BIND 10 #3263: RRset::addRRset(ConstRdataPtr&) does not validate RDATA against RRset's class

[BIND 10 Development]

#3263: RRset::addRRset(ConstRdataPtr&) does not validate RDATA against RRset's
class
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                   Reporter:  muks   |                 Owner:  UnAssigned
                       Type:         |                Status:  new
  defect                             |             Milestone:  New Tasks
                   Priority:         |              Keywords:
  medium                             |             Sensitive:  0
                  Component:         |           Sub-Project:  DNS
  libdns++                           |  Estimated Difficulty:  0
               CVSS Scoring:         |           Total Hours:  0
            Defect Severity:  N/A    |
Feature Depending on Ticket:         |
        Add Hours to Ticket:  0      |
                  Internal?:  0      |
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 There are two variants of `RRset::addRRset()`:

 * `BasicRRset::addRRset(const Rdata&)`
 * `BasicRRset::addRRset(ConstRdataPtr&)`

 Both variants need to add the Rdata into an internal
 `std::vector<ConstRdataPtr>` collection.

 In the case of the first variant, it has to create another `Rdata`
 instance with a `ConstRdataPtr` managing it. For the second one, it simply
 pushes the passed `ConstRdataPtr` into the collection.

 When RDATA of a type mismatching its RR class is added to the `RRset`
 using the second interface above, it will add it without any validation.
 The first will fail with a `bad_cast` when it tries to create a `Rdata`
 copy.

 An example is adding RDATA to an RRset with `class=NONE` (such as required
 by UPDATE). The first method throws. The second method passes. This needs
 to be made consistent or at least documented.
 Apart from handing `class=NONE` specially, we should reject RDATA that
 mismatch the class/type.

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Ticket URL: <http://bind10.isc.org/ticket/3263>
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