修改dns的继续逻辑

apps/sdlan/src/dns_proxy/dns_handler.erl

@@ -90,7 +90,7 @@ resolver0(Packet, QueryMsg = #dns_message{qc = 1, questions = [Question = #dns_q
                             RespMsg = build_response(QueryMsg, Cache),
                             {ok, dns:encode_message(RespMsg)};
                         miss ->
-                            case forward_to_upstream(Packet, QueryMsg) of
+                            case forward_to_upstream(Packet) of
                                 {ok, Resp} ->
                                     case dns:decode_message(Resp) of
                                         RespMsg = #dns_message{answers = Answers} ->
@@ -182,22 +182,21 @@ build_ip_packet(SAddr, DAddr, SPort, DPort, UdpPayload) when is_integer(SPort),
 
     <<IpHeader/binary, IpPayload/binary>>.
 
--spec forward_to_upstream(Request :: binary(), QueryMsg :: #dns_message{}) -> no_return().
-forward_to_upstream(Request, #dns_message{id = TxId, questions = [#dns_query{name = QName, type = QType, class = QClass}|_]}) ->
-    {ok, {DnsIp, DnsPort}} = application:get_env(sdlan, public_dns_server),
+-spec forward_to_upstream(Request :: binary()) -> {ok, Resp :: binary()} | {error, Reason :: any()}.
+forward_to_upstream(Request) ->
+    {DnsIp, DnsPort} = select_dns_server(),
     {ok, Socket} = gen_udp:open(0, [binary, {active, true}]),
     ok = gen_udp:send(Socket, DnsIp, DnsPort, Request),
     logger:debug("[dns_resolver] send to: ~p, packet: ~p", [{DnsIp, DnsPort}, Request]),
     receive
         {udp, Socket, DnsIp, DnsPort, Resp} ->
-            try dns:decode_message(Resp) of
-                #dns_message{id = TxId, questions = [#dns_query{name = QName, type = QType, class = QClass}|_]} ->
-                    {ok, Resp};
-                _ ->
-                    {error, invalid_dns_response}
-            catch error:Err ->
-                {error, Err}
-            end
+            {ok, Resp}
     after 2000 ->
         {error, timeout}
     end.
+
+-spec select_dns_server() -> {DnsIp :: inet:ip4_address(), DnsPort :: pos_integer()}.
+select_dns_server() ->
+    {ok, DnsServers} = application:get_env(sdlan, public_dns_server),
+    Idx = rand:uniform(length(DnsServers)),
+    lists:nth(Idx, DnsServers).