machinekoder

MQTT Retain Flag and potential Problems

This document summarizes my findings in potential problems using the MQTT retain flag as a default for every topic in an MQTT application. MQTT retain is a useful feature if used properly. However, the risks of using it (as developer and for users of the software) are rarely warned about in many guides. Only when working with IoT applications for some time and reading through user forums, the MQTT specs and with a bit experience using other middleware projects potential risks may surface. I write this document mainly for myself for future implementation of MQTT application so I can make better decision when to use and when not use the MQTT retain flag.

Note that I'm only considering the MQTT 5 specs here. This document is not a writeup in prosa (except for this section here maybe) and should be used more as a sheet of notes with links for making your own decisions. It's by no means complete and comments helping me improve this document are welcome.

Expected Beha

machinekoder

Issue

According to https://valetudo.cloud/pages/integrations/mqtt.html#mapsegmentssegments map segment ids should be reported on the topic <TOPIC PREFIX>/<IDENTIFIER>/MapData/segments.

This works well if "Provide map data" is checked in the Valetudo settings and this in line with the description in the docs.

However, when "Provide map data" is unchecked an empty JSON object is published to that topic. This undefined or at least undocumented behavior. Citing from the documentation This handle groups access to map data. It is only enabled if provideMapData is enabled in the MQTT config.

Note that <TOPIC PREFIX>/<IDENTIFIER>/MapData/map-data is still retained in this case if it was previously published.

UPDATE: When pressing "Save Configuration" in the UI switching "Provide map data" to "On" there is a ~30s delay until the segments are published on the topic. When switching from "On" to "Off" state, the message is received almost instantly. This can lead to perception of an intermittend issue if th

machinekoder

#!/usr/bin/env python
# -*- coding: utf-8 -*-
import shutil
import sys
import tarfile
import tempfile
from sh import wget
import os
import yaml

machinekoder

from ..Script import Script
class SimpleTweak(Script):
    def __init__(self):
        super().__init__()

    def getSettingDataString(self):
        return """{
            "name":"SimpleTweak (for Alex Uni-Print-3D)",
            "key": "SimpleTweak",
            "metadata":{},

machinekoder

sudo su
service docker stop
ls -d -1 /var/lib/docker/btrfs/subvolumes/* | xargs btrfs subvolume delete
rm -rf /var/lib/docker

machinekoder

# Turn commanded position -5 to +5 into 1-2 mS pulse for RC (hobby) servo
# gain   = 1 mS (range) / 50 mS (PWM period) / 10 (units)= 0.002
# offset = 1.5 mS (value) / 50 mS (PWM period) = 0.03
# Resulting PWM values should be between 0.02 and 0.04, representing a
# 1 mS to 2 mS wide pulse

def rc_servo(thread, name, range_ms, offset_ms, period_ms, min_step, max_step, in_signal, out_signal):
    gain = range_ms / pwm_ms / (max_step - min_step)
    offset = value_ms / pwm_ms

machinekoder

# derived from http://wiki.ros.org/ROSberryPi/Installing%20ROS%20Kinetic%20on%20Raspberry%20Pi


 sudo sh -c 'echo "deb http://packages.ros.org/ros/ubuntu stretch main" > /etc/apt/sources.list.d/ros-latest.list'
 wget https://raw.githubusercontent.com/ros/rosdistro/master/ros.key  -O - | sudo apt-key add -


sudo apt-get update
sudo apt-get upgrade

machinekoder

[connection]
id=Hotspot
uuid=bd4058b4-f99e-48f9-ac88-26513b9ac517
type=wifi
autoconnect=true
permissions=

[wifi]
hidden=false
mac-address=00:0F:60:06:EE:BE

machinekoder

[Number format]
post_decimals = 3
pre_decimal_zero_padding = 0
signed_values = 0
pre_decimals = 4
decimal_seperator = .
post_decimal_zero_padding = 1

[Program]
cutter_comp_left = 

machinekoder

#!/usr/bin/env bash
fileid="$1"
destination="$2"

# try to download the file
curl -c /tmp/cookie -L -o /tmp/probe.bin "https://drive.google.com/uc?export=download&id=${fileid}"
probeSize=`du -b /tmp/probe.bin | cut -f1`

# did we get a virus message?
# this will be the first line we get when trying to retrive a large file