Purpose

Purpose

Offers available actions for a specific purpose

Introduction

This framework offers the possibility to create integrate services and actions on any application without having to implement them specifically. Purpose will offer them mechanisms to list the different alternatives to execute given the requested action type and will facilitate components so that all the plugins can receive all the information they need.

Usage

There's 2 main ways of using Purpose: from C++ and QML/QtQuick.

To import it from QML, import

import org.kde.purpose 1.0

It offers different ways of integrating the actions in an application. For full control on the procedure, we can use:

  • AlternativesModel for listing the different possibilities
  • JobView for displaying a job's status, including configuration

Furthermore, there's the AlternativesView component that will integrate all the process defined below for convenience.

If you want to import in the C++ application, you can import it using CMake by calling:

find_package(KF5Purpose)

Or its QMake counterpart. Then you'll have available the Purpose library if it needs to be done specifically and PurposeWidgets for convenience.

To integrate on the UI, QtQuick will still be used, as the configuration files provided by the plugins are written in QML. The recommended way to integrate on a QtWidgets interface is by using the Purpose::Menu class that will allow us to place the integration wherever pleases us. This class will offer us a pointer to the used Purpose::AlternativesModel so that we can specify what kind of services we're interested in.

Plugins

The plugin configuration

There will be 2 files specifying the behavior of a plugin:

  • The *PluginType.json files.
  • The plugin metadata JSON file.

The plugin type will be identified by the file name. It will specify:

  • X-Purpose-InboundArguments defines the arguments the application must provide.
  • X-Purpose-OutboundArguments defines the arguments the plugin must provide by the end of the execution.

In the plugin metadata we will define:

  • X-Purpose-PluginTypes defines the purposes tackled by the plugin
  • X-Purpose-Constraints defines the conditions that make plugin is useful, given the inboundArguments. These are the currently supported constraints
    • mimeType: for example mimeType:video/*. Useful to specify which kind of files the plugin is interested in.
    • exec: for example exec:kate. Can be used to show the plugin only if an executable is present in the $PATH directories.
    • application: for example application:org.kde.okular.desktop. Checks that the specified file is present in the $XDG_DATA_DIRS/applications directories of the system.
    • dbus: for example dbus:org.kde.kdeconnect. Will only offer the plugin if a certain dbus service is running on the system.
    • []: for example `['exec:bash', 'exec:zsh']`. an array of constraints can be used to restrict to either of the conditions instead of all of them.
  • X-Purpose-Configuration provides a list of extra arguments that the plugin will need. Ideally everything should be in the plugin type but sometimes we can only wish. This allows the opportunity to the application to let the user add the missing data.

Plugin types

The application says what it wants to do, Purpose finds the correct plugins. This is how we balance decoupling of implementation but keep on top of what the framework is supposed to do.

An example of such files is the ExportPluginType.json:

1 {
2  "KPlugin": {
3  "Icon": "edit-paste",
4  "Name": "Upload..."
5  },
6  "X-Purpose-InboundArguments": [ "urls", "mimeType" ],
7  "X-Purpose-OutboundArguments": [ "url" ]
8 }

As previously discussed, here we can define the generic tasks that the different plugins will implement on top, having the inbound arguments as a given and the outbound as a requirement.

Examples of such plugin types are (hypothetically, not all implemented yet):

  • Share: where you can get the different services to share
  • GetImage that would list your scanner, camera and also some web services.
  • AddContact that would let you add a contact on your address book or in whichever plugin is offered.

Plugin creation

There's two approaches to plugin implementation: native plugins and separate processes.

Native

To implement a Qt-based plugin, it will be required to implement a Purpose::PluginBase class, that acts as a factory for its Purpose::Job instances.

These will be the jobs in charge of performing the action the plugin is meant to do.

Furthermore, a pluginname_config.qml will be provided for extra Configuration, if required.

These plugins can be optionally be executed in-process.

Separate Process

Sometimes executing some actions through Qt code can require some extra work. For those cases, it's possible to implement the plugin in a separate process. It will require some extra work when it comes to implementing the feedback process with the main process but it allows to run plugins in any imaginable technologies.

The file structure for these plugins is the one of defined by KPackage which allows to package and distributethe plugins in an archive.

To that end, we will need to provide:

  • A manifest.json file, that will define the plugin description, capabilities and requirements.
  • A code/main* file that will be executed when the plugin action needs happen.
  • A config/config.qml file that will be in charge of requesting the necessary information to the user.

Disallowing plugins

It is possible to globally disable certain plugins through configuration file called purposerc in /etc/xdg (applies to all users) or in ~/.config (applies to current user).

The disabled plugins are specified as a comma-separated list in the disabled key in the plugins group.

1 [plugins]
2 # Disable KDE Connect and Imgur sharing plugins
3 disabled=kdeconnectplugin,imgurplugin
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