Presence Service: Difference between revisions
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== Overview == |
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The '''Presence Service''' is a D-Bus service on the XO that coordinates [[activity sharing]]. It uses [[Telepathy]] to access the network. It provides information about other people on the network and what activities they are participating in. It is responsible for initiating Telepathy connections when the XO is turned on, reconnecting Telepathy connections when they are disconnected, and registering the laptop with the Jabber server. |
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Sugar provides a wrapper interface to the D-Bus API in the Python module <tt>sugar.presence</tt>. |
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Sugar's “neighborhood view” (or “mesh view”) uses the Presence Service to show who is online (“present”). This performs a function similar to that of a buddy list in a conventional instant messaging application. |
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See [[Activity sharing]] for an overview of collaboration, or [[Collaboration Tutorial]] for how to add collaboration to an activity. |
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== Presence stack == |
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[[Image:PresenceStack.png]] |
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Python activities (and Sugar) make use of the <tt>sugar.presence</tt> module to interact with Presence Service. sugar.presence provides an API for accessing Presence Service over the D-Bus session bus. |
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Presence Service in turn interacts with [[Gabble]] and [[Salut]] over the session bus, and once everything is set up (or in the case of non-Python activities) the activity can use [[Telepathy]] directly (for example, to use [[Tubes]]). |
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== Connection types == |
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Presence Service supports two Telepathy backends (connection managers): |
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* [[Telepathy Gabble]], that provides server-based Jabber/XMPP functionality. It talks to a Jabber server (e.g. olpc.collabora.co.uk) and sets up different chat rooms through which activities talk to each other. |
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* [[Telepathy Salut]], a link-local Connection Manager using reliable multicast over the local network |
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Although Telepathy hides the differences between the protocols, the Presence Services varies its behaviour a little according to which connection it is using. To achieve this, it internally uses a plugin structure, where each type of connection used has an associated plugin. |
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Only one connection manager is used at a time. The [[Presence Service]] will |
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use Gabble when it has Internet access (a valid IPv4 address) and has connected |
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to a [[Jabber server]], otherwise Salut. |
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== Active connection == |
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'''Though Presence Service is designed to run both connection managers simultaneously, at this stage only one is in effect at a time, since there is no UI support for showing which activities are shared on which connection.''' |
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Presence Service will use Gabble when it has Internet access (a valid IPv4 address) and has connected to a [[Jabber server]], otherwise Salut (but not both at the same time). Here is the sequence of events: |
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* Both plugins are started when Presence Service starts, unless PRESENCE_SERVICE_DEBUG=disable-gabble or disable-salut are set. |
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* Salut succeeds faster than Gabble, so link local buddies are shown first. |
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* PS's server plugin watches Network Manager signals on the D-Bus system bus. |
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* When NM indicates that we have a valid IPv4 address, we run the _init_connection method of the ServerPlugin instance. |
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:* Gabble is automatically run by the session bus (dbus-daemon) via service activation, the first time the Presence Service uses it, if it isn't already running. |
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:* If the Gabble connection fails, we schedule a timer (starting at 5 seconds with exponential backoff to a maximum of 5 minutes) and retry running _init_connection when the timer runs out. |
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::(classes TelepathyPlugin and ServerPlugin, methods _init_connection, _reconnect_cb, _could_connect, _handle_connection_status_change.) |
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* If the server plugin has connected to a jabber server, PS stops the link local plugin (salut). Link local buddies disappear. |
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* If NM loses the IP address, the server plugin stops itself. |
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* When the server plugin stops, PS starts the link local plugin. |
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== API == |
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Python code can use the sugar.presence library to talk to Presence Service. Non-python code can use the API that Presence Service provides over the D-Bus session bus. |
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See [[Low-level Activity API#Presence]] for the basic operations, and [[Presence Service DBus API]] for a more comprehensive, but out of date, API listing. |
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== Source == |
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Browse: http://dev.laptop.org/git?p=projects/presence-service;a=summary |
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Clone: |
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git clone git://dev.laptop.org/projects/presence-service |
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[[category:Telepathy]] |
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[[category:Collaboration]] |
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[[category:Developers]] |
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== Release process == |
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* Update NEWS |
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* Bump version in configure.ac |
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* git commit configure.ac -m "version $VERSION" |
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* git tag "$VERSION" |
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* git push |
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* make distcheck |
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* Upload the tarball to dev.laptop.org:/var/www/sugar/sources/sugar-presence-service ( https://dev.laptop.org/pub/sugar/sources/sugar-presence-service/ ) |
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* Send an announce mail to devel-announce@lists.sugarlabs.org. Include a reference to the source code tarball and an high level, user oriented list of changes. (see http://wiki.sugarlabs.org/go/ReleaseTeam#Module_release) |
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* Update sugar-presence-service rpm package for Fedora on the '''devel''' and '''F-9''' <s>OLPC-3</s> branches as explained on https://fedoraproject.org/wiki/PackageMaintainers/UpdatingPackageHowTo - note that Dennis Gilmore must then tag the packages into dist-olpc3 to get into joyride. |
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