Question

对于服务，所有操作都可以抛出一组错误，因此为了集中这些错误，我创建了一个行为FaultAdderBehavior，它将错误契约添加到服务的所有操作中。它似乎工作正常，因为合同被添加到WSDL中，客户端可以通过以下行来捕获错误：

...
catch(FaultException<MyFault> e){ ... }
...

我还制作了一个IErrorHandler，它将非故障异常转换为某种故障。见下文。问题是，错误处理程序中构造的错误无法在客户端上捕获。也就是说，它不能作为泛型 FaultException<MyFault>捕获，而只能作为FaultException捕获。如果我向操作显式添加FaultContract(typeof(MyFault))，客户端可以突然捕获通用错误异常。

所以这可能表明我的FaultAdderBehavior出了问题。或者我的错误处理程序有问题吗？

我注意到，作为fault.Action的参数给出的CreateMessage()为空。这引起了我的关注。

以下是说明问题的示例。方法ShouldThrowFault()导致头痛，而ThrowsDirectly()完全符合要求。

总结一下，我的问题是：为什么客户端在来自错误处理程序时无法捕获泛型FaultException<MyFault>？

[ServiceContract]
public interface IUncatchableFaultService
{
  [OperationContract]
//    [FaultContract(typeof(MyFault))]
  void ShouldThrowFault(string arg1);  

  [OperationContract]
  void ThrowsDirectly();
}

[FaultAdderBehavior(typeof(MyFault), typeof(MyFault2))]
[MyErrorHandlerBehavior]
internal class UncatchableFaultService : IUncatchableFaultService
{
  public void ShouldThrowFault(string arg1)
  {
    throw new Exception();
  }

  public void ThrowsDirectly()
  {
    throw new FaultException<MyFault>(new MyFault());
  }
}

[DataContract]
public class MyFault
{
}

[DataContract]
public class MyFault2
{
}

public class MyErrorHandlerBehaviorAttribute : Attribute, IServiceBehavior
{
  public void Validate(ServiceDescription serviceDescription, ServiceHostBase serviceHostBase)
  {
  }

  public void AddBindingParameters(ServiceDescription serviceDescription, ServiceHostBase serviceHostBase, Collection<ServiceEndpoint> endpoints, BindingParameterCollection bindingParameters)
  {
  }

  public void ApplyDispatchBehavior(ServiceDescription serviceDescription, ServiceHostBase serviceHostBase)
  {
    foreach (ChannelDispatcherBase dispatcherBase in serviceHostBase.ChannelDispatchers)
    {
      ChannelDispatcher channelDispatcher = dispatcherBase as ChannelDispatcher;
      if (channelDispatcher == null) continue;
      channelDispatcher.ErrorHandlers.Add(new MyErrorHandler());
    }
  }

  private class MyErrorHandler : IErrorHandler
  {

    public void ProvideFault(Exception error, MessageVersion version, ref Message message)
    {
      if (error is FaultException) return;  

      var fault = new FaultException<MyFault>(new MyFault(), "I am a fault.");
      MessageFault messageFault = fault.CreateMessageFault();
      message = Message.CreateMessage(version, messageFault, fault.Action);
    }

    public bool HandleError(Exception error)
    {
      return false;
    }
  }
}

public class FaultAdderBehaviorAttribute : Attribute, IContractBehavior
{
  private Type[] faults;

  public FaultAdderBehaviorAttribute(params Type[] faults)
  {
    this.faults = faults;
  }

  public void AddBindingParameters(ContractDescription contractDescription, ServiceEndpoint endpoint, BindingParameterCollection bindingParameters)
  {
  }

  public void ApplyClientBehavior(ContractDescription contractDescription, ServiceEndpoint endpoint, ClientRuntime clientRuntime)
  {
  }

  public void ApplyDispatchBehavior(ContractDescription contractDescription, ServiceEndpoint endpoint, DispatchRuntime dispatchRuntime)
  {
  }

  public void Validate(ContractDescription contractDescription, ServiceEndpoint endpoint)
  {
    foreach (OperationDescription op in contractDescription.Operations)
      foreach (Type fault in this.faults)
        op.Faults.Add(this.ExposeFault(fault));
  }

  private FaultDescription ExposeFault(Type fault)
  {
    string action = fault.Name;
    DescriptionAttribute attr = (DescriptionAttribute)Attribute.GetCustomAttribute(fault, typeof(DescriptionAttribute));

    if (attr != null) action = attr.Description;
    FaultDescription description = new FaultDescription(action);
    description.DetailType = fault;
    description.Name = fault.Name;
    return description;
  }
}

Answer 1

FaultAdderBehaviorAttribute存在问题，您担心fault.Action为空是正确的。

要使FaultException功能正常工作，您必须对每个故障都进行非空操作。

当您在操作本身上声明FaultContract时，您隐式使用WCF自动生成操作字符串（further details）的能力。但是，当您使用FaultAdderBehaviorAttribute时，已生成已声明操作的任何默认操作，并且您无法提供有效操作。

捕获从IErrorHandler抛出的泛型FaultException <t>？</t>

1 个答案: