path: root/spec/Channel_Dispatch_Operation.xml

<?xml version="1.0" ?>
<node name="/Channel_Dispatch_Operation"
  xmlns:tp="http://telepathy.freedesktop.org/wiki/DbusSpec#extensions-v0">

  <tp:copyright>Copyright © 2008-2009 Collabora Ltd.</tp:copyright>
  <tp:copyright>Copyright © 2008-2009 Nokia Corporation</tp:copyright>
  <tp:license xmlns="http://www.w3.org/1999/xhtml">
    <p>This library is free software; you can redistribute it and/or
      modify it under the terms of the GNU Lesser General Public
      License as published by the Free Software Foundation; either
      version 2.1 of the License, or (at your option) any later version.</p>

    <p>This library is distributed in the hope that it will be useful,
      but WITHOUT ANY WARRANTY; without even the implied warranty of
      MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
      Lesser General Public License for more details.</p>

    <p>You should have received a copy of the GNU Lesser General Public
      License along with this library; if not, write to the Free Software
      Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston,
      MA 02110-1301, USA.</p>
  </tp:license>

  <interface name="org.freedesktop.Telepathy.ChannelDispatchOperation">
    <tp:added version="0.17.UNRELEASED">(as a stable interface)</tp:added>

    <tp:docstring xmlns="http://www.w3.org/1999/xhtml">
      <p>A channel dispatch operation is an object in the ChannelDispatcher
        representing a batch of unrequested channels being announced to
        client
        <tp:dbus-ref namespace="org.freedesktop.Telepathy.Client">Approver</tp:dbus-ref>
        processes.</p>

      <p>These objects can result from new incoming channels or channels
        which are automatically created for some reason, but cannot result
        from outgoing requests for channels.</p>

      <p>More specifically, whenever the
        <tp:dbus-ref namespace="org.freedesktop.Telepathy">Connection.Interface.Requests.NewChannels</tp:dbus-ref>
        signal contains channels whose
        <tp:dbus-ref namespace="org.freedesktop.Telepathy.Channel">Requested</tp:dbus-ref>
        property is false, or whenever the
        <tp:dbus-ref namespace="org.freedesktop.Telepathy">Connection.NewChannel</tp:dbus-ref>
        signal contains a channel with suppress_handler false,
        one or more ChannelDispatchOperation objects are created for those
        channels.</p>

      <p>(If some channels in a NewChannels signal are in different bundles,
        this is an error. The channel dispatcher SHOULD recover by treating
        the NewChannels signal as if it had been several NewChannels signals
        each containing one channel.)</p>

      <p>First, the channel dispatcher SHOULD construct a list of all the
        <tp:dbus-ref
          namespace="org.freedesktop.Telepathy.Client">Handler</tp:dbus-ref>s
        that could handle all the channels (based on their <tp:dbus-ref
          namespace="org.freedesktop.Telepathy.Client.Handler">HandlerChannelFilter</tp:dbus-ref>
        property), ordered by
        priority in some implementation-dependent way. If there are handlers
        which could handle all the channels, one channel dispatch operation
        SHOULD be created for all the channels. If there are not, one channel
        dispatch operation SHOULD be created for each channel, each with
        a list of channel handlers that could handle that channel.</p>

      <p>If no handler at all can handle a channel, the channel dispatcher
        SHOULD terminate that channel instead of creating a channel dispatcher
        for it. It is RECOMMENDED that the channel dispatcher closes
        the channels using <tp:dbus-ref
          namespace="org.freedesktop.Telepathy">Channel.Interface.Destroyable.Destroy</tp:dbus-ref>
        if supported, or <tp:dbus-ref
          namespace="org.freedesktop.Telepathy">Channel.Close</tp:dbus-ref>
        otherwise. As a special case, the channel dispatcher SHOULD NOT close
        <tp:dbus-ref
          namespace="org.freedesktop.Telepathy.Channel.Type">ContactList</tp:dbus-ref>
        channels, and if Close fails, the channel dispatcher SHOULD ignore
        that channel.</p>

      <tp:rationale>
        <p>ContactList channels are strange. We hope to replace them with
          something better, such as an interface on the Connection, in a
          future version of this specification.</p>
      </tp:rationale>

      <p>When listing channel handlers, priority SHOULD be given to
        channel handlers that are already handling channels from the same
        bundle.</p>

      <p>If a handler with <tp:dbus-ref
          namespace="org.freedesktop.Telepathy.Client.Handler">BypassApproval</tp:dbus-ref>
        <code>= True</code> could handle all of the channels in the dispatch
        operation, then the channel dispatcher SHOULD call <tp:dbus-ref
          namespace="org.freedesktop.Telepathy.Client.Handler">HandleChannels</tp:dbus-ref>
        on that handler, and (assuming the call succeeds) emit
        <tp:member-ref>Finished</tp:member-ref> and stop processing those
        channels without involving any approvers.</p>

      <tp:rationale>
        <p>Some channel types can be picked up "quietly" by an existing
          channel handler. If a <tp:dbus-ref
            namespace="org.freedesktop.Telepathy.Channel.Type">Text</tp:dbus-ref>
          channel is added to an existing bundle containing a <tp:dbus-ref
            namespace="org.freedesktop.Telepathy.Channel.Type">StreamedMedia</tp:dbus-ref>
          channel, there shouldn't be
          any approvers, flashing icons or notification bubbles, if the
          the UI for the StreamedMedia channel can just add a text box
          and display the message.</p>
      </tp:rationale>

      <p>Otherwise, the channel dispatcher SHOULD send the channel dispatch
        operation to all relevant approvers (in parallel) and wait for an
        approver to claim the channels or request that they are handled.
        See
        <tp:dbus-ref
          namespace="org.freedesktop.Telepathy.Client.Approver">AddDispatchOperation</tp:dbus-ref>
        for more details on this.</p>

      <p>Finally, if the approver requested it, the channel dispatcher SHOULD
        send the channels to a handler.</p>
    </tp:docstring>

    <property name="Interfaces" tp:name-for-bindings="Interfaces"
      type="as" access="read" tp:type="DBus_Interface[]">
      <tp:docstring>
        A list of the extra interfaces provided by this channel dispatch
        operation. This property cannot change.
      </tp:docstring>
    </property>

    <property name="Connection" tp:name-for-bindings="Connection"
      type="o" access="read">
      <tp:docstring>
        The <tp:dbus-ref
          namespace="org.freedesktop.Telepathy">Connection</tp:dbus-ref>
        with which the <tp:member-ref>Channels</tp:member-ref> are
        associated. The well-known bus name to use can be derived from
        this object path by removing the leading '/' and replacing all
        subsequent '/' by '.'. This property cannot change.
      </tp:docstring>
    </property>

    <property name="Account" tp:name-for-bindings="Account"
      type="o" access="read">
      <tp:docstring>
        The <tp:dbus-ref
          namespace="org.freedesktop.Telepathy">Account</tp:dbus-ref>
        with which the <tp:member-ref>Connection</tp:member-ref>
        and <tp:member-ref>Channels</tp:member-ref> are
        associated. This property cannot change.
      </tp:docstring>
    </property>

    <property name="Channels" tp:name-for-bindings="Channels"
      type="a(oa{sv})" access="read" tp:type="Channel_Details[]">
      <tp:docstring>
        The <tp:dbus-ref
          namespace="org.freedesktop.Telepathy">Channel</tp:dbus-ref>s
        to be dispatched, and their properties. Change notification is via
        the <tp:member-ref>ChannelLost</tp:member-ref> signal (channels
        cannot be added to this property, only removed).
      </tp:docstring>
    </property>

    <signal name="ChannelLost" tp:name-for-bindings="Channel_Lost">
      <tp:docstring xmlns="http://www.w3.org/1999/xhtml">
        <p>A channel has closed before it could be claimed or handled. If
          this is emitted for the last remaining channel in a channel
          dispatch operation, it MUST immediately be followed by
          <tp:member-ref>Finished</tp:member-ref>.</p>

        <p>This signal MUST NOT be emitted until all Approvers that were
          invoked have returned (successfully or with an error) from
          their <tp:dbus-ref
            namespace="org.freedesktop.Telepathy.Client.Approver">AddDispatchOperation</tp:dbus-ref>
          method.</p>

        <tp:rationale>
          <p>This means that Approvers can connect to the ChannelLost signal
            in a race-free way. Non-approver processes that discover
            a channel dispatch operation in some way (such as observers)
            will have to follow the usual "connect to signals then recover
            state" model - first connect to ChannelLost and
            <tp:member-ref>Finished</tp:member-ref>,
            then download <tp:member-ref>Channels</tp:member-ref> (and
            on error, perhaps assume that the operation has already
            Finished).</p>
        </tp:rationale>
      </tp:docstring>

      <arg name="Channel" type="o">
        <tp:docstring>
          The <tp:dbus-ref
            namespace="org.freedesktop.Telepathy">Channel</tp:dbus-ref>
          that closed.
        </tp:docstring>
      </arg>

      <arg name="Error" type="s" tp:type="DBus_Error_Name">
        <tp:docstring xmlns="http://www.w3.org/1999/xhtml">
          <p>The name of a D-Bus error indicating why the channel closed. If
            no better reason can be found,
            <code>org.freedesktop.Telepathy.Error.NotAvailable</code> MAY
            be used as a fallback; this means that this error SHOULD NOT be
            given any more specific meaning.</p>
        </tp:docstring>
      </arg>

      <arg name="Message" type="s">
        <tp:docstring>
          A string associated with the D-Bus error.
        </tp:docstring>
      </arg>
    </signal>

    <property name="PossibleHandlers" tp:name-for-bindings="Possible_Handlers"
      type="as" access="read" tp:type="DBus_Well_Known_Name[]">
      <tp:docstring>
        <p>The well known bus names (starting with
          <code>org.freedesktop.Telepathy.Client.</code>) of the possible
          <tp:dbus-ref
            namespace="org.freedesktop.Telepathy.Client">Handler</tp:dbus-ref>s
          for these channels. The channel dispatcher MUST place the most
          preferred handlers first, according to some reasonable heuristic.
          As a result, approvers SHOULD use the first handler by default.</p>

        <p>The heuristic used to prioritize handlers SHOULD give a higher
          priority to handlers that are already running.</p>

        <tp:rationale>
          <p>If, for instance, Empathy and Kopete have similar functionality,
            and Empathy is running, we should prefer to send channels to it
            rather than launching Kopete via service activation.</p>
        </tp:rationale>
      </tp:docstring>
    </property>

    <method name="HandleWith" tp:name-for-bindings="Handle_With">
      <tp:docstring xmlns="http://www.w3.org/1999/xhtml">
        <p>Called by an approver to accept a channel bundle and request that
          the given handler be used to handle it.</p>

        <p>If successful, this method will cause the ChannelDispatchOperation
          object to disappear, emitting
          <tp:member-ref>Finished</tp:member-ref>.</p>

        <p>However, this method may fail because the dispatch has already been
          completed and the object has already gone. If this occurs, it
          indicates that another approver has asked for the bundle to be
          handled by a particular handler. The approver MUST NOT attempt
          to interact with the channels further in this case, unless it is
          separately invoked as the handler.</p>

        <p>Approvers which are also channel handlers SHOULD use
          <tp:member-ref>Claim</tp:member-ref> instead
          of HandleWith to request that they can handle a channel bundle
          themselves.</p>

        <p>(FIXME: list some possible errors)</p>

        <p>If the channel handler raises an error from <tp:dbus-ref
            namespace="org.freedesktop.Telepathy.Client.Handler">HandleChannels</tp:dbus-ref>,
          this method
          MAY respond by raising that same error, even if it is not
          specifically documented here.</p>
      </tp:docstring>

      <arg direction="in" type="s" tp:type="DBus_Bus_Name" name="Handler">
        <tp:docstring xmlns="http://www.w3.org/1999/xhtml">
          <p>The well-known bus name (starting with
            <code>org.freedesktop.Telepathy.Client.</code>) of the channel
            handler that should handle the channel, or the empty string
            if the client has no preferred channel handler.</p>
        </tp:docstring>
      </arg>

      <tp:possible-errors>
        <tp:error name="org.freedesktop.Telepathy.Error.InvalidArgument">
          <tp:docstring xmlns="http://www.w3.org/1999/xhtml">
            The selected handler is non-empty, but is not a syntactically
            correct <tp:type>DBus_Bus_Name</tp:type> or does not start with
            "<code>org.freedesktop.Telepathy.Client.</code>".
          </tp:docstring>
        </tp:error>
        <tp:error name="org.freedesktop.Telepathy.Error.NotAvailable">
          <tp:docstring>
            The selected handler is temporarily unable to handle these
            channels.
          </tp:docstring>
        </tp:error>
        <tp:error name="org.freedesktop.Telepathy.Error.NotImplemented">
          <tp:docstring>
            The selected handler is syntactically correct, but will never
            be able to handle these channels (for instance because the channels
            do not match its HandlerChannelFilter, or because HandleChannels
            raised NotImplemented).
          </tp:docstring>
        </tp:error>
        <tp:error name="org.freedesktop.Telepathy.Error.NotYours">
          <tp:docstring>
            At the time that HandleWith was called, this dispatch operation was
            processing an earlier call to HandleWith. The earlier call has
            now succeeded, so some Handler nominated by another approver is
            now responsible for the channels. In this situation, the second
            call to HandleWith MUST NOT return until the first one has
            returned successfully or unsuccessfully, and if the first call
            to HandleChannels fails, the channel dispatcher SHOULD try to obey
            the choice of Handler made by the second call to HandleWith.
          </tp:docstring>
        </tp:error>
      </tp:possible-errors>
    </method>

    <method name="Claim" tp:name-for-bindings="Claim">
      <tp:docstring xmlns="http://www.w3.org/1999/xhtml">
        <p>Called by an approver to claim channels for handling
          internally. If this method is called successfully, the process
          calling this method becomes the handler for the channel, but
          <em>does not</em> have the <tp:dbus-ref
            namespace="org.freedesktop.Telepathy.Client.Handler">HandleChannels</tp:dbus-ref>
          method called on it.</p>

        <p>Clients that call Claim on channels but do not immediately
          close them SHOULD implement the Handler interface and its
          <tp:dbus-ref
            namespace="org.freedesktop.Telepathy.Client.Handler">HandledChannels</tp:dbus-ref>
          property.</p>

        <p>Approvers wishing to reject channels MUST call this method to
          claim ownership of them, and MUST NOT call
          <tp:dbus-ref namespace="org.freedesktop.Telepathy.Channel">Close</tp:dbus-ref>
          on the channels unless/until this method returns successfully.</p>

        <tp:rationale>
          <p>The channel dispatcher can't know how best to close arbitrary
            channel types, so it leaves it up to the approver to do so.
            For instance, for Text channels it is necessary
            to acknowledge any messages that have already been displayed to
            the user first - ideally, the approver would display and then
            acknowledge the messages - or to call <tp:dbus-ref
              namespace="org.freedesktop.Telepathy">Channel.Interface.Destroyable.Destroy</tp:dbus-ref>
            if the destructive behaviour of that method is desired.</p>

          <p>Similarly, an Approver for StreamedMedia channels can close the
            channel with a reason (e.g. "busy") if desired. The channel
            dispatcher, which is designed to have no specific knowledge
            of particular channel types, can't do that.</p>
        </tp:rationale>

        <p>If successful, this method will cause the ChannelDispatchOperation
          object to disappear, emitting
          <tp:member-ref>Finished</tp:member-ref>, in the same way as for
          <tp:member-ref>HandleWith</tp:member-ref>.</p>

        <p>This method may fail because the dispatch operation has already
          been completed. Again, see HandleWith for more details. The approver
          MUST NOT attempt to interact with the channels further in this
          case.</p>

        <p>(FIXME: list some other possible errors)</p>
      </tp:docstring>

      <tp:possible-errors>
        <tp:error name="org.freedesktop.Telepathy.Error.NotYours">
          <tp:docstring>
            At the time that Claim was called, this dispatch operation was
            processing a call to HandleWith which has now succeeded, so
            some Handler nominated by another approver is now responsible for
            the channel.
          </tp:docstring>
        </tp:error>
      </tp:possible-errors>
    </method>

    <signal name="Finished" tp:name-for-bindings="Finished">
      <tp:docstring xmlns="http://www.w3.org/1999/xhtml">
        <p>Emitted when this dispatch operation finishes. The dispatch
          operation is no longer present and further methods must not be
          called on it.</p>

        <p>Approvers that have a user interface SHOULD stop notifying the user
          about the channels in response to this signal; they MAY assume that
          on errors, they would have received
          <tp:member-ref>ChannelLost</tp:member-ref> first.</p>

        <p>Its object path SHOULD NOT be reused for a subsequent dispatch
          operation; the ChannelDispatcher MUST choose object paths
          in a way that avoids immediate re-use.</p>

        <tp:rationale>
          <p>Otherwise, clients might accidentally call
            <tp:member-ref>HandleWith</tp:member-ref> or
            <tp:member-ref>Claim</tp:member-ref> on a new dispatch operation
            instead of the one they intended to handle.</p>
        </tp:rationale>

        <p>This signal MUST NOT be emitted until all Approvers that were
          invoked have returned (successfully or with an error) from
          their <tp:dbus-ref
            namespace="org.freedesktop.Telepathy.Client.Approver">AddDispatchOperation</tp:dbus-ref>
          method.</p>

        <tp:rationale>
          <p>This means that Approvers can connect to the ChannelLost signal
            in a race-free way. Non-approver processes that discover
            a channel dispatch operation in some way (such as observers)
            will have to follow the usual "connect to signals then recover
            state" model - first connect to
            <tp:member-ref>ChannelLost</tp:member-ref> and
            Finished, then download <tp:member-ref>Channels</tp:member-ref>
            (and on error, perhaps assume that the operation has already
            Finished).</p>
        </tp:rationale>
      </tp:docstring>
    </signal>

  </interface>
</node>
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