WP Custom REST Endpoint Cache with Transients.

code.php

<?php

class WPE_Simple_REST_Cache {

    const CACHE_TTL_DEFAULT = 300; // 5 minutes
    const CACHE_PREFIX = 'wpe_rest_cache_';

    /**
     * Initialise cache hooks.
     */
    public static function init() {
        add_action('init', [__CLASS__, 'register_cache_clear_hooks']);
        add_action('init', [__CLASS__, 'maybe_handle_manual_clear'], 99);
    }

    /**
     * Generate a unique cache key from a REST request.
     *
     * @param WP_REST_Request $request The REST request object.
     * @return string Cache key.
     */
    public static function get_cache_key($request) {
        $method = $request->get_method();
        $route = $request->get_route();
        $params = $request->get_params();

        $base = strtoupper($method) . '|' . $route . '|' . json_encode($params);
        return self::CACHE_PREFIX . md5($base);
    }

    /**
     * Get cached data for a request.
     *
     * @param WP_REST_Request $request
     * @return mixed|false
     */
    public static function get($request) {
        return get_transient(self::get_cache_key($request));
    }

    /**
     * Set cached data for a request.
     *
     * @param WP_REST_Request $request
     * @param mixed $data
     * @param int $TTL Optional. Cache duration in seconds.
     * @return bool
     */
    public static function set($request, $data, $TTL = self::CACHE_TTL_DEFAULT) {
        return set_transient(self::get_cache_key($request), $data, $TTL);
    }

    /**
     * Delete cache for a specific request.
     *
     * @param WP_REST_Request $request
     * @return bool
     */
    public static function delete($request) {
        return delete_transient(self::get_cache_key($request));
    }

    /**
     * Delete all cache entries created by this class.
     */
    public static function delete_all() {
        global $wpdb;

        $prefix = is_multisite() ? '_site_transient_' : '_transient_';
        $like_main = $wpdb->esc_like($prefix . self::CACHE_PREFIX) . '%';
        $like_timeout = $wpdb->esc_like($prefix . 'timeout_' . self::CACHE_PREFIX) . '%';

        $wpdb->query(
            $wpdb->prepare(
                "DELETE FROM {$wpdb->options} 
                 WHERE option_name LIKE %s OR option_name LIKE %s",
                $like_main,
                $like_timeout
            )
        );
    }

    /**
     * Register hooks for clearing cache when popular caching plugins flush their caches.
     */
    public static function register_cache_clear_hooks() {
        // Core hook for manual/custom use
        add_action('wpe_rest_cache_clear', [__CLASS__, 'delete_all']);

        // WP Rocket
        add_action('rocket_clear_cache', [__CLASS__, 'delete_all']);
        add_action('rocket_rucss_purge_complete', [__CLASS__, 'delete_all']);

        // W3 Total Cache
        add_action('w3tc_flush_all', [__CLASS__, 'delete_all']);

        // LiteSpeed Cache
        add_action('litespeed_purge_all', [__CLASS__, 'delete_all']);

        // FlyingPress
        add_action('flying_press_clear_cache_all', [__CLASS__, 'delete_all']);

        // WP Super Cache
        add_action('wp_cache_cleared', [__CLASS__, 'delete_all']);

        // Cache Enabler (KeyCDN)
        add_action('ce_action_clear_cache', [__CLASS__, 'delete_all']);

        // Autoptimize
        add_action('autoptimize_action_cachepurged', [__CLASS__, 'delete_all']);

        // Swift Performance
        add_action('swift_performance_clear_cache', [__CLASS__, 'delete_all']);

        // Hummingbird
        add_action('wphb_clear_cache', [__CLASS__, 'delete_all']);

        // Breeze (by Cloudways)
        add_action('breeze_clear_cache', [__CLASS__, 'delete_all']);

        // SG Optimizer (SiteGround)
        add_action('sg_cachepress_purge_cache', [__CLASS__, 'delete_all']);

        // NitroPack (less consistent, but safe to include)
        add_action('nitropack_clear_cache_all', [__CLASS__, 'delete_all']);
    }

     /**
     * Detect URL param and trigger full cache clear.
     */
    public static function maybe_handle_manual_clear() {
        if (isset($_GET['wpe_clear_rest_cache'])) {
            self::delete_all();
        }
    }
}

add_action('init', ['WPE_Simple_REST_Cache', 'init']);