Plugin Development

SamplePlugin.php

Each plugin requires a main class to interact with the GNU social system.

The main class usually extends the Plugin class that comes with GNU social.

The class has standard-named methods that will be called when certain events happen in the code base. These methods have names like 'onX' where X is an event name (see EVENTS.txt for the list of available events). Event handlers have pre-defined arguments, based on which event they're handling. A typical event handler:

function onSomeEvent($paramA, &$paramB)
{
    if ($paramA == 'jed') {
        throw new Exception(sprintf(_m("Invalid parameter %s"), $paramA));
    }
    $paramB = 'spock';
    return true;
}

Event Handlers

Event handlers must return a Boolean value.

If they return false, all other event handlers for this event (in other plug-in) will be skipped, and in some cases the default processing for that event would be skipped. This is great for replacing the default action of an event.

If the handler returns true, processing of other event handlers and the default processing will continue. This is great for extending existing functionality.

If the handler throws an exception, processing will stop, and the exception's error will be shown to the user.

Installation

To install a plugin (like this one), site admins add the following code to their config.php file:

addPlugin('Sample');

Plugins must be installed in one of the following directories:

local/plugins/{$pluginclass}.php
local/plugins/{$name}/{$pluginclass}.php
local/{$pluginclass}.php
local/{$name}/{$pluginclass}.php
plugins/{$pluginclass}.php
plugins/{$name}/{$pluginclass}.php

Here, {$name} is the name of the plugin, like 'Sample', and {$pluginclass} is the name of the main class, like 'SamplePlugin'. Plugins that are part of the main GNU social distribution go in 'plugins' and third-party or local ones go in 'local'.

Simple plugins can be implemented as a single module. Others are more complex and require additional modules; these should use their own directory, like 'local/plugins/{$name}/'. All files related to the plugin, including images, JavaScript, CSS, external libraries or PHP modules should go in the plugin directory.

Plugin Configuration

Plugins are configured using public instance attributes. To set their values, site administrators use this syntax:

addPlugin('Sample', array('attr1' => 'foo', 'attr2' => 'bar'));

The same plugin class can be initialized multiple times with different arguments:

addPlugin('EmailNotify', array('sendTo' => 'evan@status.net'));
addPlugin('EmailNotify', array('sendTo' => 'brionv@status.net'));

class SamplePlugin extends Plugin
{
    public $attr1 = null;
    public $attr2 = null;
}

Initialization

Plugins overload this method to do any initialization they need, like connecting to remote servers or creating paths or so on. @return boolean hook value; true means continue processing, false means stop.

function initialize()
{
    return true;
}

Clean Up

Plugins overload this method to do any cleanup they need, like disconnecting from remote servers or deleting temp files or so on.

function cleanup()
{
    return true;
}

Database schema setup

Plugins can add their own tables to the GNU social database. Plugins should use GNU social's schema interface to add or delete tables. The ensureTable() method provides an easy way to ensure a table's structure and availability.

By default, the schema is checked every time GNU social is run (say, when a Web page is hit). Admins can configure their systems to only check the schema when the checkschema.php script is run, greatly improving performance. However, they need to remember to run that script after installing or upgrading a plugin!

function onCheckSchema()
{
    $schema = Schema::get();

    // '''For storing user-submitted flags on profiles'''

    $schema->ensureTable('user_greeting_count',
                          array(new ColumnDef('user_id', 'integer', null,
                                              true, 'PRI'),
                                new ColumnDef('greeting_count', 'integer')));

    return true;
}

Load related modules when needed

Most non-trivial plugins will require extra modules to do their work. Typically these include data classes, action classes, widget classes, or external libraries.

This method receives a class name and loads the PHP file related to that class. By tradition, action classes typically have files named for the action, all lower-case. Data classes are in files with the data class name, initial letter capitalized.

Note that this method will be called for all overloaded classes, not just ones in this plugin! So, make sure to return true by default to let other plugins, and the core code, get a chance.

function onAutoload($cls)
{
    $dir = dirname(__FILE__);

    switch ($cls)
    {
    case 'HelloAction':
        include_once $dir . '/' . strtolower(mb_substr($cls, 0, -6)) . '.php';
        return false;
    case 'User_greeting_count':
        include_once $dir . '/'.$cls.'.php';
        return false;
    default:
        return true;
    }
}

Map URLs to actions

This event handler lets the plugin map URLs on the site to actions (and thus an action handler class). Note that the action handler class for an action will be named 'FoobarAction', where action = 'foobar'. The class must be loaded in the onAutoload() method.

function onRouterInitialized($m)
{
    $m->connect('main/hello',
                array('action' => 'hello'));
    return true;
}

Modify the default menu to link to our custom action

Using event handlers, it's possible to modify the default UI for pages almost without limit. In this method, we add a menu item to the default primary menu for the interface to link to our action.

Action Class

The Action class provides a rich set of events to hook, as well as output methods.

function onEndPrimaryNav($action)
{
    // '''common_local_url()''' gets the correct URL for the action name we provide

    $action->menuItem(common_local_url('hello'),
                      _m('Hello'), _m('A warm greeting'), false, 'nav_hello');
    return true;
}

function onPluginVersion(&$versions)
{
    $versions[] = array('name' => 'Sample',
                        'version' => STATUSNET_VERSION,
                        'author' => 'Brion Vibber, Evan Prodromou',
                        'homepage' => 'http://example.org/plugin',
                        'rawdescription' =>
                        _m('A sample plugin to show basics of development for new hackers.'));
    return true;
}

hello.php

This section is taken directly from the 'hello.php'. ( plugins/Sample/hello.php )

Give a warm greeting to our friendly user.

This sample action shows some basic ways of doing output in an action class.

Action classes have several output methods that they override from the parent class.

class HelloAction extends Action
{
    var $user = null;
    var $gc   = null;
}

Take arguments for running

This method is called first, and it lets the action class get all its arguments and validate them. It's also the time to fetch any relevant data from the database.

Action classes should run parent::prepare($args) as the first line of this method to make sure the default argument-processing happens.

function prepare($args)
{
    parent::prepare($args);

    $this->user = common_current_user();

    if (!empty($this->user)) {
        $this->gc = User_greeting_count::inc($this->user->id);
    }

    return true;
}

Handle request

This is the main method for handling a request. Note that most preparation should be done in the prepare() method; by the time handle() is called the action should be more or less ready to go.

function handle($args)
{
    parent::handle($args);

    $this->showPage();
}

Title of this page

Override this method to show a custom title.

function title()
{
    if (empty($this->user)) {
        return _m('Hello');
    } else {
        return sprintf(_m('Hello, %s'), $this->user->nickname);
    }
}

Show content in the content area

The default GNU social page has a lot of decorations: menus, logos, tabs, all that jazz. This method is used to show content in the content area of the page; it's the main thing you want to overload. This method also demonstrates use of a plural localized string.

function showContent()
{
    if (empty($this->user)) {
        $this->element('p', array('class' => 'greeting'),
                       _m('Hello, stranger!'));
    } else {
        $this->element('p', array('class' => 'greeting'),
                       sprintf(_m('Hello, %s'), $this->user->nickname));
        $this->element('p', array('class' => 'greeting_count'),
                       sprintf(_m('I have greeted you %d time.',
                                  'I have greeted you %d times.',
                                  $this->gc->greeting_count),
                                  $this->gc->greeting_count));
    }
}

Return true if read only.

Some actions only read from the database; others read and write. The simple database load-balancer built into GNU social will direct read-only actions to database mirrors (if they are configured) and read-write actions to the master database.

This defaults to false to avoid data integrity issues, but you should make sure to overload it for performance gains.

function isReadOnly($args)
{
    return false;
}

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