KeyValuePair Json Converter

During one of my recent projects, I was unable to serialize a C++ std::map<std::string, std::string> before sending to a C# client.

To solve this I sent the data as a JSON array of key-value pairs. For the C# client to deserialize the JSON array, I created a custom JsonConverter for KeyValuePair<TKey, TValue>. This converter allows you to serialize and deserialize a JSON array of key-value pairs into a Dictionary<TKey, TValue>.

using System;
using System.Collections.Generic;
using System.Text.Json;
using System.Text.Json.Serialization;

public class KeyValuePairConverter<TKey, TValue> : JsonConverter<Dictionary<TKey, TValue>>
  where TKey : notnull
{
  public override bool CanConvert(Type typeToConvert)
  {
    if (base.CanConvert(typeToConvert))
    {
      return true;
    }

    if (typeToConvert.GetGenericTypeDefinition() == typeof(IDictionary<,>) ||
      typeToConvert.GetGenericTypeDefinition() == typeof(IReadOnlyDictionary<,>))
    {
      var genericArguments = typeToConvert.GetGenericArguments();
      return genericArguments[0] == typeof(TKey) && genericArguments[1] == typeof(TValue);
    }

    return false;
  }

  public override Dictionary<TKey, TValue>? Read(ref Utf8JsonReader reader, Type typeToConvert, JsonSerializerOptions options)
  {
    if (reader.TokenType != JsonTokenType.StartArray)
    {
      throw new JsonException("Expected the JSON object to start with an array.");
    }

    var keyPairConverter = (JsonConverter<KeyValuePair<TKey, TValue>>)options.GetConverter(typeof(KeyValuePair<TKey, TValue>));

    var dictionary = new Dictionary<TKey, TValue>();
    while (reader.Read())
    {
      if (reader.TokenType == JsonTokenType.EndArray)
      {
        return dictionary;
      }

      var pair = keyPairConverter.Read(ref reader, typeof(KeyValuePair<TKey, TValue>), options);
      if (pair.Key is null)
      {
        throw new JsonException("Failed to read the key-value pair from JSON.");
      }

      dictionary.Add(pair.Key, pair.Value);
    }

    throw new JsonException("Failed to read the JSON object.");
  }

  public override void Write(Utf8JsonWriter writer, Dictionary<TKey, TValue> value, JsonSerializerOptions options)
  {
    writer.WriteStartArray();

    var keyPairConverter = (JsonConverter<KeyValuePair<TKey, TValue>>)options.GetConverter(typeof(KeyValuePair<TKey, TValue>));
    foreach (var pair in value)
    {
      keyPairConverter.Write(writer, pair, options);
    }

    writer.WriteEndArray();
  }
}

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