Client connection timeout

HiveMQ Client Library
1

Hello,
I’m trying to set a connection timeout for a client(blocking/async), to put simply, i just want client throw an exception when it can not connect in a certain amount of time. I’ve tried two approaches so far:

  • Async client
 Mqtt5AsyncClient client = MqttClient.builder()
          .useMqttVersion5()
          .serverHost(hivemqHost)
          .serverPort(hivemqPort)
          .identifier(clientIdMqtt5)
          .automaticReconnect(MqttClientAutoReconnectImpl.DEFAULT)
          .transportConfig()
          .mqttConnectTimeout(5, TimeUnit.SECONDS)
          .socketConnectTimeout(5,TimeUnit.SECONDS)
          .applyTransportConfig()
          .buildAsync();

        log.info("Built mqtt v5 client..");

        client.connectWith()
          .cleanStart(false)
          .noSessionExpiry()
          .send()
          .whenComplete((connAck, throwable) -> {
              if (connAck != null) {
                  log.info("whenComplete: MQTT connect success with code {}", connAck.getReasonCode());
              } else {
                  if (throwable instanceof Mqtt5ConnAckException) {
                      log.info("whenComplete: Connect failed because of Negative CONNACK with code {} ",
                        ((Mqtt5ConnAckException) throwable).getMqttMessage().getReasonCode());
                  } else {
                      log.info("whenComplete: MQTT connect failed because of {}", throwable.getMessage());
                  }
              }
          });

When hivemq broker is not running this whenComplete() callback is never called. I expect it should be called in connect timeout seconds(5s here).

  • Blocking approach:

        client = MqttClient.builder()
          .useMqttVersion5()
          .identifier(clientIdMqtt5)
          .automaticReconnect(MqttClientAutoReconnectImpl.DEFAULT)
          .transportConfig()
          .serverHost(hivemqHost)
          .serverPort(hivemqPort)
          .socketConnectTimeout(5, TimeUnit.SECONDS)
          .mqttConnectTimeout(5, TimeUnit.SECONDS)
          .applyTransportConfig()
          .build();

        log.info("Built mqtt v5 client..");

        Mqtt5ConnAck connAck = client.toBlocking()
          .connectWith()
          .cleanStart(false)
          .noSessionExpiry()
          .send();

When hivemq broker is not running this one hangs indefinetely, ignoring transport timeout parameters.
So, how can i know a connection attempt failed?

Thanks
KR

2

Hi @mtorak ,

I see that you are using automatic reconnect strategy. So you can add following two lines in order to know a connection attempt failed or succeeded:

        Mqtt5AsyncClient client = Mqtt5Client.builder()
                .serverHost("localhost")
                .serverPort(1883)
                .identifier("my-java-client")
                .automaticReconnect(MqttClientAutoReconnectImpl.DEFAULT)
                    .addConnectedListener(context -> System.out.println("connected " + LocalTime.now()))
                    .addDisconnectedListener(context -> System.out.println("disconnected " + LocalTime.now()))
                .transportConfig()
                .mqttConnectTimeout(5, TimeUnit.SECONDS)
                .socketConnectTimeout(5,TimeUnit.SECONDS)
                .applyTransportConfig()
                .buildAsync();

When the broker is not running, the client will print:

disconnected 15:17:38.346839
disconnected 15:17:41.747628
disconnected 15:17:51.353332
disconnected 15:18:07.575575
disconnected 15:18:42.680786

You can find this and more examples here: https://github.com/hivemq/hivemq-mqtt-client/tree/master/examples/src/main/java/com/hivemq/client/mqtt/examples

I hope this helps,
Kind regards,
Dasha from HiveMQ team

3

Hi Daria,
Meanwhile I’ve also discovered those connect/disconnect listeners.They are handy.
Also tried the autoReconnect option, which allows frequent checking if the server is back online.

        MqttClientAutoReconnect mqttClientAutoReconnect = MqttClientAutoReconnect.builder()
          .initialDelay(1, TimeUnit.SECONDS)
          .maxDelay(5, TimeUnit.SECONDS)
          .build();

But, still i couldn’t grasp the purpose of these two options:

 .mqttConnectTimeout(5, TimeUnit.SECONDS)
 .socketConnectTimeout(5,TimeUnit.SECONDS)

Any idea?

And also, discovered a scenario like this:

  • Started async client while HiveMQ broker is offline
  • Sent several messages via async client like this:
        client.publishWith()
          .topic(topic)
          .messageExpiryInterval(messageExpiryIntervalMs)
          .payload(payload)
          .userProperties(userPropertiesBuilder.build())
          .qos(MqttQos.AT_LEAST_ONCE)
          .send()
          .whenComplete((mqtt5Publish, throwable) -> {
              if (throwable != null) {
                  log.warn("Publish failed!! Details: " + throwable.getMessage());
              } else {
                  log.info("Published successfully to hivemq topic: " + topic);
              }
          });
  • It didn’t trigger whenComplete() callback, i expected it should… Why wasn’t it triggered?
  • After HiveMQ broker went online, client auto reconnected and sent those messages to broker.
    So hivemq-mqtt-client must be buffering those messages locally. Is this correct? If so what is limit of this behaviour(i.e. how much data can be buffered?)

P.S.
And also thank you for pointing out additional example api usages.

KR

4

Hi @mtorak ,

mqttConnectTimeout(long timeout, @NotNull TimeUnit timeUnit)
Sets the timeout between sending the Connect and receiving the ConnAck message .

socketConnectTimeout(long timeout, @NotNull TimeUnit timeUnit)
Sets the timeout for connecting the socket to the server .

Your code I could make work like this:

String topic = "topic/1";
        client.connectWith()
                .cleanStart(false)
                .noSessionExpiry()
                .keepAlive(2)
                .send()
                .thenAccept(connAck -> System.out.println("connected " + connAck))
                .thenCompose(v -> client.publishWith()
                        .topic(topic)
                        .payload("PAYLOAD".getBytes(StandardCharsets.UTF_8))
                        .send()
                        .whenComplete((mqtt5Publish, throwable) -> {
                            if (throwable != null) {
                                System.out.println("Publish failed!! Details: " + throwable.getMessage());
                            } else {
                                System.out.println("Published successfully to hivemq topic: " + topic);
                            }
                        }))
                .thenAccept(someResult -> System.out.println("Result " + someResult));

I hope this helps,
Dasha from HiveMQ team

5

Hi Daria,
Thank you for sample usage and pointing out javadoc; but i need example usage of these two methods:

          .mqttConnectTimeout(MQTT_CONNECT_TIMEOUT_S, TimeUnit.SECONDS)
          .socketConnectTimeout(SOCKET_CONNECT_TIMEOUT_S, TimeUnit.SECONDS)

As far as i can see, there are also no usages for these options in mqtt-cli code base.
So i wonder purpose/usage of them.

Thank you,
KR

6

Hi @mtorak ,

True, these two methods aren’t in the MQTT CLI. This means that MQTT CLI is reusing whatever is set in the MQTT Client library, take a look here:

    private int socketConnectTimeoutMs = MqttClientTransportConfigImpl.DEFAULT_SOCKET_CONNECT_TIMEOUT_MS;
    private int mqttConnectTimeoutMs = MqttClientTransportConfigImpl.DEFAULT_MQTT_CONNECT_TIMEOUT_MS;

I hope this helps,
Dasha from HiveMQ team