Trouble creating a valid RSS feed in PHP - php

Question

I'm trying to get an RSS feed, change some text, and then serve it again as an RSS feed. However, the code I've written doesn't validate properly. I get these errors:
line 3, column 0: Missing rss attribute: version
line 14, column 6: Undefined item element: content (10 occurrences)
Here is my code:
<?php
header("Content-type: text/xml");
echo "<?xml version='1.0' encoding='UTF-8'?>
<?xml-stylesheet type='text/xsl'?>
<?xml-stylesheet type='text/xsl' media='screen'
href='/~d/styles/rss2full.xsl'?>
<rss xmlns:content='http://purl.org/rss/1.0/modules/content/'>
<channel>
<title>Blaakdeer</title>
<description>Blog RSS</description>
<language>en-us</language>
";
$html = "";
$url = "http://feeds.feedburner.com/vga4a/mPSm";
$xml = simplexml_load_file($url);
for ($i = 0; $i < 10; $i++){
$title = $xml->channel->item[$i]->title;
$description = $xml->channel->item[$i]->description;
$content = $xml->channel->item[$i]->children("content", true);
$content = preg_replace("/The post.*/","", $content);
echo "<item>
<title>$title</title>
<description>$description</description>
<content>$content</content>
</item>";
}
echo "</channel></rss>";

Answer 1

Just as you don't treat XML as a string when parsing it, you don't treat it as as string when you create it. Use the proper tools to create your XML; in this case, the DomDocument class.
You had a number of problems with your XML; biggest is that you were creating a <content> element, but the original RSS had a <content:encoded> element. That means the element name is encoded but it's in the content namespace. Big difference between that and an element named content. I've added comments to explain the other steps.
<?php
// create the XML document with version and encoding
$xml = new DomDocument("1.0", "UTF-8");
$xml->formatOutput = true;
// add the stylesheet PI
$xml->appendChild(
$xml->createProcessingInstruction(
'xml-stylesheet',
'type="text/xsl" media="screen" href="/~d/styles/rss2full.xsl"'
)
);
// create the root element
$root = $xml->appendChild($xml->createElement('rss'));
// add the version attribute
$v = $root->appendChild($xml->createAttribute('version'));
$v->appendChild($xml->createTextNode('2.0'));
// add the namespace
$root->setAttributeNS(
'http://www.w3.org/2000/xmlns/',
'xmlns:content',
'http://purl.org/rss/1.0/modules/content/'
);
// create some child elements
$ch = $root->appendChild($xml->createElement('channel'));
// specify the text directly as second argument to
// createElement because it doesn't need escaping
$ch->appendChild($xml->createElement('title', 'Blaakdeer'));
$ch->appendChild($xml->createElement('description', 'Blog RSS'));
$ch->appendChild($xml->createElement('language', 'en-us'));
$url = "http://feeds.feedburner.com/vga4a/mPSm";
$rss = simplexml_load_file($url);
for ($i = 0; $i < 10; $i++) {
if (empty($rss->channel->item[$i])) {
continue;
}
$title = $rss->channel->item[$i]->title;
$description = $rss->channel->item[$i]->description;
$content = $rss->channel->item[$i]->children("content", true);
$content = preg_replace("/The post.*/","", $content);
$item_el = $ch->appendChild($xml->createElement('item'));
$title_el = $item_el->appendChild($xml->createElement('title'));
// this stuff is unknown so it has to be escaped
// so have to create a separate text node
$title_el->appendChild($xml->createTextNode($title));
$desc_el = $item_el->appendChild($xml->createElement('description'));
// the other alternative is to create a cdata section
$desc_el->appendChild($xml->createCDataSection($description));
// the content:encoded element is not the same as a content element
// the element must be created with the proper namespace prefix
$cont_el = $item_el->appendChild(
$xml->createElementNS(
'http://purl.org/rss/1.0/modules/content/',
'content:encoded'
)
);
$cont_el->appendChild($xml->createCDataSection($content));
}
header("Content-type: text/xml");
echo $xml->saveXML();

Answer 2

The first error is just a missing attribute, easy enough:
<rss version="2.0" ...>
For the <p> and other HTML elements, you need to escape them. The file should look like this:
<p>...
There are other ways, but this is the easiest way. In PHP you can just call a function to encode entities.
$output .= htmlspecialchars(" <p>Paragraph</p> ");
As for the <content> tag problem, it should be <description> instead. The <content> tag currently generates two errors. Changing it to <description> in both places should fix both errors.
Otherwise it looks like you understand the basics. You <open> and </close> tags and those have to match. You can also use what is called empty tags: <empty/> which exist on their own but to not include content and no closing tag.