dnsimple / dns_erlang / 28460472875

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Surface malformed EDNS COOKIE as FORMERR instead of crashing (#129)

A COOKIE option (RFC 7873) with an invalid length raises `bad_cookie` in
`do_decode_optrrdata/2`. That call sat in the `of` body of the per-record
`try ... of ... catch` in `do_decode_message_additional/4`, where exceptions
are not caught, so it escaped `dns_decode`'s own error handling and propagated
to the caller's decode loop as an uncaught crash.

Move the record parse (the `from_wire/2` decode plus the rdata decoders
`decode_optrrdata/1` and `decode_rrdata/4`) into the `try` protected
expression so any decode failure on untrusted wire data — a bad cookie, or a
bad compression pointer in an RR's rdata — surfaces as a `{formerr, _, _}`
decode-error tuple. The recursion stays in the `of` body to remain in tail
position. The same shape is applied to `do_decode_message_body/4`.

Encoding an invalid cookie remains a hard error: building such a message is a
programming error on our side.

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