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.Numerics;

​

using System.Text.Json;

using System.Text.Json.Serialization;

​

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

​

//https://stackoverflow.com/questions/64788895/serialising-biginteger-using-system-text-json

​

    public class BigIntegerConverter : JsonConverter<BigInteger>

    {

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

        {

            if (reader.TokenType != JsonTokenType.Number)

                throw new JsonException(string.Format("Found token {0} but expected token {1}", reader.TokenType, JsonTokenType.Number ));

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

            return BigInteger.Parse(doc.RootElement.GetRawText(), NumberFormatInfo.InvariantInfo);

        }

​

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

        {

            var s = value.ToString(NumberFormatInfo.InvariantInfo);

            using var doc = JsonDocument.Parse(s);

            doc.WriteTo(writer);

        }

    }

​

    class TestClass

    {

        public static void Test()

        {

            var options = new JsonSerializerOptions();

            options.Converters.Add(new BigIntegerConverter());

            var s = JsonSerializer.Serialize(new {foo = new BigInteger(ulong.MaxValue) + 1}, options);          

            Assert.AreEqual(@"{""foo"":18446744073709551616}", s);

            Console.WriteLine(s);

            var i = new BigInteger(ulong.MaxValue) + 1;

            Test(i);

            Test(i * i * i);

            Test(i * i * i * i * i * i);

            Test(-i * i * i * i * i * i);

        }

        public static void Test(BigInteger i)

        {           

            var options = new JsonSerializerOptions

            {

                Converters = { new BigIntegerConverter() },

            };

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

            Console.WriteLine(json);

            var i2 = JsonSerializer.Deserialize<BigInteger>(json, options);

            Assert.IsTrue(i == i2);

        }   

    }

​

    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 null;

        }

    }

​