BIND 10 #2420: allow loading zones containing an orphan RRSIG

[BIND 10 Development]

#2420: allow loading zones containing an orphan RRSIG
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            Reporter:  jinmei        |                        Owner:
                Type:  defect        |                       Status:  new
            Priority:  high          |                    Milestone:  Next-
           Component:  data source   |  Sprint-Proposed
           Sensitive:  0             |                     Keywords:
         Sub-Project:  DNS           |              Defect Severity:  N/A
Estimated Difficulty:  0             |  Feature Depending on Ticket:
         Total Hours:  0             |          Add Hours to Ticket:  0
                                     |                    Internal?:  0
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 We currently reject loading (to memory) an entire zone if we find
 an RRSIG that doesn't have a covered RRset:

 {{{#!cpp
     // Right now, we don't accept RRSIG without covered RRsets (this
     // should eventually allowed, but to do so we'll need to update the
     // finder).
 }}}

 This is overkill, and won't become realistic check anyway when we
 support the complete zone parser/loader because we cannot tell when
 the covered RRSIG is added (unless we maintain a possibly huge size of
 intermediate storage for the "orphan" RRSIGs).  The behavior is also
 incompatible with BIND 9.

 There's also a report from a user who is suffering from this behavior,
 so I suggest we should fix it now.  In terms of data structures it
 should already be possible, so it shouldn't be so difficult.

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Ticket URL: <http://bind10.isc.org/ticket/2420>
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BIND 10 Development