Events

Events are used to communicate between different aspects of the Nextcloud eco system. They are used in the Nextcloud server internally, for server-to-apps communcation as well as inter-app communication.

Overview

The term “events” is a bit broad in Nextcloud and there are multiple ways of emitting them.

OCP event dispatcher

This mechanism is a versatile and typed approach to events in Nextcloud’s php code. It uses objects rather than just passing primitives or untyped arrays. This should help provide a better developer experience while lowering the risk of unexpected changes in the API that are hard to find after the initial implementation.

Naming scheme

The name should reflect the subject and the actions. Prefixing event classes with Event makes it easier to recognize their purpose.

For example, if a user is created, a UserCreatedEvent will be emitted.

Events are ususally evmitted after the event has happened. If it’s emitted before, it should be prefixed with Before.

Thus BeforeUserCreatedEvent is emitted before the user data is written to the database.

Note

Although you may chose to name your event classes differently, sticking to the convention will allow Nextcloud developers understand each other’s apps more easily.

Writing events

As a rule events are dedicated classes extending \OCP\EventDispatcher\Event.

<?php

use OCP\EventDispatcher\Event;

namespace OCA\MyApp\Event;

class AddEvent extends Event {}

The event above allows signalling that something happened. But in many cases you want to actually transport data like the affected resource with the event. Then the events act as simple data transfer objects. Therefore they need a constructor that takes the arguments, private members to store them and getters to access the values in listeners.

<?php

use OCP\EventDispatcher\Event;
use OCP\IUser;

class UserCreatedEvent extends Event {

    /** @var IUser */
    private $user;

    public function __construct(IUser $user) {
        parent::__construct();
        $this->user = $user;
    }

    public function getUser(): IUser {
        return $this->user;
    }

}

Writing a listener

A listener can be a simple callback function (or anything else that is callable, or a dedicated class.

Listener callbacks

You can use simple callback to react on events. They will receive the event object as first and only parameter. You can type-hint the base Event class or the subclass you expect and register for.

<?php

use OCA\MyApp\Event\AddEvent;
use OCP\AppFramework\App;
use OCP\EventDispatcher\IEventDispatcher;

namespace OCA\MyApp\AppInfo;

class Application extends App {
    public function __construct() {
        parent::__construct('myapp');
            /* @var IEventDispatcher $eventDispatcher */
            $dispatcher = $this->getContainer()->query(IEventDispatcher::class);
            $dispatcher->addListener(AddEvent::class, function(AddEvent $event) {
                // ...
            });
    }
}

Note

Type-hinting the actual event class will give you better IDE and static analyzers support. It’s generally safe to assume the dispatcher will not give you any other objects.

Listener classes

A class that can handle an event will implement the \OCP\EventDispatcher\IEventListener interface. Class names should end with Listener.

<?php

use OCA\MyApp\Event\AddEvent;
use OCP\EventDispatcher\Event;
use OCP\EventDispatcher\IEventListener;

namespace OCA\MyApp\Event;

class AddTwoListener implements IEventListener {

    public function handle(Event $event): void {
        if (!($event instanceOf AddEvent)) {
            return;
        }

        $event->addToCounter(2);
    }
}

Note

Php parameter type hints are not allowed to be more specific than the type hints on the interface, thus you can’t use AddEvent in the method signature but use an instanceOf instead.

In the Application.php the event and the listener class are connected. The class is instantiated only when the actual event is fired.

<?php

use OCA\MyApp\Event\AddEvent;
use OCA\MyApp\Listener\AddTwoListener;
use OCP\AppFramework\App;
use OCP\EventDispatcher\IEventDispatcher;

namespace OCA\MyApp\AppInfo;

class Application extends App {
    public function __construct() {
        parent::__construct('myapp');

            /* @var IEventDispatcher $eventDispatcher */
            $dispatcher = $this->getContainer()->query(IEventDispatcher::class);
            $dispatcher->addServiceListener(AddEvent::class, AddTwoListener::class);
    }
}

Note

The listener is resolved via the DI container, therefore you can add a constructor and type-hint services required for processing the event.

Available Events

Here you find an overview of the public events that can be consumed in apps. See their source files for more details.

\OCP\Authentication\Events\LoginFailedEvent

Available in Nextcloud 19 and later.

Emitted when the authentication fails, but only if the login name can be associated with an existing user.

\OCP\Contacts\Events\ContactInteractedWithEvent

Available in Nextcloud 19 and later.

Event emitted by apps whenever there was an interaction with another user or contact.

\OCP\Mail\Events\BeforeMessageSent

Available in Nextcloud 19 and later.

Emitted before a system mail is sent. It can be used to alter the message.

\OCP\Share\Events\VerifyMountPointEvent

Available in Nextcloud 19 and later.

\OCP\User\Events\BeforeUserLoggedInWithCookieEvent

Available in Nextcloud 18 and later.

Emitted before a user is logged in via remember-me cookies.

\OCP\User\Events\UserLoggedInWithCookieEvent

Emitted when a user has been succesfully logged in via remember-me cookies.

Available in Nextcloud 18 and later.

\OCP\User\Events\BeforePasswordUpdatedEvent

Available in Nextcloud 18 and later.

Emitted before the user password is updated.

\OCP\User\Events\PasswordUpdatedEvent

Available in Nextcloud 18 and later.

Emitted when the user password has been updated.

\OCP\User\Events\BeforeUserCreatedEvent

Available in Nextcloud 18 and later.

Emitted before a new user is created on the back-end.

\OCP\User\Events\UserCreatedEvent

Available in Nextcloud 18 and later.

Emitted when a new user has been created on the back-end.

\OCP\User\Events\BeforeUserDeletedEvent

Available in Nextcloud 18 and later.

Emitted before a user is logged out.

\OCP\User\Events\UserDeletedEvent

Available in Nextcloud 18 and later.

Emitted when a user has been logged out successfully.

\OCP\User\Events\BeforeUserLoggedInEvent

Available in Nextcloud 18 and later.

\OCP\User\Events\BeforeUserLoggedOutEvent

Available in Nextcloud 18 and later.

\OCP\User\Events\CreateUserEvent

Available in Nextcloud 18 and later.

\OCP\User\Events\PostLoginEvent

Available in Nextcloud 18 and later.

\OCP\User\Events\UserChangedEvent

Available in Nextcloud 18 and later.

\OCP\User\Events\UserLoggedInEvent

Available in Nextcloud 18 and later.

\OCP\User\Events\UserLoggedOutEvent

Available in Nextcloud 18 and later.

\OCP\Security\CSP\AddContentSecurityPolicyEvent

Available in Nextcloud 17 and later.

This event is emitted so apps can modify the CSP provided by nextcloud. For example if more domains can be used to connect to. Added in Nextcloud 17.

Symfony event dispatcher

Warning

Using the Symfony event dispatcher mechanism is discouraged. Use the OCP event dispatcher abstraction instead.

tbd

Hooks

Warning

The hooks mechanism is deprecated. Use the OCP event dispatcher instead.

Hooks are used to execute code before or after an event has occurred. This is for instance useful to run cleanup code after users, groups or files have been deleted. Hooks should be registered in the app.php:

<?php
namespace OCA\MyApp\AppInfo;

$app = new Application();
$app->getContainer()->query('UserHooks')->register();

The hook logic should be in a separate class that is being registered in the Container:

<?php

namespace OCA\MyApp\AppInfo;

use \OCP\AppFramework\App;

use \OCA\MyApp\Hooks\UserHooks;


class Application extends App {

    public function __construct(array $urlParams=array()){
        parent::__construct('myapp', $urlParams);

        $container = $this->getContainer();

        /**
         * Controllers
         */
        $container->registerService('UserHooks', function($c) {
            return new UserHooks(
                $c->query('ServerContainer')->getUserManager()
            );
        });
    }
}
<?php

namespace OCA\MyApp\Hooks;

use OCP\IUserManager;

class UserHooks {

    private $userManager;

    public function __construct(IUserManager $userManager){
        $this->userManager = $userManager;
    }

    public function register() {
        $callback = function($user) {
            // your code that executes before $user is deleted
        };
        $this->userManager->listen('\OC\User', 'preDelete', $callback);
    }

}

Available hooks

The scope is the first parameter that is passed to the listen method, the second parameter is the method and the third one the callback that should be executed once the hook is being called, e.g.:

<?php

// listen on user predelete
$callback = function($user) {
    // your code that executes before $user is deleted
};
$userManager->listen('\OC\User', 'preDelete', $callback);

Hooks can also be removed by using the removeListener method on the object:

<?php

// delete previous callback
$userManager->removeListener(null, null, $callback);

The following hooks are available:

Session

Injectable from the ServerContainer by calling the method getUserSession().

Hooks available in scope \OC\User:

  • preSetPassword (\OC\User\User $user, string $password, string $recoverPassword)
  • postSetPassword (\OC\User\User $user, string $password, string $recoverPassword)
  • changeUser (\OC\User\User $user, string $feature, string $value)
  • preDelete (\OC\User\User $user)
  • postDelete (\OC\User\User $user)
  • preCreateUser (string $uid, string $password)
  • postCreateUser (\OC\User\User $user)
  • preLogin (string $user, string $password)
  • postLogin (\OC\User\User $user, string $password)
  • logout ()

UserManager

Injectable from the ServerContainer by calling the method getUserManager().

Hooks available in scope \OC\User:

  • preSetPassword (\OC\User\User $user, string $password, string $recoverPassword)
  • postSetPassword (\OC\User\User $user, string $password, string $recoverPassword)
  • preDelete (\OC\User\User $user)
  • postDelete (\OC\User\User $user)
  • preCreateUser (string $uid, string $password)
  • postCreateUser (\OC\User\User $user, string $password)

GroupManager

Hooks available in scope \OC\Group:

  • preAddUser (\OC\Group\Group $group, \OC\User\User $user)
  • postAddUser (\OC\Group\Group $group, \OC\User\User $user)
  • preRemoveUser (\OC\Group\Group $group, \OC\User\User $user)
  • postRemoveUser (\OC\Group\Group $group, \OC\User\User $user)
  • preDelete (\OC\Group\Group $group)
  • postDelete (\OC\Group\Group $group)
  • preCreate (string $groupId)
  • postCreate (\OC\Group\Group $group)

Filesystem root

Injectable from the ServerContainer by calling the method getRootFolder(), getUserFolder() or getAppFolder().

Filesystem hooks available in scope \OC\Files:

  • preWrite (\OCP\Files\Node $node)
  • postWrite (\OCP\Files\Node $node)
  • preCreate (\OCP\Files\Node $node)
  • postCreate (\OCP\Files\Node $node)
  • preDelete (\OCP\Files\Node $node)
  • postDelete (\OCP\Files\Node $node)
  • preTouch (\OCP\Files\Node $node, int $mtime)
  • postTouch (\OCP\Files\Node $node)
  • preCopy (\OCP\Files\Node $source, \OCP\Files\Node $target)
  • postCopy (\OCP\Files\Node $source, \OCP\Files\Node $target)
  • preRename (\OCP\Files\Node $source, \OCP\Files\Node $target)
  • postRename (\OCP\Files\Node $source, \OCP\Files\Node $target)

Filesystem scanner

Filesystem scanner hooks available in scope \OC\Files\Utils\Scanner:

  • scanFile (string $absolutePath)
  • scanFolder (string $absolutePath)
  • postScanFile (string $absolutePath)
  • postScanFolder (string $absolutePath)

Public emitter

Warning

The public emitter mechanism is deprecated. Use the OCP event dispatcher instead.

tbd