fair-plugin/inc/pings/namespace.php

<?php
/**
 * Replaces Pingomatic with IndexNow.
 *
 * @package FAIR
 */

namespace FAIR\Pings;

/**
 * Bootstrap.
 */
function bootstrap() {
	add_filter( 'pre_option_ping_sites', __NAMESPACE__ . '\\remove_pingomatic_from_ping_sites' );
	add_filter( 'query_vars', __NAMESPACE__ . '\\register_query_vars' );
	add_action( 'init', __NAMESPACE__ . '\\get_indexnow_key' );
	add_action( 'init', __NAMESPACE__ . '\\add_key_rewrite_rule' );
	add_action( 'template_redirect', __NAMESPACE__ . '\\handle_key_file_request' );
	add_action( 'transition_post_status', __NAMESPACE__ . '\\ping_indexnow', 10, 3 );
}

/**
 * Register query vars.
 *
 * @param array $vars Array of query vars.
 * @return array Modified array of query vars.
 */
function register_query_vars( $vars ) {
	$vars[] = 'fair_indexnow_key';
	return $vars;
}

/**
 * Remove pingomatic.com from the ping_sites option.
 *
 * @param string $value The ping_sites option value.
 */
function remove_pingomatic_from_ping_sites( $value ) {
	$value = str_replace( 'http://rpc.pingomatic.com/', '', $value );
	$value = str_replace( "\n\n", "\n", trim( $value, "\n" ) );
	return $value;
}

/**
 * Generate and store the IndexNow key if it doesn't exist.
 *
 * @return string Unique site key.
 */
function get_indexnow_key() : string {
	$key = get_option( 'fair_indexnow_key' );

	if ( ! $key ) {
		// Generate a random key that meets IndexNow requirements.
		// Must be 8-128 hexadecimal characters (a-f, 0-9).
		$key = strtolower( wp_generate_password( 40, false, false ) );

		update_option( 'fair_indexnow_key', $key );

		// Flush the rewrite rules.
		flush_rewrite_rules();
	}

	return $key;
}

/**
 * Add rewrite rule for the IndexNow key file.
 */
function add_key_rewrite_rule() {
	$key = get_indexnow_key();

	add_rewrite_rule(
		'fair-indexnow-' . $key . '$',
		'index.php?fair_indexnow_key=' . $key,
		'top'
	);
}

/**
 * Handle the IndexNow key file request.
 */
function handle_key_file_request() {
	if ( ! get_query_var( 'fair_indexnow_key' ) ) {
		return;
	}

	$key = get_indexnow_key();
	if ( ! $key || $key !== get_query_var( 'fair_indexnow_key' ) ) {
		$error = 'Invalid key: ' . get_query_var( 'fair_indexnow_key' );
		wp_die( esc_html( $error ), 'IndexNow Key Error', [ 'response' => 403 ] );
		return;
	}

	// Set the content type to text/plain.
	header( 'Content-Type: text/plain' );
	header( 'Expires: ' . gmdate( 'D, d M Y H:i:s', time() + YEAR_IN_SECONDS ) . ' GMT' );
	header( 'Cache-Control: public, max-age=' . YEAR_IN_SECONDS );

	// Output the key.
	echo esc_html( $key );
	exit;
}

/**
 * Ping IndexNow when a post status changes.
 *
 * @param string  $new_status New post status.
 * @param string  $old_status Old post status.
 * @param WP_Post $post       Post object.
 */
function ping_indexnow( $new_status, $old_status, $post ) : void {
	/*
	 * Skip if post type isn't viewable.
	 *
	 * The post type shouldn't change under normal circumstances,
	 * so it's safe to assume that both the old and new post are
	 * not viewable.
	 */
	if ( ! is_post_type_viewable( $post->post_type ) ) {
		return;
	}

	/*
	 * Skip for revisions and autosaves.
	 *
	 * The IndexNow ping for revisions will be handled by the
	 * parent post's transition_post_status hook.
	 */
	if ( wp_is_post_revision( $post ) || wp_is_post_autosave( $post ) ) {
		return;
	}

	/*
	 * Skip if both old and new statuses are private.
	 *
	 * The page will have been a 404 before and after.
	 *
	 * For pages that are newly a 404, still ping IndexNow
	 * to encourage removal of the URL from search engines.
	 */
	if (
		! is_post_status_viewable( $new_status )
		&& ! is_post_status_viewable( $old_status )
	) {
		return;
	}

	/*
	 * Prevent double pings for block editor legacy meta boxes.
	 */
	if (
		// phpcs:ignore WordPress.Security.NonceVerification.Recommended
		isset( $_GET['meta-box-loader'] )
		// phpcs:ignore WordPress.Security.NonceVerification.Recommended, WordPress.PHP.StrictComparisons.LooseComparison -- form input.
		&& '1' == $_GET['meta-box-loader']
	) {
		return;
	}

	$key = get_option( 'fair_indexnow_key' );
	if ( ! $key ) {
		return;
	}

	$url = get_permalink( $post );
	if ( ! $url ) {
		return;
	}

	// Allow for filtering the URL list.
	$url_list = apply_filters( 'fair_indexnow_url_list', [ $url ] );

	// Allow for filtering the key location.
	$key_location = apply_filters( 'fair_indexnow_key_location', trailingslashit( home_url( 'fair-indexnow-' . $key ) ) );

	// The "false" on the end of the x-source-info header determines whether this is a manual submission or not.
	$data = [
		'host'        => wp_parse_url( home_url(), PHP_URL_HOST ),
		'key'         => $key,
		'keyLocation' => $key_location,
		'urlList'     => $url_list,
	];
	$request = [
		'body'    => wp_json_encode( $data, JSON_UNESCAPED_SLASHES ),
		'headers' => [
			'Content-Type'  => 'application/json; charset=utf-8',
			'x-source-info' => 'https://example.com/fair-wp/indexnow/false',   // TODO: replace example.com with the domain we end up using.
		],
	];

	// Ping IndexNow.
	$response = wp_remote_post(
		'https://api.indexnow.org/indexnow',
		$request
	);

	// Log the response for debugging. As per https://www.indexnow.org/documentation#response, either 200 or 202 is acceptable.
	if ( is_wp_error( $response ) ) {
		/* phpcs:ignore WordPress.PHP.DevelopmentFunctions.error_log_print_r */
		error_log( 'IndexNow ping failed: ' . $response->get_error_message() . print_r( $request, true ) );
		return;
	}

	$status = wp_remote_retrieve_response_code( $response );
	if ( ! in_array( $status, [ 200, 202 ], true ) ) {
		/* phpcs:ignore WordPress.PHP.DevelopmentFunctions.error_log_print_r */
		error_log( 'IndexNow ping failed: ' . $status . print_r( $request, true ) );
	}
}