BIND 10 #3358: Default dhcp-ddns config does not have all elements

[BIND 10 Development]

#3358: Default dhcp-ddns config does not have all elements
-------------------------------------+-------------------------------------
            Reporter:  tmark         |                        Owner:
                Type:  defect        |  UnAssigned
            Priority:  high          |                       Status:
           Component:  dhcp-ddns     |  reviewing
            Keywords:                |                    Milestone:  DHCP-
           Sensitive:  0             |  Kea0.9
         Sub-Project:  DHCP          |                   Resolution:
Estimated Difficulty:  8             |                 CVSS Scoring:
         Total Hours:  0             |              Defect Severity:  N/A
                                     |  Feature Depending on Ticket:
                                     |          Add Hours to Ticket:  8
                                     |                    Internal?:  0
-------------------------------------+-------------------------------------
Changes (by tmark):

 * hours:  0 => 8
 * owner:   => UnAssigned
 * status:  new => reviewing


Comment:

 The PROBLEM:

 Upon initial creation of a Kea component (i.e. b10-dhcp4 or b10-dhcp6),
 the
 call to getFullConfig() within the configuration handler would return the
 "dhcp-ddns" portion of server's configuration  populated with all of its
 items' default values.   This is the expected behavior.

 If a dhcp-ddns item value was changed (via bindctl), such as "server-port"
 or
 "enable-updates",  this method was correctly returning "dhcp-ddns" with
 all of
 the default values MERGED with the changed value(s).  This is also the
 desired
 behavior.

 Once the server is restarted, however, the "dhcp-ddns" element is returned
 containing only the changed values.  This causes parsing to fall over with
 missing values that should have been supplied via item defaults.

 The underlying problem is in config::ConfigData::getFullConfig(). This
 method
 was doing a flat replacement of top level maps with their configured
 values,
 not a merge of both default and configured values.

 The SOLUTION:

 What was done to address the problem was to modify
 ConfigData::getFullConfig
 to call a new method, getFullValue(), to properly populate top level map
 items with a merge of default and configured values.

 When defining maps in spec files, each item can be given a default OR
 specified as part of the map's default value.  The getFullValue() method
 use
 only one of these two sources.  If the map default value is not empty
 (i.e. not "{}"), then it will use the values specified here.  Otherwise,
 it
 use the default value specified per map item:

 Note that a maps within maps, will not not work correctly without further
 modifications to make getFullValue recursive.


 ChangeLog recommendation:

 {{{

 7xx.    [bug]      tmark
     Configuration session mechanisms now return top level map items as a
     merge of their default values with any values that have been changed.
     This corrects a bug in which the DHCP servers (b10-dhcp4 and
 b10-dhpc6)
     would fail configuration parsing during start-up after one or more
     of the values in their "dhcp-ddns" configuration section were
     changed via bindctl.
     (Trac #3358, git TBD)

 }}}

-- 
Ticket URL: <https://bind10.isc.org/ticket/3358#comment:1>
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