root/trunk/wp-admin/includes/update.php

<?php

// The admin side of our 1.1 update system

function core_update_footer( $msg = '' ) {
    if ( !current_user_can('manage_options') )
        return sprintf( '| '.__( 'Version %s' ), $GLOBALS['wp_version'] );

    $cur = get_option( 'update_core' );

    switch ( $cur->response ) {
    case 'development' :
        return sprintf( '| '.__( 'You are using a development version (%s). Cool! Please <a href="%s">stay updated</a>.' ), $GLOBALS['wp_version'], $cur->url, $cur->current );
    break;

    case 'upgrade' :
        if ( current_user_can('manage_options') ) {
            return sprintf( '| <strong>'.__( '<a href="%2$s">Get Version %3$s</a>' ).'</strong>', $GLOBALS['wp_version'], $cur->url, $cur->current );
            break;
        }

    case 'latest' :
    default :
        return sprintf( '| '.__( 'Version %s' ), $GLOBALS['wp_version'], $cur->url, $cur->current );
    break;
    }
}
add_filter( 'update_footer', 'core_update_footer' );

function update_nag() {
    $cur = get_option( 'update_core' );

    if ( ! isset( $cur->response ) || $cur->response != 'upgrade' )
        return false;

    if ( current_user_can('manage_options') )
        $msg = sprintf( __('WordPress %2$s is available! <a href="%1$s">Please update now</a>.'), $cur->url, $cur->current );
    else
        $msg = sprintf( __('WordPress %2$s is available! Please notify the site administrator.'), $cur->url, $cur->current );

    echo "<div id='update-nag'>$msg</div>";
}
add_action( 'admin_notices', 'update_nag', 3 );

// Called directly from dashboard
function update_right_now_message() {
    $cur = get_option( 'update_core' );

    $msg = sprintf( __('This is WordPress version %s.'), $GLOBALS['wp_version'] );
    if ( isset( $cur->response ) && $cur->response == 'upgrade' && current_user_can('manage_options') )
        $msg .= " <a href='$cur->url' class='rbutton'>" . sprintf( __('Update to %s'), $cur->current ? $cur->current : __( 'Latest' ) ) . '</a>';

    echo "<span id='wp-version-message'>$msg</span>";
}

function wp_update_plugins() {
    global $wp_version;

    if ( !function_exists('fsockopen') )
        return false;

    $plugins = get_plugins();
    $active  = get_option( 'active_plugins' );
    $current = get_option( 'update_plugins' );

    $new_option = '';
    $new_option->last_checked = time();

    $plugin_changed = false;
    foreach ( $plugins as $file => $p ) {
        $new_option->checked[ $file ] = $p['Version'];

        if ( !isset( $current->checked[ $file ] ) ) {
            $plugin_changed = true;
            continue;
        }

        if ( strval($current->checked[ $file ]) !== strval($p['Version']) )
            $plugin_changed = true;
    }

    if (
        isset( $current->last_checked ) &&
        43200 > ( time() - $current->last_checked ) &&
        !$plugin_changed
    )
        return false;

    $to_send->plugins = $plugins;
    $to_send->active = $active;
    $send = serialize( $to_send );

    $request = 'plugins=' . urlencode( $send );
    $http_request  = "POST /plugins/update-check/1.0/ HTTP/1.0\r\n";
    $http_request .= "Host: api.wordpress.org\r\n";
    $http_request .= "Content-Type: application/x-www-form-urlencoded; charset=" . get_option('blog_charset') . "\r\n";
    $http_request .= "Content-Length: " . strlen($request) . "\r\n";
    $http_request .= 'User-Agent: WordPress/' . $wp_version . '; ' . get_bloginfo('url') . "\r\n";
    $http_request .= "\r\n";
    $http_request .= $request;

    $response = '';
    if( false != ( $fs = @fsockopen( 'api.wordpress.org', 80, $errno, $errstr, 3) ) && is_resource($fs) ) {
        fwrite($fs, $http_request);

        while ( !feof($fs) )
            $response .= fgets($fs, 1160); // One TCP-IP packet
        fclose($fs);
        $response = explode("\r\n\r\n", $response, 2);
    }

    $response = unserialize( $response[1] );

    if ( $response )
        $new_option->response = $response;

    update_option( 'update_plugins', $new_option );
}
add_action( 'load-plugins.php', 'wp_update_plugins' );

function wp_plugin_update_row( $file, $plugin_data ) {
    $current = get_option( 'update_plugins' );
    if ( !isset( $current->response[ $file ] ) )
        return false;

    $r = $current->response[ $file ];

    echo '<tr><td colspan="5" class="plugin-update">';
    if ( ! current_user_can('update_plugins') )
        printf( __('There is a new version of %1$s available. <a href="%2$s">Download version %3$s here</a>.'), $plugin_data['Name'], $r->url, $r->new_version);
    else if ( empty($r->package) )
        printf( __('There is a new version of %1$s available. <a href="%2$s">Download version %3$s here</a> <em>automatic upgrade unavailable for this plugin</em>.'), $plugin_data['Name'], $r->url, $r->new_version);
    else
        printf( __('There is a new version of %1$s available. <a href="%2$s">Download version %3$s here</a> or <a href="%4$s">upgrade automatically</a>.'), $plugin_data['Name'], $r->url, $r->new_version, wp_nonce_url('update.php?action=upgrade-plugin&amp;plugin=' . $file, 'upgrade-plugin_' . $file) );
    
    echo '</td></tr>';
}
add_action( 'after_plugin_row', 'wp_plugin_update_row', 10, 2 );

function wp_update_plugin($plugin, $feedback = '') {
    global $wp_filesystem;

    if ( !empty($feedback) )
        add_filter('update_feedback', $feedback);

    // Is an update available?
    $current = get_option( 'update_plugins' );
    if ( !isset( $current->response[ $plugin ] ) )
        return new WP_Error('up_to_date', __('The plugin is at the latest version.'));

    // Is a filesystem accessor setup?
    if ( ! $wp_filesystem || ! is_object($wp_filesystem) )
        WP_Filesystem();

    if ( ! is_object($wp_filesystem) )
        return new WP_Error('fs_unavailable', __('Could not access filesystem.'));

    if ( $wp_filesystem->errors->get_error_code() )
        return new WP_Error('fs_error', __('Filesystem error'), $wp_filesystem->errors);

    //Get the base plugin folder
    $plugins_dir = $wp_filesystem->wp_plugins_dir();
    if ( empty($plugins_dir) )
        return new WP_Error('fs_no_plugins_dir', __('Unable to locate WordPress Plugin directory.'));

    //And the same for the Content directory.
    $content_dir = $wp_filesystem->wp_content_dir();
    if( empty($content_dir) )
        return new WP_Error('fs_no_content_dir', __('Unable to locate WordPress Content directory (wp-content).'));
    
    $plugins_dir = trailingslashit( $plugins_dir );
    $content_dir = trailingslashit( $content_dir );

    // Get the URL to the zip file
    $r = $current->response[ $plugin ];

    if ( empty($r->package) )
        return new WP_Error('no_package', __('Upgrade package not available.'));

    // Download the package
    $package = $r->package;
    apply_filters('update_feedback', sprintf(__('Downloading update from %s'), $package));
    $download_file = download_url($package);

    if ( is_wp_error($download_file) )
        return new WP_Error('download_failed', __('Download failed.'), $download_file->get_error_message());

    $working_dir = $content_dir . 'upgrade/' . basename($plugin, '.php');

    // Clean up working directory
    if ( $wp_filesystem->is_dir($working_dir) )
        $wp_filesystem->delete($working_dir, true);

    apply_filters('update_feedback', __('Unpacking the update'));
    // Unzip package to working directory
    $result = unzip_file($download_file, $working_dir);
    
    // Once extracted, delete the package
    unlink($download_file);
    
    if ( is_wp_error($result) ) {
        $wp_filesystem->delete($working_dir, true);
        return $result;
    }

    if ( is_plugin_active($plugin) ) {
        //Deactivate the plugin silently, Prevent deactivation hooks from running.
        apply_filters('update_feedback', __('Deactivating the plugin'));
        deactivate_plugins($plugin, true);
    }

    // Remove the existing plugin.
    apply_filters('update_feedback', __('Removing the old version of the plugin'));
    $this_plugin_dir = trailingslashit( dirname($plugins_dir . $plugin) );
    
    // If plugin is in its own directory, recursively delete the directory.
    if ( strpos($plugin, '/') && $this_plugin_dir != $plugins_dir ) //base check on if plugin includes directory seperator AND that its not the root plugin folder
        $deleted = $wp_filesystem->delete($this_plugin_dir, true);
    else
        $deleted = $wp_filesystem->delete($plugins_dir . $plugin);

    if ( ! $deleted ) {
        $wp_filesystem->delete($working_dir, true);
        return new WP_Error('delete_failed', __('Could not remove the old plugin'));
    }

    apply_filters('update_feedback', __('Installing the latest version'));
    // Copy new version of plugin into place.
    $result = copy_dir($working_dir, $plugins_dir);
    if ( is_wp_error($result) ) {
        //$wp_filesystem->delete($working_dir, true); //TODO: Uncomment? This DOES mean that the new files are available in the upgrade folder if it fails.
        return $result;
    }

    //Get a list of the directories in the working directory before we delete it, We need to know the new folder for the plugin
    $filelist = array_keys( $wp_filesystem->dirlist($working_dir) );

    // Remove working directory
    $wp_filesystem->delete($working_dir, true);

    // Force refresh of plugin update information
    delete_option('update_plugins');
    
    if( empty($filelist) )
        return false; //We couldnt find any files in the working dir, therefor no plugin installed? Failsafe backup.
    
    $folder = $filelist[0];
    $plugin = get_plugins('/' . $folder); //Ensure to pass with leading slash
    $pluginfiles = array_keys($plugin); //Assume the requested plugin is the first in the list

    return  $folder . '/' . $pluginfiles[0];
}

?>