tiny-cache.php

<?php
/*
Plugin name: Tiny cache (MU)
Description: Cache post content in persistent object cache.
Version: 0.5.2
Plugin URI: https://developer.wordpress.org/reference/functions/the_content/
*/

/**
 * Display content from the object cache.
 */
function the_content_cached( $more_link_text = null, $strip_teaser = false ) {

    $post_id = get_the_ID();
    // Learned from W3TC Page Cache rules and WP Super Cache rules
    if ( ! wp_using_ext_object_cache() /* Object cache is unavailable */
        || is_user_logged_in() /* User is logged in */
        || ! ( isset( $_SERVER['REQUEST_METHOD'] ) && 'GET' === $_SERVER['REQUEST_METHOD'] ) /* Not a GET request */ // WPCS: input var ok.
        || ! $post_id /* Not possible to tie content to post ID */
        || ( defined( 'DONOTCACHEPAGE' ) && DONOTCACHEPAGE ) /* DO-NOT-CACHE tag present */
        || ! ( null === $more_link_text && false === $strip_teaser ) /* Pull requests are welcome! */
    ) {
        the_content( $more_link_text, $strip_teaser );

        return;
    }

    $found  = null;
    $cached = wp_cache_get( $post_id, 'the_content', false, $found );

    // Cache hit
    if ( $found ) {
        print $cached; // WPCS: XSS ok.

        return;
    }

    // Cache miss
    $save_to_cache = false;
    $post          = get_post( $post_id );
    // Public post
    if ( true === is_object( $post ) ) {
        if ( 'publish' === $post->post_status && empty( $post->post_password ) ) {
            $save_to_cache = true;
        }
    }

    // Print and save the content
    if ( true === $save_to_cache ) {
        add_filter( 'the_content', 'tiny_cache_save_the_content', PHP_INT_MAX );
    }
    the_content( $more_link_text, $strip_teaser );
    if ( true === $save_to_cache ) {
        remove_filter( 'the_content', 'tiny_cache_save_the_content', PHP_INT_MAX );
    }
}

/**
 * Retrieve content from the object cache.
 */
function get_the_content_cached( $more_link_text = null, $strip_teaser = false ) {

    $post_id = get_the_ID();
    // Learned from W3TC Page Cache rules and WP Super Cache rules
    if ( ! wp_using_ext_object_cache() /* Object cache is unavailable */
        || is_user_logged_in() /* User is logged in */
        || ! ( isset( $_SERVER['REQUEST_METHOD'] ) && 'GET' === $_SERVER['REQUEST_METHOD'] ) /* Not a GET request */ // WPCS: input var ok.
        || ! $post_id /* Not possible to tie content to post ID */
        || ! ( defined( 'DONOTCACHEPAGE' ) && DONOTCACHEPAGE ) /* DO-NOT-CACHE tag present */
        || ! ( null === $more_link_text && false === $strip_teaser ) /* Pull requests are welcome! */
    ) {
        return get_the_content( $more_link_text, $strip_teaser );
    }

    $found  = null;
    $cached = wp_cache_get( $post_id, 'get_the_content', false, $found );

    // Cache hit
    if ( $found ) {
        return $cached;
    }

    // Cache miss
    $save_to_cache = false;
    $post          = get_post( $post_id );
    // Public post
    if ( true === is_object( $post ) ) {
        if ( 'publish' === $post->post_status && empty( $post->post_password ) ) {
            $save_to_cache = true;
        }
    }

    $content = get_the_content( $more_link_text, $strip_teaser );
    if ( true === $save_to_cache ) {
        $message_tpl = '<!-- Cached content generated by Tiny cache on %s -->';
        $timestamp   = gmdate( 'c' );
        $message     = sprintf( $message_tpl, esc_html( $timestamp ) );
        wp_cache_set( $post_id, $content . $message, 'get_the_content', DAY_IN_SECONDS );
    }

    return $content;
}


/**
 * Save the content to the object cache.
 */
function tiny_cache_save_the_content( $content ) {

    $post_id = get_the_ID();
    // Tie content to post ID
    if ( $post_id ) {
        $message_tpl = '<!-- Cached content generated by Tiny cache on %s -->';
        $timestamp   = gmdate( 'c' );
        $message     = sprintf( $message_tpl, esc_html( $timestamp ) );
        wp_cache_set( $post_id, $content . $message, 'the_content', DAY_IN_SECONDS );
    }

    return $content;
}

/**
 * Delete cached content by ID.
 */
function tiny_cache_delete_the_content( $post_id ) {

    wp_cache_delete( $post_id, 'the_content' );
}

/**
 * Delete cached content on transition_post_status.
 */
function tiny_cache_post_transition( $new_status, $old_status, $post ) {

    // Post unpublished or published
    if ( ( 'publish' === $old_status && 'publish' !== $new_status )
        || ( 'publish' !== $old_status && 'publish' === $new_status )
    ) {
        tiny_cache_delete_the_content( $post->ID );
    }
}

/**
 * Hook cache delete actions.
 */
function tiny_cache_actions() {

    // Post ID is received
    add_action( 'publish_post', 'tiny_cache_delete_the_content', 0 );
    add_action( 'publish_phone', 'tiny_cache_delete_the_content', 0 );
    add_action( 'edit_post', 'tiny_cache_delete_the_content', 0 );
    add_action( 'delete_post', 'tiny_cache_delete_the_content', 0 );
    add_action( 'wp_trash_post', 'tiny_cache_delete_the_content', 0 );
    add_action( 'clean_post_cache', 'tiny_cache_delete_the_content', 0 );
    // Post as third argument
    add_action( 'transition_post_status', 'tiny_cache_post_transition', 10, 3 );
};

add_action( 'init', 'tiny_cache_actions' );