fetch_feed() │ WP 2.8.0

An example that gets and displays links to an existing RSS feed. In the example we limit the output to the last 5 posts in the feed.

<h2>Latest news from blog.ru</h2>

<?php
// make fetch_feed() available, usually this (string) is not needed
include_once ABSPATH . WPINC . '/feed.php';

// Get a feed and create a SimplePie object from it.
$rss = fetch_feed( 'http://blog.ru/feed' );

// Check that the object was successfully created
if ( ! is_wp_error( $rss ) ) {

	// Specify that we want to output a maximum of 5 feed posts
	$maxitems = $rss->get_item_quantity( 5 );

	// create an array of all feed posts, starting from the first post (0 is the beginning)
	$rss_items = $rss->get_items( 0, $maxitems );
}
?>

<ul>
	<?php
	if ( $maxitems == 0 ) {
		echo '<li>No posts.</li>';
	}
	// Run through the array and display a link to each post
	else { 
		foreach ( $rss_items as $item ) { 
			?>
			<li>
				<a href='<?php echo esc_url( $item->get_permalink() ); ?>'
				   title='<?php echo 'Posted ' . $item->get_date( 'j F Y | g:i a' ); ?>'
				>
					<?php echo esc_html( $item->get_title() ); ?>
				</a>
			</li>
			<?php
		}
	}
	?>
</ul>

Let's read the feed http://mysite.com/feed/ and get the first 5 posts from it.

include_once ABSPATH . WPINC . '/feed.php';

$rss = fetch_feed( 'http://mysite.com/feed/' );

$rss_items = $rss->get_items( 0, $rss->get_item_quantity(5) );

if ( ! $rss_items ) {
	echo 'no items';
}
else {
	foreach ( $rss_items as $item ) {
		echo '<p><a href="' . $item->get_permalink() . '">' . $item->get_title() . '</a></p>';
	}
}

The result of fetching a feed is cached for 12 hours. To change cache time for this function, you can use hook wp_feed_cache_transient_lifetime.

add_filter( 'wp_feed_cache_transient_lifetime', 'speed_up_feed', 10, 2 );

function speed_up_feed( $interval, $url ) {

	if( 'http://myexample.com/feed/' === $url ){
		return 3600; // 1 hour
	}

	return $interval;
}

In the process of manipulating the feed, it is necessary to disable the caching, otherwise it will interfere a lot. This can be done through the hook wp_feed_options.

// disable feeds caching. Only if WP_DEBUG development mode is enabled
if( defined('WP_DEBUG') && WP_DEBUG ){

	add_action( 'wp_feed_options', function( &$feed ){
		$feed->enable_cache(false);
	} );
}

Feed caching does not work with constant WP_DEBUG enabled

Keep in mind that if constant WP_DEBUG is enabled, the feed is not cached. This is the kernel code that works:

function do_not_cache_feeds(&$feed) {
	$feed->enable_cache(false);
}

if ( defined('WP_DEBUG') && WP_DEBUG ) {
	add_action( 'wp_feed_options', 'do_not_cache_feeds' );
}

Browser caching

Also note that the caching can occur in the browser, to bypass it, refresh the page via ctrl + F5. Or you can add such a hook:

// disable caching in the baruser for feed queries
add_filter( 'wp_headers', function( $headers ){

	if( !empty( $GLOBALS['wp']->query_vars['feed'] ) ){
		unset( $headers['ETag'], $headers['Last-Modified'] );
	}

	return $headers;
} );

To run the code, add the parameter ?clear_feeds_cache to the URL.

// Cleaning the cache of all feeds in WordPress
if( isset( $_GET['clear_feeds_cache'] ) ){

	global $wpdb;

	$cleared = $wpdb->query( "DELETE FROM $wpdb->options WHERE option_name LIKE '\_transient%\_feed\_%'" );

	die( var_dump( $cleared ) );
}