Prevent WordPress Plugin Update From Deleting Important Folder In Your Plugin

Many would know that i have build a powerful thumbnail plugin in WordPress. The plugin work perfectly fine for WordPress 2.8 below but once i updated my WordPress to version 2.8, something bad happen. Every single time whenever i update my WordPress plugin, WordPress will delete the plugin folder with everything included and install the latest plugin version. This post a problem to my plugin since all the images are stored inside the plugin folder. I search online but i couldn't get any help anywhere until i investigate the new version 2.8 core codes.

New Hooks in WordPress 2.8

In WordPress 2.8, it has added a new functionality to delete the previous version of the plugin and then install the latest plugin version into the exact same location. Lucky, it also includes a few more filter hook that did the delete and install process. In class-wp-upgrade.php located at /admin/includes/class-wp-upgrade.php, lines 403-409 you will notice the following few codes,

		add_filter('upgrader_pre_install', array(&$this, 'deactivate_plugin_before_upgrade'), 10, 2);
		add_filter('upgrader_clear_destination', array(&$this, 'delete_old_plugin'), 10, 4);
		//'source_selection' => array(&$this, 'source_selection'), //theres a track ticket to move up the directory for zip's which are made a bit differently, useful for non-.org plugins.

		$this->run(array(
					'package' => $r->package,
					'destination' => WP_PLUGIN_DIR,
					'clear_destination' => true,
					'clear_working' => true,
					'hook_extra' => array(
								'plugin' => $plugin
					)
				));

		//Cleanup our hooks, incase something else does a upgrade on this connection.
		remove_filter('upgrader_pre_install', array(&$this, 'deactivate_plugin_before_upgrade'));
		remove_filter('upgrader_clear_destination', array(&$this, 'delete_old_plugin'));

I went to search on Google again for these new hook and it seems like there are a couple more of these new hooks being added into WordPress 2.8. But we are particularly interested on 'upgrader_pre_install' and 'upgrader_post_install' filter hook.

Using upgrade_pre_install filter hook

function hpt_copyr($source, $dest)
{
    // Check for symlinks
    if (is_link($source)) {
        return symlink(readlink($source), $dest);
    }

    // Simple copy for a file
    if (is_file($source)) {
        return copy($source, $dest);
    }

    // Make destination directory
    if (!is_dir($dest)) {
        mkdir($dest);
    }

    // Loop through the folder
    $dir = dir($source);
    while (false !== $entry = $dir->read()) {
        // Skip pointers
        if ($entry == '.' || $entry == '..') {
            continue;
        }

        // Deep copy directories
        hpt_copyr("$source/$entry", "$dest/$entry");
    }

    // Clean up
    $dir->close();
    return true;
}
function hpt_backup()
{
	$to = dirname(__FILE__)."/../hpt_images_backup/";
	$from = dirname(__FILE__)."/images/";
	hpt_copyr($from, $to);
}
function hpt_recover()
{
	$from = dirname(__FILE__)."/../hpt_images_backup/";
	$to = dirname(__FILE__)."/images/";
	hpt_copyr($from, $to);
	if (is_dir($from)) {
		hpt_rmdirr($from);#http://putraworks.wordpress.com/2006/02/27/php-delete-a-file-or-a-folder-and-its-contents/
	}
}
add_filter('upgrader_pre_install', 'hpt_backup', 10, 2);
add_filter('upgrader_post_install', 'hpt_recover', 10, 2);

In order to prevent WordPress plugin update from deleting our important folder within our plugin, we must move that particular folder somewhere safe before it starts deleting everything in our plugin. After the update has completed, we will then move the folder that we want to preserved and overwrite any existing files in that folder. We can't remove the filter action as shown on the core WordPress code was because the filter was not added previously. Thus, removing the filter will not prevent the deletion.