Class PresenceSubscribeHandler

  • All Implemented Interfaces:
    ChannelHandler<org.xmpp.packet.Presence>, Module

    public class PresenceSubscribeHandler
    extends BasicModule
    implements ChannelHandler<org.xmpp.packet.Presence>
    Implements the presence protocol. Clients use this protocol to update presence and roster information.

    The handler must properly detect the presence type, update the user's roster, and inform presence subscribers of the session's updated presence status. Presence serves many purposes in Jabber so this handler will likely be the most complex of all handlers in the server.

    There are four basic types of presence updates:

    • Simple presence updates - addressed to the server (or to address), these updates are properly addressed by the server, and multicast to interested subscribers on the user's roster. An empty, missing, or "unavailable" type attribute indicates a simple update (there is no "available" type although it should be accepted by the server.
    • Directed presence updates - addressed to particular jabber entities, these presence updates are properly addressed and directly delivered to the entity without broadcast to roster subscribers. Any update type is possible except those reserved for subscription requests.
    • Subscription requests - these updates request presence subscription status changes. Such requests always affect the roster. The server must:
      • update the roster with the proper subscriber info
      • push the roster changes to the user
      • forward the update to the correct parties.
      The valid types include "subscribe", "subscribed", "unsubscribed", and "unsubscribe".
    • XMPPServer probes - Provides a mechanism for servers to query the presence status of users on another server. This allows users to immediately know the presence status of users when they come online rather than way for a presence update broadcast from the other server or tracking them as they are received. Requires S2S capabilities.


    There should be a way of determining whether a session has authorization to access this feature. I'm not sure it is a good idea to do authorization in each handler. It would be nice if the framework could assert authorization policies across channels.
    Iain Shigeoka
    • Constructor Detail

      • PresenceSubscribeHandler

        public PresenceSubscribeHandler()
    • Method Detail

      • process

        public void process​(org.xmpp.packet.Presence presence)
                     throws PacketException
        Description copied from interface: ChannelHandler
        Process an XMPP packet.
        Specified by:
        process in interface ChannelHandler<org.xmpp.packet.Presence>
        presence - a packet to process.
        PacketException - thrown if the packet is malformed (results in the sender's session being shutdown).
      • getStateChange

        public static PresenceSubscribeHandler.Change getStateChange​(RosterItem.SubType itemSubType,
                                                                     org.xmpp.packet.Presence.Type action,
                                                                     boolean isSending)
        Determine the changes to apply to the item, according to its subscription state. The method also turns the action and sending status into an integer code for easier processing (switch statements).

        Code relies on states being in numerical order without skipping. In addition, the receive states must parallel the send states so that (send state X) + STATE_RECV_SUBSCRIBE == (receive state X) where X is subscribe, subscribed, etc.

        itemSubType - The item to be updated
        action - The new state change request
        isSending - True if the roster owner of the item is sending the new state change request
        Change changes to apply to the item
      • initialize

        public void initialize​(XMPPServer server)
        Description copied from class: BasicModule

        Initializes the basic module.

        Inheriting classes that choose to override this method MUST call this initialize() method before accessing BasicModule resources.

        Specified by:
        initialize in interface Module
        initialize in class BasicModule
        server - the server hosting this module.