BIND 10 #1332: Implement ZoneJournalReader class

[BIND 10 Development]

#1332: Implement ZoneJournalReader class
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                   Reporter:         |                 Owner:  jinmei
  jinmei                             |                Status:  accepted
                       Type:  task   |             Milestone:
                   Priority:  major  |  Sprint-20111122
                  Component:  data   |            Resolution:
  source                             |             Sensitive:  0
                   Keywords:         |           Sub-Project:  DNS
            Defect Severity:  N/A    |  Estimated Difficulty:  5
Feature Depending on Ticket:         |           Total Hours:  0
        Add Hours to Ticket:         |
                  Internal?:  0      |
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Comment (by jinmei):

 trac1332 is ready for review.

 It depends on #1330 (and on #1331 for writing tests), and uses
 an intermediate versions of the correspoinding branches.  Hopefully
 the interfaces are fixed and we don't have to modify this branch
 due to last minute changes to these branches.  The first two commits
 are for merging these branches and should be ignored.

 I think the implementation itself is mostly straightforward.  One thing
 that may require a discussion would be how to return an error when
 an unexpected input is given (non existing zone or serials).  I chose
 to return a result code rather than an exception because these event
 are not really exceptional (an IXFR client can request a diff for
 non existent version, and, depending on how we implement the application
 non existent zone case can also happen at the level of this API), and
 especially for C++ I believe it's better not to rely on exceptions for
 normal events.  But this could be a debatable point, and right now
 it's not very consistent throughout the data source API, so we might
 also have to discuss unifying the interface either way (but that level
 of discussion will be a topic of a separate task/thread).

 This is the proposed changelog entry:
 {{{
 317.?   [func]          jinmei
         datasrc: Added C++ API for retrieving difference of two versions
         of a zone.  A new ZoneJournalReader class was introduced for this
         purpose, and a corresponding factory method was added to
         DataSourceClient.
         (Trac #1332, git TBD)
 }}}

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Ticket URL: <http://bind10.isc.org/ticket/1332#comment:6>
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