C#WCF插件的设计和实现

Question

我想得到一些建议.我正在开发一个系统,它将在运行时加载插件并要求它们通过WCF端点可用.

我将有一个仅用于配置的MVC 3 Web应用程序,以及一个将加载不同插件的类库(核心).

我会很感激如何解决这个问题.我想加载插件,然后能够创建一个在IIS 7中注册的WCF端点,以访问该插件.

提前致谢 :)

Answer 1

使用Darko动态IIS托管的WCF服务工作的衍生产品,您可以实现您想要的功能.让我们从我们可能想要托管的示例服务开始,我们称之为IMessageBroker,它的合同很简单:

[ServiceContract]
public interface IMessageBroker
{
  [OperationContract]
  string Send(string message);
}

我们将此合同用于服务和MEF出口/进口.我们还将定义一些额外的元数据:

public interface IMessageBrokerMetadata
{
  public string Name { get; }
  public string Channel { get; }
}

由于这是一个简单的项目,我会欺骗并使用一个简单的静态类来管理CompositionContainer用于组成部件的MEF :

public static class MEF
{
    private static CompositionContainer container;
    private static bool initialised;

    public static void Initialise()
    {
        var catalog = new DirectoryCatalog("bin");
        container = new CompositionContainer(catalog);
        initialised = true;
    }

    public static CompositionContainer Container
    {
        get
        {
            if (!initialised) Initialise();
            return container;
        }
    }
}

为了能够动态生成WCF服务,我们需要创建一个ServiceHostFactory,它可以访问我们的组合容器来访问我们的类型,所以你可以这样做:

public class MEFServiceHostFactory : ServiceHostFactory
{
    public override ServiceHostBase CreateServiceHost(string constructorString, System.Uri[] baseAddresses)
    {
        var serviceType = MEF.Container
            .GetExports<IMessageBroker, IMessageBrokerMetadata>()
            .Where(l => l.Metadata.Name == constructorString)
            .Select(l => l.Value.GetType())
            .Single();

        var host = new ServiceHost(serviceType, baseAddresses);

        foreach (var contract in serviceType.GetInterfaces())
        {
            var attr = contract.GetCustomAttributes(typeof(ServiceContractAttribute), true).FirstOrDefault();
            if (attr != null)
                host.AddServiceEndpoint(contract, new BasicHttpBinding(), "");
        }

        var metadata = host.Description.Behaviors
            .OfType<ServiceMetadataBehavior>()
            .FirstOrDefault();

        if (metadata == null)
        {
            metadata = new ServiceMetadataBehavior();
            metadata.HttpGetEnabled = true;
            host.Description.Behaviors.Add(metadata);
        }
        else
        {
            metadata.HttpGetEnabled = true;
        }

        return host;
    }
}

本质上,该constructorString参数用于传递我们想要的特定服务的元数据名称.接下来,我们需要处理这些服务的定位.我们现在需要的是一个VirtualPathProvider我们可以通过一个动态创建实例的方法VirtualFile.提供者看起来像:

public class ServiceVirtualPathProvider : VirtualPathProvider
{
    private bool IsServiceCall(string virtualPath)
    {
        virtualPath = VirtualPathUtility.ToAppRelative(virtualPath);
        return (virtualPath.ToLower().StartsWith("~/services/"));
    }

    public override VirtualFile GetFile(string virtualPath)
    {
        return IsServiceCall(virtualPath)
                   ? new ServiceFile(virtualPath)
                   : Previous.GetFile(virtualPath);
    }

    public override bool FileExists(string virtualPath)
    {
        if (IsServiceCall(virtualPath))
            return true;

        return Previous.FileExists(virtualPath);
    }

    public override System.Web.Caching.CacheDependency GetCacheDependency(string virtualPath, System.Collections.IEnumerable virtualPathDependencies, DateTime utcStart)
    {
        return IsServiceCall(virtualPath)
                   ? null
                   : Previous.GetCacheDependency(virtualPath, virtualPathDependencies, utcStart);
    }
}

我们正在做的是将任何调用映射/Services/到我们的MEF派生端点.该服务需要一个虚拟文件,这就是我们将它们联系在一起的地方:

public class ServiceFile : VirtualFile
{
    public ServiceFile(string virtualPath) : base(virtualPath)
    {

    }

    public string GetName(string virtualPath)
    {
        string filename = virtualPath.Substring(virtualPath.LastIndexOf("/") + 1);
        filename = filename.Substring(0, filename.LastIndexOf("."));

        return filename;
    }

    public override Stream Open()
    {
        var stream = new MemoryStream();
        var writer = new StreamWriter(stream);

        writer.Write("<%@ ServiceHost Language=\"C#\" Debug=\"true\" Service=\"" + GetName(VirtualPath) +
                     "\" Factory=\"Core.MEFServiceHostFactory, Core\" %>");
        writer.Flush();

        stream.Position = 0;
        return stream;
    }
}

虚拟文件将从虚拟路径中分解元数据名称,其中/Services/SampleMessageBroker.svc- > SampleMessageBroker.然后我们生成一些代表.svc文件标记的标记Service="SampleMessageBroker".此参数将传递到MEFServiceHostFactory我们可以选择端点的位置.因此,给出一个样本端点:

[Export(typeof(IMessageBroker)),
 ExportMetadata("Name", "SampleMessageBroker"),
 ExportMetadata("Channel", "Greetings")]
public class SampleMessageBroker : IMessagerBroker
{
  public string Send(string message)
  {
    return "Hello! " + message;
  }
}

我们现在可以动态访问它/Services/SampleMessageBroker.svc.您可能想要做的是提供静态服务,该服务允许您集成哪些端点可用,并将其反馈给您的消费客户端.

哦,不要忘记连接虚拟路径提供程序:

HostingEnvironment.RegisterVirtualPathProvider(new ServiceVirtualPathProvider());