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/67008507/convert-string-property-value-to-base64-on-serialization-for-asp-net-core-3-0

​

    public class Base64EncodedStringConverter : JsonConverter<string>

    {

        public override string Read(ref Utf8JsonReader reader, Type typeToConvert, JsonSerializerOptions options) =>

            Encoding.UTF8.GetString(reader.GetBytesFromBase64());

​

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

            writer.WriteBase64StringValue(Encoding.UTF8.GetBytes(value));

    }

    public class MyFoo 

    {

        public string Value1 { get; set; }

​

        [System.Text.Json.Serialization.JsonConverter(typeof(Base64EncodedStringConverter))] // Fully qualified attribute name used for clarity

        public string Value2 { get; set; }

    }

​

    class TestClass

    {

        public static void Test()

        {

            Test("hello");

            Test(null);

            Test(" ");

            Test("\U00029E3D\u0302");

            Test(new string('a', 2000));

        }

        public static void Test(string value)

        {

            var model = new MyFoo

            {

                Value1 = value,

                Value2 = value,

            };

            var json = JsonSerializer.Serialize(model);

            Console.WriteLine(json);

            var model2 = JsonSerializer.Deserialize<MyFoo>(json);

            Assert.AreEqual(model.Value1, model2.Value1);

            Assert.AreEqual(model.Value2, model2.Value2);

            var json2 = JsonSerializer.Serialize(model2);

            Assert.AreEqual(json, json2);

        }

    }

​

    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 "";

        }

    }

​