Paho Python MQTT 客户端连接成功但 on_connect 回调未被调用

Question

我在 Raspberry Pi 上有一个简单的脚本，它每 3 秒发布一条示例消息。我已经声明了回调 on_connect、on_publish 和 on_disconnect。此客户端连接成功但未调用 on_connect、发布并调用 on_publish、断开连接并调用 on_disconnect。

这是我的脚本

import paho.mqtt.client as mqtt
import time

def on_connect(mqttc, userdata, rc):
    print("Connected with result code "+str(rc))
    if rc!=0 :
        mqttc.reconnect()

def on_publish(mqttc, userdata, mid):
    print "Published"

def on_disconnect(mqttc, userdata, rc):
    if rc != 0:
        print("Unexpected disconnection. Reconnecting...")
        mqttc.reconnect()
    else :
        print "Disconnected successfully"

# Setup MQTT
# broker='test.mosquitto.org'
broker = 'iot.eclipse.org'
broker_port=1883

# Create a client instance
mqttc=mqtt.Client(client_id="MyClient")
mqttc.on_connect = on_connect
mqttc.on_publish = on_publish
mqttc.on_disconnect = on_disconnect

while 1:

    mqttc.connect(broker, broker_port, 60)
    # print "Connected."    # I don't want this message. 
                            # Why isn't the on_connect callback invoked?

    try:
        topic = "this/is/a/test/topic"
        payload = "test_message"
        print "Publishing " + payload + " to topic: " + topic + " ..."
        mqttc.publish(topic, payload, 0)

    except Exception as e:
        print "exception"
        log_file=open("log.txt","w")
        log_file.write(str(time.time())+" "+e.__str__())
        log_file.close()

    mqttc.disconnect()
    print ""
    time.sleep(3)

虽然这个小问题"bug"不影响消息发布，主要是我想达到的目的，但是为什么会出现这种情况，如何解决？

Answer 1

您的 on_connect() 方法声明缺少 flags(1) 参数。所以它没有被调用。 Flags 参数包含代理发送的响应。必须是

def on_connect(mqttc, userdata, flags, rc):

另外，为什么要循环连接和断开连接？尝试使用 loop_start() 和 loop_stop() 方法来处理连接断开时的自动重新连接（）。

Answer 2

这不起作用的原因是您没有调用任何 loop*() 函数。这些处理网络流量。如果您不使用，则无法保证您的外发邮件会被发送，也绝对不会处理任何传入邮件。

loop_forever() 是处理网络循环的阻塞调用 - 可能不是您想要的。

loop_start() 启动一个线程来处理网络循环，因此 returns 直接。

我会这样做：

mqttc.connect(broker, broker_port, 60) # Don't forget to handle errors
mqttc.loop_start()

while 1:
    try:
        topic = "this/is/a/test/topic"
        payload = "test_message"
        print "Publishing " + payload + " to topic: " + topic + " ..."
        mqttc.publish(topic, payload, 0)

    except Exception as e:
        print "exception"
        log_file=open("log.txt","w")
        log_file.write(str(time.time())+" "+e.__str__())
        log_file.close()

    print ""
    time.sleep(3)

如@Kiran 所说，您仍然需要修复 on_connect 回调。

无需每次都断开连接 - 事实上，当您断开连接时，无法保证您的消息已发送。您应该使用 on_publish 回调来了解消息何时发送。

如果你想做一个简单的连接-发布-断开，那么可以使用 paho.mqtt.publish 辅助模块：

import paho.mqtt.publish as publish

while 1:
    try:
        topic = "this/is/a/test/topic"
        payload = "test_message"
        print "Publishing " + payload + " to topic: " + topic + " ..."
        publish.single(topic, payload, 0, host=broker, port=broker_port)

    except Exception as e:
        print "exception"
        log_file=open("log.txt","w")
        log_file.write(str(time.time())+" "+e.__str__())
        log_file.close()

    print ""
    time.sleep(3)

Paho Python MQTT 客户端连接成功但 on_connect 回调未被调用

Paho Python MQTT client connects successfully but on_connect callback is not invoked

python

mqtt

paho