BIND 10 #2541: add addZone() interface for data source

[BIND 10 Development]

#2541: add addZone() interface for data source
-------------------------------------+-------------------------------------
                   Reporter:         |                 Owner:
  jinmei                             |                Status:  new
                       Type:  task   |             Milestone:  New Tasks
                   Priority:         |              Keywords:
  medium                             |             Sensitive:  0
                  Component:  data   |           Sub-Project:  DNS
  source                             |  Estimated Difficulty:  0
               CVSS Scoring:         |           Total Hours:  0
            Defect Severity:  N/A    |
Feature Depending on Ticket:         |
  loadzone-ng                        |
        Add Hours to Ticket:  0      |
                  Internal?:  0      |
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 To complete the loadzone-ng tool (#2380), we need some way to add a
 new zone to the "zones" table of the sqlite3 DB file (or in general
 any backend of data sources, but in practice it means sqlite3 for the
 moment); otherwise we cannot load a new zone from the scratch.

 A tentative proposal to do this is to extend the `DataSourceClient`
 class, adding the new `addZone()` method:

 {{{#!cpp
 class DataSourceClient : boost::noncopyable {
 public:
     // It first checks if the specified name of the zone exists.  If it
     // exists it returns false; otherwise it adds information of the
     // new zone in backend-dependent manner and returns true.
     // The DB-based version of this method would perform the check and add
 in
     // a single transaction.
     //
     // Throws on any unexpected failure.
     virtual bool addZone(const dns::Name& zone_name) = 0;
 };
 }}}

 And, for the DB-backend data sources, extend the `DatabaseAccessor`
 class:
 {{{#!cpp
 class DatabaseAccessor : boost::noncopyable {
 public:
     // add the specified name of zone, return the zone ID.
     virtual int addZone(const std::string& name) = 0;
 };
 }}}

 and implement it for `SQLite3Accessor`.

 We may have to heavily revisit the interface later (in which case some
 of the things done in this ticket will become a waste), but it's still
 probably better to add ad-hoc SQLite3-specific code to loadzone-ng
 itself.

-- 
Ticket URL: <http://bind10.isc.org/ticket/2541>
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