connect() blocks forever if reconnect configured and there is a known unrecoverable problem connecting to the broker

[climategadgets]

Expected behavior

connect() fails even if configured to reconnect if it is determined that reconnect attempts will always fail. Case in point, attempts to connect to MQTT 3 only broker with MQTT 5 only client will never succeed and must be abandoned with a clear error message.

See also: #302

Actual behavior

connect() hangs with no indication of why.

To Reproduce

Steps

With automatic reconnect enabled,

• Attempt to connect to a broker that doesn't support MQTT version 5 (server error message is Invalid protocol version 5 in CONNECT from ${client_ip}), or
• Attempt to connect to a broker that doesn't support SSL (server error message is Socket error on client <unknown>, disconnecting.), or
• Attempt to connect with wrong authentication credentials (same error message on the server)

Reproducer code

Standard connect() code from HiveMQ examples

Details

• Affected HiveMQ MQTT Client version(s): 1.2.2
• Used JVM version: openjdk version "11.0.11" 2021-04-20
• Used OS (name and version): Debian Stretch
• Used MQTT version: 5 on the client side, 3 on the server side
• Used MQTT broker (name and version): mosquitto 1.5.7-1+deb10u1

[SgtSilvio]

Hi @climategadgets Although you are right that we should cover the most common unrecoverable problems in the default automatic reconnect, you can currently already do this manually, for example:

Mqtt5Client.builder()
    ...
    .automaticReconnectWithDefaultConfig()
    .addDisconnectedListener(context -> {
        if (isUnrecoverable(context.getCause())) {
            context.getReconnector().reconnect(false);
        }
    })
    ...