WCF - 将空元素转换为可为空的本机类型

Question

将SOAP字段元素留空会导致本机类型的强制转换错误。 （遗憾的是，由于客户端限制，不能使用xsi：nil =“true”）

将WCF合约本机类型标记为可为空的＆lt;＆gt;似乎不足以阻止将以下错误返回给客户端。

  

字符串''不是有效的布尔值。                           在System.Xml.XmlConvert.ToBoolean（String s）      at System.Xml.XmlConverter.ToBoolean（String value）                           System.FormatException

有没有人知道指示DataContractSerializer将要反序列化的空元素转换为null的最佳方法？

我的示例WCF服务合同;

[ServiceContract()]
public interface IMyTest
{
    [OperationContract]
    string TestOperation(TestRequest request);
}

[ServiceBehavior()]
public class Settings : IMyTest
{
    public string TestOperation(TestRequest request)
    {
        if (request.TestDetail.TestBool.HasValue)
            return "Bool was specified";
        else
            return "Bool was null";
    }

}

[DataContract()]
public class TestRequest
{
    [DataMember(IsRequired = true)]
    public int ID { get; set; }

    [DataMember(IsRequired = true)]
    public TestDetail TestDetail { get; set; }
}

[DataContract()]
public class TestDetail
{
    [DataMember()]
    public bool? TestBool { get; set; }
}

我们如何让WCF接受以下提交;

<soapenv:Envelope xmlns:soapenv="http://schemas.xmlsoap.org/soap/envelope/" xmlns:ster="mynamespace">
   <soapenv:Header/>
   <soapenv:Body>
      <ster:TestOperation>
         <ster:request>
            <ster:ID>1</ster:ID>
            <ster:TestDetail>
               <ster:TestBool></ster:TestBool>
            </ster:TestDetail>
         </ster:request>
      </ster:TestOperation>
   </soapenv:Body>
</soapenv:Envelope>

客户端只能更改它插入的值<ster:TestBool>{here}</ster:TestBool>，所以true为false，或者没有什么是唯一选项。

Answer 1

好的我相信我已经通过使用操作行为在通过IDispatchMessageFormatter格式化之前修改基础消息来解决这个问题。

以下代码针对基于WCF无文件激活的服务提供了解决方案。

我想让我的IOperationBehavior以Attribute类的形式存在。然后我可以使用我的新属性简单地装饰每个Service Operation，这将启动该操作的IOperationBehavior - 对于最终用户来说非常简单和简单。

关键问题在于您应用行为的地方，这很关键。通过属性应用行为时由WCF调用的操作行为的顺序与在服务主机上应用时的顺序不同。基于属性的顺序如下：

1. System.ServiceModel.Dispatcher.OperationInvokerBehavior
2. 的 MyOperationBehaviorAttribute
3. System.ServiceModel.OperationBehaviorAttribute
4. System.ServiceModel.Description.DataContractSerializerOperationBehavior
5. System.ServiceModel.Description.DataContractSerializerOperationGenerator

由于某种原因，操作行为（仅在通过使用属性应用时）将被称为之前的 DataContractSerializerOperationBehavior。这是一个问题，因为在我的行为中，我想在我调整消息之后将反序列化委托给我的格式化程序中的DataContractSerializerOperationBehavior Formatter（作为内部格式化程序传递给我的行为）（请参阅代码）。当Microsoft提供了一个非常好的解串器时，我不想重新编写反序列化例程。我只是在第一个实例中更正了XML，以便将空格转换为在XML中正确表示的空值，以便DataContractSerializer可以将它们绑定到服务接口中的可空类型。

所以这意味着我们不能像预期那样使用基于属性的行为，因为WCF可能会在这里以相当微妙的方式被打破，因为我看不出这种现象的原因。因此我们仍然可以向操作添加IOperationBehavior，我们只需在服务主机创建阶段手动分配它，因为我们的IOperationBehavior将被插入到正确的＆＃39;序列，也就是说，在创建了DataContractSerializerOperationBehavior之后，才能获得对内部格式化程序的引用。

 // This operation behaviour changes the formatter for a specific set of operations in a web service.

[System.AttributeUsage(System.AttributeTargets.Method, AllowMultiple = false)]
public class NullifyEmptyElementsAttribute : Attribute
{
    // just a marker, does nothing
}

public class NullifyEmptyElementsBahavior : IOperationBehavior
{
    #region IOperationBehavior Members

    public void AddBindingParameters(OperationDescription operationDescription, System.ServiceModel.Channels.BindingParameterCollection bindingParameters) 
    {

    }

    public void ApplyClientBehavior(OperationDescription operationDescription, ClientOperation clientOperation) {  }

    public void ApplyDispatchBehavior(OperationDescription operationDescription, DispatchOperation dispatchOperation)
    {
        // we are the server, we need to accept client message that omit the xsi:nill on empty elements
        dispatchOperation.Formatter = new NullifyEmptyElementsFormatter(dispatchOperation.Formatter);

    }

    public void Validate(OperationDescription operationDescription) { }

    #endregion IOperationBehavior Members
}

/// <summary>
///  This customized formatter intercepts the deserialization process to perform extra processing.
/// </summary>
public class NullifyEmptyElementsFormatter : IDispatchMessageFormatter
{
    // Hold on to the original formatter so we can use it to return values for method calls we don't need.
    private IDispatchMessageFormatter _innerFormatter;

    public NullifyEmptyElementsFormatter(IDispatchMessageFormatter innerFormatter)
    {
        // Save the original formatter
        _innerFormatter = innerFormatter;
    }

    /// <summary>
    /// Check each node and add the xsi{namespace}:nil declaration if the inner text is blank
    /// </summary>
    public static void MakeNillable(XElement element)
    {
        XName _nillableAttributeName = "{http://www.w3.org/2001/XMLSchema-instance}nil"; // don't worry, the namespace is what matters, not the alias, it will work

        if (!element.HasElements) // only end nodes
        {
            var hasNillableAttribute = element.Attribute(_nillableAttributeName) != null;

            if (string.IsNullOrEmpty(element.Value))
            {
                if (!hasNillableAttribute)
                    element.Add(new XAttribute(_nillableAttributeName, true));
            }
            else
            {
                if (hasNillableAttribute)
                    element.Attribute(_nillableAttributeName).Remove();
            }
        }
    }

    public void DeserializeRequest(System.ServiceModel.Channels.Message message, object[] parameters)
    {


var buffer = message.CreateBufferedCopy(int.MaxValue);

        var messageSource = buffer.CreateMessage(); // don't affect the underlying stream

        XDocument doc = null;

        using (var messageReader = messageSource.GetReaderAtBodyContents())
        {
            doc = XDocument.Parse(messageReader.ReadOuterXml()); // few issues with encoding here (strange bytes at start of string), this technique resolves that
        }

        foreach (var element in doc.Descendants())
        {
            MakeNillable(element);
        }

        // create a new message with our corrected XML
        var messageTarget = Message.CreateMessage(messageSource.Version, null, doc.CreateReader());
        messageTarget.Headers.CopyHeadersFrom(messageSource.Headers);

        // now delegate the work to the inner formatter against our modified message, its the parameters were after
         _innerFormatter.DeserializeRequest(messageTarget, parameters);
    }

    public System.ServiceModel.Channels.Message SerializeReply(System.ServiceModel.Channels.MessageVersion messageVersion, object[] parameters, object result)
    {
        // Just delegate this to the inner formatter, we don't want to do anything with this.
        return _innerFormatter.SerializeReply(messageVersion, parameters, result);
    }
}


public class MyServiceHost : ServiceHost
{
    public MyServiceHost(Type serviceType, params Uri[] baseAddresses)
        : base(serviceType, baseAddresses) { }

     protected override void OnOpening()
    {
        base.OnOpening();

        foreach (var endpoint in this.Description.Endpoints)
        {
            foreach (var operation in endpoint.Contract.Operations)
            {
                if ((operation.BeginMethod != null && operation.BeginMethod.GetCustomAttributes(_NullifyEmptyElementsBahaviorAttributeType, false).Length > 0)
                       ||
                       (operation.SyncMethod != null && operation.SyncMethod.GetCustomAttributes(_NullifyEmptyElementsBahaviorAttributeType, false).Length > 0)
                       ||
                       (operation.EndMethod != null && operation.EndMethod.GetCustomAttributes(_NullifyEmptyElementsBahaviorAttributeType, false).Length > 0))
                {
                    operation.Behaviors.Add(new NullifyEmptyElementsBahavior());
                }
            }
        }
    }
}

也许因为我只是修改传入的消息，我可以使用IDispatchMessageInspector来删除对IDispatchMessageFormatter激活顺序的依赖。但这现在适用;）

用法：

1. 添加到您的操作

 [ServiceContract(Namespace = Namespaces.MyNamespace)]
 public interface IMyServiceContrct
 {
       [OperationContract]
       [NullifyEmptyElements]
       void MyDoSomthingMethod(string someIneteger);
 }

1. 加入您的服务

一个。如果你有.svc只是引用MyServiceHost

<%@ ServiceHost 
    Language="C#" 
    Debug="true" 
    Service="MyNameSpace.MyService"
    Factory="MyNameSpace.MyServiceHost"  %>

B中。如果您使用无文件激活服务，请将其添加到您的web.config文件

   <system.serviceModel>
        ... stuff
        <serviceHostingEnvironment multipleSiteBindingsEnabled="true" >

          <!-- WCF File-less service activation - there is no need to use .svc files anymore, WAS in IIS7 creates a host dynamically - less config needed-->
          <serviceActivations >  
            <!-- Full access to Internal services -->
            <add relativeAddress="MyService.svc" 
                 service="MyNameSpace.MyService" 
                 factory="MyNameSpace.MyServiceHost" />

          </serviceActivations>


        </serviceHostingEnvironment>
        ... stuff
    </system.serviceModel>