WCF: FaultContract集但不导致FaultException<T>在REST服务中被捕获

Question

我刚刚从WCF开始，并试图验证支持JSON和XML的WCF rest服务中的故障处理。我的测试服务生成一个错误，但无论我如何尝试，我都无法让我的当事人获取故障的详细信息(而且行为会根据请求格式和http状态代码而有所不同)：

我的测试服务生成的错误如下：

public Data GetResponse()
{
    throw new WebFaultException<ErrorDetails>(
        new ErrorDetails {ErrorMessage = "Server Config Value not set"},
        HttpStatusCode.OK
        );
}

这是通过电线相当合理地发送：

{"ErrorMessage":"Server Config Value not set"}

和：

<ErrorDetails xmlns:i="http://www.w3.org/2001/XMLSchema-instance">
    <ErrorMessage>Server Config Value not set</ErrorMessage>
</ErrorDetails>

我的客户端是用FaultContract定义的

[OperationContract]
[WebInvoke(
    UriTemplate="/response",
    Method="GET",
    RequestFormat = WebMessageFormat.Xml, // or .Json
    ResponseFormat = WebMessageFormat.Xml // or .Json
    )]
[FaultContract(typeof(ErrorDetails), Namespace="")]
Data GetResponse();

以下是(格式/状态代码)的完整错误消息：

XML/冲突：

请求响应CommunicationException:远程服务器返回一个意外响应：(409)冲突。，System.Collections.ListDictionary内部，System.ServiceModel.ProtocolException按一个键退出.

和XML/OK：

请求响应异常:无法用根名称'ErrorDetails‘和根命名空间’(用于操作'GetResponse‘和d契约('IClient'，'’)反序列化XML主体。确保将与XML相对应的类型添加到服务的知情n类型集合中。System.Collections.ListDictionaryInternal按一个键退出.

和JSON/冲突：

请求响应CommunicationException:远程服务器返回一个意外响应：(409)冲突。，System.Collections.ListDictionary内部，System.ServiceModel.ProtocolException按一个键退出.

和JSON/OK：

请求回复:请求完成按一个键退出.

客户端代码按照正确的顺序捕获异常：

try
{
    Console.WriteLine("Requesting response");
    Console.WriteLine("Response: " + client.GetResponse().Message);
    Console.WriteLine("Request complete");
}
// sanity check, just in case...
catch (WebFaultException<ErrorDetails> ex)
{
    Console.WriteLine("WebFaultException<ErrorDetails>: " + ex.Detail.ErrorMessage + ", " + ex.Reason);
}
catch (FaultException<ErrorDetails> ex)
{
    Console.WriteLine("FaultException<ErrorDetails>: " + ex.Detail.ErrorMessage + ", " + ex.Reason);
}
catch (FaultException ex)
{
    Console.WriteLine("FaultException: " + ex.Message + ", " + ex.Reason);
}
catch (CommunicationException ex)
{
    Console.WriteLine("CommunicationException: " + ex.Message + ", " + ex.Data + ", " + ex.GetType().FullName);
}
catch (Exception ex)
{
    Console.WriteLine("Exception: " + ex.Message + ", " + ex.Data);
}

如果要抛出FaultException<ErrorDetails>并访问ErrorDetails，我需要做什么？

注意：要旨应该是完全可编译和可运行的。

Answer 1

在WCF REST客户端( WCF version 4.0)服务中，不可能使用故障/FaultContract作为错误处理机制：

WCF列表中的每个一根线：

在WCF服务中，没有SOAP消息，因此不能将FaultException返回给客户端。实际上，适当的状态代码作为HTTP报头返回给请求者，允许请求者确定调用的结果。

来自一个StackOverflow邮政

故障是SOAP协议的一部分，在REST方案中不可用。

选项被认为是

FaultContract - FaultContractAttribute适用于SOAP信封，但不适用于works服务。如果您将XML发送到已格式化为SOAP信封的XML，则可能会使其正常工作，但您没有使用合理的自定义错误消息。

IErrorHandler --快速阅读文档表明这是针对服务的，并认为这是一个新手错误：“允许实现者控制返回给调用方的错误消息，并可选择地执行自定义错误处理，例如日志记录。”

信息检查器 -- AfterReceiveRequest不执行，因为首先抛出CommunicationException。

解决方案

经过相当多的研究后，我的找到一个博主建议创建一个助手类，从嵌入在异常对象中的响应流中提取信息。以下是他的实施情况：

public static void HandleRestServiceError(Exception exception, Action<TServiceResult> serviceResultHandler, Action<TServiceFault> serviceFaultHandler = null, Action<Exception> exceptionHandler = null)
{
  var serviceResultOrServiceFaultHandled = false;

  if (exception == null) throw new ArgumentNullException("exception");
  if (serviceResultHandler == null) throw new ArgumentNullException("serviceResultHandler");

  // REST uses the HTTP procol status codes to communicate errors that happens on the service side.
  // This means if we have a teller service and you need to supply username and password to login
  // and you do not supply the password, a possible scenario is that you get a 400 - Bad request.
  // However it is still possible that the expected type is returned so it would have been possible 
  // to process the response - instead it will manifest as a ProtocolException on the client side.
  var protocolException = exception as ProtocolException;
  if (protocolException != null)
  {
    var webException = protocolException.InnerException as WebException;
    if (webException != null)
    {
      var responseStream = webException.Response.GetResponseStream();
      if (responseStream != null)
      {
        try
        {
          // Debugging code to be able to see the reponse in clear text
          //SeeResponseAsClearText(responseStream);

          // Try to deserialize the returned XML to the expected result type (TServiceResult)
          var response = (TServiceResult) GetSerializer(typeof(TServiceResult)).ReadObject(responseStream);
          serviceResultHandler(response);
          serviceResultOrServiceFaultHandled = true;
        }
        catch (SerializationException serializationException)
        {
          // This happens if we try to deserialize the responseStream to type TServiceResult
          // when an error occured on the service side. An service side error serialized object 
          // is not deserializable into a TServiceResult

          // Reset responseStream to beginning and deserialize to a TServiceError instead
          responseStream.Seek(0, SeekOrigin.Begin);

          var serviceFault = (TServiceFault) GetSerializer(typeof(TServiceFault)).ReadObject(responseStream);

          if (serviceFaultHandler != null && serviceFault != null)
          {
            serviceFaultHandler(serviceFault);
            serviceResultOrServiceFaultHandled = true;
          }
          else if (serviceFaultHandler == null && serviceFault != null)
          {
            throw new WcfServiceException<TServiceFault>() { ServiceFault = serviceFault };
          }
        }
      }
    }
  }

  // If we have not handled the serviceResult or the serviceFault then we have to pass it on to the exceptionHandler delegate
  if (!serviceResultOrServiceFaultHandled && exceptionHandler != null)
  {
    exceptionHandler(exception);
  }
  else if (!serviceResultOrServiceFaultHandled && exceptionHandler == null)
  {
    // Unable to handle and no exceptionHandler passed in throw exception to be handled at a higher level
    throw exception;
  }
}

Answer 2

我用过这个：

 try
            {
              //wcf service call
            }
            catch (FaultException ex)
            {
               throw new Exception( (ex as WebFaultException<MyContractApplicationFault>).Detail.MyContractErrorMessage );                
            }