WP RSS 2.0 Image Enclosure with File Size

wp-rss2-image-enclosure.php

<?php
/**
 * Wordpress RSS Image Enclosure
 *
 * Wrap ONLY the featured image inside 'enclosure' tags.
 *
 * @author Davey Jacobson
 * @link https://www.daveyjake.dev
 *
 * @package DJ_Dev
 */

defined( 'ABSPATH' ) || exit;

// Filter the posts before they're sent to the RSS feed.
add_filter( 'pre_get_posts', 'feed_filter' );

/**
 * Apply this code only to the RSS feed.
 *
 * @since 1.0.0
 * 
 * @param WP_Query $query The current WP_Query instance.
 *
 * @return WP_Query|void Return modified feed if successful. Unmodified if not.
 */
function feed_filter( $query ) {
    if ( $query->is_feed ) {
        add_filter( 'rss2_item', 'feed_content_filter');
    }

    return $query;
}

/**
 * Add an enclosure to a wordpress RSS feed using the first image of the post
 * [with its actual length attribute value] via {@see 'pre_get_posts'}.
 *
 * @global WP_Post|object $post Current post object.
 */
function feed_content_filter() {
    global $post;

    $args = array(
        'order'          => 'ASC',
        'post_type'      => 'attachment',
        'post_parent'    => $post->ID,
        'post_mime_type' => 'image',
        'post_status'    => null,
        'posts_per_page' => 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 );
            $size  = remote_file_size( $image[0], $attachment->ID );
        }
    }

    if ( ! empty( $size ) && is_wp_error( $size ) ) {
        echo '<error>' . esc_html( $size->get_error_message() ) . '</error>';
    } elseif ( isset( $image[0] ) ) {
        echo '<enclosure url="' . esc_url( trim( $image[0] ) ) . '" length="' . absint( trim( $size ) ) . '" type="' . esc_attr( $mime ) . '"/>';
    }
}

/**
 * Get the remote file size.
 *
 * @author Resalat Haque
 * @link http://www.w3bees.com/2013/03/get-remote-file-size-using-php.html
 *
 * @param string $url           Remote file URL.
 * @param int    $attachment_id Fallback in case URL is not valid.
 * 
 * @return int File size in bytes.
 */
function remote_file_size( $url, $attachment_id = 0 ) {
    // Default file size will always be 0.
    $size = 0;

    // Make sure URL is valid.
    if ( wp_http_validate_url( $url ) ) {
        // Get all header information.
        $data = get_headers( $url, true );

        // Look up validity.
        if ( isset( $data['Content-Length'] ) ) {
            // Return file size.
            $size += (int) $data['Content-Length'];
            
            return $size;
        }
    } elseif ( $attachment_id != 0 ) {
        // If we're here, it's because we know the file exists but not the URL.
        $file = get_attached_file( $attachment_id );

        // Return file size.
        $size += (int) filesize( $file );

        return $size;
    }

    return new WP_Error( 'invalid_image', __( "The image URL `{$url}` was invalid or not found." ) );
}