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<?php

/**
 * This is a lightweight proxy for serving images, generally meant to be used alongside SSL
 *
 * Simple Machines Forum (SMF)
 *
 * @package SMF
 * @author Simple Machines http://www.simplemachines.org
 * @copyright 2019 Simple Machines and individual contributors
 * @license http://www.simplemachines.org/about/smf/license.php BSD
 *
 * @version 2.1 RC1
 */

if (!defined('SMF'))
    define('SMF', 'proxy');

if (!defined('SMF_VERSION'))
    define('SMF_VERSION', '2.1 RC1');

if (!defined('SMF_FULL_VERSION'))
    define('SMF_FULL_VERSION', 'SMF ' . SMF_VERSION);

if (!defined('SMF_SOFTWARE_YEAR'))
    define('SMF_SOFTWARE_YEAR', '2019');

global $proxyhousekeeping;

/**
 * Class ProxyServer
 */
class ProxyServer
{
    /** @var bool $enabled Whether or not this is enabled */
    protected $enabled;

    /** @var int $maxSize The maximum size for files to cache */
    protected $maxSize;

    /** @var string $secret A secret code used for hashing */
    protected $secret;

    /** @var string The cache directory */
    protected $cache;

    /** @var int $maxDays until entries get deleted */
    protected $maxDays;

    /**
     * Constructor, loads up the Settings for the proxy
     *
     * @access public
     */
    public function __construct()
    {
        global $image_proxy_enabled, $image_proxy_maxsize, $image_proxy_secret, $cachedir, $sourcedir;

        require_once(dirname(__FILE__) . '/Settings.php');
        require_once($sourcedir . '/Subs.php');

        // Turn off all error reporting; any extra junk makes for an invalid image.
        error_reporting(0);

        $this->enabled = (bool) $image_proxy_enabled;
        $this->maxSize = (int) $image_proxy_maxsize;
        $this->secret = (string) $image_proxy_secret;
        $this->cache = $cachedir . '/images';
        $this->maxDays = 5;
    }

    /**
     * Checks whether the request is valid or not
     *
     * @access public
     * @return bool Whether the request is valid
     */
    public function checkRequest()
    {
        if (!$this->enabled)
            return false;

        // Try to create the image cache directory if it doesn't exist
        if (!file_exists($this->cache))
            if (!mkdir($this->cache) || !copy(dirname($this->cache) . '/index.php', $this->cache . '/index.php'))
                return false;

        // Basic sanity check
        $_GET['request'] = validate_iri($_GET['request']);

        // We aren't going anywhere without these
        if (empty($_GET['hash']) || empty($_GET['request']))
            return false;

        $hash = $_GET['hash'];
        $request = $_GET['request'];

        if (md5($request . $this->secret) != $hash)
            return false;

        // Ensure any non-ASCII characters in the URL are encoded correctly
        $request = iri_to_url($request);

        // Attempt to cache the request if it doesn't exist
        if (!$this->isCached($request))
            return $this->cacheImage($request);

        return true;
    }

    /**
     * Serves the request
     *
     * @access public
     * @return void
     */
    public function serve()
    {
        $request = $_GET['request'];
        $cached_file = $this->getCachedPath($request);
        $cached = json_decode(file_get_contents($cached_file), true);

        // Did we get an error when trying to fetch the image
        $response = $this->checkRequest();
        if ($response === -1)
        {
            // Throw a 404
            send_http_status(404);
            exit;
        }
        // Right, image not cached? Simply redirect, then.
        if ($response === 0)
        {
            $this::redirectexit($request);
        }

        $time = time();

        // Is the cache expired?
        if (!$cached || $time - $cached['time'] > ($this->maxDays * 86400))
        {
            @unlink($cached_file);
            if ($this->checkRequest())
                $this->serve();
            $this::redirectexit($request);
        }

        $eTag = '"' . substr(sha1($request) . $cached['time'], 0, 64) . '"';
        if (!empty($_SERVER['HTTP_IF_NONE_MATCH']) && strpos($_SERVER['HTTP_IF_NONE_MATCH'], $eTag) !== false)
        {
            send_http_status(304);
            exit;
        }

        // Make sure we're serving an image
        $contentParts = explode('/', !empty($cached['content_type']) ? $cached['content_type'] : '');
        if ($contentParts[0] != 'image')
            exit;

        $max_age = $time - $cached['time'] + (5 * 86400);
        header('content-type: ' . $cached['content_type']);
        header('content-length: ' . $cached['size']);
        header('cache-control: public, max-age=' . $max_age);
        header('last-modified: ' . gmdate('D, d M Y H:i:s', $cached['time']) . ' GMT');
        header('etag: ' . $eTag);
        echo base64_decode($cached['body']);
    }

    /**
     * Returns the request's hashed filepath
     *
     * @access public
     * @param string $request The request to get the path for
     * @return string The hashed filepath for the specified request
     */
    protected function getCachedPath($request)
    {
        return $this->cache . '/' . sha1($request . $this->secret);
    }

    /**
     * Check whether the image exists in local cache or not
     *
     * @access protected
     * @param string $request The image to check for in the cache
     * @return bool Whether or not the requested image is cached
     */
    protected function isCached($request)
    {
        return file_exists($this->getCachedPath($request));
    }

    /**
     * Attempts to cache the image while validating it
     *
     * @access protected
     * @param string $request The image to cache/validate
     * @return int -1 error, 0 too big, 1 valid image
     */
    protected function cacheImage($request)
    {
        $dest = $this->getCachedPath($request);
        $ext = strtolower(pathinfo(parse_url($request, PHP_URL_PATH), PATHINFO_EXTENSION));

        $image = fetch_web_data($request);

        // Looks like nobody was home
        if (empty($image))
            return 0;

        // What kind of file did they give us?
        $finfo = finfo_open(FILEINFO_MIME_TYPE);
        $mime_type = finfo_buffer($finfo, $image);

        // SVG needs a little extra care
        if ($ext == 'svg' && $mime_type == 'text/plain')
            $mime_type = 'image/svg+xml';

        // Make sure the url is returning an image
        if (strpos($mime_type, 'image/') !== 0)
            return 0;

        // Validate the filesize
        $size = strlen($image);
        if ($size > ($this->maxSize * 1024))
            return 0;

        // Cache it for later
        return file_put_contents($dest, json_encode(array(
            'content_type' => $mime_type,
            'size' => $size,
            'time' => time(),
            'body' => base64_encode($image),
        ))) === false ? -1 : 1;
    }

    /**
     * Static helper function to redirect a request
     *
     * @access public
     * @param type $request
     * @return void
     */
    static public function redirectexit($request)
    {
        header('Location: ' . un_htmlspecialchars($request), false, 301);
        exit;
    }

    /**
     * Delete all old entries
     *
     * @access public
     * @return void
     */
    public function housekeeping()
    {
        $path = $this->cache . '/';
        if ($handle = opendir($path))
        {
            while (false !== ($file = readdir($handle)))
            {
                $filelastmodified = filemtime($path . $file);

                if ((time() - $filelastmodified) > ($this->maxDays * 86400))
                {
                    unlink($path . $file);
                }
            }

            closedir($handle);
        }
    }
}

if (empty($proxyhousekeeping))
{
    $proxy = new ProxyServer();
    $proxy->serve();
}

?>