如何扩展WCF WebHttp（REST）以支持ETags和条件获取？ [英] How do I extend WCF WebHttp (REST) to support ETags and Conditional Gets?

问题描述

我有一个只读的WCF REST服务（所有 GET 的宝贝！）我想在我的每一个操作中添加ETag /有条件获得支持服务。

基本上我对扩展本文中的技术感兴趣：

我的网站支持一对XML文件，而我的应用程序知道（并引发一个事件），当它们中的任何一个发生变化时。我不明白扩展点在哪里。如何在管道中添加这些标头，而不是一次一个地添加这些标头？

解决方案

结果不那么糟糕。我使用了一个 IDispatchMessageInspector ，并将其应用于所有服务中的ServiceBehavior。

 >公共类ConditionalGetMessageInspector：IDispatchMessageInspector $ b $我有点不舒服，请求被如何路由，但它似乎工作。 b {
 private enum GetState {Modified，Unmodified} 
 
私有字符串ETag {
 get {return XmlDataLoader.LastUpdatedTicks.ToString（）; } 
} 
 private DateTime LastModified {
 get {return new DateTime（XmlDataLoader.LastUpdatedTicks）;} 
} 
 
 public Object AfterReceiveRequest（ref Message request ，
 IClientChannel channel，InstanceContext instanceContext）
 {
 try 
 {
 WebOperationContext.Current.IncomingRequest $ b $ .CheckConditionalRetrieve（ETag）; 
} 
 catch（WebFaultException）
 {
 instanceContext.Abort（）; 
返回GetState.Unmodified; 
} 
 // No-op 
 return GetState.Modified; 
 
 $ b $ public void BeforeSendReply（ref message reply，object correlationState）
 {
 if（（GetState）correlationState == GetState.Unmodified）
 { 
 WebOperationContext.Current.OutgoingResponse.StatusCode = 
 HttpStatusCode.NotModified; 
 WebOperationContext.Current.OutgoingResponse.SuppressEntityBody = 
 true; 
} 
 else 
 {
 WebOperationContext.Current.OutgoingResponse.SetETag（ETag）; 
 WebOperationContext.Current.OutgoingResponse.LastModified = 
 LastModified; 
} 
} 
} 
  

I have a read-only WCF REST service (all GET's baby!) I'd like to add ETag/Conditional get support to every single operation in my service.

Basically I'm interested in extending the technique in this article: http://blogs.msdn.com/b/endpoint/archive/2010/02/25/conditional-get-and-etag-support-in-wcf-webhttp-services.aspx

My site is backed by a couple of XML files, and my app knows (and raises an event) when any of them change. I don't understand where the extension points are though. How do I hook into the pipeline to add these headers for every call instead of one-at-a-time?

解决方案

This turned out not to be so bad. I used an IDispatchMessageInspector which I hooked into a ServiceBehavior that's applied to all my services. I'm a little uncomfortable with how the request gets routed but it seems to work.

public class ConditionalGetMessageInspector : IDispatchMessageInspector
{
    private enum GetState { Modified, Unmodified }

    private string ETag { 
        get { return XmlDataLoader.LastUpdatedTicks.ToString(); }
    }
    private DateTime LastModified { 
        get { return new DateTime(XmlDataLoader.LastUpdatedTicks);}
    }

    public object AfterReceiveRequest(ref Message request, 
        IClientChannel channel, InstanceContext instanceContext)
    {
        try
        {
            WebOperationContext.Current.IncomingRequest
                .CheckConditionalRetrieve(ETag);
        }
        catch (WebFaultException)
        {
            instanceContext.Abort();
            return GetState.Unmodified;
        }
        // No-op
        return GetState.Modified;
    }

    public void BeforeSendReply(ref Message reply, object correlationState)
    {
        if ((GetState)correlationState == GetState.Unmodified)
        {
            WebOperationContext.Current.OutgoingResponse.StatusCode = 
                HttpStatusCode.NotModified;
            WebOperationContext.Current.OutgoingResponse.SuppressEntityBody = 
                true;
        }
        else
        {
            WebOperationContext.Current.OutgoingResponse.SetETag(ETag);
            WebOperationContext.Current.OutgoingResponse.LastModified = 
                LastModified;
        }
    }
}

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