Activity bundles

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Introduction

Activities in the Sugar environment are packaged into a self-contained "bundles". Each bundle contains all the resources and executable code (other than system-provided base libraries) which the activity needs to execute. Any resources or executable code that is not provided by the base system must be packaged within the bundle. Activity bundles are the end result of, and use a different directory structure than, activity development

See also

Rationale

Activities are meant to be shared between children. If a child doesn't have the activity, it is automatically transfered to the child when he or she joins the shared activity. Packaging activities in self-contained bundles allows easy sharing, installation, removal, and backup.

Location

Activities are installed and removed automatically by Sugar, in response to user actions. Sugar places activities in directory of its choice. Activities should not rely on being installed in a specific location, and should use relative paths where paths are necessary (i.e., for shared library linkage, activity resources such as images, sounds, etc). They should also not rely on the bundle's base directory name remaining the same. Sugar may rename the activity bundle base directory at any time to prevent bundle conflicts.

Currently Sugar on jhbuild looks for bundles in the "activities" subfolders of XDG_DATA_DIRS. Right now this is /usr/share/activities and the usr/share/activities subfolder of the jhbuild build folder.

Sugar will automatically generate and remove the .service files necessary to launch the activity through D-BUS service activation when the activity is installed or removed.

Activities should also NEVER store local state or preferences in the activity bundle itself. These should always be stored in an activity-specific directory in the user's sugar profile, available through the SUGAR_PROFILE environment variable.

Python developers can also get the profile folder this way: 

import sugar.env
profile_path = sugar.env.get_profile_path()

Bundle Structure

The activity bundle is a directory, with a name ending in ".activity". Each activity bundle must, in a subdirectory called 'activity', contain a file named "activity.info", and following a special format. For example: 

Web.activity/
    bin/
        web-activity
    locale/
        de_DE/
            activity.linfo
        zh_CN/
            activity.linfo
    activity/
        activity.info
        activity-web.svg
        contents
        contents.sig
        mimetypes.xml
    icons/
activity

All metadata about the activity is organized in this subdirectory. The contents and contents.sig are manifest and credential files for the entire bundle contents (excepting the contents and contents.sig files themselves), as described by the Manifest Specification. The optional mimetypes.xml file is a freedesktop.org MIME type file describing how to recognize the MIME types defined by the activity.

icons

Contains the icons used by the activity. When using the sugar.activity python package the path is automatically added to the default gtk icon theme.

.info File Format

.info files follow a key/value pair format, similar to the fd.o desktop entry spec, but not conforming to it. An example is shown here: 

[Activity]
name = Web
activity_version = 1
host_version = 1
bundle_id = com.redhat.Sugar.BrowserActivity
icon = activity-web
exec = sugar-activity browseractivity.BrowserActivity -s
mime_types = application/pdf;image/tiff

A more detailed explanation of the valid properties follows: 

[Activity]
The activity.info file must begin with [Activity], and only that, on the first line of the file
name = Web
This is the name is displayed in Sugar referring to the activity. A 'name' key without a bracketed language code is the "en_US" localized name of the activity. The activity.info file must have this key.
activity_version = 1
Each activity.info file must have a "activity_version" key. The version is a single positive integer. Larger versions are considered "newer". The value assigned to this key should be considered opaque to the activity; the only requirement of the activity is that it must be larger for new activity builds.
host_version = 1
Each activity.info file must have a "host_version" key. The version is a single positive integer. This specifies the version of the Sugar environment which the activity is compatible with. (fixme: need to specify sugar versions somewhere. Obviously we start with 1.)
bundle_id = com.redhat.Sugar.BrowserActivity
This is the activity bundle identifier. It is required. It is also used as the activity's default service type when the activity is shared on the network. To determine this type, the distince parts (separated by the '.' character) are reversed, any '.' is replaced by a '_' character, and the type is prefixed by a '_' character. So in this example, the default service type would be "_BrowserActivity_Sugar_redhat_com".
icon = activity-web
It points to the activity's icon. The icon is looked up in the activity bundle's base directory. It cannot contain a path. When searching for the icon in the activity bundle's base directory, only an file with the icon name and the extension '.svg' will be looked for.
exec = sugar-activity webactivity.WebActivity
The exec key specifies the executable which Sugar runs to start the activity instances. Environment variables given on the exec line are expanded. Executable files should be placed into the bin/ directory in the bundle. It should support the following arguments:
-b, --bundle-id
Identifier of the activity bundle
-a, --activity-id
Identifier of the activity instance.
-o, --object-id
Identifier of the associated datastore object.
-u, --uri
URI to load.

Python activities should generally use the generic sugar-activity executable. Other activities need to adhere to the Low-level Activity API. 

mime_types = application/pdf;image/tiff
List of mime types supported by the activity, separated by semi colons. It's used when opening a file from the web or to present to the user a list of activities which can open a certain journal object.
show_launcher = yes
This key is optional. If not present, or if present with a value of "yes", the activity is shown with its icon in the Sugar panel launcher and a valid 'icon' key/value pair is required. If specified with a value of "no", the activity is not shown in the Sugar panel launcher, and the 'icon' key is not required.

Future Properties

There are properties anticipated to be used by future Sugar versions. In general, Sugar will ignore unknown properties, and use defaults for missing properties. 

tags = ...
List of tags to categorize this activity. Not yet implemented, see #6634.
update_url = ...
URL to retrieve update information. Not specified yet, see #4951.

Activity Name Localization/Translation

Localized data lives in the locale directory. Each language stores its localized keys in a separate directory named for the language's ISO code. Localized keys from the 'activity.info' file are stored in the 'activity.linfo' files in that directory. For example, German-localized German (as opposed to Swiss-localized German) language translations are stored in the 'de_DE/activity.linfo' file: 

Example.activity/
    exampleactivity.py
    activity/
        activity.info
    locale/
        de_DE/
            activity.linfo
        de_CH/
            activity.linfo
        es/
            activity.linfo

At this time, only translations for the 'name' key from the 'activity.info' file is supported. A localized 'de_DE/activity.linfo' file would look like: 

[Activity]
name = Web

Keys in the languague-specific '.linfo' files selectively override keys from the 'activity.info' file; if a key is not present in the '.linfo' file the value from the 'activity.info' file is used instead.

Package, extension, mime type

Activity bundles should be packaged as zip files with the ".xo" extension. The mime type in the journal is "application/vnd.olpc-sugar".

Bundling Native Libraries

Sometimes you need to include a native library or two with your activity. A good strategy, the one that Develop and Model use, is to specify a shell script for the executable in the .info file: 

exec = ./model_startup.sh

The script, 'model_startup.sh', modifies the library path, python, or both paths (depending on the types of libraries you are including) to point to folders inside your bundle, then launches your application: 

#!/bin/sh

export PYTHONPATH=$SUGAR_BUNDLE_PATH/site-packages:$PYTHONPATH
export LD_LIBRARY_PATH=$SUGAR_BUNDLE_PATH/lib:$LD_LIBRARY_PATH

sugar-activity model_app.ModelActivity

Make sure to add your shell script and any native libraries to the MANIFEST before you package your bundle. You can also accomplish the same thing by throwing all your libraries in the root folder of the bundle, like the Map activity does, but that can get messy very quick.

Other Technologies Comparison

Activity bundles are similar to OS X bundles or Java JAR files; a simple mechanism to encapsulate everything you need in a single directory that can be moved around independently.

It differs from autopackage, it's not a package management system. There's no central database, no scripts get run on install/uninstall. There also is no special file format.

As compared to klik, it's not intended to replicate a local Unix directory structure inside the package; the activity can still link to system provided binaries and such. There's also no server-side component other than compressing the archive and sending it over the network.There is also no dependency checking since activities are required to be self-contained.

See also

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