Source

File: wp-includes/widgets.php

function wp_widget_rss_process( $widget_rss, $check_feed = true ) {
	$items = (int) $widget_rss['items'];
	if ( $items < 1 || 20 < $items ) {
		$items = 10;
	}
	$url          = esc_url_raw( strip_tags( $widget_rss['url'] ) );
	$title        = isset( $widget_rss['title'] ) ? trim( strip_tags( $widget_rss['title'] ) ) : '';
	$show_summary = isset( $widget_rss['show_summary'] ) ? (int) $widget_rss['show_summary'] : 0;
	$show_author  = isset( $widget_rss['show_author'] ) ? (int) $widget_rss['show_author'] : 0;
	$show_date    = isset( $widget_rss['show_date'] ) ? (int) $widget_rss['show_date'] : 0;

	if ( $check_feed ) {
		$rss   = fetch_feed( $url );
		$error = false;
		$link  = '';
		if ( is_wp_error( $rss ) ) {
			$error = $rss->get_error_message();
		} else {
			$link = esc_url( strip_tags( $rss->get_permalink() ) );
			while ( stristr( $link, 'http' ) !== $link ) {
				$link = substr( $link, 1 );
			}

			$rss->__destruct();
			unset( $rss );
		}
	}

	return compact( 'title', 'url', 'link', 'items', 'error', 'show_summary', 'show_author', 'show_date' );
}