A simple Pico CMS plugin for HTTP caching.

HttpPageCaching.php

<?php

/**
 * Pico HTTP page caching plugin
 *
 * Web server (well known are Apache2 and Nginx) come with
 * mod_cache and mod_expires specialize for static files.
 * Last-Modified HTTP header is part of it.
 *
 * This plugins gives more control on Pico http page caching.
 * 
 * @author Hexat
 * @license DBAD
 * @version 0.0.2
 */
class HttpPageCaching extends AbstractPicoPlugin
{
    const API_VERSION = 2;
  
    public function onMetaParsed(array &$pageData)
    {
        // Should it be cached?
        $doCache = isset($pageData['httpCaching']) ? $pageData['httpCaching'] : null;
        if ($doCache !== true || (is_null($doCache) && ($this->getPluginConfig('global', false) !== true))) {
            return;
        }

        // Get lastModification time
        if (!isset($pageData['last_modified'])) {
            if (isset($pageData['meta']['last_modified'])) {
                $pageData['last_modified'] = $pageData['meta']['last_modified'];
            } elseif (isset($pageData['httpCaching']['last_modified'])) {
                $pageData['last_modified'] = $pageData['httpCaching']['last_modified'];
            } if (is_file($this->getRequestFile())) {
                $pageData['last_modified'] = filemtime($this->getRequestFile());
            }
        }

        // Read client-side HTTP headers for cache
        if (!is_null($pageData['last_modified']) && isset($_SERVER['HTTP_IF_MODIFIED_SINCE']) && $pageData['last_modified'] <= strtotime($_SERVER['HTTP_IF_MODIFIED_SINCE'])) {
            header('HTTP/1.1 304 Not Modified');
            exit;
        }

        // Set headers
        $pramaCache = (isset($pageData['httpCaching']['pragma'])) ? $pageData['httpCaching']['pragma'] : 'public';
        header('Pragma: '. $pramaCache);
        if (isset($pageData['httpCaching']['expiration'])) {
            $maxAge = $pageData['httpCaching']['expiration'] - $_SERVER['REQUEST_TIME'];
            header('Cache-Control: max-age='.$maxAge.', public');
            header('Expires: '.gmdate('D, d M Y H:i:s', $pageData['httpCaching']['expiration']).' GMT');
        }
        if (isset($pageData['last_modified']) && !is_null($pageData['last_modified'])) {
            header('Last-modified: '.gmdate('D, d M Y H:i:s', $pageData['last_modified']).' GMT');
        }
    }
}

Usage:

Cache individual page

# file: content/yourpage.md

# If it isn't defined, then it returns `null` which means disabled. Set true to cache.
httpCaching: true

Cache page globally by default

# file: config/config.yml

# Applies http cache on page with `httpCaching: null`.
HttpPageCaching:
  global: true