Add support for enum dictionary keys

Remora.Rest/Json/StringEnumConverter.cs

@@ -59,7 +59,7 @@ public override TEnum Read(ref Utf8JsonReader reader, Type typeToConvert, JsonSe
 
         switch (reader.TokenType)
         {
-            case JsonTokenType.String:
+            case JsonTokenType.String or JsonTokenType.PropertyName:
             {
                 var value = reader.GetString();
                 if (value is null)
@@ -117,4 +117,23 @@ public override void Write(Utf8JsonWriter writer, TEnum value, JsonSerializerOpt
 
         writer.WriteStringValue(_enumsToNames[value]);
     }
+
+    /// <inheritdoc />
+    public override TEnum ReadAsPropertyName(ref Utf8JsonReader reader, Type typeToConvert, JsonSerializerOptions options)
+        => this.Read(ref reader, typeToConvert, options);
+
+    /// <inheritdoc/>
+    public override void WriteAsPropertyName(Utf8JsonWriter writer, TEnum value, JsonSerializerOptions options)
+    {
+        if (_asInteger)
+        {
+            writer.WritePropertyName(Enum.GetUnderlyingType(typeof(TEnum)).IsUnsigned()
+                ? Convert.ToUInt64(value).ToString()
+                : Convert.ToInt64(value).ToString());
+
+            return;
+        }
+
+        writer.WritePropertyName(_enumsToNames[value]);
+    }
 }

Tests/Remora.Rest.Tests/Tests/Json/StringEnumConverterTests.cs

@@ -0,0 +1,154 @@
+//
+//  SPDX-FileName: StringEnumConverterTests.cs
+//  SPDX-FileCopyrightText: Copyright (c) Jarl Gullberg
+//  SPDX-License-Identifier: LGPL-3.0-or-later
+//
+
+using System.Collections.Generic;
+using System.Text.Json;
+using Microsoft.Extensions.DependencyInjection;
+using Microsoft.Extensions.Options;
+using Remora.Rest.Json;
+using Remora.Rest.Json.Policies;
+using Remora.Rest.Tests.Data.DataObjects;
+using Xunit;
+
+namespace Remora.Rest.Tests.Json;
+
+/// <summary>
+/// Tests for <see cref="StringEnumConverter{TEnum}"/>.
+/// </summary>
+public class StringEnumConverterTests
+{
+    /// <summary>
+    /// Tests that the converter can serialize a dictionary where the key is an enum.
+    /// </summary>
+    [Fact]
+    public void CanSerializeDictionaryKeyAsInteger()
+    {
+        // Arrange
+        var services = new ServiceCollection()
+                       .Configure<JsonSerializerOptions>
+                       (
+                           json =>
+                           {
+                               json.PropertyNamingPolicy = new SnakeCaseNamingPolicy();
+                               json.Converters.Add(new StringEnumConverter<StringifiedEnum>(asInteger: true));
+                           })
+                       .BuildServiceProvider();
+
+        var dictionary = new Dictionary<StringifiedEnum, string>
+        {
+            { StringifiedEnum.First, "first" },
+            { StringifiedEnum.Second, "second" },
+            { StringifiedEnum.Third, "third" },
+        };
+
+        var jsonOptions = services.GetRequiredService<IOptions<JsonSerializerOptions>>().Value;
+
+        // Act
+        var result = JsonSerializer.Serialize(dictionary, jsonOptions);
+        var expected = "{\"0\":\"first\",\"1\":\"second\",\"2\":\"third\"}";
+
+        // Assert
+        Assert.Equal(expected, result);
+    }
+
+    /// <summary>
+    /// Tests that the converter can serialize a dictionary where the key is an enum.
+    /// </summary>
+    [Fact]
+    public void CanSerializeDictionaryKeyAsString()
+    {
+        // Arrange
+        var services = new ServiceCollection()
+                       .Configure<JsonSerializerOptions>
+                       (
+                           json =>
+                           {
+                               json.PropertyNamingPolicy = new SnakeCaseNamingPolicy();
+                               json.Converters.Add(new StringEnumConverter<StringifiedEnum>(json.PropertyNamingPolicy));
+                           })
+                       .BuildServiceProvider();
+
+        var dictionary = new Dictionary<StringifiedEnum, string>
+        {
+            { StringifiedEnum.First, "first" },
+            { StringifiedEnum.Second, "second" },
+            { StringifiedEnum.Third, "third" },
+        };
+
+        var jsonOptions = services.GetRequiredService<IOptions<JsonSerializerOptions>>().Value;
+
+        // Act
+        var result = JsonSerializer.Serialize(dictionary, jsonOptions);
+        var expected = "{\"first\":\"first\",\"second\":\"second\",\"third\":\"third\"}";
+
+        // Assert
+        Assert.Equal(expected, result);
+    }
+
+    /// <summary>
+    /// Tests that the converter can read a dictionary where the key is an enum.
+    /// </summary>
+    [Fact]
+    public void CanDeserializeDictionaryKeyAsInteger()
+    {
+        // Arrange
+        var services = new ServiceCollection()
+                       .Configure<JsonSerializerOptions>
+                       (
+                           json =>
+                           {
+                               json.PropertyNamingPolicy = new SnakeCaseNamingPolicy();
+                               json.Converters.Add(new StringEnumConverter<StringifiedEnum>(asInteger: true));
+                           })
+                       .BuildServiceProvider();
+
+        var jsonOptions = services.GetRequiredService<IOptions<JsonSerializerOptions>>().Value;
+
+        var json = "{\"0\":\"first\",\"1\":\"second\",\"2\":\"third\"}";
+
+        // Act
+        var result = JsonSerializer.Deserialize<Dictionary<StringifiedEnum, string>>(json, jsonOptions);
+
+        // Assert
+        Assert.NotNull(result);
+        Assert.Equal(3, result.Count);
+        Assert.Equal("first", result[StringifiedEnum.First]);
+        Assert.Equal("second", result[StringifiedEnum.Second]);
+        Assert.Equal("third", result[StringifiedEnum.Third]);
+    }
+
+    /// <summary>
+    /// Tests that the converter can read a dictionary where the key is an enum.
+    /// </summary>
+    [Fact]
+    public void CanDeserializeDictionaryKeyAsString()
+    {
+        // Arrange
+        var services = new ServiceCollection()
+                       .Configure<JsonSerializerOptions>
+                       (
+                           json =>
+                           {
+                               json.PropertyNamingPolicy = new SnakeCaseNamingPolicy();
+                               json.Converters.Add(new StringEnumConverter<StringifiedEnum>(json.PropertyNamingPolicy));
+                           })
+                       .BuildServiceProvider();
+
+        var jsonOptions = services.GetRequiredService<IOptions<JsonSerializerOptions>>().Value;
+
+        var json = "{\"first\":\"first\",\"second\":\"second\",\"third\":\"third\"}";
+
+        // Act
+        var result = JsonSerializer.Deserialize<Dictionary<StringifiedEnum, string>>(json, jsonOptions);
+
+        // Assert
+        Assert.NotNull(result);
+        Assert.Equal(3, result.Count);
+        Assert.Equal("first", result[StringifiedEnum.First]);
+        Assert.Equal("second", result[StringifiedEnum.Second]);
+        Assert.Equal("third", result[StringifiedEnum.Third]);
+    }
+}