyncID.Remove(status.SyncID);
+                    StatusByID.Remove(status.ID);
                     StatusByObject.Remove(status.Object);
 
                     status.Object.GetParent().RemoveChild(status.Object);

src/Network/SyncServer.cs

@@ -6,7 +6,6 @@ using Godot;
 public class SyncServer : Sync
 {
     private static readonly HashSet<SyncStatus> _dirtyObjects = new HashSet<SyncStatus>();
-    private static uint _syncIDCounter = 1;
 
     protected Server Server => (Server)Game;
 
@@ -18,10 +17,13 @@ public class SyncServer : Sync
     {
         var info = SyncRegistry.Get<T>();
         var obj  = info.Scene.Init<T>();
-        var status = new SyncStatus(_syncIDCounter++, obj, info){ Mode = SyncMode.Spawn };
-        StatusBySyncID.Add(status.SyncID, status);
+        var id   = Server.Objects.Add(obj);
+
+        var status = new SyncStatus(id, obj, info){ Mode = SyncMode.Spawn };
+        StatusByID.Add(status.ID, status);
         StatusByObject.Add(status.Object, status);
         _dirtyObjects.Add(status);
+
         Server.GetNode("World").AddChild(obj);
 
         return obj;
@@ -33,7 +35,7 @@ public class SyncServer : Sync
         var status = GetStatusOrThrow(obj);
 
         status.Mode = SyncMode.Destroy;
-        StatusBySyncID.Remove(status.SyncID);
+        StatusByID.Remove(status.ID);
         StatusByObject.Remove(status.Object);
         _dirtyObjects.Add(status);
 
@@ -63,7 +65,7 @@ public class SyncServer : Sync
             foreach (var prop in status.Info.PropertiesByID)
                 if ((status.DirtyProperties & (1 << prop.ID)) != 0)
                     values.Add((prop.ID, prop.Getter(status.Object)));
-            packet.Changes.Add(new SyncPacket.Object(status.Info.ID, status.SyncID, status.Mode, values));
+            packet.Changes.Add(new SyncPacket.Object(status.Info.ID, status.ID, status.Mode, values));
             // If the object has been newly spawned, now is the time to remove the "Spawn" flag.
             if (status.Mode == SyncMode.Spawn) status.Mode = SyncMode.Default;
         }
@@ -80,7 +82,7 @@ public class SyncServer : Sync
             var values = new List<(byte, object)>();
             foreach (var prop in status.Info.PropertiesByID)
                 values.Add((prop.ID, prop.Getter(status.Object)));
-            packet.Changes.Add(new SyncPacket.Object(status.Info.ID, status.SyncID, SyncMode.Spawn, values));
+            packet.Changes.Add(new SyncPacket.Object(status.Info.ID, status.ID, SyncMode.Spawn, values));
         }
         NetworkPackets.Send(server, new []{ networkID }, packet);
     }
@@ -89,6 +91,5 @@ public class SyncServer : Sync
     {
         base.Clear();
         _dirtyObjects.Clear();
-        _syncIDCounter = 1;
     }
 }

src/Objects/ObjectHolder.cs

@@ -0,0 +1,49 @@
+using System;
+using System.Collections.Generic;
+using Godot;
+
+public class ObjectHolder
+{
+    private readonly Dictionary<UniqueID, Node> _nodeByID = new Dictionary<UniqueID, Node>();
+    private readonly Dictionary<Node, UniqueID> _idByNode = new Dictionary<Node, UniqueID>();
+    private uint _newIDCounter = 1;
+
+    public UniqueID Add(Node obj)
+    {
+        UniqueID id;
+        // Keep going until we find an unused UniqueID.
+        while (_nodeByID.TryGetValue(id = new UniqueID(_newIDCounter++), out _)) {  }
+        Add(id, obj);
+        return id;
+    }
+    public void Add(UniqueID id, Node obj)
+    {
+        _nodeByID.Add(id, obj);
+        _idByNode.Add(obj, id);
+    }
+
+    public UniqueID GetSyncID(Node obj)
+        => _idByNode.TryGetValue(obj, out var value) ? value : throw new Exception(
+            $"The specified object '{obj}' does not have a UniqueID");
+    public Node GetNodeByID(UniqueID id)
+        => _nodeByID.TryGetValue(id, out var value) ? value : throw new Exception(
+            $"No object associated with {id}");
+
+    public void Clear()
+    {
+        _nodeByID.Clear();
+        _idByNode.Clear();
+    }
+}
+
+public readonly struct UniqueID : IEquatable<UniqueID>
+{
+    public uint Value { get; }
+    public UniqueID(uint value) => Value = value;
+    public override bool Equals(object obj) => (obj is UniqueID other) && Equals(other);
+    public bool Equals(UniqueID other) => Value == other.Value;
+    public override int GetHashCode() => Value.GetHashCode();
+    public override string ToString() => $"{nameof(UniqueID)}({Value})";
+    public static bool operator ==(UniqueID left, UniqueID right) => left.Equals(right);
+    public static bool operator !=(UniqueID left, UniqueID right) => !left.Equals(right);
+}

src/Scenes/Game.cs

@@ -4,6 +4,7 @@ using Godot.Collections;
 
 public abstract class Game : Node2D
 {
+    public ObjectHolder Objects { get; } = new ObjectHolder();
     public Sync Sync { get; protected set; }
 
 	// Using _EnterTree to make sure this code runs before any other.

src/Scenes/Server.cs

@@ -155,7 +155,7 @@ public readonly struct NetworkID : IEquatable<NetworkID>
     public override bool Equals(object obj) => (obj is NetworkID other) && Equals(other);
     public bool Equals(NetworkID other) => Value == other.Value;
     public override int GetHashCode() => Value.GetHashCode();
-    public override string ToString() => $"NetworkID({Value})";
+    public override string ToString() => $"{nameof(NetworkID)}({Value})";
     public static bool operator ==(NetworkID left, NetworkID right) => left.Equals(right);
     public static bool operator !=(NetworkID left, NetworkID right) => !left.Equals(right);
 }