using System;

using System.Collections;

using System.Collections.Generic;

using System.Linq;

using System.Text;

using System.Runtime.Serialization.Formatters;

using System.IO;

using System.Data;

using System.ComponentModel.DataAnnotations;

using System.Globalization;

using System.Reflection;

using System.Collections.ObjectModel;

​

using System.Text.Json;

using System.Text.Json.Serialization;

​

using NUnit.Framework; // Throws NUnit.Framework.AssertionException

​

//https://stackoverflow.com/questions/66495660/net-5-0-signature-change-of-system-text-json-jsonserializer-deserialize

​

    public class DateTimeOffsetConverter : JsonConverter<DateTimeOffset>

    {

        const string TZDateFormat = "O"; // Your custom format (not shown in your question).

        public override void Write(Utf8JsonWriter writer, DateTimeOffset value, JsonSerializerOptions options) =>

            // Write as a simple string.

            writer.WriteStringValue(value.ToString(TZDateFormat, CultureInfo.InvariantCulture));

        const string _date = "_date";

​

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

        {

            switch (reader.TokenType)

            {

                case JsonTokenType.String:

                    // A simple DateTimeOffset string "value"

                    return DateTimeOffset.ParseExact(reader.GetString(), TZDateFormat, CultureInfo.InvariantCulture);

                case JsonTokenType.StartObject:

                {

                    // A DateTimeOffset string embedded in an object { "_date" : "value" }

                    using var doc = JsonDocument.ParseValue(ref reader);

                    if (doc.RootElement.TryGetProperty(_date, out var value))

                        return DateTimeOffset.ParseExact(value.GetString(), TZDateFormat, CultureInfo.InvariantCulture);

                    return default(DateTimeOffset); // Or throw an exception?

                }

                default:

                    throw new JsonException(); // Unknown token type

            }

        }

    }

​

    public class DateTimeOffsetConverter2 : JsonConverter<DateTimeOffset>

    {

        const string TZDateFormat = "O";

        public override void Write(Utf8JsonWriter writer, DateTimeOffset value, JsonSerializerOptions options) =>

            writer.WriteStringValue(value.ToString(TZDateFormat, CultureInfo.InvariantCulture));

        class DateTimeOffsetDTO { public string _date { get; set; } }

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

        {

            switch (reader.TokenType)

            {

                case JsonTokenType.String:

                    // A simple DateTimeOffset string "value"

                    return DateTimeOffset.ParseExact(reader.GetString(), TZDateFormat, CultureInfo.InvariantCulture);

                case JsonTokenType.StartObject:

                {

                    var dto = JsonSerializer.Deserialize<DateTimeOffsetDTO>(ref reader);

                    return DateTimeOffset.ParseExact(dto._date, TZDateFormat, CultureInfo.InvariantCulture);

                }

            }

            throw new JsonException();

        }

    }

    public class DateTimeOffsetConverter3 : JsonConverter<DateTimeOffset>

    {

        const string TZDateFormat = "O";

        public override void Write(Utf8JsonWriter writer, DateTimeOffset value, JsonSerializerOptions options) =>

            writer.WriteStringValue(value.ToString(TZDateFormat, CultureInfo.InvariantCulture));

        //const string _date = "_date";

        static byte [] _date = Encoding.UTF8.GetBytes("_date");

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

        {

            switch (reader.TokenType)

            {

                case JsonTokenType.String:

                    // A simple DateTimeOffset string "value"

                    return DateTimeOffset.ParseExact(reader.GetString(), TZDateFormat, CultureInfo.InvariantCulture);

                case JsonTokenType.StartObject:

                {

                    // A DateTimeOffset string embedded in an object { "_date" : "value" }

                    DateTimeOffset? value = null;

                    while (reader.Read())

                    {

                        switch (reader.TokenType)

                        {

                            case JsonTokenType.EndObject:

                                return value.GetValueOrDefault();

                            case JsonTokenType.PropertyName:

                                var match = reader.ValueTextEquals(_date);

                                reader.Read();

                                if (match)

                                    value = DateTimeOffset.ParseExact(reader.GetString(), TZDateFormat, CultureInfo.InvariantCulture);

                                else

                                    reader.Skip();

                                break;

                            default:

                                throw new JsonException();

                        }

                    }

                }

                break;

            }

            throw new JsonException();

        }

    }

​

    public class ModelOut

    {

        public class DateTimeOffsetDTO { public DateTimeOffset _date { get; set; } }

        public DateTimeOffsetDTO end { get; set; }

    }

​

    public class Model

    {

        public DateTimeOffset end { get; set; }

    }

​

​

    class TestClass

    {

        public static void Test()

        {

            Test<DateTimeOffsetConverter>();

            Test<DateTimeOffsetConverter2>();

            Test<DateTimeOffsetConverter3>();

        }

        public static void Test<DateTimeOffsetConverter>() where DateTimeOffsetConverter : JsonConverter<DateTimeOffset>, new()

        {

            var model = new ModelOut

            {

                end = new ModelOut.DateTimeOffsetDTO { _date = DateTimeOffset.Parse("2021-04-07T18:18:00.000Z", CultureInfo.InvariantCulture) },

            };

            var options = new JsonSerializerOptions

            {

                Converters = { new DateTimeOffsetConverter() },

            };

            var json = JsonSerializer.Serialize(model, options);

            Console.WriteLine(json);

            var model2 = JsonSerializer.Deserialize<Model>(json, options);

            Assert.AreEqual(model.end._date, model2.end);

        }

    }

​

    public class Program

    {

        public static void Main()

        {

            Console.WriteLine("Environment version: {0} ({1})", System.Runtime.InteropServices.RuntimeInformation.FrameworkDescription , GetNetCoreVersion());

            Console.WriteLine("System.Text.Json version: " + typeof(JsonSerializer).Assembly.FullName);

            Console.WriteLine();

​

            try

            {

                TestClass.Test();

            }

            catch (Exception ex)

            {

                Console.WriteLine("Failed with unhandled exception: ");

                Console.WriteLine(ex);

                throw;

            }

        }

        public static string GetNetCoreVersion()

        {

            //https://techblog.dorogin.com/how-to-detect-net-core-version-in-runtime-ecd65ad695be

            //

            var assembly = typeof(System.Runtime.GCSettings).GetTypeInfo().Assembly;

            var assemblyPath = assembly.Location.Split(new[] { '/', '\\' }, StringSplitOptions.RemoveEmptyEntries);

            int netCoreAppIndex = Array.IndexOf(assemblyPath, "Microsoft.NETCore.App");

            if (netCoreAppIndex > 0 && netCoreAppIndex < assemblyPath.Length - 2)

                return assemblyPath[netCoreAppIndex + 1];

            return "";

        }

    }

​