Add custom resolver for mod settings dictionary

osu.Game/Online/API/APIMod.cs

@@ -23,6 +23,7 @@ namespace osu.Game.Online.API
 
         [JsonProperty("settings")]
         [Key(1)]
+        [MessagePackFormatter(typeof(ModSettingsDictionaryFormatter))]
         public Dictionary<string, object> Settings { get; set; } = new Dictionary<string, object>();
 
         [JsonConstructor]

osu.Game/Online/API/ModSettingsDictionaryFormatter.cs

@@ -0,0 +1,96 @@
+using System;
+using System.Collections.Generic;
+using MessagePack;
+using MessagePack.Formatters;
+using osu.Framework.Bindables;
+
+namespace osu.Game.Online.API
+{
+    public class ModSettingsDictionaryFormatter : IMessagePackFormatter<Dictionary<string, object>>
+    {
+        public int Serialize(ref byte[] bytes, int offset, Dictionary<string, object> value, IFormatterResolver formatterResolver)
+        {
+            int startOffset = offset;
+
+            offset += MessagePackBinary.WriteArrayHeader(ref bytes, offset, value.Count);
+
+            foreach (var kvp in value)
+            {
+                offset += MessagePackBinary.WriteString(ref bytes, offset, kvp.Key);
+
+                switch (kvp.Value)
+                {
+                    case Bindable<double> d:
+                        offset += MessagePackBinary.WriteDouble(ref bytes, offset, d.Value);
+                        break;
+
+                    case Bindable<float> f:
+                        offset += MessagePackBinary.WriteSingle(ref bytes, offset, f.Value);
+                        break;
+
+                    case Bindable<bool> b:
+                        offset += MessagePackBinary.WriteBoolean(ref bytes, offset, b.Value);
+                        break;
+
+                    default:
+                        throw new ArgumentException("A setting was of a type not supported by the messagepack serialiser", nameof(bytes));
+                }
+            }
+
+            return offset - startOffset;
+        }
+
+        public Dictionary<string, object> Deserialize(byte[] bytes, int offset, IFormatterResolver formatterResolver, out int readSize)
+        {
+            int startOffset = offset;
+
+            var output = new Dictionary<string, object>();
+
+            int itemCount = MessagePackBinary.ReadArrayHeader(bytes, offset, out readSize);
+            offset += readSize;
+
+            for (int i = 0; i < itemCount; i++)
+            {
+                var key = MessagePackBinary.ReadString(bytes, offset, out readSize);
+                offset += readSize;
+
+                switch (MessagePackBinary.GetMessagePackType(bytes, offset))
+                {
+                    case MessagePackType.Float:
+                    {
+                        // could be either float or double...
+                        // see https://github.com/msgpack/msgpack/blob/master/spec.md#serialization-type-to-format-conversion
+                        switch (MessagePackCode.ToFormatName(bytes[offset]))
+                        {
+                            case "float 32":
+                                output[key] = MessagePackBinary.ReadSingle(bytes, offset, out readSize);
+                                offset += readSize;
+                                break;
+
+                            case "float 64":
+                                output[key] = MessagePackBinary.ReadDouble(bytes, offset, out readSize);
+                                offset += readSize;
+                                break;
+
+                            default:
+                                throw new ArgumentException("A setting was of a type not supported by the messagepack deserialiser", nameof(bytes));
+                        }
+
+                        break;
+                    }
+
+                    case MessagePackType.Boolean:
+                        output[key] = MessagePackBinary.ReadBoolean(bytes, offset, out readSize);
+                        offset += readSize;
+                        break;
+
+                    default:
+                        throw new ArgumentException("A setting was of a type not supported by the messagepack deserialiser", nameof(bytes));
+                }
+            }
+
+            readSize = offset - startOffset;
+            return output;
+        }
+    }
+}