Question

In my MVC Web Application, I developed a function to return a Newsstand Atom Feed (for Apple’s Newsstand).
One of their requirements for this feed is that it is effectively encoded in UTF-8 and must not include a BOM.
This is how I coded my view (class names are fictional to preserve my company’s privacy):

<%@ Page Language="VB" Inherits="System.Web.Mvc.ViewPage(Of IEnumerable (Of AtomFeed))" ContentType="application/atom+xml" ResponseEncoding="UTF-8" %><?xml version="1.0" encoding="UTF-8"?>
<feed xmlns="http://www.w3.org/2005/Atom" xmlns:news="http://itunes.apple.com/2011/Newsstand"><%="" %><%  If Not Model Is Nothing Then%><%  Dim updateDate As String = ViewData("feedUpdate")%><% If (Not String.IsNullOrEmpty(updateDate)) Then%>
<updated><%= updateDate %></updated><%
End If%><% For Each f In Model%>
<entry>
    <id><%= f.id%></id>
    <updated><%= f.updated%></updated>
    <published><%= f.published%></published>
    <news:end_date><%= f.endDate%></news:end_date>
    <summary><%= f.summaryText%></summary>
    <news:cover_art_icons>
        <news:cover_art_icon size="SOURCE" src="<%= f.newspaperCover %>"/>
    </news:cover_art_icons>
</entry><%
        Next%><%
End If%>
</feed>

Today we received a mail from itunes complaining that they couldn’t import our XML, without a clue as to why it failed.
The rendered XML is compliant to their requirements so my only guess is that there is a problem with the encoding of my view.

How do I correctly return this view in UTF-8 without BOM, so that when they pull the XML from my given url, it will be processed correctly?

EDIT:

After using Darin’s implementation, I ended up with the following feed

    <?xml version="1.0" encoding="utf-8"?>
<feed xmlns:news="http://itunes.apple.com/2011/Newsstand"
xmlns="http://www.w3.org/2005/Atom">
  <title type="text"></title>
  <id>uuid:5fc48c36-a1d3-4280-a856-a1a0528e2552;id=1</id>
  <updated>2012-07-23T00:40:00Z</updated>
  <entry>
    <id>23.07.2012</id>
    <title type="text"></title>
    <summary type="text">...</summary>
    <updated>2012-07-23T00:40:00Z</updated>
    <published xmlns="">2012-07-23T00:40:00Z</published>
    <news:end_date>2012-07-24T00:40:00Z</news:end_date>
    <news:cover_art_icons>
      <news:cover_art_icon size="SOURCE"
      src="https://www.someurl.com" />
    </news:cover_art_icons>
  </entry>
  <entry>
    <id>22.07.2012</id>
    <title type="text"></title>
    <summary type="text">...</summary>
    <updated>2012-07-22T00:40:00Z</updated>
    <published xmlns="">2012-07-22T00:40:00Z</published>
    <news:end_date>2012-07-23T00:40:00Z</news:end_date>
    <news:cover_art_icons>
      <news:cover_art_icon size="SOURCE"
      src="https://www.someurl.com" />
    </news:cover_art_icons>
  </entry>
</feed>

Now Apple’s Newsstand cannot import the following feed because they say they can’t find element in this feed’s entry element.

Answer 1

Instead of generating the an XML feed manually in a view I would recommend you using the SyndicationFeed class which is designed for that purpose.

So let’s assume that you have some domain model representing your data:

public class NewsstandFeed
{
    public DateTime? Updated { get; set; }
    public IEnumerable<AtomFeed> Items { get; set; }
}

public class AtomFeed
{
    public int Id { get; set; }
    public DateTime Updated { get; set; }
    public DateTime Published { get; set; }
    public DateTime EndDate { get; set; }
    public string SummaryText { get; set; }
    public string NewspaperCover { get; set; }
}

and then a controller that will query some DAL to retrieve the domain model:

public class HomeController : Controller
{
    public ActionResult Index()
    {
        // Normally this will come from a database or something,
        // but I am hardcoding it for demonstration purposes here
        var model = new NewsstandFeed
        {
            Updated = DateTime.Now,
            Items = new[]
            {
                new AtomFeed 
                {
                    Id = 1,
                    Updated = DateTime.Now,
                    Published = DateTime.Now,
                    EndDate = DateTime.Now,
                    SummaryText = "some summary",
                    NewspaperCover = "http://www.google.com"
                }
            }
        };

        return new NewsstandFeedResult(model);
    }
}

Notice the NewsstandFeedResult that the controller action returns? Let’s implement it:

public class NewsstandFeedResult : ActionResult
{
    public const string NewsstandNS = "http://itunes.apple.com/2011/Newsstand";
    public NewsstandFeed Model { get; private set; }

    public NewsstandFeedResult(NewsstandFeed model)
    {
        Model = model;
        if (model.Items == null)
        {
            model.Items = Enumerable.Empty<AtomFeed>();
        }
    }

    public override void ExecuteResult(ControllerContext context)
    {
        var response = context.HttpContext.Response;
        response.ContentType = "application/atom+xml";

        var feed = new SyndicationFeed();
        var n = new XmlQualifiedName("news", "http://www.w3.org/2000/xmlns/");
        XNamespace newsstandNs = NewsstandNS;
        feed.AttributeExtensions.Add(n, newsstandNs.ToString());
        if (Model.Updated.HasValue)
        {
            feed.LastUpdatedTime = new DateTimeOffset(Model.Updated.Value.ToUniversalTime());
        }

        var items = new List<SyndicationItem>();
        foreach (var item in Model.Items)
        {
            var si = new SyndicationItem();
            si.Id = item.Id.ToString();
            si.LastUpdatedTime = new DateTimeOffset(item.Updated.ToUniversalTime());
            si.Summary = new TextSyndicationContent(item.SummaryText);

            si.ElementExtensions.Add(new XElement(newsstandNs + "end_date", item.EndDate.ToUniversalTime()));
            si.ElementExtensions.Add(
                new XElement(
                    newsstandNs + "cover_art_icons",
                    new XElement(
                        newsstandNs + "cover_art_icon", 
                        new XAttribute("size", "SOURCE"), 
                        new XAttribute("src", item.NewspaperCover)
                    )
                )
            );
            items.Add(si);
        }
        feed.Items = items;

        using (var writer = XmlWriter.Create(response.OutputStream))
        {
            var formatter = new Atom10FeedFormatter(feed);
            formatter.WriteTo(writer);
        }
    }
}

That’s it. Now simply navigate to /home/index and you will get a valid Atom feed respecting all industry standards so that you don’t have to worry about BOMs and stuff.