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0.3.1
Macula HTTP/3 Mesh SDK — connect, subscribe, publish, call, advertise
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Files
src/macula_gateway_system/macula_gateway_mdns_discovery.erl
%%%-------------------------------------------------------------------
%%% @doc Macula Gateway mDNS Discovery.
%%%
%%% Discovers LAN peers advertising the _macula-mesh._udp service via
%%% mDNS and populates the direct routing table with their endpoints.
%%%
%%% This enables LAN pubsub delivery WITHOUT going through the bootstrap
%%% DHT. When the pubsub router checks the direct routing table, it finds
%%% LAN peers there and connects directly.
%%%
%%% The module subscribes to mDNS discovery events via gproc and
%%% processes DNS SRV/TXT records to extract node_id and endpoint.
%%% @end
%%%-------------------------------------------------------------------
-module(macula_gateway_mdns_discovery).
-behaviour(gen_server).
-include_lib("kernel/include/logger.hrl").
-export([start_link/1]).
-export([init/1, handle_call/3, handle_cast/2, handle_info/2, terminate/2]).
-record(state, {
local_node_id :: binary(),
port :: inet:port_number()
}).
%%%===================================================================
%%% API
%%%===================================================================
-spec start_link(map()) -> {ok, pid()} | {error, term()}.
start_link(Opts) ->
gen_server:start_link({local, ?MODULE}, ?MODULE, Opts, []).
%%%===================================================================
%%% gen_server callbacks
%%%===================================================================
init(#{node_id := NodeId, port := Port, realm := Realm}) ->
%% Register this gateway for mDNS advertisement
macula_gateway_mdns_advertiser:register(NodeId, Port, Realm),
%% Start mDNS advertiser child (if mdns application available)
start_mdns_advertiser(),
%% Subscribe to mDNS discovery events for our service type
subscribe_to_mdns_events(),
?LOG_INFO("[mDNS-discovery] Started — advertising on _macula-mesh._udp, port ~p", [Port]),
{ok, #state{local_node_id = NodeId, port = Port}}.
handle_call(_Request, _From, State) ->
{reply, {error, unknown_call}, State}.
handle_cast(_Msg, State) ->
{noreply, State}.
%% @doc Handle mDNS discovery events.
%% The mdns library sends messages via gproc when services are discovered.
handle_info({mdns, _Type, {_Name, SrvRecord, TxtRecords}}, State) ->
handle_mdns_record(SrvRecord, TxtRecords, State),
{noreply, State};
handle_info({mdns, _Type, _Other}, State) ->
{noreply, State};
handle_info(_Info, State) ->
{noreply, State}.
terminate(_Reason, _State) ->
macula_gateway_mdns_advertiser:unregister(),
ok.
%%%===================================================================
%%% Internal
%%%===================================================================
%% @private Start the mDNS advertiser if the mdns application is available.
start_mdns_advertiser() ->
case whereis(mdns_advertise_sup) of
undefined ->
?LOG_DEBUG("[mDNS-discovery] mdns application not running, skipping advertiser");
_Pid ->
case mdns_advertise_sup:start_child(macula_gateway_mdns_advertiser) of
{ok, _} ->
?LOG_INFO("[mDNS-discovery] mDNS advertiser started");
{error, {already_started, _}} ->
ok;
{error, Reason} ->
?LOG_WARNING("[mDNS-discovery] Failed to start mDNS advertiser: ~p", [Reason])
end
end.
%% @private Subscribe to mDNS events for _macula-mesh._udp service.
subscribe_to_mdns_events() ->
try
mdns:subscribe(discover),
?LOG_DEBUG("[mDNS-discovery] Subscribed to mDNS discover events")
catch
_:_ ->
?LOG_DEBUG("[mDNS-discovery] mdns not available, LAN discovery disabled")
end.
%% @private Process a discovered mDNS SRV record.
handle_mdns_record(SrvRecord, TxtRecords, #state{local_node_id = LocalNodeId}) ->
case extract_peer_info(SrvRecord, TxtRecords) of
{ok, #{node_id := PeerNodeId, endpoint := Endpoint}} when PeerNodeId =/= LocalNodeId ->
?LOG_INFO("[mDNS-discovery] Discovered LAN peer: ~s at ~s",
[binary:encode_hex(PeerNodeId), Endpoint]),
%% Store in direct routing table — pubsub router will find it there
macula_direct_routing:store(PeerNodeId, Endpoint),
%% Also add to DHT routing table for completeness
add_to_routing_table(PeerNodeId, Endpoint);
{ok, _} ->
%% Our own advertisement, ignore
ok;
{error, _Reason} ->
ok
end.
%% @private Extract peer info from mDNS records.
extract_peer_info(SrvRecord, TxtRecords) ->
case SrvRecord of
{_Priority, _Weight, Port, Hostname} ->
extract_from_txt(Hostname, Port, TxtRecords);
_ ->
{error, invalid_srv}
end.
%% @private Extract node_id from TXT records and build endpoint.
extract_from_txt(Hostname, Port, TxtRecords) ->
NodeIdHex = find_txt_value("node_id", TxtRecords),
build_peer_info(NodeIdHex, Hostname, Port).
build_peer_info(undefined, _Hostname, _Port) ->
{error, no_node_id};
build_peer_info(NodeIdHex, Hostname, Port) ->
HostBin = clean_hostname(Hostname),
Endpoint = iolist_to_binary([
<<"https://">>, HostBin, <<":">>, integer_to_binary(Port)
]),
{ok, #{
node_id => binary:decode_hex(list_to_binary(NodeIdHex)),
endpoint => Endpoint
}}.
%% @private Find a value in TXT record properties.
find_txt_value(_Key, []) ->
undefined;
find_txt_value(Key, [Props | Rest]) when is_map(Props) ->
case maps:get(Key, Props, undefined) of
undefined -> find_txt_value(Key, Rest);
Value -> Value
end;
find_txt_value(Key, [_ | Rest]) ->
find_txt_value(Key, Rest).
%% @private Remove trailing dot from mDNS hostname.
clean_hostname(Hostname) when is_list(Hostname) ->
case lists:last(Hostname) of
$. -> list_to_binary(lists:droplast(Hostname));
_ -> list_to_binary(Hostname)
end;
clean_hostname(Hostname) when is_binary(Hostname) ->
case binary:last(Hostname) of
$. -> binary:part(Hostname, 0, byte_size(Hostname) - 1);
_ -> Hostname
end.
%% @private Add discovered peer to DHT routing table.
add_to_routing_table(PeerNodeId, Endpoint) ->
case whereis(macula_routing_server) of
undefined -> ok;
Pid ->
NodeInfo = #{
node_id => PeerNodeId,
endpoint => Endpoint
},
macula_routing_server:add_node(Pid, NodeInfo)
end.