PHP - getElementsByTagName('rsslink') 结果不一致的 RSS 提要

Question

I am trying to capture useful RSS feeds from different journals using getElementsByTagName('rsslink'). The following code gets the rss feeds for LINK1 but not for LINK2. Both links show similar xml pages when opened in a browser. I cannot figure out why the code does not capture the feeds for LINK2.

<?php
      //$journalLink = 'https://onlinelibrary.wiley.com/rss/journal/10.1002/(ISSN)1944-7973'; //LINK 1
      $journalLink = 'https://onlinelibrary.wiley.com/feed/2199160x/most-recent'; // LINK 2
      
      $rss = new DOMDocument();
      $rss->load($journalLink);
      $feed = array();
      foreach ($rss->getElementsByTagName('item') as $node) {
          $item = array (
              'title' => $node->getElementsByTagName('title')->item(0)->nodeValue,
              'desc' => $node->getElementsByTagName('description')->item(0)->nodeValue,
              'link' => $node->getElementsByTagName('link')->item(0)->nodeValue,
          );
          array_push($feed, $item);
      } //foreach 
      $noRSSItem  = count($feed);
      echo "noRSSItem: $noRSSItem  <br/>"; 
?> 

Answer 1

`The second url uses the Atom namespace for the item link element. Atom allows for multiple links with different relations and types.

The easiest way is to use Xpath expressions.

$document = new DOMDocument();
$document->load($journalLink);
$xpath = new DOMXpath($document);
// register a prefix for the Atom namespace
$xpath->registerNamespace('a', 'http://www.w3.org/2005/Atom');

// xpath expression can include count and conditions
// check if the amount of item elements is zero
$noRSSItem = $xpath->evaluate('count(//item) = 0');

$feed = array();
foreach ($xpath->evaluate('//item') as $itemNode) {
    $feed[] = [
        // fetch the content of the first title child element
        'title' => $xpath->evaluate('string(title)', $itemNode),
        // same for description
        'desc' => $xpath->evaluate('string(description)', $itemNode),
        // fetch the 
        'link' => $xpath->evaluate(
            'string(link|a:link[@rel="self" and @type="application/atom+xml"]/@href)', 
            $itemNode
        ),
    ];
}

var_dump($feed);

Xpath Step By Step

• Atom 'link' child elements:
  a:link
• with specific attributes:
  a:link[@rel="self" and @type="application/atom+xml"]
• the 'href' attribute:
  a:link[@rel="self" and @type="application/atom+xml"]/@href
• alternativ fetch RSS (no namespace) link child elements:
  link|a:link[@rel="self" and @type="application/atom+xml"]/@href
• Cast to string:
  string(link|a:link[@rel="self" and @type="application/atom+xml"]/@href)