Writing extensions for FreshRSS

About FreshRSS

FreshRSS is an RSS / Atom feed aggregator written in PHP dating back to October 2012. The official site is located at freshrss.org and the official repository is hosted on Github: github.com/FreshRSS/FreshRSS.

The problem

FreshRSS is limited in its technical possibilities by various factors:

While the first limitation can, in theory, be lifted by the participation of new contributors to the project, it depends on the willingness of contributors to take an interest in the source code of the entire project. In order to remove the other two limitations, most of the time it will be necessary to create a “fork”.

Another solution consists of an extension system. By allowing users to write their own extension without taking an interest in the core of the basic software, we allow for:

  1. Reducing the amount of source code a new contributor has to take in
  2. Unofficial integration of novelties
  3. No forking or main developer approval required.

Note: it is quite conceivable that the functionalities of an extension can later be officially integrated into the FreshRSS code. Extensions make it easy to propose a proof of concept.

Understanding basic mechanics (Minz and MVC)

TODO : move to 02_Minz.md

This data sheet should refer to the official FreshRSS and Minz documentation (the PHP framework on which FreshRSS is based). Unfortunately, this documentation does not yet exist. In a few words, here are the main things you should know. It is not necessary to read all the chapters in this section if you don’t need to use a feature in your extension (if you don’t need to translate your extension, no need to know more about the Minz_Translate module for example).

MVC Architecture

Minz relies on and imposes an MVC architecture on projects using it. This architecture consists of three main components:

Routing

In order to link a URL to a controller, first you have to go through a “routing” phase. In FreshRSS, this is particularly simple because it suffices to specify the name of the controller to load into the URL using a c parameter. For example, the address http://exemple.com?c=hello will execute the code contained in the hello controller.

One concept that has not yet been discussed is the “actions” system. An action is executed on a controller. Concretely, a controller is represented by a class and its actions by methods. To execute an action, it is necessary to specify an a parameter in the URL.

Code example:

<?php

class FreshRSS_hello_Controller extends Minz_ActionController {
	public function indexAction() {
		$this->view->a_variable = 'FooBar';
	}

	public function worldAction() {
		$this->view->a_variable = 'Hello World!';
	}
}

?>

When loading the address http://exemple.com?c=hello&a=world, the world action is executed on the hello controller.

Note: if c or a is not specified, the default value for each of these variables is index. So the address http://exemple.com?c=hello will execute the index action of the hello controller.

From now on, the hello/world naming convention will be used to refer to a controller/action pair.

Views

Each view is associated with a controller and an action. The view associated with hello/world will be stored in a very specific file: views/hello/world. phtml. This convention is imposed by Minz.

As explained above, the views consist of HTML mixed with PHP. Code example:

<p>
	This is a parameter passed from the controller: <?= $this->a_variable ?>
</p>

The variable $this->a_variable is passed by the controller (see previous example). The difference is that in the controller it is necessary to pass $this->view, while in the view $this suffices.

Working with GET / POST

It is often necessary to take advantage of parameters passed by GET or POST. In Minz, these parameters are accessible using the Minz_Request class. Code example:

<?php

$default_value = 'foo';
$param = Minz_Request::param('bar', $default_value);

// Display the value of the parameter `bar` (passed via GET or POST)
// or "foo" if the parameter does not exist.
echo $param;

// Sets the value of the `bar` parameter
Minz_Request::_param('bar', 'baz');

// Will necessarily display "baz" since we have just forced its value.
// Note that the second parameter (default) is optional.
echo Minz_Request::param('bar');

?>

The Minz_Request::isPost() method can be used to execute a piece of code only if it is a POST request.

Note: it is preferable to use Minz_Request only in controllers. It is likely that you will encounter this method in FreshRSS views, or even in templates, but be aware that this is not good practice.

Access session settings

The access to session parameters is strangely similar to the GET / POST parameters but passes through the Minz_Session class this time! There is no example here because you can repeat the previous example by changing all Minz_Request to Minz_Session.

Working with URLs

To take full advantage of the Minz routing system, it is strongly discouraged to write hard URLs in your code. For example, the following view should be avoided:

<p>
	Go to page <a href="http://example.com?c=hello&amp;a=world">Hello world</a>!
</p>

If one day it was decided to use a “url rewriting” system to have addresses in a http://exemple.com/controller/action format, all previous addresses would become ineffective!

So use the Minz_Url class and its display() method instead. Minz_Url::display() takes an array of the following form as its argument:

<?php

$url_array = [
	'c' => 'hello',
	'a' => 'world',
	'params' => [
		'foo' => 'bar',
	],
];

// Show something like .?c=hello&amp;a=world&amp;foo=bar
echo Minz_Url::display($url_array);

?>

Since this can become a bit tedious to use in the long run, especially in views, it is preferable to use the _url() shortcut:

<?php

// Displays the same as above
echo _url('hello', 'world', 'foo', 'bar');

?>

Note: as a general rule, the shortened form (_url()) should be used in views, while the long form (Minz_Url::display()) should be used in controllers.

Redirections

It is often necessary to redirect a user to another page. To do so, the Minz_Request class offers another useful method: forward(). This method takes the same URL format as the one seen just before as its argument.

Code example:

<?php

$url_array = [
	'c' => 'hello',
	'a' => 'world',
];

// Tells Minz to redirect the user to the hello / world page.
// Note that this is a redirection in the Minz sense of the term, not a redirection that the browser will have to manage (HTTP code 301 or 302)
// The code that follows forward() will thus be executed!
Minz_Request::forward($url_array);

// To perform a type 302 redirect, add "true".
// The code that follows will never be executed.
Minz_Request::forward($url_array, true);

?>

It is very common to want display a message to the user while performing a redirect, to tell the user how the action was carried out (validation of a form for example). Such a message is passed through a notification session variable (note: we will talk about feedback from now on to avoid confusion with a notification that can occur at any time). To facilitate this kind of very frequent action, there are two shortcuts that both perform a 302 redirect by assigning a feedback message:

<?php

$url_array = [
	'c' => 'hello',
	'a' => 'world',
];
$feedback_good = 'All went well!';
$feedback_bad = 'Oops, something went wrong.';

Minz_Request::good($feedback_good, $url_array);

// or

Minz_Request::bad($feedback_bad, $url_array);

?>

Translation Management

This part is explained here.

Configuration management

Write an extension for FreshRSS

Here we are! We’ve talked about the most useful features of Minz and how to run FreshRSS correctly and it’s about time to address the extensions themselves.

An extension allows you to easily add functionality to FreshRSS without having to touch the core of the project directly.

Make it work in Docker

When working on an extension, it’s easier to see it working directly in its environment. With Docker, you can leverage the use of the volume option when starting the container. Hopefully, you can use it without Docker-related knowledge by using the Makefile rule:

make start extensions="/full/path/to/extension/1 /full/path/to/extension/2"

Basic files and folders

The first thing to note is that all extensions must be located in the extensions directory, at the base of the FreshRSS tree. An extension is a directory containing a set of mandatory (and optional) files and subdirectories. The convention requires that the main directory name be preceded by an “x” to indicate that it is not an extension included by default in FreshRSS.

The main directory of an extension must contain at least two mandatory files:

Please note that there is a not a required link between the directory name of the extension and the name of the class inside extension.php, but you should follow our best practice: If you want to write a HelloWorld extension, the directory name should be xExtension-HelloWorld and the base class name HelloWorldExtension.

In the file freshrss/extensions/xExtension-HelloWorld/extension.php you need the structure:

class HelloWorldExtension extends Minz_Extension {
	public function init() {
		// your code here
	}
}

There is an example HelloWorld extension that you can download from our GitHub repo.

You may also need additional files or subdirectories depending on your needs:

In addition, it is good to have a LICENSE file indicating the license under which your extension is distributed and a README file giving a detailed description of it.

The metadata.json file

The metadata.json file defines your extension through a number of important elements. It must contain a valid JSON array containing the following entries:

Only the name and entrypoint fields are required.

Choosing between system and user

A user extension can be enabled by some users and not by others (typically for user preferences).

A system extension in comparison is enabled for every account.

Writing your own extension.php

This file is the core of your extension. It must define some key elements to be loaded by the extension system:

  1. The class name must be the entrypoint value defined in the metadata.json file suffixed by Extension (if your entrypoint value is HelloWorld, your class name will be HelloWorldExtension).
  2. The class must extend the Minz_Extension abstract class which defines the core methods and properties of a FreshRSS extension.
  3. The class must define the init method. This method is called only if the extension is loaded. Its purpose is to initialize the extension and its behavior during every page load.

The Minz_Extension abstract class defines a set of methods that can be overridden to fit your needs:

If your extension code is scattered in different classes, you need to load their source before using them. Of course you could include the files manually, but it’s more efficient to load them automatically. To do so, you just need to define the autoload method which will include them when needed. This method will be registered automatically when the extension is enabled.

The Minz_Extension abstract class defines another set of methods that should not be overridden:

Note that if you modify the later set of methods, you might break the extension system. Thus making FreshRSS unusable. So it’s highly recommended to let those unmodified.

The “hooks” system

You can register at the FreshRSS event system in an extensions init() method, to manipulate data when some of the core functions are executed.

class HelloWorldExtension extends Minz_Extension
{
	public function init() {
		$this->registerHook('entry_before_display', array($this, 'renderEntry'));
	}
	public function renderEntry($entry) {
		$entry->_content('<h1>Hello World</h1>' . $entry->content());
		return $entry;
	}
}

The following events are available:

Writing your own configure.phtml

When you want to support user configurations for your extension or simply display some information, you have to create the configure.phtml file.

TODO