Paho Python MQTT客户端连接成功,但未调用on_connect回调

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.此客户端成功连接但未调用on_connect,调用发布和on_publish,调用disconnectcts和on_disconnect.

这是我的剧本

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)   

虽然这个小错误"bug"不会影响消息发布,这主要是我想要实现的,但为什么会发生,我该如何解决呢？

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。它必须是

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

另外，为什么要在循环中连接和断开连接？尝试使用loop_start()和loop_stop()方法处理连接断开时的自动重新连接（示例）。

Answer 2

这不起作用的原因是你没有调用任何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消息将被发送,并且绝对不会处理任何传入消息.

loop_forever() 是一个阻止调用来处理网络循环 - 可能不是你想要的.

loop_start() 启动一个线程来处理网络循环,因此立即返回.

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)

你仍然需要修复你的on_connect回调,正如@Kiran所说.

每次都不需要断开连接 - 事实上,当您断开连接时,无法保证您的消息将被发送.您应该使用on_publish回调来了解消息的发送时间.

如果你想做一个简单的connect-publish-disconnect,那么可以使用paho.mqtt.publishhelper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)