我的mqtt协议和emqttd开源项目个人理解（8） - 客户端subscribe消息的源码分析

最新推荐文章于 2024-08-29 07:55:09 发布

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最新推荐文章于 2024-08-29 07:55:09 发布

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分类专栏： Erlang 物联网之mqtt协议和emq开源项目文章标签： emqttd erlang mqtt subscribe 源码

本文链接：https://blog.youkuaiyun.com/libaineu2004/article/details/78818607

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本文介绍了MQTT协议的工作流程及emqttd开源项目的实现细节。重点分析了emqttd中客户端连接、消息处理及订阅流程，涉及emqttd_client、emqttd_parser等关键模块。

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学习mqtt协议和emqttd开源项目http://emqtt.com/

emqttd源码版本号是v1.1.3。http://emqtt.com/downloads/1113

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。）

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}) ->

2、-module(emqttd_parser).

parse(<<Type:4, Dup:1, QoS:2, Retain:1, Rest/binary>>, {none, Limit}) ->

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;

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}) ->

5、-module(emqttd).

subscribe(ClientId, Topic, Qos) ->
    emqttd_server:subscribe(ClientId, Topic, Qos).

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).

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.