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%%% Copyright (c) 2016, NORDUnet A/S.
%%% See LICENSE for licensing information.
-module(dns).
-export([decode_rrset/1, decode_rr/1, encode_rrset/1, encode_rr/1,
canonicalize_dsrr/2]).
-record(rr, {name :: list(), % List of name labels.
type :: binary(),
class :: binary(),
ttl :: integer(),
rdata :: binary()}).
-type rr() :: #rr{}.
-spec decode_name_label(binary()) -> tuple().
decode_name_label(RRbin) ->
<<Len:8/integer, Label:Len/binary, Rest/binary>> = RRbin,
{binary_to_list(Label), Rest}.
-spec encode_name_label(string()) -> binary().
encode_name_label(Label) ->
LabelBin = list_to_binary(Label),
Len = byte_size(LabelBin),
<<Len:8/integer, LabelBin/binary>>.
decode_name(RRbin) ->
decode_name(RRbin, []).
decode_name(<<0, Rest/binary>>, Acc) ->
{lists:reverse(Acc), Rest};
decode_name(RRbin, Acc) ->
{Label, Rest} = decode_name_label(RRbin),
decode_name(Rest, [Label | Acc]).
-spec encode_name(list()) -> binary().
encode_name(Name) ->
encode_name(Name, []).
encode_name([], Acc) ->
Bin = list_to_binary(lists:reverse(Acc)),
<<Bin/binary, 0>>;
encode_name([H|T], Acc) ->
encode_name(T, [encode_name_label(H) | Acc]).
-spec decode_rr(binary()) -> {rr(), binary()}.
decode_rr(RRBin) ->
{Name, RestRR} = decode_name(RRBin),
<<Type:2/binary,
Class:2/binary,
TTL:4/integer-unit:8,
RDLength:2/integer-unit:8,
RDATA:RDLength/binary,
Rest/binary>> = RestRR,
{#rr{name = Name, type = Type, class = Class, ttl = TTL, rdata = RDATA},
Rest}.
-spec decode_rrset(binary()) -> [rr()].
decode_rrset(RRSet) ->
decode_rrset(RRSet, []).
decode_rrset(<<>>, Acc) ->
lists:reverse(Acc);
decode_rrset(RRSet, Acc) ->
{RR, Rest} = decode_rr(RRSet),
decode_rrset(Rest, [RR | Acc]).
-spec encode_rr(rr()) -> binary().
encode_rr(#rr{name = Name, type = Type, class = Class, ttl = TTL, rdata = RDATA}) ->
EncodedName = encode_name(Name),
RDLength = byte_size(RDATA),
<<EncodedName/binary,
Type:2/binary,
Class:2/binary,
TTL:4/integer-unit:8,
RDLength:2/integer-unit:8,
RDATA/binary>>.
-spec encode_rrset(list()) -> binary().
encode_rrset(RRSet) ->
encode_rrset(RRSet, []).
encode_rrset([], Acc) ->
list_to_binary(lists:reverse(Acc));
encode_rrset([H|T], Acc) ->
encode_rrset(T, [encode_rr(H) | Acc]).
%% Cacnonicalise a single DS RR according to RFC4034 section 6.2.
canonicalize_dsrr(DS, RRSIG) ->
%% 1. expand domain name
%% FIXME: What does a compressed name look like?
%% 2. lowercase
LCName = lists:map(fun(L) -> string:to_lower(L) end, DS#rr.name),
%% 3. N/A for DS
%% 4. N/A for DS FIXME: verify
%% 5. set TTL to that of the RRSIG
OrigTTL = RRSIG#rr.ttl,
DS#rr{name = LCName, ttl = OrigTTL}.
%% TODO: Add unit tests.
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