规则引擎 SQL 语句中可用的字段

SELECT 和 WHERE 子句可用的字段与事件的类型相关。其中 clientid, username 和 event 是通用字段，每种事件类型都有。

使用规则引擎 SQL 语句处理消息发布

规则引擎的 SQL 语句可以处理消息发布。 在一个规则语句中，用户可以用 FROM 子句指定一个或者多个主题，当任何消息发布到指定的主题时都会触发该规则。

示例

SELECT
  payload.msg as msg,
  clientid,
  username,
  payload,
  topic,
  qos
FROM
  "t/#"

输出

{
  "username": "u_emqx",
  "topic": "t/a",
  "qos": 1,
  "payload": "{\"msg\":\"hello\"}",
  "msg": "hello",
  "clientid": "c_emqx"
}

使用规则引擎 SQL 语句处理事件

规则引擎的 SQL 语句既可以处理消息(消息发布)，也可以处理事件(客户端上下线、客户端订阅等)。对于消息，FROM 子句后面直接跟主题名；对于事件，FROM 子句后面跟事件主题。

事件消息的主题以 "$events/" 开头，比如 "$events/client_connected", "$events/session_subscribed"。 如果想让 emqx 将事件消息发布出来，可以在 emqx_rule_engine.conf 文件中配置。

FROM 子句可用的事件主题

$events/message_delivered (消息投递)

当消息被放入底层socket时触发规则

示例

SELECT
  from_clientid,
  from_username,
  topic,
  qos,
  node,
  timestamp
FROM
  "$events/message_delivered"

输出

{
  "topic": "t/a",
  "timestamp": 1645002753259,
  "qos": 1,
  "node": "emqx@127.0.0.1",
  "from_username": "u_emqx_1",
  "from_clientid": "c_emqx_1"
}

$events/message_acked (消息确认)

当消息发送到客户端，并收到客户端回复的ack时触发规则，仅QOS1，QOS2会触发

示例

SELECT
  from_clientid,
  from_username,
  topic,
  qos,
  node,
  timestamp
FROM
  "$events/message_acked"

输出

{
  "topic": "t/a",
  "timestamp": 1645002965664,
  "qos": 1,
  "node": "emqx@127.0.0.1",
  "from_username": "u_emqx_1",
  "from_clientid": "c_emqx_1"
}

$events/message_dropped (消息在转发的过程中被丢弃)

当一条消息无任何订阅者时触发规则

示例

SELECT
  reason,
  topic,
  qos,
  node,
  timestamp
FROM
  "$events/message_dropped"

输出

{
  "topic": "t/a",
  "timestamp": 1645003103004,
  "reason": "no_subscribers",
  "qos": 1,
  "node": "emqx@127.0.0.1"
}

$events/delivery_dropped (消息在投递的过程中被丢弃)

当订阅者的消息队列已满时触发规则

示例

SELECT
  from_clientid,
  from_username,
  reason,
  topic,
  qos
FROM "$events/delivery_dropped"

输出

{
  "topic": "t/a",
  "reason": "queue_full",
  "qos": 1,
  "from_username": "u_emqx_1",
  "from_clientid": "c_emqx_1"
}

$events/client_connected (终端连接成功)

当终端连接成功时触发规则

示例

SELECT
  clientid,
  username,
  keepalive,
  is_bridge
FROM
  "$events/client_connected"

输出

{
  "username": "u_emqx",
  "keepalive": 60,
  "is_bridge": false,
  "clientid": "c_emqx"
}

$events/client_disconnected (终端连接断开)

当终端连接断开时触发规则

示例

SELECT
  clientid,
  username,
  reason,
  disconnected_at,
  node
FROM
  "$events/client_disconnected"

输出

{
  "username": "u_emqx",
  "reason": "normal",
  "node": "emqx@127.0.0.1",
  "disconnected_at": 1645003578536,
  "clientid": "c_emqx"
}

$events/client_connack (连接确认)

当服务端向客户端发送CONNACK报文时触发规则, reason_code 包含各种错误原因代码

MQTT v5.0 协议将返回码重命名为原因码，增加了一个原因码来指示更多类型的错误(Reason code and ACK - MQTT 5.0 new features (opens new window))。 因此reason_code 在MQTT v3.1.1与MQTT v5.0中有很大的不同。

MQTT v3.1.1

MQTT v5.0

示例

SELECT
  clientid,
  username,
  reason,
  node
FROM
  "$events/client_connack"

输出

{
  "username": "u_emqx",
  "reason": "success",
  "node": "emqx@127.0.0.1",
  "connected_at": 1645003578536,
  "clientid": "c_emqx"
}

$events/client_check_acl_complete (鉴权结果)

当客户端鉴权结束时触发规则

示例

SELECT
  clientid,
  username,
  topic,
  action,
  result,
  is_cache,
  node
FROM
  "$events/client_check_acl_complete"

输出

{
  "username": "u_emqx",
  "topic": "t/a",
  "action": "publish",
  "result": "allow",
  "is_cache": "false",
  "node": "emqx@127.0.0.1",
  "clientid": "c_emqx"
}

$events/session_subscribed (终端订阅成功)

当终端订阅成功时触发规则

示例

SELECT
  clientid,
  username,
  topic,
  qos
FROM
  "$events/session_subscribed"

输出

{
  "username": "u_emqx",
  "topic": "t/a",
  "qos": 1,
  "clientid": "c_emqx"
}

$events/session_unsubscribed (取消终端订阅成功)

当取消终端订阅成功时触发规则

示例

SELECT
  clientid,
  username,
  topic,
  qos
FROM
  "$events/session_unsubscribed"

输出

{
  "username": "u_emqx",
  "topic": "t/a",
  "qos": 1,
  "clientid": "c_emqx"
}

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