Paho Python MQTT客户端成功连接，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_pdisconnect。此客户端连接成功，但未调用on_connect，调用publish和on_publish，断开连接并调用on_pdisconnect。

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"错误"不会影响消息发布，这主要是我想要实现的，但为什么会发生这种情况，我该如何解决？

Answer 1

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。如果你不使用它，就不能保证你的传出消息会被发送，也绝对不会处理传入消息。

loop_forever()是一个处理网络环路的阻塞调用，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)

正如@Kiran所说，你仍然需要修复你的on_connect回调。

没有必要每次都断开连接——事实上，也不能保证当你断开连接时，你的信息会被发送出去。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连接-发布-断开连接，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)

Answer 2

您的on_connect()方法声明缺少标志（1）参数。因此，它没有被调用。Flags参数包含broker发送的响应。必须是

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

另外，为什么要在回路中连接和断开？尝试使用loop_start()和loop_stop()方法来处理断开连接时的自动重新连接（示例）。