Platform Team/Package Management System

Summary

Provides transparent for users and convenient for activity developers, method to support variety of activity dependencies and variety of dependency versions. In other words Services is a common deployment system for activity dependencies, lightweight like sugargame and hightweight like Qt.

The major difference from existed sugar deployment technics is that Services is activity developers POV system. It doesn't exclude(because reuse them) Sucrose releases or GNU/Linux distribution initiatives but gives activity developers additional(and optional) instrument.

Work flows

How it looks like for:

Users

In case of poor internet connection(and implemented Zero Install integration feature), user can switch to offline mode and won't encounter any changes in regular workflow. Switching to online mode brings additional progress bar to launch dialog for activities that have pending/not-yet-downloaded/out-dated activity dependencies.

Activity developers

Sugar Services makes sense only for activities that have non Sugar Platform dependencies and support more then one Sucrose release cycles.

For such activities development focus is shifting from Sucrose to API of services they are using. More over activity could be stuck to particular service API version(of course if service developers still support this branch) and Sugar Services will support several branches for the same service simultaneously.

To utilize Services benefits, activity developer just need to add feed file to bundle with list of urls to all services that activity uses and(if activity targeted to sugars w/o Zero Install integration) pure python library to initial launch of Services infrastructure. Services infrastructure will provide specified services(and specified versions) for activity and will export environment variables, like LD_LIBRARY_PATH or PYTHONPATH, to activity session, so activity developer shouldn't adapt code to Services.

Service developers

Services could be:

3rd party applications that are not included to Sugar Platform e.g. Qt
applications that were not included to all deployed Sugar Platforms e.g. gst-espeak came only from 0.84 and Services will let gst-espeak based activities work even in 0.82 environment
dependencies that are specific to particular activity e.g. some python activities have C libraries, using Services, activity developer should not bundle all binaries that sugar supports but provide links to binaries that he managed to build and let Services build C libraries from sources on user side in the rest of cases

To create new service developper needs to create and share proper feed file which url could be used in activity developers feed files.

Geeks

The whole Sugar Services feature is nothing but just a sugarized UI around 0install e.g. feed files that are beeing used in activity bundles are just regular 0install local feeds, so could be used to install/upgrade any software(including sugar core components).

Detailed Description

This proposal assumes that the core of sugar development(in common sense) is variety of developers rather then developers who are taking part in sugar core(glucose) development. So, it's all about seeing from activity/3rd-party developers.

From such new core POV, sugar development process will look like:

variety of sugar activities
that use Sugar Services

So, developers use a set of services that have theirs own API changes based schedules. Existed glucose could be treated as a big service and splited to several components but thats not a task for this proposal. Instead, it's about proposing basic infrastructure of Sugar Services and several services that are not part of glucose.

The corner stone of Sugar Services proposal is Saccharin service. This service provides installing/upgrading(via 0install) mechanism for all other services. The rest of services is just variety of libraries/applications.

Technically, service could be a part of glucose(or some of its releases) but from activity POV it doesn't make much sense, if activity requires some service, Saccharin will do nothing if requested service/version is a part of installed glucose or install proper service(via 0install). Various activities on the same system could use various versions of the same service, in that case Saccharin(via 0install) will just provide proper version to particular activity.

Versioning scheme

Each service has API changes based versioning scheme

<major-version>.<minor-version>

the major version starts from 0(premature state) and exposes the fact of API backwards compatibility breakage
the minor version is for bugfixes and features that don't break backwards compatibility

Documentation

List of services