luamqtt - MQTT client written in pure lua

kial Thank you very much for your help! My code required a few adjustments related to the luamqtt library, such as using ioloop_mt:iteration(), as well as modifications specific to CoppeliaSim, like ensuring the coroutine is resumed at least once per simulation step.

For anyone who might find it useful, here is the working code, it connects CoppeliaSim to a local MQTT broker in a non-blocking way :

function sysCall_init()
    sim = require('sim')

    -- Initialize MQTT
    package.path = package.path .. ";C:/Program Files/CoppeliaRobotics/CoppeliaSimEdu/lua/mqtt/?.lua"
    print("Package path updated:", package.path)

    local mqtt = require("mqtt")
    local ioloop = require("mqtt.ioloop").get()  -- Get the default ioloop instance

    if not mqtt then
        error("Failed to load MQTT library. Check the path and ensure the library exists.")
    end

    -- Create MQTT client
    client = mqtt.client{
        uri = "127.0.0.1:1883", 
        id = "robot_client",
        clean = true
    }

    if not client then
        error("Failed to create MQTT client.")
    end

    print("Created MQTT client:", client)

    -- Set up the MQTT client on events
    client:on{
        connect = function(connack)
            if connack.rc ~= 0 then
                print("Connection to broker failed:", connack:reason_string(), connack)
                return
            end
            print("Connected to broker:", connack)  

            -- Subscribe to the topic after connection
            assert(client:subscribe{
                topic = "robot/commands",
                qos = 2,
                callback = function(suback)
                    print("Subscribed to topic:", suback)
                end
            })
        end,

        message = function(msg)
            assert(client:acknowledge(msg))  
            print("Received message:", msg.topic, msg.payload)
        end,

        error = function(err)
            print("MQTT client error:", err)
        end,

        close = function()
            print("MQTT connection closed")
        end
    }

    -- Attach client to the ioloop
    local success, err = pcall(function()
        ioloop:add(client)
    end)
    if not success then
        print("Failed to add client to ioloop:", err)
        return
    end
    print("Client added to ioloop")

    -- Create the coroutine for the MQTT loop
    mqttCoroutine = coroutine.create(function()
        while true do
            local success, err = pcall(function()
                ioloop:iteration(0.1)  -- Small timeout to prevent excessive CPU usage
            end)
            if not success then
                print("Error in ioloop iteration:", err)
            end
            coroutine.yield()  -- Yield control back to CoppeliaSim
        end
    end)
end

-- Resume the coroutine in the sensing function
function sysCall_sensing()
    if coroutine.status(mqttCoroutine) ~= 'dead' then
        local ok, errorMsg = coroutine.resume(mqttCoroutine)
        if errorMsg then
            error(debug.traceback(mqttCoroutine, errorMsg), 2)
        end
    end
end