path: root/docs/en/developers/03_Backend/05_Extensions.md

# 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](https://freshrss.org) and the official repository is hosted on Github: [github.com/FreshRSS/FreshRSS](https://github.com/FreshRSS/FreshRSS).

## The problem

FreshRSS is limited in its technical possibilities by various factors:

* The number of developers
* The will to integrate certain changes
* The level of "hacking" required to integrate marginal features

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:

* The model: this is the base object that we will manipulate. In FreshRSS, categories, flows and articles are templates. The part of the code that makes it possible to manipulate them in a database is also part of the model but is separated from the base model: we speak of DAO (for "Data Access Object"). The templates are stored in a `Models` folder.
* The view: this is what the user sees. The view is therefore simply HTML code mixed with PHP to display dynamic information. The views are stored in a `views` folder.
* The controller: this is what makes it possible to link models and views. Typically, a controller will load templates from the database (like a list of items) to "pass" them to a view for display. Controllers are stored in a `Controllers` directory.

### 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
<?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:

```html
<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
<?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:

```html
<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
<?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
<?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
<?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
<?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](/docs/en/internationalization.md).

### 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:

* A `metadata.json` file that contains a description of the extension. This file is written in JSON.
* An `extension.php` file containing the entry point of the extension (which is a class that inherits Minz_Extension).

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:
```html
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](https://github.com/FreshRSS/xExtension-HelloWorld).

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

* `configure.phtml` is the file containing the form to parameterize your extension
* A `static/` directory containing CSS and JavaScript files that you will need for your extension (note that if you need to write a lot of CSS it may be more interesting to write a complete theme)
* A `Controllers` directory containing additional controllers
* An `i18n` directory containing additional translations
* `layout` and` views` directories to define new views or to overwrite the current views

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:

* `name`: the name of your extension
* `author`: your name, your e-mail address ... but there is no specific format to adopt
* `description`: a description of your extension
* `version`: the current version number of the extension
* `entrypoint`: Indicates the entry point of your extension. It must match the name of the class contained in the file `extension.php` without the suffix` Extension` (so if the entry point is `HelloWorld`, your class will be called` HelloWorldExtension`)
* `type`: Defines the type of your extension. There are two types: `system` and` user`. We will study this difference right after.

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_).
1. The class must extend the `Minz_Extension` abstract class which defines the core methods and properties of a FreshRSS extension.
1. 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:
* the `install` method is called when the user enables the extension in the configuration page. It must return _true_ when successful and a string containing an error message when not. Its purpose is to prepare FreshRSS for the extension (adding a table to the database, creating a folder tree, ...).
* the `uninstall` method is called when the user disables the extension in the configuration page. It must return _true_ when successful and a string containing an error message when not. Its purpose is to clean FreshRSS (removing a table from the database, deleting a folder tree, ...). Usually it reverts changes introduced by the `install` method.
* the `handleConfigureAction` method is called when a user loads the extension configuration panel. It contains the logic to validate and store the submitted values defined in the `configure.phtml` file.

> 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:
* the `getName`, `getEntrypoint`, `getPath`, `getAuthor`, `getDescription`, `getVersion`, and `getType` methods return the extension internal properties. Those properties are extracted from the `metadata.json` file.
* the `getFileUrl` returns the URL of the selected file. The file must exist in the `static` folder of the extension.
* the `registerController` method register an extension controller in FreshRSS. The selected controller must be defined in the extension _Controllers_ folder, its file name must be _<name>Controller.php_, and its class name must be *FreshExtension\_<name>\_Controller*.
* the `registerViews` method registers the extension views in FreshRSS.
* the `registerTranslates` method registers the extension translation files in FreshRSS.
* the `registerHook` method registers hook actions in different part of the application.
* the `getSystemConfiguration` method retrieves the extension configuration for the system.
* the `setSystemConfiguration` method stores the extension configuration for the system.
* the `removeSystemConfiguration` method removes the extension configuration for the system.
* the `getUserConfiguration` method retrieves the extension configuration for the current user.
* the `setUserConfiguration` method stores the extension configuration for the current user.
* the `removeUserConfiguration` method removes the extension configuration for the current user.

> 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.

```html
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:

* `check_url_before_add` (`function($url) -> Url | null`): will be executed every time a URL is added. The URL itself will be passed as parameter. This way a website known to have feeds which doesn't advertise it in the header can still be automatically supported.
* `entry_before_display` (`function($entry) -> Entry | null`): will be executed every time an entry is rendered. The entry itself (instance of FreshRSS\_Entry) will be passed as parameter.
* `entry_before_insert` (`function($entry) -> Entry | null`): will be executed when a feed is refreshed and new entries will be imported into the database. The new entry (instance of FreshRSS\_Entry) will be passed as parameter.
* `feed_before_actualize` (`function($feed) -> Feed | null`): will be executed when a feed is updated. The feed (instance of FreshRSS\_Feed) will be passed as parameter.
* `feed_before_insert` (`function($feed) -> Feed | null`): will be executed when a new feed is imported into the database. The new feed (instance of FreshRSS\_Feed) will be passed as parameter.
* `freshrss_init` (`function() -> none`): will be executed at the end of the initialization of FreshRSS, useful to initialize components or to do additional access checks.
* `freshrss_user_maintenance` (`function() -> none`): will be executed for each user during the `actualize_script`, useful to run some maintenance tasks on the user.
* `js_vars` (`function($vars = array) -> array | null`): will be executed if the `jsonVars` in the header will be generated.
* `menu_admin_entry` (`function() -> string`): add an entry at the end of the "Administration" menu, the returned string must be valid HTML (e.g. `<li class="item active"><a href="url">New entry</a></li>`).
* `menu_configuration_entry` (`function() -> string`): add an entry at the end of the "Configuration" menu, the returned string must be valid HTML (e.g. `<li class="item active"><a href="url">New entry</a></li>`).
* `menu_other_entry` (`function() -> string`): add an entry at the end of the header dropdown menu (i.e. after the "About" entry), the returned string must be valid HTML (e.g. `<li class="item active"><a href="url">New entry</a></li>`).
* `nav_menu` (`function() -> string`): will be executed if the navigation was built.
* `nav_reading_modes` (`function($reading_modes) -> array | null`): **TODO** add documentation.
* `post_update` (`function(none) -> none`): **TODO** add documentation.
* `simplepie_before_init` (`function($simplePie, $feed) -> none`): **TODO** add documentation.

### 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**