Problem with subscription

[MMise]

Hello!

I am using this repo to establish a connection to an AWS MQTT broker.

I can successfully create the connection:

self.client = MQTTClient(
    configuration: .init(
        target: .host(config.host, port: config.port),
        tls: .transportServices(
            TSTLSConfiguration(
                certificateVerification: .fullVerification,
                clientIdentity: config.clientIdentity,
                clientIdentityCertificates: [config.serverCertificate, config.clientCertificate]
            )
        ),
        protocolVersion: .version3_1_1,
        clientId: config.clientId
    )
)

But as soon as I create a subscription to a topic (delay is there just for debugging this issue):

self.client?.whenConnected({ [weak self] _ in
    self?.mqttConnectionState.send(.ready)
    
    DispatchQueue.main.asyncAfter(deadline: .now() + 5) {
        let subs = MQTTSubscription(topicFilter: "comm/\(config.familyId)/\(config.deviceId)",
                                    qos: .atLeastOnce)
        self?.client?.subscribe(to: [subs])
    }
})

The connection is closed:

2023-06-06T16:10:57+0300 notice nl.roebert.MQTTNIO : target=host("a6lbjjglyo36v-ats.iot.eu-north-1.amazonaws.com", port: 8883) [MQTTNIO] Connecting to broker
2023-06-06T16:10:57+0300 notice nl.roebert.MQTTNIO : target=host("a6lbjjglyo36v-ats.iot.eu-north-1.amazonaws.com", port: 8883) [MQTTNIO] Connected to broker
2023-06-06T16:11:07+0300 notice nl.roebert.MQTTNIO : [MQTTNIO] Channel closed
DISCONNECT REASON: connectionClosed(nil)

self.client?.whenDisconnected({ reason in
    print("DISCONNECT REASON: \(reason)")
    self.mqttConnectionState.send(.notConnected)
})

I did some debugging and I discovered that the underlying NIOTSConnectionChannel receives isComplete boolean from the active NWConnection and closes the connection swift-nio-transport-services/Sources/NIOTransportServices/NIOTSConnectionChannel#dataReceivedHandler(content:context:isComplete:error:)

// Next, we want to check if there's an error. If there is, we're going to deliver it, and then close the connection with
// it. Otherwise, we're going to check if we read EOF, and if we did we'll close with that instead.
if let error = error {
    self.pipeline.fireErrorCaught(error)
    self.close0(error: error, mode: .all, promise: nil)
} else if isComplete {
    self.didReadEOF()
}

...

/// Handle a read EOF.
///
/// If the user has indicated they support half-closure, we will emit the standard half-closure
/// event. If they have not, we upgrade this to regular closure.
private func didReadEOF() {
    if self.options.supportRemoteHalfClosure {
        // This is a half-closure, but the connection is still valid.
        do {
            try self.state.closeInput()
        } catch {
            return self.close0(error: error, mode: .all, promise: nil)
        }

         self.pipeline.fireUserInboundEventTriggered(ChannelEvent.inputClosed)
    } else {
        self.close0(error: ChannelError.eof, mode: .all, promise: nil)
    }
}

Is this the expected behaviour? There is nothing actively being published to the topic. The publisher entity is a piece of hardware that publishes some sensor data every once in a while. The connection stays alive if I just comment out the subscription. Publishing data from the app to that same topic works and my hardware device receives it as expected.

[MMise]

Well I figured out the problem and it was quite trivial. My MQTT version was incorrect. Changing to version 5 solved the issue.

[sroebert]

Generally when the connection gets closed, the server denies the connection. Unfortunately with the older version 3, you do not get a proper reason, so it is hard to tell what is wrong.

Glad you got it fixed though.