无法在PHP中创建有效的RSS源

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();