BIND 10 #1456: Create diff-normalizer utility functions

[BIND 10 Development]

#1456: Create diff-normalizer utility functions
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                   Reporter:  jelte  |                 Owner:  UnAssigned
                       Type:  task   |                Status:  reviewing
                   Priority:         |             Milestone:
  medium                             |  Sprint-20120529
                  Component:  DDNS   |            Resolution:
                   Keywords:         |             Sensitive:  0
            Defect Severity:  N/A    |           Sub-Project:  DNS
Feature Depending on Ticket:  DDNS   |  Estimated Difficulty:  5
        Add Hours to Ticket:  0      |           Total Hours:  0
                  Internal?:  0      |
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Changes (by jelte):

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


Comment:

 OK, it's ready for review, I called the new diff mode
 'single_update_mode', and if set upon initialization of diff.Diff(), it
 supports alternate add and delete operations.

 A few notes;

 I left it in its location for now, the ddns module can use it from there.
 We should probably move it to either util or datasrc, but I think that can
 be done as a separate cleanup ticket.

 The new mode does a few more checks (like checking SOA is added/deleted
 first, and not later), and in that sense is more strict that the original
 mode, but it is still agnostic about the actual contents. These early
 checks do help bad callers with a better error message IMO (otherwise,
 upon commit, you get the fairly cryptic datasource error 'bad operation in
 phase 0' or something like that). And perhaps we should do something
 similar to the default 'multi' mode used in xfrin.

 The diff class itself is still pretty basic, the plan is to put most of
 the smartness (like interpreting and converting NONE class RRs, and doing
 ddns special case checking, such as no removal of the last apex NS record)
 in ddns itself.

-- 
Ticket URL: <http://bind10.isc.org/ticket/1456#comment:10>
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