wcf - 如何将位置 header 设置为 WCF 4.0 REST 中另一个服务的 UriTemplate 没有魔术字符串？

Question

考虑以下两个 WCF 4.0 REST 服务:

[ServiceContract]
[AspNetCompatibilityRequirements(RequirementsMode = AspNetCompatibilityRequirementsMode.Allowed)]
[ServiceBehavior(InstanceContextMode = InstanceContextMode.PerCall)]
public class WorkspaceService
{
    [WebInvoke(UriTemplate = "{id}/documents/{name}", Method = "POST")]
    public Document CreateWorkspaceDocument(Stream stream, string id, string name) 
    {
        /* CreateDocument is omitted as it isn't relevant to the question */
        Document response = CreateDocument(id, name, stream);

        /* set the location header */
        SetLocationHeader(response.Id);
    }

    private void SetLocationHeader(string id)
    {   
        Uri uri = new Uri("https://example.com/documents/" + id);
        WebOperationContext.Current.OutgoingResponse.SetStatusAsCreated(uri);
    }

    /* methods to delete, update etc */
}

[ServiceContract]
[AspNetCompatibilityRequirements(RequirementsMode = AspNetCompatibilityRequirementsMode.Allowed)]
[ServiceBehavior(InstanceContextMode = InstanceContextMode.PerCall)]
public class DocumentService
{

    [WebGet(UriTemplate = "{id}")]
    public Document GetDocument(string id)
    {
    }

    /* methods to delete, update etc */
}

本质上，当有人在工作区中创建文档时，Location 标题设置为文档的位置，这本质上与调用 DocumentService.GetDocument 相同。手术。

我的 global.asax 如下所示:

public class Global : HttpApplication
{
    private void Application_Start(object sender, EventArgs e)
    {
        RegisterRoutes();
    }

    private void RegisterRoutes()
    {
        var webServiceHostFactory = new WebServiceHostFactory();
        RouteTable.Routes.Add(new ServiceRoute("workspaces", webServiceHostFactory, typeof (WorkspaceService)));
        RouteTable.Routes.Add(new ServiceRoute("documents", webServiceHostFactory, typeof (DocumentService)));
        /* other services */
    }
}

WorkspaceService.SetLocationHeader的实现因为它对路由的设置方式做了一些假设。如果我要改变DocumentService的路线那么由此产生的 Uri 将是不正确的。如果我改变了 DocumentService.GetDocument 的 UriTemplate ，那么由此产生的 Uri 也将是不正确的。

如果 WorkspaceService 和 DocumentService 合并为一个服务，我可以写 SetLocationHeader如下:

var itemTemplate = WebOperationContext.Current.GetUriTemplate("GetDocument");
var uri = itemTemplate.BindByPosition(WebOperationContext.Current.IncomingRequest.UriTemplateMatch.BaseUri, id);
WebOperationContext.Current.OutgoingResponse.SetStatusAsCreated(uri);

怎么写WorkspaceService.SetLocationHeader这样它将使用 Global.asax 和 UriTemplates 中定义的路由表来返回 DocumentService 的 GetDocument 操作的 Uri？

我使用的是普通的旧 WCF 4.0(不是 WCF Web API)。

Answer 1

偶然发现了an article由 José F. Romaniello 编写，它展示了如何为 WCF Web API 执行此操作并对其进行了调整。源代码在答案的末尾。

假设我有四个服务，路由注册更改为使用 ServiceRoute 的子类，我们稍后在扫描路由表时使用它来“评估”。

using System;
using System.Web;
using System.Web.Routing;

public class Global : HttpApplication
{
    private void Application_Start(object sender, EventArgs e)
    {
        RegisterRoutes();
    }

    private void RegisterRoutes()
    {
        RouteTable.Routes.Add(new ServiceRoute<Service1>("s1"));
        RouteTable.Routes.Add(new ServiceRoute<Service2>("s2"));
        RouteTable.Routes.Add(new ServiceRoute<Service3>("s3"));
        RouteTable.Routes.Add(new ServiceRoute<Service4>("s4"));
    }
}

WorkspaceService.SetLocationHeader现在看起来如下:

private void SetLocationHeader(string id)
{   
    ResourceLinker resourceLinker = new ResourceLinker();

    Uri uri = resourceLinker.GetUri<WorkspaceService>(s => s.Get(id));
    WebOperationContext.Current.OutgoingResponse.SetStatusAsCreated(uri);
}

相同的代码片段可用于从其他服务设置工作区的 uri，例如 DocumentService.Get

[WebGet("{id}")]
public Document Get(string id)
{
    // can be static
    ResourceLinker resourceLinker = new ResourceLinker();

    DocumentEntity entity = _repository.FindById(id);
    Document document = new Document();
    document.Name = entity.Name; 
    // map other properties
    document.Workspace.Name = entity.Workspace.Name;
    document.Workspace.Uri = resourceLinker.GetUri<WorkspaceService>(s => s.Get("0"));
    // map other properties
    return document;
}

使用这种方法，没有魔法字符串，更改方法名称、服务名称、路由表前缀不太可能会破坏系统。

这是改编自 article 的实现:

using System;
using System.Linq;
using System.Linq.Expressions;
using System.Reflection;
using System.ServiceModel.Activation;
using System.ServiceModel.Web;
using System.Web.Routing;

public interface IServiceRoute
{
    Type ServiceType
    {
        get;
    }

    string RoutePrefix
    {
        get;
        set;
    }
}

public class ServiceRoute<T> : ServiceRoute, IServiceRoute
{
    public ServiceRoute(string routePrefix) : this(routePrefix, new WebServiceHostFactory())
    {
    }

    public ServiceRoute(string routePrefix, ServiceHostFactoryBase serviceHostFactory)
        : base(routePrefix, serviceHostFactory, typeof (T))
    {
        RoutePrefix = routePrefix;
        ServiceType = typeof (T);
    }

    #region IServiceRoute Members

    public string RoutePrefix
    {
        get;
        set;
    }

    public Type ServiceType
    {
        get;
        private set;
    }

    #endregion
}

public static class RouteTableExtensions
{
    public static void AddService<T>(this RouteCollection routeCollection, string routePrefix)
    {
        routeCollection.Add(new ServiceRoute<T>(routePrefix));
    }

    public static string GetRoutePrefixForType<T>(this RouteCollection routeCollection)
    {
        var routeServiceType = routeCollection
            .OfType<IServiceRoute>()
            .FirstOrDefault(r => r.ServiceType == typeof (T));
        if (routeServiceType != null)
        {
            return routeServiceType.RoutePrefix;
        }
        return null;
    }
}

public interface IResourceLinker
{
    Uri GetUri<T>(Expression<Action<T>> restMethod);
}

public class ResourceLinker : IResourceLinker
{
    private readonly Uri _baseUri;

    public ResourceLinker()
        : this("http://localhost:53865")
    {
    }

    public ResourceLinker(string baseUri)
    {
        _baseUri = new Uri(baseUri, UriKind.Absolute);
    }

    #region IResourceLinker Members

    public Uri GetUri<T>(Expression<Action<T>> restMethod)
    {
        var methodCallExpression = (MethodCallExpression) restMethod.Body;
        var uriTemplateForMethod = GetUriTemplateForMethod(methodCallExpression.Method);

        var args = methodCallExpression.Method
            .GetParameters()
            .Where(p => uriTemplateForMethod.Contains("{" + p.Name + "}"))
            .ToDictionary(p => p.Name, p => ValuateExpression(methodCallExpression, p));

        var prefix = RouteTable.Routes.GetRoutePrefixForType<T>();
        var newBaseUri = new Uri(_baseUri, prefix);
        var uriMethod = new UriTemplate(uriTemplateForMethod, true);
        return uriMethod.BindByName(newBaseUri, args);
    }

    #endregion

    private static string ValuateExpression(MethodCallExpression methodCallExpression, ParameterInfo p)
    {
        var argument = methodCallExpression.Arguments[p.Position];
        var constantExpression = argument as ConstantExpression;
        if (constantExpression != null)
        {
            return constantExpression.Value.ToString();
        }

        //var memberExpression = (argument as MemberExpression);
        var lambdaExpression = Expression.Lambda(argument, Enumerable.Empty<ParameterExpression>());
        var result = lambdaExpression.Compile().DynamicInvoke().ToString();
        return result;
    }

    private static string GetUriTemplateForMethod(MethodInfo method)
    {
        var webGet = method.GetCustomAttributes(true).OfType<WebGetAttribute>().FirstOrDefault();
        if (webGet != null)
        {
            return webGet.UriTemplate ?? method.Name;
        }

        var webInvoke = method.GetCustomAttributes(true).OfType<WebInvokeAttribute>().FirstOrDefault();
        if (webInvoke != null)
        {
            return webInvoke.UriTemplate ?? method.Name;
        }

        throw new InvalidOperationException(string.Format("The method {0} is not a web method.", method.Name));
    }
}

考虑到 HTTPS 可能会在负载均衡器处终止，ResourceLinker 的默认构造函数需要进行一些更改以获取 Web 应用程序的基本 uri。这不属于这个答案。