Friendica Storage Backend Addon development

Storage backends can be added via addons. A storage backend is implemented as a class, and the plugin register the class to make it avaiable to the system.

The Storage Backend Class

The class must live in Friendica\Addon\youraddonname namespace, where youraddonname the folder name of your addon.

The class must implement Friendica\Model\Storage\IStorage interface. All method in the interface must be implemented:

namespace Friendica\Model\Storage;

interface IStorage
{
    public static function get($ref);
    public static function put($data, $ref = "");
    public static function delete($ref);
    public static function getOptions();
    public static function saveOptions($data);
}

Each storage backend can have options the admin can set in admin page.

The array returned by getOptions() is defined as:

[
    'option1name' => [ ..info.. ],
    'option2name' => [ ..info.. ],
    ...
]

An empty array can be returned if backend doesn't have any options.

The info array for each option is defined as:

[
    'type',

define the field used in form, and the type of data. one of 'checkbox', 'combobox', 'custom', 'datetime', 'input', 'intcheckbox', 'password', 'radio', 'richtext', 'select', 'select_raw', 'textarea', 'yesno'

    'label',

Translatable label of the field. This label will be shown in admin page

    value,

Current value of the option

    'help text',

Translatable description for the field. Will be shown in admin page

    extra data

Optional. Depends on which 'type' this option is:

Each label should be translatable

];

See doxygen documentation of IStorage interface for details about each method.

Register a storage backend class

Each backend must be registered in the system when the plugin is installed, to be aviable.

Friendica\Core\StorageManager::register($name, $class) is used to register the backend class. The $name must be univocal and will be shown to admin.

When the plugin is uninstalled, registered backends must be unregistered using Friendica\Core\StorageManager::unregister($class).

Example

Here an hypotetical addon which register an unusefull storage backend. Let's call it samplestorage.

This backend will discard all data we try to save and will return always the same image when we ask for some data. The image returned can be set by the administrator in admin page.

First, the backend class. The file will be addon/samplestorage/SampleStorageBackend.php:

<?php
namespace Friendica\Addon\samplestorage;

use Friendica\Model\Storage\IStorage;

use Friendica\Core\Config;
use Friendica\Core\L10n;

class SampleStorageBackend implements IStorage
{
    public static function get($ref)
    {
        // we return alwais the same image data. Which file we load is defined by
        // a config key
        $filename = Config::get("storage", "samplestorage", "sample.jpg");
        return file_get_contents($filename);
    }

    public static function put($data, $ref = "")
    {
        if ($ref === "") {
            $ref = "sample";
        }
        // we don't save $data !
        return $ref;
    }

    public static function delete($ref)
    {
        // we pretend to delete the data
        return true;
    }

    public static function getOptions()
    {
        $filename = Config::get("storage", "samplestorage", "sample.jpg");
        return [
            "filename" => [
                "input",    // will use a simple text input
                L10n::t("The file to return"),  // the label
                $filename,  // the current value
                L10n::t("Enter the path to a file"), // the help text
                // no extra data for "input" type..
        ];
    }

    public static function saveOptions($data)
    {
        // the keys in $data are the same keys we defined in getOptions()
        $newfilename = trim($data["filename"]);

        // this function should always validate the data.
        // in this example we check if file exists
        if (!file_exists($newfilename)) {
            // in case of error we return an array with
            // ["optionname" => "error message"]
            return ["filename" => "The file doesn't exists"];
        }

        Config::set("storage", "samplestorage", $newfilename);

        // no errors, return empty array
        return [];
    }
}

Now the plugin main file. Here we register and unregister the backend class.

The file is addon/samplestorage/samplestorage.php

<?php
/**
 * Name: Sample Storage Addon
 * Description: A sample addon which implements an unusefull storage backend
 * Version: 1.0.0
 * Author: Alice <https://alice.social/~alice>
 */

use Friendica\Core\StorageManager;
use Friendica\Addon\samplestorage\SampleStorageBackend;

function samplestorage_install()
{
    // on addon install, we register our class with name "Sample Storage".
    // note: we use `::class` property, which returns full class name as string
    // this save us the problem of correctly escape backslashes in class name
    StorageManager::register("Sample Storage", SampleStorageBackend::class);
}

function samplestorage_unistall()
{
    // when the plugin is uninstalled, we unregister the backend.
    StorageManager::unregister("Sample Storage");
}

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