mqtt 客户端的问题答案

【问题标题】：Issue with mqtt clientmqtt 客户端的问题
【发布时间】：2018-03-26 22:42:17
【问题描述】：

我有下面的 mqtt 客户端代码，用于从代理接收消息。如果客户端与代理断开连接，则客户端尝试再次使用connect() 调用与代理连接。我已阅读 paho 文档说 loop_start() 将处理与经纪人的重新连接。请让我知道是否可以使用connect() 呼叫与经纪人重新连接或让loop_start() 自己处理。

import paho.mqtt.client as mqtt
import json
import time

is_connect = False

# The callback for when the client receives a CONNACK response from the server.
def on_connect(client, userdata, flags, rc):
    print("Connected with result code "+str(rc))
    # Subscribing in on_connect() means that if we lose the connection and
    # reconnect then subscriptions will be renewed.
    client.subscribe("#")

# The callback for when a PUBLISH message is received from the server.
def on_message(client, userdata, msg):
    print("Message received on "+msg.topic)
    parsed_message = json.loads(msg.payload)
    print(json.dumps(parsed_message, indent=4, sort_keys=True))

def on_disconnect(client, userdata, rc):

    if rc != 0:

        print "Unexpected disconnection." , (rc)
        global is_connect
        is_connect = False
while True:
    global is_connect
    #If client is not connected, initiate connection again 
    if not is_connect:
        try:
            client = mqtt.Client(client_id='testing_purpose', clean_session=False)
            client.loop_stop()
            client.on_connect = on_connect
            client.on_message = on_message
            client.on_disconnect = on_disconnect
            client.connect("localhost", 1883, 5)
            is_connect = True
            client.loop_start()
            time.sleep(15)
        except Exception as err:
            is_connect = False


# Blocking call that processes network traffic, dispatches callbacks and
# handles reconnecting.
# Other loop*() functions are available that give a threaded interface and a
# manual interface.
#client.loop_forever()

【问题讨论】：

这里没有真正的问题。你试过这段代码看看会发生什么吗？
话虽如此，您可能希望将is_connect = True 移动到on_connect 方法中
@hardillb 此代码工作正常。但是我怀疑我在每次断开连接时都在创建 mqtt 客户端的对象。这样做会与 mqtt 代理产生任何问题。我也将 is_connect = True 移动到 on_connect()

标签： python python-2.7 mqtt paho

【解决方案1】：

好的，所以 Paho 客户端只有在您使用 loop_forever 函数时才会重新连接。

因此，如果您想控制网络循环，您可以随时使用reconnect 函数重新连接，而不是断开整个连接。但最简单的方法是只使用loop_forever 函数，如下所示：

import paho.mqtt.client as mqtt
import json

# The callback for when the client receives a CONNACK response from the server.
def on_connect(client, userdata, flags, rc):
    print("Connected with result code "+str(rc))
    # Subscribing in on_connect() means that if we lose the connection and
    # reconnect then subscriptions will be renewed.
    client.subscribe("#")

# The callback for when a PUBLISH message is received from the server.
def on_message(client, userdata, msg):
    print("Message received on "+msg.topic)
    parsed_message = json.loads(msg.payload)
    print(json.dumps(parsed_message, indent=4, sort_keys=True))

def on_disconnect(client, userdata, rc):
    if rc != 0:
        print "Unexpected disconnection." , (rc)

# Blocking call that processes network traffic, dispatches callbacks and
# handles reconnecting.
# Other loop*() functions are available that give a threaded interface and a
# manual interface.
client = mqtt.Client(client_id='testing_purpose', clean_session=False)
client.on_connect = on_connect
client.on_message = on_message
client.on_disconnect = on_disconnect
client.loop_forever()

【讨论】：