How to add an enclosure to a wordpress RSS feed using the first image of the post [with its actual length attribute value] - add to functions.php

Wordpress RSS 2.0 image enclosure [COMPLETE with IMG filesize included]

function feedFilter($query) {
	if ($query->is_feed) {
		add_filter('rss2_item', 'feedContentFilter');
		}
	return $query;
}
add_filter('pre_get_posts','feedFilter');

/* BEGIN SNIPPET
----------------------------------------- */
// Source URL: http://www.w3bees.com/2013/03/get-remote-file-size-using-php.html
// Original Author: Resalat Haque
/**
 * Get Remote File Size
 *
 * @param string $url as remote file URL
 * @return int as file size in byte
 */
function remote_file_size($url) {
	# Get all header information
	$data = get_headers($url, true);
	# Look up validity
	if (isset($data['Content-Length']))
		# Return file size
		return (int) $data['Content-Length'];
}
/* END SNIPPET
----------------------------------------- */
 
function feedContentFilter($item) {
	
	global $post;
	
	$args = array(
		'order'          => 'ASC',
		'post_type'      => 'attachment',
		'post_parent'    => $post->ID,
		'post_mime_type' => 'image',
		'post_status'    => null,
		'numberposts'    => 1,
	);
	$attachments = get_posts($args);
	if ($attachments) {
		foreach ($attachments as $attachment) {
			$image = wp_get_attachment_image_src($attachment->ID, 'large');
			$mime = get_post_mime_type($attachment->ID);
		}
	}

	if ($image) {
		echo '<enclosure url="'.$image[0].'" length="'.remote_file_size($image[0]).'" type="'.$mime.'"/>';
	} 
	return $item;
}