In DNS records, there may be rdata types that are not implemented in this library (though these should now be few). For example:
files.example.com. IN 3600 MD UDEL.ARPA.
The above entry refers to the obsolete MD resource data type. Whilst MD is a valid rdata type, it has not been implemented
in the Badcow DNS Library. When this MD record is parsed, it will parsed into an instance of Badcow\DNS\Rdata\PolymorphicRdata.
The PolymorphicRdata class is used for any valid rdata type that has not been implemented by the library and whose records
have a valid text representation. When this type is outputted to text, the data will remain unchanged, but the data cannot
be outputted in a wire format.
If, however, you are using a wholly unknown Rdata type (i.e. one which has not been specified by IANA) then the parser will
throw a ParseException. In this case, if the rdata type is valid (or apart of some specific functionality not otherwise
defined) it may be useful define a custom rdata handler.
The same record from above can be represented in a text file as:
files.example.com. IN 3600 TYPE3 \# 11 04 55 44 45 4c 04 41 52 50 41 00
This representation conforms with RFC 3597 - Handling of Unknown DNS Resource Record (RR) Types. In this case, the record
will be parsed into an instance of Badcow\DNS\Rdata\UnknownType.
The UnknownType class is used to handle records that are formatted in this way. This class can output the wire format
of the record and the text representation above. This is the preferred way of handling unknown, unsupported, or otherwise
"made up" rdata types.
If the type is implemented, then the parser will render an instance of that type instead of the UnknownType class.
Exempli Gratia:
files.example.com. IN 3600 TYPE1 \# 4 c0 a8 01 64
The above record type, TYPE1, is a known and supported type - an A record with the four octets (bytes) of the IP address
192.168.1.100. This record will be parsed to an instance of Badcow\DNS\Rdata\A and NOT as an UnknownType class.