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I am currently implementing a MQTT protocol to be used between two raspberry pis. The first is a Pi 0 and will have a pi camera connected to it. It will be converting each captured frame to a numpy array and then publish it to the master Pi which will then convert the numpy array to an image using PIL. I am doing it this way since I want the main image processing operations to be performed on the master Pi.

My problem is that no messages are being received by the master Pi. I have preformed debugging and everything is working fine on the servant script. But for some reason nothing is received by the master Pi.

Here are both scripts:

servant.py:

import paho.mqtt.client as mqtt

import time

import cv2

import numpy

import json



MQTT_SERVER = "iot.eclipse.org"

MQTT_PATH = "test_channel"



mqttc = mqtt.Client()

mqttc.connect(MQTT_SERVER, 1883, 60)



cap = cv2.VideoCapture(0)



while True:

    ret, frame = cap.read()

    frame_list = frame.tolist()

    MQTT_MESSAGE = json.dumps(frame_list)

    mqttc.publish(MQTT_PATH, MQTT_MESSAGE)

    time.sleep(1)

master.py:

import paho.mqtt.client as mqtt

import numpy as np

import json

import PIL



MQTT_SERVER = "iot.eclipse.org"

MQTT_PATH = "test_channel"



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

    print("connected with result code " + str(rc))

    client.subscribe(MQTT_PATH)



def on_message(client, userdata, msg):

    data = json.loads(msg.payload)

    array = np.array(data)

    img = PIL.Image.fromarray(array)

    cv2.imshow('image', img)

    cv2.waitKey()



client = mqtt.Client()

client.on_connect = on_connect

client.on_message = on_message

client.connect(MQTT_SERVER, 1883, 60)



client.loop_forever()

In your publishing code you are not actually giving the client any time to process the message it is trying to send. This is even more of a problem because the message is likely to be larger than a single network packet (being an image). To fix this you have to call the MQTT client loop function (or start the loop in the b

import paho.mqtt.client as mqtt

import time

import cv2

import numpy

import json



MQTT_SERVER = "iot.eclipse.org"

MQTT_PATH = "test_channel"



mqttc = mqtt.Client()

mqttc.connect(MQTT_SERVER, 1883, 60)



cap = cv2.VideoCapture(0)



while True:

    ret, frame = cap.read()

    frame_list = frame.tolist()

    MQTT_MESSAGE = json.dumps(frame_list)

    mqttc.publish(MQTT_PATH, MQTT_MESSAGE)

    mqttc.loop()

    time.sleep(1)

or like this:

import paho.mqtt.client as mqtt

import time

import cv2

import numpy

import json



MQTT_SERVER = "iot.eclipse.org"

MQTT_PATH = "test_channel"



mqttc = mqtt.Client()

mqttc.connect(MQTT_SERVER, 1883, 60)



cap = cv2.VideoCapture(0)



mqttc.start_loop()



while True:

    ret, frame = cap.read()

    frame_list = frame.tolist()

    MQTT_MESSAGE = json.dumps(frame_list)

    mqttc.publish(MQTT_PATH, MQTT_MESSAGE)

    time.sleep(1)