PollingAgent and AtomPubClient in the WCF Rest Starter kit preview 2

PollingAgent is an utility class for consuming REST services that implement conditional gets. An instance of this class will periodically invoke the service within a predefined interval of time, and fire an event on the client side when a new response is available to consume. It is internally layered on top of the HttpClient class, so all the pipeline infrastructure provided by this last one is also supported for this pooling agent.

As I discussed in the post “Conditional Get in REST”, conditional gets provide an effective and standard mechanism for caching information on the client side. It is based on the use of the  Etag/IfNoneMatch and Last-Modified/IfModifiedSince html headers. This mechanism is commonly used by the feed readers to be notified about new items in the feeds.

This pooling agent implementation internally keeps track of those headers, so it hides many of the conditional gets details from the client application.

public class PollingAgent : IDisposable

{

  public PollingAgent();

  public HttpClient HttpClient { get; set; }

  public bool IgnoreExpiresHeader { get; set; }

  public bool IgnoreNonOKStatusCodes { get; set; }

  public bool IgnoreSendErrors { get; set; }

  public TimeSpan PollingInterval { get; set; }

  public event EventHandler<ConditionalGetEventArgs> ResourceChanged;

  public void Dispose();

  public void StartPolling();

  public void StartPolling(Uri uri);

  public void StartPolling(Uri uri, EntityTag etag, DateTime? lastModifiedTime);

  public void StopPolling();

}

public class ConditionalGetEventArgs : EventArgs

{

  public ConditionalGetEventArgs();

  public HttpResponseMessage Response { get; set; }

  public Exception SendError { get; set; }

  public bool StopPolling { get; set; }

}

This public API is quite straightforward, a couple of methods to start/stop polling the REST service, an event “ResourceChanged” to be notified about changes, and some properties to configure the agent.

AtomPubClient is an specialized version of the HttpClient for consuming Atom Pub Services. It provides different overloads for creating, updating, getting or updating existing syndication entries through Atom pub.

As you can see, the WCF Rest team is definitively doing a great job to facilitate the adoption of REST services in the platform. 

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