一、工作环境准备

准备好redis server，http://blog.csdn.net/libaineu2004/article/details/76267836

erlang redis客户端使用开源项目，https://github.com/wooga/eredis

erlang连接池，https://github.com/emqtt/ecpool

emq使用的是v2.3.5版本，https://github.com/emqtt/emq-relx

我们以插件emq_auth_redis来实现，路径是/home/firecat/Prj/emq2.0/emq-relx-2.3.5/deps/emq_auth_redis

/home/firecat/Prj/emq2.0/emq-relx-2.3.5/data/loaded_plugins设置自启动插件

emq_recon. 
emq_modules. 
emq_retainer. 
emq_dashboard. 
emq_auth_redis.

二、redis数据准备

对照/home/firecat/Prj/emq2.0/emq-relx-2.3.5/deps/emq_auth_redis/README.md说明文档，往redis数据库写入username和password：

格式

HSET mqtt_user:<username> password "password"

命令

[root@localhost src]# ./redis-cli
127.0.0.1:6379> HSET mqtt_user:firecat password "123456"
(integer) 1
127.0.0.1:6379> HSET mqtt_user:lqh password "pass123"
(integer) 1
127.0.0.1:6379> HSET mqtt_user:firecatGTerm password "he2345v11t11"
(integer) 1
127.0.0.1:6379> hgetall mqtt_user
(empty list or set)
127.0.0.1:6379> HMGET mqtt_user:lqh password
1) "pass123"
127.0.0.1:6379> hgetall mqtt_user:lqh
1) "password"
2) "pass123"

源文件/home/firecat/Prj/emq2.0/emq-relx-2.3.5/deps/emqttd/src/emqttd_access_control.erl会启用校验

%% @doc Authenticate MQTT Client.
-spec(auth(Client :: mqtt_client(), Password :: password()) -> ok | {ok, boolean()} | {error, term()}).
auth(Client, Password) when is_record(Client, mqtt_client) ->
    auth(Client, Password, lookup_mods(auth)).
auth(_Client, _Password, []) ->
    case emqttd:env(allow_anonymous, false) of
        true  -> ok;
        false -> {error, "No auth module to check!"}
    end;
auth(Client, Password, [{Mod, State, _Seq} | Mods]) ->
    case catch Mod:check(Client, Password, State) of
        ok              -> ok;
        {ok, IsSuper}   -> {ok, IsSuper};
        ignore          -> auth(Client, Password, Mods);
        {error, Reason} -> {error, Reason};
        {'EXIT', Error} -> {error, Error}
    end.

源文件emq_auth_redis.erl，有校验的实施过程

check(Client, Password, #state{auth_cmd  = AuthCmd,

                              super_cmd = SuperCmd,

                              hash_type = HashType}) ->

   Result = case emq_auth_redis_cli:q(AuthCmd, Client) of

源文件emq_auth_redis_cli.erl，有redis的查询命令实现方法

%% Redis Query.

-spec(q(string(), mqtt_client()) -> {ok, undefined | binary() | list()} | {error, atom() | binary()}).

q(CmdStr, Client) ->

   io:format("1 CmdStr is: ~s  ~n", [CmdStr]),

   Cmd = string:tokens(replvar(CmdStr, Client), " "),

   io:format("2 Cms is: ~s  ~n", [Cmd]),

   ecpool:with_client(?APP, fun(C) -> eredis:q(C, Cmd) end).

ereids的使用案例，https://github.com/wooga/eredis

{ok, C} = eredis:start_link().

{ok, <<"OK">>} = eredis:q(C, ["SET", "foo", "bar"]).

{ok, <<"bar">>} = eredis:q(C, ["GET", "foo"]).

KeyValuePairs = ["key1", "value1", "key2", "value2", "key3", "value3"].

{ok, <<"OK">>} = eredis:q(C, ["MSET" | KeyValuePairs]).

{ok, Values} = eredis:q(C, ["MGET" | ["key1", "key2", "key3"]]).

string:tokens的用法可以参考erlang官方文档，http://erlang.org/doc/man/string.html

tokens(String, SeparatorList) -> Tokens

Types

String = SeparatorList = string()

Tokens = [Token :: nonempty_string()]

Returns a list of tokens in String, separated by the characters in SeparatorList.

Example:

> tokens("abc defxxghix jkl", "x ").

["abc", "def", "ghi", "jkl"]

三、除了emq_auth_redis_cli.erl上诉的查询方法，我们自己也可以实现其他查询方法：

-export([connect/1, q/2, q2/2]).
%% Redis Query.firecat add.
-spec(q2(string(), binary()) -> {ok, undefined | binary() | list()} | {error, atom() | binary()}).
q2(CmdStr, ClientId) ->
    io:format("3 CmdStr is: ~s  ~n", [CmdStr]),
    Cmd = string:tokens(replvar(CmdStr, "%c", ClientId), " "),
    io:format("4 Cms is: ~s  ~n", [Cmd]),
    ecpool:with_client(?APP, fun(C) -> eredis:q(C, Cmd) end).

这样，我在其他任意的erlang mod，都可以调用该方法，例如**.erl：

%%%% redis test
redis_test(ClientId) ->
   Result = case emq_auth_redis_cli:q2("HMGET mqtt_clientid:%c user group type", ClientId) of
                {ok, [undefined|_]} ->
                    io:format("clientid ignore: undefined  ~n"), %%firecat
                    {error, undefined};
                {ok, [User, Group, Type]} -> %%[undefined, undefined, undefined]
                    io:format("clientid is: ~s ~s ~s ~n", [User, Group, Type]),
                    ok;
                {error, Reason} ->
                    io:format("clientid error is: ~s  ~n", [Reason]),
                    {error, Reason}
             end,
   case Result of
             ok -> ok; %%firecat
             Error -> ok
             end.

四、redis插件除了可以检验username和password，还可以校验clientid的合法性。需要手动新增源文件emq_clientid_redis.erl。完整的源码请访问：

https://download.csdn.net/download/libaineu2004/10289890