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TWiki Plugins

Plug-in enhanced feature add-ons, with a Plugin API for developers

Overview

You can add Plugins to extend TWiki's functionality, without altering the core program code. A plug-in approach lets you:

Everything to do with TWiki Plugins - demos, new releases, downloads, development, general discussion - is available at TWiki.org, in the TWiki:Plugins web.

Preinstalled Plugins

TWiki comes with a set of Plugins as part of the standard installation.

Installing Plugins

Each TWikiPlugin comes with full documentation: step-by-step installation instructions, a detailed description of any special requirements, version details, and a working example for testing.

Most Plugins can be installed in three easy steps, with no programming skills required:

  1. Download the zip file containing the Plugin, documentation, and any other required files, from TWiki:Plugins.
  2. Distribute the files to their proper locations - unzip the zip archive in your TWiki installation directory - if have a standard TWiki installation, this will distribute automatically. Otherwise, place the files according to the directory paths listed on the Plugin top in TWiki:Plugins.
  3. Check the demo example on the Plugin topic: if it's working, the installation was fine!

Special Requests: Some Plugins need certain Perl modules to be preinstalled on the host system. Plugins may also use other resources, like graphics, other modules, applications, templates. In these cases, detailed instructions are in the Plugin documentation.

Each Plugin has a standard release page, located in the TWiki:Plugins web at TWiki.org. In addition to the documentation topic (SomePlugin), there's a separate development page.

On-Site Pretesting

To test new Plugins on your installation before making them public, you may want to use one of these two approaches:

Checking that Plugins are Working on a Live Server

InstalledPlugins shows which Plugins are: 1) installed, 2) loading properly and 3) what TWiki:Codev.PluginHandlers they invoke. Any failures are shown in the Errors section.

A Note on Plugin Performance

The performance of the system depends on the number of Plugins installed and on the Plugin implementation. Some Plugins impose no measurable performance decrease, some do. For example, outsidePREHandler is an expensive callback function, or a Plugin might use many Perl libraries that need to be initialized with each page view (unless you run mod_perl). It is recommended to measure the performance with and without a new Plugin. Example for Unix:
time wget -qO /dev/null http://www.denx.de/wiki/view/TWiki/AbcPlugin

In case you need to install an "expensive" Plugin and you need its functionality only in one web you can place the Plugin topic into that web. TWiki will initialize the Plugin only if the Plugin topic is found (which won't be the case for other webs.)

Managing Plugins

When you finish installing a Plugin, you should be able to read the user instructions and go. In fact, some Plugins require additional settings or offer extra options that you have to select. Also, you may want to make a Plugin available only in certain webs, or temporarily disable it. And may want to list all available Plugins in certain topics. You can handle all of these management tasks with simple procedures.

Setting Preferences

Installed Plugins can be toggled on or off, site-wide or by web, through TWikiPreferences and individual WebPreferences:

Plugin execution order in TWiki is determined by searching Plugin topics in a specific sequence: First, full web.topicname name, if specified in INSTALLEDPLUGINS; next, the TWiki web is searched; and finally, the current web.

Plugin-specific settings are done in individual Plugin topics. Two settings are standard for each Plugin:

  1. One line description, used to form the bullets describing the Plugins in the TextFormattingRules topic:
    • Set SHORTDESCRIPTION = Blah blah woof woof.
  2. Debug Plugin, output can be seen in data/debug.txt. Set to 0=off or 1=on:
    • Set DEBUG = 0

Listing Active Plugins

Plugin status variables let you list all active Plugins wherever needed. There are two list formats:

DEMO: Automatically List Active Plugins Using Variables

Using %ACTIVATEDPLUGINS%:
On this TWiki site, the active Plugins are: DefaultPlugin, SpreadSheetPlugin, CommentPlugin, ConditionalPlugin, EditTablePlugin, InterwikiPlugin, MultiLangPlugin, RenderListPlugin, SessionPlugin, SlideShowPlugin, SmiliesPlugin, TablePlugin, TocPlugin.

Using %PLUGINDESCRIPTIONS%:
You can use any of these active TWiki Plugins:

The TWiki Plugin API

The Application Programming Interface (API) for TWikiPlugins provides the specifications for hooking into the core TWiki code from your external Perl Plugin module. The Plugin API is new to the Production version of TWiki with the 01-Sep-2001 release.

Available Core Functions

The TWikiFuncModule (lib/TWiki/Func.pm) implements ALL official Plugin functions. Plugins should ONLY use functions published in this module.

ALERT! If you use functions not in Func.pm, you run the risk of creating security holes. Also, your Plugin will likely break and require updating when you upgrade to a new version of TWiki.

Predefined Hooks

In addition to TWiki core functions, Plugins can use predefined hooks, or call backs, listed in the lib/TWiki/Plugins/EmptyPlugin.pm module.

Most Plugins use either the commonTagsHandler or startRenderingHandler for rendering tasks:

TWiki:Codev/StepByStepRenderingOrder helps you decide which rendering handler to use.

Hints on Writing Fast Plugins

Plugin Version Detection

To eliminate the incompatibility problems bound to arise from active open Plugin development, a Plugin versioning system and an API GetVersion detection routine are provided for automatic compatibility checking.

Creating Plugins

With a reasonable knowledge of the Perl scripting language, you can create new Plugins or modify and extend existing ones. Basic plug-in architecture uses an Application Programming Interface (API), a set of software instructions that allow external code to interact with the main program. The TWiki Plugin API Plugins by providing a programming interface for TWiki.

The DefaultPlugin Alternative

Anatomy of a Plugin

A basic TWiki Plugin consists of two elements:

The Perl module can be a block of code that connects with TWiki alone, or it can include other elements, like other Perl modules (including other Plugins), graphics, TWiki templates, external applications (ex: a Java applet), or just about anything else it can call. In particular, files that should be web-accessible (graphics, Java applets ...) are best placed as attachments of the MyFirstPlugin topic. Other needed Perl code is best placed in a lib/TWiki/Plugins/MyFirstPlugin/ directory.

The Plugin API handles the details of connecting your Perl module with main TWiki code. When you're familiar with the Plugin API, you're ready to develop Plugins.

Creating the Perl Module

Copy file lib/TWiki/Plugins/EmptyPlugin.pm to <name>Plugin.pm. The EmptyPlugin.pm module contains mostly empty functions, so it does nothing, but it's ready to be used. Customize it. Refer to the Plugin API specs for more information.

If your Plugin uses its own modules and objects, you must include the name of the Plugin in the package name. For example, write Package MyFirstPlugin::Attrs; instead of just Package Attrs;. Then call it using:

  use TWiki::Plugins::MyFirstPlugin::Attrs;
  $var = MyFirstPlugin::Attrs->new();

Writing the Documentation Topic

The Plugin documentation topic contains usage instructions and version details. It serves the Plugin files as FileAttachments for downloading. (The doc topic is also included in the distribution package.) To create a documentation topic:

  1. Copy the Plugin topic template from TWiki.org. To copy the text, go to TWiki:Plugins/PluginPackage and:
    • enter the Plugin name in the "How to Create a Plugin" section
    • click Create
    • select all in the Edit box & copy
    • Cancel the edit
    • go back to your site to the TWiki web
    • In the GoBox enter your Plugin name, for example MyFirstPlugin, press enter and create the new topic
    • paste & save new Plugin topic on your site
  2. Customize your Plugin topic.
    • In case you plan to publish your Plugin at TWiki.org, use Interwiki names for author names, like TWiki:Main/guest.
  3. Save your topic, for use in packaging and publishing your Plugin.

OUTLINE: Doc Topic Contents
Check the Plugins web on TWiki.org for the latest Plugin doc topic template. Here's a quick overview of what's covered:

Syntax Rules: <Describe any special text formatting that will be rendered.>"

Example: <Include an example of the Plugin in action. Possibly include a static HTML version of the example to compare if the installation was a success!>"

Plugin Settings: <Description and settings for custom Plugin %VARIABLES%, and those required by TWiki.>"

Plugin Installation Instructions: <Step-by-step set-up guide, user help, whatever it takes to install and run, goes here.>"

Plugin Info: <Version, credits, history, requirements - entered in a form, displayed as a table. Both are automatically generated when you create or edit a page in the TWiki:Plugins web.>"

Packaging for Distribution

A minimum Plugin release consists of a Perl module with a WikiName that ends in Plugin, ex: MyFirstPlugin.pm, and a documentation page with the same name(MyFirstPlugin.txt).

  1. Distribute the Plugin files in a directory structure that mirrors TWiki. If your Plugin uses additional files, include them ALL:
    • lib/TWiki/Plugins/MyFirstPlugin.pm
    • data/TWiki/MyFirstPlugin.txt
    • pub/TWiki/MyFirstPlugin/uparrow.gif [a required graphic]
  2. Create a zip archive with the Plugin name (MyFirstPlugin.zip) and add the entire directory structure from Step 1. The archive should look like this:
    • lib/TWiki/Plugins/MyFirstPlugin.pm
    • data/TWiki/MyFirstPlugin.txt
    • pub/TWiki/MyFirstPlugin/uparrow.gif

Publishing for Public Use

You can release your tested, packaged Plugin to the TWiki community through the TWiki:Plugins web. All Plugins submitted to TWiki.org are available for download and further development in TWiki:Plugins/PluginPackage. Publish your Plugin in these steps:

  1. Post the Plugin documentation topic in the TWiki:Plugins/PluginPackage:
    • enter the Plugin name in the "How to Create a Plugin" section, for example MyFirstPlugin
    • paste in the topic text from Creating Plugin Documentation and save
  2. Attach the distribution zip file to the topic, ex: MyFirstPlugin.zip
  3. Link from the doc page to a new, blank page named after the Plugin, and ending in Dev, ex: MyFirstPluginDev. This is the discussion page for future development. (User support for Plugins is handled in TWiki:Support.)
  4. Put the Plugin into the CVS repository, see TWiki:Plugins/ReadmeFirst (optional)

Thank you very much for sharing your Plugin with the TWiki community smile

Recommended Storage of Plugin Data

Plugins sometimes need to store data. This can be Plugin internal data like cache data, or generated data for the browser like images. The following is a recommendation where to store the data.

Where to store Plugin Internal Data

In case the Plugin generates data just for internal use, or data which is not specific to a topic, store it in the Plugin's attachment directory.

Where to Store Data for Topics using the Plugin

In case the Plugin generates data which is specific to a topic, store it in the topic's attachment directory.

Example code to build the file name:

sub _make_filename
{
    my ( $web, $topic, $name ) = @_;

    # Create web directory "pub/$web" if needed
    my $dir = TWiki::Func::getPubDir() . "/$web";
    unless( -e "$dir" ) {
        umask( 002 );
        mkdir( $dir, 0775 );
    }
    # Create topic directory "pub/$web/$topic" if needed
    $dir .= "/$topic";
    unless( -e "$dir" ) {
        umask( 002 );
        mkdir( $dir, 0775 );
    }
    return "$dir/_FooBarPlugin_$name";
}

-- TWiki:Main/PeterThoeny - 18 May 2004
-- TWiki:Main/AndreaSterbini - 29 May 2001
-- TWiki:Main/MikeMannix - 03 Dec 2001