C# · 12月 23, 2021

c# – SignalR Typenamehandling

我试图让SignalR使用自定义JsonSerializerSettings作为其有效负载,特别是我试图设置TypeNameHandling = TypeNameHandling.Auto.

问题似乎是,SignalR使用hubConnection.JsonSerializer和GlobalHost.DependencyResolver.Resolve< JsonSerializer>()中的设置作为其内部数据结构,然后导致各种破坏(当我设置TypeNameHandling.All时内部服务器崩溃)作为最粗鲁的例子,但是使用TypeNameHandling.Auto我也会遇到问题,特别是涉及IProgress<>回调时).

是否有任何解决方法或我只是做错了?

示例代码演示:

服务器:

class Program{ static void Main(string[] args) { using (WebApp.Start(“http://localhost:8080”)) { Console.ReadLine(); } }}public class Startup{ public void Configuration(IAppBuilder app) { var hubConfig = new HubConfiguration() { EnableDetailedErrors = true }; GlobalHost.DependencyResolver.Register(typeof(JsonSerializer),ConverterSettings.GetSerializer); app.MapSignalR(hubConfig); }}public interface IFoo{ string Val { get; set; }}public class Foo : IFoo{ public string Val { get; set; }}public class MyHub : Hub{ public IFoo Send() { return new Foo { Val = “Hello World” }; }}

客户:

class Program{ static void Main(string[] args) { Task.Run(async () => await Start()).Wait(); } public static async Task Start() { var hubConnection = new HubConnection(“http://localhost:8080”); hubConnection.JsonSerializer = ConverterSettings.GetSerializer(); var proxy = hubConnection.CreateHubProxy(“MyHub”); await hubConnection.Start(); var result = await proxy.Invoke<IFoo>(“Send”); Console.WriteLine(result.GetType()); }

共享:

public static class ConverterSettings{ public static JsonSerializer GetSerializer() { return JsonSerializer.Create(new JsonSerializerSettings() { TypeNameHandling = TypeNameHandling.All }); }}解决方法 这可以通过利用您的类型和SignalR类型在不同的 assemblies中的事实来实现.想法是创建适用于程序集中所有类型的 JsonConverter.当在对象图中首次遇到来自其中一个程序集的类型(可能作为根对象)时,转换器将临时设置 jsonSerializer.TypeNameHandling = TypeNameHandling.Auto,然后继续执行该类型的标准序列化,在此期间禁用自身以防止无限递归: public class PolymorphicAssemblyRootConverter : JsonConverter{ [ThreadStatic] static bool disabled; // Disables the converter in a thread-safe manner. bool Disabled { get { return disabled; } set { disabled = value; } } public override bool CanWrite { get { return !Disabled; } } public override bool CanRead { get { return !Disabled; } } readonly HashSet<Assembly> assemblies; public PolymorphicAssemblyRootConverter(IEnumerable<Assembly> assemblies) { if (assemblies == null) throw new ArgumentNullException(); this.assemblies = new HashSet<Assembly>(assemblies); } public override bool CanConvert(Type objectType) { return assemblies.Contains(objectType.Assembly); } public override object ReadJson(JsonReader reader,Type objectType,object existingValue,JsonSerializer serializer) { using (new PushValue<bool>(true,() => Disabled,val => Disabled = val)) // Prevent infinite recursion of converters using (new PushValue<TypeNameHandling>(TypeNameHandling.Auto,() => serializer.TypeNameHandling,val => serializer.TypeNameHandling = val)) { return serializer.Deserialize(reader,objectType); } } public override void WriteJson(JsonWriter writer,object value,val => serializer.TypeNameHandling = val)) { // Force the $type to be written unconditionally by passing typeof(object) as the type being serialized. serializer.Serialize(writer,value,typeof(object)); } }}public struct PushValue<T> : IDisposable{ Action<T> setValue; T oldValue; public PushValue(T value,Func<T> getValue,Action<T> setValue) { if (getValue == null || setValue == null) throw new ArgumentNullException(); this.setValue = setValue; this.oldValue = getValue(); setValue(value); } #region IDisposable Members // By using a disposable struct we avoid the overhead of allocating and freeing an instance of a finalizable class. public void Dispose() { if (setValue != null) setValue(oldValue); } #endregion}

然后在启动时,您将此转换器添加到默认的JsonSerializer,传入要应用“$type”的程序集.

更新

如果由于某种原因在启动时传递程序集列表不方便,则可以在objectType.Namespace之前启用转换器.生成在指定命名空间中的所有类型将自动使用TypeNameHandling.Auto进行序列化.

或者,您可以引入一个属性,targets是一个程序集,类或接口,并在与适当的转换器结合使用时启用TypeNameHandling.Auto:

public class EnableJsonTypeNameHandlingConverter : JsonConverter{ [ThreadStatic] static bool disabled; // Disables the converter in a thread-safe manner. bool Disabled { get { return disabled; } set { disabled = value; } } public override bool CanWrite { get { return !Disabled; } } public override bool CanRead { get { return !Disabled; } } public override bool CanConvert(Type objectType) { if (Disabled) return false; if (objectType.Assembly.GetCustomAttributes<EnableJsonTypeNameHandlingAttribute>().Any()) return true; if (objectType.GetCustomAttributes<EnableJsonTypeNameHandlingAttribute>(true).Any()) return true; foreach (var type in objectType.GetInterfaces()) if (type.GetCustomAttributes<EnableJsonTypeNameHandlingAttribute>(true).Any()) return true; return false; } public override object ReadJson(JsonReader reader,typeof(object)); } }}[System.AttributeUsage(System.AttributeTargets.Assembly | System.AttributeTargets.Class | System.AttributeTargets.Interface)]public class EnableJsonTypeNameHandlingAttribute : System.Attribute{ public EnableJsonTypeNameHandlingAttribute() { }}

注意 – 使用各种测试用例但不测试SignalR本身,因为我目前没有安装它.

TypeNameHandling注意

使用TypeNameHandling时,请注意Newtonsoft docs中的此注意事项:

TypeNameHandling should be used with caution when your application deserializes JSON from an external source. Incoming types should be validated with a custom SerializationBinder when deserializing with a value other than None.

有关可能需要的原因的讨论,请参阅TypeNameHandling caution in Newtonsoft Json.