如何更改 qos 级别和消息保留？

Question

您好，我在 python 中有一些 mqtt publish/subscribe 的代码。我想更改 qos 值和消息保留，但我不知道如何更改，因为目前 qos 值始终只打印 0，我想将消息保留标志更改为 true 或 false，而不是 0。感谢所有帮助.

import paho.mqtt.client as mqtt
import time
class laser(mqtt.Client):
    def on_connect(self, mqttc, obj, flags, rc):
        print("rc: "+str(rc))
        print("Subscribing to topic","microscope/light_sheet_microscope/laser")
        mqttc.subscribe("microscope/light_sheet_microscope/laser")

    def on_message(self, mqttc, userdata, message):
        print("message received " ,str(message.payload.decode("utf-8")))
        print("message topic=",message.topic)
        print("message qos=",message.qos)
        print("message retain flag=",message.retain)

    def on_publish(self, mqttc, obj, mid):
        print("mid: "+str(mid))

    def on_subscribe(self, mqttc, obj, mid, granted_qos):
        print("Subscribed: "+str(mid)+" "+str(granted_qos))

    def on_log(self, mqttc, userdata, level, buf):
        print("log: ",buf)

    def run(self):
        self.connect("broker.hivemq.com", 1883, 60)

print("creating new instance")
client = laser("Laser")
client.run()

client.loop_start() #start the loop
time.sleep(2)
print("Publishing message to topic","microscope/light_sheet_microscope/laser")
client.publish("microscope/light_sheet_microscope/laser","Hello World Im a laser!")
time.sleep(2) # wait
client.loop_stop() #stop the loop

谢谢

Answer 1

来自帕霍Pythondocs

PUBLISH()

publish(topic, payload=None, qos=0, retain=False)

This causes a message to be sent to the broker and subsequently from the broker to any clients subscribing to matching topics. It takes the following arguments:

topic the topic that the message should be published on

payload the actual message to send. If not given, or set to None a zero length message will be used. Passing an int or float will result in the payload being converted to a string representing that number. If you wish to send a true int/float, use struct.pack() to create the payload you require

qos the quality of service level to use

retain if set to True, the message will be set as the “last known good”/retained message for the topic.

要将 QOS 设置为 2 并将保留标志设置为 true，请将发布行更改为以下内容：

client.publish("microscope/light_sheet_microscope/laser","Hello World Im a laser!",2,True)

如何更改 qos 级别和消息保留？

How do I change the qos level and message retain?

python-3.x

mqtt

paho