学习mqtt协议和emqttd开源项目emqtt.com/
emqttd源码版本号是v1.1.3。emqtt.com/downloads/1…
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源码写得比较绕，需要经过以下模块的调用，入口是emqttd_client模块，handle_info函数负责接收socket的数据：
（注意：gen_server:call是同步调用，cast是异步。call对应的是handle_info，cast对应的是handle_cast。）
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1、-module(emqttd_client).
handle_info({inet_async, _Sock, _Ref, {ok, Data}}, State) ->
received(Bytes, State = #client_state{parser_fun = ParserFun,
packet_opts = PacketOpts,
proto_state = ProtoState}) ->
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2、-module(emqttd_parser).
parse(<<Type:4, Dup:1, QoS:2, Retain:1, Rest/binary>>, {none, Limit}) ->
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3、-module(emqttd_protocol).
解析SUBSCRIBE消息
process(?SUBSCRIBE_PACKET(PacketId, TopicTable), State = #proto_state{session = Session}) ->
Client = client(State),
AllowDenies = [check_acl(subscribe, Topic, Client) || {Topic, _Qos} <- TopicTable],
case lists:member(deny, AllowDenies) of
true ->
?LOG(error, "Cannot SUBSCRIBE ~p for ACL Deny", [TopicTable], State),
send(?SUBACK_PACKET(PacketId, [16#80 || _ <- TopicTable]), State);
false ->
emqttd_session:subscribe(Session, PacketId, TopicTable), {ok, State}
end;
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4、-module(emqttd_session).\
subscribe(SessPid, PacketId, TopicTable) ->
From = self(),
AckFun = fun(GrantedQos) ->
From ! {suback, PacketId, GrantedQos}
end,
gen_server2:cast(SessPid, {subscribe, TopicTable, AckFun}).
handle_cast({subscribe, TopicTable0, AckFun}, Session = #session{client_id = ClientId,
subscriptions = Subscriptions}) ->
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5、-module(emqttd).\
subscribe(ClientId, Topic, Qos) ->
emqttd_server:subscribe(ClientId, Topic, Qos).
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6、-module(emqttd_server).
subscribe(ClientId, Topic, Qos) ->
From = self(), call(server(From), {subscribe, From, ClientId, Topic, ?QOS_I(Qos)}).
handle_call({subscribe, SubPid, ClientId, Topic, Qos}, _From, State) ->
pubsub_subscribe_(SubPid, Topic),
if_subsciption(State, fun() ->
add_subscription_(ClientId, Topic, Qos),
set_subscription_stats()
end),
pubsub_subscribe_(SubPid, Topic) ->
case ets:match(subscribed, {SubPid, Topic}) of
[] ->
emqttd_pubsub:async_subscribe(Topic, SubPid),
ets:insert(subscribed, {SubPid, Topic});
[_] ->
false
end.
add_subscription_(Subscription) when is_record(Subscription, mqtt_subscription) ->
mnesia:dirty_write(subscription, Subscription).
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7、-module(emqttd_pubsub).
把订阅的主题和节点名称存储在Mnesia数据库，这里考虑了集群的情况；
同时也把订阅主题和进程id存储在ETS表。
async_subscribe(Topic, SubPid) when is_binary(Topic) ->
cast(pick(Topic), {subscribe, Topic, SubPid}).
handle_cast({subscribe, Topic, SubPid}, State) ->
add_subscriber_(Topic, SubPid),
{noreply, setstats(State)};
add_subscriber_(Topic, SubPid) ->
case ets:member(subscriber, Topic) of
false ->
mnesia:transaction(fun add_topic_route_/2, [Topic, node()]),
setstats(topic);
true ->
ok
end,
ets:insert(subscriber, {Topic, SubPid}).
add_topic_route_(Topic, Node) ->
add_topic_(Topic), emqttd_router:add_route(Topic, Node).
add_topic_(Topic) ->
add_topic_(Topic, []).
add_topic_(Topic, Flags) ->
Record = #mqtt_topic{topic = Topic, flags = Flags},
case mnesia:wread({topic, Topic}) of
[] -> mnesia:write(topic, Record, write);
[_] -> ok
end.
8、-module(emqttd_router).\
add_route(Topic, Node) when is_binary(Topic), is_atom(Node) ->
add_route(#mqtt_route{topic = Topic, node = Node}).
add_route_(Route = #mqtt_route{topic = Topic}) ->
case mnesia:wread({route, Topic}) of
[] ->
case emqttd_topic:wildcard(Topic) of
true -> emqttd_trie:insert(Topic);
false -> ok
end,
mnesia:write(route, Route, write);
Records ->
case lists:member(Route, Records) of
true -> ok;
false -> mnesia:write(route, Route, write)
end
end.
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