Introduction

RSS (and Atom) is still the only widely adopted format for syndicating content. It's a simple XML format that can be consumed by a wide range of feed readers. In this post, I'll show you how to add an RSS feed to your ASP.NET Core application.

Creating the feed

Really the core of this is creating the XML document for the RSS feed. The code below takes a list of RssFeedItem objects and generates the XML for the feed. The RssFeedItem class is a simple class that represents an item in the feed. It has properties for the title, link, description, publication date, and categories.

    public string GenerateFeed(IEnumerable<RssFeedItem> items, string categoryName = "")
    {
        XNamespace atom = "http://www.w3.org/2005/Atom";
        var feed = new XDocument(
            new XDeclaration("1.0", "utf-8", null),
            new XElement("rss",    new XAttribute(XNamespace.Xmlns + "atom", atom.NamespaceName), new XAttribute("version", "2.0"),
                new XElement("channel",
                    new XElement("title", !string.IsNullOrEmpty(categoryName) ? $"mostlylucid.net for {categoryName}" : $"mostlylucid.net"),
                    new XElement("link", $"{GetSiteUrl()}/rss"),
                    new XElement("description", "The latest posts from mostlylucid.net"),
                    new XElement("pubDate", DateTime.UtcNow.ToString("R")),
                    new XElement(atom + "link", 
                        new XAttribute("href", $"{GetSiteUrl()}/rss"), 
                        new XAttribute("rel", "self"), 
                        new XAttribute("type", "application/rss+xml")),
                    from item in items
                    select new XElement("item",
                        new XElement("title", item.Title),
                        new XElement("link", item.Link),
                        new XElement("guid", item.Guid, new XAttribute("isPermaLink", "false")),
                        new XElement("description", item.Description),
                        new XElement("pubDate", item.PubDate.ToString("R")),
                        from category in item.Categories
                        select new XElement("category", category)
                    )
                )
            )
        );

        var settings = new XmlWriterSettings
        {
            Indent = true,
            Encoding = new UTF8Encoding(false) // UTF-8 without BOM
        };

        using (var memoryStream = new MemoryStream())
        using (var writer = XmlWriter.Create(memoryStream, settings))
        {
            feed.Save(writer);
            writer.Flush();
            return Encoding.UTF8.GetString(memoryStream.ToArray());
        }
    }

Things of note in the code above: We need to create the Atom namespace and inject it into the XML document to support the atom:link element.

     XNamespace atom = "http://www.w3.org/2005/Atom";
        var feed = new XDocument(
            new XDeclaration("1.0", "utf-8", null),
            new XElement("rss",    new XAttribute(XNamespace.Xmlns + "atom", atom.NamespaceName), new XAttribute("version", "2.0"),

UTF-8 Encoding

Although we specify utf-8 here well ASP.NET Core ignores that...because it's special. Instead we need to ensure that the strings generated in the document are actually UTF-8, I had thought this

   var settings = new XmlWriterSettings
        {
            Indent = true,
            Encoding = new UTF8Encoding(false) // UTF-8 without BOM
        };

But NOPE...we need to do this:

        using (var memoryStream = new MemoryStream())
        using (var writer = XmlWriter.Create(memoryStream, settings))
        {
            feed.Save(writer);
            writer.Flush();
            return Encoding.UTF8.GetString(memoryStream.ToArray());
        }

This way it ACTUALLY outputs an XML document with utf-8 encoding.

The controller

From there it's pretty simple in the RSSController, we have a method which accepts category and startdate (currently a super secret feature ??) and returns the feed.

    [HttpGet]
    public IActionResult Index([FromQuery] string category = null, [FromQuery] string startDate = null)
    {
        DateTime? startDateTime = null;
        if (DateTime.TryParseExact(startDate, "yyyy-MM-dd", CultureInfo.InvariantCulture, DateTimeStyles.None,
                out DateTime startDateTIme))
        {
            logger.LogInformation("Start date is {startDate}", startDate);
        }

        var rssFeed = rssFeedService.GenerateFeed(startDateTime, category);
        return Content(rssFeed, "application/rss+xml", Encoding.UTF8);
    }

THEN in the `_Layout.cshtml' we add a link to the feed:

        <link rel="alternate" type="application/rss+xml"
              title="RSS Feed for mostlylucid.net"
              href="/rss" />

This ensures the feed can be 'autodiscovered' by feed readers.