Json Serialization and Deserialization (#22)

* added support for serializing `Result` and `Result<T>` to JSON
* added support for deserializing`Result` and `Result<T>` from JSON
* added unit test to cover JSON serializing and deserializing

src/RailwayResult/Helpers/TypeDefinition.cs

@@ -0,0 +1,31 @@
+using System.Diagnostics.CodeAnalysis;
+
+namespace RailwayResult.Helpers;
+
+internal record TypeDefinition(string AssemblyName, string TypeName) : ISpanParsable<TypeDefinition>
+{
+	public TypeDefinition(Type type) : this(type.Assembly.GetName().Name!, type.FullName!) { }
+
+	public static TypeDefinition Parse(ReadOnlySpan<char> s, IFormatProvider? provider)
+	{
+		Span<Range> range = stackalloc Range[2];
+		s.Split(range, '/');
+
+		var assemblyName = s[range[0]];
+		var typeName = s[range[1]];
+
+		return new TypeDefinition(assemblyName.ToString(), typeName.ToString());
+	}
+
+	public static TypeDefinition Parse(string s, IFormatProvider? provider) => Parse(s.AsSpan(), provider);
+
+	public static bool TryParse(ReadOnlySpan<char> s, IFormatProvider? provider, [MaybeNullWhen(false)] out TypeDefinition result)
+	{
+		result = Parse(s, provider);
+		return true;
+	}
+
+	public static bool TryParse([NotNullWhen(true)] string? s, IFormatProvider? provider, [MaybeNullWhen(false)] out TypeDefinition result) => TryParse(s.AsSpan(), provider, out result);
+
+	public override string ToString() => $"{AssemblyName}/{TypeName}";
+}

src/RailwayResult/Helpers/Utf8JsonReaderExtensions.cs

@@ -0,0 +1,80 @@
+using System.Reflection;
+using System.Runtime.CompilerServices;
+using System.Text.Json;
+using System.Text.Json.Serialization;
+
+namespace RailwayResult.Helpers;
+
+internal static class Utf8JsonReaderExtensions
+{
+	public static void ReadOrThrow(ref this Utf8JsonReader reader, JsonTokenType type, string? errorMessage = null)
+	{
+		reader.Read();
+		if (reader.TokenType != type)
+		{
+			throw new JsonException(errorMessage);
+		}
+	}
+
+	public static string? ReadPropertyName(ref this Utf8JsonReader reader, params string[] expectedParams)
+	{
+		reader.Read();
+		var name = reader.GetString();
+		if (reader.TokenType != JsonTokenType.PropertyName || !expectedParams.Contains(name))
+		{
+			throw new JsonException($"Expected one of '{string.Join("', '", expectedParams)}'.");
+		}
+
+		return name;
+	}
+
+	public static void ReadPropertyName(ref this Utf8JsonReader reader, string expectedPropertyName)
+	{
+		reader.Read();
+		var name = reader.GetString();
+		if (reader.TokenType != JsonTokenType.PropertyName || name != expectedPropertyName)
+		{
+			throw new JsonException($"Expected property '{expectedPropertyName}'.");
+		}
+	}
+
+	public static string ReadStringValue(ref this Utf8JsonReader reader, string? errorMessage = null)
+	{
+		reader.Read();
+		if (reader.TokenType != JsonTokenType.String)
+		{
+			throw new JsonException(errorMessage);
+		}
+
+		return reader.GetString()!;
+	}
+
+	public static Type ReadErrorType(ref this Utf8JsonReader reader, string? errorMessage = null)
+	{
+		reader.Read();
+		if (reader.TokenType != JsonTokenType.String)
+		{
+			throw new JsonException(errorMessage);
+		}
+
+		var typeDefinitionString = reader.GetString()!;
+		var typeDefinition = TypeDefinition.Parse(typeDefinitionString, default);
+
+		try
+		{
+			var assembly = Assembly.Load(typeDefinition.AssemblyName);
+			return assembly.GetType(typeDefinition.TypeName)!;
+		}
+		catch
+		{
+			throw new JsonException($"Failed to load error type [{typeDefinitionString}].");
+		}
+	}
+
+	public static Error ReadError(ref this Utf8JsonReader reader, Type valueType, JsonSerializerOptions options)
+	{
+		reader.Read();
+		var converter = Unsafe.As<JsonConverter<Error>>(options.GetConverter(valueType));
+		return converter.Read(ref reader, valueType, options)!;
+	}
+}

src/RailwayResult/Helpers/Utf8JsonWriterExtensions.cs

@@ -0,0 +1,14 @@
+using System.Runtime.CompilerServices;
+using System.Text.Json;
+using System.Text.Json.Serialization;
+
+namespace RailwayResult.Helpers;
+
+internal static class Utf8JsonWriterExtensions
+{
+	public static void WriteError(this Utf8JsonWriter writer, Error error, Type valueType, JsonSerializerOptions options)
+	{
+		var converter = Unsafe.As<JsonConverter<Error>>(options.GetConverter(valueType));
+		converter.Write(writer, error, options);
+	}
+}

src/RailwayResult/JsonConverters/GenericResultJsonConverter.cs

@@ -0,0 +1,72 @@
+using System.Text.Json;
+using System.Text.Json.Serialization;
+
+using RailwayResult.Helpers;
+
+namespace RailwayResult.JsonConverters;
+
+internal sealed class GenericResultJsonConverter<T> : JsonConverter<Result<T>>
+{
+	internal const string JSON_VALUE = "Value";
+	internal const string JSON_ERROR_TYPE = "ErrorType";
+	internal const string JSON_ERROR = "Error";
+
+	private static readonly Type ValueType = typeof(T);
+
+	private readonly JsonConverter<T> _valueConverter;
+
+	public GenericResultJsonConverter(JsonSerializerOptions options)
+	{
+		_valueConverter = (JsonConverter<T>)options.GetConverter(typeof(T));
+	}
+
+	public override Result<T>? Read(ref Utf8JsonReader reader, Type typeToConvert, JsonSerializerOptions options)
+	{
+		if (reader.TokenType != JsonTokenType.StartObject)
+		{
+			throw new JsonException("Expected '{'.");
+		}
+
+		var name = reader.ReadPropertyName(JSON_ERROR_TYPE, JSON_VALUE);
+		Result<T>? result;
+
+		if (name == JSON_ERROR_TYPE)
+		{
+			var errorType = reader.ReadErrorType("Expected error type definition.");
+
+			reader.ReadPropertyName(JSON_ERROR);
+			var error = reader.ReadError(errorType, options);
+
+			result = new(error);
+		}
+		else
+		{
+			reader.Read();
+			result = _valueConverter.Read(ref reader, ValueType, options);
+		}
+
+		reader.ReadOrThrow(JsonTokenType.EndObject, "Expected '}'.");
+		return result;
+	}
+
+	public override void Write(Utf8JsonWriter writer, Result<T> value, JsonSerializerOptions options)
+	{
+		writer.WriteStartObject();
+
+		if (value!.IsSuccess)
+		{
+			writer.WritePropertyName(JSON_VALUE);
+			_valueConverter.Write(writer, value.Value, options);
+		}
+		else
+		{
+			var errorType = value.Error.GetType();
+			writer.WriteString(JSON_ERROR_TYPE, new TypeDefinition(errorType).ToString());
+
+			writer.WritePropertyName(JSON_ERROR);
+			writer.WriteError(value.Error, errorType, options);
+		}
+
+		writer.WriteEndObject();
+	}
+}

src/RailwayResult/JsonConverters/GenericResultJsonConverterFactory.cs

@@ -0,0 +1,24 @@
+using System.Reflection;
+using System.Text.Json;
+using System.Text.Json.Serialization;
+
+namespace RailwayResult.JsonConverters;
+
+internal sealed class GenericResultJsonConverterFactory : JsonConverterFactory
+{
+	private static readonly Type GenericResultType = typeof(Result<>);
+	private static readonly Type GenericResultConverterType = typeof(GenericResultJsonConverter<>);
+
+	public override bool CanConvert(Type typeToConvert)
+	{
+		return typeToConvert.IsGenericType && typeToConvert.GetGenericTypeDefinition() == GenericResultType;
+	}
+
+	public override JsonConverter? CreateConverter(Type typeToConvert, JsonSerializerOptions options)
+	{
+		var nestedType = typeToConvert.GetGenericArguments()[0];
+		var converterType = GenericResultConverterType.MakeGenericType(nestedType);
+		var flags = BindingFlags.Instance | BindingFlags.Public;
+		return Activator.CreateInstance(converterType, flags, null, [options], null) as JsonConverter;
+	}
+}

src/RailwayResult/JsonConverters/ResultJsonConverter.cs

@@ -0,0 +1,62 @@
+using System.Text.Json;
+using System.Text.Json.Serialization;
+
+using RailwayResult.Helpers;
+
+namespace RailwayResult.JsonConverters;
+
+internal sealed class ResultJsonConverter : JsonConverter<Result>
+{
+	internal const string JSON_ERROR_TYPE = "Type";
+	internal const string JSON_ERROR = "Error";
+
+	public override Result? Read(ref Utf8JsonReader reader, Type typeToConvert, JsonSerializerOptions options)
+	{
+		if (reader.TokenType != JsonTokenType.StartObject)
+		{
+			throw new JsonException("Expected '{'.");
+		}
+
+		var name = reader.ReadPropertyName(JSON_ERROR_TYPE, JSON_ERROR);
+		Result? result;
+
+		if (name == JSON_ERROR_TYPE)
+		{
+			var errorType = reader.ReadErrorType("Expected error type definition.");
+
+			reader.ReadPropertyName(JSON_ERROR);
+			var error = reader.ReadError(errorType, options);
+
+			result = new(error);
+		}
+		else
+		{
+			reader.ReadOrThrow(JsonTokenType.Null, "Expected null, failure Result has to have specified error type.");
+			result = Result.Success;
+		}
+
+		reader.ReadOrThrow(JsonTokenType.EndObject, "Expected '}'.");
+		return result;
+	}
+
+	public override void Write(Utf8JsonWriter writer, Result value, JsonSerializerOptions options)
+	{
+		writer.WriteStartObject();
+
+		if (value.IsSuccess)
+		{
+			writer.WritePropertyName(JSON_ERROR);
+			writer.WriteNullValue();
+		}
+		else
+		{
+			var errorType = value.Error.GetType();
+			writer.WriteString(JSON_ERROR_TYPE, new TypeDefinition(errorType).ToString());
+
+			writer.WritePropertyName(JSON_ERROR);
+			writer.WriteError(value.Error, errorType, options);
+		}
+
+		writer.WriteEndObject();
+	}
+}

src/RailwayResult/Result.Generic.cs

@@ -1,7 +1,11 @@
-using RailwayResult.Exceptions;
+using System.Text.Json.Serialization;
+
+using RailwayResult.Exceptions;
+using RailwayResult.JsonConverters;
 
 namespace RailwayResult;
 
+[JsonConverter(typeof(GenericResultJsonConverterFactory))]
 public sealed class Result<TValue> : IResult<TValue>
 {
 	public bool IsSuccess => _error is null;

src/RailwayResult/Result.cs

@@ -1,7 +1,11 @@
-using RailwayResult.Exceptions;
+using System.Text.Json.Serialization;
+
+using RailwayResult.Exceptions;
+using RailwayResult.JsonConverters;
 
 namespace RailwayResult;
 
+[JsonConverter(typeof(ResultJsonConverter))]
 public sealed class Result : IResult
 {
 	public bool IsSuccess { get; }
@@ -14,7 +18,7 @@ public sealed class Result : IResult
 
 	public Result(Error error)
 	{
-		IsSuccess = error is null;
+		IsSuccess = false;
 		_error = error;
 	}
 

tests/RailwayResult.Tests/Extensions/ResultExtensions.cs

@@ -0,0 +1,31 @@
+namespace RailwayResult.Tests.Extensions;
+
+public static class ResultExtensions
+{
+	public static void ShouldBe(this Result self, Result expected)
+	{
+		if (self!.IsSuccess)
+		{
+			expected.IsSuccess.Should().BeTrue();
+		}
+		else
+		{
+			expected.IsSuccess.Should().BeFalse();
+			self.Error.Should().BeEquivalentTo(expected.Error);
+		}
+	}
+
+	public static void ShouldBe<T>(this Result<T> self, Result<T> expected)
+	{
+		if (self.IsSuccess)
+		{
+			expected.IsSuccess.Should().BeTrue();
+			self.Value.Should().BeEquivalentTo(expected.Value);
+		}
+		else
+		{
+			expected.IsSuccess.Should().BeFalse();
+			self.Error.Should().BeEquivalentTo(expected.Error);
+		}
+	}
+}

tests/RailwayResult.Tests/Mocks/BasicError.cs

@@ -0,0 +1,6 @@
+namespace RailwayResults.Tests.Mocks;
+
+public sealed record BasicError(string Key, string Message) : Error(Key, Message)
+{
+	public static readonly BasicError ErrorA = new("Key", "Error A");
+}

tests/RailwayResult.Tests/Mocks/ComplexError.cs

@@ -0,0 +1,19 @@
+using static RailwayResults.Tests.Mocks.ComplexError;
+
+namespace RailwayResults.Tests.Mocks;
+
+public sealed record ComplexError(
+	string Key,
+	string Message,
+	string AdditionalString,
+	int AdditionalInt,
+	NestedRecord Record,
+	List<NestedRecord> Records) : Error(Key, Message)
+{
+	public static readonly ComplexError One = new("key", "msg", "one", 1, new(2, "two"), [
+		new(3, "three"),
+		new(4, "four")
+	]);
+
+	public record NestedRecord(int A, string B);
+}