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 Newtonsoft.Json;

using Newtonsoft.Json.Linq;

using Newtonsoft.Json.Converters;

using Newtonsoft.Json.Serialization;    

​

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

​

#nullable enable

​

//https://stackoverflow.com/questions/77271543/jsonconverter-return-empty-value

​

    public class Student

    {

        public string Name { get; set; }

        public string Phone { get; set; }

    }

​

    public class SecretData { }

​

    public class ExtendedStudent : Student

    {

        public SecretData SecretData { get; set; } = new();

    }

​

    public class RedactingContracResolver : DefaultContractResolver

    {

        // Adapted from this answer https://stackoverflow.com/a/33149572

        // By https://stackoverflow.com/users/2862621/tom-bowers

        // To https://stackoverflow.com/questions/33148957/replace-sensitive-data-value-on-json-serialization

        // To pass in a list of types + members to redact.

        readonly List<(Type type, HashSet<string> memberNames)> membersToRedact;

        public RedactingContracResolver(params (Type type, string [] memberNames) [] membersToRedact)

        {

            ArgumentNullException.ThrowIfNull(membersToRedact);

            this.membersToRedact = membersToRedact

                .Select(p => (p.type, p.memberNames.ToHashSet()))

                .ToList();

        }

        protected override JsonProperty CreateProperty(MemberInfo member, MemberSerialization memberSerialization)

        {

            var property = base.CreateProperty(member, memberSerialization);

            foreach (var toRedact in membersToRedact.Where(p => p.type.IsAssignableFrom(member.ReflectedType) == true && p.memberNames.Contains(member.Name)))

            {

                property.ValueProvider = new RedactedStringValueProvider(property.ValueProvider);

                // As it is, the returned contract will throw an error if you attempt to use it to deserialize a redacted property.

                // If you would rather the redacted property be skipped during deserialization, uncomment the following line:

                // property.ShouldDeserialize = static _ => false;

            }

            return property;

        }   

    }

    public class RedactedStringValueProvider : IValueProvider

    {

        IValueProvider? baseProvider;

        public RedactedStringValueProvider(IValueProvider? baseProvider) => this.baseProvider = baseProvider;

        public object? GetValue(object target)

        {

            var baseValue = baseProvider?.GetValue(target);

            if (baseValue is not string s || string.IsNullOrWhiteSpace(s))

                return null;

            return new string('*', s.Length);

        }

​

        public void SetValue(object target, object? value) => throw new NotSupportedException(nameof(SetValue));

    }

​

    class TestClass

    {

        public static void Test()

        {

            TestStudent();

            TestStudentOnly();

            TestExtendedStudent();

        }   

        static void TestStudent()

        {

            Student student = new(){ Name = "name", Phone = "1234" };

            string[] mask = { "Name" };

            RedactingContracResolver resolver = new((typeof(object), mask));

            JsonSerializerSettings settings = new()

            {

                ContractResolver = resolver,

                // Add other settings as required

                ReferenceLoopHandling = ReferenceLoopHandling.Ignore,

            };

            var serializedString = JsonConvert.SerializeObject(student, settings);

            Console.WriteLine(serializedString);            

​

            Assert.That(JToken.DeepEquals(JToken.Parse(serializedString), JToken.Parse("""{"Name":"****","Phone":"1234"}""")));

        }

        static void TestStudentOnly()

        {

            Student student = new(){ Name = "name extended", Phone = "1234" };

            string[] mask = { nameof(Student.Name) };

            RedactingContracResolver resolver = new((typeof(Student), mask));

            JsonSerializerSettings settings = new()

            {

                ContractResolver = resolver,

                // Add other settings as required

                ReferenceLoopHandling = ReferenceLoopHandling.Ignore,

            };

            var serializedString = JsonConvert.SerializeObject(student, settings);

            Console.WriteLine(serializedString);            

​

            Assert.That(JToken.DeepEquals(JToken.Parse(serializedString), JToken.Parse("""{"Name":"*************","Phone":"1234"}""")));

        }

        static void TestExtendedStudent()

        {

            ExtendedStudent student = new(){ Name = "Foo", Phone = "1234" };

            string[] mask = { nameof(Student.Name), nameof(ExtendedStudent.SecretData) };

            RedactingContracResolver resolver = new((typeof(Student), mask));

​

            JsonSerializerSettings settings = new()

            {

                ContractResolver = resolver,

                // Add other settings as required

                ReferenceLoopHandling = ReferenceLoopHandling.Ignore,

            };

            var serializedString = JsonConvert.SerializeObject(student, settings);

            Console.WriteLine(serializedString);        

            Assert.That(JToken.DeepEquals(JToken.Parse(serializedString), JToken.Parse("""{"SecretData":null,"Name":"***","Phone":"1234"}""")));

        }

    }

​

    public class Program

    {

        public static void Main()

        {

            Console.WriteLine("Environment version: {0} ({1}), {2}", System.Runtime.InteropServices.RuntimeInformation.FrameworkDescription , Environment.Version, Environment.OSVersion);

            Console.WriteLine("{0} version: {1}", typeof(JsonSerializer).Namespace, typeof(JsonSerializer).Assembly.FullName);

            Console.WriteLine();

​

            try

            {

                TestClass.Test();

            }

            catch (Exception ex)

            {

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

                Console.WriteLine(ex);

                throw;

            }

        }

    }

​