=> 'application/rss+xml',
		'rss-http' => 'text/xml',
		'atom'     => 'application/atom+xml',
		'rdf'      => 'application/rdf+xml',
	);

	$content_type = ( ! empty( $types[ $type ] ) ) ? $types[ $type ] : 'application/octet-stream';

	/**
	 * Filters the content type for a specific feed type.
	 *
	 * @since 2.8.0
	 *
	 * @param string $content_type Content type indicating the type of data that a feed contains.
	 * @param string $type         Type of feed. Possible values include 'rss', rss2', 'atom', and 'rdf'.
	 */
	return apply_filters( 'feed_content_type', $content_type, $type );
}

/**
 * Builds SimplePie object based on RSS or Atom feed from URL.
 *
 * @since 2.8.0
 *
 * @param string|string[] $url URL of feed to retrieve. If an array of URLs, the feeds are merged
 *                             using SimplePie's multifeed feature.
 *                             See also {@link http://simplepie.org/wiki/faq/typical_multifeed_gotchas}
 * @return SimplePie\SimplePie|WP_Error SimplePie object on success or WP_Error object on failure.
 */
function fetch_feed( $url ) {
	if ( ! class_exists( 'SimplePie\SimplePie', false ) ) {
		require_once ABSPATH . WPINC . '/class-simplepie.php';
	}

	require_once ABSPATH . WPINC . '/class-wp-feed-cache-transient.php';
	require_once ABSPATH . WPINC . '/class-wp-simplepie-file.php';
	require_once ABSPATH . WPINC . '/class-wp-simplepie-sanitize-kses.php';

	$feed = new SimplePie\SimplePie();

	$feed->set_sanitize_class( 'WP_SimplePie_Sanitize_KSES' );
	/*
	 * We must manually overwrite $feed->sanitize because SimplePie's constructor
	 * sets it before we have a chance to set the sanitization class.
	 */
	$feed->sanitize = new WP_SimplePie_Sanitize_KSES();

	// Register the cache handler using the recommended method for SimplePie 1.3 or later.
	if ( method_exists( 'SimplePie_Cache', 'register' ) ) {
		SimplePie_Cache::register( 'wp_transient', 'WP_Feed_Cache_Transient' );
		$feed->set_cache_location( 'wp_transient' );
	} else {
		// Back-compat for SimplePie 1.2.x.
		require_once ABSPATH . WPINC . '/class-wp-feed-cache.php';
		$feed->set_cache_class( 'WP_Feed_Cache' );
	}

	$feed->set_file_class( 'WP_SimplePie_File' );

	$feed->set_feed_url( $url );
	/** This filter is documented in wp-includes/class-wp-feed-cache-transient.php */
	$feed->set_cache_duration( apply_filters( 'wp_feed_cache_transient_lifetime', 12 * HOUR_IN_SECONDS, $url ) );

	/**
	 * Fires just before processing the SimplePie feed object.
	 *
	 * @since 3.0.0
	 *
	 * @param SimplePie\SimplePie $feed SimplePie feed object (passed by reference).
	 * @param string|string[]     $url  URL of feed or array of URLs of feeds to retrieve.
	 */
	do_action_ref_array( 'wp_feed_options', array( &$feed, $url ) );

	$feed->init();
	$feed->set_output_encoding( get_bloginfo( 'charset' ) );

	if ( $feed->error() ) {
		return new WP_Error( 'simplepie-error', $feed->error() );
	}

	return $feed;
}
<br />
<b>Fatal error</b>:  require(): Failed opening required '/home/kordian1/domains/ostrabrama.pl/public_html/wp-includes/class-wp-http-streams.php' (include_path='.:/opt/alt/php74/usr/share/pear') in <b>/home/kordian1/domains/ostrabrama.pl/public_html/wp-settings.php</b> on line <b>270</b><br />
<br />
<b>Fatal error</b>:  Uncaught Error: Call to a member function set() on null in /home/kordian1/domains/ostrabrama.pl/public_html/wp-includes/l10n.php:857
Stack trace:
#0 /home/kordian1/domains/ostrabrama.pl/public_html/wp-includes/l10n.php(960): load_textdomain('default', '/home/kordian1/...', 'pl_PL')
#1 /home/kordian1/domains/ostrabrama.pl/public_html/wp-includes/class-wp-fatal-error-handler.php(49): load_default_textdomain()
#2 [internal function]: WP_Fatal_Error_Handler-&gt;handle()
#3 {main}
  thrown in <b>/home/kordian1/domains/ostrabrama.pl/public_html/wp-includes/l10n.php</b> on line <b>857</b><br />