net: add barebones optional converter

does not support property omission at this time, will need to be added
later using a separate converter and base marker class.

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Discord.Net.sln

@@ -11,6 +11,10 @@ Project("{2150E333-8FDC-42A3-9474-1A3956D46DE8}") = "sample", "sample", "{479564
 EndProject
 Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "idn", "sample\idn\idn.csproj", "{5BE5DE89-53B7-4243-AEA8-FD8A6420908A}"
 EndProject
+Project("{2150E333-8FDC-42A3-9474-1A3956D46DE8}") = "test", "test", "{68EE1EAC-F487-4BAC-917B-233370B3AEA1}"
+EndProject
+Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "Discord.Tests.Unit", "test\Discord.Tests.Unit\Discord.Tests.Unit.csproj", "{6AD4FF67-D45E-4E7E-8853-990390D35C9F}"
+EndProject
 Global
 	GlobalSection(SolutionConfigurationPlatforms) = preSolution
 		Debug|Any CPU = Debug|Any CPU
@@ -48,9 +52,22 @@ Global
 		{5BE5DE89-53B7-4243-AEA8-FD8A6420908A}.Release|x64.Build.0 = Release|Any CPU
 		{5BE5DE89-53B7-4243-AEA8-FD8A6420908A}.Release|x86.ActiveCfg = Release|Any CPU
 		{5BE5DE89-53B7-4243-AEA8-FD8A6420908A}.Release|x86.Build.0 = Release|Any CPU
+		{6AD4FF67-D45E-4E7E-8853-990390D35C9F}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
+		{6AD4FF67-D45E-4E7E-8853-990390D35C9F}.Debug|Any CPU.Build.0 = Debug|Any CPU
+		{6AD4FF67-D45E-4E7E-8853-990390D35C9F}.Debug|x64.ActiveCfg = Debug|Any CPU
+		{6AD4FF67-D45E-4E7E-8853-990390D35C9F}.Debug|x64.Build.0 = Debug|Any CPU
+		{6AD4FF67-D45E-4E7E-8853-990390D35C9F}.Debug|x86.ActiveCfg = Debug|Any CPU
+		{6AD4FF67-D45E-4E7E-8853-990390D35C9F}.Debug|x86.Build.0 = Debug|Any CPU
+		{6AD4FF67-D45E-4E7E-8853-990390D35C9F}.Release|Any CPU.ActiveCfg = Release|Any CPU
+		{6AD4FF67-D45E-4E7E-8853-990390D35C9F}.Release|Any CPU.Build.0 = Release|Any CPU
+		{6AD4FF67-D45E-4E7E-8853-990390D35C9F}.Release|x64.ActiveCfg = Release|Any CPU
+		{6AD4FF67-D45E-4E7E-8853-990390D35C9F}.Release|x64.Build.0 = Release|Any CPU
+		{6AD4FF67-D45E-4E7E-8853-990390D35C9F}.Release|x86.ActiveCfg = Release|Any CPU
+		{6AD4FF67-D45E-4E7E-8853-990390D35C9F}.Release|x86.Build.0 = Release|Any CPU
 	EndGlobalSection
 	GlobalSection(NestedProjects) = preSolution
 		{3194F5DC-C0AF-4459-AAA3-91CB8FB8C370} = {5DAC796B-0B77-4F84-B790-83DB78C6DFFE}
 		{5BE5DE89-53B7-4243-AEA8-FD8A6420908A} = {4795640A-030C-4A9A-A9B0-20C56AF4DA3F}
+		{6AD4FF67-D45E-4E7E-8853-990390D35C9F} = {68EE1EAC-F487-4BAC-917B-233370B3AEA1}
 	EndGlobalSection
 EndGlobal

src/Discord.Net/Rest/DiscordRestApi.cs

@@ -1,10 +1,10 @@
 using System.Text.Json;
 using System.Threading.Tasks;
-using Refit;
-using Discord.Models;
 using System.Net.Http.Headers;
-using System;
 using System.Net.Http;
+using Refit;
+using Discord.Models;
+using Discord.Serialization;
 
 // This is essentially a reimplementation of Wumpus.Net.Rest
 namespace Discord.Rest
@@ -26,6 +26,7 @@ namespace Discord.Rest
             };
 
             var jsonOptions = new JsonSerializerOptions();
+            jsonOptions.Converters.Add(new OptionalConverter());
             var refitSettings = new RefitSettings
             {
                 ContentSerializer = new JsonContentSerializer(jsonOptions),

src/Discord.Net/Serialization/OptionalConverter.cs

@@ -1,22 +1,41 @@
 using System;
-using System.Collections.Generic;
-using System.Text;
 using System.Text.Json;
 using System.Text.Json.Serialization;
 
 namespace Discord.Serialization
 {
-    // 😅
-    public class OptionalConverter<T> : JsonConverter<Optional<T>>
+    // TODO: This does not allow us to omit properties at runtime
+    // Need to evaluate which cases need us to omit properties and write a separate converter
+    // for those. At this time I can only think of the outgoing REST PATCH requests. Incoming
+    // omitted properties will be correctly treated as Optional.Unspecified (the default)
+    public class OptionalConverter : JsonConverterFactory
     {
-        public override Optional<T> Read(ref Utf8JsonReader reader, Type typeToConvert, JsonSerializerOptions options)
+        private class OptionalTypeConverter<T> : JsonConverter<Optional<T>>
         {
-            throw new NotImplementedException();
+            public override Optional<T> Read(ref Utf8JsonReader reader, Type typeToConvert, JsonSerializerOptions options)
+            {
+                if (reader.TokenType == JsonTokenType.Null)
+                    return Optional<T>.Unspecified;
+                else
+                    return new Optional<T>(JsonSerializer.Deserialize<T>(ref reader, options));
+            }
+
+            public override void Write(Utf8JsonWriter writer, Optional<T> value, JsonSerializerOptions options)
+            {
+                if (!value.IsSpecified)
+                    writer.WriteNullValue();
+                else
+                    JsonSerializer.Serialize(writer, value.Value, options);
+            }
         }
 
-        public override void Write(Utf8JsonWriter writer, Optional<T> value, JsonSerializerOptions options)
+        public override bool CanConvert(Type typeToConvert)
+            => typeToConvert.IsGenericType && typeToConvert.GetGenericTypeDefinition() == typeof(Optional<>);
+        public override JsonConverter CreateConverter(Type typeToConvert, JsonSerializerOptions options)
         {
-            throw new NotImplementedException();
+            var innerType = typeToConvert.GetGenericArguments()[0];
+            var converterType = typeof(OptionalTypeConverter<>).MakeGenericType(innerType);
+            return (JsonConverter)Activator.CreateInstance(converterType);
         }
     }
 }

src/Discord.Net/Utilities/Optional.cs

@@ -6,7 +6,57 @@ namespace Discord
 {
     public struct Optional<T>
     {
-        public bool IsSpecified { get; private set; }
-        public T Value { get; set; }
+        public static Optional<T> Unspecified => default;
+
+        public bool IsSpecified { get; }
+        private readonly T _innerValue;
+
+        public T Value
+        {
+            get
+            {
+                if (!IsSpecified)
+                    throw new UnspecifiedOptionalException();
+                return _innerValue;
+            }
+        }
+
+        public Optional(T value)
+        {
+            IsSpecified = true;
+            _innerValue = value;
+        }
+
+        public override string ToString()
+        {
+            return $"<Optional IsSpecified={IsSpecified}, Value={(IsSpecified ? Value?.ToString() ?? "null" : "(unspecified)")}>";
+        }
+
+        public override bool Equals(object obj)
+        {
+            if (obj is Optional<T> opt)
+            {
+                if (IsSpecified && opt.IsSpecified)
+                    return Value?.Equals(opt.Value) ?? opt.Value == null;
+                return IsSpecified == opt.IsSpecified;
+            }
+            return base.Equals(obj);
+        }
+
+        public override int GetHashCode()
+            => IsSpecified ? Value?.GetHashCode() ?? 0 : 0;
+
+        public static bool operator ==(Optional<T> a, Optional<T> b)
+            => a.Equals(b);
+        public static bool operator !=(Optional<T> a, Optional<T> b)
+            => !a.Equals(b);
+
+        // todo: implement comparing, GetValueOrDefault, hash codes etc
+    }
+
+
+    public class UnspecifiedOptionalException : Exception
+    {
+        public UnspecifiedOptionalException() : base("An attempt was made to access an unspecified optional value") { }
     }
 }

test/Discord.Tests.Unit/Discord.Tests.Unit.csproj

@@ -0,0 +1,20 @@
+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <TargetFramework>netcoreapp3.1</TargetFramework>
+
+    <IsPackable>false</IsPackable>
+  </PropertyGroup>
+
+  <ItemGroup>
+    <PackageReference Include="Microsoft.NET.Test.Sdk" Version="16.2.0" />
+    <PackageReference Include="xunit" Version="2.4.0" />
+    <PackageReference Include="xunit.runner.visualstudio" Version="2.4.0" />
+    <PackageReference Include="coverlet.collector" Version="1.0.1" />
+  </ItemGroup>
+
+  <ItemGroup>
+    <ProjectReference Include="..\..\src\Discord.Net\Discord.Net.csproj" />
+  </ItemGroup>
+
+</Project>

test/Discord.Tests.Unit/Serialization/OptionalConverterTests.cs

@@ -0,0 +1,118 @@
+using System.Text.Json;
+using System.Text.Json.Serialization;
+using Xunit;
+using Discord.Serialization;
+
+namespace Discord.Tests.Unit.Serialization
+{
+    public class OptionalConverterTests
+    {
+        private readonly JsonSerializerOptions _jsonOptions;
+
+        public OptionalConverterTests()
+        {
+            _jsonOptions = new JsonSerializerOptions();
+            _jsonOptions.Converters.Add(new OptionalConverter());
+        }
+
+        public class SampleOptionalClass
+        {
+            [JsonPropertyName("optional_number")]
+            public Optional<int> OptionalNumber { get; set; }
+            [JsonPropertyName("required_number")]
+            public int RequiredNumber { get; set; }
+
+            public override bool Equals(object obj)
+                => (obj is SampleOptionalClass other) && (other.OptionalNumber == OptionalNumber && other.RequiredNumber == RequiredNumber);
+            public override int GetHashCode()
+                => OptionalNumber.GetHashCode() ^ RequiredNumber.GetHashCode();
+        }
+
+        private string expectedOptionalUnset = "{\"optional_number\":null,\"required_number\":10}";
+        private SampleOptionalClass withOptionalUnset = new SampleOptionalClass
+        {
+            OptionalNumber = Optional<int>.Unspecified,
+            RequiredNumber = 10,
+        };
+        private string expectedOptionalSet = "{\"optional_number\":11,\"required_number\":10}";
+        private SampleOptionalClass withOptionalSet = new SampleOptionalClass
+        {
+            OptionalNumber = new Optional<int>(11),
+            RequiredNumber = 10,
+        };
+
+        [Fact]
+        public void OptionalConverter_Can_Write()
+        {
+            // todo: is STJ deterministic in writing order? want to make sure this test doesn't fail because of cosmic rays
+            var unsetString = JsonSerializer.Serialize(withOptionalUnset, _jsonOptions);
+            Assert.Equal(expectedOptionalUnset, unsetString);
+            
+            var setString = JsonSerializer.Serialize(withOptionalSet, _jsonOptions);
+            Assert.Equal(expectedOptionalSet, setString);
+        }
+
+        [Fact]
+        public void OptionalConverter_Can_Read()
+        {
+            var unset = JsonSerializer.Deserialize<SampleOptionalClass>(expectedOptionalUnset, _jsonOptions);
+            Assert.Equal(withOptionalUnset, unset);
+
+            var set = JsonSerializer.Deserialize<SampleOptionalClass>(expectedOptionalSet, _jsonOptions);
+            Assert.Equal(withOptionalSet, set);
+        }
+
+        public class NestedPoco
+        {
+            [JsonPropertyName("name")]
+            public string Name { get; set; }
+            [JsonPropertyName("age")]
+            public int Age { get; set; }
+
+            public override bool Equals(object obj)
+                => (obj is NestedPoco other) && (Name == other.Name && Age == other.Age);
+            public override int GetHashCode()
+                => Name.GetHashCode() ^ Age.GetHashCode();
+            
+        }
+        public class NestedSampleClass
+        {
+            [JsonPropertyName("nested")]
+            public Optional<NestedPoco> Nested { get; set; }
+        }
+
+        private string expectedNestedWithUnset = "{\"nested\":null}";
+        private NestedSampleClass nestedWithUnset = new NestedSampleClass
+        {
+            Nested = Optional<NestedPoco>.Unspecified
+        };
+        private string expectedNestedWithSet = "{\"nested\":{\"name\":\"Ashley\",\"age\":23}}";
+        private NestedSampleClass nestedWithSet = new NestedSampleClass
+        {
+            Nested = new Optional<NestedPoco>(new NestedPoco
+            {
+                Name = "Ashley",
+                Age = 23
+            }),
+        };
+
+        [Fact]
+        public void OptionalConverter_Can_Write_Nested_Poco()
+        {
+            var unset = JsonSerializer.Serialize(nestedWithUnset, _jsonOptions);
+            Assert.Equal(expectedNestedWithUnset, unset);
+
+            var set = JsonSerializer.Serialize(nestedWithSet, _jsonOptions);
+            Assert.Equal(expectedNestedWithSet, set);
+        }
+        [Fact]
+        public void OptionalConverter_Can_Read_Nested_Poco()
+        {
+            var unset = JsonSerializer.Deserialize<NestedSampleClass>(expectedNestedWithUnset, _jsonOptions);
+            Assert.Equal(nestedWithUnset.Nested, unset.Nested);
+
+            var set = JsonSerializer.Deserialize<NestedSampleClass>(expectedNestedWithSet, _jsonOptions);
+            Assert.Equal(nestedWithSet.Nested, set.Nested);
+        }
+    }
+}

test/Discord.Tests.Unit/UnitTest1.cs

@@ -0,0 +1,13 @@
+using Xunit;
+
+namespace Discord.Tests.Unit
+{
+    public class UnitTest1
+    {
+        [Fact]
+        public void Test1()
+        {
+            Assert.True(true);
+        }
+    }
+}