So, I have an ESP8266. On this board I’m running the newest Version of the MicroPython firmware (1Mib).

I have a Java Vaadin Web Application with 2 Buttons. One Button is for publishing, that the LED should turn off and one Button for turn the LED on.

The MicroPython program on the ESP is running good, till I publish from the Vaadin App. I get the OSError -1 with no other args.

Some informations:
Broker: hivemq in dockerhub localhost
Program for flashing: Thonny

Here is my MicroPython code: (I deleted the ssid and password for data protection -> the client sucessfully connect with the wifi)

from umqtt.simple import MQTTClient
import network
import time

ssid = "ssid"
password = "password"
wlan = network.WLAN(network.STA_IF)

wlan.active(True)
wlan.connect(ssid, password)

while not wlan.isconnected():
    pass

print("hallo")

MQTT_TOPIC = "led/control"

LEDstatus = "off"

ClientID = "Alabama"

LED_PIN = machine.Pin(2, machine.Pin.OUT)
LED_PIN.value(1)

def mqtt_callback(topic, msg):
    if msg.decode() == "on":
        LEDstatus = "on"
        LED_PIN.value(0)
    elif msg.decode() == "off":
        LEDstatus = "off"
        LED_PIN.value(1)

client = MQTTClient(b"Alabama", b"192.168.2.125", 1883)
client.set_callback(mqtt_callback)

client.connect()
client.subscribe(MQTT_TOPIC)

while True:
    try:
        client.check_msg()
        time.sleep(10)
    except OSError as e:
        print("Fehler beim Empfangen der Nachricht:")
        print(e.args)
        client.disconnect()
        break```

here is my subscribe publish method in Java Vaadin:

```public void publishToDashboard(String topic, String message, String clientID)
            throws ExecutionException, InterruptedException, JsonProcessingException {
        ObjectMapper objectMapper = new ObjectMapper();
        Map<String, String> payload = new HashMap<>();
        payload.put("clientID", clientID);
        payload.put("message", message);

        String strPayload = objectMapper.writeValueAsString(payload);

        Mqtt5Publish mqttMessage = Mqtt5Publish.builder()
                .topic(topic)
                .payload(strPayload.getBytes())
                .contentType("json")
                .qos(MqttQos.AT_LEAST_ONCE)
                .build();

        this.client.publish(mqttMessage).get();
        System.out.println("published");
    }```


also for the Java MQTT Client i'm using this one from hivemq.

and here is the method, that I call when a Button get clicked:

```private void publishLED(ClickEvent<Button> event, String msg, String clientID) {
        CompletableFuture.runAsync(() -> {
            try {
                client.publishToDashboard("led/control", msg, clientID);
            } catch (ExecutionException | InterruptedException | JsonProcessingException ex) {
                throw new RuntimeException(ex);
            }
        });
    }```

It's my first project with ESP8266 and MQTT, and I literally searched 5h for this Exception but i did'nt find something.

If any informations missing please let me know.

Thank you for trying to help me. :)

Have a good one

Tried: Published message from Web App with button
Expected: ESP8266 catch the message with subscribe and turn LED on or off
What happened: OSError -1