using System;

using System.Net;

using System.Text.Json;

using System.Text.Json.Serialization;

​

public class Program

{

    public static void Main()

    {

        var ip = IPAddress.Parse("192.168.1.2");

        var message = new ClientRegistered("Foo", ip);

        var jsonserializeroptions = new JsonSerializerOptions() {

            Converters = { new IPAddressJsonConverter()},

            WriteIndented = true    //Just for demo purposes, irrelevant

        };

        Console.WriteLine(JsonSerializer.Serialize(message, jsonserializeroptions));

    }

}

​

public record ClientRegistered(string Client, IPAddress IPAddress);

​

public class IPAddressJsonConverter : JsonConverter<IPAddress>

{

    public override IPAddress Read(ref Utf8JsonReader reader, Type typeToConvert, JsonSerializerOptions options)

        => IPAddress.TryParse(reader.GetString(), out var result) ? result : IPAddress.None;

​

    public override void Write(Utf8JsonWriter writer, IPAddress value, JsonSerializerOptions options)

        => writer.WriteStringValue(value.ToString());

}