BIND 10 #2018: Use updater's finder in DDNS

[BIND 10 Development]

#2018: Use updater's finder in DDNS
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                   Reporter:  jelte  |                 Owner:  UnAssigned
                       Type:         |                Status:  reviewing
  defect                             |             Milestone:
                   Priority:         |  Sprint-20120612
  medium                             |            Resolution:
                  Component:         |             Sensitive:  0
  Unclassified                       |           Sub-Project:  DNS
                   Keywords:         |  Estimated Difficulty:  0
            Defect Severity:  N/A    |           Total Hours:  0
Feature Depending on Ticket:         |
        Add Hours to Ticket:  0      |
                  Internal?:  0      |
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Changes (by jelte):

 * owner:  jelte => UnAssigned
 * status:  assigned => reviewing


Comment:

 OK, ready for review, instead of creating a new zonefinder, it now created
 the Diff as a member method as well, then proceeds to use the diff's
 updater instead of a finder (ZoneUpdater provides the find interface).

 There is, however, a catch; as you may notice in the unit tests, I needed
 to explicitely destroy the _session, otherwise some tests would fail with
 a database is locked error.

 There may be some dangling references around the tests (especially when
 they create multiple sessions), but still this surprised me somewhat. I am
 kind of thinking that maybe we should refactor this some more, and do
 something a little bit more RAII-style in handle(), for instance do
 something like
 {{{
 with self.__get_update_zone(zname):
     self.__check_acl()
     self.__check_prereqs()
     ...etc
 }}}

 And have a small container object that creates the diff and updater and
 closes it as soon as scope leaves that part of handle().

 However, that change seemed worthy of discussion first, so for now I just
 went the simple naive way. If the reviewer thinks this is worthy of
 pursuing i can either create (yet) another ticket, or do it here, most of
 the changes in this branch would be the same I think.

-- 
Ticket URL: <http://bind10.isc.org/ticket/2018#comment:3>
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