BIND 10 #1915: Convenient way of receiving and sending notifications

[BIND 10 Development]

#1915: Convenient way of receiving and sending notifications
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            Reporter:  vorner        |                        Owner:
                Type:  task          |                       Status:  new
            Priority:  medium        |                    Milestone:  Next-
           Component:  msgq          |  Sprint-Proposed
           Sensitive:  0             |                     Keywords:
         Sub-Project:  Core          |              Defect Severity:  N/A
Estimated Difficulty:  0             |  Feature Depending on Ticket:  msgq-
         Total Hours:  0             |  ng
                                     |          Add Hours to Ticket:  0
                                     |                    Internal?:  0
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 The CC library should have a function to:
  * Send a notification by the name of the notification and possibly
 parameters (slim wrapper around group_sendmsg, mostly just mangling the
 recipient name).
  * Register a callback which will be called whenever there's a
 notification of a given name.
  * Unregister a notification.

 We said the notifications will use some part of the channel namespace, so
 for
 example to notify about a new zone, we'd send a message to the address
 `notifications/new-zone-data` with parameter containing the zone origin
 and
 class, maybe even which datasource it is in. The used convention should be
 documented.

 The receiving of notifications might depend on #1914, but it is maybe
 easier to
 solve by a CC-global map of channels and callbacks independently. Maybe at
 least the callback class (or whatever it will be) from #1914 should be
 reused.

 It should be considered what happens when the same notification is
 registered
 multiple times with different callbacks and how to unregister them. While
 being
 able to receive multiple callbacks from the same event is more convenient
 as
 independent parts of code need not to worry about it, it might also be
 more
 complex inside CC then. The decision should be clarified in documentation.

-- 
Ticket URL: <http://bind10.isc.org/ticket/1915>
BIND 10 Development <http://bind10.isc.org>
BIND 10 Development