c# - SignalR类型名处理

我试图让signaler使用其有效负载的自定义jsonserializersettings，特别是我试图设置TypeNameHandling = TypeNameHandling.Auto。
问题似乎是，signaler对其内部数据结构使用了hubConnection.JsonSerializer和GlobalHost.DependencyResolver.Resolve<JsonSerializer>()中的设置，这也会导致各种破坏（当我将TypeNameHandling.All设置为最严重的示例时，内部服务器崩溃，但是使用TypeNameHandling.Auto时，我也会遇到问题，特别是当涉及到IProgress<>回调时）。
有什么解决办法吗？还是我做错了？
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
        });
    }
}

最佳答案

这可以通过利用您的类型和信号器类型不同的事实来实现。其思想是创建一个assemblies应用于程序集中的所有类型。当在对象图中首次遇到来自某个程序集的类型（可能作为根对象）时，转换器将临时设置JsonConverter，然后继续对该类型进行标准序列化，并在持续时间内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, 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))
        {
            // 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，将此转换器添加到默认的jsonSerializer.TypeNameHandling = TypeNameHandling.Auto，传入要应用JsonSerializer的程序集。
更新
如果由于任何原因在启动时不方便传递程序集列表，可以通过"$type"启用转换器。生活在指定命名空间中的所有类型都将自动通过objectType.Namespace进行序列化。
或者，您可以引入一个TypeNameHandling.Auto，它Attribute一个程序集、类或接口，并在与适当的转换器结合时启用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, 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, 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))
        {
            // Force the $type to be written unconditionally by passing typeof(object) as the type being serialized.
            serializer.Serialize(writer, value, typeof(object));
        }
    }
}

[System.AttributeUsage(System.AttributeTargets.Assembly | System.AttributeTargets.Class | System.AttributeTargets.Interface)]
public class EnableJsonTypeNameHandlingAttribute : System.Attribute
{
    public EnableJsonTypeNameHandlingAttribute()
    {
    }
}

注-测试了各种测试用例，但没有信号器本身，因为我目前没有安装它。
TypeNameHandling注意
使用TypeNameHandling时，请注意targets中的注意事项：
当应用程序从外部源反序列化json时，应谨慎使用typenameholling。使用非“无”值反序列化时，应使用自定义序列化绑定器验证传入类型。
有关为什么需要这样做的讨论，请参见Newtonsoft docs。