ipc: add custom serializer for IGameObject

fixes #1924

Dalamud/Plugin/Ipc/Internal/CallGateChannel.cs

@@ -4,6 +4,8 @@ using System.Linq;
 using System.Reflection;
 
 using Dalamud.Plugin.Ipc.Exceptions;
+using Dalamud.Plugin.Ipc.Internal.Converters;
+
 using Newtonsoft.Json;
 using Serilog;
 
@@ -206,7 +208,10 @@ internal class CallGateChannel
         if (obj is null)
             return null;
 
-        var json = JsonConvert.SerializeObject(obj);
+        var settings = new JsonSerializerSettings();
+        settings.Converters.Add(new GameObjectConverter());
+
+        var json = JsonConvert.SerializeObject(obj, settings);
 
         try
         {
@@ -241,7 +246,7 @@ internal class CallGateChannel
 
         try
         {
-            return JsonConvert.DeserializeObject(json, type);
+            return JsonConvert.DeserializeObject(json, type, settings);
         }
         catch (Exception ex)
         {

Dalamud/Plugin/Ipc/Internal/Converters/GameObjectConverter.cs

@@ -0,0 +1,49 @@
+using System.IO;
+
+using Dalamud.Game.ClientState.Objects;
+using Dalamud.Game.ClientState.Objects.Types;
+using Dalamud.Utility;
+
+using Newtonsoft.Json;
+
+namespace Dalamud.Plugin.Ipc.Internal.Converters;
+
+/// <summary>
+/// JSON converter for IGameObject and its derived types.
+/// </summary>
+internal sealed class GameObjectConverter : JsonConverter<IGameObject>
+{
+    /// <inheritdoc/>
+    public override void WriteJson(JsonWriter writer, IGameObject? value, JsonSerializer serializer) =>
+        writer.WriteValue(value?.Address.ToString());
+
+    /// <inheritdoc/>
+    public override IGameObject? ReadJson(
+        JsonReader reader,
+        Type objectType,
+        IGameObject? existingValue,
+        bool hasExistingValue,
+        JsonSerializer serializer)
+    {
+        if (reader.TokenType == JsonToken.Null)
+            return null;
+
+        if (reader.TokenType != JsonToken.String)
+            throw new InvalidDataException("String is expected.");
+        
+        if (!nint.TryParse(reader.Value as string, out var v))
+            throw new InvalidDataException("Could not parse address.");
+        
+        if (!ThreadSafety.IsMainThread)
+            throw new InvalidOperationException("Cannot send GameObjects from non-main thread over IPC.");
+        
+        var ot = Service<ObjectTable>.Get();
+        foreach (var go in ot)
+        {
+            if (go.Address == v)
+                return go;
+        }
+
+        return ot.CreateObjectReference(v);
+    }
+}