WCF后续之旅(6): 通过WCF Extension实现Context信息的传递

在上一篇文章中,我们讨论了如何通过CallContextInitializer实现Localization的例子,具体的做法是将client端的culture通过SOAP header传到service端,然后通过自定义的CallContextInitializer设置当前方法执行的线程culture。在client端,当前culture信息是通过OperationContext.Current.OutgoingMessageHeaders手工至于SOAP Header中的。实际上,我们可以通过基于WCF的另一个可扩展对象来实现这段逻辑,这个可扩展对象就是MessageInspector。我们今天来讨论MessageInspector应用的另外一个场景:如何通过MessageInspector来传递Context信息。

一、 Ambient Context

在一个多层结构的应用中,我们需要传递一些上下文的信息在各层之间传递,比如:为了进行Audit,需要传递一些当前当前user profile的一些信息。在一些分布式的环境中也可能遇到context信息从client到server的传递。如何实现这种形式的Context信息的传递呢?我们有两种方案:

  • 将Context作为参数传递:将context作为API的一部分,context的提供者在调用context接收者的API的时候显式地设置这些Context信息,context的接收者则直接通过参数将context取出。这虽然能够解决问题,但决不是一个好的解决方案,因为API应该只和具体的业务逻辑有关,而context 一般是与非业务逻辑服务的,比如Audit、Logging等等。此外,将context纳入API作为其一部分,将降低API的稳定性, 比如,今天只需要当前user所在组织的信息,明天可能需求获取当前客户端的IP地址,你的API可以会经常变动,这显然是不允许的。
  • 创建Ambient Context来保存这些context信息:Ambient Context可以在不同的层次之间、甚至是分布式环境中每个节点之间共享或者传递。比如在ASP.NET 应用中,我们通过SessionSate来存储当前Session的信息;通过HttpContext来存储当前Http request的信息。在非Web应用中,我们通过CallContext将context信息存储在TLS(Thread Local Storage)中,当前线程下执行的所有代码都可以访问并设置这些context数据。

二、Application Context

介于上面所述,我创建一个名为Application Context的Ambient Context容器,Application Context实际上是一个dictionary对象,通过key-value pair进行context元素的设置,通过key获取相对应的context元素。Application Context通过CallContext实现,定义很简单: 

   1: namespace Artech.ContextPropagation
   2: {
   3:     [Serializable]
   4:     public class ApplicationContext : Dictionary<string, object>
   5:     {
   6:         private const string CallContextKey = "__ApplicationContext";
   7:         internal const string ContextHeaderLocalName = "__ApplicationContext";
   8:         internal const string ContextHeaderNamespace = "urn:artech.com";
   9:  
  10:         private void EnsureSerializable(object value)
  11:         {
  12:             if (value == null)
  13:             {
  14:                 throw new ArgumentNullException("value");
  15:             }
  16:             if (!value.GetType().IsSerializable)
  17:             {
  18:                 throw new ArgumentException(string.Format("The argument of the type \"{0}\" is not serializable!", value.GetType().FullName));
  19:             }
  20:         }
  21:  
  22:         public new object this[string key]
  23:         {
  24:             get{return base[key];}
  25:             set
  26:             {this.EnsureSerializable(value);base[key] = value;}
  27:         }
  28:  
  29:         public int Counter
  30:         {
  31:             get{return (int)this["__Count"];}
  32:             set{this["__Count"] = value;}
  33:         }
  34:  
  35:         public static ApplicationContext Current
  36:         {
  37:             get
  38:             {
  39:                 if (CallContext.GetData(CallContextKey) == null)
  40:                 {
  41:                     CallContext.SetData(CallContextKey, new ApplicationContext());
  42:                 }
  43:  
  44:                 return CallContext.GetData(CallContextKey) as ApplicationContext;
  45:             }
  46:             set
  47:             {
  48:                 CallContext.SetData(CallContextKey, value);
  49:             }
  50:         }
  51:     }
  52: }

由于此Context将会置于SOAP Header中从client端向service端进行传递,我们需要为此message header指定一个local name和namespace,那么在service端,才能通过此local name和namespace获得此message header。同时,在lcoal domain, client或者service,context是通过CallContext进行存取的,CallContext也是一个类似于disctionary的结构,也需要为此定义一个Key:

private const string CallContextKey = "__ApplicationContext"; internal const string ContextHeaderLocalName = "__ApplicationContext";
internal const string ContextHeaderNamespace = "urn:artech.com";

由于ApplicaitonContext直接继承自Dictionary<string,object>,我们可以通过Index进行元素的设置和提取,考虑到context的跨域传播,需要进行序列化,所以重写了Indexer,并添加了可序列化的验证。为了后面演示方面,我们定义一个context item:Counter。

Static类型的Current属性通过CallContext的SetData和GetData方法对当前的ApplicationContext进行设置和提取:

   1: public static ApplicationContext Current
   2: {
   3:     get
   4:     {
   5:         if (CallContext.GetData(CallContextKey) == null)
   6:         {
   7:             CallContext.SetData(CallContextKey, new ApplicationContext());
   8:         }
   9:  
  10:         return CallContext.GetData(CallContextKey) as ApplicationContext;
  11:     }
  12:     set
  13:     {
  14:         CallContext.SetData(CallContextKey, value);
  15:     }
  16: } 

三、通过MessageInspector将AppContext置于SOAP header中

通过本系列第3部分对Dispatching system的介绍了,我们知道了在client端和service端,可以通过MessageInspector对request message或者reply message (incoming message或者outgoings message)进行检验。MessageInspector可以对MessageHeader进行自由的添加、修改和删除。在service端的MessageInspector被称为DispatchMessageInspector,相对地,client端被称为ClientMessageInspector。我们现在自定义我们自己的ClientMessageInspector。

   1: namespace Artech.ContextPropagation
   2: {
   3:     public class ContextAttachingMessageInspector : IClientMessageInspector
   4:     {
   5:         public bool IsBidirectional{ get; set; }
   6:  
   7:         public ContextAttachingMessageInspector(): this(false){ }
   8:  
   9:         public ContextAttachingMessageInspector(bool isBidirectional)
  10:         {
  11:             this.IsBidirectional = IsBidirectional;
  12:         }
  13:  
  14:         public void AfterReceiveReply(ref Message reply, object correlationState)
  15:         {
  16:             if (IsBidirectional){return;}
  17:             if (reply.Headers.FindHeader(ApplicationContext.ContextHeaderLocalName, ApplicationContext.ContextHeaderNamespace) < 0){return;}
  18:             ApplicationContext context = reply.Headers.GetHeader<ApplicationContext>(ApplicationContext.ContextHeaderLocalName, ApplicationContext.ContextHeaderNamespace);
  19:             if (context == null){return;}
  20:             ApplicationContext.Current = context;
  21:         }
  22:  
  23:         public object BeforeSendRequest(ref Message request, IClientChannel channel)
  24:         {
  25:             MessageHeader<ApplicationContext> contextHeader = new MessageHeader<ApplicationContext>(ApplicationContext.Current);
  26:             request.Headers.Add(contextHeader.GetUntypedHeader(ApplicationContext.ContextHeaderLocalName, ApplicationContext.ContextHeaderNamespace));
  27:             return null;
  28:         }
  29:  
  30:     }
  31: } 

一般地,我们仅仅需要Context的单向传递,也就是从client端向service端传递,而不需要从service端向client端传递。不过回来应付将来潜在的需求,也许可能需要这样的功能:context从client端传向service端,service对其进行修改后需要将其返回到client端。为此,我们家了一个属性:IsBidirectional表明是否支持双向传递。

在BeforeSendRequest,我们将ApplicationContext.Current封装成一个MessageHeader, 并将此MessageHeader添加到request message 的header集合中,local name和namespace采用的是定义在ApplicationContext中常量:

   1: public object BeforeSendRequest(ref Message request, IClientChannel channel)
   2: {
   3:             MessageHeader<ApplicationContext> contextHeader = new MessageHeader<ApplicationContext>(ApplicationContext.Current);
   4:             request.Headers.Add(contextHeader.GetUntypedHeader(ApplicationContext.ContextHeaderLocalName, ApplicationContext.ContextHeaderNamespace));
   5:             return null;
   6: } 

如何支持context的双向传递,我们在AfterReceiveReply负责从reply message中接收从service传回的context,并将其设置成当前的context:

   1: public void AfterReceiveReply(ref Message reply, object correlationState)
   2: {
   3:     if (IsBidirectional){return;}
   4:     if (reply.Headers.FindHeader(ApplicationContext.ContextHeaderLocalName, ApplicationContext.ContextHeaderNamespace) < 0){return;}
   5:     ApplicationContext context = reply.Headers.GetHeader<ApplicationContext>(ApplicationContext.ContextHeaderLocalName, ApplicationContext.ContextHeaderNamespace);
   6:     if (context == null){return;}
   7:     ApplicationContext.Current = context;
   8: }

四、通过ContextInitializer实现对Context的接收

上面我们介绍了在client端通过ClientMessageInspector将context信息存储到request message header中,照理说我们通过可以通过DispatchMessageInspector实现对context信息的提取,但是考虑到我们设置context是通过CallContext来实现了,我们最好还是使用CallContextInitializer来做比较好一些。CallContextInitializer的定义,我们在上面一章已经作了详细的介绍了,在这里就不用多说什么了。

   1: namespace Artech.ContextPropagation
   2: {
   3:     public class ContextReceivalCallContextInitializer : ICallContextInitializer
   4:     {
   5:         public bool IsBidirectional{ get; set; }
   6:         public ContextReceivalCallContextInitializer(): this(false){ }
   7:         public ContextReceivalCallContextInitializer(bool isBidirectional)
   8:         {
   9:             this.IsBidirectional = isBidirectional;
  10:         }
  11:         public void AfterInvoke(object correlationState)
  12:         {
  13:             if (!this.IsBidirectional)
  14:             {
  15:                 return;
  16:             }
  17:  
  18:             ApplicationContext context = correlationState as ApplicationContext;
  19:             if (context == null)
  20:             {
  21:                 return;
  22:             }
  23:             MessageHeader<ApplicationContext> contextHeader = new MessageHeader<ApplicationContext>(context);
  24:             OperationContext.Current.OutgoingMessageHeaders.Add(contextHeader.GetUntypedHeader(ApplicationContext.ContextHeaderLocalName, ApplicationContext.ContextHeaderNamespace));
  25:             ApplicationContext.Current = null;
  26:         }
  27:  
  28:         public object BeforeInvoke(InstanceContext instanceContext, IClientChannel channel, Message message)
  29:         {
  30:             ApplicationContext context = message.Headers.GetHeader<ApplicationContext>(ApplicationContext.ContextHeaderLocalName, ApplicationContext.ContextHeaderNamespace);
  31:             if (context == null){return null;}
  32:  
  33:             ApplicationContext.Current = context;
  34:             return ApplicationContext.Current;
  35:         }
  36:     }
  37: } 

代码其实很简单,BeforeInvoke中通过local name和namespace提取context对应的message header,并设置当前的ApplicationContext。如果需要双向传递,则通过AfterInvoke方法将context保存到reply message的header中被送回client端。

五、为MessageInspector和CallContextInitializer创建behavior

   1: namespace Artech.ContextPropagation
   2: {
   3:     public class ContextPropagationBehavior : IEndpointBehavior
   4:     {
   5:         public bool IsBidirectional{ get; set; }
   6:         public ContextPropagationBehavior(): this(false){ }
   7:         public ContextPropagationBehavior(bool isBidirectional)
   8:         {
   9:             this.IsBidirectional = isBidirectional;
  10:         }
  11:         public void AddBindingParameters(ServiceEndpoint endpoint, BindingParameterCollection bindingParameters){}
  12:         public void ApplyClientBehavior(ServiceEndpoint endpoint, ClientRuntime clientRuntime)
  13:         {
  14:             clientRuntime.MessageInspectors.Add(new ContextAttachingMessageInspector(this.IsBidirectional));
  15:         }
  16:         public void ApplyDispatchBehavior(ServiceEndpoint endpoint, EndpointDispatcher endpointDispatcher)
  17:         {
  18:             foreach (var operation in endpointDispatcher.DispatchRuntime.Operations)
  19:             {
  20:                 operation.CallContextInitializers.Add(new ContextReceivalCallContextInitializer(this.IsBidirectional));
  21:             }
  22:         }
  23:         public void Validate(ServiceEndpoint endpoint){}
  24:     }
  25: } 

在ApplyClientBehavior中,创建我们的ContextAttachingMessageInspector对象,并将其放置到ClientRuntime 的MessageInspectors集合中;在ApplyDispatchBehavior,将ContextReceivalCallContextInitializer对象放到每个DispatchOperation的CallContextInitializers集合中。

因为我们需要通过配置的方式来使用我们的ContextPropagationBehavior,我们还需要定义对应的BehaviorExtensionElement:

   1: namespace Artech.ContextPropagation
   2: {
   3:     public class ContextPropagationBehaviorElement : BehaviorExtensionElement
   4:     {
   5:         [ConfigurationProperty("isBidirectional", DefaultValue = false)]
   6:         public bool IsBidirectional
   7:         {
   8:             get{return (bool)this["isBidirectional"];}
   9:             set{this["isBidirectional"] = value;}
  10:         }
  11:         public override Type BehaviorType
  12:         {
  13:             get{return typeof(ContextPropagationBehavior);}
  14:         }
  15:         protected override object CreateBehavior()
  16:         {
  17:             return new ContextPropagationBehavior(this.IsBidirectional);
  18:         }
  19:     }
  20: } 

我们IsBidirectional则可以通过配置的方式来指定。

六、Context Propagation的运用

我们现在将上面创建的对象应用到真正的WCF调用环境中。我们依然创建我们经典的4层结构:

wcf_02_06_01

Artech.ContextPropagation.Contract:

   1: namespace Artech.ContextPropagation.Contract
   2: {
   3:     [ServiceContract]
   4:     public interface IContract
   5:     {
   6:         [OperationContract]
   7:         void DoSomething();
   8:     }
   9: } 

Artech.ContextPropagation.Services

   1: namespace Artech.ContextPropagation.Services
   2: {
   3:     public class Service:IContract
   4:     {
   5:         public void DoSomething()
   6:         {
   7:             Console.WriteLine("ApplicationContext.Current.Count = {0}", ApplicationContext.Current.Counter);
   8:             ApplicationContext.Current.Counter++;
   9:         } 
  10:     }
  11: } 

打印出ApplicationContext.Current.Count 的值,并加1。

Hosting的配置:

   1: <configuration>
   2:     <system.serviceModel>
   3:         <behaviors>
   4:             <endpointBehaviors>
   5:                 <behavior name="contextPropagationBehavior">
   6:                     <contextPropagationElement isBidirectional="true" />
   7:                 </behavior>
   8:             </endpointBehaviors>
   9:         </behaviors>
  10:         <client>
  11:             <endpoint address="http://127.0.0.1/service" behaviorConfiguration="contextPropagationBehavior"
  12:                 binding="basicHttpBinding" contract="Artech.ContextPropagation.Contract.IContract"
  13:                 name="service" />
  14:         </client>
  15:         <extensions>
  16:             <behaviorExtensions>
  17:                 <add name="contextPropagationElement" type="Artech.ContextPropagation.ContextPropagationBehaviorElement, Artech.ContextPropagation, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null" />
  18:             </behaviorExtensions>
  19:         </extensions>
  20:     </system.serviceModel>
  21: </configuration>

Artech.ContextPropagation.Client 

   1: namespace Artech.ContextPropagation.Client
   2: {
   3:     class Program
   4:     {
   5:         static void Main(string[] args)
   6:         {
   7:             using (ChannelFactory<IContract> channelFactory = new ChannelFactory<IContract>("service"))
   8:             {
   9:                 IContract proxy = channelFactory.CreateChannel();
  10:                 ApplicationContext.Current.Counter = 100;
  11:                 Console.WriteLine("Brfore service invocation: ApplicationContext.Current.Count = {0}", ApplicationContext.Current.Counter);
  12:                 proxy.DoSomething();
  13:                 Console.WriteLine("After service invocation: ApplicationContext.Current.Count = {0}", ApplicationContext.Current.Counter);
  14:                 Console.Read();
  15:             }
  16:         }
  17:     }
  18: } 

以及config:

   1: <configuration>
   2:     <system.serviceModel>
   3:         <behaviors>
   4:             <endpointBehaviors>
   5:                <behavior name="contextPropagationBehavior">
   6:                     <contextPropagationElement isBidirectional="true" />
   7:                 </behavior>
   8:             </endpointBehaviors>
   9:         </behaviors>
  10:         <client>
  11:             <endpoint address="http://127.0.0.1/service" behaviorConfiguration="contextPropagationBehavior"
  12:                 binding="basicHttpBinding" contract="Artech.ContextPropagation.Contract.IContract"
  13:                 name="service" />
  14:         </client>
  15:         <extensions>
  16:             <behaviorExtensions>
  17:                 <add name="contextPropagationElement" type="Artech.ContextPropagation.ContextPropagationBehaviorElement, Artech.ContextPropagation, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null" />
  18:             </behaviorExtensions>
  19:         </extensions>
  20:     </system.serviceModel>
  21: </configuration> 

我们运行整个程序,你将会看到如下的输出结果:

wcf_02_06_02

可见,Context被成功传播到service端。再看看client端的输出:

wcf_02_06_03

由此可见,在service端设置的context的值也成功返回到client端,真正实现了双向传递。

 

P.S: SOA主张Stateless的service,也就是说每次调用service都应该是相互独立的。context的传递实际上却是让每次访问有了状态,这实际上是违背了SOA的原则。所以,如何对于真正的SOA的设计与架构,个人觉得这种方式是不值得推荐的。但是,如何你仅仅是将WCF作为传统的分布式手段,那么这可能会给你的应用带了很大的便利。 

 

WCF后续之旅:
WCF后续之旅(1): WCF是如何通过Binding进行通信的
WCF后续之旅(2): 如何对Channel Layer进行扩展——创建自定义Channel
WCF后续之旅(3): WCF Service Mode Layer 的中枢—Dispatcher
WCF后续之旅(4):WCF Extension Point 概览
WCF后续之旅(5): 通过WCF Extension实现Localization
WCF后续之旅(6): 通过WCF Extension实现Context信息的传递
WCF后续之旅(7):通过WCF Extension实现和Enterprise Library Unity Container的集成
WCF后续之旅(8):通过WCF Extension 实现与MS Enterprise Library Policy Injection Application Block 的集成
WCF后续之旅(9):通过WCF的双向通信实现Session管理[Part I]
WCF后续之旅(9): 通过WCF双向通信实现Session管理[Part II]
WCF后续之旅(10): 通过WCF Extension实现以对象池的方式创建Service Instance
WCF后续之旅(11): 关于并发、回调的线程关联性(Thread Affinity)
WCF后续之旅(12): 线程关联性(Thread Affinity)对WCF并发访问的影响
WCF后续之旅(13): 创建一个简单的WCF SOAP Message拦截、转发工具[上篇]
WCF后续之旅(13):创建一个简单的SOAP Message拦截、转发工具[下篇]
WCF后续之旅(14):TCP端口共享
WCF后续之旅(15): 逻辑地址和物理地址
WCF后续之旅(16): 消息是如何分发到Endpoint的--消息筛选(Message Filter)
WCF后续之旅(17):通过tcpTracer进行消息的路由

 

posted @ 2008-07-24 09:06  Artech  阅读(...)  评论(... 编辑 收藏