How To Create An RSS 2.0 Feed

I’m lack­ing in work sam­ples so I spent the last few days of my vaca­tion cod­ing. Since I enjoy blog­ging, I decided to cre­ate a light-weight and very sim­plis­tic blog­ging plat­form. It’s called Slash­blog and you can look at the code so far here.

Every blog needs an RSS feed. The fact that I have no idea of how to cre­ate one makes it a pleas­ant task. Hope­fully, it’ll also be an edu­ca­tional expe­ri­ence that I can share with you.

The RSS 2.0 spec­i­fi­ca­tion was released in 2003 so there is plenty of infor­ma­tion around. What I already know is that RSS feeds are basi­cally XML. Since my appli­ca­tion already stores posts as XML, my ini­tial thought was; why not make my XML fit the RSS format?

    
http://www.linktosomeblog.com/
        This is the description of some kind of blog, probably.
        
http://www.linktosomeblog.com/thepost
            This could be an excerpt from the blog post or it could be the entire content.
Tue, 29 April 2008 08:56:02 GMT
    
    

A sim­ple RSS 2.0 struc­ture. The title, link and description ele­ments of channel are required. We have a fixed set of ele­ments to work with in item, none of which are actu­ally required but these are the ones I’ll be using. Did I decide to use this for­mat to store my posts?

No. The fact is that it would be a blow to the scal­a­bil­ity of my appli­ca­tion. RSS can be extended to sup­port ele­ments out­side its spec­i­fi­ca­tion but only with the use of name­spaces. Besides from XML, the appli­ca­tion can also store data in flat­files and I’ll prob­a­bly add sup­port for MySQL.

Using name­spaces would be messy as the XML ele­ment names would dif­fer from any SQL fields names. This can be fixed but it would require more code to process. We would also be respon­si­ble for keep­ing the XML file con­stantly up to date, every time we pub­lish, delete or edit a post. It makes much more sense to have a func­tion print the posts as RSS on demand.

I ended up with a method of the class Blog called PrintRSS(). My code may look a bit odd to you since it’s object-oriented but hope­fully it still makes sense.

public function PrintRSS()
{
    if(!$this->PostsLoaded()) // If no posts are loaded...
        $this->LoadPosts(); // ...then load them now.

    // Compose all sections of the RSS data.
    $header = '' . PHP_EOL . '' . PHP_EOL . '' . PHP_EOL;
    $header .= '' . PHP_EOL;
    $header .= '' . $this->GetSetting("DESCRIPTION") . '' . PHP_EOL;
    $header .= '
' . $this->GetSetting("URL") . '' . PHP_EOL;
    $items = "";
    foreach($this->posts as $post)
    {
        $items .= '' . PHP_EOL;
        $items .= '' . PHP_EOL;
        $items .= '' . $post->GetContent() . '' . PHP_EOL;
        $items .= '
' . $post->GetDate() . '' . PHP_EOL;
        $items .= '
' . $this->GetSetting("URL") . 'index.php?post=' . $post->GetID() . '' . PHP_EOL;
        $items .= '' . PHP_EOL;
    }
    $footer = '' . PHP_EOL . '';

    echo $header . $items . $footer; // Write it all to file.
}

Now we just need a file that loads all of my posts and actu­ally calls the method to dis­play the RSS. Short and sweet, as follows.

LoadPosts();
    $blog->PrintRSS();
?>

That’s it, works per­fectly. What we have is a dynam­i­cally cre­ated, RSS for­mat­ted XML file. It’s avail­able at dev.slashblogger.com/rss.php for now and I’ve tried it out in Google Reader. To be hon­est, I expected it to be more advanced than this. But the job is done.

Resources

PHP and RSS: Get­ting it together
RSS at Wikipedia
RSS 2.0 Specification

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