When the mqttv3 client connects() to a server where the message broker is not operating, it does not throw an exception.

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- [x] Bug exists Release Version 1.2.5 ( Master Branch)
- [ ] Bug exists in MQTTv3 Client on Snapshot Version 1.2.6-SNAPSHOT (Develop Branch)
- [ ] Bug exists in MQTTv5 Client on Snapshot Version 1.2.6-SNAPSHOT (Develop Branch)

public class Test {

    public static void main(String[] args) throws IOException, MqttException {


        MqttConnectOptions mqttConnectOptions = new MqttConnectOptions();

        mqttConnectOptions.setUserName("test");

        mqttConnectOptions.setPassword("test".toCharArray());

        mqttConnectOptions.setCleanSession(true);

        mqttConnectOptions.setKeepAliveInterval(30);

        mqttConnectOptions.setConnectionTimeout(2);

        MqttAsyncClient mq = new MqttAsyncClient("tcp://127.0.0.1:61611","test", new MemoryPersistence());

        try {

            IMqttToken token = mq.connect(mqttConnectOptions);

            Thread.sleep(5000);

            System.out.println(token.isComplete());

        } catch (Exception e) {

            e.printStackTrace();

        }

    }

}

The above example is a code that makes a connect request to any server without a message broker.

If you follow the code inside the library(package org.eclipse.paho.client.mqttv3.internal.TCPNetworkModule(line:67 start())

	public void start() throws IOException, MqttException {

		final String methodName = "start";

		try {

			// @TRACE 252=connect to host {0} port {1} timeout {2}

			log.fine(CLASS_NAME,methodName, "252", new Object[] {host, Integer.valueOf(port), Long.valueOf(conTimeout*1000)});

			SocketAddress sockaddr = new InetSocketAddress(host, port);

			socket = factory.createSocket();

			socket.connect(sockaddr, conTimeout*1000);

			socket.setSoTimeout(1000);

		}

		catch (ConnectException ex) {

			//@TRACE 250=Failed to create TCP socket

			log.fine(CLASS_NAME,methodName,"250",null,ex);

			throw new MqttException(MqttException.REASON_CODE_SERVER_CONNECT_ERROR, ex);

		}

	}

you will call Socket connect.
Socket connect() for non-operating servers will cause ConnectException.
On the code, the generated ConnectException is thrown as MqttException.
But I can't get any reception, the project I made doesn't work normally.
Am I misunderstanding and using it?

Start with org.eclipse.paho.client.mqttv3.internal.TCPNetworkModule.start(), especially the socket connection and ConnectException handling shown in the report. Reproduce the connection attempt against the unavailable endpoint and trace how the asynchronous MqttAsyncClient token exposes the failure; done means the expected exception behavior is documented or covered by a regression test.

Written by the indexing model from the issue text.