Hooks: event-driven model

Basics

Along with the flexibility of a plugin-oriented framework comes always the need for an event-oriented mechanism to link the plugins together. This is very important to avoid introducing hard dependencies from one plugin to another, by directly calling a plugin method from within another.

Instead, the first plugin will trigger an event (here, a hook), that will be handled by a central manager, without much knowledge of what will happen to this event. The event can “transport” some bit of informations, like a node, or anything else that makes sense.

On the other side, any plugin can register to the central manager, to be informed of whenever this event is triggered. That way, Plugin A actually triggers a function inside Plugin B (and / or plugin C, D, etc), without knowing anything about the existence of plugin B.

Hooks

In Pydio, hooks are declared as needed directly in the PHP code, by simply calling the Controller::applyHook() method. Thus, the available hooks list is gathered by a script that does some code introspection. The result is visible in the Settings panel, under Developer Resources > Hooks Definitions. Currently, there are 3 types of hooks : node.* (informing a change on a data node), user.* (informing about users creation/deletion), and msg.* (used for transporting any specific messages, generally in an “instant” manner).

To register a listener to a given hook, a plugin will add a callback inside the <hooks> element of its manifest.xml, declaring a method of the plugin class. For example :

<hooks>
    <serverCallback hookName="node.info" methodName="loadNodeInfo"/>
</hooks>

The serverCallback will take an optional defer attribute, that would apply the node at the very end of the script, after all output is sent to the user.

Examples

The figure below show some of the hooks triggered during the life of a node when a file is uploaded (node1) or when listing a directory content (node 2).

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