BIND 10 #1457: use the difference normalizer in the DDNS module

[BIND 10 Development]

#1457: use the difference normalizer in the DDNS module
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                   Reporter:  jelte  |                 Owner:  vorner
                       Type:  task   |                Status:  reviewing
                   Priority:         |             Milestone:
  medium                             |  Sprint-20120612
                  Component:  DDNS   |            Resolution:
                   Keywords:         |             Sensitive:  0
            Defect Severity:  N/A    |           Sub-Project:  DNS
Feature Depending on Ticket:  DDNS   |  Estimated Difficulty:  3
        Add Hours to Ticket:  0      |           Total Hours:  22
                  Internal?:  0      |
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Changes (by jelte):

 * owner:  jelte => vorner


Comment:

 Ok, just pushed the collection changes

 I have not (yet) changed the finder to the updaters finder, but jinmei is
 indeed right

 - changes are mostly for prerequisite checking (where the example from the
 rfc actually has a similar approach)
 - this actually breaks what we had already (ns apex special case, unless
 the ns set was already exactly one rr is is now deleted when told to do
 so)
 - disabled test for that and added a comment about the problem

 Created #2016 to fix the issues with additions and deletions, and a
 smarter diff buffer

 and i already have a couple of comments myself;
 - using foreach_rr is in effect useless now; PRESERVE_ORDER happens to
 already do something like it. I'm thinking that we could still leave it
 in, just in case the message does not consist of 1-rr rrsets, but
 currently it is really just unnecessary creation of new rrsets. One way to
 solve that is to make it simply return the given rrset if it happens to
 consist of 1 rr, but it should work as-is right now
 - we now have a dead test (pending at the very least #2016)

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Ticket URL: <http://bind10.isc.org/ticket/1457#comment:19>
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