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Erlang Authoritative DNS Server

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erldns src pipes erldns_sorter.erl
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src/pipes/erldns_sorter.erl 

-module(erldns_sorter).

-moduledoc """

Sorts the answers, ensuring that CNAME RRs are ordered first.



Should be ran after all resolvers are ran.

""".



-include_lib("dns_erlang/include/dns.hrl").



-behaviour(erldns_pipeline).



-export([call/2]).



-doc "`c:erldns_pipeline:call/2` callback.".

-spec call(dns:message(), erldns_pipeline:opts()) -> dns:message().

call(#dns_message{answers = []} = Msg, _) ->

    Msg;

call(#dns_message{answers = Answers} = Msg, _) ->

    Msg#dns_message{answers = lists:usort(fun sort_fun/2, Answers)}.



-spec sort_fun(dns:rr(), dns:rr()) -> boolean().

sort_fun(

    #dns_rr{type = ?DNS_TYPE_CNAME, data = #dns_rrdata_cname{dname = Name}},

    #dns_rr{type = ?DNS_TYPE_CNAME, name = Name}

) ->

    true;

sort_fun(

    #dns_rr{type = ?DNS_TYPE_CNAME, name = Name},

    #dns_rr{type = ?DNS_TYPE_CNAME, data = #dns_rrdata_cname{dname = Name}}

) ->

    false;

sort_fun(#dns_rr{type = ?DNS_TYPE_CNAME}, #dns_rr{}) ->

    true;

sort_fun(#dns_rr{}, #dns_rr{type = ?DNS_TYPE_CNAME}) ->

    false;

sort_fun(A, B) ->

    A =< B.