Question

您好，我正在尝试从树莓派2设备传输数据，并通过mqtt在另一台计算机的终端上接收数据。我在json上发布mosquitto信息的部分工作正常。我订阅的部分如下：

import time
import paho.mqtt.client as mqtt

broker="test.mosquitto.org"

#define callback
def on_message(client, userdata, message):
    time.sleep(1)
    try:
        print("received message =", str(message.payload.decode("utf-8")))
    except None:
        print("")

client=mqtt.Client()

client.on_message = on_message
#####
print("connecting to broker ",broker)
client.connect(broker)

client.loop_start() #start loop to process received messages

print("subscribing ")
client.subscribe("DHT22_cimti_project_pe") #subscribe

client.loop_forever()

问题是，当我在MacBooks Terminal上运行此程序时，它正在工作，但最终总是因以下错误而崩溃：

Traceback (most recent call last):
  File "mqtt2.py", line 26, in <module>
    client.loop_forever()
  File "/anaconda3/lib/python3.6/site-packages/paho/mqtt/client.py",    line 1481, in loop_forever
    rc = self.loop(timeout, max_packets)
  File "/anaconda3/lib/python3.6/site-packages/paho/mqtt/client.py", line 1003, in loop
    rc = self.loop_read(max_packets)
  File "/anaconda3/lib/python3.6/site-packages/paho/mqtt/client.py", line 1284, in loop_read
    rc = self._packet_read()
  File "/anaconda3/lib/python3.6/site-packages/paho/mqtt/client.py", line 1849, in _packet_read
    rc = self._packet_handle()
  File "/anaconda3/lib/python3.6/site-packages/paho/mqtt/client.py", line 2305, in _packet_handle
    return self._handle_publish()
  File "/anaconda3/lib/python3.6/site-packages/paho/mqtt/client.py", line 2464, in _handle_publish
    (slen, packet) = struct.unpack(pack_format, self._in_packet['packet'])
struct.error: bad char in struct format

我试图做一个try except方法，但是它没有用，所以我决定在Windows计算机上使用。但是，这甚至更糟，因为该程序甚至没有给我发送到mqtt服务器的数据。我直接收到以下错误：

[WinError 10038] An operation was attempted on something that is not a socket.

所以我的问题是。为什么在Windows上Mac可以正常工作（即使它崩溃了）时却出现此错误？我该如何解决此问题（在Windows上，如果可能的话在Mac上为什么不可以）。

Answer 1

首先，您尝试两次启动网络循环，但永远无法进行。

接下来，您真的应该在订阅之前等待连接确认，因此添加on_connect回调是一个好主意。

import paho.mqtt.client as mqtt

broker="test.mosquitto.org"

#define callback
def on_message(client, userdata, message):
  try:
    print("received message =", str(message.payload.decode("utf-8")))
  except None:
    print("")

def on_connect(client, userdata, flags, rc):
  print("Connection returned result: "+connack_string(rc))
  print("subscribing ")
  client.subscribe("DHT22_cimti_project_pe") #subscribe

client=mqtt.Client()

client.on_message = on_message
client.on_connect = on_connect

#####
print("connecting to broker ",broker)
client.connect(broker)

client.loop_forever() #start loop to process received messages

最后，实际上您不应该阻止on_message回调，因此请删除time.sleep(1)

在终端（mosquitto）上显示来自mqtt服务器的json消息

1 个答案: