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How to: Expose a Feed as Both Atom and RSS

Windows Communication Foundation (WCF) allows you to create a service that exposes a syndication feed. This topic discusses how to create a syndication service that exposes a syndication feed using both Atom 1.0 and RSS 2.0. This service exposes one endpoint that can return either syndication format. For simplicity the service used in this sample is self hosted. In a production environment a service of this type would be hosted under IIS or WAS. For more information about the different WCF hosting options, see Hosting.

To create a basic syndication service

  1. Define a service contract using an interface marked with the WebGetAttribute attribute. Each operation that is exposed as a syndication feed returns a SyndicationFeedFormatter object. Note the parameters for the WebGetAttribute. UriTemplate specifies the URL used to invoke this service operation. The string for this parameter contains literals and a variable in braces ({format}). This variable corresponds to the service operation's format parameter. For more information, see UriTemplate. BodyStyle affects how the messages that this service operation sends and receives are written. Bare specifies that the data sent to and from this service operation are not wrapped by infrastructure-defined XML elements. For more information, see WebMessageBodyStyle.

    
    <ServiceContract()> _
    <ServiceKnownType(GetType(Atom10FeedFormatter))> _
    <ServiceKnownType(GetType(Rss20FeedFormatter))> _
    Public Interface IBlog
        <OperationContract()> _
        <WebGet(UriTemplate:="GetBlog?format={format}")> _
        Function GetBlog(ByVal format As String) As SyndicationFeedFormatter
    End Interface
    
    
    
    Note Note

    Use the ServiceKnownTypeAttribute to specify the types that are returned by the service operations in this interface.

  2. Implement the service contract.

    
    Public Class BlogService
        implements IBlog
    
        Public Function GetBlog(ByVal format As String) As SyndicationFeedFormatter Implements IBlog.GetBlog
            Dim feed As New SyndicationFeed("My Blog Feed", "This is a test feed", New Uri("http://SomeURI"))
            feed.Authors.Add(New SyndicationPerson("someone@microsoft.com"))
            feed.Categories.Add(New SyndicationCategory("How To Sample Code"))
            feed.Description = New TextSyndicationContent("This is a sample that demonstrates how to expose a feed through RSS and Atom with WCF")
            Dim item1 As New SyndicationItem( _
                "Item One", _
                "This is the content for item one", _
                New Uri("http://localhost/Content/One"), _
                "ItemOneID", _
                DateTime.Now)
    
            Dim item2 As New SyndicationItem( _
                "Item Two", _
                "This is the content for item two", _
                New Uri("http://localhost/Content/Two"), _
                "ItemTwoID", _
                DateTime.Now)
    
            Dim item3 As New SyndicationItem( _
                "Item Three", _
                "This is the content for item three", _
                New Uri("http://localhost/Content/three"), _
                "ItemThreeID", _
                DateTime.Now)
            Dim items As New List(Of SyndicationItem)()
            items.Add(item1)
            items.Add(item2)
            items.Add(item3)
    
            feed.Items = items
    
            If (format = "rss") Then
                Return New Rss20FeedFormatter(feed)
            Else
                Return New Atom10FeedFormatter(feed)
            End If
        End Function
    End Class
    
    
    
  3. Create a SyndicationFeed object and add an author, category, and description.

    
    Dim feed As New SyndicationFeed("My Blog Feed", "This is a test feed", New Uri("http://SomeURI"))
    feed.Authors.Add(New SyndicationPerson("someone@microsoft.com"))
    feed.Categories.Add(New SyndicationCategory("How To Sample Code"))
    feed.Description = New TextSyndicationContent("This is a sample that demonstrates how to expose a feed through RSS and Atom with WCF")
    
    
    
  4. Create several SyndicationItem objects.

    
    Dim item1 As New SyndicationItem( _
        "Item One", _
        "This is the content for item one", _
        New Uri("http://localhost/Content/One"), _
        "ItemOneID", _
        DateTime.Now)
    
    Dim item2 As New SyndicationItem( _
        "Item Two", _
        "This is the content for item two", _
        New Uri("http://localhost/Content/Two"), _
        "ItemTwoID", _
        DateTime.Now)
    
    Dim item3 As New SyndicationItem( _
        "Item Three", _
        "This is the content for item three", _
        New Uri("http://localhost/Content/three"), _
        "ItemThreeID", _
        DateTime.Now)
    
    
    
  5. Add the SyndicationItem objects to the feed.

    
    Dim items As New List(Of SyndicationItem)()
    items.Add(item1)
    items.Add(item2)
    items.Add(item3)
    
    feed.Items = items
    
    
    
  6. Use the format parameter to return the requested format.

    
    If (format = "rss") Then
        Return New Rss20FeedFormatter(feed)
    Else
        Return New Atom10FeedFormatter(feed)
    End If
    
    
    

To host the service

  1. Create a WebServiceHost object. The WebServiceHost class automatically adds an endpoint at the service's base address unless one is specified in code or configuration. In this sample, no endpoints are specified so the default endpoint is exposed.

    
    Dim address As New Uri("http://localhost:8000/BlogService/")
    Dim svcHost As New WebServiceHost(GetType(BlogService), address)
    
    
    
  2. Open the service host, load the feed from the service, display the feed, and wait for the user to press ENTER.

    
    svcHost.Open()
    Console.WriteLine("Service is running")
    
    Console.WriteLine("Loading feed in Atom 1.0 format.")
    Dim atomReader As XmlReader = XmlReader.Create("http://localhost:8000/BlogService/GetBlog?format=atom")
    Dim atomFeed As SyndicationFeed = SyndicationFeed.Load(atomReader)
    Console.WriteLine(atomFeed.Title.Text)
    Console.WriteLine("Items:")
    For Each item As SyndicationItem In atomFeed.Items
        Console.WriteLine("Title: {0}", item.Title.Text)
        Console.WriteLine("Content: {0}", CType(item.Content, TextSyndicationContent).Text)
    Next
    
    Console.WriteLine("Loading feed in RSS 2.0 format.")
    Dim rssReader As XmlReader = XmlReader.Create("http://localhost:8000/BlogService/GetBlog?format=rss")
    Dim rssFeed As SyndicationFeed = SyndicationFeed.Load(rssReader)
    Console.WriteLine(rssFeed.Title.Text)
    Console.WriteLine("Items:")
    For Each item As SyndicationItem In rssFeed.Items
        Console.WriteLine("Title: {0}", item.Title.Text)
        Console.WriteLine("Content: {0}", CType(item.Content, TextSyndicationContent).Text)
    Next
    
    
    Console.WriteLine("Press <ENTER> to quit...")
    Console.ReadLine()
    svcHost.Close()
    
    
    

To call GetBlog with an HTTP GET

  • Open Internet Explorer, type the following URL, and press ENTER. http://localhost:8000/BlogService/GetBlog

    The URL contains the base address of the service (http://localhost:8000/BlogService), the relative address of the endpoint, and the service operation to call.

To call GetBlog() from code

  1. Create an XmlReader with the base address and the method you are calling.

    
    Dim atomReader As XmlReader = XmlReader.Create("http://localhost:8000/BlogService/GetBlog?format=atom")
    
    
    
  2. Call the static Load(XmlReader) method, passing in the XmlReader you just created.

    
    Dim feed As SyndicationFeed = SyndicationFeed.Load(atomReader)
    
    
    

    This invokes the service operation and populates a new SyndicationFeed with the formatter returned from the service operation.

  3. Access the feed object.

    
    Console.WriteLine(feed.Title.Text)
    Console.WriteLine("Items:")
    For Each item As SyndicationItem In feed.Items
        Console.WriteLine("Title: {0}", item.Title.Text)
        Console.WriteLine("Content: {0}", (CType(item.Content, TextSyndicationContent).Text))
    Next
    
    
    

The following is the full code listing for this example.


using System;
using System.Xml;
using System.Collections.Generic;
using System.ServiceModel;
using System.ServiceModel.Description;
using System.ServiceModel.Syndication;
using System.ServiceModel.Web;
namespace Service
{
    [ServiceContract]
    [ServiceKnownType(typeof(Atom10FeedFormatter))]
    [ServiceKnownType(typeof(Rss20FeedFormatter))]
    public interface IBlog
    {
        [OperationContract]
        [WebGet(UriTemplate = "GetBlog?format={format}")]
        SyndicationFeedFormatter GetBlog(string format);
    }

    public class BlogService : IBlog
    {
        public SyndicationFeedFormatter GetBlog(string format)
        {
            SyndicationFeed feed = new SyndicationFeed("My Blog Feed", "This is a test feed", new Uri("http://SomeURI"));
            feed.Authors.Add(new SyndicationPerson("someone@microsoft.com"));
            feed.Categories.Add(new SyndicationCategory("How To Sample Code"));
            feed.Description = new TextSyndicationContent("This is a sample that demonstrates how to expose a feed through RSS and Atom with WCF");
            SyndicationItem item1 = new SyndicationItem(
                "Item One",
                "This is the content for item one",
                new Uri("http://localhost/Content/One"),
                "ItemOneID",
                DateTime.Now);

            SyndicationItem item2 = new SyndicationItem(
                "Item Two",
                "This is the content for item two",
                new Uri("http://localhost/Content/Two"),
                "ItemTwoID",
                DateTime.Now);

            SyndicationItem item3 = new SyndicationItem(
                "Item Three",
                "This is the content for item three",
                new Uri("http://localhost/Content/three"),
                "ItemThreeID",
                DateTime.Now);
            List<SyndicationItem> items = new List<SyndicationItem>();
            items.Add(item1);
            items.Add(item2);
            items.Add(item3);

            feed.Items = items;

            if (format == "rss")
                return new Rss20FeedFormatter(feed);
            else if (format == "atom")
                return new Atom10FeedFormatter(feed);
            else return null;
        }
    }

    public class Host
    {
        static void Main(string[] args)
        {
            Uri address = new Uri("http://localhost:8000/BlogService/");
            WebServiceHost svcHost = new WebServiceHost(typeof(BlogService), address);
            try
            {
                svcHost.Open();
                Console.WriteLine("Service is running");

                Console.WriteLine("Loading feed in Atom 1.0 format.");
                XmlReader atomReader = XmlReader.Create("http://localhost:8000/BlogService/GetBlog?format=atom");
                SyndicationFeed atomFeed = SyndicationFeed.Load(atomReader);
                Console.WriteLine(atomFeed.Title.Text);
                Console.WriteLine("Items:");
                foreach (SyndicationItem item in atomFeed.Items)
                {
                    Console.WriteLine("Title: {0}", item.Title.Text);
                    Console.WriteLine("Content: {0}", ((TextSyndicationContent)item.Content).Text);
                }

                Console.WriteLine("Loading feed in RSS 2.0 format.");
                XmlReader rssReader = XmlReader.Create("http://localhost:8000/BlogService/GetBlog?format=rss");
                SyndicationFeed rssFeed = SyndicationFeed.Load(rssReader);
                Console.WriteLine(rssFeed.Title.Text);
                Console.WriteLine("Items:");
                foreach (SyndicationItem item in rssFeed.Items)
                {
                    Console.WriteLine("Title: {0}", item.Title.Text);
                    // Notice we are using item.Summary here instead of item.Content. This is because
                    // of the differences between Atom 1.0 and RSS 2.0 specs.
                    Console.WriteLine("Content: {0}", ((TextSyndicationContent)item.Summary).Text);
                }

                Console.WriteLine("Press <ENTER> to quit...");
                Console.ReadLine();
                svcHost.Close();
            }
            catch (CommunicationException ce)
            {
                Console.WriteLine("An exception occurred: {0}", ce.Message);
                svcHost.Abort();
            }
        }
    }
}


When compiling the preceding code, reference System.ServiceModel.dll and System.ServiceModel.Web.dll.

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