Recipe: Creating an Atom Feed in Rails

Your website is now functionally complete, and it’s got a good selection of quality content to interest potential viewers. You’d like to make it easy for those potential viewers to discover your content. One of the best ways to do this is to add a feed to your site.

Feeds can be read by software referred to as a feed reader. Interested users can subscribe to your feed using their feed reader, allowing them to quickly become aware of new content when it’s added to your web site. Feed readers are widely available, so any user who’s interested in following feeds in this way should be able to find one. Even most web browsers now include a feed-reading capability.

Feeds are generally created to accomplish one of the goals below:

In this article, we’re going to create an Atom feed for the KeenerTech.com blog using Ruby on Rails, with the goal of driving traffic to the blog web site. All reasonably well-supported feed readers support both Atom and the various versions of the RSS standard. For our purposes, though, Atom is a better choice since our blog content will contain HTML tags.

The Atom Syndication Standard

The Atom Syndication Format, now at version 1.0, is a standard for syndicating content, very similar to RSS. Like RSS, information is packaged into an XML file.

Atom is, in some respects, an enhanced RSS-like standard that provides better support than RSS for diverse content types, internationalization and modularity. Many people, in fact, use RSS as an umbrella term for feed standards (e.g. — RSS 1.0, RSS 1.1, RSS 2.0, etc.) and just lump Atom in as “another” RSS standard, even though, strictly speaking, that is not correct.

What Does an Atom Feed Look Like?

An Atom feed is just an XML file that adheres to the Atom Syndication Standard. A sample Atom feed is shown in Listing 1.

Listing 1: Sample KT.com Blog Feed

<!--?xml version="1.0" encoding="utf-8"?-->
<feed xml:lang="en"
      xmlns="http://www.w3.org/2005/Atom">
   <title>KT.com Articles</title>
   <link href="http://www.kt.com/feeds"
         rel="alternate" />
   <link href="http://www.kt.com/arts.atom"
         rel="self"
         type="application/atom+xml" />
   <id>http://www.kt.com/arts.atom<id>
   <updated>2009-08-30T18:56:14Z</updated>
   <generator uri="http://www.kt.com">
      kt.com
   </generator>
   <entry>
     <title><![CDATA[Maven Introductory
         Presentation Available Online]]></title>
     <link
      href="http://www.kt.com/arts/2009/08/23/maven"
      rel="alternate">
     <id>tag:kt.com,2009-08-23:321</id>
     <author>
       <name>Steve Keener</name>
       <uri>
          http://www.kt.com/profiles/steve_keener
       </uri>
     </author>
     <updated>2009-08-24T01:26:16Z</updated>
     <published>2009-08-23T00:00:00Z</published>
     <summary type="html">My presentation,
        <a href="http://www.kt.com/docs/Maven.pdf">
        Maven: Managing Software Projects for
        Repeatable Results</&;gt;, is now available
        online. Find out how to leverage this
        sophisticated build tool to automate
        key tasks for your next Java project.
     </summary>
</entry></feed>

Feed Summary Elements

The summary section of the Atom feed consists of the elements defined in Table 1. An asterisk indicates elements that are required to be present for a valid Atom feed. Notes about how the element will be handled for the feed we are building in this article will be in italics.

Table 1: Feed Summary Elements

Entry Elements

The Atom feed includes one or more entries, where each entry provides information about a blog entry. The Atom Syndication Format provides a set of standard elements for describing content entries.

Table 2: Standard Atom Entry Elements

Onwards to the Code

Implementing an Atom feed in Ruby is a straight-forward task. Ruby provides the Builder module which automates creating XML documents. The general technique shown in most technical books is to create a controller that retrieves a list of content items from the database. The controller then makes that list available to a view, which includes Builder code to generate the necessary XML.

My technique is a little different. In Listing 2, I pull the Ruby code to produce the feed into the model. By doing this, it’s easier to write unit tests for the Atom generation code. It’s also easier to share the code if you need to produce multiple Atom feeds, e.g. — a separate feed for each category.

Listing 2: The Ruby Code Behind the Atom Feed

 class Entry < ActiveRecord::Base

    def self.generate_atom_feed(title, entries, options = {})
      feed_ref_url = 'http://www.kt.com/feeds'
      feed_url = 'http://www.kt.com/arts.atom'
      base_entry_url ='http://www.kt.com/arts/'
      buffer = ''
  
      xml = options[:builder] ||= Builder::XmlMarkup.new(:indent => 
        options[:indent], :target => buffer)
      xml.instruct! :xml, :version=>'1.0', :encoding=>'utf-8'
  
      xml.feed 'xmlns' => 
          'http://www.w3.org/2005/Atom', 'xml:lang' => 'en' do
        xml.title title
        xml.link 'rel' => 'alternate', 'href' => feed_ref_url 
        xml.link 'rel' => 'self', 
                 'href' => feed_url,
                 'type' => 'application/atom+xml'
        xml.id feed_url
        xml.updated Time.now.utc.strftime("%Y-%m-%dT%H:%M:%SZ")
        xml.generator 'KT.com', 'uri' => 'http://www.kt.com'
  
        entries.each do |entry|
          if !entry.name.nil?
            xml.entry do
              # Create Atom entry elements
              xml << "    \n"
              xml.link  "rel" => "alternate", 
                "href" => base_entry_url + 
                entry.display_date.strftime('%Y/%m/%d/') + entry.url_name
  
              xml.id "tag:kt.com,#{entry.display_date.strftime
                ('%Y-%m-%d')}:#{entry.id}"
              xml.author do
                xml.name "#{entry.user.first_name} #{entry.user.last_name}"
                xml.uri entry.user.first_name + "_" + entry.user.last_name
              end
              xml.updated entry.updated_at.strftime("%Y-%m-%dT%H:%M:%SZ")
              xml.published entry.display_date.strftime
                ("%Y-%m-%dT%H:%M:%SZ")
              xml << "    
" + 
                 Entry.escape_html(entry.summary) + "
\n"
            end
          end
        end
  
      end
      
      buffer
    end
  
  protected

    def self.escape_html(str)
      return str.to_s.gsub('&', '&').gsub('<', '<').gsub('>', '>') if str
    end

 end

In the code above, I’ve hard-coded the feed paths. If I were to generalize this code to produce multiple Atom feeds, such as for different categories, I’d need to re-factor this code slightly since each feed should have its own distinct URL.

To produce the XML, the caller must pass in the title of the feed, the list of entries to be included in the feed and any options. The options are passed directly to Builder::XmlMarkup; the only option that is really supported is the “:indent” option, which specifies how many spaces each level of XML should be indented. The Builder::XmlMarkup object will direct its output into the “buffer” string.

The Builder::XmlMarkup object makes it easy to produce XML. A statement like:

xml.title title

will produce the XML below:

<title>KT.com Articles</title>

Likewise, a statement like this:

xml.generator ‘KT.com’, ‘uri’ => ‘http://www.kt.com’

will produce an XML element that includes both content and an attribute:

<generator uri=”https://www.keenertech.com”>KeenerTech.com</generator>

Since I’ve pulled the Atom generation code into the model, the controller will need to call the Entry.generate_atom_feed method in order to produce the output. The controller will then receive the XML as a string, which it will then render without benefit of a view. The controller code is shown in Listing 3.

Listing 3: Controller Code

  def index
    @articles = Entry.find(:all, 
                           :include => :user, 
                           :order => "entries.display_date desc")
                           
    respond_to do |wants|
            wants.html do               
              render :layout => 'kt' 
            end
            wants.atom do
              xml = Entry.generate_atom_feed('KT.com Articles',
                @articles, :indent => 2)
              render :text => xml, :content_type => 'application/atom+xml'
            end
          end     
  end

The controller generates the list of articles using the find method. Note that it uses the “:include” option to incorporate user information into the list. Since the user information has been pre-fetched by find, traversing from an entry to its corresponding user will not generate additional database calls (which is something that the Atom generation code will be doing).

The controller uses the respond_to statement to determine what type of content the caller wants to produce. If HTML, Rails will use a view to generate the appropriate HTML output. If the caller has specified Atom, then the code generates the Atom output by calling the model. It then renders the content directly.

Does this break the MVC paradigm? It probably bends the rules a little bit, but the advantages outweigh the disadvantages.

The primary advantage is that the code for producing the Atom output is centralized in the model, where it can easily be shared and unit-tested. Meanwhile, the model and controller still have clearly defined roles in producing the output.

The model simply produces the output; it doesn’t render it. The controller determines what data elements will appear in the feed, gets the Atom output from the model and then causes the output to be rendered. While the controller causes the content to be rendered, it doesn’t otherwise manipulate it. We could have a view that renders the Atom output string, but it seems kind of pointless to have a one-line view.

Atom Validation

After producing the feed, you should validate it using the Feed Validator. This free service will perform a detailed analysis of Atom and RSS feeds. It produces excellent diagnostic output, as well as good recommendations for items that optional. Don’t even think about considering your feed to be “finished” until you’ve successfully validated it.

References

There are a number of relevant references available that can be useful for those producing Atom feeds:

• Atom Syndication Format – Introduction
  http://www.atomenabled.org/developers/syndication/
  This web page provides a detailed and extremely useful overview of the Atom Syndication format.
• Builder Documentation
  http://builder.rubyforge.org/ 
  RDoc documentation for the Builder module, including Builder::XmlMarkup.
• Feed Validator
  http://www.feedvalidator.org/
  A free online service for validating RSS, Atom and KML feeds. Highly recommended.