gistfile1.cs

[ServiceContract]
public class HelloWorldResource {

  [WebGet(UriTemplate="")]
  public void Get(HttpRequestMessage req, HttpResponseMessage resp) {
    if (req.IfNoneMatch.Contains("HW")) {
      resp.StatusCode = HttpStatusCode.NotModified;
      return;
    }

    resp.HttpContent.Create("Hello World Resource", "text/html");
    resp.StatusCode = HttpStatusCode.OK;
    resp.Headers.Tag = "HW"; //set the tag
  }
}