基于HTTP-GET的元数据发布方式与基于WS-MEX原理类似,但是ServiceMetadataBehavior需要做的更多额外的工作。原因很简单,由于在WS-MEX模式下,我们为寄宿的服务添加了相应的MEX终结点,那么当服务被成功寄宿后,WCF已经为元数据的消息交换建立了如图1所示的分发体系,我们需要做的仅仅是对MEX终结点的DispatchRuntime进行相应的定制而已。
图1 WCF服务端分发体系
但是如果采用HTTP-GET模式,实际上我们需要从ChannelDispatcher开始,重新构建整个分发体系。接下来,我们在《WS-MEX原理》提供实例的基础上,对我们自定义ServiceMetadataBehaviorAttribute进行进一步的完善,使之同时对两种模式的元数据发布提供支持。 (Source Code从这里下载)
首先,我们需要定义一个新的服务契约接口:IHttpGetMetadata,Get操作处理任何形式的消息请求,因为它的输入参数和返回类型均为Message,并且Action和ReplyAction为*。
1: using System.ServiceModel;
2: using System.ServiceModel.Channels;
3: namespace ServiceMetadataBehaviorSimulator
4: {
5: [ServiceContract(Name = "IHttpGetMetadata", Namespace = "http://www.artech.com/")]
6: public interface IHttpGetMetadata
7: {
8: [OperationContract(Action = "*", ReplyAction = "*")]
9: Message Get(Message msg);
10: }
11: }
然后我们让前面定义的MetadataProvisionService实现IHttpGetMetadata接口,在这里无需再写任何多余的代码,因为MetadataProvisionService已经具有了一个Get方法。
1: public class MetadataProvisionService : IMetadataProvisionService, IHttpGetMetadata
2: {
3: //省略成员
4: }
接下来的工作就是构建一个全新的ChannelDispatcher,以及关联EndpointDispatcher,最后对EndpointDispatcher的DispatchRuntime进行定制。为此,我单独写了一个方法:CreateHttpGetChannelDispatcher。
1: [AttributeUsage(AttributeTargets.Class)]
2: public class ServiceMetadataBehaviorAttribute : Attribute, IServiceBehavior
3: {
4: //其他成员
5: private const string SingletonInstanceContextProviderType = "System.ServiceModel.Dispatcher.SingletonInstanceContextProvider,System.ServiceModel, Version=3.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089";
6: private const string SyncMethodInvokerType = "System.ServiceModel.Dispatcher.SyncMethodInvoker,System.ServiceModel, Version=3.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089";
7: private const string MessageOperationFormatterType = "System.ServiceModel.Dispatcher.MessageOperationFormatter, System.ServiceModel, Version=3.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089";
8:
9: private static void CreateHttpGetChannelDispatcher(ServiceHostBase host, Uri listenUri, MetadataSet metadata)
10: {
11: //创建Binding
12: TextMessageEncodingBindingElement messageEncodingElement = new TextMessageEncodingBindingElement() { MessageVersion = MessageVersion.None };
13: HttpTransportBindingElement transportElement = new HttpTransportBindingElement();
14: Utility.SetPropertyValue(transportElement, "Method", "GET");
15: Binding binding = new CustomBinding(messageEncodingElement, transportElement);
16:
17: //创建ChannelListener
18: IChannelListener listener = binding.BuildChannelListener<IReplyChannel>(listenUri, string.Empty, ListenUriMode.Explicit, new BindingParameterCollection());
19: ChannelDispatcher dispatcher = new ChannelDispatcher(listener, "ServiceMetadataBehaviorHttpGetBinding", binding) { MessageVersion = binding.MessageVersion };
20:
21: //创建EndpointDispatcher
22: EndpointDispatcher endpoint = new EndpointDispatcher(new EndpointAddress(listenUri), "IHttpGetMetadata", "http://www.artech.com/");
23:
24: //创建DispatchOperation,并设置DispatchMessageFormatter和OperationInvoker
25: DispatchOperation operation = new DispatchOperation(endpoint.DispatchRuntime, "Get", "*", "*");
26: operation.Formatter = Utility.CreateInstance<IDispatchMessageFormatter>(MessageOperationFormatterType, Type.EmptyTypes, new object[0]);
27: MethodInfo method = typeof(IHttpGetMetadata).GetMethod("Get");
28: operation.Invoker = Utility.CreateInstance<IOperationInvoker>(SyncMethodInvokerType, new Type[] { typeof(MethodInfo) }, new object[] { method });
29: endpoint.DispatchRuntime.Operations.Add(operation);
30:
31: //设置SingletonInstanceContext和InstanceContextProvider
32: MetadataProvisionService serviceInstance = new MetadataProvisionService(metadata);
33: endpoint.DispatchRuntime.SingletonInstanceContext = new InstanceContext(host, serviceInstance);
34: endpoint.DispatchRuntime.InstanceContextProvider = Utility.CreateInstance<IInstanceContextProvider>(SingletonInstanceContextProviderType, new Type[] { typeof(DispatchRuntime) }, new object[] { endpoint.DispatchRuntime });
35: dispatcher.Endpoints.Add(endpoint);
36:
37: //设置ContractFilter和AddressFilter
38: endpoint.ContractFilter = new MatchAllMessageFilter();
39: endpoint.AddressFilter = new MatchAllMessageFilter();
40:
41: host.ChannelDispatchers.Add(dispatcher);
42: }
43: }
大体上介绍一下创建ChannelDispatcher的逻辑。首先创建绑定对象,该绑定由两个绑定元素构成:TextMessageEncodingBindingElement和HttpTransportBindingElement,这些因为元数据请求消息就是单纯的HTTP-GET请求消息,并不是一个SOAP,所以需要将HttpTransportBindingElement的消息版本设为None,并将Method属性(这是一个internal属性)设为GET。
然后利用创建的绑定对象创建ChannelListener,并基于该ChannelListener创建ChannelDispatcher对象。当ChannelDispatcher成功创建,开始创建EndpointDispatcher对象,并定制该EndpointDispatcher的DispatchRuntime。这其中包括创建DispatchOperation对象以及相关的消息格式化器以及操作执行器。然后是我们熟悉的对InstanceContextProvider和SingletonInstanceContext的设定。最后需要设置EndpointDispatcher的两个消息筛选器:契约筛选器和地址筛选器,在这将它们设置成MatchAllMessageFilter类型,使之能够匹配所有的请求消息。关于WCF的消息筛选机制,在《WCF技术剖析(卷1)》第2章有详细介绍。
待DispatchRuntime被成功定制,将创建的EndpointDispatcher添加到ChannelDispatcher的EndpointDispatcher列表,最终再将ChannelDispatcher添加到ServiceHost的ChannelDispatcher列表中。
然后,我们在ServiceMetadataBehaviorAttribute添加两个属性:HttpGetEnabled和HttpGetUrl,前者表示是否采用基于HTTP-GET的元数据发布模式,后者指定元数据发布的地址。并将上面定义的CreateHttpGetChannelDispatcher添加到ApplyDispatchBehavior方法中。
1: [AttributeUsage(AttributeTargets.Class)]
2: public class ServiceMetadataBehaviorAttribute : Attribute, IServiceBehavior
3: {
4: //其他成员
5: public bool HttpGetEnabled
6: { get; set; }
7: public string HttpGetUrl
8: { get; set; }
9: public void ApplyDispatchBehavior(ServiceDescription serviceDescription, ServiceHostBase serviceHostBase)
10: {
11: MetadataSet metadata = GetExportedMetadata(serviceDescription);
12: CustomizeMexEndpoints(serviceDescription, serviceHostBase, metadata);
13: if (this.HttpGetEnabled)
14: {
15: CreateHttpGetChannelDispatcher(serviceHostBase, new Uri(this.HttpGetUrl), metadata);
16: }
17: }
18: }
那么现在我们就可以通过下面的方式将ServiceMetadataBehaviorAttribute应用到我们的CalculatorService,并通过HttpGetUrl属性指定原数据发布的目标地址:
1: [ServiceMetadataBehavior(HttpGetEnabled = true, HttpGetUrl = "http://127.0.0.1:9999/calculatorservice/mex")]
2: public class CalculatorService : ICalculator, IMetadataProvisionService
3: {
4: //省略成员
5: }
如果CalculatorService被成功寄宿,直接通过浏览器访问元数据发布的地址(http://127.0.0.1:9999/calculatorservice/mex),你可以看到与图2一样的结果。
图2 通过IE获取发布的元数据
出处:http://artech.cnblogs.com
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