Análisis de código fuente del complemento MySQL de almacenamiento de datos de mensajes emqx (2)

1. Análisis del código fuente del módulo emqx_backend_mysql_cli

-module(emqx_backend_mysql_cli).

-include("emqx/include/emqx.hrl").

%% 导出接口函数
-export([client_connected/2,
         subscribe_lookup/2,
         client_disconnected/2,
         message_fetch/3,
         lookup_retain/2,
         message_publish/2,
         message_store/2,
         message_retain/2,
         delete_retain/2,
         message_acked/2,
         run_mysql_sql/3]).

-export([record_to_msg/1]).

-export([connect/1, send_batch/2]).

%% 已经连接的客户端
client_connected(Pool, Msg) ->
    mysql_execute(Pool, client_connected_query,
                 
                  [proplists:get_value(clientid, Msg),
                   1,
                   atom_to_list(node()),
                   1,
                   atom_to_list(node())]),
    ok.

%% 订阅查找配置
subscribe_lookup(Pool, Msg) ->
case mysql_execute(Pool,subscribe_lookup_query,feed_var([<<"${clientid}">>], Msg)) of
    %% 空                  
    {ok, _Cols, []} -> [];
    %% 错误
    {error, Error} ->
            logger:error("Lookup retain error: ~p", [Error]),
            [];
    %% 返回数据
    {ok, _Cols, Rows} ->
            %% 从返回的行数总，提取Topic和qos，组成列表
            [{Topic, #{qos => Qos}} || [Topic, Qos] <- Rows]
    end.

%% 查询已经断开客户端
client_disconnected(Pool, Msg) ->
    mysql_execute(Pool,client_disconnected_query,
                  [0, proplists:get_value(clientid, Msg)]),
    ok.

%% 消息
message_fetch(Pool, Msg, Opts) ->
    %% 获取配置的主题
    Topic = proplists:get_value(topic, Msg),
    %% 获取客户端ID
    ClientId = proplists:get_value(clientid, Msg),
    %% 执行查询
    case mysql_execute(Pool,message_fetch_query,
                       feed_var([<<"${topic}">>, <<"${clientid}">>], Msg)) of
        
        {ok, [_], []} ->
            %% 查询Topic最新的message数据
            MsgId = case mysql_execute(Pool,message_lastid_query, [Topic]) of
                        {ok, [_], []} -> 0;
                        {ok, [_], [[MId]]} -> MId;
                        {error, Error2} ->
                            logger:error("Lookup msg error: ~p", [Error2]),
                            0
                    end,
            %% 查询插入的消息回馈
            mysql_execute(Pool,insert_acked_query, [ClientId, Topic, MsgId]),           
            [];
        {ok, [_], [[AckId]]} ->
            %% 构造sql查询语句
            Sql = <<"select id, topic, msgid, sender, qos, "
                    "payload, retain, UNIX_TIMESTAMP(arrived) "
                    "as arrived from mqtt_msg where id > "
                    "? and topic = ? ">>,
            {Sql1, Params1} = case proplists:get_value(time_range,Opts) of
                                  undefined ->
                                      {<<" order by id DESC ">>,
                                       [AckId, Topic]};
                                  TimeRange ->
                                      Time = erlang:system_time(seconds) -TimeRange,
                                                 
                                      {<<" and arrived >= FROM_UNIXTIME(?) order "
                                         "by id DESC ">>,
                                       [AckId, Topic, Time]}
                              end,

            {Sql2, Params2} = case
                                  proplists:get_value(max_returned_count, Opts)
                                  of
                                  undefined -> {<<"">>, Params1};
                                  MaxReturnedCount ->
                                      {<<" limit ?">>,
                                       Params1 ++ [MaxReturnedCount]}
                              end,
        %% 执行查询
        case mysql_query(Pool,<<Sql/binary, Sql1/binary, Sql2/binary>>, Params2) of
                             
                {ok, _Cols, []} -> [];
                {ok, Cols, Rows} ->
                    [begin
                         M = record_to_msg(lists:zip(Cols, Row)),
                         M#message{id = emqx_guid:from_base62(M#message.id)}
                     end || Row <- lists:reverse(Rows)];
                     
                {error, Error1} ->
                    logger:error("Lookup msg error: ~p", [Error1]),
                    []
            end;
        {error, Error} ->
            logger:error("Lookup msg error: ~p", [Error]),
            []
    end.