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真实世界：使用WCF扩展记录服务调用时间
WCF 可扩展性
WCF 提供了许多扩展点供开发人员自定义运行时行为。 WCF 在 Channel Layer 之上还提供了一个高级运行时，主要是针对应用程序开发人员。在 WCF 文档中，它常被称为服务模型层（Service Model Layer）。该高级运行时主要由一个称作 Dispatcher（在 ServiceHost 的 Context 中）的组件和一个称作 Proxy（在客户端的 Context 中）的组件组成。
（图片引自 MSDN Magazine : Extending WCF with Custom Behaviors）
每个扩展点都使用接口定义来扩展。
| Stage | Interceptor Interface | Description |
|---|---|---|
| Parameter Inspection | IParameterInspector | Called before and after invocation to inspect and modify parameter values. |
| Message Formatting | IDispatchMessageFormatter IClientFormatter | Called to perform serialization and deserialization. |
| Message Inspection | IDispatchMessageInspector IClientMessageInspector | Called before send or after receive to inspect and replace message contents. |
| Operation Selection | IDispatchOperationSelector IClientOperationSelector | Called to select the operation to invoke for the given message. |
| Operation Invoker | IOperationInvoker | Called to invoke the operation. |
Behavior 是一种特殊类型的类，它在 ServiceHost/ChannelFactory 初始化过程中扩展运行时行为。WCF 有四种类型的行为：服务行为、终结点行为、契约行为和操作行为。
| Scope | Interface | Potential Impact | |||
|---|---|---|---|---|---|
| Service | Endpoint | Contract | Operation | ||
| Service | IServiceBehavior | ✗ | ✗ | ✗ | ✗ |
| Endpoint | IEndpointBehavior | ✗ | ✗ | ✗ | |
| Contract | IContractBehavior | ✗ | ✗ | ||
| Operation | IOperationBehavior | ✗ | |||
每种行为类型也是通过不同的接口定义来扩展，它们都共用一组相同的方法。一个例外是，IServiceBehavior 没有 ApplyClientBehavior 方法，因为服务行为不能用于客户端。
| Method | Description |
|---|---|
| Validate | Called just before the runtime is built—allows you to perform custom validation on the service description. |
| AddBindingParameters | Called in the first step of building the runtime, before the underlying channel is constructed, allows you to add parameters to influence the underlying channel stack. |
| ApplyClientBehavior | Allows behavior to inject proxy (client) extensions. Note that this method is not present on IServiceBehavior. |
| ApplyDispatchBehavior | Allows behavior to inject dispatcher extensions. |
WCF扩展点
（图片引自 lovecindywang = lovecherry 博客）
案例：使用WCF扩展记录服务调用时间
服务定义：
1 [ServiceContract]
2 public interface ICalculatorService
3 {
4 [OperationContract]
5 int Add(int a, int b);
6 }
服务实现：
1 public class CalculatorService : ICalculatorService
2 {
3 public int Add(int a, int b)
4 {
5 return a + b;
6 }
7 }
配置文件：
1 <system.serviceModel>
2 <services>
3 <service name="WcfExtensibilityTestServiceConsole.CalculatorService">
4 <endpoint address="" binding="netTcpBinding" bindingConfiguration=""
5 contract="WcfExtensibilityTestServiceConsole.ICalculatorService"
6 name="myCalculatorServiceEndpoint"/>
7 <endpoint address="mex" binding="mexTcpBinding" contract="IMetadataExchange"/>
8 <host>
9 <baseAddresses>
10 <add baseAddress="net.tcp://localhost:12345/CalculatorService"/>
11 </baseAddresses>
12 </host>
13 </service>
14 </services>
15 <behaviors>
16 <serviceBehaviors>
17 <behavior>
18 <serviceMetadata/>
19 <serviceDebug includeExceptionDetailInFaults="true"/>
20 </behavior>
21 </serviceBehaviors>
22 </behaviors>
23 </system.serviceModel>
问题描述
现在需要记录每次服务调用执行所需的时间，比如可以将测量的方法执行时间传递给 PerformanceCounter 用于性能计数，或者直接写入到日志中等。
方式一：直接在方法内测量
1 public class CalculatorService : ICalculatorService
2 {
3 public int Add(int a, int b)
4 {
5 Stopwatch watch = Stopwatch.StartNew();
6
7 int result = a + b;
8 Thread.Sleep(TimeSpan.FromMilliseconds(123)); // waste time here
9
10 Debug.WriteLine(string.Format("Method [{0}] execution cost [{1}] milliseconds.",
11 "Add", watch.ElapsedMilliseconds));
12
13 return result;
14 }
15 }
这种方法浅显易懂，但如果服务所提供的功能过多，会导致大量冗余代码。
方式二：形成测量类简化代码
1 public class CalculatorService : ICalculatorService
2 {
3 public int Add(int a, int b)
4 {
5 using (var measure = Measure.StartNew("Add"))
6 {
7 Thread.Sleep(TimeSpan.FromMilliseconds(123)); // waste time here
8 return a + b;
9 }
10 }
11 }
此种方式简化了代码，但仍然需要在各自方法内实现，并需提供方法名作为参数。
使用 Message Inspection 来解决问题
我们定义类 IncomingMessageLoggerInspector 来实现 IDispatchMessageInspector 接口。
1 #region IDispatchMessageInspector Members
2
3 public object AfterReceiveRequest(
4 ref Message request,
5 IClientChannel channel,
6 InstanceContext instanceContext)
7 {
8 var context = OperationContext.Current;
9 if (context == null) return null;
10
11 var operationName = ParseOperationName(context.IncomingMessageHeaders.Action);
12
13 return MarkStartOfOperation(
14 context.EndpointDispatcher.ContractName, operationName,
15 context.SessionId);
16 }
17
18 public void BeforeSendReply(ref Message reply, object correlationState)
19 {
20 var context = OperationContext.Current;
21 if (context == null) return;
22
23 var operationName = ParseOperationName(context.IncomingMessageHeaders.Action);
24
25 MarkEndOfOperation(
26 context.EndpointDispatcher.ContractName, operationName,
27 context.SessionId, correlationState);
28 }
29
30 #endregion
通过服务的当前上下文实例，我们可以获取到服务被调用的契约名称 ContractName，并且可以在 IncomingMessageHeaders 总解析出被调用的 OperationName。
我们在方法 MarkStartOfOperation 中启动 Stopwatch 开始测量执行时间，在方法执行完毕后服务模型会调用 BeforeSendReply 并将 Stopwatch 实例引用传递至 correlationState，此时我们可以在方法 MarkEndOfOperation 中解决时间测量，并打印日志。
1 #region Private Methods
2
3 private static string ParseOperationName(string action)
4 {
5 if (string.IsNullOrEmpty(action)) return action;
6
7 string actionName = action;
8
9 int index = action.LastIndexOf('/');
10 if (index >= 0)
11 {
12 actionName = action.Substring(index + 1);
13 }
14
15 return actionName;
16 }
17
18 private static object MarkStartOfOperation(
19 string inspectorType, string operationName, string sessionId)
20 {
21 var message = string.Format(CultureInfo.InvariantCulture,
22 "Operation [{0}] was called at [{1}] on [{2}] in thread [{3}].",
23 operationName, inspectorType,
24 DateTime.Now.ToString(@"yyyy-MM-dd HH:mm:ss.ffffff", CultureInfo.InvariantCulture),
25 Thread.CurrentThread.ManagedThreadId);
26
27 Debug.WriteLine(message);
28
29 return Stopwatch.StartNew();
30 }
31
32 private static void MarkEndOfOperation(
33 string inspectorType, string operationName,
34 string sessionId, object correlationState)
35 {
36 var watch = (Stopwatch)correlationState;
37 watch.Stop();
38
39 var message = string.Format(CultureInfo.InvariantCulture,
40 "Operation [{0}] returned after [{1}] milliseconds at [{2}] on [{3}] in thread [{4}].",
41 operationName, watch.ElapsedMilliseconds, inspectorType,
42 DateTime.Now.ToString(@"yyyy-MM-dd HH:mm:ss.ffffff", CultureInfo.InvariantCulture),
43 Thread.CurrentThread.ManagedThreadId);
44
45 Debug.WriteLine(message);
46 }
47
48 #endregion
此时，我们需要定义 EndpointBehavior 来讲 Inspector 设置到 DispatchRuntime 中。
1 public class IncomingMessageLoggerEndpointBehavior : IEndpointBehavior
2 {
3 #region IEndpointBehavior Members
4
5 public void AddBindingParameters(
6 ServiceEndpoint endpoint,
7 BindingParameterCollection bindingParameters)
8 {
9 }
10
11 public void ApplyClientBehavior(
12 ServiceEndpoint endpoint,
13 ClientRuntime clientRuntime)
14 {
15 }
16
17 public void ApplyDispatchBehavior(
18 ServiceEndpoint endpoint,
19 EndpointDispatcher endpointDispatcher)
20 {
21 if (endpointDispatcher != null)
22 {
23 endpointDispatcher.DispatchRuntime.MessageInspectors.Add(
24 new IncomingMessageLoggerInspector());
25 }
26 }
27
28 public void Validate(ServiceEndpoint endpoint)
29 {
30 }
31
32 #endregion
33 }
然后，我们在 ServiceHost 实例化后，未Open前，将 IncomingMessageLoggerEndpointBehavior 添加至 Endpoint 的 Behaviors 中。
1 class Program
2 {
3 static void Main(string[] args)
4 {
5 ServiceHost host = new ServiceHost(typeof(CalculatorService));
6
7 foreach (var endpoint in host.Description.Endpoints)
8 {
9 endpoint.Behaviors.Add(new IncomingMessageLoggerEndpointBehavior());
10 }
11
12 host.Opened += new EventHandler(delegate(object obj, EventArgs e)
13 {
14 Debug.WriteLine(typeof(CalculatorService).Name + " 服务已经启动！");
15 });
16
17 host.Open();
18
19 Console.ReadKey();
20 }
21 }
使用 WcfTestClient.exe 调用服务，执行 2 + 3 查看结果，
在 Debug 输出中可以看到，
使用配置文件定制
使用配置文件定制扩展的优点就是可以按需添加和删除扩展，而无需改动代码。比如当发现系统有性能问题时，添加该扩展来查看具体哪个方法执行速度慢。
需要定义类来实现 BehaviorExtensionElement 抽象类。
1 public class IncomingMessageLoggerEndpointBehaviorExtension : BehaviorExtensionElement
2 {
3 public override Type BehaviorType
4 {
5 get { return typeof(IncomingMessageLoggerEndpointBehavior); }
6 }
7
8 protected override object CreateBehavior()
9 {
10 return new IncomingMessageLoggerEndpointBehavior();
11 }
12 }
在配置文件中添加扩展项，
1 <extensions>
2 <behaviorExtensions>
3 <add name="incomingMessageLogger"
4 type="WcfExtensibilityTestServiceConsole.Extensions.IncomingMessageLoggerEndpointBehaviorExtension, WcfExtensibilityTestServiceConsole"/>
5 </behaviorExtensions>
6 </extensions>
在终结点行为中添加该扩展定义，
1 <behaviors>
2 <serviceBehaviors>
3 <behavior>
4 <serviceMetadata/>
5 <serviceDebug includeExceptionDetailInFaults="true"/>
6 </behavior>
7 </serviceBehaviors>
8 <endpointBehaviors>
9 <behavior>
10 <incomingMessageLogger/>
11 </behavior>
12 </endpointBehaviors>
13 </behaviors>
使用 ServiceBehavior 扩展
同理，如果服务实现了多个 Endpoint，则想在所有 Endpoint 上添加该扩展，除了可以逐个添加或者使用 behaviorConfiguration 来配置。
另一个方法是可以借助 IServiceBehavior 的扩展实现。
1 public class IncomingMessageLoggerServiceBehavior : IServiceBehavior
2 {
3 #region IServiceBehavior Members
4
5 public void AddBindingParameters(
6 ServiceDescription serviceDescription,
7 ServiceHostBase serviceHostBase,
8 Collection<ServiceEndpoint> endpoints,
9 BindingParameterCollection bindingParameters)
10 {
11 }
12
13 public void ApplyDispatchBehavior(
14 ServiceDescription serviceDescription,
15 ServiceHostBase serviceHostBase)
16 {
17 if (serviceHostBase != null)
18 {
19 foreach (ChannelDispatcher channelDispatcher in serviceHostBase.ChannelDispatchers)
20 {
21 foreach (EndpointDispatcher endpointDispatcher in channelDispatcher.Endpoints)
22 {
23 endpointDispatcher.DispatchRuntime.MessageInspectors.Add(
24 new IncomingMessageLoggerInspector());
25 }
26 }
27 }
28 }
29
30 public void Validate(
31 ServiceDescription serviceDescription,
32 ServiceHostBase serviceHostBase)
33 {
34 }
35
36 #endregion
37 }
原理相同，仅是遍历通道分配器中所有的终结点，逐一添加 Inspector。
同理，如果需要在配置文件中使用，也需要实现一个 BehaviorExtensionElement 类。
1 public class IncomingMessageLoggerServiceBehaviorExtension : BehaviorExtensionElement
2 {
3 public override Type BehaviorType
4 {
5 get { return typeof(IncomingMessageLoggerServiceBehavior); }
6 }
7
8 protected override object CreateBehavior()
9 {
10 return new IncomingMessageLoggerServiceBehavior();
11 }
12 }
此时的配置文件描述如下：
1 <behaviors>
2 <serviceBehaviors>
3 <behavior>
4 <serviceMetadata/>
5 <serviceDebug includeExceptionDetailInFaults="true"/>
6 <incomingMessageLogger/>
7 </behavior>
8 </serviceBehaviors>
9 </behaviors>
10 <extensions>
11 <behaviorExtensions>
12 <add name="incomingMessageLogger"
13 type="WcfExtensibilityTestServiceConsole.Extensions.IncomingMessageLoggerServiceBehaviorExtension, WcfExtensibilityTestServiceConsole"/>
14 </behaviorExtensions>
15 </extensions>