# MQTT Erlang 客户端库
emqtt (opens new window) 是开源 MQTT Broker EMQX 官方提供的客户端库，适用于 Erlang 语言。
Erlang 生态有多个 MQTT Broker 实现，如通过插件支持 MQTT 的 RabbitMQ ，VerenMQ、EMQX 等。但受限于语言小众性，可用的 MQTT 客户端库几乎没有选择的余地，MQTT 社区收录的 Erlang 客户端库中 emqtt (opens new window) 是最佳选择。
emqtt 完全由 Erlang 实现，完成整支持 MQTT v3.1.1 和 MQTT v5.0 协议版本，支持 SSL 单双向认证与 WebSocket 连接。另一款 MQTT 基准测试工具 emqtt_bench (opens new window) 就基于该客户端库构建。
# emqtt 使用示例
本示例包含 Erlang 的 emqtt 客户端库连接 EMQX Broker，并进行消息收发完整代码：
ClientId = <<"test">>. {ok, ConnPid} = emqtt:start_link([{clientid, ClientId}]). {ok, _Props} = emqtt:connect(ConnPid). Topic = <<"guide/#">>. QoS = 1. {ok, _Props, _ReasonCodes} = emqtt:subscribe(ConnPid, {Topic, QoS}). {ok, _PktId} = emqtt:publish(ConnPid, <<"guide/1">>, <<"Hello World!">>, QoS). %% If the qos of publish packet is 0, `publish` function would not return packetid. ok = emqtt:publish(ConnPid, <<"guide/2">>, <<"Hello World!">>, 0). %% Recursively get messages from mail box. Y = fun (Proc) -> ((fun (F) -> F(F) end)((fun(ProcGen) -> Proc(fun() -> (ProcGen(ProcGen))() end) end))) end. Rec = fun(Receive) -> fun()-> receive {publish, Msg} -> io:format("Msg: ~p~n", [Msg]), Receive(); _Other -> Receive() after 5 -> ok end end end. (Y(Rec))(). %% If you don't like y combinator, you can also try named function to recursively get messages in erlang shell. Receive = fun Rec() -> receive {publish, Msg} -> io:format("Msg: ~p~n", [Msg]), Rec(); _Other -> Rec() after 5 -> ok end end. Receive(). {ok, _Props, _ReasonCode} = emqtt:unsubscribe(ConnPid, <<"guide/#">>). ok = emqtt:disconnect(ConnPid).Copied!
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
# emqtt MQTT 5.0 支持
目前 emqtt 已经完整支持 MQTT 5.0。