Fix JSON converters for Activities

src/Discord.Net.Core/Entities/Activities/GameParty.cs

@@ -2,7 +2,7 @@
 {
     public class GameParty
     {
-        public ulong[] Size { get; internal set; }
-        public ulong Id { get; internal set; }
+        public string Id { get; internal set; }
+        public int[] Size { get; internal set; }
     }
 }

src/Discord.Net.Core/Entities/Activities/GameTimestamps.cs

@@ -4,10 +4,10 @@ namespace Discord
 {
     public class GameTimestamps
     {
-        public DateTimeOffset Start { get; }
-        public DateTimeOffset End { get; }
+        public DateTimeOffset? Start { get; }
+        public DateTimeOffset? End { get; }
 
-        public GameTimestamps(DateTimeOffset start, DateTimeOffset end)
+        public GameTimestamps(DateTimeOffset? start, DateTimeOffset? end)
         {
             Start = start;
             End = end;

src/Discord.Net.Rest/API/Common/GameParty.cs

@@ -5,8 +5,8 @@ namespace Discord.API
     internal class GameParty
     {
         [JsonProperty("id")]
-        public ulong Id { get; set; }
+        public string Id { get; set; }
         [JsonProperty("size")]
-        public ulong[] Size { get; set; }
+        public int[] Size { get; set; }
     }
 }

src/Discord.Net.Rest/API/Common/GameTimestamps.cs

@@ -6,8 +6,10 @@ namespace Discord.API
     internal class GameTimestamps
     {
         [JsonProperty("start")]
-        public DateTimeOffset Start { get; set; }
+        [UnixTimestamp]
+        public Optional<DateTimeOffset> Start { get; set; }
         [JsonProperty("end")]
-        public DateTimeOffset End { get; set; }
+        [UnixTimestamp]
+        public Optional<DateTimeOffset> End { get; set; }
     }
 }

src/Discord.Net.Rest/API/UnixTimestampAttribute.cs

@@ -0,0 +1,7 @@
+using System;
+
+namespace Discord.API
+{
+    [AttributeUsage(AttributeTargets.Property)]
+    internal class UnixTimestampAttribute : Attribute { }
+}

src/Discord.Net.Rest/Net/Converters/DiscordContractResolver.cs

@@ -66,6 +66,12 @@ namespace Discord.Net.Converters
                 if (type == typeof(ulong))
                     return UInt64Converter.Instance;
             }
+            bool hasUnixStamp = propInfo.GetCustomAttribute<UnixTimestampAttribute>() != null;
+            if (hasUnixStamp)
+            {
+                if (type == typeof(DateTimeOffset))
+                    return UnixTimestampConverter.Instance;
+            }
 
             //Enums
             if (type == typeof(PermissionTarget))

src/Discord.Net.Rest/Net/Converters/UnixTimestampConverter.cs

@@ -0,0 +1,28 @@
+using System;
+using Newtonsoft.Json;
+
+namespace Discord.Net.Converters
+{
+    public class UnixTimestampConverter : JsonConverter
+    {
+        public static readonly UnixTimestampConverter Instance = new UnixTimestampConverter();
+
+        public override bool CanConvert(Type objectType) => true;
+        public override bool CanRead => true;
+        public override bool CanWrite => true;
+
+        public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)
+        {
+            // Discord doesn't validate if timestamps contain decimals or not
+            if (reader.Value is double d)
+                return new DateTimeOffset(1970, 1, 1, 0, 0, 0, 0, TimeSpan.Zero).AddMilliseconds(d);
+            long offset = (long)reader.Value;
+            return new DateTimeOffset(1970, 1, 1, 0, 0, 0, 0, TimeSpan.Zero).AddMilliseconds(offset);
+        }
+
+        public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer)
+        {
+            throw new NotImplementedException();
+        }
+    }
+}

src/Discord.Net.WebSocket/Extensions/EntityExtensions.cs

@@ -69,7 +69,7 @@
 
         public static GameTimestamps ToEntity(this API.GameTimestamps model)
         {
-            return new GameTimestamps(model.Start, model.End);
+            return new GameTimestamps(model.Start.ToNullable(), model.End.ToNullable());
         }
     }
 }