【カスタムフィード】WordPressでカスタムフィードを作成する方法

class My_RSS {

    public function __construct() {
        add_action( 'init', [$this, 'custom_feed'] );
    }

    /**
     * feedの登録
     */
    public function custom_feed() {
        add_feed( 'my_rss', [$this, 'load_feed_template']);
    }

    /**
     * feedの読み込み
     */
    public function load_feed_template() {
        $feed_template = plugins_url( 'feeds/my_rss.php', __FILE__ );
        load_template( $feed_template );
    }
}

<?php 
/**
 * my rss
 */

$post_args = [
    'post_type'            => 'post',
    'orderby'              => 'date',
    'order'                => 'DESC',
    'ignore_stickey_posts' => true,
    'posts_per_page'       => 20,
    'post_status'          => 'publish',
    'meta_query'           => [
        'relation' => 'OR',
        [
            'key'     => 'my_rss_display',
            'value'   => 'not_display',
            'compare' => '!='
        ],
        [
            'key'     => 'my_rss_display',
            'compare' => 'NOT EXISTS'
        ]
    ]
];
$query = new WP_Query( $post_args );

header( 'Content-Type: ' . feed_content_type( 'rss2' ) . '; charset=' . get_option( 'blog_charset' ), true );
echo '<?xml version="1.0" encoding="' . get_option( 'blog_charset' ) . '"?' . '>';
?>
<rss version="2.0"
xmlns:content="http://purl.org/rss/1.0/modules/content/"
     xmlns:dc="http://purl.org/dc/elements/1.1/"
     xmlns:media="http://search.yahoo.com/mrss/">
<channel>
    <title><?php wp_title_rss(); ?></title>
    <link><?php bloginfo_rss('url'); ?></link>
    <description><?php bloginfo_rss('description'); ?></description>
    <lastBuildDate><?php echo get_feed_build_date( 'r' ); ?></lastBuildDate>
    <pubDate><?php echo get_feed_build_date( 'r' ); ?></pubDate>
    <language><?php bloginfo_rss( 'language' ); ?></language>
    <ttl>1</ttl>
    <?php if ( $query->have_posts() ) : while ( $query->have_posts() ) : $query->the_post(); ?>
    <item>
        <title><?php the_title_rss(); ?></title>
        <link><?php the_permalink_rss(); ?></link>
        <pubDate><?php echo get_post_time( 'r', true, $post, false ); ?></pubDate>
        <description><![CDATA[<?php the_excerpt_rss(); ?>]]></description>
        <content:encoded><![CDATA[<?php the_content(); ?>]]></content:encoded>
    </item>
    <?php endwhile; endif; ?>
</channel>
</rss>

<?php
wp_reset_postdata();

function basic_auth( $auth_list, $realm = 'Restricted Area', $failed_text = '認証に失敗しました' ){
    if ( isset( $_SERVER['PHP_AUTH_USER'] ) && isset( $auth_list[$_SERVER['PHP_AUTH_USER']] ) ) {
        if ( $auth_list[$_SERVER['PHP_AUTH_USER']] == $_SERVER['PHP_AUTH_PW'] ) {
            return $_SERVER['PHP_AUTH_USER'];
        }
    }
    header( 'WWW-Authenticate: Basic realm="' . $realm . '"' );
    header( 'HTTP/1.0 401 Unauthorized' );
    header( 'Content-type: text/html; charset=' . mb_internal_encoding() );
    die( $failed_text );
}

function image_urlencode( $str ) {
    return preg_replace_callback(
    '/[^\x21-\x7e]+/',
    function( $matches ) {
        return urlencode( $matches[0] );
    },
    $str );
}