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+%% Copyright (c) 2019 EMQ Technologies Co., Ltd. All Rights Reserved.
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+%%
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+%% Licensed under the Apache License, Version 2.0 (the "License");
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+%% you may not use this file except in compliance with the License.
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+%% You may obtain a copy of the License at
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+%%
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+%% http://www.apache.org/licenses/LICENSE-2.0
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+%%
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+%% Unless required by applicable law or agreed to in writing, software
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+%% distributed under the License is distributed on an "AS IS" BASIS,
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+%% WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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+%% See the License for the specific language governing permissions and
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+%% limitations under the License.
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+
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+%% @doc This module implements EMQX Portal transport layer on top of MQTT protocol
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+
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+-module(emqx_portal_mqtt).
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+-behaviour(emqx_portal_connect).
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+
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+%% behaviour callbacks
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+-export([start/1,
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+ send/2,
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+ stop/2
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+ ]).
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+
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+-include("emqx_mqtt.hrl").
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+
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+-define(ACK_REF(ClientPid, PktId), {ClientPid, PktId}).
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+
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+%% Messages towards ack collector process
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+-define(SENT(MaxPktId), {sent, MaxPktId}).
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+-define(ACKED(AnyPktId), {acked, AnyPktId}).
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+-define(STOP(Ref), {stop, Ref}).
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+
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+start(Config) ->
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+ Ref = make_ref(),
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+ Parent = self(),
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+ AckCollector = spawn_link(fun() -> ack_collector(Parent, Ref) end),
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+ Handlers = make_hdlr(Parent, AckCollector, Ref),
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+ case emqx_client:start_link(Config#{msg_handler => Handlers, owner => AckCollector}) of
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+ {ok, Pid} ->
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+ case emqx_client:connect(Pid) of
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+ {ok, _} ->
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+ %% ack collector is always a new pid every reconnect.
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+ %% use it as a connection reference
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+ {ok, Ref, #{ack_collector => AckCollector,
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+ client_pid => Pid}};
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+ {error, Reason} ->
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+ ok = stop(AckCollector, Pid),
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+ {error, Reason}
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+ end;
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+ {error, Reason} ->
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+ {error, Reason}
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+ end.
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+
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+stop(Ref, #{ack_collector := AckCollector,
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+ client_pid := Pid}) ->
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+ MRef = monitor(process, AckCollector),
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+ unlink(AckCollector),
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+ _ = AckCollector ! ?STOP(Ref),
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+ receive
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+ {'DOWN', MRef, _, _, _} ->
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+ ok
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+ after
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+ 1000 ->
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+ exit(AckCollector, kill)
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+ end,
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+ _ = emqx_client:stop(Pid),
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+ ok.
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+
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+send(#{client_pid := ClientPid, ack_collector := AckCollector}, Batch) ->
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+ send_loop(ClientPid, AckCollector, Batch).
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+
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+send_loop(ClientPid, AckCollector, [Msg | Rest]) ->
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+ case emqx_client:publish(ClientPid, Msg) of
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+ {ok, PktId} when Rest =:= [] ->
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+ Rest =:= [] andalso AckCollector ! ?SENT(PktId),
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+ {ok, PktId};
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+ {ok, _PktId} ->
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+ send_loop(ClientPid, AckCollector, Rest);
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+ {error, {_PacketId, inflight_full}} ->
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+ timer:sleep(100),
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+ send_loop(ClientPid, AckCollector, [Msg | Rest]);
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+ {error, Reason} ->
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+ %% There is no partial sucess of a batch and recover from the middle
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+ %% only to retry all messages in one batch
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+ {error, Reason}
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+ end.
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+
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+ack_collector(Parent, ConnRef) ->
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+ ack_collector(Parent, ConnRef, []).
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+
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+ack_collector(Parent, ConnRef, PktIds) ->
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+ NewIds =
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+ receive
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+ ?STOP(ConnRef) ->
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+ exit(normal);
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+ ?SENT(PktId) ->
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+ %% this ++ only happens per-BATCH, hence no optimization
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+ PktIds ++ [PktId];
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+ ?ACKED(PktId) ->
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+ handle_ack(Parent, PktId, PktIds)
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+ after
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+ 200 ->
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+ PktIds
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+ end,
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+ ack_collector(Parent, ConnRef, NewIds).
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+
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+handle_ack(Parent, PktId, [PktId | Rest]) ->
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+ %% A batch is finished, time to ack portal
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+ ok = emqx_portal:handle_ack(Parent, PktId),
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+ Rest;
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+handle_ack(_Parent, PktId, [BatchMaxPktId | _] = All) ->
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+ %% partial ack of a batch, terminate here.
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+ true = (PktId < BatchMaxPktId), %% bad order otherwise
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+ All.
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+
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+%% When puback for QoS-1 message is received from remote MQTT broker
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+%% NOTE: no support for QoS-2
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+handle_puback(AckCollector, #{packet_id := PktId, reason_code := RC}) ->
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+ RC =:= ?RC_SUCCESS andalso error(RC),
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+ AckCollector ! ?ACKED(PktId),
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+ ok.
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+
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+%% Message published from remote broker. Import to local broker.
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+import_msg(Msg) ->
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+ %% auto-ack should be enabled in emqx_client, hence dummy ack-fun.
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+ emqx_portal:import_batch([Msg], _AckFun = fun() -> ok end).
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+
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+make_hdlr(Parent, AckCollector, Ref) ->
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+ #{puback => fun(Ack) -> handle_puback(AckCollector, Ack) end,
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+ publish => fun(Msg) -> import_msg(Msg) end,
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+ disconnected => fun(RC, _Properties) -> Parent ! {disconnected, Ref, RC}, ok end
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+ }.
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+
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spring2maz