using System;

using System.Collections;

using System.Collections.Generic;

using System.Linq;

using System.Text;

using System.IO;

​

using System.Text.Json;

using System.Text.Json.Serialization;

using System.Text.Json.Serialization.Metadata;

​

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

​

//https://stackoverflow.com/questions/74995241/asp-net-core-system-text-json-how-to-reject-unknown-properties-in-payload

​

#nullable enable

​

    public static class JsonExtensions

    {

        public static DefaultJsonTypeInfoResolver AddMissingMemberHandlingError(this DefaultJsonTypeInfoResolver resolver)

        {

            resolver.Modifiers.Add(typeInfo => 

                                   {

                                       if (typeInfo.Kind != JsonTypeInfoKind.Object)

                                           return;

                                       if (typeInfo.Properties.Any(p => p.IsExtensionData))

                                           return;

                                       var property = typeInfo.CreateJsonPropertyInfo(typeof(Dictionary<string, JsonElement>), "<>ExtensionData");

                                       property.IsExtensionData = true;

                                       property.Get = static (obj) => null;

                                       property.Set = static (obj, val) => 

                                       {

                                           var dictionary = (Dictionary<string, JsonElement>?)val;

                                           if (dictionary != null)

                                               throw new JsonException();

                                       };

                                       typeInfo.Properties.Add(property);

                                   });

            return resolver;

        }

    }

​

    public class Model

    {

        public string? Value { get; set; }

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

    }

​

    public class Inner

    {

        [JsonExtensionData]

        public Dictionary<string, object>? ExtensionData { get; set; }

    }

​

    class TestClass

    {

        public static void Test()

        {

            foreach (var json in GetBadJson())

            {

                TestBadJson(json);

            }

            foreach (var json in GetGoodJson())

            {

                TestGoodJson(json);

            }

        }   

​

        static void TestGoodJson(string json)

        {

            var options = new JsonSerializerOptions

            {

                TypeInfoResolver = new DefaultJsonTypeInfoResolver()

                    .AddMissingMemberHandlingError(),

            };

            Assert.DoesNotThrow(() => JsonSerializer.Deserialize<Model>(json, options));

        }

        static void TestBadJson(string json)

        {

            var options = new JsonSerializerOptions

            {

                TypeInfoResolver = new DefaultJsonTypeInfoResolver()

                    .AddMissingMemberHandlingError(),

            };

            var ex = Assert.Throws(Is.InstanceOf(typeof(JsonException)), () => JsonSerializer.Deserialize<Model>(json, options));

            Console.WriteLine("Caught expected exception:\n{0}", ex);

        }

        static IEnumerable<string> GetBadJson() => new []

        {

            """

            {

                "Value" : "some Value",

                "Inner" :

                {

                    "foo" : "bar"

                },

                "Unknown" : 111

            }

            """

        };

        static IEnumerable<string> GetGoodJson() => new []

        {

            """

            {

                "Value" : "some Value",

                "Inner" :

                {

                    "foo" : "bar"

                }

            }

            """,

            """

            {

                "Value" : "some Value",

                "Inner" :

                {

                }

            }

            """

        };

    }

​

    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("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;

            }

        }

    }

​