MQTT を file に変換するプログラム

次のシステムを構築する常駐プログラムです。
Grove IoT スターターキット for SORACOM で作るリモートカメラシステム

mqtt_to_file.py

#! /usr/bin/python3
#
#	mqtt_to_file.py
#
#					Aug/22/2021
# ------------------------------------------------------------------
import paho.mqtt.client as mqtt
import json

MQTT_HOST = "www2.ekzemplaro.org"
MQTT_TOPIC = "sample/imageTopic"
MQTT_PORT = 1883
MQTT_KEEP_ALIVE = 60
#
# ------------------------------------------------------------------
def on_connect(mqttc, obj, flags, rc):
	print("rc: " + str(rc))
#
# ------------------------------------------------------------------
def file_write_proc(file_name,str_out):
#
	fp_out = open(file_name,mode='w',encoding='utf-8')
	fp_out.write(str_out)
	fp_out.close()
# ------------------------------------------------------------------
def on_message(mqttc, obj, msg):
	file_name = "/var/tmp/mqtt_work/status.json"
#
	print(msg.topic + " " + str(msg.qos))
	str_out = msg.payload.decode()
	print(len(str_out))
#
	if len(str_out) < 100:
		print(str_out)
#
	unit_aa = json.loads(str_out)
	if "button" in unit_aa:
		print(unit_aa["button"])
		if (unit_aa["button"] == "on"):
			file_write_proc(file_name,str_out)
	elif "status" in unit_aa:
		print(unit_aa["status"])
		file_write_proc(file_name,str_out)
# ------------------------------------------------------------------
mqttc = mqtt.Client()
mqttc.on_message = on_message
mqttc.on_connect = on_connect
mqttc.connect(MQTT_HOST, MQTT_PORT, MQTT_KEEP_ALIVE)
mqttc.subscribe(MQTT_TOPIC)

mqttc.loop_forever()
# ------------------------------------------------------------------

実行時の様子

$ ./mqtt_to_file.py 
rc: 0
sample/imageTopic 0
16
{"button":"off"}
off
sample/imageTopic 0
15
{"button":"on"}
on
sample/imageTopic 0
16
{"button":"off"}
off

systemd で常駐化する。

ワンショットサービスの作成

/opt/one_shot/one_shot.sh

#!/bin/bash
#
#	one_shot.sh
#
LOG_FILE="/tmp/one_shot.log"
date >> $LOG_FILE
/var/www/html/mqtt/mqtt_to_file/mqtt_to_file.py >> $LOG_FILE
echo "one_shot" >> $LOG_FILE
date >> $LOG_FILE
#

/etc/systemd/system/one_shot.service

[Unit]
Description=one_shot shell
After=[e-mail]

[Service]
# Environment=NODE_PORT=3000
Type=simple
User=www-data
Restart=on-failure
ExecStart=/bin/bash /opt/one_shot/one_shot.sh
WorkingDirectory=/tmp

[Install]
WantedBy=multi-user.target

起動

sudo systemctl start one_shot

OS再起動で起動するように設定

sudo systemctl enable one_shot