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.
