Dynamic Plugin Requirements

Author: John Reese

Status: Feedback / Bugfixing

This is a proposal for a very lightweight method of including a plugin/hook system for Mantis. It should be able to handle not only minor enhancements for areas such as outputting text, but adding new pages, menu items, and entire features to the application. It should be very simple, but very powerful.

This feature is meant as a counter point to the Add-Ons Support Requirements by offering a much simpler and easier to use plugin system without sacrificing flexibility or power.

Plugins will be very simple packages, extracted into the Mantis/plugins directory and enabled through the Management interface. There will be a simple event system that will handle hooking functionality in various forms, including data processing, list retrieval, and output. Events will be called at various points in the normal flow of Mantis, and the plugin API will handle calling any necessary plugin functions.

When a plugin is loaded at runtime, it will register basic information about itself to Mantis, including its name, author, description, version, and dependencies (Mantis version, other plugins). It will then register a callback function for each event that it would like to handle. When an event occurs, any plugin callbacks will be called in the order they are registered. The event type will determine how callback parameters and return values are processed.

New content pages will be added by creating scripts in a special directory of the plugin, and links to that page will be created with an API call to simplify the task. Plugin pages will not need to load the Mantis core, but will need to call the html_page_top() or html_page_bottom() functions as necessary.

To simplify the usage of language files, plugins will simply need to supply a lang/ directory with appropriate strings files. The language API will search for strings in the main language files first, and only load the current plugin's language files if a needed string is not found elsewhere.

There will need to be a simple and unified method for plugins to maintain their database schema, otherwise plugins will get released without proper upgrade paths for users. The plugin manager should provide an automated schema upgrade mechanism that works the same as the Mantis upgrade mechanism. For performance reasons, the schema for plugins should only be checked when the plugin management screens are accessed, where it should notify the user of the need to upgrade the schema.

These should be the basic event types, from which all (or most) events can be formed.

Execute event

• Simplest type of event.
• No parameters
• No return value
• Includes EVENT_PLUGIN_INIT

Output event

• Event giving plugins a chance to output content. Strings returned from callback are cleaned for display and appended back to back with a separator string.
• Parameters:
  • separator string to output between plugins
• No return value
• Includes EVENT_PAGE_TOP and EVENT_PAGE_BOTTOM

Chain event

• Event allowing a plugin to process an input string and return a modified version to the originator.
• Parameters:
  • Input string
• Return value:
  • Modified input string
• Includes EVENT_TEXT_GENERAL for bug links, bugnote links, wiki links, and other markup options.

Default event

• Can be used for everything else.
• Parameters
  • Array of key/value pairs as direct parameters to the callback
• Return value
  • Array of key/value pairs directly from the callback

• Create table mantis_plugin_table
  • basename varchar(40) primary key, the directory name for the plugin
  • enabled boolean index

• plugins_enabled (default ON)
• manage_plugin_threshold (default ADMINISTRATOR)

This flow of action should occur during normal Mantis execution. It should be possible to bypass this by either disabling plugins from config_inc.php or by a page declaring a special flag before including core.php.

• List of enabled plugins is retrieved from database.
• For each enabled plugin:
  • Include plugins/<basename>/register.php
  • Call plugin_callback_<basename>_info() function
  • Call plugin_callback_<basename>_register() function
• Send EVENT_PLUGIN_INIT signal
• Execute normal page contents with events as necessary

This flow of action should occur whenever an event is signaled, assuming plugins are enabled.

• Prepare parameters from event origin
• For each registered callback:
  • Include plugins/<basename>/events.php
  • Call plugin_event_<basename>_<function_name>()
  • Alter parameters for next callback if necessary
• Output content if necessary
• Return callback values to event originator if necessary

<basename> represents the plugin's directory name, and should be a short, unique name that does not include version names or other changing identifiers. 'mantis' is a reserved basename, and represents a virtual plugin used for allowing dependencies based on Mantis versions.

mantis/
  plugins/
    <basename>/
      register.php
      events.php
      lang/
        ...
      pages/
        ...

• register.php is the only file required for a plugin to be valid. It must contain two callbacks for plugin information and event registrations. This file should only have the following callbacks, but may include additional functions or callbacks for more complex plugins.
  • plugin_callback_<basename>_info() - This function must return an array of plugin information, including name, version, ad dependencies.
  • plugin_callback_<basename>_init() - This function must set up the plugin, and hook any events needed.
  • plugin_callback_<basename>_schema() - This function is only required if the plugin needs to maintain changes or additions to the Mantis schema. It must return an array of schema upgrades in the same format as the admin/schema.php upgrade script.
• events.php is required for using event hooks. It should contain all the event callback functions, or include additional scripts with the necessary callbacks. All event callback functions must be named as plugin_event_callback_<basename>_<name>(). This script will only be loaded if the plugin has registered for an event.
• lang/ is only required if the plugin needs to use language strings that don't appear in the standard language files. These files will only be loaded if the requested strings cannot be found otherwise.
• pages/ is only required if a plugin needs to have its own pages. They can be accessed by linking a url returned by the plugin_page() function. These pages need not load the core libraries, as it will already be loaded for them.

This is a very minimal plugin.

Directory Structure

mantis/
  plugins/
    supercow/
      register.php
      events.php

sample/register.php

<?php

/**
 * Return plugin details to the API.
 * @return array Plugin details
 */
function plugin_callback_supercow_info() {
  return array(
    'name' => 'Super Cow Powers',
    'description' => 'Gives your Mantis installation super cow powers.',
    'version' => '1.0',
    'author' => 'John Reese',
    'contact' => 'jreese@leetcode.net',
    'url' => 'http://leetcode.net',
  );
}

/**
 * Intitialize the plugin.
 */
function plugin_callback_supercow_init() {
  plugin_event_hook( 'EVENT_PLUGIN_INIT', 'header' );
}

sample/events.php

<?php

/**
 * Handle the EVENT_PLUGIN_INIT callback.
 */
function plugin_event_supercow_header() {
  header( 'X-Mantis: This Mantis has super cow powers.' );
}

• (vboctor): EVENT_TEXT_GENERAL - You might need to differentiate where this text is going, e.g. normal text (like string_display()), text within an edit box (like string_attribute()).
  • (jreese) For now, TEXT_GENERAL is for basic string_display(), with a TEXT_LINKS event for string_display_links(), etc. Once the plugins make it into CVS Head, we should make a full effort to litter events throughout the codebase, and make sure we have full documentation of it all.
• (vboctor): EVENT_TEXT_GENERAL - I am assuming that you will be pipelining the results of one plug-in into another, right?
  • (jreese) That is the defined behavior of a processing type event, which TEXT_GENERAL is. Other event types have different behaviors.
• (vboctor): EVENT_TEXT_GENERAL - If you look at the current implementation you will notice that the order of applying the display filters affects the final results. How are we going to handle such cases? The order sensitivity is mainly relating to html tags.
  • (jreese) Any plugins that have order sensitivity should define a dependency on appropriate plugins. (jreese)
• (vboctor): Default event - With the default events, how are you going to handle the return values returned by all these plug-ins? Are you going to run one plugin, then dependent on the return value, decide whether to continue with the chain or not?
  • (jreese) The default event type will have each plugin run independent of each other, all given the same parameters. The return values of each plugin will be returned as an element of an array, and it will be up to the caller to determine how to handle that.
• (vboctor): How is the admin going to enable/disable plug-ins after unpacking them in the right place in the directory structure?
  • (jreese) The manage plugins interface allows an admin to install/uninstall plugins at will (assuming dependencies are met).
• (vboctor): Some plug-ins may like to change the terminology of Mantis, for example, use 'ticket' rather than 'issue'. You current approach only allows adding new strings.
  • (jreese) In this case, it should be perfectly feasible for a plugin to register a callback for the PLUGIN_INIT event that does nothing but force a lang_load() of the appropriate strings files in the plugin's path, which will then override any already-defined strings.
• (vboctor): We need to rationalize how custom functions / plug-ins will overlap. For example, if a developer have overridden a custom function to do some generically useful behavior, then he/she may want to share this in the form of a plug-in.
  • (jreese) I believe the best way to handle this is to market plugins as ways to enhance Mantis, not to change how its core functionality works, which is what custom functions should do (and should still do).
• (vboctor): I would love to allow the development of Mantis Packs which provide a way to develop a plugin that makes Mantis work better with a certain development process (e.g. scrum) or work better for users migrating their installations from a specific bug tracker (for example, the statuses, reports, custom fields, etc).
  • (jreese) Certainly any plugin could easily do nothing but provide pages that allow for migrating or exporting data. Integration with other applications would be trickier, but the key way to allow this is by providing a smart and useful array of events for plugins to hook into.
• (vboctor): We need to support attachment preview plug-ins.
  • (jreese) I think this would be better added as a core feature.
• (vboctor): We need to allow plug-ins to add new blocks to pages like issue view, update, etc.
  • (jreese) Easily allowed by placing appropriate output type events in view pages.
• (vboctor): It should be easy to develop features like Twitter notifications as plug-ins. Once we do that, then the community can have plugins for all similar services like SMS, Jaiku, Pownce, etc.
  • (jreese) Once again, this comes down to picking appropriate and useful events.
• (DGtlRift): In the above explanation and examples should plugin_callback_<basename>_register() be plugin_callback_<basename>_init()?